// WebSocket proxy — routes WSS through Rust to bypass self-signed cert rejection.
// JS sends/receives messages via Tauri events instead of native WebSocket.
//
// Implements TOFU (Trust On First Use) certificate pinning:
// - On first connect to a host, the cert SHA-256 fingerprint is stored.
// - On subsequent connects, the fingerprint is compared with the stored value.
// - If the fingerprint changes, the connection is rejected (potential MitM).

use futures_util::{SinkExt, StreamExt};
use log::{debug, error, info, warn};
use ring::digest::{digest, SHA256};
use serde_json::Value;
use std::sync::Arc;
use std::time::Duration;
use tauri::{AppHandle, Emitter, Runtime};
use tauri_plugin_store::StoreExt;
use tokio::sync::{mpsc, Mutex};
use tokio::task::JoinSet;
use tokio_tungstenite::tungstenite::Message;

/// Maximum time to wait for the WebSocket handshake to complete.
const CONNECT_TIMEOUT: Duration = Duration::from_secs(10);

use crate::constants::CERTS_STORE;

/// Sender half kept in Tauri state so `ws_send` can push messages.
/// `tx` is wrapped in `Arc` so the monitoring task can clone a reference
/// into its closure and clear the sender even after a worker task panic.
pub struct WsState {
    tx: Arc<Mutex<Option<mpsc::Sender<String>>>>,
}

impl WsState {
    pub fn new() -> Self {
        Self {
            tx: Arc::new(Mutex::new(None)),
        }
    }
}

/// Shared fingerprint captured during TLS handshake.
type CapturedFingerprint = Arc<std::sync::Mutex<Option<String>>>;

/// TOFU certificate verifier that captures the server cert fingerprint
/// during the TLS handshake. Still accepts self-signed certs (required
/// for self-hosted servers), but records the fingerprint for comparison
/// with the stored value after the connection is established.
#[derive(Debug)]
struct TofuVerifier {
    captured: CapturedFingerprint,
}

impl TofuVerifier {
    fn new() -> (Self, CapturedFingerprint) {
        let fp = Arc::new(std::sync::Mutex::new(None));
        (Self { captured: fp.clone() }, fp)
    }
}

impl rustls::client::danger::ServerCertVerifier for TofuVerifier {
    fn verify_server_cert(
        &self,
        end_entity: &rustls::pki_types::CertificateDer<'_>,
        _intermediates: &[rustls::pki_types::CertificateDer<'_>],
        _server_name: &rustls::pki_types::ServerName<'_>,
        _ocsp_response: &[u8],
        _now: rustls::pki_types::UnixTime,
    ) -> Result<rustls::client::danger::ServerCertVerified, rustls::Error> {
        // Compute SHA-256 fingerprint of the DER-encoded leaf certificate.
        let hash = digest(&SHA256, end_entity.as_ref());
        let hex = hash
            .as_ref()
            .iter()
            .map(|b| format!("{b:02x}"))
            .collect::<Vec<_>>()
            .join(":");

        if let Ok(mut guard) = self.captured.lock() {
            *guard = Some(hex);
        }

        // Accept the cert — TOFU check happens after the handshake completes.
        Ok(rustls::client::danger::ServerCertVerified::assertion())
    }

    fn verify_tls12_signature(
        &self,
        message: &[u8],
        cert: &rustls::pki_types::CertificateDer<'_>,
        dss: &rustls::DigitallySignedStruct,
    ) -> Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error> {
        rustls::crypto::verify_tls12_signature(
            message,
            cert,
            dss,
            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
        )
    }

    fn verify_tls13_signature(
        &self,
        message: &[u8],
        cert: &rustls::pki_types::CertificateDer<'_>,
        dss: &rustls::DigitallySignedStruct,
    ) -> Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error> {
        rustls::crypto::verify_tls13_signature(
            message,
            cert,
            dss,
            &rustls::crypto::ring::default_provider().signature_verification_algorithms,
        )
    }

    fn supported_verify_schemes(&self) -> Vec<rustls::SignatureScheme> {
        vec![
            rustls::SignatureScheme::RSA_PKCS1_SHA256,
            rustls::SignatureScheme::RSA_PKCS1_SHA384,
            rustls::SignatureScheme::RSA_PKCS1_SHA512,
            rustls::SignatureScheme::ECDSA_NISTP256_SHA256,
            rustls::SignatureScheme::ECDSA_NISTP384_SHA384,
            rustls::SignatureScheme::ECDSA_NISTP521_SHA512,
            rustls::SignatureScheme::RSA_PSS_SHA256,
            rustls::SignatureScheme::RSA_PSS_SHA384,
            rustls::SignatureScheme::RSA_PSS_SHA512,
            rustls::SignatureScheme::ED25519,
            rustls::SignatureScheme::ED448,
        ]
    }
}

/// Extract the host (with port) from a wss:// URL.
fn extract_host(url: &str) -> String {
    url.strip_prefix("wss://")
        .unwrap_or(url)
        .split('/')
        .next()
        .unwrap_or(url)
        .to_string()
}

/// Perform TOFU fingerprint check against the Tauri cert store.
/// Returns Ok(()) if trusted, Err(message) if fingerprint mismatch.
fn tofu_check<R: Runtime>(
    app: &AppHandle<R>,
    host: &str,
    fingerprint: &str,
) -> Result<String, String> {
    let store = app
        .store(CERTS_STORE)
        .map_err(|e| format!("failed to open certs store: {e}"))?;

    let stored = store.get(host).and_then(|v| {
        if let Value::String(s) = v {
            Some(s)
        } else {
            None
        }
    });

    match stored {
        None => {
            // First use — store the fingerprint.
            // Capture old value before mutating (None here, but consistent pattern).
            let old_value = store.get(host);
            store.set(host, Value::String(fingerprint.to_string()));
            if let Err(e) = store.save() {
                // Restore previous in-memory state: put back old value or delete
                // if there was none, keeping in-memory consistent with on-disk.
                match old_value {
                    Some(v) => { let _ = store.set(host, v); }
                    None    => { let _ = store.delete(host); }
                }
                return Err(format!("failed to persist cert fingerprint: {e}"));
            }
            Ok("trusted_first_use".to_string())
        }
        Some(ref stored_fp) if stored_fp == fingerprint => {
            Ok("trusted".to_string())
        }
        Some(stored_fp) => {
            Err(format!(
                "Certificate fingerprint changed for {host}.\n\
                 Stored:  {stored_fp}\n\
                 Current: {fingerprint}\n\
                 This may indicate a man-in-the-middle attack or a server certificate rotation.\n\
                 Use accept_cert_fingerprint to trust the new certificate."
            ))
        }
    }
}

/// Single call site for ws-state events — keeps tauri-typegen from generating duplicates.
fn emit_ws_state<R: Runtime>(app: &AppHandle<R>, state: &str) {
    let _ = app.emit("ws-state", state);
}

/// Single call site for cert-tofu events — keeps tauri-typegen from generating duplicates.
fn emit_cert_tofu<R: Runtime>(app: &AppHandle<R>, payload: serde_json::Value) {
    let _ = app.emit("cert-tofu", payload);
}

/// Connect to a WSS server. Spawns a background task that:
/// - Emits `ws-message` events for incoming server messages
/// - Emits `ws-state` events for connection state changes
/// - Emits `cert-tofu` events for TOFU fingerprint status
/// - Reads from an mpsc channel for outgoing messages
#[tauri::command]
pub async fn ws_connect<R: Runtime>(
    app: AppHandle<R>,
    state: tauri::State<'_, WsState>,
    url: String,
) -> Result<(), String> {
    info!("[ws_proxy] connecting to {}", url);

    // Drop any existing connection
    {
        let mut tx_lock = state.tx.lock().await;
        if tx_lock.is_some() {
            debug!("[ws_proxy] dropping existing connection");
        }
        *tx_lock = None;
    }

    // Only allow secure WebSocket connections
    if !url.starts_with("wss://") {
        warn!("[ws_proxy] rejected non-wss URL: {}", url);
        return Err("Only wss:// connections are permitted".into());
    }

    emit_ws_state(&app, "connecting");

    // Create TOFU verifier that captures the cert fingerprint during handshake.
    let (verifier, captured_fp) = TofuVerifier::new();

    let tls_config = rustls::ClientConfig::builder()
        .dangerous()
        .with_custom_certificate_verifier(Arc::new(verifier))
        .with_no_client_auth();

    let connector =
        tokio_tungstenite::Connector::Rustls(Arc::new(tls_config));

    let connect_future = tokio_tungstenite::connect_async_tls_with_config(
        &url,
        None,
        false,
        Some(connector),
    );

    let (ws_stream, _response) = tokio::time::timeout(CONNECT_TIMEOUT, connect_future)
        .await
        .map_err(|_| {
            error!("[ws_proxy] connect timed out after {}s to {}", CONNECT_TIMEOUT.as_secs(), url);
            format!("ws connect timed out after {}s", CONNECT_TIMEOUT.as_secs())
        })?
        .map_err(|e| {
            error!("[ws_proxy] connect failed to {}: {}", url, e);
            format!("ws connect failed: {e}")
        })?;

    debug!("[ws_proxy] WebSocket handshake complete");

    // ── TOFU check ───────────────────────────────────────────────────────
    let host = extract_host(&url);
    let fingerprint = captured_fp
        .lock()
        .map_err(|e| format!("failed to read captured fingerprint: {e}"))?
        .clone()
        .unwrap_or_default();

    if fingerprint.is_empty() {
        return Err("TLS handshake completed but no certificate fingerprint was captured".into());
    }

    match tofu_check(&app, &host, &fingerprint) {
        Ok(status) => {
            info!("[ws_proxy] TOFU check passed for {}: {}", host, status);
            emit_cert_tofu(&app, serde_json::json!({
                "host": host,
                "fingerprint": fingerprint,
                "status": status,
            }));
        }
        Err(mismatch_msg) => {
            warn!("[ws_proxy] TOFU check FAILED for {} — certificate fingerprint mismatch", host);
            debug!("[ws_proxy] TOFU detail: {}", mismatch_msg);
            emit_cert_tofu(&app, serde_json::json!({
                "host": host,
                "fingerprint": fingerprint,
                "status": "mismatch",
                "message": mismatch_msg,
            }));
            // Reject the connection — do not proceed.
            return Err(mismatch_msg);
        }
    }
    // ── End TOFU check ───────────────────────────────────────────────────

    info!("[ws_proxy] connected to {}", host);
    emit_ws_state(&app, "open");

    let (mut sink, mut stream) = ws_stream.split();

    // Channel for JS → server messages (bounded for backpressure)
    let (tx, mut rx) = mpsc::channel::<String>(256);
    {
        let mut tx_lock = state.tx.lock().await;
        *tx_lock = Some(tx);
    }

    let app_read = app.clone();
    let app_state = app.clone();
    // Clone the Arc so the monitoring closure can clear tx on any exit path,
    // including worker task panics, without needing tauri::State.
    let tx_arc = Arc::clone(&state.tx);

    // Single outer task owns a JoinSet containing read and write workers.
    // join_next() blocks until the first worker finishes (normally or via panic),
    // then abort_all() + drain guarantees both workers and their sockets are
    // cleaned up before the closed event is emitted.
    tokio::spawn(async move {
        let mut set = JoinSet::new();

        // Task: forward server → JS
        set.spawn(async move {
            while let Some(msg) = stream.next().await {
                match msg {
                    Ok(Message::Text(text)) => {
                        let _ = app_read.emit("ws-message", text.to_string());
                    }
                    Ok(Message::Close(frame)) => {
                        debug!("[ws_proxy] server sent Close frame: {:?}", frame);
                        break;
                    }
                    Err(e) => {
                        warn!("[ws_proxy] read error: {}", e);
                        let _ = app_read.emit("ws-error", format!("{e}"));
                        break;
                    }
                    _ => {} // ignore binary/ping/pong
                }
            }
        });

        // Task: forward JS → server
        set.spawn(async move {
            while let Some(msg) = rx.recv().await {
                if sink.send(Message::Text(msg.into())).await.is_err() {
                    break;
                }
            }
        });

        // Block until the first worker finishes (normal exit or panic).
        let first = set.join_next().await;

        // Cancel the sibling and drain it so sockets close cleanly before
        // emitting state. abort_all() is a no-op if only one task remains.
        set.abort_all();
        while set.join_next().await.is_some() {}

        match first {
            Some(Err(ref e)) if e.is_panic() => {
                error!("[ws_proxy] worker task panicked: {:?}", e);
            }
            _ => {
                info!("[ws_proxy] connection closed");
            }
        }

        // Clear the sender so ws_send returns "not connected". This runs on
        // every exit path — normal close, graceful disconnect, and panic.
        {
            let mut tx_lock = tx_arc.lock().await;
            *tx_lock = None;
        }

        // Always emit closed, even after a panic.
        emit_ws_state(&app_state, "closed");
    });

    Ok(())
}

/// Send a text message through the proxy WebSocket.
#[tauri::command]
pub async fn ws_send(
    state: tauri::State<'_, WsState>,
    message: String,
) -> Result<(), String> {
    let tx_lock = state.tx.lock().await;
    if let Some(tx) = tx_lock.as_ref() {
        match tx.try_send(message) {
            Ok(()) => Ok(()),
            Err(tokio::sync::mpsc::error::TrySendError::Full(_)) => {
                warn!("[ws_proxy] ws_send: outbound channel full, message dropped");
                Err("ws_send: channel full, message dropped".into())
            }
            Err(tokio::sync::mpsc::error::TrySendError::Closed(_)) => {
                Err("ws_send: channel closed".into())
            }
        }
    } else {
        Err("WebSocket not connected".into())
    }
}

/// Disconnect the proxy WebSocket.
#[tauri::command]
pub async fn ws_disconnect(state: tauri::State<'_, WsState>) -> Result<(), String> {
    let mut tx_lock = state.tx.lock().await;
    *tx_lock = None; // dropping the sender closes the channel → write task ends
    Ok(())
}

/// Accept a changed certificate fingerprint for a host.
/// Call this after the user acknowledges a cert-mismatch warning.
#[tauri::command]
pub fn accept_cert_fingerprint<R: Runtime>(
    app: AppHandle<R>,
    host: String,
    fingerprint: String,
) -> Result<(), String> {
    if host.is_empty() || fingerprint.is_empty() {
        return Err("host and fingerprint must not be empty".into());
    }

    // Validate SHA-256 colon-hex format: XX:XX:XX:... (32 pairs = 95 chars)
    let valid = fingerprint.len() == 95
        && fingerprint.bytes().enumerate().all(|(i, b)| {
            if (i + 1) % 3 == 0 {
                b == b':'
            } else {
                b.is_ascii_hexdigit()
            }
        });
    if !valid {
        return Err("fingerprint must be SHA-256 colon-hex format (e.g. aa:bb:cc:...)".into());
    }

    let store = app
        .store(CERTS_STORE)
        .map_err(|e| format!("failed to open certs store: {e}"))?;

    // Capture old value before mutating so we can restore it if save fails.
    let old_value = store.get(&host);
    store.set(&host, Value::String(fingerprint));
    if let Err(e) = store.save() {
        // Restore previous in-memory state: put back old fingerprint if one
        // existed, or delete if there was none. Without this, the new
        // fingerprint would be trusted in-process even though it was never
        // persisted to certs.json.
        match old_value {
            Some(v) => { let _ = store.set(&host, v); }
            None    => { let _ = store.delete(&host); }
        }
        return Err(format!("failed to persist cert fingerprint: {e}"));
    }
    Ok(())
}

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

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

    #[test]
    fn extract_host_basic_wss_url() {
        assert_eq!(extract_host("wss://example.com/chat"), "example.com");
    }

    #[test]
    fn extract_host_with_port() {
        assert_eq!(extract_host("wss://example.com:8443/chat"), "example.com:8443");
    }

    #[test]
    fn extract_host_no_path() {
        assert_eq!(extract_host("wss://example.com"), "example.com");
    }

    #[test]
    fn extract_host_no_scheme() {
        assert_eq!(extract_host("example.com/path"), "example.com");
    }

    #[test]
    fn extract_host_empty() {
        assert_eq!(extract_host(""), "");
    }

    #[test]
    fn extract_host_with_port_and_deep_path() {
        assert_eq!(extract_host("wss://myhost:9443/api/v1/ws"), "myhost:9443");
    }
}