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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
-- No need to keep references to callbacks
promise._pending_on_fulfilled = nil;
promise._pending_on_rejected = nil;
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;
}
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