<?php

class Qs_Validate_File_PngHasTransparency extends Zend_Validate_Abstract
{
    const NOT_READABLE    = 'notReadable';
    const NOT_PNG         = 'notPng';
    const NO_TRANSPARENCY = 'noTransparency';

    protected $_messageTemplates = array(
        self::NOT_READABLE    => 'The uploaded file can not be read',
        self::NOT_PNG         => 'The uploaded file is not PNG image',
        self::NO_TRANSPARENCY => 'The uploaded PNG has no transparency',
    );

    /**
     * Indicates the need for additional pixels transparency check
     * @var bool
     */
    protected $_pixelsCheck = false;

    /**
     * Pixel coordinates for additional transparency check [x, y, alpha]
     * @var array
     */
    protected $_pixelsMap = array(
        array(0, 0, 0),
        array(0, -1, 0),
        array(-1, 0, 0),
        array(-1, -1, 0),
    );

    function __construct($options = null)
    {
        if ($options instanceof Zend_Config) {
            $options = $options->toArray();
        }
        if ($options && is_array($options)) {
            $this->setOptions($options);
        }
        return $this;
    }

    public function setOptions($options)
    {
        if (isset($options['options'])) {
            unset($options['options']);
        }
        foreach ($options as $key => $value) {
            $method = 'set' . ucfirst($key);
            if (method_exists($this, $method)) {
                $this->$method($value);
            }
        }
        return $this;
    }

    /**
     * @param bool $flag
     * @return Qs_Validate_File_PngHasTransparency
     */
    public function setPixelsCheck($flag)
    {
        $this->_pixelsCheck = (bool) $flag;
        return $this;
    }

    public function getPixelsCheck()
    {
        return $this->_pixelsCheck;
    }

    /**
     * Pixel coordinates for additional transparency check [x, y, alpha]
     * @param array $pixelsMap
     * @return Qs_Validate_File_PngHasTransparency
     */
    public function setPixelsMap(array $pixelsMap)
    {
        if ($pixelsMap && is_array($pixelsMap)) {
            $_pixelsMap = array();
            foreach ($pixelsMap as $spec) {
                list($x, $y, $a) = $spec;
                $_pixelsMap[] = array((int) $x, (int) $y, (int) $a);
            }
            $this->_pixelsMap = $_pixelsMap;
        }
        return $this;
    }

    /**
     * @return array
     */
    public function getPixelsMap()
    {
        return $this->_pixelsMap;
    }

    /**
     * @param mixed|string $value Image Filename
     * @param array|null $file File data from Zend_File_Transfer
     * @return bool
     */
    public function isValid($value, $file = null)
    {
        if (empty($value) || !is_readable($value)) {
            $this->_error(self::NOT_READABLE, $value);
            return false;
        }

        $validSignature = chr(0x89) . chr(0x50) . chr(0x4E) . chr(0x47);
        if ($validSignature !== file_get_contents($value, false, null, 0, 4)) {
            $this->_error(self::NOT_PNG, $value);
            return false;
        }

        if ((ord(file_get_contents($value, false, null, 25, 1)) & 4)
            || (($contents = file_get_contents($value))
                && false !== strpos($contents, 'PLTE') && false !== strpos($contents, 'tRNS'))
        ) {
            return ($this->_pixelsCheck)
                ? $this->_checkPixelTransparency($value)
                : true;
        }

        $this->_error(self::NO_TRANSPARENCY, $file);
        return false;
    }

    /**
     * Check pixel transparency on png image according to $_pixelsMap
     * @param $filename
     * @return bool|string
     */
    protected function _checkPixelTransparency($filename)
    {
        if (!$this->_pixelsCheck && empty($this->_pixelsMap)) {
            return true;
        }

        if (false !== ($image = imagecreatefrompng($filename))
            && false !== ($size = getimagesize($filename))
        ) {
            list($width, $height) = $size;
            foreach ($this->_pixelsMap as $spec) {
                list($x, $y, $a) = $spec;
                $x = ($x < 0) ? $width - $x : $x;
                $x = ($x < 0) ? 0 : (($x > $width) ? $width - 1 : $x);

                $y = ($y < 0) ? $height - $y : $y;
                $y = ($y < 0) ? 0 : (($y > $height) ? $height - 1 : $y);

                $pixelColor = imagecolorat($image, (int) $x, (int) $y);
                $colorInfo = imagecolorsforindex($image, $pixelColor);
                if ($colorInfo['alpha'] > $a) {
                    return true;
                }
            }
        }
        return false;
    }

}