index.js

/*
  Made by Mund & Mart for their profielwerkstuk to show a possible js implementation of
  ellementary cellular automata
*/
'use strict'

const assert = require('assert')
class Eca {
  constructor (rule, options = {}) {
    this.neighbors = options.neighbors || 2
    this.states = options.states || 2
    assert.equal(typeof this.neighbors && typeof this.states, 'number', 'eca: Expected neighbors and states to be a number.')

    this.lattices = []
    this.lookup = this._makeLookup(rule)
    this._initialLattice(options.seed, options.width)
  }

  _makeLookup (rule = 30) {
    if (typeof rule === 'string') return rule
    assert.equal(typeof rule, 'number', 'eca: Expected the rule to be a number or a binary string.')

    const patterns = Math.pow(this.states, this.neighbors + 1)
    const max = Math.pow(this.states, patterns) - 1
    assert.ok(rule >= 0 && rule <= max, 'eca: Expected the rule to be between 0 and 255.')

    return rule.toString(this.states).padStart(patterns, 0)
  }

  // Generates the initial lattice from a seed
  _initialLattice (seed = '1', width = 11) {
    assert.ok(seed.length <= width, 'eca: Expected the seed to be smaller than or equal to the width of the eca.')
    assert.equal(typeof seed, 'string', 'eca: Expected the seed to be a string.')

    this.lattices.push(seed)
    let margin = (width - seed.length) / 2
    
    if (margin % 1 !== 0) {
      this.lattices[0] += '0'
      margin = Math.floor(margin)
    }
  
    for (let i = 0; i < margin; i++) {
      this.lattices[0] += '0'
      this.lattices[0] = '0' + this.lattices[0]
    }
  }

  genLattice () {
    let newLattice = ''
    const lattice = this.lattices[this.lattices.length - 1]

    for (let i = 0; i < lattice.length; i++) {
      const neighbor = this.neighbors / 2
      const a = i - neighbor
      const b = i + 1 + neighbor
      const neighborhood = lattice.substring(a, b)

      const index = this.lookup.length - (parseInt(neighborhood, this.states) + 1)
      newLattice += this.lookup.charAt(index)
    }

    this.lattices.push(newLattice)
    return newLattice
  }

  generateLattices (n) {
    const lattices = []
    for (var i = 0; i < n; i++) {
      lattices.push(this.genLattice())
    }
    return lattices
  }
}

function eca (rule, options = {}) {
  return new Eca(rule, options)
}

module.exports = eca