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

use aes::Aes128;  // 改为AES-128（协商算法是aes128-ctr）
use ctr::Ctr128BE;
use hmac::{Hmac, Mac};
use sha2::Sha256;
use cipher::{KeyIvInit, StreamCipher};
use std::io::Write;
use anyhow::{Result, anyhow};
use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
use log::{info, debug, warn};
use super::crypto::SessionKeys;

type Aes128Ctr = Ctr128BE<Aes128>;  // AES-128-CTR（16字节密钥）
type HmacSha256 = Hmac<Sha256>;

/// 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
    pub mac_key_stoc: Vec<u8>,         // 服务器→客户端MAC密钥
    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）
    pub cipher_stoc: Option<Aes128Ctr>,  // 服务器→客户端cipher实例（持久化）
}

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,
        }
    }
}

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
        }
    }
    
    /// 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）
        
        let mut mac = HmacSha256::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）
    /// AES-CTR模式：所有数据加密（包括packet_length）
    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;
        
        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）
    /// AES-CTR模式：写入完整加密packet + MAC
    pub fn write<W: std::io::Write>(&self, stream: &mut W) -> Result<()> {
        info!("Writing AES-CTR encrypted packet: total_encrypted_len={}, mac_len={}", 
            self.payload.len(), self.mac.len());
        
        // AES-CTR: 整个packet已加密（包括packet_length），直接写入
        stream.write_all(&self.payload)?;
        info!("Wrote encrypted packet ({} bytes)", self.payload.len());
        
        // 写入MAC
        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）
    /// OpenSSH packet.c: AES-CTR先解密第一个块，再提取packet_length
    /// aadlen = 0 (没有EtM或authenticated encryption), packet_length被加密
    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;
        
        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);
        
        // 3. 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);
        
        // 4. 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));
        }
        
        // 3. 计算剩余加密数据长度
        // packet_length = padding_length(1) + payload + padding
        // 总加密数据 = packet_length(4) + packet_length = packet_length + 4
        // 已读取16字节，剩余 = packet_length + 4 - 16
        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);
        
        // 4. 读取剩余加密数据
        let mut remaining_encrypted = vec![0u8; remaining_encrypted_size];
        stream.read_exact(&mut remaining_encrypted)?;
        
        // 5. 继续解密（使用同一个cipher）
        cipher.apply_keystream(&mut remaining_encrypted);
        
        info!("Remaining decrypted data: {:?}", &remaining_encrypted);
        
        // 6. 提取payload和padding
        // payload长度 = packet_length - padding_length - 1
        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();
        
        // 9. 读取MAC
        info!("Reading MAC (32 bytes)...");
        let mut mac = vec![0u8; 32];
        stream.read_exact(&mut mac)?;
        info!("MAC read successfully");
        
        // 10. 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());
    }
}