<?php

/**
 * fast-image-size image type png
 *
 * @package       fast-image-size
 * @copyright (c) Marc Alexander <[email protected]>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Nextend\Framework\FastImageSize\Type;

class TypePng extends TypeBase {

    /** @var string PNG header */
    const PNG_HEADER = "\x89\x50\x4e\x47\x0d\x0a\x1a\x0a";

    /** @var int PNG IHDR offset */
    const PNG_IHDR_OFFSET = 12;

    /**
     * {@inheritdoc}
     */
    public function getSize($filename) {
        // Retrieve image data including the header, the IHDR tag, and the
        // following 2 chunks for the image width and height
        $data = $this->fastImageSize->getImage($filename, 0, self::PNG_IHDR_OFFSET + 3 * self::LONG_SIZE);

        // Check if header fits expected format specified by RFC 2083
        if (substr($data, 0, self::PNG_IHDR_OFFSET - self::LONG_SIZE) !== self::PNG_HEADER || substr($data, self::PNG_IHDR_OFFSET, self::LONG_SIZE) !== 'IHDR') {
            return;
        }

        $size = unpack('Nwidth/Nheight', substr($data, self::PNG_IHDR_OFFSET + self::LONG_SIZE, self::LONG_SIZE * 2));
        $this->fastImageSize->setSize($size);
        $this->fastImageSize->setImageType(IMAGETYPE_PNG);
    }
}