import Foundation
import Citadel

/// SSH+CLI transport fallback for RouterOS devices/firmware without the REST API (pre-7.1).
///
/// Known limitation (tracked for M7 hardening): host key validation currently accepts any key.
/// This is acceptable for now because REST already provides certificate TOFU on the primary
/// path and this fallback is used for local-network devices only, but it should get the same
/// trust-on-first-use treatment before wider distribution.
final class SSHTransport: RouterOSTransport {
    let kind: RouterOSTransportKind = .ssh

    private let credentials: RouterOSCredentials
    private var client: SSHClient?

    init(credentials: RouterOSCredentials) {
        self.credentials = credentials
    }

    func connect() async throws {
        do {
            client = try await SSHClient.connect(
                host: credentials.host,
                port: credentials.sshPort,
                authenticationMethod: .passwordBased(username: credentials.username, password: credentials.password),
                hostKeyValidator: .acceptAnything(),
                reconnect: .never,
                // RouterOS' SSH server typically only offers legacy algorithms
                // (diffie-hellman-group14-sha1 key exchange, RSA host keys) that
                // Citadel's defaults don't include — `.all` adds them.
                algorithms: .all
            )
        } catch {
            // NIOSSHError's `.localizedDescription` is a useless generic NSError-bridged string
            // ("The operation couldn't be completed."); its real diagnostics only surface via
            // CustomStringConvertible, which `String(describing:)` picks up.
            throw RouterOSError.transportUnavailable("SSH-Verbindung fehlgeschlagen: \(String(describing: error))")
        }
    }

    func fetchDeviceInfo() async throws -> RouterDeviceInfo {
        let output = try await run("/system resource print without-paging")
        return RouterOSCliParser.parseDeviceInfo(output)
    }

    func fetchInterfaces() async throws -> [NetworkInterface] {
        let output = try await run("/interface print without-paging terse")
        return RouterOSCliParser.parseInterfaces(output)
    }

    func disconnect() async {
        try? await client?.close()
        client = nil
    }

    /// Full human-readable config export (`/export terse`), used for local backups.
    func exportConfiguration() async throws -> String {
        try await run("/export terse")
    }

    func fetchFirewallRuleCounts() async throws -> FirewallRuleCounts {
        let filterOutput = try await run("/ip firewall filter print count-only")
        let natOutput = try await run("/ip firewall nat print count-only")
        let filterCount = Int(filterOutput.trimmingCharacters(in: .whitespacesAndNewlines)) ?? 0
        let natCount = Int(natOutput.trimmingCharacters(in: .whitespacesAndNewlines)) ?? 0
        return FirewallRuleCounts(filterRuleCount: filterCount, natRuleCount: natCount)
    }

    func apply(_ command: RouterOSCommand) async throws {
        _ = try await run(command.cliLine)
    }

    /// Restores RouterOS' own vendor-default configuration and reboots the device. See
    /// FactoryResetService for why this bypasses the RouterOSCommand add/set model entirely.
    func resetToFactoryDefaults() async throws {
        _ = try await run("/system reset-configuration no-defaults=no skip-backup=no")
    }

    /// Runs a command via `executeCommandStream` (not the simpler `executeCommand`), because
    /// `executeCommand` discards whatever output it already collected the moment the command
    /// exits non-zero — exactly the RouterOS error text we need. Collecting the stream ourselves
    /// keeps that text available even when the command fails.
    private func run(_ command: String) async throws -> String {
        guard let client else { throw RouterOSError.notConnected }

        var output = ""
        do {
            let stream = try await client.executeCommandStream(command)
            for try await chunk in stream {
                switch chunk {
                case .stdout(let buffer), .stderr(let buffer):
                    output += String(buffer: buffer)
                }
            }
            return output
        } catch let failure as SSHClient.CommandFailed {
            let detail = output.trimmingCharacters(in: .whitespacesAndNewlines)
            throw RouterOSError.invalidResponse(
                "RouterOS meldete Fehler (Exit-Code \(failure.exitCode)) für \"\(command)\""
                    + (detail.isEmpty ? "" : ": \(detail)")
            )
        }
    }
}