import Foundation
import NIO
import Citadel

final class SFTPService: NASTransferProtocol {
    private var client: SSHClient?
    private var sftp: SFTPClient?
    private(set) var isConnected: Bool = false

    func connect(to host: String, port: Int, username: String, password: String) async throws {
        do {
            let c = try await SSHClient.connect(
                host: host,
                port: port,
                authenticationMethod: .passwordBased(username: username, password: password),
                hostKeyValidator: .acceptAnything(),
                reconnect: .never
            )
            let sftpClient = try await c.openSFTP()
            self.client = c
            self.sftp = sftpClient
            self.isConnected = true
        } catch {
            throw BackupError.connectionFailed(host)
        }
    }

    func disconnect() {
        Task {
            try? await sftp?.close()
            client = nil
        }
        sftp = nil
        isConnected = false
    }

    func listShares() async throws -> [String] { [] }

    func listDirectory(at path: String) async throws -> [NASItem] {
        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
        do {
            let batches = try await sftp.listDirectory(atPath: path)
            // listDirectory returns [SFTPMessage.Name]; each Name contains multiple SFTPPathComponent
            let components = batches.flatMap { $0.components }
            return components.compactMap { component -> NASItem? in
                guard component.filename != "." && component.filename != ".." else { return nil }
                let fullPath = path.hasSuffix("/")
                    ? "\(path)\(component.filename)"
                    : "\(path)/\(component.filename)"
                let isDir = component.attributes.permissions.map { ($0 & 0o170000) == 0o040000 } ?? false
                return NASItem(
                    name: component.filename,
                    path: fullPath,
                    isDirectory: isDir,
                    size: Int64(component.attributes.size ?? 0),
                    modifiedDate: nil
                )
            }
        } catch {
            throw BackupError.directoryListFailed(path)
        }
    }

    func createDirectory(at path: String) async throws {
        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
        do {
            try await sftp.createDirectory(atPath: path)
        } catch {
            throw BackupError.directoryCreateFailed(path)
        }
    }

    func fileExists(at remotePath: String) async throws -> Bool {
        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
        do {
            _ = try await sftp.getAttributes(at: remotePath)
            return true
        } catch {
            return false
        }
    }

    func downloadData(at remotePath: String) async throws -> Data {
        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
        return try await sftp.withFile(filePath: remotePath, flags: [.read]) { file in
            let buf = try await file.readAll()
            return Data(buf.readableBytesView)
        }
    }

    func upload(localURL: URL, remotePath: String, progress: @escaping (Int64, Int64) -> Void) async throws {
        guard let sftp else { throw BackupError.connectionFailed("Not connected") }
        let filename = localURL.lastPathComponent
        do {
            let data = try Data(contentsOf: localURL)
            let total = Int64(data.count)
            progress(0, total)
            try await sftp.withFile(
                filePath: remotePath,
                flags: [.write, .create, .truncate]
            ) { file in
                let buffer = ByteBuffer(data: data)
                try await file.write(buffer, at: 0)
            }
            progress(total, total)
        } catch {
            throw BackupError.uploadFailed(filename, underlying: error)
        }
    }
}