j2s/lib/promise.ts

define("promise", () => {
    const syms = {
        callbacks: internals.symbol('Promise.callbacks'),
        state: internals.symbol('Promise.state'),
        value: internals.symbol('Promise.value'),
        handled: internals.symbol('Promise.handled'),
    } as {
        readonly callbacks: unique symbol,
        readonly state: unique symbol,
        readonly value: unique symbol,
        readonly handled: unique symbol,
    }

    type Callback<T> = [ PromiseFulfillFunc<T>, PromiseRejectFunc ];
    enum State {
        Pending,
        Fulfilled,
        Rejected,
    }

    function isAwaitable(val: unknown): val is Thenable<any> {
        return (
            typeof val === 'object' &&
            val !== null &&
            'then' in val &&
            typeof val.then === 'function'
        );
    }
    function resolve(promise: Promise<any>, v: any, state: State) {
        if (promise[syms.state] === State.Pending) {
            if (typeof v === 'object' && v !== null && 'then' in v && typeof v.then === 'function') {
                v.then(
                    (res: any) => resolve(promise, res, state),
                    (res: any) => resolve(promise, res, State.Rejected)
                );
                return;
            }
            promise[syms.value] = v;
            promise[syms.state] = state;

            for (let i = 0; i < promise[syms.callbacks]!.length; i++) {
                promise[syms.handled] = true;
                promise[syms.callbacks]![i][state - 1](v);
            }

            promise[syms.callbacks] = undefined;

            internals.pushMessage(true, internals.setEnv(() => {
                if (!promise[syms.handled] && state === State.Rejected) {
                    log('Uncaught (in promise) ' + promise[syms.value]);
                }
            }, env), undefined, []);
        }
    }

    class Promise<T> {
        public static isAwaitable(val: unknown): val is Thenable<any> {
            return isAwaitable(val);
        }

        public static resolve<T>(val: T): Promise<Awaited<T>> {
            return new Promise(res => res(val as any));
        }
        public static reject<T>(val: T): Promise<Awaited<T>> {
            return new Promise((_, rej) => rej(val as any));
        }

        public static race<T>(vals: T[]): Promise<Awaited<T>> {
            if (typeof vals.length !== 'number') throw new TypeError('vals must be an array. Note that Promise.race is not variadic.');
            return new Promise((res, rej) => {
                for (let i = 0; i < vals.length; i++) {
                    const val = vals[i];
                    if (this.isAwaitable(val)) val.then(res, rej);
                    else res(val as any);
                }
            });
        }
        public static any<T>(vals: T[]): Promise<Awaited<T>> {
            if (typeof vals.length !== 'number') throw new TypeError('vals must be an array. Note that Promise.any is not variadic.');
            return new Promise((res, rej) => {
                let n = 0;

                for (let i = 0; i < vals.length; i++) {
                    const val = vals[i];
                    if (this.isAwaitable(val)) val.then(res, (err) => {
                        n++;
                        if (n === vals.length) throw Error('No promise resolved.');
                    });
                    else res(val as any);
                }

                if (vals.length === 0) throw Error('No promise resolved.');
            });
        }
        public static all(vals: any[]): Promise<any[]> {
            if (typeof vals.length !== 'number') throw new TypeError('vals must be an array. Note that Promise.all is not variadic.');
            return new Promise((res, rej) => {
                const result: any[] = [];
                let n = 0;

                for (let i = 0; i < vals.length; i++) {
                    const val = vals[i];
                    if (this.isAwaitable(val)) val.then(
                        val => {
                            n++;
                            result[i] = val;
                            if (n === vals.length) res(result);
                        },
                        rej
                    );
                    else {
                        n++;
                        result[i] = val;
                    }
                }

                if (vals.length === n) res(result);
            });
        }
        public static allSettled(vals: any[]): Promise<any[]> {
            if (typeof vals.length !== 'number') throw new TypeError('vals must be an array. Note that Promise.allSettled is not variadic.');
            return new Promise((res, rej) => {
                const result: any[] = [];
                let n = 0;

                for (let i = 0; i < vals.length; i++) {
                    const value = vals[i];
                    if (this.isAwaitable(value)) value.then(
                        value => {
                            n++;
                            result[i] = { status: 'fulfilled', value };
                            if (n === vals.length) res(result);
                        },
                        reason => {
                            n++;
                            result[i] = { status: 'rejected', reason };
                            if (n === vals.length) res(result);
                        },
                    );
                    else {
                        n++;
                        result[i] = { status: 'fulfilled', value };
                    }
                }

                if (vals.length === n) res(result);
            });
        }

        [syms.callbacks]?: Callback<T>[] = [];
        [syms.handled] = false;
        [syms.state] = State.Pending;
        [syms.value]?: T | unknown;

        public then(onFulfil?: PromiseFulfillFunc<T>, onReject?: PromiseRejectFunc) {
            return new Promise((resolve, reject) => {
                onFulfil ??= v => v;
                onReject ??= v => v;

                const callback = (func: (val: any) => any) => (v: any) => {
                    try { resolve(func(v)); }
                    catch (e) { reject(e); }
                }
                switch (this[syms.state]) {
                    case State.Pending:
                        this[syms.callbacks]![this[syms.callbacks]!.length] = [callback(onFulfil), callback(onReject)];
                        break;
                    case State.Fulfilled:
                        this[syms.handled] = true;
                        callback(onFulfil)(this[syms.value]);
                        break;
                    case State.Rejected:
                        this[syms.handled] = true;
                        callback(onReject)(this[syms.value]);
                        break;
                }
            })
        }
        public catch(func: PromiseRejectFunc) {
            return this.then(undefined, func);
        }
        public finally(func: () => void) {
            return this.then(
                v => {
                    func();
                    return v;
                },
                v => {
                    func();
                    throw v;
                }
            );
        }

        public constructor(func: PromiseFunc<T>) {
            internals.pushMessage(true, func, undefined, [
                ((v) => resolve(this, v, State.Fulfilled)) as PromiseFulfillFunc<T>,
                ((err) => resolve(this, err, State.Rejected)) as PromiseRejectFunc
            ]);
        }
    }
    env.global.Promise = Promise as any;
});