--[[- Provides a "pretty printer", for rendering data structures in an
aesthetically pleasing manner.

In order to display something using @{cc.pretty}, you build up a series of
@{Doc|documents}. These behave a little bit like strings; you can concatenate
them together and then print them to the screen.

However, documents also allow you to control how they should be printed. There
are several functions (such as @{nest} and @{group}) which allow you to control
the "layout" of the document. When you come to display the document, the 'best'
(most compact) layout is used.

The structure of this module is based on [A Prettier Printer][prettier].

[prettier]: https://homepages.inf.ed.ac.uk/wadler/papers/prettier/prettier.pdf "A Prettier Printer"

@module cc.pretty
@usage Print a table to the terminal
    local pretty = require "cc.pretty"
    pretty.print(pretty.pretty({ 1, 2, 3 }))

@usage Build a custom document and display it
    local pretty = require "cc.pretty"
    pretty.print(pretty.group(pretty.text("hello") .. pretty.space_line .. pretty.text("world")))
]]

local expect = require "cc.expect"
local expect, field = expect.expect, expect.field

local type, getmetatable, setmetatable, colours, str_write, tostring = type, getmetatable, setmetatable, colours, write, tostring
local debug_info, debug_local = debug.getinfo, debug.getlocal

--- @{table.insert} alternative, but with the length stored inline.
local function append(out, value)
    local n = out.n + 1
    out[n], out.n = value, n
end

--- A document containing formatted text, with multiple possible layouts.
--
-- Documents effectively represent a sequence of strings in alternative layouts,
-- which we will try to print in the most compact form necessary.
--
-- @type Doc
local Doc = { }

local function mk_doc(tbl) return setmetatable(tbl, Doc) end

--- An empty document.
local empty = mk_doc({ tag = "nil" })

--- A document with a single space in it.
local space = mk_doc({ tag = "text", text = " " })

--- A line break. When collapsed with @{group}, this will be replaced with @{empty}.
local line = mk_doc({ tag = "line", flat = empty })

--- A line break. When collapsed with @{group}, this will be replaced with @{space}.
local space_line = mk_doc({ tag = "line", flat = space })

local text_cache = { [""] = empty, [" "] = space, ["\n"] = space_line }

local function mk_text(text, colour)
    return text_cache[text] or setmetatable({ tag = "text", text = text, colour = colour }, Doc)
end

--- Create a new document from a string.
--
-- If your string contains multiple lines, @{group} will flatten the string
-- into a single line, with spaces between each line.
--
-- @tparam      string text   The string to construct a new document with.
-- @tparam[opt] number colour The colour this text should be printed with. If not given, we default to the current
-- colour.
-- @treturn Doc The document with the provided text.
-- @usage Write some blue text.
--     local pretty = require "cc.pretty"
--     pretty.print(pretty.text("Hello!", colours.blue))
local function text(text, colour)
    expect(1, text, "string")
    expect(2, colour, "number", "nil")

    local cached = text_cache[text]
    if cached then return cached end

    local new_line = text:find("\n", 1)
    if not new_line then return mk_text(text, colour) end

    -- Split the string by "\n". With a micro-optimisation to skip empty strings.
    local doc = setmetatable({ tag = "concat", n = 0 }, Doc)
    if new_line ~= 1 then append(doc, mk_text(text:sub(1, new_line - 1), colour)) end

    new_line = new_line + 1
    while true do
        local next_line = text:find("\n", new_line)
        append(doc, space_line)
        if not next_line then
            if new_line <= #text then append(doc, mk_text(text:sub(new_line), colour)) end
            return doc
        else
            if new_line <= next_line - 1 then
                append(doc, mk_text(text:sub(new_line, next_line - 1), colour))
            end
            new_line = next_line + 1
        end
    end
end

--- Concatenate several documents together. This behaves very similar to string concatenation.
--
-- @tparam Doc|string ... The documents to concatenate.
-- @treturn Doc The concatenated documents.
-- @usage
--     local pretty = require "cc.pretty"
--     local doc1, doc2 = pretty.text("doc1"), pretty.text("doc2")
--     print(pretty.concat(doc1, " - ", doc2))
--     print(doc1 .. " - " .. doc2) -- Also supports ..
local function concat(...)
    local args = table.pack(...)
    for i = 1, args.n do
        if type(args[i]) == "string" then args[i] = text(args[i]) end
        if getmetatable(args[i]) ~= Doc then expect(i, args[i], "document") end
    end

    if args.n == 0 then return empty end
    if args.n == 1 then return args[1] end

    args.tag = "concat"
    return setmetatable(args, Doc)
end

Doc.__concat = concat --- @local

--- Indent later lines of the given document with the given number of spaces.
--
-- For instance, nesting the document
-- ```txt
-- foo
-- bar
-- ```
-- by two spaces will produce
-- ```txt
-- foo
--   bar
-- ```
--
-- @tparam number depth The number of spaces with which the document should be indented.
-- @tparam Doc    doc   The document to indent.
-- @treturn Doc The nested document.
-- @usage
--     local pretty = require "cc.pretty"
--     print(pretty.nest(2, pretty.text("foo\nbar")))
local function nest(depth, doc)
    expect(1, depth, "number")
    if getmetatable(doc) ~= Doc then expect(2, doc, "document") end
    if depth <= 0 then error("depth must be a positive number", 2) end

    return setmetatable({ tag = "nest", depth = depth, doc }, Doc)
end

local function flatten(doc)
    if doc.flat then return doc.flat end

    local kind = doc.tag
    if kind == "nil" or kind == "text" then
        return doc
    elseif kind == "concat" then
        local out = setmetatable({ tag = "concat", n = doc.n }, Doc)
        for i = 1, doc.n do out[i] = flatten(doc[i]) end
        doc.flat, out.flat = out, out -- cache the flattened node
        return out
    elseif kind == "nest" then
        return flatten(doc[1])
    elseif kind == "group" then
        return doc[1]
    else
        error("Unknown doc " .. kind)
    end
end

--- Builds a document which is displayed on a single line if there is enough
-- room, or as normal if not.
--
-- @tparam Doc doc The document to group.
-- @treturn Doc The grouped document.
-- @usage Uses group to show things being displayed on one or multiple lines.
--
--     local pretty = require "cc.pretty"
--     local doc = pretty.group("Hello" .. pretty.space_line .. "World")
--     print(pretty.render(doc, 5)) -- On multiple lines
--     print(pretty.render(doc, 20)) -- Collapsed onto one.
local function group(doc)
    if getmetatable(doc) ~= Doc then expect(1, doc, "document") end

    if doc.tag == "group" then return doc end -- Skip if already grouped.

    local flattened = flatten(doc)
    if flattened == doc then return doc end -- Also skip if flattening does nothing.
    return setmetatable({ tag = "group", flattened, doc }, Doc)
end

local function get_remaining(doc, width)
    local kind = doc.tag
    if kind == "nil" or kind == "line" then
        return width
    elseif kind == "text" then
        return width - #doc.text
    elseif kind == "concat" then
        for i = 1, doc.n do
            width = get_remaining(doc[i], width)
            if width < 0 then break end
        end
        return width
    elseif kind == "group" or kind == "nest" then
        return get_remaining(kind[1])
    else
        error("Unknown doc " .. kind)
    end
end

--- Display a document on the terminal.
--
-- @tparam      Doc     doc         The document to render
-- @tparam[opt] number  ribbon_frac The maximum fraction of the width that we should write in.
local function write(doc, ribbon_frac)
    if getmetatable(doc) ~= Doc then expect(1, doc, "document") end
    expect(2, ribbon_frac, "number", "nil")

    local term = term
    local width, height = term.getSize()
    local ribbon_width = (ribbon_frac or 0.6) * width
    if ribbon_width < 0 then ribbon_width = 0 end
    if ribbon_width > width then ribbon_width = width end

    local def_colour = term.getTextColour()
    local current_colour = def_colour

    local function go(doc, indent, col)
        local kind = doc.tag
        if kind == "nil" then
            return col
        elseif kind == "text" then
            local doc_colour = doc.colour or def_colour
            if doc_colour ~= current_colour then
                term.setTextColour(doc_colour)
                current_colour = doc_colour
            end

            str_write(doc.text)

            return col + #doc.text
        elseif kind == "line" then
            local _, y = term.getCursorPos()
            if y < height then
                term.setCursorPos(indent + 1, y + 1)
            else
                term.scroll(1)
                term.setCursorPos(indent + 1, height)
            end

            return indent
        elseif kind == "concat" then
            for i = 1, doc.n do col = go(doc[i], indent, col) end
            return col
        elseif kind == "nest" then
            return go(doc[1], indent + doc.depth, col)
        elseif kind == "group" then
            if get_remaining(doc[1], math.min(width, ribbon_width + indent) - col) >= 0 then
                return go(doc[1], indent, col)
            else
                return go(doc[2], indent, col)
            end
        else
            error("Unknown doc " .. kind)
        end
    end

    local col = math.max(term.getCursorPos() - 1, 0)
    go(doc, 0, col)
    if current_colour ~= def_colour then term.setTextColour(def_colour) end
end

--- Display a document on the terminal with a trailing new line.
--
-- @tparam      Doc     doc         The document to render.
-- @tparam[opt] number  ribbon_frac The maximum fraction of the width that we should write in.
local function print(doc, ribbon_frac)
    if getmetatable(doc) ~= Doc then expect(1, doc, "document") end
    expect(2, ribbon_frac, "number", "nil")
    write(doc, ribbon_frac)
    str_write("\n")
end

--- Render a document, converting it into a string.
--
-- @tparam      Doc     doc         The document to render.
-- @tparam[opt] number  width       The maximum width of this document. Note that long strings will not be wrapped to
-- fit this width - it is only used for finding the best layout.
-- @tparam[opt] number  ribbon_frac The maximum fraction of the width that we should write in.
-- @treturn string The rendered document as a string.
local function render(doc, width, ribbon_frac)
    if getmetatable(doc) ~= Doc then expect(1, doc, "document") end
    expect(2, width, "number", "nil")
    expect(3, ribbon_frac, "number", "nil")

    local ribbon_width
    if width then
        ribbon_width = (ribbon_frac or 0.6) * width
        if ribbon_width < 0 then ribbon_width = 0 end
        if ribbon_width > width then ribbon_width = width end
    end

    local out = { n = 0 }
    local function go(doc, indent, col)
        local kind = doc.tag
        if kind == "nil" then
            return col
        elseif kind == "text" then
            append(out, doc.text)
            return col + #doc.text
        elseif kind == "line" then
            append(out, "\n" .. (" "):rep(indent))
            return indent
        elseif kind == "concat" then
            for i = 1, doc.n do col = go(doc[i], indent, col) end
            return col
        elseif kind == "nest" then
            return go(doc[1], indent + doc.depth, col)
        elseif kind == "group" then
            if not width or get_remaining(doc[1], math.min(width, ribbon_width + indent) - col) >= 0 then
                return go(doc[1], indent, col)
            else
                return go(doc[2], indent, col)
            end
        else
            error("Unknown doc " .. kind)
        end
    end

    go(doc, 0, 0)
    return table.concat(out, "", 1, out.n)
end

Doc.__tostring = render --- @local

local keywords = {
    ["and"] = true, ["break"] = true, ["do"] = true, ["else"] = true,
    ["elseif"] = true, ["end"] = true, ["false"] = true, ["for"] = true,
    ["function"] = true, ["if"] = true, ["in"] = true, ["local"] = true,
    ["nil"] = true, ["not"] = true, ["or"] = true, ["repeat"] = true, ["return"] = true,
    ["then"] = true, ["true"] = true, ["until"] = true, ["while"] = true,
  }

local comma = text(",")
local braces = text("{}")
local obrace, cbrace = text("{"), text("}")
local obracket, cbracket = text("["), text("] = ")

local function key_compare(a, b)
    local ta, tb = type(a), type(b)

    if ta == "string" then return tb ~= "string" or a < b
    elseif tb == "string" then return false
    end

    if ta == "number" then return tb ~= "number" or a < b end
    return false
end

local function show_function(fn, options)
    local info = debug_info and debug_info(fn, "Su")

    -- Include function source position if available
    local name
    if options.function_source and info and info.short_src and info.linedefined and info.linedefined >= 1 then
        name = "function<" .. info.short_src .. ":" .. info.linedefined .. ">"
    else
        name = tostring(fn)
    end

    -- Include arguments if a Lua function and if available. Lua will report "C"
    -- functions as variadic.
    if options.function_args and info and info.what == "Lua" and info.nparams and debug_local then
        local args = {}
        for i = 1, info.nparams do args[i] = debug_local(fn, i) or "?" end
        if info.isvararg then args[#args + 1] = "..." end
        name = name .. "(" .. table.concat(args, ", ") .. ")"
    end

    return name
end

local function pretty_impl(obj, options, tracking)
    local obj_type = type(obj)
    if obj_type == "string" then
        local formatted = ("%q"):format(obj):gsub("\\\n", "\\n")
        return text(formatted, colours.red)
    elseif obj_type == "number" then
        return text(tostring(obj), colours.magenta)
    elseif obj_type == "function" then
        return text(show_function(obj, options), colours.lightGrey)
    elseif obj_type ~= "table" or tracking[obj] then
        return text(tostring(obj), colours.lightGrey)
    elseif getmetatable(obj) ~= nil and getmetatable(obj).__tostring then
        return text(tostring(obj))
    elseif next(obj) == nil then
        return braces
    else
        tracking[obj] = true
        local doc = setmetatable({ tag = "concat", n = 1, space_line }, Doc)

        local length, keys, keysn = #obj, {}, 1
        for k in pairs(obj) do
            if type(k) ~= "number" or k % 1 ~= 0 or k < 1 or k > length then
                keys[keysn], keysn = k, keysn + 1
            end
        end
        table.sort(keys, key_compare)

        for i = 1, length do
            if i > 1 then append(doc, comma) append(doc, space_line) end
            append(doc, pretty_impl(obj[i], options, tracking))
        end

        for i = 1, keysn - 1 do
            if i > 1 or length >= 1 then append(doc, comma) append(doc, space_line) end

            local k = keys[i]
            local v = obj[k]
            if type(k) == "string" and not keywords[k] and k:match("^[%a_][%a%d_]*$") then
                append(doc, text(k .. " = "))
                append(doc, pretty_impl(v, options, tracking))
            else
                append(doc, obracket)
                append(doc, pretty_impl(k, options, tracking))
                append(doc, cbracket)
                append(doc, pretty_impl(v, options, tracking))
            end
        end

        tracking[obj] = nil
        return group(concat(obrace, nest(2, concat(table.unpack(doc, 1, doc.n))), space_line, cbrace))
    end
end

--- Pretty-print an arbitrary object, converting it into a document.
--
-- This can then be rendered with @{write} or @{print}.
--
-- @param obj The object to pretty-print.
-- @tparam[opt] { function_args = boolean, function_source = boolean } options
-- Controls how various properties are displayed.
--  - `function_args`: Show the arguments to a function if known (`false` by default).
--  - `function_source`: Show where the function was defined, instead of
--    `function: xxxxxxxx` (`false` by default).
-- @treturn Doc The object formatted as a document.
-- @usage Display a table on the screen
--     local pretty = require "cc.pretty"
--     pretty.print(pretty.pretty({ 1, 2, 3 }))
local function pretty(obj, options)
    expect(2, options, "table", "nil")
    options = options or {}

    local actual_options = {
        function_source = field(options, "function_source", "boolean", "nil") or false,
        function_args = field(options, "function_args", "boolean", "nil") or false,
    }
    return pretty_impl(obj, actual_options, {})
end

return {
    empty = empty,
    space = space,
    line = line,
    space_line = space_line,
    text = text,
    concat = concat,
    nest = nest,
    group = group,

    write = write,
    print = print,
    render = render,

    pretty = pretty,
}