rustdi 0.1.0

use crate::errors::*;
use crate::session::Session;
use ring::{agreement, digest, hmac, hkdf, rand};
use std::sync::Arc;

/// Tahapan handshake Noise
#[derive(Debug, Clone, PartialEq)]
pub enum HandshakeState {
    /// Belum memulai handshake
    Idle,
    /// Telah mengirim Client Hello
    ClientHelloSent,
    /// Telah menerima Server Hello
    ServerHelloReceived,
    /// Telah mengirim Client Finish
    ClientFinishSent,
    /// Handshake selesai
    Complete,
}

/// Struktur untuk handshake
pub struct Handshake {
    state: HandshakeState,
    client_keys: Option<ClientKeys>,
    server_keys: Option<ServerKeys>,
    shared_secret: Option<Vec<u8>>,
}

#[derive(Debug)]
struct ClientKeys {
    ephemeral_private: agreement::EphemeralPrivateKey,
    ephemeral_public: Vec<u8>,
    static_private: agreement::EphemeralPrivateKey,
    static_public: Vec<u8>,
}

#[derive(Debug)]
struct ServerKeys {
    ephemeral_public: Vec<u8>,
    static_encrypted: Vec<u8>,
    certificate_encrypted: Vec<u8>,
}

impl Handshake {
    /// Membuat instance handshake baru
    pub fn new() -> Result<Self> {
        Ok(Handshake {
            state: HandshakeState::Idle,
            client_keys: None,
            server_keys: None,
            shared_secret: None,
        })
    }

    /// Memulai handshake Noise
    pub fn start(&mut self) -> Result<Vec<u8>> {
        if self.state != HandshakeState::Idle {
            return Err("Handshake already started".into());
        }

        // Generate keys
        let client_keys = self.generate_client_keys()?;
        self.client_keys = Some(client_keys.clone());

        // Bangun ClientHello message
        let mut message = vec![0x01]; // Type: ClientHello
        message.extend_from_slice(&[0x00, 0x01]); // Version: 1
        message.extend_from_slice(&client_keys.ephemeral_public);

        self.state = HandshakeState::ClientHelloSent;
        Ok(message)
    }

    /// Proses ServerHello yang diterima dari server
    pub fn process_server_hello(&mut self, server_hello: &[u8]) -> Result<Vec<u8>> {
        if self.state != HandshakeState::ClientHelloSent {
            return Err("Invalid handshake state for processing server hello".into());
        }

        if server_hello.len() < 1 {
            return Err("Server hello message too short".into());
        }

        // Parse server hello
        let server_keys = self.parse_server_hello(server_hello)?;
        self.server_keys = Some(server_keys.clone());

        // Compute shared secret using server ephemeral public key
        let client_keys = self.client_keys.as_ref().ok_or("Client keys not available")?;
        let shared_secret = self.compute_shared_secret(
            &client_keys.ephemeral_private,
            &server_keys.ephemeral_public
        )?;

        self.shared_secret = Some(shared_secret.clone());

        // Decrypt server's static key using shared secret and client's static key
        let decrypted_static = self.decrypt_server_static(&shared_secret, &server_keys.static_encrypted)?;

        // Validate server certificate
        self.validate_server_certificate(&server_keys.certificate_encrypted, &shared_secret)?;

        // Bangun ClientFinish message
        let mut finish_message = vec![0x02]; // Type: ClientFinish
        finish_message.extend_from_slice(&client_keys.static_public);

        // Buat dan enkripsi payload (containing tokens, etc.)
        let client_payload = self.build_client_payload()?;
        let encrypted_payload = self.encrypt_payload(&client_payload, &shared_secret)?;
        finish_message.extend_from_slice(&encrypted_payload);

        self.state = HandshakeState::ClientFinishSent;
        Ok(finish_message)
    }

    /// Selesaikan handshake setelah mengirim ClientFinish
    pub fn finalize(&mut self, session: &mut Session) -> Result<()> {
        if self.state != HandshakeState::ClientFinishSent {
            return Err("Invalid handshake state for finalization".into());
        }

        // Generate final session keys
        let shared_secret = self.shared_secret.as_ref().ok_or("Shared secret not available")?;
        let final_keys = self.derive_final_keys(shared_secret)?;

        // Update session dengan kunci baru
        session.update_encryption_keys(final_keys.enc_key, final_keys.mac_key);

        self.state = HandshakeState::Complete;
        Ok(())
    }

    /// Cek apakah handshake selesai
    pub fn is_complete(&self) -> bool {
        self.state == HandshakeState::Complete
    }

    fn generate_client_keys(&mut self) -> Result<ClientKeys> {
        let rng = rand::SystemRandom::new();

        // Generate ephemeral key pair
        let ephemeral_private = agreement::EphemeralPrivateKey::generate(&agreement::X25519, &rng)
            .map_err(|_| "Failed to generate ephemeral private key")?;
        let ephemeral_public = ephemeral_private.compute_public_key()
            .map_err(|_| "Failed to compute ephemeral public key")?
            .as_ref().to_vec();

        // Generate static key pair
        let static_private = agreement::EphemeralPrivateKey::generate(&agreement::X25519, &rng)
            .map_err(|_| "Failed to generate static private key")?;
        let static_public = static_private.compute_public_key()
            .map_err(|_| "Failed to compute static public key")?
            .as_ref().to_vec();

        Ok(ClientKeys {
            ephemeral_private,
            ephemeral_public,
            static_private,
            static_public,
        })
    }

    fn parse_server_hello(&self, hello: &[u8]) -> Result<ServerKeys> {
        
        if hello.len() < 33 { // minimal 1 byte header + 32 byte public key
            return Err("Server hello too short".into());
        }

        // Ambil public key dari server (32 byte)
        let ephemeral_public = hello[1..33].to_vec();

        // Ambil encrypted static key dan certificate
        let static_encrypted_start = 33;
        let static_encrypted_end = hello.len(); // dalam implementasi nyata akan lebih kompleks
        let static_encrypted = hello[static_encrypted_start..static_encrypted_end.min(hello.len())].to_vec();

        
        let certificate_encrypted = Vec::new(); // Placeholder

        Ok(ServerKeys {
            ephemeral_public,
            static_encrypted,
            certificate_encrypted,
        })
    }

    fn compute_shared_secret(
        &self,
        private_key: &agreement::EphemeralPrivateKey,
        server_public: &[u8]
    ) -> Result<Vec<u8>> {
        let server_public_key = agreement::UnparsedPublicKey::new(&agreement::X25519, server_public);
        let shared_secret = agreement::agree_ephemeral(
            private_key.clone(),
            &server_public_key,
            |shared_secret| shared_secret.to_vec(),
        ).map_err(|_| "Failed to compute shared secret")?;

        Ok(shared_secret)
    }

    fn decrypt_server_static(&self, shared_secret: &[u8], encrypted_static: &[u8]) -> Result<Vec<u8>> {
        // Dalam implementasi nyata, akan dilakukan dekripsi aktual
        // Ini hanya placeholder
        Ok(encrypted_static.to_vec())
    }

    fn validate_server_certificate(&self, encrypted_cert: &[u8], shared_secret: &[u8]) -> Result<()> {
        // Dalam implementasi nyata, akan dilakukan validasi sertifikat
        // Placeholder - selalu sukses
        Ok(())
    }

    fn build_client_payload(&self) -> Result<Vec<u8>> {
        // Bangun payload klien berisi token, identitas, dll.
        // Ini hanya placeholder
        Ok(vec![0x01, 0x02, 0x03, 0x04]) // Placeholder
    }

    fn encrypt_payload(&self, payload: &[u8], shared_secret: &[u8]) -> Result<Vec<u8>> {
        // Dalam implementasi nyata, akan menggunakan cipher yang sesuai
        // Ini hanya placeholder
        Ok(payload.to_vec())
    }

    fn derive_final_keys(&self, shared_secret: &[u8]) -> Result<crate::crypto::SessionKeys> {
        // Gunakan HKDF untuk menurunkan kunci final dari secret bersama
        let salt = [0u8; 32]; // Salt nol seperti dalam protokol WhatsApp
        let hkdf_salt = hkdf::Salt::new(hkdf::HKDF_SHA256, &salt);
        let pseudo_random_key = hkdf_salt.extract(shared_secret);

        let mut expanded_secret = [0u8; 96]; // WhatsApp mengembangkan hingga 96 byte
        pseudo_random_key.expand(&[], &mut expanded_secret)
            .map_err(|_| "Failed to expand shared secret")?;

        let enc_key = expanded_secret[0..32].to_vec();
        let mac_key = expanded_secret[32..64].to_vec();

        Ok(crate::crypto::SessionKeys {
            enc_key,
            mac_key,
        })
    }
}