import Foundation

public enum OffloadError: Error, Equatable {
    case fileNotFound(String)
    case readFailed(String)
    case writeFailed(String)
    case verifyFailed(path: String, expected: String, actual: String)
    case destinationConflict(String)
}

/// Chunked file hashing — constant memory over multi-GB camera files.
public enum FileHasher {
    static let chunkSize = 4 * 1024 * 1024

    public static func xxh64(path: String) throws -> String {
        var hasher = XXHash64()
        try stream(path: path) { hasher.update($0) }
        return XXHash64.hexString(hasher.finalize())
    }

    public static func md5(path: String) throws -> String {
        var hasher = MD5()
        try stream(path: path) { hasher.update($0) }
        return hasher.finalize().map { String(format: "%02x", $0) }.joined()
    }

    private static func stream(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)
        }
    }
}