import Foundation

/// Host-Key-Prüfung OHNE interaktiven Yes/No-Prompt (der kommt ohne echtes
/// Terminal/Ctty nicht an — ssh bricht dann mit „Host key verification failed." ab).
/// Ablauf: ssh-keyscan → Fingerprint → Popup (akzeptieren/ablehnen) → known_hosts.
/// Nutzt bewusst ~/.ssh/known_hosts gemeinsam mit Terminal.app.
enum HostKeyStatus: Equatable {
    case known
    case unknown(HostKeyInfo)
    case changed(HostKeyInfo)
    case unreachable(String)
}

struct HostKeyInfo: Equatable {
    var host: String
    var port: Int
    var keyType: String
    var fingerprintSHA256: String
    var fingerprintMD5: String
    var allKeyLines: [String]
}

enum HostKeyService {
    static var knownHostsPath = NSHomeDirectory() + "/.ssh/known_hosts"
    static var scanTimeoutSeconds = "5"

    static func canonicalHost(_ host: String, port: Int) -> String {
        port == 22 ? host : "[\(host)]:\(port)"
    }

    @discardableResult
    static func run(_ exe: String, _ args: [String]) -> (Int32, String) {
        let p = Process()
        p.executableURL = URL(fileURLWithPath: exe)
        p.arguments = args
        let out = Pipe()
        p.standardOutput = out
        p.standardError = Pipe()
        do {
            try p.run()
        } catch {
            return (-1, "")
        }
        p.waitUntilExit()
        let data = out.fileHandleForReading.readDataToEndOfFile()
        return (p.terminationStatus, String(data: data, encoding: .utf8) ?? "")
    }

    /// Rohe Key-Zeilen vom Server (ohne #-Kommentare).
    static func keyscan(host: String, port: Int) -> [String] {
        let (code, out) = run("/usr/bin/ssh-keyscan", ["-T", scanTimeoutSeconds, "-p", "\(port)", host])
        guard code == 0 else { return [] }
        return out.split(separator: "\n").map(String.init).filter { line in
            let t = line.trimmingCharacters(in: .whitespaces)
            return !t.isEmpty && !t.hasPrefix("#") && t.contains(" ")
        }
    }

    static func knownHostsContent() -> String {
        (try? String(contentsOfFile: knownHostsPath, encoding: .utf8)) ?? ""
    }

    static func status(host: String, port: Int) -> HostKeyStatus {
        let h = host.trimmingCharacters(in: .whitespacesAndNewlines)
        guard !h.isEmpty else { return .unreachable("Kein Host.") }
        let lines = keyscan(host: h, port: port)
        guard !lines.isEmpty else {
            return .unreachable("Host-Key nicht abfragbar (ssh-keyscan ohne Antwort).")
        }
        guard let info = info(host: h, port: port, lines: lines) else {
            return .unreachable("Fingerprint nicht berechenbar.")
        }
        let (fcode, fout) = run("/usr/bin/ssh-keygen", ["-F", canonicalHost(h, port: port), "-f", knownHostsPath])
        let hasEntry = fcode == 0 && fout.contains("found:")
        if hasEntry {
            let knownKeys = lines.compactMap { $0.split(separator: " ").last.map(String.init) }
            if knownKeys.contains(where: { knownHostsContent().contains($0) }) {
                return .known
            }
            return .changed(info)
        }
        return .unknown(info)
    }

    /// Bevorzugter Key (ed25519 > ecdsa > Rest) + Fingerprints via ssh-keygen.
    static func info(host: String, port: Int, lines: [String]) -> HostKeyInfo? {
        func rank(_ l: String) -> Int {
            if l.contains("ssh-ed25519") { return 0 }
            if l.contains("ecdsa-") { return 1 }
            return 2
        }
        guard let line = lines.sorted(by: { rank($0) < rank($1) }).first else { return nil }
        let parts = line.split(separator: " ")
        guard parts.count >= 3 else { return nil }
        let tmp = FileManager.default.temporaryDirectory.appendingPathComponent("rmm-fp-\(UUID().uuidString)")
        do {
            try (line + "\n").write(to: tmp, atomically: true, encoding: .utf8)
            defer { try? FileManager.default.removeItem(at: tmp) }
            let (_, sha) = run("/usr/bin/ssh-keygen", ["-l", "-f", tmp.path])
            let (_, md5) = run("/usr/bin/ssh-keygen", ["-l", "-E", "md5", "-f", tmp.path])
            return HostKeyInfo(host: host, port: port, keyType: String(parts[1]),
                               fingerprintSHA256: parseFP(sha), fingerprintMD5: parseFP(md5),
                               allKeyLines: lines)
        } catch {
            return nil
        }
    }

    /// Aus `256 SHA256:XYZ host (ED25519)` wird `SHA256:XYZ`.
    static func parseFP(_ out: String) -> String {
        let parts = out.trimmingCharacters(in: .whitespacesAndNewlines).split(separator: " ")
        guard parts.count >= 2 else { return out.trimmingCharacters(in: .whitespacesAndNewlines) }
        return String(parts[1])
    }

    /// Fehlende Key-Zeilen an known_hosts anhängen (0600, ~/.ssh 0700).
    static func accept(_ info: HostKeyInfo) -> Bool {
        let dir = (knownHostsPath as NSString).deletingLastPathComponent
        do {
            try FileManager.default.createDirectory(atPath: dir, withIntermediateDirectories: true,
                                                    attributes: [.posixPermissions: 0o700])
            let existing = knownHostsContent()
            let missing = info.allKeyLines.filter { line in
                let key = line.split(separator: " ").last.map(String.init) ?? line
                return !existing.contains(key)
            }
            guard !missing.isEmpty else { return true }
            if !FileManager.default.fileExists(atPath: knownHostsPath) {
                FileManager.default.createFile(atPath: knownHostsPath, contents: nil,
                                               attributes: [.posixPermissions: 0o600])
            }
            let fh = try FileHandle(forWritingTo: URL(fileURLWithPath: knownHostsPath))
            defer { try? fh.close() }
            try fh.seekToEnd()
            fh.write(((missing.joined(separator: "\n")) + "\n").data(using: .utf8)!)
            try FileManager.default.setAttributes([.posixPermissions: 0o600], ofItemAtPath: knownHostsPath)
            return true
        } catch {
            return false
        }
    }

    /// Alle Einträge für Host entfernen (ssh-keygen -R).
    static func revoke(host: String, port: Int) -> Bool {
        let (code, _) = run("/usr/bin/ssh-keygen", ["-R", canonicalHost(host, port: port), "-f", knownHostsPath])
        return code == 0
    }
}