<?php

declare(strict_types=1);

namespace BattleForge\Application;

final class ImageValidator
{
    /**
     * @return array{string, string} [canonicalMime, extension] for a recognized image, or null.
     */
    private static function detect(string $header): ?array
    {
        if (substr($header, 0, 8) === "\x89PNG\r\n\x1a\n") {
            return ['image/png', 'png'];
        }

        if (substr($header, 0, 3) === "\xff\xd8\xff") {
            return ['image/jpeg', 'jpg'];
        }

        if (substr($header, 0, 6) === 'GIF87a' || substr($header, 0, 6) === 'GIF89a') {
            return ['image/gif', 'gif'];
        }

        if (substr($header, 0, 4) === 'RIFF' && substr($header, 8, 4) === 'WEBP') {
            return ['image/webp', 'webp'];
        }

        return null;
    }

    public static function validate(
        string $tempPath,
        string $declaredMime,
        int $maxBytes = 2_000_000,
        int $maxDimension = 512,
    ): ValidatedImage {
        if (!is_file($tempPath)) {
            throw new InvalidImageException('Upload is not a file.');
        }

        $size = filesize($tempPath);
        if ($size === false || $size > $maxBytes) {
            throw new InvalidImageException("File exceeds the {$maxBytes} byte limit.");
        }

        $handle = fopen($tempPath, 'rb');
        if ($handle === false) {
            throw new InvalidImageException('Could not read upload.');
        }
        $header = fread($handle, 12);
        fclose($handle);
        if ($header === false || strlen($header) < 12) {
            throw new InvalidImageException('Upload is too small to be an image.');
        }

        $detected = self::detect($header);
        if ($detected === null) {
            throw new InvalidImageException('File is not a supported image type.');
        }

        [$canonical, $extension] = $detected;

        if ($declaredMime !== $canonical) {
            throw new InvalidImageException('Declared MIME does not match file contents.');
        }

        $info = getimagesize($tempPath);
        if ($info === false) {
            throw new InvalidImageException('Image is corrupt or unreadable.');
        }

        [$width, $height] = $info;
        if ($width > $maxDimension || $height > $maxDimension) {
            throw new InvalidImageException("Image dimensions exceed the {$maxDimension} pixel limit.");
        }

        return new ValidatedImage($canonical, $extension);
    }
}