local lpc = require('lpc')
local sizes = { i4 = 4, u4 = 4, c = 1 }
local function read_u4(rh)
	local value = 0
	for i = 1, sizes.u4 do
		local byte = rh:read(1):byte()
		value = value + byte * (2 ^ ((sizes.u4 - i) * 8))
	end
	return value
end
local function read_c(rh)
	return rh:read(sizes.c)
end
local function read_channel(rh)
	local channel = read_c(rh)
	local length = read_u4(rh)
	if channel == 'I' or channel == 'L' then
		return channel, length
	else
		return channel, rh:read(length)
	end
end
local Client = {}
Client.__index = Client
function Client.connect(rh, wh)
	local client = {}
	setmetatable(client, Client)
	client.rh = rh
	client.wh = wh
	client:read_hello()
	return client
end
function Client.open(repo)
	local cmd = { 'hg', 'serve', '--cmdserver', 'pipe', '--config', 'ui.interactive=True' }
	if repo ~= nil then
		table.insert(cmd, '-R')
		table.insert(cmd, repo)
	end
	local pid, wh, rh = lpc.run(unpack(cmd))
	local client = Client.connect(rh, wh)
	client.lpcpid = pid
	return client
end
function Client:close()
	if self.wh ~= nil then self.wh:close() end
	if self.rh ~= nil then self.rh:close() end
	if self.lpcpid ~= nil then lpc.wait(self.lpcpid) end
end
function Client:read_hello()
	local channel, message = read_channel(self.rh)
	assert(channel == 'o', 'channel for the hello message must be "o"')
	local index = 1
	while index <= #message do
		local nexteol = message:find('\n', index + 1, true)
		if nexteol == nil then nexteol = #message + 1 end
		local line = message:sub(index, nexteol - 1)
		local ci = line:find(': ', 1, true)
		if ci ~= nil then
			local key, value = line:sub(1, ci - 1), line:sub(ci + 2)
			if key == 'capabilities' then
				self.capabilities = {}
				for cap in value:gmatch('%S+') do
					self.capabilities[cap] = true
				end
			elseif key == 'encoding' then
				self.encoding = value
			elseif key == 'pid' then
				self.pid = tonumber(value)
			elseif key == 'pgid' then
				self.pgid = tonumber(value)
			end
		end
		index = nexteol + 1
	end
end
function Client:getencoding()
	if not self.capabilities.getencoding then
		return nil, 'getencoding is not supported by this command server'
	end
	self.wh:write('getencoding\n')
	self.wh:flush()
	local channel, message = read_channel(self.rh)
	if channel == 'r' then
		return message
	elseif channel == 'e' then
		return nil, message
	end
end
return {
	read_u4 = read_u4,
	read_c = read_c,
	read_channel = read_channel,
	Client = Client
}