local html = require'garkup.html'
local T = html.T
local prose = require'garkup.prose'

local function highlight(code, lang)
	-- you'd better not already be using that file
	local infile = assert(io.open("/tmp/highlighter_input","w"))
	assert(infile:write(code))
	local outhandle = assert(io.popen("highlight -f -S "..lang.." --inline-css --enclose-pre </tmp/highlighter_input", "r"))
	local output = assert(outhandle:read"a")

	outhandle:close()
	infile:close()

	return html.safe(output)
end

local function mode_code(S)
	local lang = S:line():match("^```(%w+) ?(.*)")

	local text = ""
	for line in S:lines() do
		if line:match("^```") then
			break
		else
			text = text .. line
		end
	end
	S:emit(highlight(text, lang))
end

local function mode_list(S)
	local items = {}
	for line in S:lines() do
		if line:match("^%*") then
			local content = line:gsub("^%*%s*","")
			table.insert(items, T.li(prose(S,content)))
		else
			S:unline(line)
			break
		end
	end
	S:emit(T.ul(items))
end

local function mode_heading(S)
	local level, line = S:line():match("^#*()%s*(.*)")
	level = level - 1 -- because () capture is offset by 1
	level = level + (S.heading_level or 0)
	S:emit(html.tag('h'..level, prose(S,line)))
end

local function mode_hr(S)
	local line = S:line()
	S:emit(html.T.hr"")
end

local mode_patterns = {
	{ "^```", mode_code },
	{ "^*", mode_list },
	{ "^#", mode_heading },
	{ "^%-%-%-", mode_hr },
}

local function match_mode_pattern(S, line)
	for i, row in ipairs(mode_patterns) do
		local pattern, mode = row[1], row[2]
		if line:match(pattern) then return mode end
	end
end

local function mode_paragraphs(S)
	local para = ""
	local function finish()
		local processed = prose(S, para)
		if tostring(html.html(processed)):match("%S") then
			S:emit(T.p(processed))
		end
		para = ""
	end

	for line in S:lines() do
		local newmode = match_mode_pattern(S, line)
		if newmode then
			S:unline(line)
			finish()
			return newmode(S)
		elseif line:match("%S") then
			para = para .. line
		else
			finish()
		end
	end
	finish()
end

local function split_lines(text)
	local lines = {}
	for x in text:gmatch("[^\n]*") do
		table.insert(lines, x.."\n")
	end
	return lines
end

local State = {}
function State.new(input, options)
	options = options or {}
	local self = {
		the_lines = split_lines(input),
		output = "",
	}
	for k,v in pairs(options) do self[k] = v end
	return setmetatable(self, {__index=State})
end

function State.emit(self, x)
	self.output = self.output..tostring(html.html(x)).."\n"
end
function State.line(self)
	return table.remove(self.the_lines, 1)
end
function State.unline(self, line)
	table.insert(self.the_lines, 1, line)
end
function State.lines(self)
	return State.line, self
end
function State.remaining(self)
	return #self.the_lines > 0
end
function State.toplevel(self)
	while self:remaining() do
		mode_paragraphs(self)
	end
	return self.output
end

local function garkup(...)
	local S = State.new(...)
	return S:toplevel(), S
end


-- print(garkup(io.read"a")
return garkup