/*****************************************************************************

Tag.c - JavaScript to play tag with a computer.

<IMG SRC = "Tag.GIF" NAME = "Tag" >

The size of the image is the playing field.

*****************************************************************************/

// These values are constants which do not change

// obstacles (rubber posts)
var posts_x = [140, 280, 420, 140, 280, 420];
var posts_y = [120, 120, 120, 240, 240, 240];
var post_width = 31;
var sprite_diameter = 63;
var sprite_radius = 31;

// These values are constants which are calculated at run-time

// These variables track the playing field
var image_width, image_height, right_wall, bottom_wall;

// These values are not constants

// These variables track the mouse
var mouse_x, mouse_y;

// This object tracks the person
var person = [];

// This object tracks the robot
var robot = [];

// These variables keep score
var round = 0;
var score_high = 0;

var timer_id = 0;

/***************************************************************************

  Startup initialization

  This source depends on the functions provided in Tools.c which
  must be included before this source file.

  <SCR IPT TYPE = "text/javascript" SRC = "../Tools.c"></SCRIPT>

  <SCR IPT TYPE = "text/javascript" SRC = "Tag.c"></SCRIPT>

***************************************************************************/

Sprite_Make ("Person");

// Save person values
person.x = 0;
person.y = 0;
Sprite_Move (Tag, Person, person.x, person.y);

// Calculate square of distance to post
post_d = (sprite_diameter + post_width) >> 1;
post_sq = Math.pow (post_d, 2)
post_d += 1;

// Save field size which can't change
image_width = Tag.clientWidth;
image_height = Tag.clientHeight;
right_wall = image_width - sprite_diameter;
bottom_wall = image_height - sprite_diameter;

Sprite_Make ("Robot");

// Save robot values
robot.x = right_wall;
robot.y = bottom_wall;
robot.dx = 0;
robot.dy = 0;
robot_sq = Math.pow (sprite_diameter, 2)
Sprite_Move (Tag, Robot, robot.x, robot.y);

Scores_List ();

document.onmousemove = handlerMM;
document.onclick = Play_Start;

Tag_Message.innerText = "Click on the field to start the game.";

/******************************************************************************

  Mouse move handler

******************************************************************************/
function handlerMM ()
	{

	mouse_x = document.body.scrollLeft + window.event.clientX - Tag.offsetLeft;
	mouse_y = document.body.scrollTop + window.event.clientY - Tag.offsetTop;
	}

/******************************************************************************

  Click handler to start play
  
******************************************************************************/
function Play_Start () 
	{

	// Already playing?
	if (round)
		return;

	score_high = 0;
	Score_Time.innerText = score_high;

	Sprite_Move (Tag, Person, person.x, person.y);
	Sprite_Move (Tag, Robot, robot.x, robot.y);

	Round_Start ();
	}

/******************************************************************************

  Start the next round
  
******************************************************************************/
function Round_Start ()
	{

	person.x = 0;
	person.y = 0;
	person.dx = 0;
	person.dy = 0;

	robot.x = right_wall;
	robot.y = bottom_wall;
	robot.dx = 0;
	robot.dy = 0;

	++round;
	if (round > 2)
		{
		
		Scores_Update ();

		round = 0;
		Tag_Message.innerText = "Click on the field to start the game.";
		return;
		}

	if (round & 1)
		Tag_Message.innerText = "Run! Go tag the computer!";
	else
		Tag_Message.innerText = "Run! The computer is coming to tag you!";

	setTimeout ("Play_Move ()", 1000);
	}

/******************************************************************************

  timer function for moves during play
  
******************************************************************************/
function Play_Move () 
	{
	var dmax;

	if (round & 1)
		--score_high;
	else
		++score_high
	Score_Time.innerText = score_high;

	Move_Object (person, mouse_x, mouse_y);
	Sprite_Move (Tag, Person, person.x, person.y);

	if (round & 1)
		Robot_Run ();
	else
		Move_Object (robot, person.x, person.y);
	Sprite_Move (Tag, Robot, robot.x, robot.y);

	// Slow down the robot.
	dmax = Math.floor (20 + score_high / 100);
	if (dmax < 0)
		dmax = 0;

	if (dmax < Math.abs (robot.dx))
	{
		if (robot.dx < 0)
			robot.dx = - dmax;
		else
			robot.dx = dmax;
	}

	if (dmax < Math.abs (robot.dy))
	{
		if (robot.dy < 0)
			robot.dy = - dmax;
		else
			robot.dy = dmax;
	}

	if (Robot_Tag ())
		{
		if (0 != timer_id)
			clearInterval (timer_id);
		timer_id = 0;

		Round_Start ();
		}
	else
		{
		if (0 == timer_id)
			timer_id = setInterval ("Play_Move ()", 50);
		}
	}

/******************************************************************************

  The sprite makes the moves
  
******************************************************************************/
function Move_Object (sprite, dx, dy) 
	{
	var x, y, i;

	// Which way does the pointer say to run
	x = dx - sprite.x - sprite_radius;
	x = x - Factorial (sprite.dx);
	if (x < sprite.dx)
		--sprite.dx;
	if (x > sprite.dx)
		++sprite.dx;

	y = dy - sprite.y - sprite_radius;
	y = y - Factorial (sprite.dy);
	if (y < sprite.dy)
		--sprite.dy;
	if (y > sprite.dy)
		++sprite.dy;

	sprite.x += sprite.dx;
	sprite.y += sprite.dy;

	for (var i in posts_x)
		Post_Crash (sprite, posts_x[i], posts_y[i]);

	// crash into left wall?
	if (sprite.x < 0)
		{
		sprite.x = 0;
		sprite.dx = 0;
		}

	// crash into right wall?
	if (sprite.x > right_wall)
		{
		sprite.x = right_wall;
		sprite.dx = 0;
		}

	// crash into top wall?
	if (sprite.y < 0)
		{
		sprite.y = 0;
		sprite.dy = 0;
		}

	// crash into bottom wall?
	if (sprite.y > bottom_wall)
		{
		sprite.y = bottom_wall;
		sprite.dy = 0;
		}

	}

/******************************************************************************

  the robot runs away
  
******************************************************************************/
function Robot_Run ()
{
	var x, y;

	x = posts_x[5] - sprite_radius + posts_x[5] - person.x;
	y = posts_y[5] - sprite_radius + posts_y[5] - person.y;
	Move_Object (robot, x, y);
}

/******************************************************************************

  Calculate factorial

******************************************************************************/
function Factorial (x)
	{

	y = 0;
	while (x)
		{
		y += x;
		if (x < 0)
			++x;
		else
			--x;
		}
	return y;
	}

/******************************************************************************

  Crash into a post?

******************************************************************************/
function Post_Crash (sprite, x, y)
	{

	// How far are we from that post?
	dx = sprite.x + sprite_radius - x;
	dy = sprite.y + sprite_radius - y;
	d = Math.pow (dx, 2) + Math.pow (dy, 2);

	// Did we crash?
	if (post_sq > d)
		{

		// Bounce back a little bit
		angle = Math.atan2 (dx ,dy);

		dx = Math.ceil (post_d * Math.sin (angle));
		dy = Math.ceil (post_d * Math.cos (angle));

		sprite.x = x + dx - sprite_radius;
		sprite.y = y + dy - sprite_radius;
		}
	}

/******************************************************************************

  Tag robot?

******************************************************************************/
function Robot_Tag ()
	{

	d = Math.pow (person.x - robot.x, 2) + Math.pow (person.y - robot.y, 2);

	// Did we tag?
	if (robot_sq < d)
		return false;

	return true;
	}