explorata/src/modules/automata.js

// handles negative index and index bigger than its array length
function guard(index, array) {
  if (index > array.length - 1) return 0;
  if (index < 0) return array.length - 1;
  return index;
}

// get the next evolution of a 1D CA initial state
function evolve1d(state, rules) {
  function getCell(index) {
    const safeIndex = guard(index, state);
    return state[safeIndex];
  }
  const newState = state.map((_, x) => {
    const cells = [getCell(x - 1), getCell(x), getCell(x + 1)];
    return rules[cells.join("")];
  });

  return newState.map(Number);
}

// create a 2D board from a 1D CA initial state
// function createBoard(state, rules, height) {
//   function createBoardAcc(s, h, acc) {
//     if (h === 0) return acc;
//     const newState = evolve1d(s, rules);
//     const newAcc = acc.concat([s]);
//     return createBoardAcc(newState, h - 1, newAcc);
//   }
//   return createBoardAcc(state, height, []);
// }

// performance "choke point" in full imperative
function createBoard(state, rules, height) {
  var board = [];
  let prevState = [];
  for (let i = 0; i < height; i++) {
    let nextState = [];
    if (i == 0) {
      nextState = evolve1d(state, rules);
    } else {
      nextState = evolve1d(prevState, rules);
    }
    board = board.concat([nextState]);
    prevState = nextState;
  }
  return board;
}

// Find the neighbor of a given cell in a 2D CA board
function getCellNeighbors(board, cellCoordinates) {
  const [x, y] = cellCoordinates;
  const rowLength = board[0].length; // caca?

  // handles board edges where the cell is missing neighbors
  function getCell(xx, yy) {
    const safeX = guard(xx, board);
    const safeY = guard(yy, rowLength);
    return board[safeX][safeY];
  }

  // the current cell is not included in the result
  return [
    getCell(x - 1, y - 1),
    getCell(x, y - 1),
    getCell(x + 1, y - 1),
    getCell(x - 1, y),
    getCell(x + 1, y),
    getCell(x - 1, y + 1),
    getCell(x, y + 1),
    getCell(x + 1, y - 1),
  ];
}

// Sums the value of a cell's neighbors
function getNeighborsSum(cells) {
  return cells.reduce((cell, acc) => cell + acc, 0);
}

// Get the next evolution of a cell according to
// Conway's game of life rules
function conwayRules(cell, neighbors) {
  // loneliness rule
  if (cell === 1 && neighbors < 2) return 0;
  // overpopulation rule
  if (cell === 1 && neighbors > 3) return 0;
  // born when three live neighbors rule
  if (cell === 0 && neighbors === 3) return 1;
  // the cell remains the same if none apply
  return cell;
}

// get the next evolution of a 2D CA initial state
// Rules : Moore neighborhood
function evolve2d(board, rulesFn) {
  return board.map((row, x) =>
    row.map((cell, y) => {
      const neighbors = getCellNeighbors(board, [x, y]);
      const sum = getNeighborsSum(neighbors);
      return rulesFn(cell, sum);
    })
  );
}

function getDrawingValues(state, acc, cell) {
  const d = cell.dimension;
  return Object.keys(state).map((key) => {
    const fillStyle = (() => {
      if (state[key] === "1") return cell.liveColor;
      return cell.deadColor;
    })();

    return {
      move: [key * d, acc * d],
      fill: [key * d, acc * d, d, d],
      fillStyle,
    };
  });
}

// Populates the first state with a single living cell in the center
function create1dStateOneCell(width) {
  return [...Array(width)].map((cell, index) => {
    if (index === width / 2 || index === width + 1 / 2) return 1;
    return 0;
  });
}

// Populates the first state of a 1D CA with cells returned
// by initFn
function create1dState(width, initFn, args) {
  return [...Array(width)].map(() => initFn(...args));
}

// Populates the first state of a 2D CA with cells returned
// by initFn
function create2dState(width, height, initFn, args) {
  return [...Array(height)].map(() =>
    [...Array(width)].map(() => initFn(...args))
  );
}

export {
  getDrawingValues,
  create1dState,
  create2dState,
  createBoard,
  create1dStateOneCell,
  conwayRules,
  evolve1d,
  evolve2d,
};