<?php
/**
 * This class will create a square png according to a given size and fill it with pixels.
 * @author JPT
 */
class BoxImage {

	/**
	 * @var resource
	 */
	protected $image;

	/**
	 * @var int
	 */
	protected $width;

	/**
	 * @var int
	 */
	protected $height;

	/**
	 * @var int
	 */
	protected $pointer_x;

	/**
	 * @var int
	 */
	protected $pointer_y;

	/**
	 * Basic constructor.
	 * @param int $size
	 * @return void
	 * @throws Exception
	 */
	public function __construct($size) {
		if($size < 1) throw new Exception("This cannot be done!");

			//determine width+height
		$this->height = ceil(sqrt($size));
		$this->width = $this->height;

			//prepare image for PNG with transparency using the calculated size.
		$this->image = imagecreatetruecolor($this->width, $this->height);

			//set the alpha stuff
		imagesavealpha($this->image, TRUE);
		imagealphablending($this->image, FALSE);

			//initialize pointers.
		$this->resetPointer();
	}

	/**
	 * Resets pointer.
	 * @return void
	 */
	public function resetPointer() {
		$this->pointer_x = 0;
		$this->pointer_y = 0;
	}

	/**
	 * Fills the image with the given color.
	 * @param int $r 0 - 255
	 * @param int $g 0 - 255
	 * @param int $b 0 - 255
	 * @param int $a 127 - 0
	 * @return void
	 */
	public function fillImage($r, $g, $b, $a) {
		$color = imagecolorallocatealpha($this->image, $r, $g, $b, $a);
		imagefill($this->image, 0, 0, $color);
		imagecolordeallocate($this->image, $color);
	}

	/**
	 * Sets the current pixel to the given color, moves the "pointer" of the image.
	 * @param int $r 0 - 255
	 * @param int $g 0 - 255
	 * @param int $b 0 - 255
	 * @param int $a 127 - 0
	 * @return void
	 */
	public function setCurrentPixel($r, $g, $b, $a) {
		$color = imagecolorallocatealpha($this->image, $r, $g, $b, $a);
		imagesetpixel($this->image, $this->pointer_x, $this->pointer_y, $color);
		imagecolordeallocate($this->image, $color);
	}

	/**
	 * Moves the x and y pointers of the image according to the offset.
	 * @param int $offset
	 * @throws Exception
	 * @return void
	 */
	public function movePointer($offset) {
		if($offset === 0) return;
		if($offset > 0) $step = 1;
		if($offset < 0){
			$step = -1;
			$offset = $offset * -1;
		}

		if(!isset($step)) throw new Exception("What the fuck?");

		for($i = $offset; $i > 0; $i--) {
				//if we go back
			if($step === -1) {
					//decrease x-pointer
				$this->pointer_x--;
					//handle y-jumps
				if($this->pointer_x === 0) {
					$this->pointer_x = $width;
					$this->pointer_y--;
						//out of range?
					if($this->pointer_y < 0) throw new Exception("Out of range! (width)");
				}

				//if we go forward
			} elseif($step === 1) {
			 		//increase x-pointer
				$this->pointer_x++;
					//handle y-jumps
				if($this->pointer_x === $this->width) {
					$this->pointer_x = 0;
					$this->pointer_y++;
						//out of range?
					if($this->pointer_y > $this->height) throw new Exception("Out of range! (height)");
				}
			} //end of if
		} //end of for
	} //end of function

	/**
	 * Writes the PNG to a file.
	 * @param string $filename
	 * @param int $compression 0-9
	 * @return boolean
	 */
	public function writeToFile($filename, $compression) {
		return imagepng($this->image, $filename, $compression);
	}

}