// Copyright 2026 The BoringSSL Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! TLS Session support for BoringSSL.

use alloc::vec::Vec;
use core::ptr::{
    NonNull,
    null_mut, //
};

use crate::{
    call_slice_getter,
    config::ProtocolVersion,
    context::TlsContext,
    errors::Error,
    ffi::{
        Alloc,
        sanitize_slice,
        slice_into_ffi_raw_parts, //
    }, //
};

/// A TLS session.
///
/// See [RFC 8446 Section 2.2](https://datatracker.ietf.org/doc/html/rfc8446#section-2.2).
///
/// # Example
///
/// ```rust,no_run
/// # use bssl_tls::{context::TlsContext, sessions::TlsSession};
/// # use bssl_tls::context::{Client, TlsMode};
/// # use bssl_tls::connection::lifecycle::EstablishedTlsConnection;
/// // Assuming `conn` is an `EstablishedTlsConnection`
/// # let conn: EstablishedTlsConnection<'_, Client, TlsMode> = todo!();
/// # let ctx: TlsContext = todo!();
/// if let Some(session) = conn.get_session() {
///     // Serialize the session to store it
///     let session_bytes = session.to_bytes().unwrap();
///
///     // Deserialize the session to resume it later
///     let recovered_session = TlsSession::from_bytes(&session_bytes, &ctx).unwrap();
/// }
/// ```
pub struct TlsSession(pub(crate) NonNull<bssl_sys::SSL_SESSION>);

// Safety: once constructed an `SSL_SESSION` is immutable and has no thread-local data.
unsafe impl Send for TlsSession {}
unsafe impl Sync for TlsSession {}

impl Drop for TlsSession {
    fn drop(&mut self) {
        unsafe {
            // Safety: self.ptr() is valid and we own a reference.
            bssl_sys::SSL_SESSION_free(self.ptr());
        }
    }
}

impl Clone for TlsSession {
    fn clone(&self) -> Self {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_up_ref(self.ptr());
        }
        Self(self.0)
    }
}

impl TlsSession {
    pub(crate) fn ptr(&self) -> *mut bssl_sys::SSL_SESSION {
        self.0.as_ptr()
    }

    /// Serializes the session into a newly allocated buffer.
    pub fn to_bytes(&self) -> Result<Vec<u8>, Error> {
        let mut out_data: *mut u8 = core::ptr::null_mut();
        let mut out_len: usize = 0;
        let rc = unsafe {
            // Safety: `self.ptr()` is still valid.
            bssl_sys::SSL_SESSION_to_bytes(self.ptr(), &raw mut out_data, &raw mut out_len)
        };
        if rc != 1 {
            return Err(Error::extract_lib_err());
        }
        let out_data = Alloc(out_data);
        let slice = unsafe {
            // Safety: out_data.0 and out_len are returned by BoringSSL and are valid.
            sanitize_slice(out_data.0, out_len).unwrap()
        };
        Ok(slice.to_vec())
    }

    /// Serializes the session for a ticket, excluding the session ID.
    pub fn to_bytes_for_ticket(&self) -> Result<Vec<u8>, Error> {
        let mut out_data: *mut u8 = core::ptr::null_mut();
        let mut out_len: usize = 0;
        let rc = unsafe {
            // Safety: `self.ptr()` is still valid.
            bssl_sys::SSL_SESSION_to_bytes_for_ticket(self.ptr(), &mut out_data, &mut out_len)
        };
        if rc != 1 {
            return Err(Error::extract_lib_err());
        }
        let out_data = Alloc(out_data);
        let slice = unsafe {
            // Safety: out_data.0 and out_len are returned by BoringSSL and are valid.
            sanitize_slice(out_data.0, out_len).unwrap()
        };
        Ok(slice.to_vec())
    }

    /// Parses a serialized session from bytes.
    pub fn from_bytes<M>(bytes: &[u8], ctx: &TlsContext<M>) -> Result<Self, Error> {
        let (ptr, len) = slice_into_ffi_raw_parts(bytes);
        let ptr = unsafe {
            // Safety: bytes is a valid slice and the context is still valid.
            bssl_sys::SSL_SESSION_from_bytes(ptr, len, ctx.ptr())
        };
        let ptr = NonNull::new(ptr).ok_or_else(|| Error::extract_lib_err())?;
        Ok(Self(ptr))
    }

    /// Get the protocol version of the session.
    pub fn get_protocol_version(&self) -> Option<ProtocolVersion> {
        let version = unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_get_protocol_version(self.ptr())
        };
        version.try_into().ok()
    }

    /// Get the session creation time in seconds since the epoch.
    pub fn get_time(&self) -> u64 {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_get_time(self.ptr())
        }
    }

    /// Get the session timeout in seconds.
    pub fn get_timeout(&self) -> u64 {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_get_timeout(self.ptr()).into()
        }
    }

    /// Get the peer certificates as a list of DER-encoded certificates.
    pub fn get_peer_certificates(&self) -> Result<Vec<Vec<u8>>, Error> {
        let sk = unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_get0_peer_certificates(self.ptr())
        };
        if sk.is_null() {
            return Ok(Vec::new());
        }
        let len = unsafe {
            // Safety: `sk` is valid.
            bssl_sys::sk_CRYPTO_BUFFER_num(sk)
        };
        let mut res = Vec::new();
        for i in 0..len {
            let buf = unsafe {
                // Safety: `sk` is valid and `i` is in bounds.
                bssl_sys::sk_CRYPTO_BUFFER_value(sk, i)
            };
            if buf.is_null() {
                continue;
            }
            let (data, len) = unsafe {
                // Safety: `buf` is valid.
                (
                    bssl_sys::CRYPTO_BUFFER_data(buf),
                    bssl_sys::CRYPTO_BUFFER_len(buf),
                )
            };
            let Some(slice) = (unsafe {
                // Safety: data and len are valid.
                sanitize_slice(data, len)
            }) else {
                continue;
            };
            res.push(slice.to_vec());
        }
        Ok(res)
    }

    // TODO(@xfding): Implement SSL_SESSION_get0_peer_rpk when needed.

    /// Get the signed certificate timestamp list, if any.
    pub fn get0_signed_cert_timestamp_list(&self) -> Option<&[u8]> {
        call_slice_getter!(
            bssl_sys::SSL_SESSION_get0_signed_cert_timestamp_list,
            self.ptr()
        )
    }

    /// Get the OCSP response, if any.
    ///
    /// See [RFC 8446 §4.4.2.1](https://datatracker.ietf.org/doc/html/rfc8446#section-4.4.2.1).
    pub fn get_ocsp_response(&self) -> Option<&[u8]> {
        call_slice_getter!(bssl_sys::SSL_SESSION_get0_ocsp_response, self.ptr())
    }

    /// Get the master key.
    ///
    /// In TLS 1.3, this returns the **Resumption Master Secret**.
    /// See [RFC 8446 §7.1](https://datatracker.ietf.org/doc/html/rfc8446#section-7.1).
    ///
    /// BoringSSL uses this secret to automatically derive the Pre-Shared Key (PSK) for
    /// session resumption. Users should not attempt to manually expand this secret or
    /// perform manual cryptography; BoringSSL handles the key expansion internally when
    /// a session is configured for resumption.
    ///
    /// # Example
    ///
    /// If you need to derive a PSK for external use (e.g. for external PSK resumption),
    /// you can use `bssl_crypto::hkdf`:
    ///
    /// ```rust,no_run
    /// # use bssl_tls::sessions::TlsSession;
    /// # // Assuming `session` is a `TlsSession`
    /// # let session: TlsSession = todo!();
    /// let master_key = session.get_master_key();
    ///
    /// // Treat the master key as a PRK in HKDF
    /// let prk = bssl_crypto::hkdf::Prk::new::<bssl_crypto::digest::Sha256>(&master_key)
    ///     .expect("Invalid master key length");
    ///
    /// // Expand it to derive a PSK
    /// let mut psk = vec![0u8; 32];
    /// prk.expand_into(b"resumption psk", &mut psk)
    ///     .expect("HKDF expansion failed");
    /// ```
    pub fn get_master_key(&self) -> Vec<u8> {
        let len = unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_get_master_key(self.ptr(), null_mut(), 0)
        };
        let mut out = vec![0u8; len];
        let len = unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_get_master_key(self.ptr(), out.as_mut_ptr(), out.len())
        };
        out.truncate(len);
        out
    }

    /// Check if the session should be single use.
    pub fn should_be_single_use(&self) -> bool {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_should_be_single_use(self.ptr()) == 1
        }
    }

    /// Check if the session is resumable.
    pub fn is_resumable(&self) -> bool {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_is_resumable(self.ptr()) == 1
        }
    }

    /// Check if the session has a ticket.
    pub fn has_ticket(&self) -> bool {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_has_ticket(self.ptr()) == 1
        }
    }

    /// Get the ticket, if any.
    pub fn get_ticket(&self) -> Option<&[u8]> {
        call_slice_getter!(bssl_sys::SSL_SESSION_get0_ticket, self.ptr())
    }

    /// Check if the session has a peer SHA256.
    pub fn has_peer_sha256(&self) -> bool {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_has_peer_sha256(self.ptr()) == 1
        }
    }

    /// Get the peer SHA256, if any.
    pub fn get_peer_sha256(&self) -> Option<&[u8]> {
        call_slice_getter!(bssl_sys::SSL_SESSION_get0_peer_sha256, self.ptr())
    }

    /// Check if the session is resumable across names.
    pub fn is_resumable_across_names(&self) -> bool {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_is_resumable_across_names(self.ptr()) == 1
        }
    }

    /// Check if the session is early data capable.
    pub fn early_data_capable(&self) -> bool {
        unsafe {
            // Safety: self.ptr() is valid.
            bssl_sys::SSL_SESSION_early_data_capable(self.ptr()) == 1
        }
    }
}

#[cfg(test)]
mod tests {
    use core::pin::Pin;

    use futures::future::try_join;

    use super::*;

    use crate::tests::create_mock_pipe;
    use crate::{
        context::TlsContextBuilder,
        credentials::{
            PskHash,
            TlsCredential, //
        }, //
    };

    const TEST_KEY: &[u8; 32] = b"0123456789abcdef0123456789abcdef";
    const TEST_IDENTITY: &[u8] = b"test-identity";
    const TEST_CONTEXT: &[u8] = b"test-context";

    #[test]
    fn test_session_ops() {
        let ctx = TlsContextBuilder::new_tls().build();
        let dummy_bytes = vec![0u8; 32];
        let res = TlsSession::from_bytes(&dummy_bytes, &ctx);
        assert!(res.is_err());
    }

    #[test]
    fn test_psk_resumption() {
        let cred_client = TlsCredential::new_pre_shared_key(
            TEST_KEY,
            TEST_IDENTITY,
            PskHash::Sha256,
            TEST_CONTEXT,
        )
        .unwrap();
        let cred_server = TlsCredential::new_pre_shared_key(
            TEST_KEY,
            TEST_IDENTITY,
            PskHash::Sha256,
            TEST_CONTEXT,
        )
        .unwrap();

        let mut ctx_client = TlsContextBuilder::new_tls();
        ctx_client.with_credential(cred_client).unwrap();
        let ctx_client = ctx_client.build();

        let mut ctx_server = TlsContextBuilder::new_tls();
        ctx_server.with_credential(cred_server).unwrap();
        let ctx_server = ctx_server.build();

        let mut conn_client = ctx_client.new_client_connection(None).unwrap().build();
        let mut conn_server = ctx_server.new_server_connection(None).unwrap().build();

        let (sock_client, sock_server, mut executor) = create_mock_pipe();

        conn_client.set_io(sock_client).unwrap();
        conn_server.set_io(sock_server).unwrap();

        executor
            .run(try_join(
                conn_client.in_handshake().unwrap().async_handshake(),
                conn_server.in_handshake().unwrap().async_handshake(),
            ))
            .unwrap();

        let est_client = conn_client.established().unwrap();
        let session = est_client.get_session().unwrap();

        let session_bytes = session.to_bytes().unwrap();
        assert!(!session_bytes.is_empty());

        let session_recovered = TlsSession::from_bytes(&session_bytes, &ctx_client).unwrap();

        let session_bytes_2 = session_recovered.to_bytes().unwrap();
        assert_eq!(session_bytes, session_bytes_2);
    }

    #[test]
    fn test_ticket_based_resumption() {
        let cred_client = TlsCredential::new_pre_shared_key(
            TEST_KEY,
            TEST_IDENTITY,
            PskHash::Sha256,
            TEST_CONTEXT,
        )
        .unwrap();
        let cred_server = TlsCredential::new_pre_shared_key(
            TEST_KEY,
            TEST_IDENTITY,
            PskHash::Sha256,
            TEST_CONTEXT,
        )
        .unwrap();

        let mut ctx_client = TlsContextBuilder::new_tls();
        ctx_client.with_credential(cred_client).unwrap();
        let ctx_client = ctx_client.build();

        let mut ctx_server = TlsContextBuilder::new_tls();
        ctx_server.with_credential(cred_server).unwrap();
        let ctx_server = ctx_server.build();
        let mut conn_client = ctx_client.new_client_connection(None).unwrap().build();
        let mut conn_server = ctx_server.new_server_connection(None).unwrap().build();

        let (sock_client, sock_server, mut executor) = create_mock_pipe();

        conn_client.set_io(sock_client).unwrap();
        conn_server.set_io(sock_server).unwrap();

        executor
            .run(try_join(
                conn_client.in_handshake().unwrap().async_handshake(),
                conn_server.in_handshake().unwrap().async_handshake(),
            ))
            .unwrap();

        let est_client = conn_client.established().unwrap();
        let session = est_client.get_session().unwrap();
        let peer = session.get_peer_sha256().unwrap();

        // === SESSION RESUMPTION ===
        // Use the session for a new connection
        let (sock_client_2, sock_server_2, mut executor) = create_mock_pipe();

        let mut builder_client_2 = ctx_client.new_client_connection(None).unwrap();
        builder_client_2.with_session(&session);
        let mut conn_client_2 = builder_client_2.build();

        let builder_server_2 = ctx_server.new_server_connection(None).unwrap();
        let mut conn_server_2 = builder_server_2.build();

        conn_client_2.set_io(sock_client_2).unwrap();
        conn_server_2.set_io(sock_server_2).unwrap();

        executor
            .run(try_join(
                Pin::new(&mut conn_client_2).async_write(b"hello"),
                Pin::new(&mut conn_server_2).async_write(b"world"),
            ))
            .unwrap();
        // The peer identity should be the same as before
        assert_eq!(
            conn_client_2
                .established()
                .unwrap()
                .get_session()
                .unwrap()
                .get_peer_sha256()
                .unwrap(),
            peer
        );
    }
}