opus/sys/apis/ui.lua

local Canvas     = require('ui.canvas')
local class      = require('class')
local Event      = require('event')
local Input      = require('input')
local Peripheral = require('peripheral')
local Transition = require('ui.transition')
local Util       = require('util')

local _rep       = string.rep
local _sub       = string.sub
local colors     = _G.colors
local device     = _G.device
local fs         = _G.fs
local os         = _G.os
local term       = _G.term

--[[
  Using the shorthand window definition, elements are created from
  the bottom up. Once reaching the top, setParent is called top down.

  On :init(), elements do not know the parent or can calculate sizing.
]]

local function safeValue(v)
  local t = type(v)
  if t == 'string' or t == 'number' then
    return v
  end
  return tostring(v)
end

-- need to add offsets to this test
local function getPosition(element)
  local x, y = 1, 1
  repeat
    x = element.x + x - 1
    y = element.y + y - 1
    element = element.parent
  until not element
  return x, y
end

--[[-- Top Level Manager --]]--
local Manager = class()
function Manager:init()
  local function keyFunction(event, code, held)
    local ch = Input:translate(event, code, held)

    if ch and self.currentPage then
      local target = self.currentPage.focused or self.currentPage
      self:inputEvent(target,
        { type = 'key', key = ch, element = target })
      self.currentPage:sync()
    end
  end

  local handlers = {
    char = keyFunction,
    key_up = keyFunction,
    key = keyFunction,

    term_resize = function(_, side)
      if self.currentPage then
        -- the parent doesn't have any children set...
        -- that's why we have to resize both the parent and the current page
        -- kinda makes sense
        if self.currentPage.parent.device.side == side then
          self.currentPage.parent:resize()

          self.currentPage:resize()
          self.currentPage:draw()
          self.currentPage:sync()
        end
      end
    end,

    mouse_scroll = function(_, direction, x, y)
      if self.currentPage then
        local event = self.currentPage:pointToChild(x, y)
        local directions = {
          [ -1 ] = 'up',
          [  1 ] = 'down'
        }
        -- revisit - should send out scroll_up and scroll_down events
        -- let the element convert them to up / down
        self:inputEvent(event.element,
          { type = 'key', key = directions[direction] })
        self.currentPage:sync()
      end
    end,

    -- this should be moved to the device !
    monitor_touch = function(_, side, x, y)
      Input:translate('mouse_click', 1, x, y)
      local ch = Input:translate('mouse_up', 1, x, y)
      if self.currentPage then
        if self.currentPage.parent.device.side == side then
          self:click(ch, 1, x, y)
        end
      end
    end,

    mouse_click = function(_, button, x, y)
      Input:translate('mouse_click', button, x, y)

      if self.currentPage then
        if not self.currentPage.parent.device.side then
          local event = self.currentPage:pointToChild(x, y)
          if event.element.focus and not event.element.inactive then
            self.currentPage:setFocus(event.element)
            self.currentPage:sync()
          end
        end
      end
    end,

    mouse_up = function(_, button, x, y)
      local ch = Input:translate('mouse_up', button, x, y)

      if ch == 'control-shift-mouse_click' then -- hack
        local event = self.currentPage:pointToChild(x, y)
        _ENV.multishell.openTab({
          path = 'sys/apps/Lua.lua',
          args = { event.element },
          focused = true })

      elseif ch and self.currentPage then
        --if not self.currentPage.parent.device.side then
          self:click(ch, button, x, y)
        --end
      end
    end,

    mouse_drag = function(_, button, x, y)
      local ch = Input:translate('mouse_drag', button, x, y)
      if ch and self.currentPage then
        local event = self.currentPage:pointToChild(x, y)
        event.type = ch
        self:inputEvent(event.element, event)
        self.currentPage:sync()
      end
    end,

    paste = function(_, text)
      Input:translate('paste')
      self:emitEvent({ type = 'paste', text = text })
      self.currentPage:sync()
    end,
  }

  -- use 1 handler to single thread all events
  Event.on({
    'char', 'key_up', 'key', 'term_resize',
    'mouse_scroll', 'monitor_touch', 'mouse_click',
    'mouse_up', 'mouse_drag', 'paste' },
    function(event, ...)
      handlers[event](event, ...)
    end)
end

function Manager:configure(appName, ...)
  local options = {
    device     = { arg = 'd', type = 'string',
                   desc = 'Device type' },
    textScale  = { arg = 't', type = 'number',
                   desc = 'Text scale' },
  }
  local defaults = Util.loadTable('usr/config/' .. appName) or { }
  if not defaults.device then
    defaults.device = { }
  end

  Util.getOptions(options, { ... }, true)
  local optionValues = {
    name = options.device.value,
    textScale = options.textScale.value,
  }

  Util.merge(defaults.device, optionValues)

  if defaults.device.name then

    local dev

    if defaults.device.name == 'terminal' then
      dev = term.current()
    else
      dev = Peripheral.lookup(defaults.device.name) --- device[defaults.device.name]
    end

    if not dev then
      error('Invalid display device')
    end
    self:setDefaultDevice(self.Device({
      device = dev,
      textScale = defaults.device.textScale,
    }))
  end

  if defaults.theme then
    for k,v in pairs(defaults.theme) do
      if self[k] and self[k].defaults then
        Util.merge(self[k].defaults, v)
      end
    end
  end
end

function Manager:disableEffects()
  self.defaultDevice.effectsEnabled = false
end

function Manager:loadTheme(filename)
  if fs.exists(filename) then
    local theme, err = Util.loadTable(filename)
    if not theme then
      error(err)
    end
    for k,v in pairs(theme) do
      if self[k] and self[k].defaults then
        Util.merge(self[k].defaults, v)
      end
    end
  end
end

function Manager:emitEvent(event)
  if self.currentPage and self.currentPage.focused then
    return self.currentPage.focused:emit(event)
  end
end

function Manager:inputEvent(parent, event)
  while parent do
    if parent.accelerators then
      local acc = parent.accelerators[event.key]
      if acc then
        if parent:emit({ type = acc, element = parent }) then
          return true
        end
      end
    end
    if parent.eventHandler then
      if parent:eventHandler(event) then
        return true
      end
    end
    parent = parent.parent
  end
end

function Manager:click(code, button, x, y)
  if self.currentPage then

    local target = self.currentPage

    -- need to add offsets into this check
    --[[
    if x < target.x or y < target.y or
      x > target.x + target.width - 1 or
      y > target.y + target.height - 1 then
      target:emit({ type = 'mouse_out' })

      target = self.currentPage
    end
    --]]

    local clickEvent = target:pointToChild(x, y)

    if code == 'mouse_doubleclick' then
      if self.doubleClickElement ~= clickEvent.element then
        return
      end
    else
      self.doubleClickElement = clickEvent.element
    end

    clickEvent.button = button
    clickEvent.type = code
    clickEvent.key = code

    if clickEvent.element.focus then
      self.currentPage:setFocus(clickEvent.element)
    end
    if not self:inputEvent(clickEvent.element, clickEvent) then
      --[[
      if button == 3 then
        -- if the double-click was not captured
        -- send through a single-click
        clickEvent.button = 1
        clickEvent.type = events[1]
        clickEvent.key = events[1]
        self:inputEvent(clickEvent.element, clickEvent)
      end
      ]]
    end

    self.currentPage:sync()
  end
end

function Manager:setDefaultDevice(dev)
  self.defaultDevice = dev
  self.term = dev
end

function Manager:addPage(name, page)
  self.pages[name] = page
end

function Manager:setPages(pages)
  self.pages = pages
end

function Manager:getPage(pageName)
  local page = self.pages[pageName]

  if not page then
    error('UI:getPage: Invalid page: ' .. tostring(pageName), 2)
  end

  return page
end

function Manager:setPage(pageOrName, ...)
  local page = pageOrName

  if type(pageOrName) == 'string' then
    page = self.pages[pageOrName] or error('Invalid page: ' .. pageOrName)
  end

  if page == self.currentPage then
    page:draw()
  else
    local needSync
    if self.currentPage then
      if self.currentPage.focused then
        self.currentPage.focused.focused = false
        self.currentPage.focused:focus()
      end
      self.currentPage:disable()
      page.previousPage = self.currentPage
    else
      needSync = true
    end
    self.currentPage = page
    self.currentPage:clear(page.backgroundColor)
    page:enable(...)
    page:draw()
    if self.currentPage.focused then
      self.currentPage.focused.focused = true
      self.currentPage.focused:focus()
    end
    if needSync then
      page:sync() -- first time a page has been set
    end
  end
end

function Manager:getCurrentPage()
  return self.currentPage
end

function Manager:setPreviousPage()
  if self.currentPage.previousPage then
    local previousPage = self.currentPage.previousPage.previousPage
    self:setPage(self.currentPage.previousPage)
    self.currentPage.previousPage = previousPage
  end
end

function Manager:getDefaults(element, args)
  local defaults = Util.deepCopy(element.defaults)
  if args then
    Manager:mergeProperties(defaults, args)
  end
  return defaults
end

function Manager:mergeProperties(obj, args)
  if args then
    for k,v in pairs(args) do
      if k == 'accelerators' then
        if obj.accelerators then
          Util.merge(obj.accelerators, args.accelerators)
        else
          obj[k] = v
        end
      else
        obj[k] = v
      end
    end
  end
end

function Manager:pullEvents(...)
  Event.pullEvents(...)
  self.term:reset()
end

function Manager:exitPullEvents()
  Event.exitPullEvents()
end

local UI = Manager()

--[[-- Basic drawable area --]]--
UI.Window = class()
UI.Window.uid = 1
UI.Window.defaults = {
  UIElement = 'Window',
  x = 1,
  y = 1,
  -- z = 0, -- eventually...
  offx = 0,
  offy = 0,
  cursorX = 1,
  cursorY = 1,
}
function UI.Window:init(args)
  -- merge defaults for all subclasses
  local defaults = args
  local m = getmetatable(self)  -- get the class for this instance
  repeat
    defaults = UI:getDefaults(m, defaults)
    m = m._base
  until not m
  UI:mergeProperties(self, defaults)

  -- each element has a unique ID
  self.uid = UI.Window.uid
  UI.Window.uid = UI.Window.uid + 1

  -- at this time, the object has all the properties set

  -- postInit is a special constructor. the element does not need to implement
  -- the method. But we need to guarantee that each subclass which has this
  -- method is called.
  m = self
  local lpi
  repeat
    if m.postInit and m.postInit ~= lpi then
      m.postInit(self)
      lpi = m.postInit
    end
    m = m._base
  until not m
end

function UI.Window:postInit()
  if self.parent then
    -- this will cascade down the whole tree of elements starting at the
    -- top level window (which has a device as a parent)
    self:setParent()
  end
end

function UI.Window:initChildren()
  local children = self.children

  -- insert any UI elements created using the shorthand
  -- window definition into the children array
  for k,child in pairs(self) do
    if k ~= 'parent' then -- reserved
      if type(child) == 'table' and child.UIElement and not child.parent then
        if not children then
          children = { }
        end
        table.insert(children, child)
      end
    end
  end
  if children then
    for _,child in pairs(children) do
      if not child.parent then
        child.parent = self
        child:setParent()
        -- child:reposition() -- maybe
        if self.enabled then
          child:enable()
        end
      end
    end
    self.children = children
  end
end

local function setSize(self)
  if self.x < 0 then
    self.x = self.parent.width + self.x + 1
  end
  if self.y < 0 then
    self.y = self.parent.height + self.y + 1
  end

  if self.ex then
    local ex = self.ex
    if self.ex <= 1 then
      ex = self.parent.width + self.ex + 1
    end
    if self.width then
      self.x = ex - self.width + 1
    else
      self.width = ex - self.x + 1
    end
  end
  if self.ey then
    local ey = self.ey
    if self.ey <= 1 then
      ey = self.parent.height + self.ey + 1
    end
    if self.height then
      self.y = ey - self.height + 1
    else
      self.height = ey - self.y + 1
    end
  end

  if not self.width then
    self.width = self.parent.width - self.x + 1
  end
  if not self.height then
    self.height = self.parent.height - self.y + 1
  end
end

-- bad name... should be called something like postInit
-- normally used to determine sizes since the parent is
-- only known at this point
function UI.Window:setParent()
  self.oh, self.ow = self.height, self.width
  self.ox, self.oy = self.x, self.y

  setSize(self)

  self:initChildren()
end

function UI.Window:resize()
  self.height, self.width = self.oh, self.ow
  self.x, self.y = self.ox, self.oy

  setSize(self)

  if self.children then
    for _,child in ipairs(self.children) do
      child:resize()
    end
  end
end

function UI.Window:add(children)
  UI:mergeProperties(self, children)
  self:initChildren()
end

function UI.Window:getCursorPos()
  return self.cursorX, self.cursorY
end

function UI.Window:setCursorPos(x, y)
  self.cursorX = x
  self.cursorY = y
  self.parent:setCursorPos(self.x + x - 1, self.y + y - 1)
end

function UI.Window:setCursorBlink(blink)
  self.parent:setCursorBlink(blink)
end

function UI.Window:draw()
  self:clear(self.backgroundColor)
  if self.children then
    for _,child in pairs(self.children) do
      if child.enabled then
        child:draw()
      end
    end
  end
end

function UI.Window:sync()
  if self.parent then
    self.parent:sync()
  end
end

function UI.Window:enable()
  self.enabled = true
  if self.children then
    for _,child in pairs(self.children) do
      child:enable()
    end
  end
end

function UI.Window:disable()
  self.enabled = false
  if self.children then
    for _,child in pairs(self.children) do
      child:disable()
    end
  end
end

function UI.Window:setTextScale(textScale)
  self.textScale = textScale
  self.parent:setTextScale(textScale)
end

function UI.Window:clear(bg, fg)
  if self.canvas then
    self.canvas:clear(bg or self.backgroundColor, fg or self.textColor)
  else
    self:clearArea(1 + self.offx, 1 + self.offy, self.width, self.height, bg)
  end
end

function UI.Window:clearLine(y, bg)
  self:write(1, y, _rep(' ', self.width), bg)
end

function UI.Window:clearArea(x, y, width, height, bg)
  if width > 0 then
    local filler = _rep(' ', width)
    for i = 0, height - 1 do
      self:write(x, y + i, filler, bg)
    end
  end
end

function UI.Window:write(x, y, text, bg, tc)
  bg = bg or self.backgroundColor
  tc = tc or self.textColor
  x = x - self.offx
  y = y - self.offy
  if y <= self.height and y > 0 then
    if self.canvas then
      self.canvas:write(x, y, text, bg, tc)
    else
      self.parent:write(
        self.x + x - 1, self.y + y - 1, tostring(text), bg, tc)
    end
  end
end

function UI.Window:centeredWrite(y, text, bg, fg)
  if #text >= self.width then
    self:write(1, y, text, bg, fg)
  else
    local space = math.floor((self.width-#text) / 2)
    local filler = _rep(' ', space + 1)
    local str = _sub(filler, 1, space) .. text
    str = str .. _sub(filler, self.width - #str + 1)
    self:write(1, y, str, bg, fg)
  end
end

function UI.Window:print(text, bg, fg)
  local marginLeft = self.marginLeft or 0
  local marginRight = self.marginRight or 0
  local width = self.width - marginLeft - marginRight

  local function nextWord(line, cx)
    local result = { line:find("(%w+)", cx) }
    if #result > 1 and result[2] > cx then
      return _sub(line, cx, result[2] + 1)
    elseif #result > 0 and result[1] == cx then
      result = { line:find("(%w+)", result[2]) }
      if #result > 0 then
        return _sub(line, cx, result[1] + 1)
      end
    end
    if cx <= #line then
      return _sub(line, cx, #line)
    end
  end

  local function pieces(f, bg, fg)
    local pos = 1
    local t = { }
    while true do
      local s = string.find(f, '\027', pos, true)
      if not s then
        break
      end
      if pos < s then
        table.insert(t, _sub(f, pos, s - 1))
      end
      local seq = _sub(f, s)
      seq = seq:match("\027%[([%d;]+)m")
      local e = { }
      for color in string.gmatch(seq, "%d+") do
        color = tonumber(color)
        if color == 0 then
          e.fg = fg
          e.bg = bg
        elseif color > 20 then
          e.bg = 2 ^ (color - 21)
        else
          e.fg = 2 ^ (color - 1)
        end
      end
      table.insert(t, e)
      pos = s + #seq + 3
    end
    if pos <= #f then
      table.insert(t, _sub(f, pos))
    end
    return t
  end

  local lines = Util.split(text)
  for k,line in pairs(lines) do
    local fragments = pieces(line, bg, fg)
    for _, fragment in ipairs(fragments) do
      local lx = 1
      if type(fragment) == 'table' then -- ansi sequence
        fg = fragment.fg
        bg = fragment.bg
      else
        while true do
          local word = nextWord(fragment, lx)
          if not word then
            break
          end
          local w = word
          if self.cursorX + #word > width then
            self.cursorX = marginLeft + 1
            self.cursorY = self.cursorY + 1
            w = word:gsub('^ ', '')
          end
          self:write(self.cursorX, self.cursorY, w, bg, fg)
          self.cursorX = self.cursorX + #w
          lx = lx + #word
        end
      end
    end
    if lines[k + 1] then
      self.cursorX = marginLeft + 1
      self.cursorY = self.cursorY + 1
    end
  end

  return self.cursorX, self.cursorY
end

function UI.Window:setFocus(focus)
  if self.parent then
    self.parent:setFocus(focus)
  end
end

function UI.Window:capture(child)
  if self.parent then
    self.parent:capture(child)
  end
end

function UI.Window:release(child)
  if self.parent then
    self.parent:release(child)
  end
end

function UI.Window:pointToChild(x, y)
  x = x + self.offx - self.x + 1
  y = y + self.offy - self.y + 1
  if self.children then
    for _,child in pairs(self.children) do
      if child.enabled and not child.inactive and
         x >= child.x and x < child.x + child.width and
         y >= child.y and y < child.y + child.height then
        local c = child:pointToChild(x, y)
        if c then
          return c
        end
      end
    end
  end
  return {
    element = self,
    x = x,
    y = y
  }
end

function UI.Window:getFocusables()
  local focusable = { }

  local function focusSort(a, b)
    if a.y == b.y then
      return a.x < b.x
    end
    return a.y < b.y
  end

  local function getFocusable(parent, x, y)
    for _,child in Util.spairs(parent.children, focusSort) do
      if child.enabled and child.focus and not child.inactive then
        table.insert(focusable, child)
      end
      if child.children then
        getFocusable(child, child.x + x, child.y + y)
      end
    end
  end

  if self.children then
    getFocusable(self, self.x, self.y)
  end

  return focusable
end

function UI.Window:focusFirst()
  local focusables = self:getFocusables()
  local focused = focusables[1]
  if focused then
    self:setFocus(focused)
  end
end

function UI.Window:refocus()
  local el = self
  while el do
    local focusables = el:getFocusables()
    if focusables[1] then
      self:setFocus(focusables[1])
      break
    end
    el = el.parent
  end
end

function UI.Window:scrollIntoView()
  local parent = self.parent

  if self.x <= parent.offx then
    parent.offx = math.max(0, self.x - 1)
    parent:draw()
  elseif self.x + self.width > parent.width + parent.offx then
    parent.offx = self.x + self.width - parent.width - 1
    parent:draw()
  end

  if self.y <= parent.offy then
    parent.offy = math.max(0, self.y - 1)
    parent:draw()
  elseif self.y + self.height > parent.height + parent.offy then
    parent.offy = self.y + self.height - parent.height - 1
    parent:draw()
  end
end

function UI.Window:getCanvas()
  local el = self
  repeat
    if el.canvas then
      return el.canvas
    end
    el = el.parent
  until not el
end

function UI.Window:addLayer(bg, fg)
  local canvas = self:getCanvas()
  canvas = canvas:addLayer(self, bg, fg)
  canvas:clear(bg or self.backgroundColor, fg or self.textColor)
  return canvas
end

function UI.Window:addTransition(effect, args)
  if self.parent then
    args = args or { }
    if not args.x then -- not good
      args.x, args.y = getPosition(self)
      args.width = self.width
      args.height = self.height
    end

    args.canvas = args.canvas or self.canvas
    self.parent:addTransition(effect, args)
  end
end

function UI.Window:emit(event)
  local parent = self
  while parent do
    if parent.eventHandler then
      if parent:eventHandler(event) then
        return true
      end
    end
    parent = parent.parent
  end
end

function UI.Window:find(uid)
  if self.children then
    return Util.find(self.children, 'uid', uid)
  end
end

function UI.Window:eventHandler(event)
  return false
end

--[[-- Terminal for computer / advanced computer / monitor --]]--
UI.Device = class(UI.Window)
UI.Device.defaults = {
  UIElement = 'Device',
  backgroundColor = colors.black,
  textColor = colors.white,
  textScale = 1,
  effectsEnabled = true,
}
function UI.Device:postInit()
  self.device = self.device or term.current()

  if self.deviceType then
    self.device = device[self.deviceType]
  end

  if not self.device.setTextScale then
    self.device.setTextScale = function() end
  end

  self.device.setTextScale(self.textScale)
  self.width, self.height = self.device.getSize()

  self.isColor = self.device.isColor()

  self.canvas = Canvas({
    x = 1, y = 1, width = self.width, height = self.height,
    isColor = self.isColor,
  })
  self.canvas:clear(self.backgroundColor, self.textColor)
end

function UI.Device:resize()
  self.width, self.height = self.device.getSize()
  self.lines = { }
  self.canvas:resize(self.width, self.height)
  self.canvas:clear(self.backgroundColor, self.textColor)
end

function UI.Device:setCursorPos(x, y)
  self.cursorX = x
  self.cursorY = y
end

function UI.Device:getCursorBlink()
  return self.cursorBlink
end

function UI.Device:setCursorBlink(blink)
  self.cursorBlink = blink
  self.device.setCursorBlink(blink)
end

function UI.Device:setTextScale(textScale)
  self.textScale = textScale
  self.device.setTextScale(self.textScale)
end

function UI.Device:reset()
  self.device.setBackgroundColor(colors.black)
  self.device.setTextColor(colors.white)
  self.device.clear()
  self.device.setCursorPos(1, 1)
end

function UI.Device:addTransition(effect, args)
  if not self.transitions then
    self.transitions = { }
  end

  args = args or { }
  args.ex = args.x + args.width - 1
  args.ey = args.y + args.height - 1
  args.canvas = args.canvas or self.canvas

  if type(effect) == 'string' then
    effect = Transition[effect]
    if not effect then
      error('Invalid transition')
    end
  end

  table.insert(self.transitions, { update = effect(args), args = args })
end

function UI.Device:runTransitions(transitions, canvas)
  for _,t in ipairs(transitions) do
    canvas:punch(t.args)               -- punch out the effect areas
  end
  canvas:blitClipped(self.device) -- and blit the remainder
  canvas:reset()

  while true do
    for _,k in ipairs(Util.keys(transitions)) do
      local transition = transitions[k]
      if not transition.update(self.device) then
        transitions[k] = nil
      end
    end
    if Util.empty(transitions) then
      break
    end
    os.sleep(0)
  end
end

function UI.Device:sync()
  local transitions
  if self.transitions and self.effectsEnabled then
    transitions = self.transitions
    self.transitions = nil
  end

  if self:getCursorBlink() then
    self.device.setCursorBlink(false)
  end

  if transitions then
    self:runTransitions(transitions, self.canvas)
  else
    self.canvas:render(self.device)
  end

  if self:getCursorBlink() then
    self.device.setCursorPos(self.cursorX, self.cursorY)
    self.device.setCursorBlink(true)
  end
end

--[[-- StringBuffer --]]--
-- justs optimizes string concatenations
UI.StringBuffer = class()
function UI.StringBuffer:init(bufSize)
  self.bufSize = bufSize
  self.buffer = {}
end

function UI.StringBuffer:insert(s, width)
  local len = #tostring(s or '')
  if len > width then
    s = _sub(s, 1, width)
  end
  table.insert(self.buffer, s)
  if len < width then
    table.insert(self.buffer, _rep(' ', width - len))
  end
end

function UI.StringBuffer:get(sep)
  return Util.widthify(table.concat(self.buffer, sep or ''), self.bufSize)
end

function UI.StringBuffer:clear()
  self.buffer = { }
end

-- For manipulating text in a fixed width string
local SB = { }
function SB:new(width)
  return setmetatable({
    width = width,
    buf = _rep(' ', width)
  }, { __index = SB })
end
function SB:insert(x, str, width)
  if x < 1 then
    x = self.width + x + 1
  end
  width = width or #str
  if x + width - 1 > self.width then
    width = self.width - x
  end
  if width > 0 then
    self.buf = _sub(self.buf, 1, x - 1) .. _sub(str, 1, width) .. _sub(self.buf, x + width)
  end
end
function SB:fill(x, ch, width)
  width = width or self.width - x + 1
  self:insert(x, _rep(ch, width))
end
function SB:center(str)
  self:insert(math.max(1, math.ceil((self.width - #str + 1) / 2)), str)
end
function SB:get()
  return self.buf
end

--[[-- Page (focus manager) --]]--
UI.Page = class(UI.Window)
UI.Page.defaults = {
  UIElement = 'Page',
  accelerators = {
    down = 'focus_next',
    enter = 'focus_next',
    tab = 'focus_next',
    ['shift-tab' ] = 'focus_prev',
    up = 'focus_prev',
  },
  backgroundColor = colors.cyan,
  textColor = colors.white,
}
function UI.Page:postInit()
  self.parent = self.parent or UI.defaultDevice
  self.__target = self
end

function UI.Page:setParent()
  UI.Window.setParent(self)
  if self.z then
    self.canvas = self:addLayer(self.backgroundColor, self.textColor)
    self.canvas:clear(self.backgroundColor, self.textColor)
  else
    self.canvas = self.parent.canvas
  end
end

function UI.Page:enable()
  self.canvas.visible = true
  UI.Window.enable(self)

  if not self.focused or not self.focused.enabled then
    self:focusFirst()
  end
end

function UI.Page:disable()
  if self.z then
    self.canvas.visible = false
  end
end

function UI.Page:capture(child)
  self.__target = child
end

function UI.Page:release(child)
  if self.__target == child then
    self.__target = self
  end
end

function UI.Page:pointToChild(x, y)
  if self.__target == self then
    return UI.Window.pointToChild(self, x, y)
  end
  x = x + self.offx - self.x + 1
  y = y + self.offy - self.y + 1
  return self.__target:pointToChild(x, y)
end

function UI.Page:getFocusables()
  if self.__target == self or self.__target.pageType ~= 'modal' then
    return UI.Window.getFocusables(self)
  end
  return self.__target:getFocusables()
end

function UI.Page:getFocused()
  return self.focused
end

function UI.Page:focusPrevious()
  local function getPreviousFocus(focused)
    local focusables = self:getFocusables()
    local k = Util.contains(focusables, focused)
    if k then
      if k > 1 then
        return focusables[k - 1]
      end
      return focusables[#focusables]
    end
  end

  local focused = getPreviousFocus(self.focused)
  if focused then
    self:setFocus(focused)
  end
end

function UI.Page:focusNext()
  local function getNextFocus(focused)
    local focusables = self:getFocusables()
    local k = Util.contains(focusables, focused)
    if k then
      if k < #focusables then
        return focusables[k + 1]
      end
      return focusables[1]
    end
  end

  local focused = getNextFocus(self.focused)
  if focused then
    self:setFocus(focused)
  end
end

function UI.Page:setFocus(child)
  if not child.focus then
    return
  end

  if self.focused and self.focused ~= child then
    self.focused.focused = false
    self.focused:focus()
    self.focused:emit({ type = 'focus_lost', focused = child })
  end

  self.focused = child
  if not child.focused then
    child.focused = true
    self:emit({ type = 'focus_change', focused = child })
  end

  child:focus()
end

function UI.Page:eventHandler(event)
  if self.focused then
    if event.type == 'focus_next' then
      self:focusNext()
      return true
    elseif event.type == 'focus_prev' then
      self:focusPrevious()
      return true
    end
  end
end

--[[-- Grid --]]--
UI.Grid = class(UI.Window)
UI.Grid.defaults = {
  UIElement = 'Grid',
  index = 1,
  inverseSort = false,
  disableHeader = false,
  marginRight = 0,
  textColor = colors.white,
  textSelectedColor = colors.white,
  backgroundColor = colors.black,
  backgroundSelectedColor = colors.gray,
  headerBackgroundColor = colors.cyan,
  headerTextColor = colors.white,
  unfocusedTextSelectedColor = colors.white,
  unfocusedBackgroundSelectedColor = colors.gray,
  focusIndicator = '>',
  sortIndicator = ' ',
  inverseSortIndicator = '^',
  values = { },
  columns = { },
  accelerators = {
    enter           = 'key_enter',
    [ 'control-c' ] = 'copy',
    down            = 'scroll_down',
    up              = 'scroll_up',
    home            = 'scroll_top',
    [ 'end' ]       = 'scroll_bottom',
    pageUp          = 'scroll_pageUp',
    [ 'control-b' ] = 'scroll_pageUp',
    pageDown        = 'scroll_pageDown',
    [ 'control-f' ] = 'scroll_pageDown',
  },
}
function UI.Grid:setParent()
  UI.Window.setParent(self)

  for _,c in pairs(self.columns) do
    c.cw = c.width
    if not c.heading then
      c.heading = ''
    end
  end

  self:update()

  if not self.pageSize then
    if self.disableHeader then
      self.pageSize = self.height
    else
      self.pageSize = self.height - 1
    end
  end
end

function UI.Grid:resize()
  UI.Window.resize(self)

  if self.disableHeader then
    self.pageSize = self.height
  else
    self.pageSize = self.height - 1
  end
  self:adjustWidth()
end

function UI.Grid:adjustWidth()
  local t = { }        -- cols without width
  local w = self.width - #self.columns - 1 - self.marginRight -- width remaining

  for _,c in pairs(self.columns) do
    if c.width then
      c.cw = c.width
      w = w - c.cw
    else
      table.insert(t, c)
    end
  end

  if #t == 0 then
    return
  end

  if #t == 1 then
    t[1].cw = #(t[1].heading or '')
    t[1].cw = math.max(t[1].cw, w)
    return
  end

  if not self.autospace then
    for k,c in ipairs(t) do
      c.cw = math.floor(w / (#t - k + 1))
      w = w - c.cw
    end

  else
    for _,c in ipairs(t) do
      c.cw = #(c.heading or '')
      w = w - c.cw
    end
    -- adjust the size to the length of the value
    for key,row in pairs(self.values) do
      if w <= 0 then
        break
      end
      row = self:getDisplayValues(row, key)
      for _,col in pairs(t) do
        local value = row[col.key]
        if value then
          value = tostring(value)
          if #value > col.cw then
            w = w + col.cw
            col.cw = math.min(#value, w)
            w = w - col.cw
            if w <= 0 then
              break
            end
          end
        end
      end
    end

    -- last column does not get padding (right alignment)
    if not self.columns[#self.columns].width then
      Util.removeByValue(t, self.columns[#self.columns])
    end

    -- got some extra room - add some padding
    if w > 0 then
      for k,c in ipairs(t) do
        local padding = math.floor(w / (#t - k + 1))
        c.cw = c.cw + padding
        w = w - padding
      end
    end
  end
end

function UI.Grid:setPageSize(pageSize)
  self.pageSize = pageSize
end

function UI.Grid:getValues()
  return self.values
end

function UI.Grid:setValues(t)
  self.values = t
  self:update()
end

function UI.Grid:setInverseSort(inverseSort)
  self.inverseSort = inverseSort
  self:update()
  self:setIndex(self.index)
end

function UI.Grid:setSortColumn(column)
  self.sortColumn = column
end

function UI.Grid:getDisplayValues(row, key)
  return row
end

function UI.Grid:getSelected()
  if self.sorted then
    return self.values[self.sorted[self.index]], self.sorted[self.index]
  end
end

function UI.Grid:focus()
  self:drawRows()
end

function UI.Grid:draw()
  if not self.disableHeader then
    self:drawHeadings()
  end

  if self.index <= 0 then
    self:setIndex(1)
  elseif self.index > #self.sorted then
    self:setIndex(#self.sorted)
  end
  self:drawRows()
end

-- Something about the displayed table has changed
-- resort the table
function UI.Grid:update()
  local function sort(a, b)
    if not a[self.sortColumn] then
      return false
    elseif not b[self.sortColumn] then
      return true
    end
    return self:sortCompare(a, b)
  end

  local function inverseSort(a, b)
    return not sort(a, b)
  end

  local order
  if self.sortColumn then
    order = sort
    if self.inverseSort then
      order = inverseSort
    end
  end

  self.sorted = Util.keys(self.values)
  if order then
    table.sort(self.sorted, function(a,b)
      return order(self.values[a], self.values[b])
    end)
  end

  self:adjustWidth()
end

function UI.Grid:drawHeadings()
  local sb = UI.StringBuffer(self.width)
  for _,col in ipairs(self.columns) do
    local ind = ' '
    if col.key == self.sortColumn then
      if self.inverseSort then
        ind = self.inverseSortIndicator
      else
        ind = self.sortIndicator
      end
    end
    sb:insert(ind .. col.heading, col.cw + 1)
  end
  self:write(1, 1, sb:get(), self.headerBackgroundColor, self.headerTextColor)
end

function UI.Grid:sortCompare(a, b)
  a = safeValue(a[self.sortColumn])
  b = safeValue(b[self.sortColumn])
  if type(a) == type(b) then
    return a < b
  end
  return tostring(a) < tostring(b)
end

function UI.Grid:drawRows()
  local y = 1
  local startRow = math.max(1, self:getStartRow())
  local sb = UI.StringBuffer(self.width)

  if not self.disableHeader then
    y = y + 1
  end

  local lastRow = math.min(startRow + self.pageSize - 1, #self.sorted)
  for index = startRow, lastRow do

    local sindex = self.sorted[index]
    local rawRow = self.values[sindex]
    local key = sindex
    local row = self:getDisplayValues(rawRow, key)

    sb:clear()

    local ind = ' '
    if self.focused and index == self.index and not self.inactive then
      ind = self.focusIndicator
    end

    for _,col in pairs(self.columns) do
      sb:insert(ind .. safeValue(row[col.key] or ''), col.cw + 1)
      ind = ' '
    end

    local selected = index == self.index and not self.inactive

    self:write(1, y, sb:get(),
      self:getRowBackgroundColor(rawRow, selected),
      self:getRowTextColor(rawRow, selected))

    y = y + 1
  end

  if y <= self.height then
    self:clearArea(1, y, self.width, self.height - y + 1)
  end
end

function UI.Grid:getRowTextColor(row, selected)
  if selected then
    if self.focused then
      return self.textSelectedColor
    end
    return self.unfocusedTextSelectedColor
  end
  return self.textColor
end

function UI.Grid:getRowBackgroundColor(row, selected)
  if selected then
    if self.focused then
      return self.backgroundSelectedColor
    end
    return self.unfocusedBackgroundSelectedColor
  end
  return self.backgroundColor
end

function UI.Grid:getIndex()
  return self.index
end

function UI.Grid:setIndex(index)
  index = math.max(1, index)
  self.index = math.min(index, #self.sorted)

  local selected = self:getSelected()
  if selected ~= self.selected then
    self:drawRows()
    self.selected = selected
    if selected then
      self:emit({ type = 'grid_focus_row', selected = selected, element = self })
    end
  end
end

function UI.Grid:getStartRow()
  return math.floor((self.index - 1) / self.pageSize) * self.pageSize + 1
end

function UI.Grid:getPage()
  return math.floor(self.index / self.pageSize) + 1
end

function UI.Grid:getPageCount()
  local tableSize = Util.size(self.values)
  local pc = math.floor(tableSize / self.pageSize)
  if tableSize % self.pageSize > 0 then
    pc = pc + 1
  end
  return pc
end

function UI.Grid:nextPage()
  self:setPage(self:getPage() + 1)
end

function UI.Grid:previousPage()
  self:setPage(self:getPage() - 1)
end

function UI.Grid:setPage(pageNo)
  -- 1 based paging
  self:setIndex((pageNo-1) * self.pageSize + 1)
end

function UI.Grid:eventHandler(event)
  if event.type == 'mouse_click' or
     event.type == 'mouse_rightclick' or
     event.type == 'mouse_doubleclick' then
    if not self.disableHeader then
      if event.y == 1 then
        local col = 2
        for _,c in ipairs(self.columns) do
          if event.x < col + c.cw then
            if self.sortColumn == c.key then
              self:setInverseSort(not self.inverseSort)
            else
              self.sortColumn = c.key
              self:setInverseSort(false)
            end
            self:draw()
            break
          end
          col = col + c.cw + 1
        end
        return true
      end
    end
    local row = self:getStartRow() + event.y - 1
    if not self.disableHeader then
      row = row - 1
    end
    if row > 0 and row <= Util.size(self.values) then
      self:setIndex(row)
      if event.type == 'mouse_doubleclick' then
        self:emit({ type = 'key_enter' })
      elseif event.type == 'mouse_rightclick' then
        self:emit({ type = 'grid_select_right', selected = self.selected, element = self })
      end
      return true
    end
    return false

  elseif event.type == 'scroll_down' then
    self:setIndex(self.index + 1)
  elseif event.type == 'scroll_up' then
    self:setIndex(self.index - 1)
  elseif event.type == 'scroll_top' then
    self:setIndex(1)
  elseif event.type == 'scroll_bottom' then
    self:setIndex(Util.size(self.values))
  elseif event.type == 'scroll_pageUp' then
    self:setIndex(self.index - self.pageSize)
  elseif event.type == 'scroll_pageDown' then
    self:setIndex(self.index + self.pageSize)
  elseif event.type == 'key_enter' then
    if self.selected then
      self:emit({ type = 'grid_select', selected = self.selected, element = self })
    end
  elseif event.type == 'copy' then
    if self.selected then
      os.queueEvent('clipboard_copy', self.selected)
    end
  else
    return false
  end
  return true
end

--[[-- ScrollingGrid  --]]--
UI.ScrollingGrid = class(UI.Grid)
UI.ScrollingGrid.defaults = {
  UIElement = 'ScrollingGrid',
  scrollOffset = 0,
  marginRight = 1,
}
function UI.ScrollingGrid:postInit()
  self.scrollBar = UI.ScrollBar()
end

function UI.ScrollingGrid:drawRows()
  UI.Grid.drawRows(self)
  self.scrollBar:draw()
end

function UI.ScrollingGrid:getViewArea()
  local y = 1
  if not self.disableHeader then
    y = 2
  end
  return {
    static      = true,                    -- the container doesn't scroll
    y           = y,                       -- scrollbar Y
    height      = self.pageSize,           -- viewable height
    totalHeight = Util.size(self.values),  -- total height
    offsetY     = self.scrollOffset,       -- scroll offset
  }
end

function UI.ScrollingGrid:getStartRow()
  local ts = Util.size(self.values)
  if ts < self.pageSize then
    self.scrollOffset = 0
  end
  return self.scrollOffset + 1
end

function UI.ScrollingGrid:setIndex(index)
  if index < self.scrollOffset + 1 then
    self.scrollOffset = index - 1
  elseif index - self.scrollOffset > self.pageSize then
    self.scrollOffset = index - self.pageSize
  end

  if self.scrollOffset < 0 then
    self.scrollOffset = 0
  else
    local ts = Util.size(self.values)
    if self.pageSize + self.scrollOffset + 1 > ts then
      self.scrollOffset = math.max(0, ts - self.pageSize)
    end
  end
  UI.Grid.setIndex(self, index)
end

--[[-- Menu --]]--
UI.Menu = class(UI.Grid)
UI.Menu.defaults = {
  UIElement = 'Menu',
  disableHeader = true,
  columns = { { heading = 'Prompt', key = 'prompt', width = 20 } },
}
function UI.Menu:postInit()
  self.values = self.menuItems
  self.pageSize = #self.menuItems
end

function UI.Menu:setParent()
  UI.Grid.setParent(self)
  self.itemWidth = 1
  for _,v in pairs(self.values) do
    if #v.prompt > self.itemWidth then
      self.itemWidth = #v.prompt
    end
  end
  self.columns[1].width = self.itemWidth

  if self.centered then
    self:center()
  else
    self.width = self.itemWidth + 2
  end
end

function UI.Menu:center()
  self.x = (self.width - self.itemWidth + 2) / 2
  self.width = self.itemWidth + 2
end

function UI.Menu:eventHandler(event)
  if event.type == 'key' then
    if event.key == 'enter' then
      local selected = self.menuItems[self.index]
      self:emit({
        type = selected.event or 'menu_select',
        selected = selected
      })
      return true
    end
  elseif event.type == 'mouse_click' then
    if event.y <= #self.menuItems then
      UI.Grid.setIndex(self, event.y)
      local selected = self.menuItems[self.index]
      self:emit({
        type = selected.event or 'menu_select',
        selected = selected
      })
      return true
    end
  end
  return UI.Grid.eventHandler(self, event)
end

--[[-- Viewport --]]--
UI.Viewport = class(UI.Window)
UI.Viewport.defaults = {
  UIElement = 'Viewport',
  backgroundColor = colors.cyan,
  accelerators = {
    down            = 'scroll_down',
    up              = 'scroll_up',
    home            = 'scroll_top',
    [ 'end' ]       = 'scroll_bottom',
    pageUp          = 'scroll_pageUp',
    [ 'control-b' ] = 'scroll_pageUp',
    pageDown        = 'scroll_pageDown',
    [ 'control-f' ] = 'scroll_pageDown',
  },
}
function UI.Viewport:setScrollPosition(offset)
  local oldOffset = self.offy
  self.offy = math.max(offset, 0)
  local max = self.ymax or self.height
  if self.children then
    for _, child in ipairs(self.children) do
      if child ~= self.scrollBar then                         -- hack !
        max = math.max(child.y + child.height - 1, max)
      end
    end
  end
  self.offy = math.min(self.offy, math.max(max, self.height) - self.height)
  if self.offy ~= oldOffset then
    self:draw()
  end
end

function UI.Viewport:reset()
  self.offy = 0
end

function UI.Viewport:getViewArea()
  return {
    y           = (self.offy or 0) + 1,
    height      = self.height,
    totalHeight = self.ymax,
    offsetY     = self.offy or 0,
  }
end

function UI.Viewport:eventHandler(event)
  if event.type == 'scroll_down' then
    self:setScrollPosition(self.offy + 1)
  elseif event.type == 'scroll_up' then
    self:setScrollPosition(self.offy - 1)
  elseif event.type == 'scroll_top' then
    self:setScrollPosition(0)
  elseif event.type == 'scroll_bottom' then
    self:setScrollPosition(10000000)
  elseif event.type == 'scroll_pageUp' then
    self:setScrollPosition(self.offy - self.height)
  elseif event.type == 'scroll_pageDown' then
    self:setScrollPosition(self.offy + self.height)
  else
    return false
  end
  return true
end

--[[-- TitleBar --]]--
UI.TitleBar = class(UI.Window)
UI.TitleBar.defaults = {
  UIElement = 'TitleBar',
  height = 1,
  textColor = colors.white,
  backgroundColor = colors.cyan,
  title = '',
  frameChar = '-',
  closeInd = '*',
}
function UI.TitleBar:draw()
  local sb = SB:new(self.width)
  sb:fill(2, self.frameChar, sb.width - 3)
  sb:center(string.format(' %s ', self.title))
  if self.previousPage or self.event then
    sb:insert(-1, self.closeInd)
  end
  self:write(1, 1, sb:get())
end

function UI.TitleBar:eventHandler(event)
  if event.type == 'mouse_click' then
    if (self.previousPage or self.event) and event.x == self.width then
      if self.event then
        self:emit({ type = self.event, element = self })
      elseif type(self.previousPage) == 'string' or
         type(self.previousPage) == 'table' then
        UI:setPage(self.previousPage)
      else
        UI:setPreviousPage()
      end
      return true
    end
  end
end

--[[-- Button --]]--
UI.Button = class(UI.Window)
UI.Button.defaults = {
  UIElement = 'Button',
  text = 'button',
  backgroundColor = colors.lightGray,
  backgroundFocusColor = colors.gray,
  textFocusColor = colors.white,
  textInactiveColor = colors.gray,
  textColor = colors.black,
  centered = true,
  height = 1,
  focusIndicator = ' ',
  event = 'button_press',
  accelerators = {
    space = 'button_activate',
    enter = 'button_activate',
    mouse_click = 'button_activate',
  }
}
function UI.Button:setParent()
  if not self.width and not self.ex then
    self.width = #self.text + 2
  end
  UI.Window.setParent(self)
end

function UI.Button:draw()
  local fg = self.textColor
  local bg = self.backgroundColor
  local ind = ' '
  if self.focused then
    bg = self.backgroundFocusColor
    fg = self.textFocusColor
    ind = self.focusIndicator
  elseif self.inactive then
    fg = self.textInactiveColor
  end
  local text = ind .. self.text .. ' '
  if self.centered then
    self:clear(bg)
    self:centeredWrite(1 + math.floor(self.height / 2), text, bg, fg)
  else
    self:write(1, 1, Util.widthify(text, self.width), bg, fg)
  end
end

function UI.Button:focus()
  if self.focused then
    self:scrollIntoView()
  end
  self:draw()
end

function UI.Button:eventHandler(event)
  if event.type == 'button_activate' then
    self:emit({ type = self.event, button = self })
    return true
  end
  return false
end

--[[-- MenuItem --]]--
UI.MenuItem = class(UI.Button)
UI.MenuItem.defaults = {
  UIElement = 'MenuItem',
  textColor = colors.black,
  backgroundColor = colors.lightGray,
  textFocusColor = colors.white,
  backgroundFocusColor = colors.lightGray,
}

--[[-- MenuBar --]]--
UI.MenuBar = class(UI.Window)
UI.MenuBar.defaults = {
  UIElement = 'MenuBar',
  buttons = { },
  height = 1,
  backgroundColor = colors.lightGray,
  textColor = colors.black,
  spacing = 2,
  lastx = 1,
  showBackButton = false,
  buttonClass = 'MenuItem',
}
UI.MenuBar.spacer = { spacer = true, text = 'spacer', inactive = true }

function UI.MenuBar:postInit()
  self:addButtons(self.buttons)
end

function UI.MenuBar:addButtons(buttons)
  if not self.children then
    self.children = { }
  end

  for _,button in pairs(buttons) do
    if button.UIElement then
      table.insert(self.children, button)
    else
      local buttonProperties = {
        x = self.lastx,
        width = #button.text + self.spacing,
        centered = false,
      }
      self.lastx = self.lastx + buttonProperties.width
      UI:mergeProperties(buttonProperties, button)

      button = UI[self.buttonClass](buttonProperties)
      if button.name then
        self[button.name] = button
      else
        table.insert(self.children, button)
      end

      if button.dropdown then
        button.dropmenu = UI.DropMenu { buttons = button.dropdown }
      end
    end
  end
  if self.parent then
    self:initChildren()
  end
end

function UI.MenuBar:getActive(menuItem)
  return not menuItem.inactive
end

function UI.MenuBar:eventHandler(event)
  if event.type == 'button_press' and event.button.dropmenu then
    if event.button.dropmenu.enabled then
      event.button.dropmenu:hide()
      return true
    else
      local x, y = getPosition(event.button)
      if x + event.button.dropmenu.width > self.width then
        x = self.width - event.button.dropmenu.width + 1
      end
      for _,c in pairs(event.button.dropmenu.children) do
        if not c.spacer then
          c.inactive = not self:getActive(c)
        end
      end
      event.button.dropmenu:show(x, y + 1)
    end
    return true
  end
end

--[[-- DropMenuItem --]]--
UI.DropMenuItem = class(UI.Button)
UI.DropMenuItem.defaults = {
  UIElement = 'DropMenuItem',
  textColor = colors.black,
  backgroundColor = colors.white,
  textFocusColor = colors.white,
  textInactiveColor = colors.lightGray,
  backgroundFocusColor = colors.lightGray,
}
function UI.DropMenuItem:eventHandler(event)
  if event.type == 'button_activate' then
    self.parent:hide()
  end
  return UI.Button.eventHandler(self, event)
end

--[[-- DropMenu --]]--
UI.DropMenu = class(UI.MenuBar)
UI.DropMenu.defaults = {
  UIElement = 'DropMenu',
  backgroundColor = colors.white,
  buttonClass = 'DropMenuItem',
}
function UI.DropMenu:setParent()
  UI.MenuBar.setParent(self)

  local maxWidth = 1
  for y,child in ipairs(self.children) do
    child.x = 1
    child.y = y
    if #(child.text or '') > maxWidth then
      maxWidth = #child.text
    end
  end
  for _,child in ipairs(self.children) do
    child.width = maxWidth + 2
    if child.spacer then
      child.text = string.rep('-', child.width - 2)
    end
  end

  self.height = #self.children + 1
  self.width = maxWidth + 2
  self.ow = self.width

  self.canvas = self:addLayer()
end

function UI.DropMenu:enable()
  self.enabled = false
end

function UI.DropMenu:show(x, y)
  self.x, self.y = x, y
  self.canvas:move(x, y)
  self.canvas:setVisible(true)

  self.enabled = true
  for _,child in pairs(self.children) do
    child:enable()
  end

  self:draw()
  self:capture(self)
  self:focusFirst()
end

function UI.DropMenu:hide()
  self:disable()
  self.canvas:setVisible(false)
  self:release(self)
end

function UI.DropMenu:eventHandler(event)
  if event.type == 'focus_lost' and self.enabled then
    if not Util.contains(self.children, event.focused) then
      self:hide()
    end
  elseif event.type == 'mouse_out' and self.enabled then
    self:hide()
    self:refocus()
  else
    return UI.MenuBar.eventHandler(self, event)
  end
  return true
end

--[[-- TabBarMenuItem --]]--
UI.TabBarMenuItem = class(UI.Button)
UI.TabBarMenuItem.defaults = {
  UIElement = 'TabBarMenuItem',
  event = 'tab_select',
  textColor = colors.black,
  selectedBackgroundColor = colors.cyan,
  unselectedBackgroundColor = colors.lightGray,
  backgroundColor = colors.lightGray,
}
function UI.TabBarMenuItem:draw()
  if self.selected then
    self.backgroundColor = self.selectedBackgroundColor
    self.backgroundFocusColor = self.selectedBackgroundColor
  else
    self.backgroundColor = self.unselectedBackgroundColor
    self.backgroundFocusColor = self.unselectedBackgroundColor
  end
  UI.Button.draw(self)
end

--[[-- TabBar --]]--
UI.TabBar = class(UI.MenuBar)
UI.TabBar.defaults = {
  UIElement = 'TabBar',
  buttonClass = 'TabBarMenuItem',
  selectedBackgroundColor = colors.cyan,
}
function UI.TabBar:enable()
  UI.MenuBar.enable(self)
  if not Util.find(self.children, 'selected', true) then
    local menuItem = self:getFocusables()[1]
    if menuItem then
      menuItem.selected = true
    end
  end
end

function UI.TabBar:eventHandler(event)
  if event.type == 'tab_select' then
    local selected, si = Util.find(self:getFocusables(), 'uid', event.button.uid)
    local previous, pi = Util.find(self:getFocusables(), 'selected', true)

    if si ~= pi then
      selected.selected = true
      previous.selected = false
      self:emit({ type = 'tab_change', current = si, last = pi, tab = selected })
    end
    UI.MenuBar.draw(self)
  end
  return UI.MenuBar.eventHandler(self, event)
end

function UI.TabBar:selectTab(text)
  local menuItem = Util.find(self.children, 'text', text)
  if menuItem then
    menuItem.selected = true
  end
end

--[[-- Tabs --]]--
UI.Tabs = class(UI.Window)
UI.Tabs.defaults = {
  UIElement = 'Tabs',
}
function UI.Tabs:postInit()
  self:add(self)
end

function UI.Tabs:add(children)
  local buttons = { }
  for _,child in pairs(children) do
    if type(child) == 'table' and child.UIElement and child.tabTitle then
      child.y = 2
      table.insert(buttons, {
        text = child.tabTitle,
        event = 'tab_select',
        tabUid = child.uid,
      })
    end
  end

  if not self.tabBar then
    self.tabBar = UI.TabBar({
      buttons = buttons,
    })
  else
    self.tabBar:addButtons(buttons)
  end

  if self.parent then
    return UI.Window.add(self, children)
  end
end

function UI.Tabs:enable()
  self.enabled = true
  self.tabBar:enable()

  local menuItem = Util.find(self.tabBar.children, 'selected', true)

  for _,child in pairs(self.children) do
    if child.uid == menuItem.tabUid then
      child:enable()
      self:emit({ type = 'tab_activate', activated = child })
    elseif child.tabTitle then
      child:disable()
    end
  end
end

function UI.Tabs:eventHandler(event)
  if event.type == 'tab_change' then
    local tab = self:find(event.tab.tabUid)
    if event.current > event.last then
      tab:addTransition('slideLeft')
    else
      tab:addTransition('slideRight')
    end

    for _,child in pairs(self.children) do
      if child.uid == event.tab.tabUid then
        child:enable()
      elseif child.tabTitle then
        child:disable()
      end
    end
    self:emit({ type = 'tab_activate', activated = tab })
    tab:draw()
  end
end

--[[-- Wizard --]]--
UI.Wizard = class(UI.Window)
UI.Wizard.defaults = {
  UIElement = 'Wizard',
  pages = { },
}
function UI.Wizard:postInit()
  self.cancelButton = UI.Button {
    x = 2, y = -1,
    text = 'Cancel',
    event = 'cancel',
  }
  self.previousButton = UI.Button {
    x = -18, y = -1,
    text = '< Back',
    event = 'previousView',
  }
  self.nextButton = UI.Button {
    x = -9, y = -1,
    text = 'Next >',
    event = 'nextView',
  }

  Util.merge(self, self.pages)
  for _, child in pairs(self.pages) do
    child.ey = -2
  end
end

function UI.Wizard:add(pages)
  Util.merge(self.pages, pages)
  Util.merge(self, pages)

  for _, child in pairs(self.pages) do
    child.ey = child.ey or -2
  end

  if self.parent then
    self:initChildren()
  end
end

function UI.Wizard:enable()
  self.enabled = true
  for _,child in ipairs(self.children) do
    if not child.index then
      child:enable()
    elseif child.index == 1 then
      child:enable()
    else
      child:disable()
    end
  end
  self:emit({ type = 'enable_view', view = Util.find(self.pages, 'index', 1) })
end

function UI.Wizard:nextView()
  local currentView = Util.find(self.pages, 'enabled', true)
  local nextView = Util.find(self.pages, 'index', currentView.index + 1)

  if nextView then
    self:emit({ type = 'enable_view', view = nextView })
    self:addTransition('slideLeft')
    currentView:disable()
    nextView:enable()
  end
end

function UI.Wizard:prevView()
  local currentView = Util.find(self.pages, 'enabled', true)
  local nextView = Util.find(self.pages, 'index', currentView.index - 1)

  if nextView then
    self:emit({ type = 'enable_view', view = nextView })
    self:addTransition('slideRight')
    currentView:disable()
    nextView:enable()
  end
end

function UI.Wizard:eventHandler(event)
  if event.type == 'nextView' then
    self:nextView()
    self:draw()
    return true

  elseif event.type == 'previousView' then
    self:prevView()
    self:draw()
    return true

  elseif event.type == 'enable_view' then
    if Util.find(self.pages, 'index', event.view.index - 1) then
      self.previousButton:enable()
    else
      self.previousButton:disable()
    end

    if Util.find(self.pages, 'index', event.view.index + 1) then
      self.nextButton.text = 'Next >'
      self.nextButton.event = 'nextView'
    else
      self.nextButton.text = 'Accept'
      self.nextButton.event = 'accept'
    end
  end
end

--[[-- SlideOut --]]--
UI.SlideOut = class(UI.Window)
UI.SlideOut.defaults = {
  UIElement = 'SlideOut',
  pageType = 'modal',
}
function UI.SlideOut:setParent()
  UI.Window.setParent(self)
  self.canvas = self:addLayer()
end

function UI.SlideOut:enable()
  self.enabled = false
end

function UI.SlideOut:show()
  self:addTransition('expandUp')
  self.canvas:setVisible(true)
  self.enabled = true
  for _,child in pairs(self.children) do
    child:enable()
  end
  self:draw()
  self:capture(self)
  self:focusFirst()
end

function UI.SlideOut:disable()
  self.canvas:setVisible(false)
  self.enabled = false
  if self.children then
    for _,child in pairs(self.children) do
      child:disable()
    end
  end
end

function UI.SlideOut:hide()
  self:disable()
  self:release(self)
  self:refocus()
end

function UI.SlideOut:eventHandler(event)
  if event.type == 'slide_show' then
    self:show()
    return true

  elseif event.type == 'slide_hide' then
    self:hide()
    return true
  end
end

--[[-- Notification --]]--
UI.Notification = class(UI.Window)
UI.Notification.defaults = {
  UIElement = 'Notification',
  backgroundColor = colors.gray,
  height = 3,
}
function UI.Notification:draw()
end

function UI.Notification:enable()
  self.enabled = false
end

function UI.Notification:error(value, timeout)
  self.backgroundColor = colors.red
  self:display(value, timeout)
end

function UI.Notification:info(value, timeout)
  self.backgroundColor = colors.gray
  self:display(value, timeout)
end

function UI.Notification:success(value, timeout)
  self.backgroundColor = colors.green
  self:display(value, timeout)
end

function UI.Notification:cancel()
  if self.canvas then
    Event.cancelNamedTimer('notificationTimer')
    self.enabled = false
    self.canvas:removeLayer()
    self.canvas = nil
  end
end

function UI.Notification:display(value, timeout)
  self.enabled = true
  local lines = Util.wordWrap(value, self.width - 2)
  self.height = #lines + 1
  self.y = self.parent.height - self.height + 1
  if self.canvas then
    self.canvas:removeLayer()
  end

  self.canvas = self:addLayer(self.backgroundColor, self.textColor)
  self:addTransition('expandUp', { ticks = self.height })
  self.canvas:setVisible(true)
  self:clear()
  for k,v in pairs(lines) do
    self:write(2, k, v)
  end

  Event.addNamedTimer('notificationTimer', timeout or 3, false, function()
    self:cancel()
    self:sync()
  end)
end

--[[-- Throttle --]]--
UI.Throttle = class(UI.Window)
UI.Throttle.defaults = {
  UIElement = 'Throttle',
  backgroundColor = colors.gray,
  height = 6,
  width = 10,
  timeout = .095,
  ctr = 0,
  image = {
    '  //)    (O )~@ &~&-( ?Q        ',
    '  //)    (O )- @  \\-( ?)  &&    ',
    '  //)    (O ), @  \\-(?)     &&  ',
    '  //)    (O ). @  \\-d )      (@ '
  }
}
function UI.Throttle:setParent()
  self.x = math.ceil((self.parent.width - self.width) / 2)
  self.y = math.ceil((self.parent.height - self.height) / 2)
  UI.Window.setParent(self)
end

function UI.Throttle:enable()
  self.enabled = false
end

function UI.Throttle:disable()
  if self.canvas then
    self.enabled = false
    self.canvas:removeLayer()
    self.canvas = nil
    self.c = nil
  end
end

function UI.Throttle:update()
  local cc = os.clock()
  if not self.c then
    self.c = cc
  elseif cc > self.c + self.timeout then
    os.sleep(0)
    self.c = os.clock()
    self.enabled = true
    if not self.canvas then
      self.canvas = self:addLayer(self.backgroundColor, colors.cyan)
      self.canvas:setVisible(true)
      self:clear(colors.cyan)
    end
    local image = self.image[self.ctr + 1]
    local width = self.width - 2
    for i = 0, #self.image do
      self:write(2, i + 2, image:sub(width * i + 1, width * i + width), colors.black, colors.white)
    end

    self.ctr = (self.ctr + 1) % #self.image

    self:sync()
  end
end

--[[-- StatusBar --]]--
UI.StatusBar = class(UI.Window)
UI.StatusBar.defaults = {
  UIElement = 'StatusBar',
  backgroundColor = colors.lightGray,
  textColor = colors.gray,
  height = 1,
  ey = -1,
}
function UI.StatusBar:adjustWidth()
  -- Can only have 1 adjustable width
  if self.columns then
    local w = self.width - #self.columns - 1
    for _,c in pairs(self.columns) do
      if c.width then
        c.cw = c.width  -- computed width
        w = w - c.width
      end
    end
    for _,c in pairs(self.columns) do
      if not c.width then
        c.cw = w
      end
    end
  end
end

function UI.StatusBar:resize()
  UI.Window.resize(self)
  self:adjustWidth()
end

function UI.StatusBar:setParent()
  UI.Window.setParent(self)
  self:adjustWidth()
end

function UI.StatusBar:setStatus(status)
  if self.values ~= status then
    self.values = status
    self:draw()
  end
end

function UI.StatusBar:setValue(name, value)
  if not self.values then
    self.values = { }
  end
  self.values[name] = value
end

function UI.StatusBar:getValue(name)
  if self.values then
    return self.values[name]
  end
end

function UI.StatusBar:timedStatus(status, timeout)
  timeout = timeout or 3
  self:write(2, 1, Util.widthify(status, self.width-2), self.backgroundColor)
  Event.addNamedTimer('statusTimer', timeout, false, function()
    if self.parent.enabled then
      self:draw()
      self:sync()
    end
  end)
end

function UI.StatusBar:getColumnWidth(name)
  local c = Util.find(self.columns, 'key', name)
  return c and c.cw
end

function UI.StatusBar:setColumnWidth(name, width)
  local c = Util.find(self.columns, 'key', name)
  if c then
    c.cw = width
  end
end

function UI.StatusBar:draw()
  if not self.values then
    self:clear()
  elseif type(self.values) == 'string' then
    self:write(1, 1, Util.widthify(' ' .. self.values, self.width))
  else
    local s = ''
    for _,c in ipairs(self.columns) do
      s = s .. ' ' .. Util.widthify(tostring(self.values[c.key] or ''), c.cw)
    end
    self:write(1, 1, Util.widthify(s, self.width))
  end
end

--[[-- ProgressBar --]]--
UI.ProgressBar = class(UI.Window)
UI.ProgressBar.defaults = {
  UIElement = 'ProgressBar',
  progressColor = colors.lime,
  backgroundColor = colors.gray,
  height = 1,
  value = 0,
}
function UI.ProgressBar:draw()
  self:clear()
  local width = math.ceil(self.value / 100 * self.width)
  self:clearArea(1, 1, width, self.height, self.progressColor)
end

--[[-- VerticalMeter --]]--
UI.VerticalMeter = class(UI.Window)
UI.VerticalMeter.defaults = {
  UIElement = 'VerticalMeter',
  backgroundColor = colors.gray,
  meterColor = colors.lime,
  width = 1,
  value = 0,
}
function UI.VerticalMeter:draw()
  local height = self.height - math.ceil(self.value / 100 * self.height)
  self:clear()
  self:clearArea(1, height + 1, self.width, self.height, self.meterColor)
end

--[[-- TextEntry --]]--
UI.TextEntry = class(UI.Window)
UI.TextEntry.defaults = {
  UIElement = 'TextEntry',
  value = '',
  shadowText = '',
  focused = false,
  textColor = colors.white,
  shadowTextColor = colors.gray,
  backgroundColor = colors.black, -- colors.lightGray,
  backgroundFocusColor = colors.black, --lightGray,
  height = 1,
  limit = 6,
  pos = 0,
  accelerators = {
    [ 'control-c' ] = 'copy',
  }
}
function UI.TextEntry:postInit()
  self.value = tostring(self.value)
end

function UI.TextEntry:setValue(value)
  self.value = value
end

function UI.TextEntry:setPosition(pos)
  self.pos = pos
end

function UI.TextEntry:updateScroll()
  if not self.scroll then
    self.scroll = 0
  end

  if not self.pos then
    self.pos = #tostring(self.value)
    self.scroll = 0
  elseif self.pos > #tostring(self.value) then
    self.pos = #tostring(self.value)
    self.scroll = 0
  end

  if self.pos - self.scroll > self.width - 2 then
    self.scroll = self.pos - (self.width - 2)
  elseif self.pos < self.scroll then
    self.scroll = self.pos
  end
end

function UI.TextEntry:draw()
  local bg = self.backgroundColor
  local tc = self.textColor
  if self.focused then
    bg = self.backgroundFocusColor
  end

  self:updateScroll()
  local text = tostring(self.value)
  if #text > 0 then
    if self.scroll and self.scroll > 0 then
      text = text:sub(1 + self.scroll)
    end
    if self.mask then
      text = _rep('*', #text)
    end
  else
    tc = self.shadowTextColor
    text = self.shadowText
  end

  self:write(1, 1, ' ' .. Util.widthify(text, self.width - 2) .. ' ', bg, tc)
  if self.focused then
    self:setCursorPos(self.pos-self.scroll+2, 1)
  end
end

function UI.TextEntry:reset()
  self.pos = 0
  self.value = ''
  self:draw()
  self:updateCursor()
end

function UI.TextEntry:updateCursor()
  self:updateScroll()
  self:setCursorPos(self.pos-self.scroll+2, 1)
end

function UI.TextEntry:focus()
  self:draw()
  if self.focused then
    self:setCursorBlink(true)
  else
    self:setCursorBlink(false)
  end
end

--[[
  A few lines below from theoriginalbit
  http://www.computercraft.info/forums2/index.php?/topic/16070-read-and-limit-length-of-the-input-field/
--]]
function UI.TextEntry:eventHandler(event)
  if event.type == 'key' then
    local ch = event.key
    if ch == 'left' then
      if self.pos > 0 then
        self.pos = math.max(self.pos-1, 0)
        self:draw()
      end
    elseif ch == 'right' then
      local input = tostring(self.value)
      if self.pos < #input then
        self.pos = math.min(self.pos+1, #input)
        self:draw()
      end
    elseif ch == 'home' then
      self.pos = 0
      self:draw()
    elseif ch == 'end' then
      self.pos = #tostring(self.value)
      self:draw()
    elseif ch == 'backspace' then
      if self.pos > 0 then
        local input = tostring(self.value)
        self.value = input:sub(1, self.pos-1) .. input:sub(self.pos+1)
        self.pos = self.pos - 1
        self:draw()
        self:emit({ type = 'text_change', text = self.value, element = self })
      end
    elseif ch == 'delete' then
      local input = tostring(self.value)
      if self.pos < #input then
        self.value = input:sub(1, self.pos) .. input:sub(self.pos+2)
        self:draw()
        self:emit({ type = 'text_change', text = self.value, element = self })
      end
    elseif #ch == 1 then
      local input = tostring(self.value)
      if #input < self.limit then
        self.value = input:sub(1, self.pos) .. ch .. input:sub(self.pos+1)
        self.pos = self.pos + 1
        self:draw()
        self:emit({ type = 'text_change', text = self.value, element = self })
      end
    else
      return false
    end
    return true

  elseif event.type == 'copy' then
    os.queueEvent('clipboard_copy', self.value)

  elseif event.type == 'paste' then
    local input = tostring(self.value)
    local text = event.text
    if #input + #text > self.limit then
      text = text:sub(1, self.limit-#input)
    end
    self.value = input:sub(1, self.pos) .. text .. input:sub(self.pos+1)
    self.pos = self.pos + #text
    self:draw()
    self:updateCursor()
    self:emit({ type = 'text_change', text = self.value, element = self })
    return true

  elseif event.type == 'mouse_click' then
    if self.focused and event.x > 1 then
      self.pos = event.x + self.scroll - 2
      self:updateCursor()
      return true
    end
  elseif event.type == 'mouse_rightclick' then
    local input = tostring(self.value)
    if #input > 0 then
      self:reset()
      self:emit({ type = 'text_change', text = self.value, element = self })
    end
  end

  return false
end

--[[-- Chooser --]]--
UI.Chooser = class(UI.Window)
UI.Chooser.defaults = {
  UIElement = 'Chooser',
  choices = { },
  nochoice = 'Select',
  backgroundFocusColor = colors.lightGray,
  height = 1,
}
function UI.Chooser:setParent()
  if not self.width and not self.ex then
    self.width = 1
    for _,v in pairs(self.choices) do
      if #v.name > self.width then
        self.width = #v.name
      end
    end
    self.width = self.width + 4
  end
  UI.Window.setParent(self)
end

function UI.Chooser:draw()
  local bg = self.backgroundColor
  if self.focused then
    bg = self.backgroundFocusColor
  end
  local choice = Util.find(self.choices, 'value', self.value)
  local value = self.nochoice
  if choice then
    value = choice.name
  end
  self:write(1, 1, '<', bg, colors.black)
  self:write(2, 1, ' ' .. Util.widthify(value, self.width-4) .. ' ', bg)
  self:write(self.width, 1, '>', bg, colors.black)
end

function UI.Chooser:focus()
  self:draw()
end

function UI.Chooser:eventHandler(event)
  if event.type == 'key' then
    if event.key == 'right' or event.key == 'space' then
      local _,k = Util.find(self.choices, 'value', self.value)
      if k and k < #self.choices then
        self.value = self.choices[k+1].value
      else
        self.value = self.choices[1].value
      end
      self:emit({ type = 'choice_change', value = self.value })
      self:draw()
      return true
    elseif event.key == 'left' then
      local _,k = Util.find(self.choices, 'value', self.value)
      if k and k > 1 then
        self.value = self.choices[k-1].value
      else
        self.value = self.choices[#self.choices].value
      end
      self:emit({ type = 'choice_change', value = self.value })
      self:draw()
      return true
    end
  elseif event.type == 'mouse_click' then
    if event.x == 1 then
      self:emit({ type = 'key', key = 'left' })
      return true
    elseif event.x == self.width then
      self:emit({ type = 'key', key = 'right' })
      return true
    end
  end
end

--[[-- Text --]]--
UI.Text = class(UI.Window)
UI.Text.defaults = {
  UIElement = 'Text',
  value = '',
  height = 1,
}
function UI.Text:setParent()
  if not self.width and not self.ex then
    self.width = #tostring(self.value)
  end
  UI.Window.setParent(self)
end

function UI.Text:draw()
  self:write(1, 1, Util.widthify(self.value or '', self.width), self.backgroundColor)
end

--[[-- ScrollBar --]]--
UI.ScrollBar = class(UI.Window)
UI.ScrollBar.defaults = {
  UIElement = 'ScrollBar',
  lineChar = '|',
  sliderChar = '#',
  upArrowChar = '^',
  downArrowChar = 'v',
  scrollbarColor = colors.lightGray,
  value = '',
  width = 1,
  x = -1,
  ey = -1,
}
function UI.ScrollBar:draw()
  local parent = self.parent
  local view = parent:getViewArea()

  if view.totalHeight > view.height then
    local maxScroll = view.totalHeight - view.height
    local percent = view.offsetY / maxScroll
    local sliderSize = math.max(1, Util.round(view.height / view.totalHeight * (view.height - 2)))
    local x = self.width

    local row = view.y
    if not view.static then  -- does the container scroll ?
      self.y = row           -- if so, move the scrollbar onscreen
      row = 1
    end

    for i = 1, view.height - 2 do
      self:write(x, row + i, self.lineChar, nil, self.scrollbarColor)
    end

    local y = Util.round((view.height - 2 - sliderSize) * percent)
    for i = 1, sliderSize do
      self:write(x, row + y + i, self.sliderChar, nil, self.scrollbarColor)
    end

    local color = self.scrollbarColor
    if view.offsetY > 0 then
      color = colors.white
    end
    self:write(x, row, self.upArrowChar, nil, color)

    color = self.scrollbarColor
    if view.offsetY + view.height < view.totalHeight then
      color = colors.white
    end
    self:write(x, row + view.height - 1, self.downArrowChar, nil, color)
  end
end

function UI.ScrollBar:eventHandler(event)
  if event.type == 'mouse_click' or event.type == 'mouse_doubleclick' then
    if event.x == 1 then
      local view = self.parent:getViewArea()
      if view.totalHeight > view.height then
        if event.y == view.y then
          self:emit({ type = 'scroll_up'})
        elseif event.y == self.height then
          self:emit({ type = 'scroll_down'})
          -- else
          -- ... percentage ...
        end
      end
      return true
    end
  end
end

--[[-- TextArea --]]--
UI.TextArea = class(UI.Viewport)
UI.TextArea.defaults = {
  UIElement = 'TextArea',
  marginRight = 2,
  value = '',
}
function UI.TextArea:postInit()
  self.scrollBar = UI.ScrollBar()
end

function UI.TextArea:setText(text)
  self.offy = 0
  self.ymax = nil
  self.value = text
  self:draw()
end

function UI.TextArea:focus()
  -- allow keyboard scrolling
end

function UI.TextArea:draw()
  self:clear()
--  self:setCursorPos(1, 1)
  self.cursorX, self.cursorY = 1, 1
  self:print(self.value)
  self.ymax = self.cursorY + 1

  for _,child in pairs(self.children) do
    if child.enabled then
      child:draw()
    end
  end
end

--[[-- Form --]]--
UI.Form = class(UI.Window)
UI.Form.defaults = {
  UIElement = 'Form',
  values = { },
  margin = 2,
  event = 'form_complete',
}
function UI.Form:postInit()
  self:createForm()
end

function UI.Form:reset()
  for _,child in pairs(self.children) do
    if child.reset then
      child:reset()
    end
  end
end

function UI.Form:setValues(values)
  self:reset()
  self.values = values
  for _,child in pairs(self.children) do
    if child.formKey then
      -- this should be child:setValue(self.values[child.formKey])
      -- so chooser can set default choice if null
      -- null should be valid as well
      child.value = self.values[child.formKey] or ''
    end
  end
end

function UI.Form:createForm()
  self.children = self.children or { }

  if not self.labelWidth then
    self.labelWidth = 1
    for _, child in pairs(self) do
      if type(child) == 'table' and child.UIElement then
        if child.formLabel then
          self.labelWidth = math.max(self.labelWidth, #child.formLabel + 2)
        end
      end
    end
  end

  local y = self.margin
  for _, child in pairs(self) do
    if type(child) == 'table' and child.UIElement then
      if child.formKey then
        child.value = self.values[child.formKey] or ''
      end
      if child.formLabel then
        child.x = self.labelWidth + self.margin - 1
        child.y = y
        if not child.width and not child.ex then
          child.ex = -self.margin
        end

        table.insert(self.children, UI.Text {
          x = self.margin,
          y = y,
          textColor = colors.black,
          width = #child.formLabel,
          value = child.formLabel,
        })
      end
      if child.formKey or child.formLabel then
        y = y + 1
      end
    end
  end

  table.insert(self.children, UI.Button {
    y = -self.margin, x = -12 - self.margin,
    text = 'Ok',
    event = 'form_ok',
  })
  table.insert(self.children, UI.Button {
    y = -self.margin, x = -7 - self.margin,
    text = 'Cancel',
    event = 'form_cancel',
  })
end

function UI.Form:validateField(field)
  if field.required then
    if not field.value or #tostring(field.value) == 0 then
      return false, 'Field is required'
    end
  end
  return true
end

function UI.Form:eventHandler(event)
  if event.type == 'form_ok' then
    for _,child in pairs(self.children) do
      if child.formKey  then
        local s, m = self:validateField(child)
        if not s then
          self:setFocus(child)
          self:emit({ type = 'form_invalid', message = m, field = child })
          return false
        end
      end
    end
    for _,child in pairs(self.children) do
      if child.formKey then
        self.values[child.formKey] = child.value
      end
    end
    self:emit({ type = self.event, UIElement = self })
  else
    return UI.Window.eventHandler(self, event)
  end
  return true
end

--[[-- Dialog --]]--
UI.Dialog = class(UI.Page)
UI.Dialog.defaults = {
  UIElement = 'Dialog',
  x = 7,
  y = 4,
  z = 2,
  height = 7,
  textColor = colors.black,
  backgroundColor = colors.white,
}
function UI.Dialog:postInit()
  self.titleBar = UI.TitleBar({ previousPage = true, title = self.title })
end

function UI.Dialog:setParent()
  if not self.width then
    self.width = self.parent.width - 11
  end
  if self.width > self.parent.width then
    self.width = self.parent.width
  end
  self.x = math.floor((self.parent.width - self.width) / 2) + 1
  self.y = math.floor((self.parent.height - self.height) / 2) + 1
  UI.Page.setParent(self)
end

function UI.Dialog:disable()
  self.previousPage.canvas.palette = self.oldPalette
  UI.Page.disable(self)
end

function UI.Dialog:enable(...)
  self.oldPalette = self.previousPage.canvas.palette
  self.previousPage.canvas:applyPalette(Canvas.darkPalette)
  self:addTransition('grow')
  UI.Page.enable(self, ...)
end

function UI.Dialog:eventHandler(event)
  if event.type == 'cancel' then
    UI:setPreviousPage()
  end
  return UI.Page.eventHandler(self, event)
end

--[[-- Image --]]--
UI.Image = class(UI.Window)
UI.Image.defaults = {
  UIElement = 'Image',
  event = 'button_press',
}
function UI.Image:setParent()
  if self.image then
    self.height = #self.image
  end
  if self.image and not self.width then
    self.width = #self.image[1]
  end
  UI.Window.setParent(self)
end

function UI.Image:draw()
  self:clear()
  if self.image then
    for y = 1, #self.image do
      local line = self.image[y]
      for x = 1, #line do
        local ch = line[x]
        if type(ch) == 'number' then
          if ch > 0 then
            self:write(x, y, ' ', ch)
          end
        else
          self:write(x, y, ch)
        end
      end
    end
  end
end

function UI.Image:setImage(image)
  self.image = image
end

--[[-- NftImage --]]--
UI.NftImage = class(UI.Window)
UI.NftImage.defaults = {
  UIElement = 'NftImage',
  event = 'button_press',
}
function UI.NftImage:setParent()
  if self.image then
    self.height = self.image.height
  end
  if self.image and not self.width then
    self.width = self.image.width
  end
  UI.Window.setParent(self)
end

function UI.NftImage:draw()
  if self.image then
    for y = 1, self.image.height do
      for x = 1, #self.image.text[y] do
        self:write(x, y, self.image.text[y][x], self.image.bg[y][x], self.image.fg[y][x])
      end
    end
  else
    self:clear()
  end
end

function UI.NftImage:setImage(image)
  self.image = image
end

UI:loadTheme('usr/config/ui.theme')
if Util.getVersion() >= 1.76 then
  UI:loadTheme('sys/etc/ext.theme')
end

UI:setDefaultDevice(UI.Device({ device = term.current() }))

return UI