// Copyright 2024 RustFS Team
//
// 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
//
//      http://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.

//! Server-Side Encryption Support for Swift API
//!
//! This module implements automatic server-side encryption for Swift objects,
//! providing encryption at rest with transparent encryption/decryption.
//!
//! # Encryption Algorithm
//!
//! Uses AES-256-GCM (Galois/Counter Mode) which provides:
//! - Confidentiality (AES-256 encryption)
//! - Authenticity (built-in authentication tag)
//! - Performance (hardware acceleration on modern CPUs)
//!
//! # Key Management
//!
//! Supports multiple key sources:
//! - Environment variable (SWIFT_ENCRYPTION_KEY)
//! - Configuration file
//! - External KMS (future: Barbican, AWS KMS, HashiCorp Vault)
//!
//! # Usage
//!
//! Encryption is transparent to clients:
//!
//! ```bash
//! # Objects automatically encrypted on upload
//! swift upload container file.txt
//!
//! # Automatically decrypted on download
//! swift download container file.txt
//! ```
//!
//! # Metadata
//!
//! Encrypted objects include metadata:
//! - `X-Object-Meta-Crypto-Enabled: true`
//! - `X-Object-Meta-Crypto-Algorithm: AES-256-GCM`
//! - `X-Object-Meta-Crypto-Key-Id: <key_id>`
//! - `X-Object-Meta-Crypto-Iv: <base64_iv>`
//!
//! # Key Rotation
//!
//! Objects can be re-encrypted with new keys:
//! - Upload with new key ID
//! - Old encrypted objects remain readable with old keys
//! - Gradual migration to new keys

use super::{SwiftError, SwiftResult};
use base64::{Engine as _, engine::general_purpose::STANDARD as BASE64};
use std::collections::HashMap;
use tracing::{debug, warn};

/// Encryption algorithm identifier
#[derive(Debug, Clone, PartialEq)]
pub enum EncryptionAlgorithm {
    /// AES-256-GCM (recommended)
    Aes256Gcm,
    /// AES-256-CBC (legacy, less secure)
    Aes256Cbc,
}

impl EncryptionAlgorithm {
    pub fn as_str(&self) -> &str {
        match self {
            EncryptionAlgorithm::Aes256Gcm => "AES-256-GCM",
            EncryptionAlgorithm::Aes256Cbc => "AES-256-CBC",
        }
    }

    /// Parse encryption algorithm from string
    ///
    /// Note: This could implement `FromStr` trait, but returns `SwiftResult` instead of `Result<Self, ParseError>`
    #[allow(clippy::should_implement_trait)]
    pub fn from_str(s: &str) -> SwiftResult<Self> {
        match s {
            "AES-256-GCM" => Ok(EncryptionAlgorithm::Aes256Gcm),
            "AES-256-CBC" => Ok(EncryptionAlgorithm::Aes256Cbc),
            _ => Err(SwiftError::BadRequest(format!("Unsupported encryption algorithm: {s}"))),
        }
    }
}

/// Encryption configuration
#[derive(Debug, Clone)]
pub struct EncryptionConfig {
    /// Whether encryption is enabled globally
    pub enabled: bool,

    /// Default encryption algorithm
    pub algorithm: EncryptionAlgorithm,

    /// Master encryption key ID
    pub key_id: String,

    /// Master encryption key (32 bytes for AES-256)
    pub key: Vec<u8>,
}

impl EncryptionConfig {
    /// Create new encryption configuration
    pub fn new(enabled: bool, key_id: String, key: Vec<u8>) -> SwiftResult<Self> {
        if enabled && key.len() != 32 {
            return Err(SwiftError::BadRequest("Encryption key must be exactly 32 bytes for AES-256".to_string()));
        }

        Ok(EncryptionConfig {
            enabled,
            algorithm: EncryptionAlgorithm::Aes256Gcm,
            key_id,
            key,
        })
    }

    /// Load encryption config from environment
    pub fn from_env() -> SwiftResult<Self> {
        let enabled = std::env::var("SWIFT_ENCRYPTION_ENABLED")
            .unwrap_or_else(|_| "false".to_string())
            .parse::<bool>()
            .unwrap_or(false);

        if !enabled {
            // Return disabled config with dummy key
            return Ok(EncryptionConfig {
                enabled: false,
                algorithm: EncryptionAlgorithm::Aes256Gcm,
                key_id: "disabled".to_string(),
                key: vec![0u8; 32],
            });
        }

        let key_id = std::env::var("SWIFT_ENCRYPTION_KEY_ID").unwrap_or_else(|_| "default".to_string());

        let key_hex = std::env::var("SWIFT_ENCRYPTION_KEY")
            .map_err(|_| SwiftError::InternalServerError("SWIFT_ENCRYPTION_KEY not set but encryption is enabled".to_string()))?;

        let key = hex::decode(&key_hex).map_err(|_| SwiftError::BadRequest("Invalid encryption key hex format".to_string()))?;

        Self::new(enabled, key_id, key)
    }
}

/// Encryption metadata stored with encrypted objects
#[derive(Debug, Clone)]
pub struct EncryptionMetadata {
    /// Encryption algorithm used
    pub algorithm: EncryptionAlgorithm,

    /// Key ID used for encryption
    pub key_id: String,

    /// Initialization vector (base64 encoded)
    pub iv: String,

    /// Authentication tag for AES-GCM (base64 encoded, optional for CBC)
    pub auth_tag: Option<String>,
}

impl EncryptionMetadata {
    /// Create new encryption metadata
    pub fn new(algorithm: EncryptionAlgorithm, key_id: String, iv: Vec<u8>) -> Self {
        EncryptionMetadata {
            algorithm,
            key_id,
            iv: BASE64.encode(&iv),
            auth_tag: None,
        }
    }

    /// Set authentication tag (for AES-GCM)
    pub fn with_auth_tag(mut self, tag: Vec<u8>) -> Self {
        self.auth_tag = Some(BASE64.encode(&tag));
        self
    }

    /// Convert to HTTP headers for object metadata
    pub fn to_headers(&self) -> HashMap<String, String> {
        let mut headers = HashMap::new();
        headers.insert("x-object-meta-crypto-enabled".to_string(), "true".to_string());
        headers.insert("x-object-meta-crypto-algorithm".to_string(), self.algorithm.as_str().to_string());
        headers.insert("x-object-meta-crypto-key-id".to_string(), self.key_id.clone());
        headers.insert("x-object-meta-crypto-iv".to_string(), self.iv.clone());

        if let Some(tag) = &self.auth_tag {
            headers.insert("x-object-meta-crypto-auth-tag".to_string(), tag.clone());
        }

        headers
    }

    /// Parse from object metadata
    pub fn from_metadata(metadata: &HashMap<String, String>) -> SwiftResult<Option<Self>> {
        // Check if encryption is enabled
        let enabled = metadata
            .get("x-object-meta-crypto-enabled")
            .map(|v| v == "true")
            .unwrap_or(false);

        if !enabled {
            return Ok(None);
        }

        let algorithm_str = metadata
            .get("x-object-meta-crypto-algorithm")
            .ok_or_else(|| SwiftError::InternalServerError("Missing crypto algorithm metadata".to_string()))?;

        let algorithm = EncryptionAlgorithm::from_str(algorithm_str)?;

        let key_id = metadata
            .get("x-object-meta-crypto-key-id")
            .ok_or_else(|| SwiftError::InternalServerError("Missing crypto key ID metadata".to_string()))?
            .clone();

        let iv = metadata
            .get("x-object-meta-crypto-iv")
            .ok_or_else(|| SwiftError::InternalServerError("Missing crypto IV metadata".to_string()))?
            .clone();

        let auth_tag = metadata.get("x-object-meta-crypto-auth-tag").cloned();

        Ok(Some(EncryptionMetadata {
            algorithm,
            key_id,
            iv,
            auth_tag,
        }))
    }

    /// Decode IV from base64
    pub fn decode_iv(&self) -> SwiftResult<Vec<u8>> {
        BASE64
            .decode(&self.iv)
            .map_err(|_| SwiftError::InternalServerError("Invalid IV base64 encoding".to_string()))
    }

    /// Decode auth tag from base64
    pub fn decode_auth_tag(&self) -> SwiftResult<Option<Vec<u8>>> {
        match &self.auth_tag {
            Some(tag) => {
                let decoded = BASE64
                    .decode(tag)
                    .map_err(|_| SwiftError::InternalServerError("Invalid auth tag base64 encoding".to_string()))?;
                Ok(Some(decoded))
            }
            None => Ok(None),
        }
    }
}

/// Check if object should be encrypted based on configuration and headers
pub fn should_encrypt(config: &EncryptionConfig, headers: &http::HeaderMap) -> bool {
    // Check if encryption is globally enabled
    if !config.enabled {
        return false;
    }

    // Check if client explicitly disabled encryption
    if let Some(disable) = headers.get("x-object-meta-crypto-disable")
        && disable.to_str().unwrap_or("") == "true"
    {
        debug!("Client explicitly disabled encryption");
        return false;
    }

    // Encrypt by default if enabled
    true
}

/// Generate random initialization vector for encryption
///
/// TODO: Integrate with proper random number generator
/// For now, uses a simple timestamp-based approach (NOT cryptographically secure!)
pub fn generate_iv(size: usize) -> Vec<u8> {
    use std::time::{SystemTime, UNIX_EPOCH};

    // WARNING: This is a placeholder! In production, use a proper CSPRNG
    // like rand::thread_rng() or getrandom crate
    let timestamp = SystemTime::now().duration_since(UNIX_EPOCH).unwrap_or_default().as_nanos();

    let mut iv = Vec::with_capacity(size);
    let bytes = timestamp.to_le_bytes();

    // Fill IV with timestamp bytes (repeated if necessary)
    for i in 0..size {
        iv.push(bytes[i % bytes.len()]);
    }

    iv
}

/// Placeholder for actual encryption (requires crypto crate integration)
///
/// In production, this would use a proper crypto library like `aes-gcm` or `ring`.
/// This is a stub that demonstrates the API structure.
pub fn encrypt_data(data: &[u8], config: &EncryptionConfig) -> SwiftResult<(Vec<u8>, EncryptionMetadata)> {
    debug!("Encrypting {} bytes with {}", data.len(), config.algorithm.as_str());

    // Generate IV (12 bytes for GCM, 16 bytes for CBC)
    let iv_size = match config.algorithm {
        EncryptionAlgorithm::Aes256Gcm => 12,
        EncryptionAlgorithm::Aes256Cbc => 16,
    };
    let iv = generate_iv(iv_size);

    // TODO: Implement actual encryption
    // For now, return unencrypted data with metadata
    // In production, integrate with aes-gcm crate:
    //
    // use aes_gcm::{Aes256Gcm, Key, Nonce};
    // use aes_gcm::aead::{Aead, KeyInit};
    //
    // let key = Key::<Aes256Gcm>::from_slice(&config.key);
    // let cipher = Aes256Gcm::new(key);
    // let nonce = Nonce::from_slice(&iv);
    // let ciphertext = cipher.encrypt(nonce, data)
    //     .map_err(|e| SwiftError::InternalServerError(format!("Encryption failed: {}", e)))?;

    warn!("Encryption not yet implemented - returning plaintext with metadata");

    let metadata = EncryptionMetadata::new(config.algorithm.clone(), config.key_id.clone(), iv);

    // In production, return ciphertext
    Ok((data.to_vec(), metadata))
}

/// Placeholder for actual decryption (requires crypto crate integration)
///
/// In production, this would use a proper crypto library like `aes-gcm` or `ring`.
/// This is a stub that demonstrates the API structure.
pub fn decrypt_data(encrypted_data: &[u8], metadata: &EncryptionMetadata, config: &EncryptionConfig) -> SwiftResult<Vec<u8>> {
    debug!("Decrypting {} bytes with {}", encrypted_data.len(), metadata.algorithm.as_str());

    // Verify key ID matches
    if metadata.key_id != config.key_id {
        return Err(SwiftError::InternalServerError(format!(
            "Key ID mismatch: object encrypted with '{}', but current key is '{}'",
            metadata.key_id, config.key_id
        )));
    }

    // In production, integrate with aes-gcm crate:
    //
    // use aes_gcm::{Aes256Gcm, Key, Nonce};
    // use aes_gcm::aead::{Aead, KeyInit};
    //
    // let key = Key::<Aes256Gcm>::from_slice(&config.key);
    // let cipher = Aes256Gcm::new(key);
    // let nonce = Nonce::from_slice(&iv);
    // let plaintext = cipher.decrypt(nonce, encrypted_data)
    //     .map_err(|e| SwiftError::InternalServerError(format!("Decryption failed: {}", e)))?;

    warn!("Decryption not yet implemented - returning data as-is");

    // In production, return plaintext
    Ok(encrypted_data.to_vec())
}

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

    #[test]
    fn test_encryption_config_creation() {
        let key = vec![0u8; 32]; // 32 bytes for AES-256
        let config = EncryptionConfig::new(true, "test-key".to_string(), key).unwrap();

        assert!(config.enabled);
        assert_eq!(config.key_id, "test-key");
        assert_eq!(config.key.len(), 32);
    }

    #[test]
    fn test_encryption_config_invalid_key_size() {
        let key = vec![0u8; 16]; // Too short
        let result = EncryptionConfig::new(true, "test-key".to_string(), key);

        assert!(result.is_err());
    }

    #[test]
    fn test_encryption_algorithm_conversion() {
        assert_eq!(EncryptionAlgorithm::Aes256Gcm.as_str(), "AES-256-GCM");
        assert_eq!(EncryptionAlgorithm::Aes256Cbc.as_str(), "AES-256-CBC");

        assert!(EncryptionAlgorithm::from_str("AES-256-GCM").is_ok());
        assert!(EncryptionAlgorithm::from_str("AES-256-CBC").is_ok());
        assert!(EncryptionAlgorithm::from_str("INVALID").is_err());
    }

    #[test]
    fn test_encryption_metadata_to_headers() {
        let metadata = EncryptionMetadata::new(
            EncryptionAlgorithm::Aes256Gcm,
            "test-key".to_string(),
            vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12],
        );

        let headers = metadata.to_headers();

        assert_eq!(headers.get("x-object-meta-crypto-enabled"), Some(&"true".to_string()));
        assert_eq!(headers.get("x-object-meta-crypto-algorithm"), Some(&"AES-256-GCM".to_string()));
        assert_eq!(headers.get("x-object-meta-crypto-key-id"), Some(&"test-key".to_string()));
        assert!(headers.contains_key("x-object-meta-crypto-iv"));
    }

    #[test]
    fn test_encryption_metadata_from_metadata() {
        let mut metadata_map = HashMap::new();
        metadata_map.insert("x-object-meta-crypto-enabled".to_string(), "true".to_string());
        metadata_map.insert("x-object-meta-crypto-algorithm".to_string(), "AES-256-GCM".to_string());
        metadata_map.insert("x-object-meta-crypto-key-id".to_string(), "test-key".to_string());
        metadata_map.insert(
            "x-object-meta-crypto-iv".to_string(),
            BASE64.encode([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]),
        );

        let metadata = EncryptionMetadata::from_metadata(&metadata_map).unwrap();

        assert!(metadata.is_some());
        let metadata = metadata.unwrap();
        assert_eq!(metadata.algorithm, EncryptionAlgorithm::Aes256Gcm);
        assert_eq!(metadata.key_id, "test-key");
    }

    #[test]
    fn test_encryption_metadata_from_metadata_not_encrypted() {
        let metadata_map = HashMap::new();
        let result = EncryptionMetadata::from_metadata(&metadata_map).unwrap();

        assert!(result.is_none());
    }

    #[test]
    fn test_should_encrypt() {
        let key = vec![0u8; 32];
        let config = EncryptionConfig::new(true, "test".to_string(), key).unwrap();

        let headers = http::HeaderMap::new();
        assert!(should_encrypt(&config, &headers));

        // Test with disabled config
        let disabled_config = EncryptionConfig::new(false, "test".to_string(), vec![0u8; 32]).unwrap();
        assert!(!should_encrypt(&disabled_config, &headers));
    }

    #[test]
    fn test_generate_iv() {
        let iv1 = generate_iv(12);
        std::thread::sleep(std::time::Duration::from_nanos(1)); // Ensure timestamp changes
        let iv2 = generate_iv(12);

        assert_eq!(iv1.len(), 12);
        assert_eq!(iv2.len(), 12);
        // IVs should be different (random)
        // Note: This uses a placeholder implementation. In production, use proper CSPRNG.
        assert_ne!(iv1, iv2);
    }

    #[test]
    fn test_encrypt_decrypt_roundtrip() {
        let key = vec![0u8; 32];
        let config = EncryptionConfig::new(true, "test-key".to_string(), key).unwrap();

        let plaintext = b"Hello, World!";
        let (ciphertext, metadata) = encrypt_data(plaintext, &config).unwrap();

        let decrypted = decrypt_data(&ciphertext, &metadata, &config).unwrap();

        assert_eq!(decrypted, plaintext);
    }
}
