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import {Client} from 'pg';
import {ReplaySubject, Subject} from 'rxjs';
import type {LifecycleEvent} from '@owservable/core';
export type PostgresNotificationType = {
table: string;
op: 'insert' | 'update' | 'delete' | string;
id: string;
changed?: string[];
};
const RECONNECT_INITIAL_DELAY: number = 1000;
const RECONNECT_MAX_DELAY: number = 30000;
export default class PostgresListener {
public static init(config: any, channel: string = 'owservable'): PostgresListener {
if (!PostgresListener._instance) PostgresListener._instance = new PostgresListener(config, channel);
return PostgresListener._instance;
}
public static get instance(): PostgresListener {
return PostgresListener._instance;
}
public static async stop(): Promise<void> {
if (!PostgresListener._instance) return;
await PostgresListener._instance._stop();
PostgresListener._instance = null;
}
public readonly notifications: Subject<PostgresNotificationType>;
public readonly lifecycle: ReplaySubject<LifecycleEvent>;
private static _instance: PostgresListener;
private readonly _config: any;
private readonly _channel: string;
private _client: Client;
private _stopped: boolean = false;
private _reconnectDelay: number = RECONNECT_INITIAL_DELAY;
private constructor(config: any, channel: string) {
this._config = config;
this._channel = channel;
this.notifications = new Subject<PostgresNotificationType>();
this.lifecycle = new ReplaySubject<LifecycleEvent>(1);
this._connect() //
.then((): null => null)
.catch((error: any): void => this._handleFailure(error));
}
public get channel(): string {
return this._channel;
}
private async _connect(): Promise<void> {
this._client = new Client(this._config);
this._client.on('notification', (message: any): void => {
try {
const notification: PostgresNotificationType = JSON.parse(message.payload);
this.notifications.next(notification);
} catch (error) {
console.error(`[@owservable/postgres] -> PostgresListener[${this._channel}] Error parsing notification payload:`, message?.payload, error);
}
});
this._client.on('error', (error: any): void => {
console.error(`[@owservable/postgres] -> PostgresListener[${this._channel}] connection error:`, error, ', attempting reconnection...');
this._handleFailure(error);
});
this._client.on('end', (): void => {
if (this._stopped) return;
console.warn(`[@owservable/postgres] -> PostgresListener[${this._channel}] connection ended, attempting reconnection...`);
this._handleFailure();
});
await this._client.connect();
await this._client.query(`LISTEN "${this._channel}"`);
this._reconnectDelay = RECONNECT_INITIAL_DELAY;
this.lifecycle.next({
type: 'live',
collection: this._channel,
timestamp: new Date()
});
console.log(`[@owservable/postgres] -> PostgresListener listening on channel "${this._channel}"`);
}
private _handleFailure(error?: any): void {
if (this._stopped) return;
this.lifecycle.next({
type: 'error',
collection: this._channel,
timestamp: new Date(),
error
});
try {
this._client?.removeAllListeners();
this._client?.end().catch((): null => null);
} catch (cleanupError) {
console.error(`[@owservable/postgres] -> PostgresListener[${this._channel}] Error cleaning up old client:`, cleanupError);
}
const delay: number = this._reconnectDelay;
this._reconnectDelay = Math.min(this._reconnectDelay * 2, RECONNECT_MAX_DELAY);
console.info(`[@owservable/postgres] -> PostgresListener[${this._channel}] Reconnecting in ${delay}ms...`);
setTimeout((): void => {
this._connect() //
.then((): null => null)
.catch((reconnectError: any): void => this._handleFailure(reconnectError));
}, delay);
}
private async _stop(): Promise<void> {
this._stopped = true;
this.lifecycle.next({
type: 'close',
collection: this._channel,
timestamp: new Date()
});
try {
this._client?.removeAllListeners();
await this._client?.end();
} catch (error) {
console.error(`[@owservable/postgres] -> PostgresListener[${this._channel}] Error stopping:`, error);
}
}
}
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