population.js

const Organism = require('./organism.js');
const PluginManager = require('./pluginManager.js');
const Mitt = require('mitt');

class Population {
    constructor(geneAmount, popSize) {
        this.organisms = [];
        this.popSize = popSize;
        this.matingPool = [];

        for (let i = 0; i < this.popSize; i++) {
            this.organisms[i] = new Organism(geneAmount);
        }
        this.emitter = new Mitt();
        PluginManager.registerEmitter('population', this.emitter);
    }

    evaluate(target) {
        this.emitter.emit('beforeAllFitnessCalculated', this);

        let calcFitnessResults = this.organisms.map((organism) => {
            return new Promise((resolve) => {
                setImmediate(() => {                    
                    resolve(organism.calcFitness(target));
                });
            });
        });
        
        return Promise
            .all(calcFitnessResults)
            .then(() => {
                this.emitter.emit('afterAllFitnessCalculated', this);

                // Find max fitness
                let maxFit = 0;
                for (let i = 0; i < this.organisms.length; i++) {
                    maxFit = Math.max(this.organisms[i].fitness, maxFit);
                }

                // Map fitness between 0 and 1.        
                for (let i = 0; i < this.organisms.length; i++) {
                    this.organisms[i].fitness /= maxFit;
                }

                // Adds the organisms N times to mating pool according to its fitness proportional value. Multiplies N by 100 to give a minimum of 1 option for the lowest ranked organism
                this.matingPool = [];
                for (let i = 0; i < this.organisms.length; i++) {
                    let n = this.organisms[i].fitness * 100;
                    for (let j = 0; j < n; j++) {
                        this.matingPool.push(this.organisms[i]);
                    }
                }
            });
    }

    selection() {
        // Randomly choose two partners from mating pool and mate them
        let newOrganisms = [];
        for (let i = 0; i < this.organisms.length; i++) {
            const parentA = p5i.random(this.matingPool);
            const parentB = p5i.random(this.matingPool);
            const child = parentA.mate(parentB);
            newOrganisms[i] = child;
        }
        this.organisms = newOrganisms;
    }
}

module.exports = Population;