/**
 * Conway's Game of Life
 *
 * Rules:
 *   1. Any live cell with fewer than two live neighbours dies, as if by underpopulation.
 *   2. Any live cell with two or three live neighbours lives on to the next generation.
 *   3. Any live cell with more than three live neighbours dies, as if by overpopulation.
 *   4. Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.
 *
 * Example usage:
 * const boardScheme = '......\n' +
 *                     '***...\n' +
 *                     '......\n' +
 *                     '......\n' +
 *                     '......\n' +
 *                     '......\n';
 * const world = createWorld(board);
 * world.evolve();
 * print(world);
 * 
 * ---------------------------
 * .*....
 * .*....
 * .*....
 * ......
 * ......
 * .*....
 */

const CELL_CHAR = {
  ALIVE: '*',
  DEAD: '.',
};

/**
 * Represents a World rule determining if a Cell lives or dies.
 *
 * @constructor
 * @param {string} ruleStr
 * @return {Rule}
 */
class Rule {
  constructor(ruleStr) {
    const [born, survival] = ruleStr.split('/');
    this.born = born.split('').map(Number);
    this.survival = survival.split('').map(Number);
  }
}

/**
 * Represents a single Cell on the Board.
 *
 * @constructor
 * @param {boolean} state - State of a Cell (Alive | Dead)
 * @return {Cell}
 */
class Cell {
  constructor(state) {
    this.state = state;
  }

  get isAlive() {
    return this.state;
  }
}

/**
 * Represents a Location on the Board.
 *
 * @constructor
 * @param {number} rowIndex
 * @param {number} colIndex
 * @return {Location}
 */
class Location {
  constructor(rowIndex, colIndex) {
    this.row = rowIndex;
    this.col = colIndex;
  }
}

/**
 * Represents the game World.
 *
 * @constructor
 * @param {Array} board - Representation of the Board on which the Game of Life unfolds.
 * @return {World}
 */
class World {
  constructor(board = []) {
    this.validateBoard(board);
    this.rows = board.length;
    this.cols = board[0].length;
    this.board = board;
    this.generation = 0;
    this.rule = new Rule('3/23'); // B3/S23 (Conway's Life)
  }

  validateBoard(board) {
    if (!board.length) {
      throw Error('Board is empty');
    }
    const set = new Set(board.map(row => row.length));
    if (set.size > 1) {
      throw Error('Rows must be of the same length');
    }
  }

  getCell(location) {
    return this.board[location.row][location.col];
  }

  /**
   * Evolves the current World state one generation using the rules of the game.
   *
   * @public
   */
  evolve() {
    this.board = this.evolveBoard(this.board);
    this.generation++;
    return this;
  }

  evolveBoard(board) {
    return board.map((row, rowIndex) => this.evolveRow(rowIndex, row));
  }

  evolveRow(rowIndex, row) {
    return row.map((cell, colIndex) => this.evolveCell(new Location(rowIndex, colIndex), cell));
  }

  evolveCell(cellLocation, cell) {
    const aliveNeighbours = this.countAliveNeighbours(cellLocation);
    return cell.isAlive
      ? new Cell(this.rule.survival.some(surviveCount => surviveCount === aliveNeighbours))
      : new Cell(this.rule.born.some(bornCount => bornCount === aliveNeighbours));
  }

  countAliveNeighbours(location) {
    const cellNeighbourPositions = [[0, -1], [1, -1], [1, 0], [1, 1], [0, 1], [-1, 1], [-1, 0], [-1, -1]];

    return cellNeighbourPositions.reduce((count, [rowPos, colPos]) => {
      let neighbourLocation = new Location(location.row + rowPos, location.col + colPos);

      if (this.inBounds(neighbourLocation)) {
        let neighbourCell = this.getCell(neighbourLocation);
        if (neighbourCell.isAlive) {
          count++;
        }
        return count;
      }
    }, 0);
  }

  /**
   * Checks if a location is within the World bounds.
   */
  inBounds(location) {
    if (location.row > (this.rows - 1) || location.row < 0) {
      return false;
    }

    if (location.col > (this.cols - 1) || location.col < 0) {
      return false;
    }

    return true;
  }

  /**
   * Prints the current state of the World board.
   *
   * @public
   */
  print() {
    let str = '';
    for (const row of this.board) {
      for (const cell of row) {
        str += cell.isAlive ? CELL_CHAR.ALIVE : CELL_CHAR.DEAD;
      }
      str += '\n';
    }
    console.log(str);
  }
}

/**
 * Helper for creating a new world from a string.
 *
 * @param {string} boardScheme
 * @return {World}
 */
function createWorld(boardScheme) {
  const board = createBoard(boardScheme);
  return new World(board);
}

function createBoard(boardScheme) {
  const board = getBoardRows(boardScheme);
  return board.map((row) => createRowCells(row));
}

function getBoardRows(boardScheme) {
  return boardScheme.split('\n').slice(0, -1);
}

function createRowCells(row) {
  return row.split('').map((char) => convertCharToCell(char));
}

function convertCharToCell(char) {
  return new Cell(char === CELL_CHAR.ALIVE);
}

/**
 * Helper for printing the state of the game world.
 *
 * @param {World} world
 */

function print(world) {
  let str = '';
  for (const row of world.board) {
    for (const cell of row) {
      str += cell.isAlive ? CELL_CHAR.ALIVE : CELL_CHAR.DEAD;
    }
    str += '\n';
  }
  console.log(str);
}

function test() {
  const boardScheme =
    '........\n' +
    '........\n' +
    '...***..\n' +
    '........\n' +
    '........\n' +
    '........\n';

  const world = createWorld(boardScheme);
  print(world);
  world.evolve();
  print(world);
}

test();