const SNES_WIDTH = 256;
const SNES_HEIGHT = 224;

const Orientation = {
  UP: 'up',
  DOWN: 'down',
  LEFT: 'left',
  RIGHT: 'right'
}

function bound(low, x, high) {
  return Math.max(low, Math.min(x, high));
}

// Representation of the state of the buttons on an SNES controller. (This may
// be the result of keyboard or gamepad input, which get mapped to the
// standard SNES buttons.)
class SnesInput {
  constructor() {
    this.reset();
  }

  reset() {
    this.up = false;
    this.down = false;
    this.left = false;
    this.right = false;
    this.a = false;
    this.b = false;
    this.x = false;
    this.y = false;
    this.l = false;
    this.r = false;
    this.select = false;
    this.start = false;
  }

  copyFrom(other) {
    this.up = other.up;
    this.down = other.down;
    this.left = other.left;
    this.right = other.right;
    this.a = other.a;
    this.b = other.b;
    this.x = other.x;
    this.y = other.y;
    this.l = other.l;
    this.r = other.r;
    this.select = other.select;
    this.start = other.start;
  }

  toString() {
    let result = '';

    if (this.up) {
      result += '^';
    } else if (this.down) {
      result += 'v';
    } else {
      result += '-';
    }

    if (this.left) {
      result += '<';
    } else if (this.right) {
      result += '>';
    } else {
      result += '-';
    }

    result += ' ';

    if (this.a) {
      result += 'A';
    }
    if (this.b) {
      result += 'B';
    }
    if (this.x) {
      result += 'X';
    }
    if (this.y) {
      result += 'Y';
    }
    if (this.l) {
      result += 'L';
    }
    if (this.r) {
      result += 'R';
    }
    if (this.select) {
      result += 's';
    }
    if (this.start) {
      result += 'S';
    }
    return result;
  }
}

class SnesGamepad {
  update(input) {
    const gamepads = navigator.getGamepads();
    if (gamepads.length < 1 || !gamepads[0] || !gamepads[0].connected) {
      input.reset();
      return;
    }
    this.wasConnected = true;
    // TODO: have a config screen instead of hard-coding the 8Bitdo SNES30 pad.
    const gamepad = gamepads[0];
    input.up = gamepad.axes[1] < 0;
    input.down = gamepad.axes[1] > 0;
    input.left = gamepad.axes[0] < 0;
    input.right = gamepad.axes[0] > 0;
    input.a = gamepad.buttons[0].pressed;
    input.b = gamepad.buttons[1].pressed;
    input.x = gamepad.buttons[3].pressed;
    input.y = gamepad.buttons[4].pressed;
    input.l = gamepad.buttons[6].pressed;
    input.r = gamepad.buttons[7].pressed;
    input.select = gamepad.buttons[10].pressed;
    input.start = gamepad.buttons[11].pressed;
  }
}

class InputHandler {
  constructor() {
    this.keysPressed = {};
    this.gamepad = new SnesGamepad();
    window.addEventListener(
        'gamepadconnected', (e) => this.gamepadConnected(e));
    window.addEventListener(
        'gamepaddisconnected', (e) => this.gamepadDisconnected(e));
    document.addEventListener('keydown', (e) => this.keyDown(e));
    document.addEventListener('keyup', (e) => this.keyUp(e));
  }

  keyDown(e) {
    this.keysPressed[e.key] = true;
  }

  keyUp(e) {
    this.keysPressed[e.key] = false;
  }

  update(input) {
    this.gamepad.update(input);

    // Default ZSNES keybindings. See:
    // http://zsnes-docs.sourceforge.net/html/readme.htm#default_keys
    input.up |= this.keysPressed['ArrowUp'];
    input.down |= this.keysPressed['ArrowDown'];
    input.left |= this.keysPressed['ArrowLeft'];
    input.right |= this.keysPressed['ArrowRight'];
    input.start |= this.keysPressed['Enter'];
    input.select |= this.keysPressed['Shift'];
    input.a |= this.keysPressed['x'];
    input.b |= this.keysPressed['z'];
    input.x |= this.keysPressed['s'];
    input.y |= this.keysPressed['a'];
    input.l |= this.keysPressed['d'];
    input.r |= this.keysPressed['c'];

    debug(input.toString());
  }

  gamepadConnected(e) {
    debug('gamepad connected! :)');
    console.log('gamepad connected @ index %d: %d buttons, %d axes\n[%s]',
        e.gamepad.index, e.gamepad.buttons.length, e.gamepad.axes.length,
        e.gamepad.id);
  }

  gamepadDisconnected(e) {
    debug('gamepad disconnected :(');
    console.log('gamepad disconnected @ index %d:\n[%s]', e.gamepad.index,
        e.gamepad.id);
  }
}

class Graphics {
  constructor(canvas) {
    this.canvas_ = canvas;
    this.ctx_ = canvas.getContext('2d');
    this.ctx_.imageSmoothingEnabled = false;
  }

  get width() {
    return this.canvas_.width;
  }

  get height() {
    return this.canvas_.height;
  }

  fill(color) {
    this.ctx_.fillStyle = color;
    this.ctx_.beginPath();
    this.ctx_.rect(0, 0, this.canvas_.width, this.canvas_.height);
    this.ctx_.fill();
    this.ctx_.closePath();
  }

  circle(x, y, radius, color) {
    this.ctx_.fillStyle = color;
    this.ctx_.beginPath();
    this.ctx_.arc(x, y, radius, 0, 2 * Math.PI)
    this.ctx_.fill();
    this.ctx_.closePath();
  }

  // TODO: replace with custom sprite-based text rendering.
  text(string, x, y, size, color) {
    this.ctx_.fillStyle = color;
    this.ctx_.font = '' + size + 'px monospace';
    this.ctx_.fillText(string, x, y);
  }

  drawSprite(sprite, dx, dy) {
    this.ctx_.drawImage(
      sprite.image,
      sprite.ulx, sprite.uly,
      sprite.width, sprite.height,
      dx, dy,
      sprite.width, sprite.height);
  }
}

class FpsCounter {
  constructor() {
    this.fps = 0;
    this.frameTimes_ = new Array(60);
    this.idx_ = 0;
  }

  update(timestampMs) {
    if (this.frameTimes_[this.idx_]) {
      const timeElapsed = (timestampMs - this.frameTimes_[this.idx_]) / 1000;
      this.fps = this.frameTimes_.length / timeElapsed;
    }
    this.frameTimes_[this.idx_] = timestampMs;
    this.idx_++;
    if (this.idx_ == this.frameTimes_.length) {
      this.idx_ = 0;
    }
  }

  draw(gfx) {
    const fpsDiv = document.getElementById('fps');
    fpsDiv.innerText = 'FPS: ' + Math.round(this.fps);
  }
}

class World {
  constructor() {
    this.state_ = null;
    this.fpsCounter_ = new FpsCounter();
    this.inputHandler_ = new InputHandler();
    this.input_ = new SnesInput();
    this.lastInput_ = new SnesInput();
    this.player_ = new Player();

    this.layer1_ = [
        "~~888888888888~~",
        "~8..,_.--.,.*.8~",
        "~._.*._.,.--,._~",
        "~_``_.,_..._..`~",
        "~,.`.....'...._~",
        "~.`_'*...._.._.~",
        "~,'.'_-'...__.`~",
        "~....,'...*,'..~",
        "~_..'_......_..~",
        "~*..``.,.,..,.,~",
        "~..'._'*'..___.~",
        "~._'.-....,.`..~",
        "~2_.*_,'-...`-2~",
        "~~222222222222~~"];
     this.layer2_ = [
        "        T       ",
        "                ",
        "                ",
        "                ",
        "                ",
        "                ",
        "       o        ",
        "  c          c  ",
        "                ",
        "     c    c     ",
        "                ",
        "                ",
        "                ",
        "                "];

    // TODO: move rendering stuff to a separate object.
    this.resources_ = new Resources();
    this.tileRenderer_ = new TileRenderer();
    this.playerRenderer_ = new PlayerRenderer();
    this.gamepadRenderer_ = new GamepadRenderer();
  }

  update(timestampMs) {
    this.fpsCounter_.update(timestampMs);

    // We copy values to avoid allocating new SnesInput objects every frame.
    // TODO: is this actually worth it?
    this.lastInput_.copyFrom(this.input_);
    this.inputHandler_.update(this.input_);

    if (!this.lastInput_.r && this.input_.r) {
      this.player_.cycleSprite();
    }
    if (this.input_.left) {
      this.player_.moveLeft();
    }
    if (this.input_.right) {
      this.player_.moveRight();
    }
    if (this.input_.up) {
      this.player_.moveUp();
    }
    if (this.input_.down) {
      this.player_.moveDown();
    }
  }

  draw(gfx) {
    gfx.fill('black');
    this.tileRenderer_.draw(gfx, this.resources_.sprites, this.layer1_);
    this.playerRenderer_.draw(gfx, this.resources_.sprites, this.player_);
    this.tileRenderer_.draw(gfx, this.resources_.sprites, this.layer2_);

    // this.gamepadRenderer_.draw(gfx, this.input_);
    this.fpsCounter_.draw(gfx);
  }
}

class Sprite {
  constructor(image, ulx, uly, width, height) {
    this.image = image;
    this.ulx = ulx;
    this.uly = uly;
    this.width = width;
    this.height = height;
  }
}

class CharacterSprite {
  constructor(image, ulx, uly, tileWidth, tileHeight) {
    // Assumption: a character sprite consists of 4 rows, which include the
    // character facing down, left, right, up (in that order). Each row has 3
    // columns, which can be used for a walking animation.
    this.down = [];
    this.left = [];
    this.right = [];
    this.up = [];
    for (let i = 0; i < 3; i++) {
      const x = ulx + i * tileWidth;
      this.down.push(new Sprite(
          image, x, uly, tileWidth, tileHeight));
      this.left.push(new Sprite(
          image, x, uly + tileHeight, tileWidth, tileHeight));
      this.right.push(new Sprite(
          image, x, uly + tileHeight * 2, tileWidth, tileHeight));
      this.up.push(new Sprite(
          image, x, uly + tileHeight * 3, tileWidth, tileHeight));
    }
  }
}

class Resources {
  constructor() {
    const terrain = document.getElementById('terrain');
    const inside = document.getElementById('inside');
    const outside = document.getElementById('outside');
    const water = document.getElementById('water');
    const witch = document.getElementById('witch');
    const spritesheet = document.getElementById('spritesheet');
    const ts = 16;
    this.sprites = {
      'ground0':        new Sprite(terrain, 2 * ts, 1 * ts, 16, 16),
      'ground1':        new Sprite(terrain, 3 * ts, 1 * ts, 16, 16),
      'ground2':        new Sprite(terrain, 4 * ts, 1 * ts, 16, 16),
      'ground3':        new Sprite(terrain, 5 * ts, 1 * ts, 16, 16),
      'ground4':        new Sprite(terrain, 6 * ts, 1 * ts, 16, 16),
      'ground5':        new Sprite(terrain, 2 * ts, 2 * ts, 16, 16),
      'ground6':        new Sprite(terrain, 6 * ts, 2 * ts, 16, 16),
      'water_ul':       new Sprite(water, 1 * ts, 9 * ts, 16, 16),
      'water_uc':       new Sprite(water, 2 * ts, 9 * ts, 16, 16),
      'water_ur':       new Sprite(water, 3 * ts, 9 * ts, 16, 16),
      'water_ml':       new Sprite(water, 1 * ts, 10 * ts, 16, 16),
      'water_mc':       new Sprite(water, 2 * ts, 10 * ts, 16, 16),
      'water_mr':       new Sprite(water, 3 * ts, 10 * ts, 16, 16),
      'water_ll':       new Sprite(water, 1 * ts, 11 * ts, 16, 16),
      'water_lc':       new Sprite(water, 2 * ts, 11 * ts, 16, 16),
      'water_lr':       new Sprite(water, 3 * ts, 11 * ts, 16, 16),
      'cauldron_blue':  new Sprite(witch, 0, 0, 32, 32),
      'cauldron_green': new Sprite(witch, 32, 0, 32, 32),
      'cup':            new Sprite(inside, 41 * ts, 27 * ts, 16, 16),
      'teapot':         new Sprite(inside, 36 * ts, 25 * ts, 16, 16),
      'bigtree':        new Sprite(outside, 528, 16, 96, 96),
    }

    for (const key in spritesheet_json) {
      const sprite_data = spritesheet_json[key];

      this.sprites[sprite_data['name']] = new CharacterSprite(
          spritesheet, sprite_data['x'], sprite_data['y'],
          sprite_data['width'] / 3, sprite_data['height'] / 4);
    }
  }
}

class Player {
  // TODO: stop hard-coding player bounding box.
  constructor() {
    this.x = (SNES_WIDTH - 26) / 2;
    this.y = (SNES_HEIGHT - 36) / 2 - 28;
    this.orientation = Orientation.DOWN;
    this.spriteNames_ = [];
    for (const name in spritesheet_json) {
      this.spriteNames_.push(name);
    }
    this.spriteNamesIdx_ = 0;
  }

  get spriteName() {
    return this.spriteNames_[this.spriteNamesIdx_];
  }

  cycleSprite() {
    this.spriteNamesIdx_++;
    if (this.spriteNamesIdx_ >= this.spriteNames_.length) {
      this.spriteNamesIdx_ = 0;
    }
  }

  moveLeft() {
    this.orientation = Orientation.LEFT;
    this.x -= 2;
    if (this.x < -2) {
      this.x = -2;
    }
  }

  moveRight() {
    this.orientation = Orientation.RIGHT;
    this.x += 2;
    if (this.x > SNES_WIDTH - 23) {
      this.x = SNES_WIDTH - 23;
    }
  }

  moveUp() {
    this.orientation = Orientation.UP;
    this.y -= 2;
    if (this.y < -2) {
      this.y = -2;
    }
  }

  moveDown() {
    this.orientation = Orientation.DOWN;
    this.y += 2;
    if (this.y > SNES_HEIGHT - 36) {
      this.y = SNES_HEIGHT - 36;
    }
  }
}

class PlayerRenderer {
  constructor() {
    this.frameNum = 0;
  }

  draw(gfx, sprites, player) {
    let spriteIndex = Math.floor((this.frameNum % 40) / 10);
    if (spriteIndex == 3) { spriteIndex = 1; }
    const charSprite = sprites[player.spriteName][player.orientation][spriteIndex];
    gfx.drawSprite(charSprite, player.x, player.y);
    this.frameNum++;
  }
}

class TileRenderer {
  draw(gfx, sprites, layer) {
    const tileSize = 16;
    // The screen is 14 x 16 tiles by default.
    const rows = gfx.height / tileSize;
    const columns = gfx.width / tileSize;
    const spriteLookup = {
      '.': sprites.ground0,
      ',': sprites.ground1,
      '_': sprites.ground2,
      '`': sprites.ground3,
      '-': sprites.ground4,
      '*': sprites.ground5,
      "'": sprites.ground6,
      '~': sprites.water_mc,
      '2': sprites.water_uc,
      '8': sprites.water_lc,
      'O': sprites.cauldron_blue,
      'o': sprites.cauldron_green,
      'c': sprites.cup,
      't': sprites.teapot,
      'T': sprites.bigtree,
    };
    for (let j = 0; j < columns; j++) {
      for (let i = 0; i < rows; i++) {
        const dx = tileSize * j;
        const dy = tileSize * i;
        const sprite = spriteLookup[layer[i][j]];
        if (sprite) {
          gfx.drawSprite(sprite, dx, dy);
        }
      }
    }
  }
}

class GamepadRenderer {
  draw(gfx, input) {
    const centerX = gfx.width / 2;
    const centerY = gfx.height / 2;

    // Select & Start
    gfx.circle(centerX + 12, centerY, 8, input.start ? 'cyan' : 'grey');
    gfx.circle(centerX - 12, centerY, 8, input.select ? 'cyan' : 'grey');

    // Y X B A
    gfx.circle(centerX + 48, centerY, 8, input.y ? 'cyan' : 'grey');
    gfx.circle(centerX + 64, centerY - 16, 8, input.x ? 'cyan' : 'grey');
    gfx.circle(centerX + 64, centerY + 16, 8, input.b ? 'cyan' : 'grey');
    gfx.circle(centerX + 80, centerY, 8, input.a ? 'cyan' : 'grey');

    // dpad
    gfx.circle(centerX - 48, centerY, 8, input.right ? 'cyan' : 'grey');
    gfx.circle(centerX - 64, centerY - 16, 8, input.up ? 'cyan' : 'grey');
    gfx.circle(centerX - 64, centerY + 16, 8, input.down ? 'cyan' : 'grey');
    gfx.circle(centerX - 80, centerY, 8, input.left ? 'cyan' : 'grey');

    // L & R
    gfx.circle(centerX + 30, centerY - 32, 8, input.r ? 'cyan' : 'grey');
    gfx.circle(centerX - 30, centerY - 32, 8, input.l ? 'cyan' : 'grey');
  }
}

function debug(message) {
  const debugDiv = document.getElementById('debug');
  debugDiv.innerText = message;
}

function loop(world, gfx) {
  return timestampMs => {
    world.update(timestampMs);
    world.draw(gfx);
    window.requestAnimationFrame(loop(world, gfx));
  };
}

function setCanvasScale(scale) {
  const canvas = document.getElementById('canvas');
  canvas.style.width = '' + SNES_WIDTH * scale + 'px';
  canvas.style.height = '' + SNES_HEIGHT * scale + 'px';
  canvas.style.display = '';
  debug('set scale to ' + scale + 'x');
}

function setAutoCanvasScale() {
  const widthAspect = Math.floor(window.innerWidth / SNES_WIDTH);
  const heightAspect = Math.floor(window.innerHeight / SNES_HEIGHT);
  const scale = bound(1, Math.min(widthAspect, heightAspect), 8);
  setCanvasScale(scale);
}

function init() {
  const world = new World();
  const gfx = new Graphics(document.getElementById('canvas'));

  document.getElementById('1x').onclick = () => setCanvasScale(1);
  document.getElementById('2x').onclick = () => setCanvasScale(2);
  document.getElementById('3x').onclick = () => setCanvasScale(3);
  document.getElementById('4x').onclick = () => setCanvasScale(4);
  document.getElementById('5x').onclick = () => setCanvasScale(5);
  document.getElementById('6x').onclick = () => setCanvasScale(6);
  document.getElementById('7x').onclick = () => setCanvasScale(7);
  document.getElementById('8x').onclick = () => setCanvasScale(8);
  setAutoCanvasScale();
  window.requestAnimationFrame(loop(world, gfx));
}

init();