type BetterPromiseCallback = (resolve: (res: any) => void, reject:(err: Error | null) => void) => void;

class BetterPromise<T> {
    state: 'Pending' | 'Resolved' | 'Rejected';
    result: T | null;
    error: Error | null;
    resolve(res: T|null): void {
        this.state = 'Resolved';
        this.result = res;
        return;
    }
    reject(err: Error | null): void {
        this.state = 'Rejected';
        this.error = err;
        return;
    }
    then(callback: (data: T|null, error: Error | null) =>any) {
        return new BetterPromise((resolve,reject) => {
            try {
                const result = callback(this.result, this.error);
                resolve(result);
            } catch(error) {
                reject(error);
            }
        } )
    }

    constructor(callback: BetterPromiseCallback) {
        this.state = 'Pending';
        callback(this.resolve, this.reject);
    }
}