VERSION = "0.1.0"
PLUGIN_NAME = "flow"

local micro  = import("micro")
local config = import("micro/config")
local util   = import("micro/util")
local buffer = import("micro/buffer")

function init()
	config.MakeCommand(PLUGIN_NAME,               flowIndent,  config.NoComplete)
	config.MakeCommand(PLUGIN_NAME .. ".left",    flowLeft,    config.NoComplete)
	config.MakeCommand(PLUGIN_NAME .. ".right",   flowRight,   config.NoComplete)
	config.MakeCommand(PLUGIN_NAME .. ".center",  flowCenter,  config.NoComplete)
	-- config.MakeCommand(PLUGIN_NAME .. ".justify", flowJustify, config.NoComplete)
end

function flowIndent(bufferPane)
	return flow(bufferPane, "indent")
end

function flowLeft(bufferPane)
	return flow(bufferPane, "left")
end

function flowRight(bufferPane)
	return flow(bufferPane, "right")
end

function flowCenter(bufferPane)
	return flow(bufferPane, "center")
end

function flowJustify(bufferPane)
	return flow(bufferPane, "justify")
end

function flow(bufferPane, align)
	local cursor = bufferPane.Buf:GetActiveCursor()
	if not (cursor and cursor:HasSelection()) then return end

	-- TODO: if there is no selection, operate on the start and end of
	-- the currently selected paragraph, which is demarcated by double line
	-- breaks/beginning/end of file

	local sstart, send = nil, nil
        if cursor.CurSelection[1]:GreaterThan(-cursor.CurSelection[2]) then
            sstart, send = cursor.CurSelection[2], cursor.CurSelection[1]
        else
            sstart, send = cursor.CurSelection[1], cursor.CurSelection[2]
        end
        sstart = buffer.Loc(sstart.X, sstart.Y)
        send   = buffer.Loc(send.X, send.Y)
        
	local selection = util.String(cursor:GetSelection())
	bufferPane.Buf:Replace(sstart, send, reflow(selection, align, colorColumn()))
end

function reflow(text, alignment, columns)
	local trailingBreak = text:sub(#text, #text) == "\n"

	-- get indentation information
	local firstLineIndent, middleLineIndent, inputLines = splitIndentation(text)
	firstLineIndent  = firstLineIndent  or ""
	middleLineIndent = middleLineIndent or ""
	
	-- tokenize
	local tokens = { }
	for _, line in ipairs(inputLines) do
		tokens = append(tokens, tokenize(line))
	end

	-- format tokens
	local result = ""
	local line   = ""
	local currentColumns = columns - measure(firstLineIndent)
	function addLine()
		local first = false
		if result == "" then
			first = true
		else
			result = result .. "\n"
		end
		if alignment == "indent" then
			if first then
				line = firstLineIndent .. line
			else
				line = middleLineIndent .. line
			end
		else
			line = align(line, alignment, columns)
		end
		result = result .. line
		currentColumns = columns - measure(middleLineIndent)
	end
	for _, token in ipairs(tokens) do
		local forecast = #line + 1 + #token
		if forecast > currentColumns then
			addLine()
			line = ""
		end
		if line ~= "" then line = line .. " " end
		line = line .. token
	end
	addLine()

	if trailingBreak then result = result .. "\n" end
	return result
end

-- assumes the text begins directly at the start of the file or directly after
-- a line break. returns the indentation for the first line, lines in the
-- middle, and the last line.
function splitIndentation(text)
	local indents = { }
	local lines   = { }
	for line in text:gmatch("([^\n]*)\n?") do
		local indent = line:match("^[ \t/#*-]+") or ""
		table.insert(indents, indent)
		table.insert(lines, line:sub(#indent + 1))
	end
	if #indents < 1 then
		return "", "", "", lines
	end
	local firstLineIndent  = indents[1] or ""
	local middleLineIndent = indents[2] or ""
	return firstLineIndent, middleLineIndent, lines
end

function align(line, alignment, columns)
	local gap = columns - #line
	if alignment == "right" then
		return string.rep(" ", gap) .. line
	elseif alignment == "center" then
		return string.rep(" ", math.floor(gap / 2)) .. line
	else
		return line
	end
end

function tokenize(text)
	local tokens = { }
	for token in text:gmatch("%S+") do
		table.insert(tokens, token)
	end
	return tokens
end

function measure(text)
	if not text then return 0 end
	local width = 0
	for index = 1, #text do
		if text:sub(index, index) == "\t" then
			width = math.ceil((width + 1) / 8) * 8
		else
			width = width + 1
		end
	end
	return width
end

function append(dest, src)
	for index = 1, #src do
		dest[#dest + 1] = src[index]
	end
	return dest
end

function colorColumn()
	return config.GetGlobalOption("colorcolumn")
end