/********************************
 * CS2510 Fall 2011
 * Lecture #8
 * Designing Snake
 ********************************/

import tester.*;
import image.*;
import world.*;

// Represents the SnakeGame world
class SnakeWorld extends World {
    Snake snake;
    Food food;
    
    /**
     * Template
     * 
     * Fields
     *   snake -- Snake
     *   food  -- Food
     * 
     * Methods
     *   onTick -- SnakeWorld
     *   onDraw -- Scene
     *   onKey  -- SnakeWorld
     */

    SnakeWorld(Snake snake, Food food) {
        this.snake = snake;
        this.food = food;
    }
    
    // Sets the speed of the world
    public double tickRate() {
        return 0.25;
    }
    
    // Draws the world with the snake and food
    public Scene onDraw() {
        return snake.draw(food.draw(new EmptyScene(food.WIDTH,food.HEIGHT)));
    }
    
    // Makes our snake move each tick
    public SnakeWorld onTick() {
        return new SnakeWorld(snake.move(),food);
    }
    
    // Sets the direction of the snake based on key presses
    public SnakeWorld onKey(String str) {
        return new SnakeWorld(snake.changeDir(str),food);
    }
}

// Represents a grid position in our world
abstract class AGrid extends Posn {
    
    // Some constants about our grid
    int CELL_SIZE = 20;
    int WIDTH_INCELLS = 20;
    int HEIGHT_INCELLS = 20;
    
    int WIDTH = WIDTH_INCELLS * CELL_SIZE;
    int HEIGHT = HEIGHT_INCELLS * CELL_SIZE;

    AGrid(int x, int y) {
        super(x, y);
    }
    
    /**
     * Template
     * Fields:
     *   this.x -- int
     *   this.y -- int
     * Methods:
     *   this.cell2Pixel() -- Posn
     */
    
    // Converts a cell to its pixel position
    Posn cell2Pixel() {
        return new Posn(CELL_SIZE * x + CELL_SIZE/2,
                        CELL_SIZE * y + CELL_SIZE/2);
    }
}

// Represents a food object in our SnakeWorld
class Food extends AGrid {

    Food(int x, int y) {
        super(x, y);
    }
    
    /**
     * Template
     * 
     * Fields:
     *   this.x -- int
     *   this.y -- int
     * Methods:
     *   this.draw(Scene) -- Scene
     */
    
    // Draws the Food in the scene
    Scene draw(Scene s) {
        return s.placeImage(new Circle(CELL_SIZE/2-1, "solid", "purple"),
                this.cell2Pixel());
    }
}

// Represents a Segment in our SnakeWorld
class Seg extends AGrid {

    Seg(int x, int y) {
        super(x, y);
    }
    
    /**
     * Template
     * 
     * Fields:
     *   this.x -- int
     *   this.y -- int
     * Methods:
     *   this.draw(Scene)  -- Scene
     *   this.move(String) -- Seg
     */
    
    // Draws the segment into the scene
    Scene draw(Scene s) {
        return s.placeImage(new Circle(CELL_SIZE/2-1, "solid", "black"),
                this.cell2Pixel());
    }
    
    // Returns a moved segment based on key presses
    Seg move(String dir) {
        if(dir.equals("up")) {
            return new Seg(x,y-1);
        } else if(dir.equals("down")) {
            return new Seg(x,y+1);
        } else if(dir.equals("left")) {
            return new Seg(x-1,y);
        } else if(dir.equals("right")) {
            return new Seg(x+1,y);
        } else {
            return this;
        }
    }
    
}

// List of Segments
interface ILoS {
    /**
     * Template
     * 
     * Methods:
     *   this.draw(Scene) -- Scene
     *   this.move(dir)   -- ILoS
     *   this.dropLast()  -- ILoS
     *   this.onlyOne()   -- boolean
     */
    
    Scene draw(Scene s);
    ILoS move(String dir);
    ILoS dropLast();
    boolean onlyOne();
}

// A one segment list item
class OneLoS implements ILoS {
    Seg first;

    OneLoS(Seg first) {
        this.first = first;
    }
    
    /**
     * Template
     * 
     * Fields:
     *   this.first -- Seg
     * Methods:
     *   this.draw(Scene) -- Scene
     */
    
    // Draws the only segment in the list
    public Scene draw(Scene s) {
        return first.draw(s);
    }
    
    // Moves the only segment
    public ILoS move(String dir) {
        return new OneLoS(first.move(dir));
    }
    
    // This list has only 1 element
    public boolean onlyOne() {
        return true;
    }
    
    // Can not drop last, only one element
    public ILoS dropLast() {
        throw new Error("No last to drop");
    }
    
    
}

// A cons list item for segments
class ConsLoS implements ILoS {
    Seg first;
    ILoS rest;

    ConsLoS(Seg first, ILoS rest) {
        this.first = first;
        this.rest = rest;
    }
    
    /**
     * Template
     * 
     * Fields:
     *   this.first -- Seg
     *   this.rest  -- ILoS
     * Methods:
     *   this.draw(Scene) -- Scene
     *   this.dropLast()  -- ILoS
     */    
    
    // Draws this segment with the rest of the segments
    public Scene draw(Scene s) {
        return rest.draw(first.draw(s));
    }
    
    // Adds a moved segment and drops the last segment
    public ILoS move(String dir) {
        return new ConsLoS(first.move(dir),this.dropLast());
    }
    
    // Removes the last segment from the list
    public ILoS dropLast() {
        if (rest.onlyOne()) {
            return new OneLoS(first);
        } else {
            return new ConsLoS(first,rest.dropLast());
        }
    }
    
    // This list has more than 1 element
    public boolean onlyOne() {
        return false;
    }
}

class Snake {
    ILoS segs;
    String dir;

    Snake(ILoS segs, String dir) {
        super();
        this.segs = segs;
        this.dir = dir;
    }
    
    /**
     * Template
     * 
     * Fields:
     *   this.segs -- ILoS
     *   this.dir  -- String
     *   
     * Methods
     *   this.draw(s) -- Scene
     *   this.changeDir(String) -- Snake
     *   this.move() -- Snake
     */
    
    // Draws the snake segments
    Scene draw(Scene s) {
        return segs.draw(s);
    }
    
    // Sets a new direction for the snake
    Snake changeDir(String dir) {
        return new Snake(segs, dir);
    }
    
    // Moves the snake one step in current direction
    Snake move() {
        return new Snake(segs.move(dir),dir);
    }
    
}

// Examples and tests of our SnakeWorld objects
class SnakeWorldExamples {
    Food f1 = new Food(3,3);
    Seg seg1 = new Seg(10,10);
    Seg seg2 = new Seg(10,11);
    Seg seg3 = new Seg(10,12);
    ILoS segs = new ConsLoS(seg1, new OneLoS(seg2));
    Snake snake = new Snake(segs,"up");
    SnakeWorld world = new SnakeWorld(snake,f1);
    World bang = world.bigBang();
    
    boolean testCells(Tester t) {
        return(t.checkExpect(f1.cell2Pixel(),new Posn(70,70)) &&
               t.checkExpect(seg1.cell2Pixel(),new Posn(90,110)));
    }
}