<?php
declare(strict_types=1);

namespace App\Service;

/**
 * Scales covers down to JPEG thumbnails. Smaller images are never enlarged.
 */
class CoverThumbnailer {
	private const int JPEG_QUALITY = 85;

	/**
	 * Sizes are twice the display size, for high-density screens.
	 *
	 * @var array<string, array{int, int}> maximum width and height by size name
	 */
	public const array SIZES = [
		'list' => [150, 225],
		'details' => [600, 900],
	];

	/**
	 * @param string $data the image file's contents
	 * @param callable(string): string $targetPath gives the file for a size name
	 *
	 * @throws CoverProcessingException
	 */
	public function createThumbnails(string $data, callable $targetPath): void {
		$image = $data === '' ? false : @imagecreatefromstring($data);

		if ($image === false) {
			throw new CoverProcessingException('The file could not be read as an image.');
		}

		$image = self::applyExifOrientation($image, $data);

		foreach (self::SIZES as $name => [$maxWidth, $maxHeight]) {
			if (!imagejpeg(self::scale($image, $maxWidth, $maxHeight), $targetPath($name), self::JPEG_QUALITY)) {
				throw new CoverProcessingException('The thumbnail could not be written.');
			}
		}
	}

	private static function scale(\GdImage $image, int $maxWidth, int $maxHeight): \GdImage {
		$width = imagesx($image);
		$height = imagesy($image);
		$ratio = min(1, $maxWidth / $width, $maxHeight / $height);
		$targetWidth = max(1, (int)round($width * $ratio));
		$targetHeight = max(1, (int)round($height * $ratio));

		// JPEG has no transparency, so transparent PNG and WebP covers go on a white background.
		$thumbnail = imagecreatetruecolor($targetWidth, $targetHeight);
		imagefill($thumbnail, 0, 0, (int)imagecolorallocate($thumbnail, 255, 255, 255));
		imagecopyresampled($thumbnail, $image, 0, 0, 0, 0, $targetWidth, $targetHeight, $width, $height);

		return $thumbnail;
	}

	/**
	 * Phones store the rotation of a photo as metadata, which thumbnails would otherwise lose.
	 */
	private static function applyExifOrientation(\GdImage $image, string $data): \GdImage {
		if (\IMAGETYPE_JPEG !== (@getimagesizefromstring($data)[2] ?? null)) {
			return $image;
		}

		$orientation = @exif_read_data('data://image/jpeg;base64,' . base64_encode($data))['Orientation'] ?? 1;

		if (\in_array($orientation, [2, 4, 5, 7], true)) {
			imageflip($image, \IMG_FLIP_HORIZONTAL);
		}

		$angle = match ($orientation) {
			3, 4 => 180,
			5, 8 => 90,
			6, 7 => 270,
			default => 0,
		};

		return $angle === 0 ? $image : imagerotate($image, $angle, 0);
	}
}