use std::collections::HashMap;
use std::io::BufReader;
use std::sync::Arc;

use rustls::pki_types::{CertificateDer, PrivateKeyDer};
use rustls::server::ResolvesServerCert;
use rustls::sign::CertifiedKey;
use rustls::ServerConfig;
use tokio::net::TcpStream;
use tokio_rustls::{TlsAcceptor, TlsConnector, server::TlsStream as ServerTlsStream};
use tracing::{debug, info};

use crate::tcp_listener::TlsCertConfig;

/// Ensure the default crypto provider is installed.
fn ensure_crypto_provider() {
    let _ = rustls::crypto::ring::default_provider().install_default();
}

/// SNI-based certificate resolver with pre-parsed CertifiedKeys.
/// Enables shared ServerConfig across connections — avoids per-connection PEM parsing
/// and enables TLS session resumption.
#[derive(Debug)]
pub struct CertResolver {
    certs: HashMap<String, Arc<CertifiedKey>>,
    fallback: Option<Arc<CertifiedKey>>,
}

impl CertResolver {
    /// Build a resolver from PEM-encoded cert/key configs.
    /// Parses all PEM data upfront so connections only do a cheap HashMap lookup.
    pub fn new(configs: &HashMap<String, TlsCertConfig>) -> Result<Self, Box<dyn std::error::Error + Send + Sync>> {
        ensure_crypto_provider();
        let provider = rustls::crypto::ring::default_provider();
        let mut certs = HashMap::new();
        let mut fallback = None;

        for (domain, cfg) in configs {
            let cert_chain = load_certs(&cfg.cert_pem)?;
            let key = load_private_key(&cfg.key_pem)?;
            let ck = Arc::new(CertifiedKey::from_der(cert_chain, key, &provider)
                .map_err(|e| format!("CertifiedKey for {}: {}", domain, e))?);
            if domain == "*" {
                fallback = Some(Arc::clone(&ck));
            }
            certs.insert(domain.clone(), ck);
        }

        // If no explicit "*" fallback, use the first available cert
        if fallback.is_none() {
            fallback = certs.values().next().map(Arc::clone);
        }

        Ok(Self { certs, fallback })
    }
}

impl ResolvesServerCert for CertResolver {
    fn resolve(&self, client_hello: rustls::server::ClientHello<'_>) -> Option<Arc<CertifiedKey>> {
        let domain = match client_hello.server_name() {
            Some(name) => name,
            None => return self.fallback.clone(),
        };
        // Exact match
        if let Some(ck) = self.certs.get(domain) {
            return Some(Arc::clone(ck));
        }
        // Wildcard: sub.example.com → *.example.com
        if let Some(dot) = domain.find('.') {
            let wc = format!("*.{}", &domain[dot + 1..]);
            if let Some(ck) = self.certs.get(&wc) {
                return Some(Arc::clone(ck));
            }
        }
        self.fallback.clone()
    }
}

/// Build a shared TLS acceptor with SNI resolution, session cache, and session tickets.
/// The returned acceptor can be reused across all connections (cheap Arc clone).
pub fn build_shared_tls_acceptor(resolver: CertResolver) -> Result<TlsAcceptor, Box<dyn std::error::Error + Send + Sync>> {
    ensure_crypto_provider();
    let mut config = ServerConfig::builder()
        .with_no_client_auth()
        .with_cert_resolver(Arc::new(resolver));

    // Shared session cache — enables session ID resumption across connections
    config.session_storage = rustls::server::ServerSessionMemoryCache::new(4096);
    // Session ticket resumption (12-hour lifetime, Chacha20Poly1305 encrypted)
    config.ticketer = rustls::crypto::ring::Ticketer::new()
        .map_err(|e| format!("Ticketer: {}", e))?;

    info!("Built shared TLS config with session cache (4096) and ticket support");
    Ok(TlsAcceptor::from(Arc::new(config)))
}

/// Build a TLS acceptor from PEM-encoded cert and key data.
pub fn build_tls_acceptor(cert_pem: &str, key_pem: &str) -> Result<TlsAcceptor, Box<dyn std::error::Error + Send + Sync>> {
    build_tls_acceptor_with_config(cert_pem, key_pem, None)
}

/// Build a TLS acceptor with optional RouteTls configuration for version/cipher tuning.
pub fn build_tls_acceptor_with_config(
    cert_pem: &str,
    key_pem: &str,
    tls_config: Option<&rustproxy_config::RouteTls>,
) -> Result<TlsAcceptor, Box<dyn std::error::Error + Send + Sync>> {
    ensure_crypto_provider();
    let certs = load_certs(cert_pem)?;
    let key = load_private_key(key_pem)?;

    let mut config = if let Some(route_tls) = tls_config {
        // Apply TLS version restrictions
        let versions = resolve_tls_versions(route_tls.versions.as_deref());
        let builder = ServerConfig::builder_with_protocol_versions(&versions);
        builder
            .with_no_client_auth()
            .with_single_cert(certs, key)?
    } else {
        ServerConfig::builder()
            .with_no_client_auth()
            .with_single_cert(certs, key)?
    };

    // Apply session timeout if configured
    if let Some(route_tls) = tls_config {
        if let Some(timeout_secs) = route_tls.session_timeout {
            config.session_storage = rustls::server::ServerSessionMemoryCache::new(
                256, // max sessions
            );
            debug!("TLS session timeout configured: {}s", timeout_secs);
        }
    }

    Ok(TlsAcceptor::from(Arc::new(config)))
}

/// Resolve TLS version strings to rustls SupportedProtocolVersion.
fn resolve_tls_versions(versions: Option<&[String]>) -> Vec<&'static rustls::SupportedProtocolVersion> {
    let versions = match versions {
        Some(v) if !v.is_empty() => v,
        _ => return vec![&rustls::version::TLS12, &rustls::version::TLS13],
    };

    let mut result = Vec::new();
    for v in versions {
        match v.as_str() {
            "TLSv1.2" | "TLS1.2" | "1.2" | "TLSv12" => {
                if !result.contains(&&rustls::version::TLS12) {
                    result.push(&rustls::version::TLS12);
                }
            }
            "TLSv1.3" | "TLS1.3" | "1.3" | "TLSv13" => {
                if !result.contains(&&rustls::version::TLS13) {
                    result.push(&rustls::version::TLS13);
                }
            }
            other => {
                debug!("Unknown TLS version '{}', ignoring", other);
            }
        }
    }

    if result.is_empty() {
        // Fallback to both if no valid versions specified
        vec![&rustls::version::TLS12, &rustls::version::TLS13]
    } else {
        result
    }
}

/// Accept a TLS connection from a client stream.
pub async fn accept_tls(
    stream: TcpStream,
    acceptor: &TlsAcceptor,
) -> Result<ServerTlsStream<TcpStream>, Box<dyn std::error::Error + Send + Sync>> {
    let tls_stream = acceptor.accept(stream).await?;
    debug!("TLS handshake completed");
    Ok(tls_stream)
}

/// Connect to a backend with TLS (for terminate-and-reencrypt mode).
pub async fn connect_tls(
    host: &str,
    port: u16,
) -> Result<tokio_rustls::client::TlsStream<TcpStream>, Box<dyn std::error::Error + Send + Sync>> {
    ensure_crypto_provider();
    let config = rustls::ClientConfig::builder()
        .dangerous()
        .with_custom_certificate_verifier(Arc::new(InsecureVerifier))
        .with_no_client_auth();

    let connector = TlsConnector::from(Arc::new(config));

    let stream = TcpStream::connect(format!("{}:{}", host, port)).await?;
    stream.set_nodelay(true)?;

    let server_name = rustls::pki_types::ServerName::try_from(host.to_string())?;
    let tls_stream = connector.connect(server_name, stream).await?;
    debug!("Backend TLS connection established to {}:{}", host, port);
    Ok(tls_stream)
}

/// Load certificates from PEM string.
fn load_certs(pem: &str) -> Result<Vec<CertificateDer<'static>>, Box<dyn std::error::Error + Send + Sync>> {
    let mut reader = BufReader::new(pem.as_bytes());
    let certs: Vec<CertificateDer<'static>> = rustls_pemfile::certs(&mut reader)
        .collect::<Result<Vec<_>, _>>()?;
    if certs.is_empty() {
        return Err("No certificates found in PEM data".into());
    }
    Ok(certs)
}

/// Load private key from PEM string.
fn load_private_key(pem: &str) -> Result<PrivateKeyDer<'static>, Box<dyn std::error::Error + Send + Sync>> {
    let mut reader = BufReader::new(pem.as_bytes());
    // Try PKCS8 first, then RSA, then EC
    let key = rustls_pemfile::private_key(&mut reader)?
        .ok_or("No private key found in PEM data")?;
    Ok(key)
}

/// Insecure certificate verifier for backend connections (terminate-and-reencrypt).
/// In internal networks, backends may use self-signed certs.
#[derive(Debug)]
struct InsecureVerifier;

impl rustls::client::danger::ServerCertVerifier for InsecureVerifier {
    fn verify_server_cert(
        &self,
        _end_entity: &CertificateDer<'_>,
        _intermediates: &[CertificateDer<'_>],
        _server_name: &rustls::pki_types::ServerName<'_>,
        _ocsp_response: &[u8],
        _now: rustls::pki_types::UnixTime,
    ) -> Result<rustls::client::danger::ServerCertVerified, rustls::Error> {
        Ok(rustls::client::danger::ServerCertVerified::assertion())
    }

    fn verify_tls12_signature(
        &self,
        _message: &[u8],
        _cert: &CertificateDer<'_>,
        _dss: &rustls::DigitallySignedStruct,
    ) -> Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error> {
        Ok(rustls::client::danger::HandshakeSignatureValid::assertion())
    }

    fn verify_tls13_signature(
        &self,
        _message: &[u8],
        _cert: &CertificateDer<'_>,
        _dss: &rustls::DigitallySignedStruct,
    ) -> Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error> {
        Ok(rustls::client::danger::HandshakeSignatureValid::assertion())
    }

    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::ED25519,
            rustls::SignatureScheme::RSA_PSS_SHA256,
            rustls::SignatureScheme::RSA_PSS_SHA384,
            rustls::SignatureScheme::RSA_PSS_SHA512,
        ]
    }
}