<?php
declare(strict_types=1);

/**
 * Minimal raw Snappy encoder for the V038 native TFS decoder.
 *
 * The head unit advertises application/x-snappy-framed, but the native
 * response path calls snappy::Uncompress on a raw Snappy block. Literal-only
 * blocks are valid raw Snappy and avoid a platform extension dependency.
 */
final class NiroRawSnappy
{
    public static function encodeLiteral(string $plain): string
    {
        $length = strlen($plain);
        if ($length > 8 * 1024 * 1024) {
            throw new InvalidArgumentException('Snappy input exceeds limit');
        }

        $encoded = self::varint($length);
        $offset = 0;
        while ($offset < $length) {
            $chunkLength = min(65536, $length - $offset);
            $encoded .= self::literalTag($chunkLength);
            $encoded .= substr($plain, $offset, $chunkLength);
            $offset += $chunkLength;
        }
        return $encoded;
    }

    private static function varint(int $value): string
    {
        $encoded = '';
        do {
            $byte = $value & 0x7f;
            $value >>= 7;
            if ($value !== 0) {
                $byte |= 0x80;
            }
            $encoded .= chr($byte);
        } while ($value !== 0);
        return $encoded;
    }

    private static function literalTag(int $length): string
    {
        if ($length < 1 || $length > 65536) {
            throw new InvalidArgumentException('Invalid Snappy literal length');
        }
        if ($length <= 60) {
            return chr(($length - 1) << 2);
        }

        $value = $length - 1;
        $bytes = '';
        while ($value !== 0) {
            $bytes .= chr($value & 0xff);
            $value >>= 8;
        }
        return chr((59 + strlen($bytes)) << 2) . $bytes;
    }
}