<?php
/**
 * Reads the EXIF Orientation tag from JPEG bytes without the exif extension.
 *
 * @package Fitzaro
 */

namespace Fitzaro\Image;

defined( 'ABSPATH' ) || exit;

/**
 * Phone cameras store the sensor's pixels and record the rotation in EXIF.
 * Many shared hosts disable ext/exif, so this walks the JPEG segments itself.
 *
 * Every read is bounds-checked; malformed data returns 1 (no rotation) instead of failing.
 */
final class ExifOrientation {

	public const NORMAL = 1;

	private const TAG_ORIENTATION = 0x0112;

	/**
	 * Orientation value 1–8, or 1 when absent or unreadable.
	 *
	 * @param string $jpeg JPEG file bytes.
	 */
	public static function from_jpeg( string $jpeg ): int {
		$length = strlen( $jpeg );
		if ( $length < 4 || "\xFF\xD8" !== substr( $jpeg, 0, 2 ) ) {
			return self::NORMAL;
		}

		$offset = 2;
		while ( $offset + 4 <= $length ) {
			if ( "\xFF" !== $jpeg[ $offset ] ) {
				return self::NORMAL;
			}

			$marker = ord( $jpeg[ $offset + 1 ] );
			// Start of scan or end of image: metadata segments come before these.
			if ( 0xDA === $marker || 0xD9 === $marker ) {
				return self::NORMAL;
			}

			$segment_length = self::u16( $jpeg, $offset + 2, true );
			if ( $segment_length < 2 || $offset + 2 + $segment_length > $length ) {
				return self::NORMAL;
			}

			if ( 0xE1 === $marker && "Exif\0\0" === substr( $jpeg, $offset + 4, 6 ) ) {
				return self::from_tiff( substr( $jpeg, $offset + 10, $segment_length - 8 ) );
			}

			$offset += 2 + $segment_length;
		}

		return self::NORMAL;
	}

	/**
	 * Reads the tag from IFD0 of a TIFF block.
	 *
	 * @param string $tiff TIFF header and IFDs.
	 */
	private static function from_tiff( string $tiff ): int {
		$length = strlen( $tiff );
		if ( $length < 8 ) {
			return self::NORMAL;
		}

		$order = substr( $tiff, 0, 2 );
		if ( 'MM' !== $order && 'II' !== $order ) {
			return self::NORMAL;
		}
		$big_endian = 'MM' === $order;

		$ifd = self::u32( $tiff, 4, $big_endian );
		if ( $ifd + 2 > $length ) {
			return self::NORMAL;
		}

		$entries = self::u16( $tiff, $ifd, $big_endian );
		for ( $i = 0; $i < $entries; $i++ ) {
			$entry = $ifd + 2 + $i * 12;
			if ( $entry + 12 > $length ) {
				return self::NORMAL;
			}

			if ( self::TAG_ORIENTATION === self::u16( $tiff, $entry, $big_endian ) ) {
				$value = self::u16( $tiff, $entry + 8, $big_endian );
				return ( $value >= 1 && $value <= 8 ) ? $value : self::NORMAL;
			}
		}

		return self::NORMAL;
	}

	/**
	 * Unsigned 16-bit integer at $offset.
	 *
	 * @param string $bytes      Data.
	 * @param int    $offset     Byte offset.
	 * @param bool   $big_endian Byte order.
	 */
	private static function u16( string $bytes, int $offset, bool $big_endian ): int {
		$unpacked = unpack( $big_endian ? 'n' : 'v', $bytes, $offset );
		return false === $unpacked ? 0 : (int) $unpacked[1];
	}

	/**
	 * Unsigned 32-bit integer at $offset.
	 *
	 * @param string $bytes      Data.
	 * @param int    $offset     Byte offset.
	 * @param bool   $big_endian Byte order.
	 */
	private static function u32( string $bytes, int $offset, bool $big_endian ): int {
		$unpacked = unpack( $big_endian ? 'N' : 'V', $bytes, $offset );
		return false === $unpacked ? 0 : (int) $unpacked[1];
	}
}