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| /**
* Copyright 2017 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import { fail } from '../util/assert';
export type FulfilledHandler<T, R> =
| ((result: T) => R | PersistencePromise<R>)
| null;
export type RejectedHandler<R> =
| ((reason: Error) => R | PersistencePromise<R>)
| null;
export type Resolver<T> = (value?: T) => void;
export type Rejector = (error: Error) => void;
/**
* PersistencePromise<> is essentially a re-implementation of Promise<> except
* it has a .next() method instead of .then() and .next() and .catch() callbacks
* are executed synchronously when a PersistencePromise resolves rather than
* asynchronously (Promise<> implementations use setImmediate() or similar).
*
* This is necessary to interoperate with IndexedDB which will automatically
* commit transactions if control is returned to the event loop without
* synchronously initiating another operation on the transaction.
*
* NOTE: .then() and .catch() only allow a single consumer, unlike normal
* Promises.
*/
export class PersistencePromise<T> {
// NOTE: next/catchCallback will always point to our own wrapper functions,
// not the user's raw next() or catch() callbacks.
// tslint:disable-next-line:no-any Accept any result type for the next call in the Promise chain.
private nextCallback: FulfilledHandler<T, any> = null;
// tslint:disable-next-line:no-any Accept any result type for the error handler.
private catchCallback: RejectedHandler<any> = null;
// When the operation resolves, we'll set result or error and mark isDone.
private result: T | undefined = undefined;
private error: Error | undefined = undefined;
private isDone = false;
// Set to true when .then() or .catch() are called and prevents additional
// chaining.
private callbackAttached = false;
constructor(callback: (resolve: Resolver<T>, reject: Rejector) => void) {
callback(
value => {
this.isDone = true;
this.result = value;
if (this.nextCallback) {
// value should be defined unless T is Void, but we can't express
// that in the type system.
this.nextCallback(value!);
}
},
error => {
this.isDone = true;
this.error = error;
if (this.catchCallback) {
this.catchCallback(error);
}
}
);
}
catch<R>(
fn: (error: Error) => R | PersistencePromise<R>
): PersistencePromise<R> {
return this.next(undefined, fn);
}
next<R>(
nextFn?: FulfilledHandler<T, R>,
catchFn?: RejectedHandler<R>
): PersistencePromise<R> {
Iif (this.callbackAttached) {
fail('Called next() or catch() twice for PersistencePromise');
}
this.callbackAttached = true;
if (this.isDone) {
if (!this.error) {
return this.wrapSuccess(nextFn, this.result!);
} else {
return this.wrapFailure(catchFn, this.error);
}
} else {
return new PersistencePromise<R>((resolve, reject) => {
this.nextCallback = (value: T) => {
this.wrapSuccess(nextFn, value).next(resolve, reject);
};
this.catchCallback = (error: Error) => {
this.wrapFailure(catchFn, error).next(resolve, reject);
};
});
}
}
toPromise(): Promise<T> {
return new Promise((resolve, reject) => {
this.next(resolve, reject);
});
}
private wrapUserFunction<R>(
fn: () => R | PersistencePromise<R>
): PersistencePromise<R> {
try {
const result = fn();
if (result instanceof PersistencePromise) {
return result;
} else {
return PersistencePromise.resolve(result);
}
} catch (e) {
return PersistencePromise.reject<R>(e);
}
}
private wrapSuccess<R>(
nextFn: FulfilledHandler<T, R> | undefined,
value: T
): PersistencePromise<R> {
if (nextFn) {
return this.wrapUserFunction(() => nextFn(value));
} else {
// If there's no nextFn, then R must be the same as T but we
// can't express that in the type system.
// tslint:disable-next-line:no-any
return PersistencePromise.resolve<R>(value as any);
}
}
private wrapFailure<R>(
catchFn: RejectedHandler<R> | undefined,
error: Error
): PersistencePromise<R> {
if (catchFn) {
return this.wrapUserFunction(() => catchFn(error));
} else {
return PersistencePromise.reject<R>(error);
}
}
static resolve(): PersistencePromise<void>;
static resolve<R>(result: R): PersistencePromise<R>;
static resolve<R>(result?: R): PersistencePromise<R | void> {
return new PersistencePromise<R>((resolve, reject) => {
resolve(result);
});
}
static reject<R>(error: Error): PersistencePromise<R> {
return new PersistencePromise<R>((resolve, reject) => {
reject(error);
});
}
static waitFor(
// tslint:disable-next-line:no-any Accept all Promise types in waitFor().
all: Array<PersistencePromise<any>>
): PersistencePromise<void> {
return all.reduce((promise, nextPromise, idx) => {
return promise.next(() => {
return nextPromise;
});
}, PersistencePromise.resolve());
}
static map<R>(all: Array<PersistencePromise<R>>): PersistencePromise<R[]> {
const results: R[] = [];
let first = true;
// initial is ignored, so we can cheat on the type.
// tslint:disable-next-line:no-any
const initial = PersistencePromise.resolve<R>(null as any);
return all
.reduce((promise, nextPromise) => {
return promise.next(result => {
if (!first) {
results.push(result);
}
first = false;
return nextPromise;
});
}, initial)
.next(result => {
results.push(result);
return results;
});
}
}
|