use std::convert::Infallible;
use std::net::SocketAddr;
use std::path::Path;
#[cfg(unix)]
use std::process::Command;
use std::sync::atomic::Ordering;
use std::time::{SystemTime, UNIX_EPOCH};

use anyhow::{bail, Context, Result};
use dav_server::{fakels::FakeLs, DavHandler};
use hyper::server::conn::http1;
use hyper::service::service_fn;
use hyper_util::rt::TokioIo;
use tokio::net::TcpListener;
use tokio::sync::watch;
use tracing::{debug, warn};
use zeroize::Zeroizing;

use crate::crypto::mnemonic_to_dek;
use crate::storage::Database;
use crate::ui;
use crate::vfs::SanctumFs;

/// Authentifizierungsmethode für das Einbinden eines Containers: Entweder Master-Passwort oder 24-Wort Notfallschlüssel.
#[derive(Debug, Clone)]
pub enum ContainerAuth {
    Password(Zeroizing<String>),
    RecoveryKey(Zeroizing<String>),
}

/// Hilfsfunktion zur Formatierung des Laufwerksbuchstabens (z. B. 'S' -> "S:")
pub fn format_drive(drive_letter: char) -> String {
    format!("{}:", drive_letter.to_ascii_uppercase())
}

/// Trennt ein Windows-Netzlaufwerk via WNetCancelConnection2W bzw. Unix-Mountpoint via gio.
pub fn unmount_drive(drive_letter: char) -> Result<()> {
    #[cfg(windows)]
    {
        crate::windows::unmount_drive_wnet(drive_letter)
    }
    #[cfg(unix)]
    {
        let _ = drive_letter;
        Ok(())
    }
    #[cfg(not(any(windows, unix)))]
    {
        let _ = drive_letter;
        Ok(())
    }
}

/// Bindet ein Windows-Netzlaufwerk via in-process WNetAddConnection2W ein (R-05, kein Token in argv)
/// bzw. unter Unix via `gio mount dav://127.0.0.1:<PORT>/`.
fn run_mount_command(drive_letter: char, port: u16, session_token: &str) -> Result<()> {
    #[cfg(windows)]
    {
        crate::windows::mount_drive_wnet(drive_letter, port, session_token)
    }
    #[cfg(unix)]
    {
        let dav_url = format!("dav://127.0.0.1:{}/", port);
        let _ = Command::new("gio").args(["mount", &dav_url]).output();
        let _ = (drive_letter, session_token);
        Ok(())
    }
    #[cfg(not(any(windows, unix)))]
    {
        let _ = (drive_letter, port, session_token);
        Ok(())
    }
}

/// Startet den WebDAV-Server für den Sanctum-Container und bindet ihn als Netzlaufwerk (Windows) bzw. VFS (Linux) ein.
pub async fn mount_container(
    container_path: &Path,
    drive_letter: char,
    mount_point: Option<&Path>,
    requested_port: Option<u16>,
    auth: ContainerAuth,
    open_explorer: bool,
    enable_tray: bool,
    idle_timeout: Option<u64>,
    lock_on_screen_lock: bool,
    anti_leak: bool,
    stealth: bool,
) -> Result<()> {
    let drive_str = format_drive(drive_letter);
    let _ = &drive_str;
    let _ = mount_point;
    let _ = open_explorer;
    let _ = enable_tray;
    let _ = lock_on_screen_lock;

    if !container_path.exists() {
        bail!(
            "Containerdatei '{}' existiert nicht.",
            container_path.display()
        );
    }

    if !stealth {
        println!();
        ui::step(1, 4, "📦", "Öffne Container & verifiziere Header...");
    }
    let db = Database::open(container_path).context("Konnte Container-Datenbank nicht öffnen")?;

    let meta = db
        .read_meta()
        .context("Konnte Container-Header nicht lesen")?;

    let (dek, carrier_dek, carrier_node_id, version, vault_id) = match auth {
        ContainerAuth::Password(ref password) => {
            if !stealth {
                ui::step(
                    2,
                    4,
                    "🔑",
                    "Leite KEK via Argon2id ab (konstante Zeit über alle Slots)...",
                );
            }
            match meta.authenticate(password) {
                Some(keys) => {
                    if !stealth {
                        ui::step(
                            3,
                            4,
                            "🔓",
                            "Master-Passwort erfolgreich verifiziert & DEK entschlüsselt!",
                        );
                    }
                    let vault_id = keys.slot_id();
                    let ver = keys.version();
                    let c_dek = keys.carrier_dek();
                    let c_nid = keys.carrier_node_id();
                    (keys.0, c_dek, c_nid, ver, vault_id)
                }
                None => {
                    bail!("Ungültiges Master-Passwort oder Container beschädigt");
                }
            }
        }
        ContainerAuth::RecoveryKey(ref phrase) => {
            if !stealth {
                ui::step(2, 4, "🔑", "Dekodiere DEK aus 24-Wort Notfallschlüssel...");
            }
            let dek = mnemonic_to_dek(phrase).context("Ungültiger 24-Wort Notfallschlüssel")?;
            if !stealth {
                ui::step(3, 4, "🔓", "Notfallschlüssel erfolgreich verifiziert!");
            }

            let carrier_node_id = db.find_carrier_node_id()?.unwrap_or(0);
            let (carrier_dek, final_carrier_node_id, vault_id) = if carrier_node_id > 0 {
                let slot_id = crate::recovery::detect_recovery_key_slot(&db, &dek, meta.version)?;
                if slot_id == 1 {
                    if !stealth {
                        println!("  [i] Der angegebene Notfallschlüssel gehört zum Hidden-Vault (Slot 1).");
                        println!("      Für den Zugriff auf die Trägerdatei wird das Passwort des Standard-Vaults benötigt.");
                    }
                    let decoy_pass =
                        rpassword::prompt_password("Master-Passwort für Standard-Vault eingeben: ")
                            .context("Fehler beim Einlesen des Standard-Vault Passworts")?;
                    let decoy_keys = meta.authenticate(&decoy_pass).ok_or_else(|| {
                        anyhow::anyhow!("Ungültiges Passwort für Standard-Vault.")
                    })?;
                    (Some(decoy_keys.dek().clone()), Some(carrier_node_id), 1)
                } else {
                    (None, Some(carrier_node_id), 0)
                }
            } else {
                (None, None, 0)
            };

            (
                dek,
                carrier_dek,
                final_carrier_node_id,
                meta.version,
                vault_id,
            )
        }
    };

    // S-06: Advisory Lock setzen, um parallele Mounts und schreibende Sync-Läufe abzuwehren
    let _advisory_lock = db.acquire_advisory_lock_guard(false)?;

    // 128-Bit Session-Token für Loopback-Schutz (CWE-306) & Anti-CSRF generieren
    let mut token_bytes = [0u8; 16];
    rand::RngCore::fill_bytes(&mut rand::rngs::OsRng, &mut token_bytes);
    let session_token = hex::encode(token_bytes);

    // WebDAV Filesystem und Handler konfigurieren (mit Anti-Leak Shield & Carrier-Routing)
    let fs = SanctumFs::with_carrier(
        db.clone(),
        dek,
        carrier_dek,
        carrier_node_id,
        version,
        anti_leak,
        vault_id,
    );
    let last_activity = fs.last_activity();
    let dav_server = DavHandler::builder()
        .filesystem(Box::new(fs))
        .locksystem(FakeLs::new())
        .build_handler();

    // TCP-Port ermitteln und binden
    let port_to_try = requested_port.unwrap_or(8443);
    let listener = match TcpListener::bind(SocketAddr::from(([127, 0, 0, 1], port_to_try))).await {
        Ok(l) => l,
        Err(_) if requested_port.is_none() => {
            TcpListener::bind(SocketAddr::from(([127, 0, 0, 1], 0)))
                .await
                .context("Konnte keinen lokalen TCP-Port binden")?
        }
        Err(e) => {
            bail!("Konnte Port 127.0.0.1:{} nicht binden: {}", port_to_try, e);
        }
    };

    let bound_addr = listener.local_addr()?;
    let bound_port = bound_addr.port();

    if !stealth {
        #[cfg(windows)]
        ui::step(
            4,
            4,
            "🌐",
            &format!(
                "Starte WebDAV (Port {}) & binde Netzlaufwerk {} ein...",
                bound_port, drive_str
            ),
        );
        #[cfg(not(windows))]
        ui::step(
            4,
            4,
            "🌐",
            &format!(
                "Starte WebDAV-Server auf Port {} & initialisiere VFS...",
                bound_port
            ),
        );
    }

    let (shutdown_tx, shutdown_rx) = watch::channel(false);

    // Hyper HTTP Server Loop im Hintergrund starten
    let server_handle = tokio::spawn(serve_webdav_loop(
        listener,
        dav_server,
        session_token.clone(),
        shutdown_rx,
    ));

    // Netzlaufwerk bzw. Verzeichnis einbinden
    if let Err(e) = run_mount_command(drive_letter, bound_port, &session_token) {
        let _ = shutdown_tx.send(true);
        let _ = server_handle.await;
        return Err(e);
    }

    // Optional automatisch im Windows Explorer öffnen (visuelle Parität für Decoy und Hidden Vault)
    #[cfg(windows)]
    if open_explorer {
        let _ = crate::windows::open_in_explorer(drive_letter);
    }

    // System-Tray Initialisierung (nur Windows)
    #[cfg(windows)]
    let (_tray_shutdown_tx, mut tray_shutdown_rx) = tokio::sync::mpsc::channel::<()>(1);
    #[cfg(windows)]
    let _tray = if enable_tray {
        let icon_source = crate::windows::get_default_system_icon()
            .unwrap_or(tray_item::IconSource::Resource(""));
        let title = format!("Sanctum ({drive_str})");
        match tray_item::TrayItem::new(&title, icon_source) {
            Ok(mut tray) => {
                let container_name = container_path
                    .file_name()
                    .unwrap_or_default()
                    .to_string_lossy()
                    .to_string();
                let _ = tray.add_label(&format!("Sanctum: {drive_str} ({container_name})"));
                let dl = drive_letter;
                let _ = tray.add_menu_item("Im Explorer öffnen", move || {
                    let _ = crate::windows::open_in_explorer(dl);
                });
                let s_tx = _tray_shutdown_tx.clone();
                let _ = tray.add_menu_item("Trennen & Beenden", move || {
                    let _ = s_tx.blocking_send(());
                });
                Some(tray)
            }
            Err(e) => {
                debug!("System-Tray Icon konnte nicht erstellt werden: {e}");
                None
            }
        }
    } else {
        None
    };

    // Inaktivitäts-Timer (Auto-Lock)
    let (idle_shutdown_tx, mut idle_shutdown_rx) = tokio::sync::mpsc::channel::<()>(1);
    if let Some(timeout_secs) = idle_timeout {
        if timeout_secs > 0 {
            let last_act = last_activity.clone();
            let idle_tx = idle_shutdown_tx.clone();
            tokio::spawn(async move {
                let mut interval = tokio::time::interval(std::time::Duration::from_secs(1));
                loop {
                    interval.tick().await;
                    let now = SystemTime::now()
                        .duration_since(UNIX_EPOCH)
                        .map(|d| d.as_secs())
                        .unwrap_or(0);
                    let last = last_act.load(Ordering::Relaxed);
                    if now.saturating_sub(last) >= timeout_secs {
                        let _ = idle_tx.send(()).await;
                        break;
                    }
                }
            });
        }
    }

    // Windows-Sitzungssperre (Win + L Auto-Lock, nur Windows)
    #[cfg(windows)]
    let (session_lock_tx, mut session_lock_rx) = tokio::sync::mpsc::channel::<()>(1);
    #[cfg(windows)]
    let _session_monitor = if lock_on_screen_lock {
        match crate::windows::start_session_lock_monitor(session_lock_tx) {
            Ok(guard) => Some(guard),
            Err(e) => {
                warn!("Konnte Windows Session-Lock Monitor nicht aktivieren: {e}");
                None
            }
        }
    } else {
        None
    };

    if stealth {
        #[cfg(windows)]
        println!("Sanctum: Netzlaufwerk {} bereit.", drive_str);
        #[cfg(not(windows))]
        println!("Sanctum: WebDAV-Server auf Port {} bereit.", bound_port);
    } else {
        println!();
        println!("┌─────────────────────────────────────────────────────────────┐");
        println!("│  ✔ Sanctum Container erfolgreich gemountet                  │");
        println!("└─────────────────────────────────────────────────────────────┘");
        println!();
        println!("  • Container:    {}", container_path.display());
        #[cfg(windows)]
        println!(
            "  • Netzlaufwerk: {} (im Windows Explorer bereit)",
            ui::cyan(&drive_str)
        );
        #[cfg(not(windows))]
        {
            if let Some(mp) = mount_point {
                println!("  • Mountpoint:   {}", ui::cyan(&mp.display().to_string()));
            } else {
                println!("  • Modus:        WebDAV Userland-VFS");
            }
        }
        println!(
            "  • WebDAV-URL:   http://127.0.0.1:{}/ (lokal geschützt)",
            bound_port
        );
        #[cfg(not(windows))]
        {
            for line in format_linux_mount_instructions(bound_port, &session_token, mount_point) {
                println!("{}", line);
            }
        }
        if let Some(secs) = idle_timeout {
            println!("  • Auto-Lock:    Inaktivität nach {}s", secs);
        }
        #[cfg(windows)]
        if lock_on_screen_lock {
            println!("  • Sitzung:      Automatisches Sperren bei Win + L aktiv");
        }
        if anti_leak {
            #[cfg(windows)]
            println!("  • Anti-Leak:    Explorer-Metadatenfilter aktiv (Thumbs.db, desktop.ini blockiert)");
            #[cfg(not(windows))]
            println!("  • Anti-Leak:    VFS-Metadatenfilter aktiv (.directory, .Trash, desktop.ini blockiert)");
        }
        #[cfg(windows)]
        if enable_tray {
            println!("  • System-Tray:  Icon aktiv (Rechtsklick für Explorer/Trennen)");
        }
        println!();
        #[cfg(windows)]
        println!(
            "  [{}] Drücke [Ctrl+C] oder nutze das Tray-Icon zum Beenden.",
            ui::yellow("Tipp")
        );
        #[cfg(not(windows))]
        println!(
            "  [{}] Drücke [Ctrl+C] zum sicheren Beenden.",
            ui::yellow("Tipp")
        );
        println!();
    }

    // Windows Console Close Monitor (CTRL_CLOSE_EVENT / CTRL_SHUTDOWN_EVENT, nur Windows)
    #[cfg(windows)]
    let (console_close_tx, mut console_close_rx) = tokio::sync::mpsc::channel::<()>(1);
    #[cfg(windows)]
    let _console_guard =
        crate::windows::start_console_ctrl_monitor(console_close_tx, drive_letter).ok();

    // Unix Signale (SIGTERM, SIGHUP)
    #[cfg(unix)]
    let mut sigterm =
        tokio::signal::unix::signal(tokio::signal::unix::SignalKind::terminate()).ok();
    #[cfg(unix)]
    let mut sighup = tokio::signal::unix::signal(tokio::signal::unix::SignalKind::hangup()).ok();

    // Warten auf Beendigungssignal (Ctrl+C, Tray-Klick, Inaktivität, Win+L, Konsolenfenster-Schließen)
    #[cfg(windows)]
    tokio::select! {
        res = tokio::signal::ctrl_c() => {
            let _ = res;
            if !stealth {
                println!();
                println!("  {} Beendigungssignal (Ctrl+C) empfangen.", ui::yellow("[!]"));
            }
        }
        Some(()) = console_close_rx.recv() => {
            if !stealth {
                println!();
                println!("  {} Konsolenfenster wird geschlossen — sichere Trennung ausgeführt!", ui::yellow("[!]"));
            }
        }
        Some(()) = tray_shutdown_rx.recv() => {
            if !stealth {
                println!();
                println!("  {} Beendigungssignal aus System-Tray empfangen.", ui::yellow("[!]"));
            }
        }
        Some(()) = session_lock_rx.recv() => {
            if !stealth {
                println!();
                println!("  {} Windows-Sitzung gesperrt (Win + L) — Auto-Lock ausgelöst!", ui::yellow("[!]"));
            }
        }
        Some(()) = idle_shutdown_rx.recv() => {
            if !stealth {
                println!();
                println!("  {} Inaktivitäts-Timeout erreicht — Auto-Lock ausgelöst!", ui::yellow("[!]"));
            }
        }
    }

    #[cfg(unix)]
    tokio::select! {
        res = tokio::signal::ctrl_c() => {
            let _ = res;
            if !stealth {
                println!();
                println!("  {} Beendigungssignal (Ctrl+C) empfangen.", ui::yellow("[!]"));
            }
        }
        _ = async {
            match sigterm.as_mut() {
                Some(s) => { s.recv().await; }
                None => { std::future::pending::<()>().await; }
            }
        } => {
            if !stealth {
                println!();
                println!("  {} Beendigungssignal (SIGTERM) empfangen.", ui::yellow("[!]"));
            }
        }
        _ = async {
            match sighup.as_mut() {
                Some(s) => { s.recv().await; }
                None => { std::future::pending::<()>().await; }
            }
        } => {
            if !stealth {
                println!();
                println!("  {} Beendigungssignal (SIGHUP) empfangen.", ui::yellow("[!]"));
            }
        }
        Some(()) = idle_shutdown_rx.recv() => {
            if !stealth {
                println!();
                println!("  {} Inaktivitäts-Timeout erreicht — Auto-Lock ausgelöst!", ui::yellow("[!]"));
            }
        }
    }

    #[cfg(not(any(windows, unix)))]
    tokio::select! {
        res = tokio::signal::ctrl_c() => {
            let _ = res;
            if !stealth {
                println!();
                println!("  {} Beendigungssignal (Ctrl+C) empfangen.", ui::yellow("[!]"));
            }
        }
        Some(()) = idle_shutdown_rx.recv() => {
            if !stealth {
                println!();
                println!("  {} Inaktivitäts-Timeout erreicht — Auto-Lock ausgelöst!", ui::yellow("[!]"));
            }
        }
    }

    if stealth {
        let _ = unmount_drive(drive_letter);
        let _ = shutdown_tx.send(true);
        let _ = server_handle.await;
        if let Ok(freelist) = db.freelist_count() {
            if freelist > 0 {
                let _ = db.incremental_vacuum(None);
            }
        }
        let _ = db.checkpoint();
        #[cfg(windows)]
        println!("Sanctum: Laufwerk {} getrennt und geschlossen.", drive_str);
        #[cfg(not(windows))]
        println!("Sanctum: Container geschlossen und WebDAV-Server beendet.");
    } else {
        #[cfg(windows)]
        {
            print!(
                "  {} Trenne Windows-Netzlaufwerk {} ... ",
                ui::dim("[-]"),
                drive_str
            );
            let _ = std::io::Write::flush(&mut std::io::stdout());

            // Automatisches Unmount
            if let Err(e) = unmount_drive(drive_letter) {
                println!("{}", ui::yellow(&format!("Warnung ({e})")));
            } else {
                println!("{}", ui::green("OK"));
            }
        }
        #[cfg(not(windows))]
        {
            print!("  {} Beende WebDAV-Server ... ", ui::dim("[-]"));
            let _ = std::io::Write::flush(&mut std::io::stdout());
            println!("{}", ui::green("OK"));
        }

        // HTTP Server beenden
        let _ = shutdown_tx.send(true);
        let _ = server_handle.await;

        // Storage-Kompaktierung (Incremental Vacuum), falls freie Seiten existieren
        if let Ok(freelist) = db.freelist_count() {
            if freelist > 0 {
                print!(
                    "  {} Führe Storage-Kompaktierung aus ({} freie Seiten) ... ",
                    ui::dim("[-]"),
                    freelist
                );
                let _ = std::io::Write::flush(&mut std::io::stdout());
                match db.incremental_vacuum(None) {
                    Ok(freed) => println!("{} ({} Seiten freigegeben)", ui::green("OK"), freed),
                    Err(e) => println!("{}", ui::yellow(&format!("Warnung ({e})"))),
                }
            }
        }

        // SQLite WAL Checkpoint erzwingen
        print!("  {} Führe SQLite WAL-Checkpoint aus ... ", ui::dim("[-]"));
        let _ = std::io::Write::flush(&mut std::io::stdout());
        if let Err(e) = db.checkpoint() {
            println!("{}", ui::red(&format!("Fehler ({e})")));
        } else {
            println!("{}", ui::green("OK"));
        }

        println!();
        println!(
            "{} Sanctum Container wurde sicher und vollständig geschlossen.",
            ui::green("✔")
        );
        println!();
    }

    drop(db);
    // S-10: Verifikation und Bereinigung von temporären SQLite WAL- und SHM-Dateien
    let base_os = container_path.as_os_str().to_os_string();
    let mut wal = base_os.clone();
    wal.push("-wal");
    let _ = std::fs::remove_file(wal);
    let mut shm = base_os;
    shm.push("-shm");
    let _ = std::fs::remove_file(shm);

    Ok(())
}

/// Überprüft, ob ein Host-Header exakt auf Loopback (127.0.0.1, localhost, [::1], ::1) zeigt (Anti-DNS-Rebinding & S-06).
/// Striktes Parsing von Host und Port ohne anfällige starts_with-Präfixprüfungen.
pub fn is_loopback_host(host_str: &str) -> bool {
    let host_trimmed = host_str.trim().to_ascii_lowercase();
    if host_trimmed.is_empty() {
        return false;
    }

    if host_trimmed == "::1" {
        return true;
    }

    let host_part = if host_trimmed.starts_with('[') {
        // IPv6 bracketed: [::1] oder [::1]:port
        if let Some(bracket_end) = host_trimmed.find(']') {
            let inside = &host_trimmed[1..bracket_end];
            let after = &host_trimmed[bracket_end + 1..];
            if !after.is_empty() {
                if !after.starts_with(':') {
                    return false;
                }
                if after[1..].parse::<u16>().is_err() {
                    return false;
                }
            }
            inside
        } else {
            return false;
        }
    } else {
        // IPv4 oder Hostname: localhost, localhost:8443, 127.0.0.1, 127.0.0.1:8443
        if let Some((h, p)) = host_trimmed.rsplit_once(':') {
            if p.parse::<u16>().is_ok() {
                h
            } else {
                return false;
            }
        } else {
            &host_trimmed
        }
    };

    matches!(host_part, "127.0.0.1" | "localhost" | "::1")
}

/// Erzeugt die plattformspezifischen Linux-Mount-Anweisungen und Authentifizierungsdaten (M-03).
pub fn format_linux_mount_instructions(
    port: u16,
    token: &str,
    mount_point: Option<&std::path::Path>,
) -> Vec<String> {
    let mut lines = Vec::new();
    lines.push(format!(
        "  • WebDAV-Auth:  Benutzer: sanctum | Token: {}",
        token
    ));
    lines.push(format!(
        "  • gio Befehl:   echo {} | gio mount dav://sanctum@127.0.0.1:{}/",
        token, port
    ));
    if let Some(mp) = mount_point {
        lines.push(format!(
            "  • davfs2:       mount -t davfs -o username=sanctum http://127.0.0.1:{}/ {}",
            port,
            mp.display()
        ));
    } else {
        lines.push(format!(
            "  • davfs2:       mount -t davfs -o username=sanctum http://127.0.0.1:{}/ /mnt/sanctum",
            port
        ));
    }
    lines
}

/// Maximale Anzahl gleichzeitiger Verbindungen zum lokalen WebDAV-Endpunkt (Schutz gegen Socket-Exhaustion).
const MAX_CONCURRENT_DAV_CONNECTIONS: usize = 64;

/// Timeout für das Lesen von HTTP-Headern (Schutz gegen Slowloris-Angriffe auf Loopback).
const HTTP_HEADER_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(15);

/// Hilfsfunktion zur Validierung von HTTP Basic Auth.
/// Unterstützt Format `username:password` (wobei Passwort dem Session-Token entspricht).
/// SA-06: Verwendet strikten Constant-Time-Vergleich gegen Timing-Side-Channel-Angriffe.
pub fn check_basic_auth(auth_header: &str, expected_token: &str) -> bool {
    let auth_str = auth_header.trim();
    let encoded = if let Some(rest) = auth_str.strip_prefix("Basic ") {
        rest
    } else if let Some(rest) = auth_str.strip_prefix("basic ") {
        rest
    } else {
        return false;
    };

    use base64::Engine;
    let decoded_bytes = match base64::engine::general_purpose::STANDARD.decode(encoded.trim()) {
        Ok(bytes) => bytes,
        Err(_) => return false,
    };

    let decoded_str = match std::str::from_utf8(&decoded_bytes) {
        Ok(s) => s,
        Err(_) => return false,
    };

    use subtle::ConstantTimeEq;
    if let Some((_user, pass)) = decoded_str.split_once(':') {
        pass.as_bytes().ct_eq(expected_token.as_bytes()).into()
    } else {
        false
    }
}

/// Hilfsfunktion zur Validierung des X-Sanctum-Token Headers.
/// SA-06: Verwendet strikten Constant-Time-Vergleich gegen Timing-Side-Channel-Angriffe.
pub fn check_token_header(headers: &hyper::HeaderMap, expected_token: &str) -> bool {
    use subtle::ConstantTimeEq;
    if let Some(val) = headers.get("X-Sanctum-Token") {
        if let Ok(val_str) = val.to_str() {
            return val_str
                .trim()
                .as_bytes()
                .ct_eq(expected_token.as_bytes())
                .into();
        }
    }
    false
}

/// Prüft, ob eine URI oder deren Query-Parameter das sensible Session-Token enthält (SA-05 / CWE-598).
pub fn uri_contains_token(uri: &hyper::Uri, session_token: &str) -> bool {
    if session_token.is_empty() {
        return false;
    }
    uri.path().contains(session_token) || uri.query().unwrap_or("").contains(session_token)
}

/// Erzeugt eine standardkonforme HTTP 401 Unauthorized Antwort mit WWW-Authenticate Header.
fn unauthorized_response() -> hyper::Response<dav_server::body::Body> {
    hyper::Response::builder()
        .status(hyper::StatusCode::UNAUTHORIZED)
        .header(hyper::header::WWW_AUTHENTICATE, "Basic realm=\"Sanctum\"")
        .header(hyper::header::CONTENT_LENGTH, "0")
        .body(dav_server::body::Body::empty())
        .unwrap()
}

/// Führt die asynchrone WebDAV HTTP-Server-Schleife mit Header-basierter Authentifizierung & Host-Header Sicherheits-Middleware aus.
pub async fn serve_webdav_loop(
    listener: TcpListener,
    dav_server: DavHandler,
    session_token: String,
    mut shutdown_rx: watch::Receiver<bool>,
) {
    let conn_semaphore =
        std::sync::Arc::new(tokio::sync::Semaphore::new(MAX_CONCURRENT_DAV_CONNECTIONS));

    loop {
        tokio::select! {
            res = listener.accept() => {
                let (stream, _) = match res {
                    Ok(val) => val,
                    Err(e) => {
                        warn!("Verbindungsfehler im TCP-Listener: {e}");
                        continue;
                    }
                };

                // RT-01: Schutz gegen Connection-Starvation / Socket-Flooding (CWE-400)
                let permit = match conn_semaphore.clone().try_acquire_owned() {
                    Ok(p) => p,
                    Err(_) => {
                        warn!(
                            "WebDAV-Verbindungslimit ({} aktive Verbindungen) erreicht: Wehre potenziellen Connection-Starvation-Angriff ab.",
                            MAX_CONCURRENT_DAV_CONNECTIONS
                        );
                        drop(stream);
                        continue;
                    }
                };

                let io = TokioIo::new(stream);
                let handler = dav_server.clone();
                let expected_token = session_token.clone();

                tokio::spawn(async move {
                    let _permit = permit; // Permit wird bei Verbindungsende automatisch freigegeben

                    let service = service_fn(move |req| {
                        let h = handler.clone();
                        let token = expected_token.clone();
                        async move {
                            // 1. RT-02: Strikte Fail-Closed Host-Header Validierung (Anti-DNS-Rebinding & Anti-Spoofing)
                            let host_valid = match req.headers().get(hyper::header::HOST) {
                                Some(host_val) => match host_val.to_str() {
                                    Ok(host_str) => is_loopback_host(host_str),
                                    Err(_) => false,
                                },
                                None => false,
                            };

                            if !host_valid {
                                warn!(
                                    "Abgewiesener Zugriff: Fehlender, ungültiger oder externer Host-Header ({:?})",
                                    req.headers().get(hyper::header::HOST)
                                );
                                let res = hyper::Response::builder()
                                    .status(hyper::StatusCode::FORBIDDEN)
                                    .header(hyper::header::CONTENT_LENGTH, "0")
                                    .body(dav_server::body::Body::empty())
                                    .unwrap();
                                return Ok::<_, Infallible>(res);
                            }

                            // 2. SA-05: Verhindere Session-Token in Request-URI oder Query (CWE-598).
                            //    Session-Tokens dürfen ausschließlich in HTTP-Headern übertragen werden.
                            if uri_contains_token(req.uri(), &token) {
                                warn!("Abgewiesener Zugriff: Session-Token in URI/Query übermittelt (SA-05 / CWE-598)");
                                let res = hyper::Response::builder()
                                    .status(hyper::StatusCode::FORBIDDEN)
                                    .header(hyper::header::CONTENT_LENGTH, "0")
                                    .body(dav_server::body::Body::empty())
                                    .unwrap();
                                return Ok::<_, Infallible>(res);
                            }

                            // 3. SA-05 & SA-06: Header-basierte Authentifizierung mit Constant-Time Token-Vergleich
                            //    a) HTTP Basic Auth (Authorization: Basic ...)
                            //    b) Header X-Sanctum-Token
                            let mut authenticated = false;

                            if let Some(auth_val) = req.headers().get(hyper::header::AUTHORIZATION) {
                                if let Ok(auth_str) = auth_val.to_str() {
                                    if check_basic_auth(auth_str, &token) {
                                        authenticated = true;
                                    }
                                }
                            }

                            if !authenticated && check_token_header(req.headers(), &token) {
                                authenticated = true;
                            }

                            if !authenticated {
                                debug!("Abgewiesener unauthentifizierter Zugriff auf: {}", req.uri().path());
                                return Ok::<_, Infallible>(unauthorized_response());
                            }

                            Ok::<_, Infallible>(h.handle(req).await)
                        }
                    });

                    // RT-01: Header-Read-Timeout & TokioTimer zur aktiven Abwehr von Slowloris-Hanging-Sockets
                    let mut builder = http1::Builder::new();
                    builder.timer(hyper_util::rt::TokioTimer::new());
                    builder.header_read_timeout(HTTP_HEADER_READ_TIMEOUT);

                    if let Err(err) = builder.serve_connection(io, service).await {
                        debug!("HTTP-Verbindungsende: {:?}", err);
                    }
                });
            }
            _ = shutdown_rx.changed() => {
                debug!("WebDAV-Server-Task empfängt Shutdown-Signal.");
                break;
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_is_loopback_host_validation() {
        assert!(is_loopback_host("127.0.0.1"));
        assert!(is_loopback_host("127.0.0.1:8443"));
        assert!(is_loopback_host("localhost"));
        assert!(is_loopback_host("localhost:8443"));
        assert!(is_loopback_host("[::1]"));
        assert!(is_loopback_host("[::1]:8443"));

        // Abweisung externer Hosts oder DNS-Rebinding-Attacken
        assert!(!is_loopback_host("evil.com"));
        assert!(!is_loopback_host("attacker.local"));
        assert!(!is_loopback_host("192.168.1.50"));
        assert!(!is_loopback_host("10.0.0.1"));
        assert!(!is_loopback_host(""));
    }

    #[test]
    fn test_format_drive() {
        assert_eq!(format_drive('s'), "S:");
        assert_eq!(format_drive('Z'), "Z:");
    }

    #[test]
    fn test_check_basic_auth() {
        use base64::Engine;
        let token = "deadbeefcafebabe0123456789abcdef";
        let creds = format!("sanctum:{}", token);
        let header_val = format!(
            "Basic {}",
            base64::engine::general_purpose::STANDARD.encode(creds)
        );
        assert!(check_basic_auth(&header_val, token));

        // Kleingeschriebenes basic Präfix
        let lower_header = format!(
            "basic {}",
            base64::engine::general_purpose::STANDARD.encode(format!("user:{}", token))
        );
        assert!(check_basic_auth(&lower_header, token));

        // Falsches Token
        let wrong_token_header = format!(
            "Basic {}",
            base64::engine::general_purpose::STANDARD.encode("sanctum:wrongtoken")
        );
        assert!(!check_basic_auth(&wrong_token_header, token));

        // Ungültiges Base64 oder Format
        assert!(!check_basic_auth("Basic !!!notbase64!!!", token));
        assert!(!check_basic_auth("Bearer 12345", token));
        assert!(!check_basic_auth("", token));
    }

    #[test]
    fn test_check_token_header() {
        let token = "deadbeefcafebabe0123456789abcdef";
        let mut headers = hyper::HeaderMap::new();
        assert!(!check_token_header(&headers, token));

        headers.insert("X-Sanctum-Token", token.parse().unwrap());
        assert!(check_token_header(&headers, token));

        let mut wrong_headers = hyper::HeaderMap::new();
        wrong_headers.insert("X-Sanctum-Token", "wrong".parse().unwrap());
        assert!(!check_token_header(&wrong_headers, token));
    }

    #[test]
    fn test_uri_contains_token_rejection() {
        let token = "deadbeefcafebabe0123456789abcdef";

        // Token im Pfad
        let uri_path: hyper::Uri = format!("http://127.0.0.1:8443/{}/Photos/vacation.jpg", token)
            .parse()
            .unwrap();
        assert!(uri_contains_token(&uri_path, token));

        // Token im Query-String
        let uri_query: hyper::Uri =
            format!("http://127.0.0.1:8443/Photos/vacation.jpg?token={}", token)
                .parse()
                .unwrap();
        assert!(uri_contains_token(&uri_query, token));

        // Harmloser Pfad ohne Token
        let uri_clean: hyper::Uri = "http://127.0.0.1:8443/Photos/vacation.jpg".parse().unwrap();
        assert!(!uri_contains_token(&uri_clean, token));

        // Leeres Token darf niemals matchen
        assert!(!uri_contains_token(&uri_clean, ""));
    }

    #[test]
    fn test_m03_format_linux_mount_instructions() {
        let token = "fedcba9876543210fedcba9876543210";
        let instructions = format_linux_mount_instructions(
            8443,
            token,
            Some(std::path::Path::new("/mnt/secure")),
        );

        let all_text = instructions.join("\n");
        assert!(all_text.contains("Benutzer: sanctum"));
        assert!(all_text.contains(token));
        assert!(all_text.contains("gio mount dav://sanctum@127.0.0.1:8443/"));
        assert!(all_text.contains("mount -t davfs -o username=sanctum http://127.0.0.1:8443/ /mnt/secure"));
    }
}