<?php
declare(strict_types=1);

/**
 * Content-addressed store for the pixels of pixel art (#130): `data/pixels/{sha256}.px`.
 *
 * One file is one cel – the palette indices of one layer on one frame (see `src/core/model/pixelCel.ts`).
 * The editor names a cel from its bytes before it uploads it, so the project can point at it right
 * away; the name this store answers with is the check that both sides hashed the same bytes.
 *
 * Only the format is checked, never what the pixels mean. Like textures, a file stays when nothing
 * names it any more: undo after a reload can still find it.
 */
final class PixelStore
{
    private const MAGIC = 'GMPX';
    private const VERSION = 1;
    private const HEADER_BYTES = 10;
    /** The largest side a canvas may have; the same number as `PIXEL_CANVAS_MAX` in the editor. */
    public const MAX_SIDE = 512;
    public const MAX_BYTES = self::HEADER_BYTES + self::MAX_SIDE * self::MAX_SIDE;

    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 pixel directory {$this->dir}");
        }
    }

    public static function isValidName(string $name): bool
    {
        return (bool) preg_match('/^[a-f0-9]{64}\.px$/', $name);
    }

    /**
     * @return array{file:string,bytes:int}
     * @throws InvalidPixelsException when the bytes are not a cel
     */
    public function store(string $bytes): array
    {
        $length = strlen($bytes);
        if ($length < self::HEADER_BYTES || substr($bytes, 0, 4) !== self::MAGIC || ord($bytes[4]) !== self::VERSION) {
            throw new InvalidPixelsException('Not a pixel cel');
        }
        $width = ord($bytes[6]) | (ord($bytes[7]) << 8);
        $height = ord($bytes[8]) | (ord($bytes[9]) << 8);
        if ($width < 1 || $height < 1 || $width > self::MAX_SIDE || $height > self::MAX_SIDE) {
            throw new InvalidPixelsException('A cel is 1 to ' . self::MAX_SIDE . ' pixels per side');
        }
        if ($length !== self::HEADER_BYTES + $width * $height) {
            throw new InvalidPixelsException('The cel does not hold ' . $width . ' x ' . $height . ' pixels');
        }

        $file = hash('sha256', $bytes) . '.px';
        $path = $this->dir . '/' . $file;
        if (!is_file($path)) {
            $tmp = $path . '.' . bin2hex(random_bytes(4)) . '.tmp';
            if (file_put_contents($tmp, $bytes, LOCK_EX) === false || !rename($tmp, $path)) {
                if (is_file($tmp)) {
                    unlink($tmp);
                }
                throw new RuntimeException('Cannot write pixel file');
            }
            chmod($path, 0664);
        }
        return ['file' => $file, 'bytes' => $length];
    }
}

/** Thrown by PixelStore::store when the uploaded bytes are not a cel. */
final class InvalidPixelsException extends RuntimeException
{
}