require('dotenv').config();


module.exports = class PostgresSingleton {
    static instance;

    constructor() {
        if (PostgresSingleton.instance)
            return this.instance;
        PostgresSingleton.instance = this;
    }

    static getInstance() {
        if (!PostgresSingleton.instance)
            PostgresSingleton.instance = new PostgresSingleton();
        return PostgresSingleton.instance;
    }

    setup() {
        if (this.postgres === null || typeof this.postgres == 'undefined')
            this.postgres = require('postgres')({
                host: process.env.POSTGRES_HOST, post: process.env.POSTGRES_PORT, database: process.env.POSTGRES_DATABASE,
                username: process.env.POSTGRES_USERNAME, password: process.env.POSTGRES_PASSWORD
            });
    }
    async start() {
        if (this.postgres === null || typeof this.postgres == 'undefined')
            this.setup();
    }
    async stop() {}

    async query(query, parameters) {
        const evaluated = Object.entries(parameters)
            .reduce((a, [k, v]) => a.concat(`const ${k}=${JSON.stringify(v)}`), '');

        return await eval(`(async () => { ${evaluated} return await this.postgres\`${query}\`; })();`);
    }
}