-- cqueue filesystem with luaposix
-- TODO: closing files
-- TODO: error handling. right now it *always* returns errno instead of
-- throwing it, which may be what we want. code depends on this
local unistd = require("posix.unistd")
local cqueues = require("cqueues")
local dkjson = require("dkjson")

local file = {}

function file.new(fd, mode)
	if not mode then mode = "r" end
	local f = setmetatable({}, { __index = file })
	f.pollfd = fd
	f.mode = mode
	if string.match(mode, "r") then
		f.rbuf = {}
	end

	if string.match(mode, "w") then
		f.wbuf = {}
	end

	return f
end

function file.events(f)
	return f.mode
end

-- input/output buffers
--
-- buffers are arrays of objects containing "data" (a string) and "index" (their position)
-- indexing allows us to avoid recreating string objects

function buffer_length(buf)
	local total = 0
	for _, entry in ipairs(buf) do
		total = total + #entry.data - entry.index + 1
	end
	return total
end

-- returns nil on empty length
function buffer_get(buf, length)
	local out = {}
	if not length then length = buffer_length(buf) end
	while length > 0 do
		assert(#buf > 0)
		
		local x = string.sub(buf[1].data, buf[1].index, buf[1].index + length - 1)
		table.insert(out, x)
		if #buf[1].data - buf[1].index + 1 <= length then
			table.remove(buf, 1)
		else
			buf[1].index = buf[1].index + length
		end
		length = length - #x
	end
	if out[1] then return table.concat(out) else return nil end
end

function buffer_char_index(buf, char)
	local num = 1
	for _, entry in ipairs(buf) do
		if string.find(entry.data, char, entry.index, true) then
			return num + string.find(entry.data, char, entry.index, true) - entry.index
		else
			num = num + #entry.data - entry.index + 1
		end
	end

	return nil
end

do
	local test_buf = { { data = "abcde", index = 2 }, { data = "\na", index = 1 } }
	assert(buffer_length(test_buf) == 6)
	assert(buffer_char_index(test_buf, "\n") == 5)
	assert(buffer_get(test_buf, 5) == "bcde\n")
	assert(buffer_length(test_buf) == 1)
end

function try_read(buffer, fd, max)
	cqueues.poll({ pollfd = fd, events = function () return "r" end })

	local data, _, errno = unistd.read(fd, max)

	if not data then return nil, errno end
	if #data == 0 then return nil end

	table.insert(buffer, { data = data, index = 1 })

	return #data
end

function file.read(f, what)
	assert(f.rbuf)

	if (type(what) == "number" and what > 0) then
		while buffer_length(f.rbuf) < what do
			if not try_read(f.rbuf, f.pollfd, what - buffer_length(f.rbuf)) then
				break
			end
		end

		return buffer_get(f.rbuf, math.min(what, buffer_length(f.rbuf)))
	elseif (type(what) == "number" and what < 0) then
		while buffer_length(f.rbuf) == 0 do
			if not try_read(f.rbuf, f.pollfd, 0 - what) then return nil end
		end
		return buffer_get(f.rbuf, math.min(0 - what, buffer_length(f.rbuf)))
	elseif what == "*l" or what == "*L" then
		while not buffer_char_index(f.rbuf, "\n") do
			-- TODO: constantize this
			local x = try_read(f.rbuf, f.pollfd, 1024)
			if not x then
				break
			end
		end

		local line = buffer_get(f.rbuf, buffer_char_index(f.rbuf, "\n"))

		if not line then
			return nil
		end
		local ret = string.gsub(
			line,
			"\n",
			(what == "*l" and "" or "\n")
		)

		return ret
	else
		-- TODO
	end
end

function file.lines(f, what)
	return function () return file.read(f, what or "*l") end
end

function file.write(f, data)
	local index = 1
	while index <= #data do
		cqueues.poll({ pollfd = f.pollfd, events = function () return "w" end })
		local nb, _, errno = unistd.write(f.pollfd, string.sub(data, index))
		if nb then
			index = index + nb
		else
			return nil, errno -- TODO?
		end
	end

	return f
end

function file.close(f)
	cqueues.cancel(f.pollfd)
end

return file