scenario.js

function Scenario() {
  var roadImage = new Image();
  var roadImageWidth = 500;
  var roadImageHeight = 600;

  this.trees = [];

  this.initialize = function (canvas) {
    this.canvas = canvas;
    this.canvas.style.backgroundColor = "green";

    this.x = canvas.width / 2 - roadImageWidth / 2;
    this.y = 0;
    this.y2 = -roadImageHeight;

    roadImage.src = "sprites/scenario/road.jpg";

    this.createTrees();
  };

  this.drawRoad = function (context) {
    context.drawImage(
      roadImage,
      this.x,
      this.y,
      roadImageWidth,
      roadImageHeight
    );
    context.drawImage(
      roadImage,
      this.x,
      this.y2,
      roadImageWidth,
      roadImageHeight
    );

    if (this.isThereOil()) {
      this.oil.draw(context);
    }

    if (this.isTherePothole()) {
      this.pothole.draw(context);
    }

    for (var i = 0; i < this.trees.length; i++) {
      this.trees[i].draw(context);
    }
  };

  this.updateRoad = function (emptyLane) {
    this.y += 1;
    if (this.y >= roadImageHeight) {
      this.y = 0;
    }

    this.y2 += 1;
    if (this.y2 >= 0) {
      this.y2 = -roadImageHeight;
    }

    if (this.hasObstaclesOnRoad()) {
      this.updateObstacles();
    } else {
      this.tryPutAnObstacleOnRoad(emptyLane);
    }

    this.updateTrees();
  };

  this.updateObstacles = function () {
    if (this.isThereOil()) {
      this.oil.update(this.canvas.height);
    }

    if (this.isTherePothole()) {
      this.pothole.update(this.canvas.height);
    }
  };

  this.updateTrees = function () {
    for (var i = 0; i < this.trees.length; i++) {
      this.trees[i].update(this.canvas.height);
    }
  };

  this.tryPutAnObstacleOnRoad = function (emptyLane) {
    var newObstacleProbability = Math.random();

    if (newObstacleProbability < 0.002) {
      this.putAnObstacleOnRoad(emptyLane);
    }
  };

  this.putAnObstacleOnRoad = function (emptyLane) {
    var typeObstacleProbability = Math.random();

    if (typeObstacleProbability < 0.7) {
      this.createPothole(emptyLane);
    } else {
      this.createOil(emptyLane);
    }
  };

  this.createPothole = function (emptyLane) {
    if (!this.pothole) {
      this.pothole = new Obstacle();
    }
    this.pothole.initialize(emptyLane, GameConfig.obstacle.pothole);
  };

  this.createOil = function (emptyLane) {
    if (!this.oil) {
      this.oil = new Obstacle();
    }
    this.oil.initialize(emptyLane, GameConfig.obstacle.oil);
  };

  this.hasObstaclesOnRoad = function () {
    return this.isThereOil() || this.isTherePothole();
  };

  this.isThereOil = function () {
    return this.oil && this.oil.isOnRoad;
  };

  this.isTherePothole = function () {
    return this.pothole && this.pothole.isOnRoad;
  };

  this.createTrees = function () {
    var treePositionIndex = 0;
    var treeSide = 0;
    for (var i = 0; i < 10; i++) {
      this.trees[i] = new Tree();
      this.trees[i].initialize(treePositionIndex, treeSide);

      if (treePositionIndex > 3) {
        treePositionIndex = 0;
        treeSide = 1;
      } else {
        treePositionIndex++;
      }
    }
  };
}