/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

import { ExtHostContext, ObjectIdentifier, IExtHostContext } from '../node/extHost.protocol';
import { createDecorator } from 'vs/platform/instantiation/common/instantiation';
import { registerSingleton } from 'vs/platform/instantiation/common/extensions';
import { Event, Emitter } from 'vs/base/common/event';
import { IDisposable } from 'vs/base/common/lifecycle';
import { extHostCustomer } from 'vs/workbench/api/electron-browser/extHostCustomers';
import { GCSignal } from 'gc-signals';

export const IHeapService = createDecorator<IHeapService>('heapService');

export interface IHeapService {
	_serviceBrand: any;

	readonly onGarbageCollection: Event<number[]>;

	/**
	 * Track gc-collection for the given object
	 */
	trackObject(obj: ObjectIdentifier): void;
}

export class HeapService implements IHeapService {

	_serviceBrand: any;

	private readonly _onGarbageCollection: Emitter<number[]> = new Emitter<number[]>();
	public readonly onGarbageCollection: Event<number[]> = this._onGarbageCollection.event;

	private _activeSignals = new WeakMap<any, object>();
	private _activeIds = new Set<number>();

	private _consumeHandle: any;
	private _ctor: { new(id: number): GCSignal };
	private _ctorInit: Promise<void>;

	constructor() {
		//
	}

	dispose() {
		clearInterval(this._consumeHandle);
	}

	trackObject(obj: ObjectIdentifier | undefined | null): void {
		if (!obj) {
			return;
		}

		const ident = obj.$ident;
		if (typeof ident !== 'number') {
			return;
		}

		if (this._activeIds.has(ident)) {
			return;
		}

		if (this._ctor) {
			// track and leave
			this._activeIds.add(ident);
			this._activeSignals.set(obj, new this._ctor(ident));

		} else {
			// make sure to load gc-signals, then track and leave
			if (!this._ctorInit) {
				this._ctorInit = import('gc-signals').then(({ GCSignal, consumeSignals }) => {
					this._ctor = GCSignal;
					this._consumeHandle = setInterval(() => {
						const ids = consumeSignals();

						if (ids.length > 0) {
							// local book-keeping
							for (const id of ids) {
								this._activeIds.delete(id);
							}
							// fire event
							this._onGarbageCollection.fire(ids);
						}
					}, 15 * 1000);
				});
			}

			this._ctorInit.then(() => {
				this._activeIds.add(ident);
				this._activeSignals.set(obj, new this._ctor(ident));
			});
		}
	}
}

@extHostCustomer
export class MainThreadHeapService {

	private readonly _toDispose: IDisposable;

	constructor(
		extHostContext: IExtHostContext,
		@IHeapService heapService: IHeapService,
	) {
		const proxy = extHostContext.getProxy(ExtHostContext.ExtHostHeapService);
		this._toDispose = heapService.onGarbageCollection((ids) => {
			// send to ext host
			proxy.$onGarbageCollection(ids);
		});
	}

	public dispose(): void {
		this._toDispose.dispose();
	}

}

registerSingleton(IHeapService, HeapService, true);