A jigsaw puzzle implementation

jigsaw.js

// Node >= v2 required
const util = require('util');

const TOP = 0;
const RIGHT = 1;
const BOTTOM = 2;
const LEFT = 3;

const SIDES = [TOP, RIGHT, BOTTOM, LEFT];

const TAB = 'tab';
const HOLE = 'hole';
const FLAT = 'flat';

function randomType() {
  return Math.floor(Math.random() * 2) > 0 ? TAB : HOLE;
}

class Piece {
  constructor(x, y, sides) {
    this.x = x;
    this.y = y;
    this.sides = sides;
  }

  getOppositeSide(side) {
    const sidePair = {
      [TOP]: BOTTOM,
      [RIGHT]: LEFT,
      [BOTTOM]: TOP,
      [LEFT]: RIGHT,
    };

    const oppositeSide = sidePair[side];

    return this.sides[oppositeSide];
  }
}

class Puzzle {
  constructor(width, height) {
    this.width = width;
    this.height = height;
    this.matrix = this.createMatrix();

    this.fillMatrix();
  }

  createMatrix() {
    const matrix = [];

    while (matrix.length < this.height) {
      matrix.push([]);
    }

    return matrix;
  }

  getAdjacentPieces(x, y) {
    const rowAbove = this.matrix[y - 1];
    const rowBelow = this.matrix[y + 1];

    return [
      rowAbove && rowAbove[x], // top
      this.matrix[y][x + 1], // right
      rowBelow && rowBelow[x], // bottom
      this.matrix[y][x - 1], // left
    ];
  }

  isEdge(x, y, side) {
    const tests = {
      [TOP]: (x, y) => y === 0,
      [RIGHT]: (x, y) => x === this.width - 1,
      [BOTTOM]: (x, y) => y === this.height - 1,
      [LEFT]: (x, y) => x === 0,
    };

    return tests[side](x, y);
  }

  assignSide(neighbors, side, axis) {
    const isEdge = this.isEdge(...axis, side);

    if (isEdge) {
      return FLAT;
    }

    const adjacentPiece = neighbors[side];

    if (!adjacentPiece) {
      return randomType();
    }

    if (adjacentPiece.getOppositeSide(side) === TAB) {
      return HOLE;
    }

    return TAB;
  }

  fillMatrix() {
    this.matrix.forEach((row, yIndex) => {
      while (row.length < this.width) {
        const xIndex = row.length;
        const axis = [xIndex, yIndex];

        const adjacentPieces = this.getAdjacentPieces(...axis);
        const sides = SIDES.map(side => this.assignSide(adjacentPieces, side, axis));

        row.push(new Piece(xIndex, yIndex, sides));
      }
    });
  }
}

const puzzle = new Puzzle(4, 4);
console.log(util.inspect(puzzle.matrix, false, null, true));