<?php
declare(strict_types=1);

/**
 * Content-addressed font store: `data/fonts/{folder}/{sha256}.{ext}` (see HashedFileStore).
 *
 * A font is stored byte for byte. There is no re-encoding step as there is for images, so what
 * the browser loads is exactly what was picked. The picker shows each face by rendering with it,
 * so a record has nothing to read out of the file.
 */
final class FontStore extends HashedFileStore
{
    /**
     * Accepted formats, keyed by the four bytes every one of them starts with. Bitmap and
     * collection formats are absent: a `.ttc` holds several faces and `@font-face` cannot say
     * which, and SVG fonts can carry script.
     */
    private const SIGNATURES = [
        "\x00\x01\x00\x00" => 'ttf',
        'true' => 'ttf',
        'OTTO' => 'otf',
        'wOFF' => 'woff',
        'wOF2' => 'woff2',
    ];

    protected static function filePattern(): string
    {
        return '[a-f0-9]{64}\.(ttf|otf|woff|woff2)';
    }

    /**
     * Stores the raw bytes of a typeface and returns its record.
     *
     * The format is read from the file's own signature, never from anything the client says.
     * `finfo` is not consulted the way it is for images: it reports fonts inconsistently across
     * libmagic versions (`font/sfnt`, `application/vnd.ms-opentype`, plain `application/octet-stream`),
     * so a second opinion from it would reject valid files rather than catch bad ones.
     *
     * `$originalName` is kept beside the file as a caption (see OriginalName): the hash says
     * nothing, and the name inside the font is deliberately never read (see `gm-font-` families).
     *
     * @return array{file:string,name:string,bytes:int}
     * @throws InvalidFontException when the bytes are not a supported font
     */
    public function store(string $bytes, string $originalName, string $folder): array
    {
        $extension = self::SIGNATURES[substr($bytes, 0, 4)] ?? '';
        if ($extension === '') {
            throw new InvalidFontException('Not a font file – use TTF, OTF, WOFF or WOFF2');
        }
        // The shortest thing that can still be a font: a table directory and one entry.
        if (strlen($bytes) < 28) {
            throw new InvalidFontException('Font file is truncated');
        }

        return $this->keep($bytes, $extension, $originalName, $folder);
    }
}

/** Thrown by FontStore::store when the uploaded bytes are not a usable font. */
final class InvalidFontException extends RuntimeException
{
}