local html = require 'html'
local md5 = require 'md5'

local M = {}

M.env = os.getenv

local header_written
local function header(h, v)
	header_written = true
	assert(not h:match "[: \n]")
	assert(h:lower() == h)
	assert(not (tostring(v)):match "\n")
	print(("%s: %s"):format(h, v))
end

local function serve(headers, body)
	assert(not header_written)
	if type(headers) == 'string' then
		headers = {content_type = headers}
	end
	headers.etag = ('"%s"'):format(md5.sumhexa(body))
	headers.content_length = #body
	for h, v in pairs(headers) do
		if type(v) == 'table' then
			for _, v in ipairs(v) do
				header(h:gsub("_", "-"), v)
			end
		else
			header(h:gsub("_", "-"), v)
		end
	end
	print()
	io.stdout:write(body)
end

function M.abort(...)
	coroutine.yield(M.abort, ...)
end

function M.redirect(...)
	coroutine.yield(M.redirect, ...)
end

function M.decode_path(path)
	local p = {}
	for location in path:gmatch '([^/]+)' do
		table.insert(p, html.url_decode(location))
	end
	return p
end

function M.parse_qs(str,sep)
	sep = sep or '&'

	local values = {}
	for key, val in str:gmatch(('([^%q=]+)(=*[^%q=]*)'):format(sep, sep)) do
		local key = html.url_decode(key)
		
		local keys = {}
		key = key:gsub('%[([^%]]*)%]', function(v)
				-- extract keys between balanced brackets
				if string.find(v, "^-?%d+$") then
					v = tonumber(v)
				else
					v = html.url_decode(v)
				end
				table.insert(keys, v)
				return "="
		end)
		key = key:gsub('=+.*$', "")
		key = key:gsub('%s', "_") -- remove spaces in parameter name
		val = val:gsub('^=+', "")

		if not values[key] then
			values[key] = {}
		end
		if #keys > 0 and type(values[key]) ~= 'table' then
			values[key] = {}
		elseif #keys == 0 and type(values[key]) == 'table' then
			values[key] = html.url_decode(val)
		end

		local t = values[key]
		for i,k in ipairs(keys) do
			if type(t) ~= 'table' then
				t = {}
			end
			if k == "" then
				k = #t+1
			end
			if not t[k] then
				t[k] = {}
			end
			if i == #keys then
				t[k] = html.url_decode(val)
			end
			t = t[k]
		end
	end
	return values
end

local redir_statuses = {
	[301] = "301 Moved Permanently",
	[301] = "302 Found",
	[302] = "302 See Other",
	[307] = "307 Temporary Redirect",
	[308] = "308 Permanent Redirect",
}

local function redirect_page(code, url)
	return {
		content = 'text/html', status = redir_statuses[code] or code,
		location = url
	}, html.render_doc(function()
		html.h1 "redirect"
		html.p(function()
			html.a({href = url}, url)
		end)
	end)
end

function M.serve(methods, error_page)
	local co = coroutine.create(function()
		local path = M.env 'PATH_INFO'
		local query = M.parse_qs(M.env 'QUERY_STRING')
		local form
		local content_type = M.env 'CONTENT_TYPE'
		if content_type == 'application/x-www-form-urlencoded' then
			form = M.parse_qs(io.read 'a')
		end
		local cookie = {}
		if M.env 'HTTP_COOKIE' then
			cookie = M.parse_qs(M.env 'HTTP_COOKIE', '; ')
		end

		if methods[M.env 'REQUEST_METHOD'] then
			local info = {query = query, form = form, cookie = cookie}
			serve(methods[M.env 'REQUEST_METHOD'](info, path))
		else
			M.abort(405)
		end
	end)

	local ok, err, code, arg = coroutine.resume(co)
	if ok and coroutine.status(co) ~= "dead" then
		if err == M.abort then
			serve(error_page(code, arg))
		elseif err == M.redirect then
			serve(redirect_page(code, arg))
		else
			ok = false err = "invalid yield"
		end
	end
	if not ok then
		io.stderr:write('\n'..debug.traceback(co, err)..'\n')
		serve(error_page(500))
	end
end

return M