-- a cqueues utility for handling a bunch of editor processes
-- it runs in the same process as the main program to make it easier
-- to pass around lua data. as a result of this, it greedily blocks
-- SIGCHILD; since this is the only time we make subprocesses in the scope
-- of this program, this is fine.

local signal = require("cqueues.signal")

local wait = require("posix.sys.wait")

local std = require("posix.unistd")

local fifo = require("fifo")
local fs = require("fs")

local mom = {}

-- initialize a new mom
-- this starts the sigblocking handler; only one will work at a time
-- otherwise the blocking system is not portable
function mom.new(loop)
	local m = setmetatable({}, { __index = mom })
	m.loop = loop
	m.pids = {}
	-- actual clients. each of the keys is a unique table that gets returned to
	-- the caller when they make a new ed process
	-- you could argue this is unnecessary, and that the caller should be in charge of
	-- making its own process. i don't really care either way; this is easier and does
	-- what we want
	m.clients = {}

	loop:wrap(function () mom.tend(m) end)

	return m
end

-- create a new process in it
-- returns process (unique id object), tx_queue, rx_queue
-- you need to give it an identifier (this can be anything, and it isn't the id
-- that it uses internally). things pushed to the rx_queue will look like
-- { IDENTIFIER, "line", "meow" }
-- this is to make multiplexing easier
-- you must also give it a queue to send to (the rx_queue)
function mom.create(m, command, rx_id, rx_queue)
	local id = {}

	m.clients[id] = {
		command = assert(command),
		rx_id = assert(rx_id),
		tx_queue = fifo.new(),
		rx_queue = assert(rx_queue),
		tx_fds = fifo.new(),
		rx_fds = fifo.new(),
	}

	mom.start_process(m, id)
	m.loop:wrap(function() mom.handle_from_ed(m, id) end)
	m.loop:wrap(function() mom.handle_to_ed(m, id) end)
	return id, m.clients[id].tx_queue, m.clients[id].rx_queue
end

function mom.start_process(m, id)
	local proc_out_rx, proc_out_tx = std.pipe()
	if not (proc_out_rx and proc_out_tx) then return nil, "can't create pipe" end
	local proc_in_rx, proc_in_tx = std.pipe()
	if not (proc_in_rx and proc_in_tx) then return nil, "can't create pipe" end

	local pid, err = std.fork()
	if not pid then return nil, "couldn't create process: " .. err end

	if pid == 0 then
		std.close(proc_out_rx)
		std.close(proc_in_tx)
		std.dup2(proc_in_rx, std.STDIN_FILENO)
		std.dup2(proc_out_tx, std.STDOUT_FILENO)
		std.execp(m.clients[id].command[1], { select(2, table.unpack(m.clients[id].command)) }) -- meh
		os.exit(100) -- TODO
	else
		m.pids[pid] = id
		std.close(proc_in_rx)
		std.close(proc_out_tx)

		m.clients[id].tx_fds:put(fs.new(proc_in_tx, "w"))
		m.clients[id].rx_fds:put(fs.new(proc_out_rx, "r"))
	end

	return m
end

function mom.handle_from_ed(m, id)
	local client = m.clients[id]

	for inp in client.rx_fds:iter() do
		for line in inp:lines() do
			client.rx_queue:put({ client.rx_id, "line", line })
		end

		inp:close()
		client.rx_queue:put({ client.rx_id, "quit" })
	end
end

function mom.handle_to_ed(m, id)
	local client = m.clients[id]

	local out = client.tx_fds:get()
	while true do
		local line = client.tx_queue:get()
		while true do
			local good, err = out:write(line .. "\n")

			if good then break end

			out:close()
			out = client.tx_fds:get()
		end
	end
end

function mom.tend(m)
	signal.block(signal.SIGCHLD)
	local l = signal.listen(signal.SIGCHLD)

	while true do
		l:wait()
		local pid, status = wait.wait(-1, wait.WNOHANG | wait.WUNTRACED)

		if pid and status ~= "running" then
			local client_id = m.pids[pid]
			m.pids[pid] = nil
			-- TODO: only restart sometimes
			mom.start_process(m, client_id)
			m.clients[client_id].rx_queue:put({ "quit" })
		end
	end
end

return mom