local promise_methods = {};

local promise_mt = { __name = "promise", __index = promise_methods };

local xpcall = require "util.xpcall".xpcall;

function promise_mt:__tostring()

	return  "promise (" .. (self._state or "invalid") .. ")";

end

local function is_promise(o)

	local mt = getmetatable(o);

	return mt == promise_mt;

end

local function wrap_handler(f, resolve, reject, default)

	if not f then

		return default;

	end

	return function (param)

		local ok, ret = xpcall(f, debug.traceback, param);

		if ok then

			resolve(ret);

		else

			reject(ret);

		end

		return true;

	end;

end

local function next_pending(self, on_fulfilled, on_rejected, resolve, reject)

	table.insert(self._pending_on_fulfilled, wrap_handler(on_fulfilled, resolve, reject, resolve));

	table.insert(self._pending_on_rejected, wrap_handler(on_rejected, resolve, reject, reject));

end

local function next_fulfilled(promise, on_fulfilled, on_rejected, resolve, reject) -- luacheck: ignore 212/on_rejected

	wrap_handler(on_fulfilled, resolve, reject, resolve)(promise.value);

end

local function next_rejected(promise, on_fulfilled, on_rejected, resolve, reject) -- luacheck: ignore 212/on_fulfilled

	wrap_handler(on_rejected, resolve, reject, reject)(promise.reason);

end

local function promise_settle(promise, new_state, new_next, cbs, value)

	if promise._state ~= "pending" then

		return;

	end

	promise._state = new_state;

	promise._next = new_next;

	for _, cb in ipairs(cbs) do

		cb(value);

	end

	return true;

end

local function new_resolve_functions(p)

	local resolved = false;

	local function _resolve(v)

		if resolved then return; end

		resolved = true;

		if is_promise(v) then

			v:next(new_resolve_functions(p));

		elseif promise_settle(p, "fulfilled", next_fulfilled, p._pending_on_fulfilled, v) then

			p.value = v;

		end

	end

	local function _reject(e)

		if resolved then return; end

		resolved = true;

		if promise_settle(p, "rejected", next_rejected, p._pending_on_rejected, e) then

			p.reason = e;

		end

	end

	return _resolve, _reject;

end

local function new(f)

	local p = setmetatable({ _state = "pending", _next = next_pending, _pending_on_fulfilled = {}, _pending_on_rejected = {} }, promise_mt);

	if f then

		local resolve, reject = new_resolve_functions(p);

		local ok, ret = pcall(f, resolve, reject);

		if not ok and p._state == "pending" then

			reject(ret);

		end

	end

	return p;

end

local function all(promises)

	return new(function (resolve, reject)

		local count, total, results = 0, #promises, {};

		for i = 1, total do

			promises[i]:next(function (v)

				results[i] = v;

				count = count + 1;

				if count == total then

					resolve(results);

				end

			end, reject);

		end

	end);

end

local function race(promises)

	return new(function (resolve, reject)

		for i = 1, #promises do

			promises[i]:next(resolve, reject);

		end

	end);

end

local function resolve(v)

	return new(function (_resolve)

		_resolve(v);

	end);

end

local function reject(v)

	return new(function (_, _reject)

		_reject(v);

	end);

end

local function try(f)

	return resolve():next(function () return f(); end);

end

function promise_methods:next(on_fulfilled, on_rejected)

	return new(function (resolve, reject) --luacheck: ignore 431/resolve 431/reject

		self:_next(on_fulfilled, on_rejected, resolve, reject);

	end);

end

function promise_methods:catch(on_rejected)

	return self:next(nil, on_rejected);

end

function promise_methods:finally(on_finally)

	local function _on_finally(value) on_finally(); return value; end

	local function _on_catch_finally(err) on_finally(); return reject(err); end

	return self:next(_on_finally, _on_catch_finally);

end

return {

	new = new;

	resolve = resolve;

	reject = reject;

	all = all;

	race = race;

	try = try;

	is_promise = is_promise;

}