import java.awt.*;
import javax.swing.*;
import java.awt.event.*; // needed for event handling

public class Snake {
  
  static final int SCREEN_SIZE_X=40;         // In units of snake sections.
  static final int SCREEN_SIZE_Y=30;
  
  final int MAX_SNAKE_LENGTH = 1000;
  
  // While a snake is created with a very large number of snake sections,
  // determined by the constant variable MAX_SNAKE_LENGTH, the actual
  // apparent length of the snake in the game will be controlled by the
  // variable snakeLength. At each time step, the program will only draw
  // snakeLength snake sections for each snake. 
  //
  // Each time the snake eats some "food" (a yellow box on the screen), 
  // the snakeLength for that snake will
  // grow by the value of the food, which is printed in the box representing the
  // food. 
  
  int snakeLength = 5;                      // Start snakes with length 5.
  SnakeSection [] snakeSecs = new SnakeSection[MAX_SNAKE_LENGTH];
   
  // These variables represent the direction the snake is going.
  // Each time step, the snake moves in the direction represented by these
  // variables. The program does this by adding these values to the previous
  // head position of the snake. For example, the snake goes left initially, 
  // since by adding -1 to the x value (dirX = -1) and adding 0 to the y value
  // (dirY=0), the head of the snake moves one square to the left.

  int dirX=-1;
  int dirY=0;
  
  Color color;               // Holds the color of the snake.
  
  public Snake(SnakeSection startPos,int dx,int dy,Color color) {
    // Here, we are creating a large number of snake sections (1000 of them) so
    // that we don't have to worry about creating them later.
    for (int i=0; i<MAX_SNAKE_LENGTH; i++) 
      snakeSecs[i]=new SnakeSection(0,0);
    
    // Set the color of the snake based upon the formal parameter.    
    this.color=color;
    
    // Here, we create and INITIALIZE the snake sections that are going to be visible
    // at the beginning. We give these locations using a starting position, and offsets
    // from the start position.
    //
    // NOTE: Strictly speaking, it is unnecessary to CREATE the snake sections below
    //       using the new command, since these snake sections have already been created
    //       in the code just above, and all we really want to do is initialize the coordinates
    //       of the snake sections. However, in this case, it is easiest to use the
    //       constructor to initialize the snake sections to the values we want. In order
    //       to use the constructor, we must call new, and thus create the same snake
    //       sections again. It is a little bit of wasted effort, but it won't hurt anything.

    for (int i=0; i<snakeLength; i++) 
      snakeSecs[i]=new SnakeSection(startPos.x+i*dx,startPos.y+i*dy);
  }
  
  // This method returns true if EITHER the head or the body of a snake matches the given coordinates (x,y).
  
  public boolean contains(int x,int y) {  
    SnakeSection s=new SnakeSection(x,y);
    return s.match(snakeSecs[0]) || checkBodyPositions(s);
  }

  // This method returns true if any snake section in the body of a snake matches the given SnakeSection s.
  
  public boolean checkBodyPositions(SnakeSection s) {
    boolean collision=false;
    for (int i=1; i<snakeLength; i++) {
      if (s.match(snakeSecs[i]))
        collision=true;
    }
    return collision;
  }

  public void move() {
    for (int i=snakeLength-1; i>0; i--)
      snakeSecs[i]=snakeSecs[i-1];
    
    int newX=(snakeSecs[1].x + dirX + SCREEN_SIZE_X) % SCREEN_SIZE_X;
    int newY=(snakeSecs[1].y + dirY + SCREEN_SIZE_Y) % SCREEN_SIZE_Y;
    snakeSecs[0]=new SnakeSection(newX,newY);
  }
  
  // A snake is painted by drawing a square for each snake section. Each square is 20 by 20 pixels.
  
  public void paint(Graphics g) { 
    g.setColor(color);
    for (int i=0; i<snakeLength; i++) {
      g.setColor(new Color((float) Math.random(), (float) Math.random(), (float) Math.random()));
      g.drawRect(snakeSecs[i].x*20,snakeSecs[i].y*20,20,20);
    }
  }
}