local os = _G.os

local Event = {
  uid       = 1,       -- unique id for handlers
  routines  = { },     -- coroutines
  types     = { },     -- event handlers
  timers    = { },     -- named timers
  terminate = false,
}

local Routine = { }

function Routine:isDead()
  if not self.co then
    return true
  end
  return coroutine.status(self.co) == 'dead'
end

function Routine:terminate()
  if self.co then
    self:resume('terminate')
  end
end

function Routine:resume(event, ...)
  --if coroutine.status(self.co) == 'running' then
    --return
  --end

  if not self.co then
    error('Cannot resume a dead routine')
  end

  if not self.filter or self.filter == event or event == "terminate" then
    local s, m = coroutine.resume(self.co, event, ...)

    if coroutine.status(self.co) == 'dead' then
      self.co = nil
      self.filter = nil
      Event.routines[self.uid] = nil
    else
      self.filter = m
    end

    if not s and event ~= 'terminate' then
      error('\n' .. (m or 'Error processing event'))
    end

    return s, m
  end

  return true, self.filter
end

local function nextUID()
  Event.uid = Event.uid + 1
  return Event.uid - 1
end

function Event.on(event, fn)

  local handlers = Event.types[event]
  if not handlers then
    handlers = { }
    Event.types[event] = handlers
  end

  local handler = {
    uid     = nextUID(),
    event   = event,
    fn      = fn,
  }
  handlers[handler.uid] = handler
  setmetatable(handler, { __index = Routine })

  return handler
end

function Event.off(h)
  if h and h.event then
    Event.types[h.event][h.uid] = nil
  end
end

local function addTimer(interval, recurring, fn)

  local timerId = os.startTimer(interval)
  local handler

  handler = Event.on('timer', function(t, id)
    if timerId == id then
      fn(t, id)
      if recurring then
        timerId = os.startTimer(interval)
      else
        Event.off(handler)
      end
    end
  end)

  return handler
end

function Event.onInterval(interval, fn)
  return addTimer(interval, true, fn)
end

function Event.onTimeout(timeout, fn)
  return addTimer(timeout, false, fn)
end

function Event.addNamedTimer(name, interval, recurring, fn)
  Event.cancelNamedTimer(name)
  Event.timers[name] = addTimer(interval, recurring, fn)
end

function Event.cancelNamedTimer(name)
  local timer = Event.timers[name]
  if timer then
    Event.off(timer)
  end
end

function Event.waitForEvent(event, timeout)
  local timerId = os.startTimer(timeout)
  repeat
    local e = { os.pullEvent() }
    if e[1] == event then
      return table.unpack(e)
    end
  until e[1] == 'timer' and e[2] == timerId
end

function Event.addRoutine(fn)
  local r = {
    co  = coroutine.create(fn),
    uid = nextUID()
  }
  setmetatable(r, { __index = Routine })
  Event.routines[r.uid] = r

  r:resume()

  return r
end

function Event.pullEvents(...)

  for _, fn in ipairs({ ... }) do
    Event.addRoutine(fn)
  end

  repeat
    local e = Event.pullEvent()
  until e[1] == 'terminate'
end

function Event.exitPullEvents()
  Event.terminate = true
  os.sleep(0)
end

local function processHandlers(event)

  local handlers = Event.types[event]
  if handlers then
    for _,h in pairs(handlers) do
      if not h.co then
        -- callbacks are single threaded (only 1 co per handler)
        h.co = coroutine.create(h.fn)
        Event.routines[h.uid] = h
      end
    end
  end
end

local function tokeys(t)
  local keys = { }
  for k in pairs(t) do
    keys[#keys+1] = k
  end
  return keys
end

local function processRoutines(...)

  local keys = tokeys(Event.routines)
  for _,key in ipairs(keys) do
    local r = Event.routines[key]
    if r then
      r:resume(...)
    end
  end
end

function Event.processEvent(e)
  processHandlers(e[1])
  processRoutines(table.unpack(e))
end

function Event.pullEvent(eventType)

  while true do
    local e = { os.pullEventRaw() }

    processHandlers(e[1])
    processRoutines(table.unpack(e))

    if Event.terminate or e[1] == 'terminate' then
      Event.terminate = false
      return { 'terminate' }
    end

    if not eventType or e[1] == eventType then
      return e
    end
  end
end

return Event