use sha2::{Digest, Sha256};
use std::collections::HashMap;
use std::net::IpAddr;
use std::sync::Arc;
use std::time::Instant;
use tokio::sync::RwLock;
use zeroize::Zeroize;

const FULL_SESSION_TTL: u64 = 86400; // 24 hours of inactivity
const PENDING_SESSION_TTL: u64 = 300; // 5 minutes
const MAX_TOTP_ATTEMPTS: u8 = 5;
const MAX_CONCURRENT_SESSIONS: usize = 5;

#[derive(Clone)]
enum SessionType {
    Full,
    PendingTotp {
        totp_secret: Vec<u8>,
        attempts: u8,
    },
}

impl Drop for SessionType {
    fn drop(&mut self) {
        if let SessionType::PendingTotp { totp_secret, .. } = self {
            totp_secret.zeroize();
        }
    }
}

#[derive(Clone)]
struct Session {
    created_at: Instant,
    last_activity: Instant,
    session_type: SessionType,
}

#[derive(Clone)]
pub struct SessionStore {
    sessions: Arc<RwLock<HashMap<[u8; 32], Session>>>,
}

impl SessionStore {
    pub fn new() -> Self {
        Self {
            sessions: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    /// Create a full (authenticated) session. Returns the plaintext token.
    /// Enforces max concurrent sessions by evicting the oldest if limit reached.
    pub async fn create(&self) -> String {
        let token_bytes: [u8; 32] = rand::random();
        let token = hex::encode(token_bytes);
        let hash = hash_token(&token);
        let now = Instant::now();
        let session = Session {
            created_at: now,
            last_activity: now,
            session_type: SessionType::Full,
        };

        let mut sessions = self.sessions.write().await;
        self.evict_if_over_limit(&mut sessions);
        sessions.insert(hash, session);
        token
    }

    /// Create a pending TOTP session (password verified, awaiting TOTP).
    /// Caches the decrypted TOTP secret in memory for verification.
    pub async fn create_pending(&self, totp_secret: Vec<u8>) -> String {
        let token_bytes: [u8; 32] = rand::random();
        let token = hex::encode(token_bytes);
        let hash = hash_token(&token);
        let now = Instant::now();
        let session = Session {
            created_at: now,
            last_activity: now,
            session_type: SessionType::PendingTotp {
                totp_secret,
                attempts: 0,
            },
        };
        self.sessions.write().await.insert(hash, session);
        token
    }

    /// Validate a full session token. Returns true if the session exists and hasn't expired.
    /// Updates last_activity on successful validation (inactivity-based expiry).
    pub async fn validate(&self, token: &str) -> bool {
        let hash = hash_token(token);
        let mut sessions = self.sessions.write().await;
        if let Some(session) = sessions.get_mut(&hash) {
            if !matches!(session.session_type, SessionType::Full) {
                return false;
            }
            if session.last_activity.elapsed().as_secs() >= FULL_SESSION_TTL {
                sessions.remove(&hash);
                return false;
            }
            session.last_activity = Instant::now();
            true
        } else {
            false
        }
    }

    /// Get the TOTP secret from a pending session. Returns None if not a valid pending session.
    /// Increments the attempt counter.
    pub async fn get_pending_secret(&self, token: &str) -> Option<Vec<u8>> {
        let hash = hash_token(token);
        let mut sessions = self.sessions.write().await;
        if let Some(session) = sessions.get_mut(&hash) {
            if session.created_at.elapsed().as_secs() >= PENDING_SESSION_TTL {
                sessions.remove(&hash);
                return None;
            }
            if let SessionType::PendingTotp {
                ref totp_secret,
                ref mut attempts,
            } = session.session_type
            {
                *attempts += 1;
                if *attempts > MAX_TOTP_ATTEMPTS {
                    sessions.remove(&hash); // Too many attempts, force re-login
                    return None;
                }
                return Some(totp_secret.clone());
            }
        }
        None
    }

    /// Upgrade a pending session to a full session.
    pub async fn upgrade_to_full(&self, token: &str) {
        let hash = hash_token(token);
        let mut sessions = self.sessions.write().await;
        if let Some(session) = sessions.get_mut(&hash) {
            session.session_type = SessionType::Full;
            let now = Instant::now();
            session.created_at = now;
            session.last_activity = now;
        }
    }

    pub async fn remove(&self, token: &str) {
        let hash = hash_token(token);
        self.sessions.write().await.remove(&hash);
    }

    /// Invalidate all sessions except the one matching the given token.
    /// Used after sensitive operations like password change.
    pub async fn invalidate_all_except(&self, keep_token: &str) {
        let keep_hash = hash_token(keep_token);
        let mut sessions = self.sessions.write().await;
        sessions.retain(|hash, _| *hash == keep_hash);
    }

    /// Rotate a session: invalidate the old token and create a new one.
    /// Returns the new plaintext token.
    pub async fn rotate(&self, old_token: &str) -> String {
        let old_hash = hash_token(old_token);
        let new_token_bytes: [u8; 32] = rand::random();
        let new_token = hex::encode(new_token_bytes);
        let new_hash = hash_token(&new_token);
        let now = Instant::now();

        let mut sessions = self.sessions.write().await;
        sessions.remove(&old_hash);
        sessions.insert(
            new_hash,
            Session {
                created_at: now,
                last_activity: now,
                session_type: SessionType::Full,
            },
        );
        new_token
    }

    /// Remove all expired sessions (cleanup).
    pub async fn cleanup_expired(&self) {
        let mut sessions = self.sessions.write().await;
        sessions.retain(|_, session| {
            match &session.session_type {
                SessionType::Full => session.last_activity.elapsed().as_secs() < FULL_SESSION_TTL,
                SessionType::PendingTotp { .. } => {
                    session.created_at.elapsed().as_secs() < PENDING_SESSION_TTL
                }
            }
        });
    }

    /// Evict the oldest full session if at or over the concurrent limit.
    fn evict_if_over_limit(&self, sessions: &mut HashMap<[u8; 32], Session>) {
        let full_count = sessions
            .values()
            .filter(|s| matches!(s.session_type, SessionType::Full))
            .count();

        if full_count >= MAX_CONCURRENT_SESSIONS {
            // Find the oldest full session by last_activity
            if let Some(oldest_hash) = sessions
                .iter()
                .filter(|(_, s)| matches!(s.session_type, SessionType::Full))
                .min_by_key(|(_, s)| s.last_activity)
                .map(|(h, _)| *h)
            {
                sessions.remove(&oldest_hash);
            }
        }
    }

    /// Get the number of active full sessions.
    pub async fn active_session_count(&self) -> usize {
        let sessions = self.sessions.read().await;
        sessions
            .values()
            .filter(|s| {
                matches!(s.session_type, SessionType::Full)
                    && s.last_activity.elapsed().as_secs() < FULL_SESSION_TTL
            })
            .count()
    }
}

fn hash_token(token: &str) -> [u8; 32] {
    let mut hasher = Sha256::new();
    hasher.update(token.as_bytes());
    hasher.finalize().into()
}

/// Extract the session token from a Cookie header value.
pub fn extract_session_cookie(headers: &hyper::HeaderMap) -> Option<String> {
    headers
        .get("cookie")
        .and_then(|v| v.to_str().ok())
        .and_then(|cookies| {
            cookies.split(';').find_map(|c| {
                let c = c.trim();
                c.strip_prefix("session=").map(|v| v.to_string())
            })
        })
        .filter(|v| !v.is_empty())
}

/// Rate limiter for login attempts: max 5 failures per 60 seconds per IP.
#[derive(Clone)]
pub struct LoginRateLimiter {
    attempts: Arc<RwLock<HashMap<IpAddr, Vec<Instant>>>>,
}

const MAX_ATTEMPTS: usize = 5;
const WINDOW_SECS: u64 = 60;

impl LoginRateLimiter {
    pub fn new() -> Self {
        Self {
            attempts: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    pub async fn check(&self, ip: IpAddr) -> bool {
        let mut attempts = self.attempts.write().await;
        let now = Instant::now();
        let entry = attempts.entry(ip).or_default();
        entry.retain(|t| now.duration_since(*t).as_secs() < WINDOW_SECS);
        entry.len() < MAX_ATTEMPTS
    }

    pub async fn record_failure(&self, ip: IpAddr) {
        let mut attempts = self.attempts.write().await;
        let entry = attempts.entry(ip).or_default();
        entry.push(Instant::now());
    }
}

/// General-purpose rate limiter for sensitive endpoints.
/// Tracks request counts per (method, IP) with configurable limits and windows.
#[derive(Clone)]
pub struct EndpointRateLimiter {
    /// Map of (method, ip) -> list of request timestamps
    requests: Arc<RwLock<HashMap<(String, IpAddr), Vec<Instant>>>>,
    /// Per-method configuration: (max_requests, window_secs)
    limits: Arc<HashMap<String, (usize, u64)>>,
}

impl EndpointRateLimiter {
    pub fn new() -> Self {
        let mut limits = HashMap::new();
        // Financial operations: strict limits
        limits.insert("wallet.send".to_string(), (5usize, 300u64));
        limits.insert("wallet.ecash-send".to_string(), (10, 300));
        limits.insert("lnd.sendcoins".to_string(), (5, 300));
        limits.insert("lnd.payinvoice".to_string(), (10, 300));
        limits.insert("lnd.openchannel".to_string(), (3, 300));
        limits.insert("lnd.closechannel".to_string(), (3, 300));
        limits.insert("lnd.create-psbt".to_string(), (5, 300));
        limits.insert("lnd.finalize-psbt".to_string(), (5, 300));
        // Identity/credential operations
        limits.insert("identity.create".to_string(), (10, 300));
        limits.insert("identity.issue-credential".to_string(), (20, 300));
        // Backup operations (resource-intensive)
        limits.insert("backup.create".to_string(), (3, 600));
        limits.insert("backup.restore".to_string(), (2, 600));
        // Container operations
        limits.insert("container-install".to_string(), (5, 300));
        limits.insert("package.install".to_string(), (5, 300));
        // System operations
        limits.insert("update.apply".to_string(), (2, 600));
        limits.insert("system.reboot".to_string(), (2, 300));
        limits.insert("system.shutdown".to_string(), (2, 300));
        // Password changes
        limits.insert("auth.changePassword".to_string(), (3, 300));

        Self {
            requests: Arc::new(RwLock::new(HashMap::new())),
            limits: Arc::new(limits),
        }
    }

    /// Check if a request is allowed. Returns true if within limits.
    pub async fn check(&self, method: &str, ip: IpAddr) -> bool {
        let (max_req, window) = match self.limits.get(method) {
            Some(config) => *config,
            None => return true, // Not rate-limited
        };

        let key = (method.to_string(), ip);
        let mut requests = self.requests.write().await;
        let now = Instant::now();
        let entry = requests.entry(key).or_default();
        entry.retain(|t| now.duration_since(*t).as_secs() < window);
        entry.len() < max_req
    }

    /// Record a request for rate limiting purposes.
    pub async fn record(&self, method: &str, ip: IpAddr) {
        if !self.limits.contains_key(method) {
            return; // Not rate-limited, skip tracking
        }
        let key = (method.to_string(), ip);
        let mut requests = self.requests.write().await;
        let entry = requests.entry(key).or_default();
        entry.push(Instant::now());
    }

    /// Periodic cleanup of expired entries.
    pub async fn cleanup(&self) {
        let mut requests = self.requests.write().await;
        let now = Instant::now();
        requests.retain(|(method, _), timestamps| {
            let window = self
                .limits
                .get(method)
                .map(|(_, w)| *w)
                .unwrap_or(300);
            timestamps.retain(|t| now.duration_since(*t).as_secs() < window);
            !timestamps.is_empty()
        });
    }
}

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

    #[tokio::test]
    async fn test_session_create_and_validate() {
        let store = SessionStore::new();
        let token = store.create().await;

        assert!(store.validate(&token).await);
    }

    #[tokio::test]
    async fn test_session_invalid_token() {
        let store = SessionStore::new();
        assert!(!store.validate("nonexistent_token").await);
    }

    #[tokio::test]
    async fn test_session_remove() {
        let store = SessionStore::new();
        let token = store.create().await;

        assert!(store.validate(&token).await);
        store.remove(&token).await;
        assert!(!store.validate(&token).await);
    }

    #[tokio::test]
    async fn test_pending_session_upgrade() {
        let store = SessionStore::new();
        let secret = vec![1, 2, 3, 4];
        let token = store.create_pending(secret.clone()).await;

        // Pending session should not validate as full
        assert!(!store.validate(&token).await);

        // Can get the TOTP secret
        let got = store.get_pending_secret(&token).await;
        assert_eq!(got, Some(secret));

        // Upgrade to full
        store.upgrade_to_full(&token).await;
        assert!(store.validate(&token).await);
    }

    #[tokio::test]
    async fn test_pending_session_max_attempts() {
        let store = SessionStore::new();
        let secret = vec![1, 2, 3];
        let token = store.create_pending(secret).await;

        // Exhaust MAX_TOTP_ATTEMPTS (5) + 1 to trigger removal
        for _ in 0..MAX_TOTP_ATTEMPTS {
            assert!(store.get_pending_secret(&token).await.is_some());
        }
        // 6th attempt should fail (session removed)
        assert!(store.get_pending_secret(&token).await.is_none());
    }

    #[tokio::test]
    async fn test_extract_session_cookie() {
        let mut headers = hyper::HeaderMap::new();
        headers.insert("cookie", "session=abc123; other=xyz".parse().unwrap());

        assert_eq!(extract_session_cookie(&headers), Some("abc123".to_string()));
    }

    #[tokio::test]
    async fn test_extract_session_cookie_missing() {
        let headers = hyper::HeaderMap::new();
        assert_eq!(extract_session_cookie(&headers), None);
    }

    #[tokio::test]
    async fn test_rate_limiter_allows_under_limit() {
        let limiter = LoginRateLimiter::new();
        let ip: IpAddr = "127.0.0.1".parse().unwrap();

        for _ in 0..MAX_ATTEMPTS {
            assert!(limiter.check(ip).await);
            limiter.record_failure(ip).await;
        }
    }

    #[tokio::test]
    async fn test_rate_limiter_blocks_over_limit() {
        let limiter = LoginRateLimiter::new();
        let ip: IpAddr = "127.0.0.1".parse().unwrap();

        for _ in 0..MAX_ATTEMPTS {
            limiter.record_failure(ip).await;
        }

        assert!(!limiter.check(ip).await);
    }

    #[tokio::test]
    async fn test_rate_limiter_different_ips() {
        let limiter = LoginRateLimiter::new();
        let ip1: IpAddr = "127.0.0.1".parse().unwrap();
        let ip2: IpAddr = "192.168.1.1".parse().unwrap();

        for _ in 0..MAX_ATTEMPTS {
            limiter.record_failure(ip1).await;
        }

        // ip1 should be blocked
        assert!(!limiter.check(ip1).await);
        // ip2 should still be allowed
        assert!(limiter.check(ip2).await);
    }

    #[tokio::test]
    async fn test_session_activity_updates_on_validate() {
        let store = SessionStore::new();
        let token = store.create().await;

        // First validation should succeed and touch last_activity
        assert!(store.validate(&token).await);

        // Still valid after another validation
        assert!(store.validate(&token).await);
    }

    #[tokio::test]
    async fn test_invalidate_all_except() {
        let store = SessionStore::new();
        let token1 = store.create().await;
        let token2 = store.create().await;
        let token3 = store.create().await;

        // Invalidate all except token2
        store.invalidate_all_except(&token2).await;

        assert!(!store.validate(&token1).await);
        assert!(store.validate(&token2).await);
        assert!(!store.validate(&token3).await);
    }

    #[tokio::test]
    async fn test_session_rotate() {
        let store = SessionStore::new();
        let old_token = store.create().await;

        assert!(store.validate(&old_token).await);

        let new_token = store.rotate(&old_token).await;

        // Old token should be invalid
        assert!(!store.validate(&old_token).await);
        // New token should be valid
        assert!(store.validate(&new_token).await);
    }

    #[tokio::test]
    async fn test_max_concurrent_sessions() {
        let store = SessionStore::new();
        let mut tokens = Vec::new();

        // Create MAX_CONCURRENT_SESSIONS sessions
        for _ in 0..MAX_CONCURRENT_SESSIONS {
            tokens.push(store.create().await);
        }

        // All should be valid
        for token in &tokens {
            assert!(store.validate(token).await);
        }

        // Creating one more should evict the oldest
        let new_token = store.create().await;
        assert!(store.validate(&new_token).await);

        // The first token (oldest) should have been evicted
        assert!(!store.validate(&tokens[0]).await);

        // The rest should still be valid
        for token in &tokens[1..] {
            assert!(store.validate(token).await);
        }
    }

    #[tokio::test]
    async fn test_active_session_count() {
        let store = SessionStore::new();
        assert_eq!(store.active_session_count().await, 0);

        let token1 = store.create().await;
        assert_eq!(store.active_session_count().await, 1);

        let _token2 = store.create().await;
        assert_eq!(store.active_session_count().await, 2);

        store.remove(&token1).await;
        assert_eq!(store.active_session_count().await, 1);
    }

    #[tokio::test]
    async fn test_cleanup_expired_removes_stale() {
        let store = SessionStore::new();
        let token = store.create().await;

        assert!(store.validate(&token).await);
        assert_eq!(store.active_session_count().await, 1);

        // Cleanup shouldn't remove active sessions
        store.cleanup_expired().await;
        assert_eq!(store.active_session_count().await, 1);
    }

    #[tokio::test]
    async fn test_rotate_preserves_session_count() {
        let store = SessionStore::new();
        let token = store.create().await;
        assert_eq!(store.active_session_count().await, 1);

        let new_token = store.rotate(&token).await;
        assert_eq!(store.active_session_count().await, 1);
        assert!(store.validate(&new_token).await);
    }
}