const { createPool, createConnection } = require( 'mysql2/promise' );
const cpus = require( 'os' ).cpus().length

let clientOpts = {
    host: process.env.DB_HOST || 'localhost',
    user: 'benchmarkdbuser',
    password: 'benchmarkdbpass',
    database: 'hello_world'
};

let pool

const execute = async ( text, values ) => ( await pool.execute( text, values || undefined ) )[0]

module.exports = {
    async init() {
        const client = await createConnection( clientOpts )
        const res = await client.query( 'SHOW VARIABLES LIKE "max_connections"' )
        let maxConnections = Math.floor( res[0][0].Value * 0.9 / cpus )
        //1 worker per cpu, each worker pool gets a fraction of the max connections
        //only use 90% to avoid too many clients errors
        pool = createPool( Object.assign( { ...clientOpts }, { max: maxConnections } ) )
        await client.end()
    },
    allFortunes: async () =>
        execute( 'SELECT * FROM fortune' ),

    worldById: async ( id ) =>
        execute( 'SELECT * FROM world WHERE id = ?', [id] )
            .then( arr => arr[0] ),

    allWorlds: async () =>
        execute( 'SELECT * FROM world' ),

    bulkUpdateWorld: async worlds => Promise.all(
        worlds.map( world =>
            execute( 'UPDATE world SET randomnumber = ? WHERE id = ?',
                [world.randomnumber, world.id] ) )
    ).then( () => worlds )
}