import Foundation

/// Checksum algorithms supported for offload/MHL. Element names match
/// ASC MHL v2.0 spec hash-element vocabulary.
public enum HashAlgorithm: String, Sendable, CaseIterable {
    case xxh64
    case xxh3
    case xxh128
    case md5
    case sha1

    public var mhlElement: String {
        rawValue
    }

    /// In-memory one-shot (test/reference path).
    public static func hashInMemory(_ data: Data, algorithm: HashAlgorithm) -> String {
        switch algorithm {
        case .xxh64:
            return XXHash64.hexString(XXHash64.hash(data))
        case .xxh3:
            return XXH3.hexString64(XXH3.hash64(data))
        case .xxh128:
            return XXH3.hash128(data).hexString
        case .md5:
            return MD5.hexString(data)
        case .sha1:
            return SHA1.hexString(data)
        }
    }
}

extension FileHasher {
    /// Chunked file hash with algorithm dispatch.
    public static func hash(path: String, algorithm: HashAlgorithm) throws -> String {
        switch algorithm {
        case .xxh64:
            return try xxh64(path: path)
        case .md5:
            return try md5(path: path)
        case .xxh3:
            let s = XXH3.Streaming(bits: .h64)
            try streamFile(path: path) { s.update($0) }
            return XXH3.hexString64(s.digest64())
        case .xxh128:
            let s = XXH3.Streaming(bits: .h128)
            try streamFile(path: path) { s.update($0) }
            return s.digest128().hexString
        case .sha1:
            var sha = SHA1()
            try streamFile(path: path) { sha.update($0) }
            return sha.finalize().map { String(format: "%02x", $0) }.joined()
        }
    }

    static func streamFile(path: String, _ body: (Data) -> Void) throws {
        guard let handle = FileHandle(forReadingAtPath: path) else {
            throw OffloadError.fileNotFound(path)
        }
        defer { try? handle.close() }
        while true {
            guard let chunk = try handle.read(upToCount: chunkSize), !chunk.isEmpty else { break }
            body(chunk)
        }
    }
}