import { BackgroundManagerNotOpenError } from './BackgroundManagerNotOpenError.mjs';
import { BackgroundProcessManagerState } from './types.mjs';

// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
/**
 * @private For internal Amplify use.
 *
 * Creates a new scope for promises, observables, and other types of work or
 * processes that may be running in the background. This manager provides
 * an singular entrypoint to request termination and await completion.
 *
 * As work completes on its own prior to close, the manager removes them
 * from the registry to avoid holding references to completed jobs.
 */
class BackgroundProcessManager {
    constructor() {
        /**
         * A string indicating whether the manager is accepting new work ("Open"),
         * waiting for work to complete ("Closing"), or fully done with all
         * submitted work and *not* accepting new jobs ("Closed").
         */
        this._state = BackgroundProcessManagerState.Open;
        /**
         * The list of outstanding jobs we'll need to wait for upon `close()`
         */
        this.jobs = new Set();
    }
    add(jobOrDescription, optionalDescription) {
        let job;
        let description;
        if (typeof jobOrDescription === 'string') {
            job = undefined;
            description = jobOrDescription;
        }
        else {
            job = jobOrDescription;
            description = optionalDescription;
        }
        const error = this.closedFailure(description);
        if (error)
            return error;
        if (job === undefined) {
            return this.addHook(description);
        }
        else if (typeof job === 'function') {
            return this.addFunction(job, description);
        }
        else if (job instanceof BackgroundProcessManager) {
            this.addManager(job, description);
        }
        else {
            throw new Error('If `job` is provided, it must be an Observable, Function, or BackgroundProcessManager.');
        }
    }
    /**
     * Adds a **cleaner** function that doesn't immediately get executed.
     * Instead, the caller gets a **terminate** function back. The *cleaner* is
     * invoked only once the mananger *closes* or the returned **terminate**
     * function is called.
     *
     * @param clean The cleanup function.
     * @param description Optional description to help identify pending jobs.
     * @returns A terminate function.
     */
    addCleaner(clean, description) {
        const { resolve, onTerminate } = this.addHook(description);
        const proxy = async () => {
            await clean();
            resolve();
        };
        onTerminate.then(proxy);
        return proxy;
    }
    addFunction(job, description) {
        // the function we call when we want to try to terminate this job.
        let terminate;
        // the promise the job can opt into listening to for termination.
        const onTerminate = new Promise(resolve => {
            terminate = resolve;
        });
        // finally! start the job.
        const jobResult = job(onTerminate);
        // depending on what the job gives back, register the result
        // so we can monitor for completion.
        if (typeof jobResult?.then === 'function') {
            this.registerPromise(jobResult, terminate, description);
        }
        // At the end of the day, or you know, method call, it doesn't matter
        // what the return value is at all; we just pass it through to the
        // caller.
        return jobResult;
    }
    addManager(manager, description) {
        this.addCleaner(async () => manager.close(), description);
    }
    /**
     * Creates and registers a fabricated job for processes that need to operate
     * with callbacks/hooks. The returned `resolve` and `reject`
     * functions can be used to signal the job is done successfully or not.
     * The returned `onTerminate` is a promise that will resolve when the
     * manager is requesting the termination of the job.
     *
     * @param description Optional description to help identify pending jobs.
     * @returns `{ resolve, reject, onTerminate }`
     */
    addHook(description) {
        // the resolve/reject functions we'll provide to the caller to signal
        // the state of the job.
        let promiseResolve;
        let promiseReject;
        // the underlying promise we'll use to manage it, pretty much like
        // any other promise.
        const promise = new Promise((resolve, reject) => {
            promiseResolve = resolve;
            promiseReject = reject;
        });
        // the function we call when we want to try to terminate this job.
        let terminate;
        // the promise the job can opt into listening to for termination.
        const onTerminate = new Promise(resolve => {
            terminate = resolve;
        });
        this.registerPromise(promise, terminate, description);
        return {
            resolve: promiseResolve,
            reject: promiseReject,
            onTerminate,
        };
    }
    /**
     * Adds a Promise based job to the list of jobs for monitoring and listens
     * for either a success or failure, upon which the job is considered "done"
     * and removed from the registry.
     *
     * @param promise A promise that is on its way to being returned to a
     * caller, which needs to be tracked as a background job.
     * @param terminate The termination function to register, which can be
     * invoked to request the job stop.
     * @param description Optional description to help identify pending jobs.
     */
    registerPromise(promise, terminate, description) {
        const jobEntry = { promise, terminate, description };
        this.jobs.add(jobEntry);
        // in all of my testing, it is safe to multi-subscribe to a promise.
        // so, rather than create another layer of promising, we're just going
        // to hook into the promise we already have, and when it's done
        // (successfully or not), we no longer need to wait for it upon close.
        //
        // sorry this is a bit hand-wavy:
        //
        // i believe we use `.then` and `.catch` instead of `.finally` because
        // `.finally` is invoked in a different order in the sequence, and this
        // breaks assumptions throughout and causes failures.
        promise
            .then(() => {
            this.jobs.delete(jobEntry);
        })
            .catch(() => {
            this.jobs.delete(jobEntry);
        });
    }
    /**
     * The number of jobs being waited on.
     *
     * We don't use this for anything. It's just informational for the caller,
     * and can be used in logging and testing.
     *
     * @returns the number of jobs.
     */
    get length() {
        return this.jobs.size;
    }
    /**
     * The execution state of the manager. One of:
     *
     * 1. "Open" -> Accepting new jobs
     * 1. "Closing" -> Not accepting new work. Waiting for jobs to complete.
     * 1. "Closed" -> Not accepting new work. All submitted jobs are complete.
     */
    get state() {
        return this._state;
    }
    /**
     * The registered `description` of all still-pending jobs.
     *
     * @returns descriptions as an array.
     */
    get pending() {
        return Array.from(this.jobs).map(job => job.description);
    }
    /**
     * Whether the manager is accepting new jobs.
     */
    get isOpen() {
        return this._state === BackgroundProcessManagerState.Open;
    }
    /**
     * Whether the manager is rejecting new work, but still waiting for
     * submitted work to complete.
     */
    get isClosing() {
        return this._state === BackgroundProcessManagerState.Closing;
    }
    /**
     * Whether the manager is rejecting work and done waiting for submitted
     * work to complete.
     */
    get isClosed() {
        return this._state === BackgroundProcessManagerState.Closed;
    }
    closedFailure(description) {
        if (!this.isOpen) {
            return Promise.reject(new BackgroundManagerNotOpenError([
                `The manager is ${this.state}.`,
                `You tried to add "${description}".`,
                `Pending jobs: [\n${this.pending
                    .map(t => '    ' + t)
                    .join(',\n')}\n]`,
            ].join('\n')));
        }
    }
    /**
     * Signals jobs to stop (for those that accept interruptions) and waits
     * for confirmation that jobs have stopped.
     *
     * This immediately puts the manager into a closing state and just begins
     * to reject new work. After all work in the manager is complete, the
     * manager goes into a `Completed` state and `close()` returns.
     *
     * This call is idempotent.
     *
     * If the manager is already closing or closed, `finalCleaup` is not executed.
     *
     * @param onClosed
     * @returns The settled results of each still-running job's promise. If the
     * manager is already closed, this will contain the results as of when the
     * manager's `close()` was called in an `Open` state.
     */
    async close() {
        if (this.isOpen) {
            this._state = BackgroundProcessManagerState.Closing;
            for (const job of Array.from(this.jobs)) {
                try {
                    job.terminate();
                }
                catch (error) {
                    // Due to potential races with a job's natural completion, it's
                    // reasonable to expect the termination call to fail. Hence,
                    // not logging as an error.
                    console.warn(`Failed to send termination signal to job. Error: ${error.message}`, job);
                }
            }
            // Use `allSettled()` because we want to wait for all to finish. We do
            // not want to stop waiting if there is a failure.
            this._closingPromise = Promise.allSettled(Array.from(this.jobs).map(j => j.promise));
            await this._closingPromise;
            this._state = BackgroundProcessManagerState.Closed;
        }
        return this._closingPromise;
    }
    /**
     * Signals the manager to start accepting work (again) and returns once
     * the manager is ready to do so.
     *
     * If the state is already `Open`, this call is a no-op.
     *
     * If the state is `Closed`, this call simply updates state and returns.
     *
     * If the state is `Closing`, this call waits for completion before it
     * updates the state and returns.
     */
    async open() {
        if (this.isClosing) {
            await this.close();
        }
        this._state = BackgroundProcessManagerState.Open;
    }
}

export { BackgroundProcessManager };
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