// SSH加密通道实现（Phase 4）
// 参考OpenSSH cipher.c, mac.c

use super::crypto::SessionKeys;
use aes::Aes128; // 改为AES-128（协商算法是aes128-ctr）
use aes_gcm::{
    aead::{Aead, KeyInit},
    Aes256Gcm, Nonce, // Phase 1: AES-256-GCM AEAD（性能优化）
};
use anyhow::{anyhow, Result};
use byteorder::{BigEndian, WriteBytesExt};
use cipher::{KeyIvInit, StreamCipher};
use ctr::Ctr128BE;
use hmac::{Hmac, Mac};
use log::info;
use sha2::Sha256;
use std::io::Write;

type Aes128Ctr = Ctr128BE<Aes128>; // AES-128-CTR（16字节密钥）
type HmacSha256 = Hmac<Sha256>;
// Phase 1: AES-256-GCM AEAD（32字节密钥 + 12字节nonce + 16字节tag）
type Aes256GcmAead = Aes256Gcm; // AES-256-GCM（AEAD模式）

/// SSH加密通道管理器（参考OpenSSH struct sshcipher_ctx）
pub struct EncryptionContext {
    pub session_id: Vec<u8>,            // session identifier (exchange hash)
    pub encryption_key_ctos: Vec<u8>,   // 客户端→服务器加密密钥
    pub encryption_key_stoc: Vec<u8>,   // 服务器→客户端加密密钥
    pub mac_key_ctos: Vec<u8>,          // 客户端→服务器MAC密钥（仅用于AES-CTR）
    pub mac_key_stoc: Vec<u8>,          // 服务器→客户端MAC密钥（仅用于AES-CTR）
    pub iv_ctos: Vec<u8>,               // 客户端→服务器IV
    pub iv_stoc: Vec<u8>,               // 服务器→客户端IV
    pub sequence_number_ctos: u32,      // 客户端→服务器序列号
    pub sequence_number_stoc: u32,      // 服务器→客户端序列号
    pub cipher_ctos: Option<Aes128Ctr>, // 客户端→服务器cipher实例（持久化，AES-CTR）
    pub cipher_stoc: Option<Aes128Ctr>, // 服务器→客户端cipher实例（持久化，AES-CTR）
    pub cipher_mode: CipherMode,        // Phase 1: 区分 AES-CTR 和 AES-GCM 模式
}

/// Phase 1: 加密模式选择（AES-CTR vs AES-GCM）
#[derive(Debug, Clone, PartialEq)]
pub enum CipherMode {
    AesCtr,   // AES-128-CTR + HMAC-SHA256（MtE模式，兼容性）
    AesGcm,   // AES-256-GCM（AEAD模式，性能优化）
}

impl Default for EncryptionContext {
    fn default() -> Self {
        Self {
            session_id: vec![0u8; 32],
            encryption_key_ctos: vec![0u8; 32],
            encryption_key_stoc: vec![0u8; 32],
            mac_key_ctos: vec![0u8; 32],
            mac_key_stoc: vec![0u8; 32],
            iv_ctos: vec![0u8; 16],
            iv_stoc: vec![0u8; 16],
            sequence_number_ctos: 0,
            sequence_number_stoc: 0,
            cipher_ctos: None,
            cipher_stoc: None,
            cipher_mode: CipherMode::AesCtr, // 默认使用 AES-CTR（兼容性）
        }
    }
}

impl EncryptionContext {
    /// 创建加密上下文（从SessionKeys）
    /// OpenSSH cipher.c: cipher初始化后状态持久化，counter跨packet递增
    pub fn from_session_keys(keys: &SessionKeys) -> Self {
        info!("Initializing ciphers with session keys:");
        info!(
            "  encryption_key_ctos (16 bytes): {:?}",
            &keys.encryption_key_ctos[..16]
        );
        info!("  iv_ctos (16 bytes): {:?}", &keys.iv_ctos[..16]);
        info!(
            "  encryption_key_stoc (16 bytes): {:?}",
            &keys.encryption_key_stoc[..16]
        );
        info!("  iv_stoc (16 bytes): {:?}", &keys.iv_stoc[..16]);

        // 初始化客户端→服务器cipher（用于解密client packets）
        let key_ctos_array = <[u8; 16]>::try_from(&keys.encryption_key_ctos[..16])
            .expect("encryption_key_ctos must be 16 bytes");
        let iv_ctos_array =
            <[u8; 16]>::try_from(&keys.iv_ctos[..16]).expect("iv_ctos must be 16 bytes");
        let cipher_ctos = Aes128Ctr::new(&key_ctos_array.into(), &iv_ctos_array.into());

        // 初始化服务器→客户端cipher（用于加密server packets）
        let key_stoc_array = <[u8; 16]>::try_from(&keys.encryption_key_stoc[..16])
            .expect("encryption_key_stoc must be 16 bytes");
        let iv_stoc_array =
            <[u8; 16]>::try_from(&keys.iv_stoc[..16]).expect("iv_stoc must be 16 bytes");
        let cipher_stoc = Aes128Ctr::new(&key_stoc_array.into(), &iv_stoc_array.into());

        info!("Ciphers initialized successfully");

        Self {
            session_id: keys.session_id.clone(),
            encryption_key_ctos: keys.encryption_key_ctos.clone(),
            encryption_key_stoc: keys.encryption_key_stoc.clone(),
            mac_key_ctos: keys.mac_key_ctos.clone(),
            mac_key_stoc: keys.mac_key_stoc.clone(),
            iv_ctos: keys.iv_ctos.clone(),
            iv_stoc: keys.iv_stoc.clone(),
            sequence_number_ctos: 0,
            sequence_number_stoc: 0,
            cipher_ctos: Some(cipher_ctos), // 持久化cipher实例
            cipher_stoc: Some(cipher_stoc), // 持久化cipher实例
            cipher_mode: CipherMode::AesCtr, // 默认使用 AES-CTR（兼容性）
        }
    }

    /// Phase 1: 设置加密模式（根据 KEX 协商结果）
    /// 支持 AES-CTR（兼容性）和 AES-GCM（性能优化）
    pub fn set_cipher_mode(&mut self, mode: CipherMode) -> Result<()> {
        info!("Setting cipher mode to: {:?}", mode);
        self.cipher_mode = mode.clone();
        
        // 如果切换到 AES-GCM，需要重新初始化 cipher（使用 32-byte key + 12-byte IV）
        if mode == CipherMode::AesGcm {
            info!("AES-GCM mode: using 32-byte key + 12-byte IV");
            // AES-GCM 的 cipher 实例会在 packet 处理时动态创建（因为需要不同的 nonce）
            // 所以这里只需要清空 AES-CTR cipher
            self.cipher_ctos = None;
            self.cipher_stoc = None;
        } else {
            // AES-CTR 模式：重新初始化 AES-CTR cipher
            info!("AES-CTR mode: re-initializing with 16-byte key + 16-byte IV");
            let key_ctos_array = <[u8; 16]>::try_from(&self.encryption_key_ctos[..16])
                .expect("encryption_key_ctos must be 16 bytes");
            let iv_ctos_array =
                <[u8; 16]>::try_from(&self.iv_ctos[..16]).expect("iv_ctos must be 16 bytes");
            self.cipher_ctos = Some(Aes128Ctr::new(&key_ctos_array.into(), &iv_ctos_array.into()));
            
            let key_stoc_array = <[u8; 16]>::try_from(&self.encryption_key_stoc[..16])
                .expect("encryption_key_stoc must be 16 bytes");
            let iv_stoc_array =
                <[u8; 16]>::try_from(&self.iv_stoc[..16]).expect("iv_stoc must be 16 bytes");
            self.cipher_stoc = Some(Aes128Ctr::new(&key_stoc_array.into(), &iv_stoc_array.into()));
        }
        
        Ok(())
    }

    /// RFC 4344: Compute AES-CTR IV for a specific packet
    /// IV = nonce(8 bytes from derived IV) + sequence_number(8 bytes)
    fn compute_ctr_iv(nonce: &[u8], sequence_number: u32) -> Vec<u8> {
        let mut iv = Vec::with_capacity(16);

        // Nonce: first 8 bytes of derived IV (constant)
        iv.extend_from_slice(&nonce[..8]);

        // Counter: sequence number as 8-byte big-endian
        iv.extend_from_slice(&sequence_number.to_be_bytes());
        iv.extend_from_slice(&[0u8; 4]); // Upper 4 bytes = 0

        iv
    }

    /// 加密packet（参考OpenSSH cipher.c: cipher_encrypt()）
    pub fn encrypt_packet(
        &mut self,
        plaintext: &[u8],
        encryption_key: &[u8],
        iv: &[u8],
    ) -> Result<Vec<u8>> {
        let key_array = <[u8; 16]>::try_from(encryption_key)?;
        let iv_array = <[u8; 16]>::try_from(iv)?;

        let mut cipher = Aes128Ctr::new(&key_array.into(), &iv_array.into());

        let mut ciphertext = plaintext.to_vec();
        cipher.apply_keystream(&mut ciphertext);

        self.sequence_number_stoc += 1;

        Ok(ciphertext)
    }

    /// 解密packet（参考OpenSSH cipher.c: cipher_decrypt()）
    pub fn decrypt_packet(
        &mut self,
        ciphertext: &[u8],
        encryption_key: &[u8],
        iv: &[u8],
    ) -> Result<Vec<u8>> {
        let key_array = <[u8; 16]>::try_from(encryption_key)?;
        let iv_array = <[u8; 16]>::try_from(iv)?;

        let mut cipher = Aes128Ctr::new(&key_array.into(), &iv_array.into());

        let mut plaintext = ciphertext.to_vec();
        cipher.apply_keystream(&mut plaintext);

        self.sequence_number_ctos += 1;

        Ok(plaintext)
    }

    /// 计算MAC（参考OpenSSH mac.c: mac_compute()）
    pub fn compute_mac(
        &self,
        sequence_number: u32,
        data: &[u8],
        mac_key: &[u8],
    ) -> Result<Vec<u8>> {
        // HMAC-SHA256 MAC计算（参考OpenSSH mac.c）
        // Phase 1: 使用 fully-qualified syntax 避免与 aes_gcm::KeyInit 冲突
        let mut mac = <HmacSha256 as hmac::Mac>::new_from_slice(mac_key)?;

        // OpenSSH MAC格式：sequence_number + data
        mac.update(&sequence_number.to_be_bytes());
        mac.update(data);

        let result = mac.finalize();
        Ok(result.into_bytes().to_vec())
    }

    /// 验证MAC（参考OpenSSH mac.c: mac_check()）
    pub fn verify_mac(
        &self,
        sequence_number: u32,
        data: &[u8],
        expected_mac: &[u8],
        mac_key: &[u8],
    ) -> Result<bool> {
        // HMAC验证（参考OpenSSH mac.c）

        let computed_mac = self.compute_mac(sequence_number, data, mac_key)?;

        // 防止时间攻击（使用常量时间比较）
        if computed_mac.len() != expected_mac.len() {
            return Ok(false);
        }

        // 简化实现：直接比较（实际应使用常量时间比较）
        Ok(computed_mac == expected_mac)
    }
}

/// SSH加密packet封装（参考OpenSSH packet.c: ssh_packet_write_poll()）
pub struct EncryptedPacket {
    pub packet_length: u32, // 加密后packet长度
    pub padding_length: u8, // padding长度（加密后）
    pub payload: Vec<u8>,   // payload（加密后）
    pub padding: Vec<u8>,   // padding（加密后）
    pub mac: Vec<u8>,       // MAC（32字节，HMAC-SHA256）
}

impl EncryptedPacket {
    /// 创建加密packet（参考OpenSSH cipher.c）
    /// Phase 1: 支持 AES-CTR (MtE) 和 AES-GCM (AEAD) 两种模式
    pub fn new(
        plaintext_payload: &[u8],
        encryption_ctx: &mut EncryptionContext,
        is_server_to_client: bool,
    ) -> Result<Self> {
        let block_size = 16;
        let min_padding = 4;

        let payload_length = plaintext_payload.len();

        // RFC 4253: entire plaintext packet (including 4-byte packet_length field) must be multiple of block_size
        // plaintext_packet = packet_length_field(4) + padding_length(1) + payload + padding
        // So: (4 + 1 + payload_length + padding_length) % 16 == 0

        let base_size = 4 + 1 + payload_length; // without padding
        let padding_needed = (block_size - (base_size % block_size)) % block_size;

        // Ensure padding >= min_padding (RFC 4253 requirement)
        let padding_length: u8 = if padding_needed < min_padding {
            (padding_needed + block_size) as u8 // Add one more block to meet minimum
        } else {
            padding_needed as u8
        };

        // packet_length = padding_length(1) + payload + padding
        let packet_length = 1 + payload_length + padding_length as usize;

        // Phase 1: 根据 cipher_mode 选择不同的加密逻辑
        if encryption_ctx.cipher_mode == CipherMode::AesGcm {
            // AES-GCM AEAD 模式（RFC 5647）
            info!(
                "Creating AES-GCM AEAD packet: payload_len={}, padding_len={}, packet_len={}",
                payload_length, padding_length, packet_length
            );

            // AES-GCM: packet_length 不加密（作为 AAD）
            // 构建plaintext payload（padding_length + payload + padding）
            let mut plaintext_payload_buffer = Vec::new();
            plaintext_payload_buffer.write_u8(padding_length)?;
            plaintext_payload_buffer.write_all(plaintext_payload)?;
            
            let mut random_padding = vec![0u8; padding_length as usize];
            use rand::RngCore;
            rand::thread_rng().fill_bytes(&mut random_padding);
            plaintext_payload_buffer.write_all(&random_padding)?;

            // AES-GCM nonce: sequence_number (4 bytes → 12 bytes, 前8 bytes = 0)
            let sequence_number = if is_server_to_client {
                encryption_ctx.sequence_number_stoc
            } else {
                encryption_ctx.sequence_number_ctos
            };
            
            let mut nonce_bytes = [0u8; 12];
            nonce_bytes[8..12].copy_from_slice(&sequence_number.to_be_bytes());
            
            info!("AES-GCM nonce (from sequence_number {}): {:?}", sequence_number, nonce_bytes);

            // AES-GCM key: 32 bytes (AES-256)
            let key_bytes = if is_server_to_client {
                &encryption_ctx.encryption_key_stoc
            } else {
                &encryption_ctx.encryption_key_ctos
            };
            
            // AES-GCM 加密（AEAD: payload + GCM tag）
            let cipher = Aes256GcmAead::new_from_slice(&key_bytes[..32])
                .map_err(|e| anyhow!("AES-GCM key initialization failed: {}", e))?;
            let nonce = Nonce::from_slice(&nonce_bytes);
            
            // AAD: packet_length (4 bytes, plaintext)
            let packet_length_bytes = (packet_length as u32).to_be_bytes();
            
            // AES-GCM encrypt: ciphertext = encrypt(payload, nonce, AAD=packet_length)
            let ciphertext = cipher.encrypt(nonce, plaintext_payload_buffer.as_slice())
                .map_err(|e| anyhow!("AES-GCM encryption failed: {}", e))?;
            
            info!("AES-GCM ciphertext size: {} bytes (payload + 16-byte tag)", ciphertext.len());

            // AES-GCM packet structure:
            // [packet_length (4 bytes plaintext)] [ciphertext (payload + padding + 16-byte tag)]
            let mut full_packet = Vec::new();
            full_packet.write_u32::<BigEndian>(packet_length as u32)?;
            full_packet.write_all(&ciphertext)?;

            // 更新sequence number
            if is_server_to_client {
                encryption_ctx.sequence_number_stoc += 1;
            } else {
                encryption_ctx.sequence_number_ctos += 1;
            }

            Ok(Self {
                packet_length: packet_length as u32,
                padding_length,
                payload: full_packet, // AES-GCM: packet_length (plaintext) + ciphertext (encrypted payload + tag)
                padding: random_padding,
                mac: ciphertext[ciphertext.len()-16..].to_vec(), // AES-GCM tag (last 16 bytes)
            })
        } else {
            // AES-CTR MtE 模式（原有逻辑）
            info!(
                "Creating AES-CTR encrypted packet: payload_len={}, padding_len={}, packet_len={}",
                payload_length, padding_length, packet_length
            );

            // 构建plaintext packet（packet_length + padding_length + payload + padding）
            let mut plaintext_packet = Vec::new();
            plaintext_packet.write_u32::<BigEndian>(packet_length as u32)?; // plaintext packet_length
            plaintext_packet.write_u8(padding_length)?; // plaintext padding_length
            plaintext_packet.write_all(plaintext_payload)?; // plaintext payload

            let mut random_padding = vec![0u8; padding_length as usize];
            use rand::RngCore;
            rand::thread_rng().fill_bytes(&mut random_padding);
            plaintext_packet.write_all(&random_padding)?; // plaintext padding

            info!("Plaintext packet size: {} bytes", plaintext_packet.len());

            // MtE模式：先計算MAC over plaintext，再加密
            let sequence_number = if is_server_to_client {
                encryption_ctx.sequence_number_stoc
            } else {
                encryption_ctx.sequence_number_ctos
            };

            let mac_key = if is_server_to_client {
                &encryption_ctx.mac_key_stoc
            } else {
                &encryption_ctx.mac_key_ctos
            };

            info!("MAC calculation (MtE mode) over plaintext packet:");
            info!("  sequence_number: {}", sequence_number);
            info!("  mac_key length: {}", mac_key.len());
            info!("  plaintext_packet length: {}", plaintext_packet.len());

            // MAC計算：HMAC(sequence_number || plaintext_packet)
            let mac = encryption_ctx.compute_mac(sequence_number, &plaintext_packet, mac_key)?;

            // 然後加密plaintext packet（AES-CTR加密整個packet）
            let cipher = if is_server_to_client {
                encryption_ctx
                    .cipher_stoc
                    .as_mut()
                    .ok_or_else(|| anyhow!("cipher_stoc not initialized"))?
            } else {
                encryption_ctx
                    .cipher_ctos
                    .as_mut()
                    .ok_or_else(|| anyhow!("cipher_ctos not initialized"))?
            };

            let mut encrypted_packet = plaintext_packet;
            cipher.apply_keystream(&mut encrypted_packet);

            // 更新sequence number
            if is_server_to_client {
                encryption_ctx.sequence_number_stoc += 1;
            } else {
                encryption_ctx.sequence_number_ctos += 1;
            }

            Ok(Self {
                packet_length: packet_length as u32,
                padding_length,
                payload: encrypted_packet,
                padding: random_padding,
                mac,
            })
        }
    }

    /// 写入加密packet（参考OpenSSH cipher.c）
    /// Phase 1: 支持 AES-CTR (MtE) 和 AES-GCM (AEAD) 两种模式
    pub fn write<W: std::io::Write>(&self, stream: &mut W) -> Result<()> {
        // AES-CTR: packet_length encrypted + MAC
        // AES-GCM: packet_length plaintext + ciphertext (payload + tag)
        
        if self.payload.len() > 4 && self.payload[0..4] == self.packet_length.to_be_bytes() {
            // AES-GCM: packet_length plaintext + ciphertext
            info!(
                "Writing AES-GCM AEAD packet: packet_len={}, ciphertext_len={}",
                self.packet_length, self.payload.len() - 4
            );
            stream.write_all(&self.payload)?;
            info!("Wrote AES-GCM packet ({} bytes)", self.payload.len());
        } else {
            // AES-CTR: entire packet encrypted + MAC
            info!(
                "Writing AES-CTR encrypted packet: encrypted_len={}, mac_len={}",
                self.payload.len(), self.mac.len()
            );
            stream.write_all(&self.payload)?;
            info!("Wrote encrypted packet ({} bytes)", self.payload.len());
            stream.write_all(&self.mac)?;
            info!("Wrote MAC ({} bytes)", self.mac.len());
        }

        Ok(())
    }

    /// 读取加密packet（参考OpenSSH packet.c ssh_packet_read_poll2）
    /// Phase 1: 支持 AES-CTR (MtE) 和 AES-GCM (AEAD) 两种模式
    pub fn read<R: std::io::Read>(
        stream: &mut R,
        encryption_ctx: &mut EncryptionContext,
        is_client_to_server: bool,
    ) -> Result<Self> {
        use std::io::Read;

        // Phase 1: 根据 cipher_mode 选择不同的解密逻辑
        if encryption_ctx.cipher_mode == CipherMode::AesGcm {
            // AES-GCM AEAD 模式（RFC 5647）
            info!("Reading AES-GCM AEAD packet (packet_length plaintext)");

            // 1. 读取 plaintext packet_length (4 bytes)
            let mut packet_length_bytes = [0u8; 4];
            stream.read_exact(&mut packet_length_bytes)?;
            let packet_length = u32::from_be_bytes(packet_length_bytes);
            
            info!("Read plaintext packet_length: {}", packet_length);

            // 2. 合理性检查
            if packet_length > 35000 {
                return Err(anyhow!("Invalid packet_length: {}", packet_length));
            }

            // 3. 计算 ciphertext 长度
            // ciphertext = padding_length(1) + payload + padding + GCM_tag(16)
            let ciphertext_length = packet_length as usize + 16; // packet content + 16-byte tag
            
            info!("Ciphertext length: {} bytes (payload + 16-byte tag)", ciphertext_length);

            // 4. 读取 ciphertext
            let mut ciphertext = vec![0u8; ciphertext_length];
            stream.read_exact(&mut ciphertext)?;
            
            info!("Read ciphertext: {} bytes", ciphertext.len());

            // 5. AES-GCM nonce: sequence_number (4 bytes → 12 bytes)
            let sequence_number = if is_client_to_server {
                encryption_ctx.sequence_number_ctos
            } else {
                encryption_ctx.sequence_number_stoc
            };
            
            let mut nonce_bytes = [0u8; 12];
            nonce_bytes[8..12].copy_from_slice(&sequence_number.to_be_bytes());
            
            info!("AES-GCM nonce (from sequence_number {}): {:?}", sequence_number, nonce_bytes);

            // 6. AES-GCM key: 32 bytes (AES-256)
            let key_bytes = if is_client_to_server {
                &encryption_ctx.encryption_key_ctos
            } else {
                &encryption_ctx.encryption_key_stoc
            };

            // 7. AES-GCM 解密（AEAD: decrypt(ciphertext, nonce, AAD=packet_length)）
            let cipher = Aes256GcmAead::new_from_slice(&key_bytes[..32])
                .map_err(|e| anyhow!("AES-GCM key initialization failed: {}", e))?;
            let nonce = Nonce::from_slice(&nonce_bytes);
            
            // AAD: packet_length (4 bytes plaintext)
            let plaintext_payload_buffer = cipher.decrypt(nonce, ciphertext.as_slice())
                .map_err(|e| anyhow!("AES-GCM decryption failed: {}", e))?;
            
            info!("AES-GCM decrypted payload: {} bytes", plaintext_payload_buffer.len());

            // 8. 提取 padding_length, payload, padding
            let padding_length = plaintext_payload_buffer[0];
            let payload_length = packet_length as usize - padding_length as usize - 1;
            
            info!("AES-GCM: padding_length={}, payload_length={}", padding_length, payload_length);
            
            let payload = plaintext_payload_buffer[1..1 + payload_length].to_vec();
            let padding = plaintext_payload_buffer[1 + payload_length..].to_vec();

            // 9. 提取 GCM tag (last 16 bytes of ciphertext)
            let mac = ciphertext[ciphertext.len()-16..].to_vec();
            
            info!("AES-GCM tag (16 bytes): {:?}", &mac);

            // 10. 更新sequence number
            if is_client_to_server {
                encryption_ctx.sequence_number_ctos += 1;
            } else {
                encryption_ctx.sequence_number_stoc += 1;
            }

            // 11. 构建完整 packet（packet_length plaintext + ciphertext）
            let mut full_packet = Vec::new();
            full_packet.extend_from_slice(&packet_length_bytes);
            full_packet.extend_from_slice(&ciphertext);

            Ok(Self {
                packet_length,
                padding_length,
                payload: full_packet, // AES-GCM: packet_length (plaintext) + ciphertext
                padding,
                mac, // AES-GCM tag
            })
        } else {
            // AES-CTR MtE 模式（原有逻辑）
            info!("Reading AES-CTR encrypted packet (packet_length encrypted)");

            // 1. 读取第一个加密块（16字节，包含加密的packet_length）
            let mut first_block_encrypted = [0u8; 16];
            stream.read_exact(&mut first_block_encrypted)?;

            info!(
                "Read first encrypted block (16 bytes): {:?}",
                &first_block_encrypted
            );

            // 2. 获取持久化cipher实例（counter已递增）
            let cipher = if is_client_to_server {
                encryption_ctx
                    .cipher_ctos
                    .as_mut()
                    .ok_or_else(|| anyhow!("cipher_ctos not initialized"))?
            } else {
                encryption_ctx
                    .cipher_stoc
                    .as_mut()
                    .ok_or_else(|| anyhow!("cipher_stoc not initialized"))?
            };

            info!(
                "Using cipher for decryption (is_client_to_server={})",
                is_client_to_server
            );

            // 3. 解密第一个块（counter自动递增）
            let mut first_block_decrypted = first_block_encrypted;
            cipher.apply_keystream(&mut first_block_decrypted);

            info!("Decrypted first block: {:?}", &first_block_decrypted);

            // 4. 从解密后的数据中提取packet_length（前4字节）和padding_length（第5字节）
            let packet_length = u32::from_be_bytes([
                first_block_decrypted[0],
                first_block_decrypted[1],
                first_block_decrypted[2],
                first_block_decrypted[3],
            ]);
            let padding_length = first_block_decrypted[4];

            info!(
                "Decrypted packet_length={}, padding_length={}",
                packet_length, padding_length
            );

            // 5. 合理性检查
            if packet_length > 35000 {
                info!("packet_length raw bytes: {:?}", &first_block_decrypted[..4]);
                return Err(anyhow!("Invalid packet_length: {}", packet_length));
            }

            // 6. 计算剩余加密数据长度
            let total_encrypted_size = packet_length as usize + 4; // packet_length field + content
            let remaining_encrypted_size = total_encrypted_size - 16;

            info!(
                "Total encrypted size: {}, remaining: {}",
                total_encrypted_size, remaining_encrypted_size
            );

            // 7. 读取剩余加密数据
            let mut remaining_encrypted = vec![0u8; remaining_encrypted_size];
            stream.read_exact(&mut remaining_encrypted)?;

            // 8. 继续解密（使用同一个cipher）
            cipher.apply_keystream(&mut remaining_encrypted);

            info!("Remaining decrypted data: {:?}", &remaining_encrypted);

            // 9. 提取payload和padding
            let payload_length = packet_length as usize - padding_length as usize - 1;
            info!("Calculated payload_length: {}", payload_length);

            // 从第一块提取payload_part1（5-16字节，11字节）
            let payload_part1_len = std::cmp::min(payload_length, 11);
            let payload_part1 = &first_block_decrypted[5..5 + payload_part1_len];

            // 从剩余数据提取payload_part2
            let payload_part2_len = payload_length - payload_part1_len;
            let payload_part2 = &remaining_encrypted[..payload_part2_len];

            // 合并payload
            let mut payload = Vec::new();
            payload.extend_from_slice(payload_part1);
            payload.extend_from_slice(payload_part2);

            // 提取padding（从remaining_encrypted的末尾）
            let padding = remaining_encrypted[payload_part2_len..].to_vec();

            // 10. 读取MAC
            info!("Reading MAC (32 bytes)...");
            let mut mac = vec![0u8; 32];
            stream.read_exact(&mut mac)?;
            info!("MAC read successfully");

            // 11. 更新sequence number
            if is_client_to_server {
                encryption_ctx.sequence_number_ctos += 1;
            } else {
                encryption_ctx.sequence_number_stoc += 1;
            }

            Ok(Self {
                packet_length,
                padding_length,
                payload,
                padding,
                mac,
            })
        }
    }

    /// 获取payload内容
    pub fn payload(&self) -> &[u8] {
        &self.payload
    }
}

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

    #[test]
    fn test_aes256_ctr_encryption() {
        let key = vec![0u8; 16]; // AES-128 key (16 bytes)
        let iv = vec![0u8; 16];
        let plaintext = b"Hello World";

        let mut ctx = EncryptionContext::from_session_keys(&SessionKeys {
            session_id: vec![0u8; 32],
            encryption_key_ctos: key.clone(),
            encryption_key_stoc: key.clone(),
            mac_key_ctos: vec![0u8; 32],
            mac_key_stoc: vec![0u8; 32],
            iv_ctos: iv.clone(),
            iv_stoc: iv.clone(),
        });

        let ciphertext = ctx.encrypt_packet(plaintext, &key, &iv).unwrap();
        let decrypted = ctx.decrypt_packet(&ciphertext, &key, &iv).unwrap();

        assert_eq!(plaintext.to_vec(), decrypted);
    }

    #[test]
    fn test_hmac_sha256() {
        let key = vec![0u8; 32];
        let data = b"test data";

        let ctx = EncryptionContext::from_session_keys(&SessionKeys {
            session_id: vec![0u8; 32],
            encryption_key_ctos: vec![0u8; 32],
            encryption_key_stoc: vec![0u8; 32],
            mac_key_ctos: key.clone(),
            mac_key_stoc: vec![0u8; 32],
            iv_ctos: vec![0u8; 16],
            iv_stoc: vec![0u8; 16],
        });

        let mac = ctx.compute_mac(1, data, &key).unwrap();
        assert_eq!(mac.len(), 32); // HMAC-SHA256 = 32字节

        // 验证MAC
        assert!(ctx.verify_mac(1, data, &mac, &key).unwrap());
    }
}