<?php
declare(strict_types=1);

/**
 * Content-addressed image store: `data/textures/{sha256}.{ext}`.
 *
 * The name of a file is the hash of its bytes, which buys four things at once:
 * uploading the same image twice costs one file, a stored file can be cached forever
 * (its URL cannot ever mean different bytes), projects reference a short string instead
 * of embedding megabytes of base64, and deleting a texture asset is undoable for free
 * because nothing here is removed when it stops being referenced.
 *
 * The flip side is that files outlive the projects that used them: nothing collects the
 * unreferenced ones. They stay pickable instead – `GET ?r=textures` is what the editor's
 * image picker offers, so a picture one project dropped is still there for the next.
 */
final class TextureStore
{
    /** Accepted formats. SVG is deliberately absent: it can carry script. */
    private const EXTENSIONS = [
        IMAGETYPE_PNG => 'png',
        IMAGETYPE_JPEG => 'jpg',
        IMAGETYPE_WEBP => 'webp',
        IMAGETYPE_GIF => 'gif',
    ];

    private const MIME_TYPES = [
        'image/png' => IMAGETYPE_PNG,
        'image/jpeg' => IMAGETYPE_JPEG,
        'image/webp' => IMAGETYPE_WEBP,
        'image/gif' => IMAGETYPE_GIF,
    ];

    /**
     * Refuses images no display can use anyway. Dimensions come from the header, so a
     * "decompression bomb" (tiny file, gigantic canvas) is rejected before anything
     * allocates memory for it.
     */
    private const MAX_DIMENSION = 8192;

    public function __construct(private readonly string $dir)
    {
        if (!is_dir($this->dir) && !mkdir($this->dir, 0775, true) && !is_dir($this->dir)) {
            throw new RuntimeException("Cannot create texture directory {$this->dir}");
        }
    }

    /** A stored file name, as it appears in a project document. */
    public static function isValidName(string $name): bool
    {
        return (bool) preg_match('/^[a-f0-9]{64}\.(png|jpg|webp|gif)$/', $name);
    }

    /**
     * Stores the raw bytes of an image and returns its record.
     *
     * The extension is derived from the sniffed content, never from anything the client
     * says, so no request can choose the name or the type of the file it creates.
     *
     * @return array{file:string,width:int,height:int,bytes:int}
     * @throws InvalidImageException when the bytes are not a supported image
     */
    public function store(string $bytes): array
    {
        $size = @getimagesizefromstring($bytes);
        if ($size === false) {
            throw new InvalidImageException('Not a readable image');
        }
        [$width, $height, $type] = $size;
        $extension = self::EXTENSIONS[$type] ?? '';
        if ($extension === '') {
            throw new InvalidImageException('Unsupported image format – use PNG, JPEG, WebP or GIF');
        }

        // Two independent sniffs must agree; a file that reads as one type by header and as
        // another by content is a polyglot, and we would rather not find out what it is.
        $mime = (new finfo(FILEINFO_MIME_TYPE))->buffer($bytes);
        if ((self::MIME_TYPES[$mime] ?? 0) !== $type) {
            throw new InvalidImageException('Image content does not match its format');
        }

        if ($width < 1 || $height < 1 || $width > self::MAX_DIMENSION || $height > self::MAX_DIMENSION) {
            throw new InvalidImageException('Image must be between 1 and ' . self::MAX_DIMENSION . ' pixels per side');
        }

        $file = hash('sha256', $bytes) . '.' . $extension;
        $path = $this->dir . '/' . $file;
        if (!is_file($path)) {
            $this->writeFile($path, $bytes);
        }

        return ['file' => $file, 'width' => $width, 'height' => $height, 'bytes' => strlen($bytes)];
    }

    /**
     * Every stored file, newest first – what the image picker offers.
     *
     * The pixel size is read from each header rather than left to the client: a texture asset
     * records the size, so a picker that only knew the file name could not create one without
     * decoding the picture first. An unreadable file reports 0 × 0 and the picker skips it.
     *
     * @return list<array{file:string,width:int,height:int,bytes:int,updatedAt:string}>
     */
    public function list(): array
    {
        $items = [];
        foreach (glob($this->dir . '/*.*') ?: [] as $path) {
            $file = basename($path);
            if (!self::isValidName($file)) {
                continue;
            }
            $size = @getimagesize($path);
            $items[] = [
                'file' => $file,
                'width' => (int) ($size[0] ?? 0),
                'height' => (int) ($size[1] ?? 0),
                'bytes' => (int) filesize($path),
                'updatedAt' => gmdate('c', (int) filemtime($path)),
            ];
        }
        usort($items, static fn(array $a, array $b): int => strcmp($b['updatedAt'], $a['updatedAt']));
        return $items;
    }

    public function delete(string $file): bool
    {
        if (!self::isValidName($file)) {
            return false;
        }
        $path = $this->dir . '/' . $file;
        return is_file($path) && unlink($path);
    }

    /**
     * Writes via a temp file in the same directory, so a reader never sees a half-written
     * image: the name only ever appears once the bytes behind it are complete.
     */
    private function writeFile(string $path, string $bytes): void
    {
        $tmp = $path . '.' . bin2hex(random_bytes(4)) . '.tmp';
        if (file_put_contents($tmp, $bytes, LOCK_EX) === false || !rename($tmp, $path)) {
            @unlink($tmp);
            throw new RuntimeException('Cannot write texture file');
        }
        @chmod($path, 0664);
    }
}

/** Thrown by TextureStore::store when the uploaded bytes are not a usable image. */
final class InvalidImageException extends RuntimeException
{
}