<?php
    /**
     * @author Gasper Kozak
     * @copyright 2007-2011
     **/

    /**
     * GetMask operation class.
     */
    class WideImage_Operation_GetMask
    {
        /**
         * Returns a mask.
         *
         * @param WideImage_Image $image
         *
         * @return WideImage_Image
         */
        public function execute($image)
        {
            $width = $image->getWidth();
            $height = $image->getHeight();

            $mask = WideImage_TrueColorImage::create($width, $height);
            $mask->setTransparentColor(-1);
            $mask->alphaBlending(false);
            $mask->saveAlpha(false);

            for ($i = 0; $i <= 255; $i++) {
                $greyscale[$i] = imagecolorallocate($mask->getHandle(), $i, $i, $i);
            }

            imagefilledrectangle($mask->getHandle(), 0, 0, $width, $height, $greyscale[255]);

            $transparentColor = $image->getTransparentColor();
            $alphaToGreyRatio = 255 / 127;
            for ($x = 0; $x < $width; $x++) {
                for ($y = 0; $y < $height; $y++) {
                    $color = $image->getColorAt($x, $y);
                    if ($color == $transparentColor) {
                        $rgba['alpha'] = 127;
                    } else {
                        $rgba = $image->getColorRGB($color);
                    }
                    imagesetpixel($mask->getHandle(), $x, $y, $greyscale[255 - round($rgba['alpha'] * $alphaToGreyRatio)]);
                }
            }

            return $mask;
        }
    }
