use async_trait::async_trait;
use base64::engine::general_purpose::STANDARD as BASE64;
use base64::Engine as _;
use serde_json::{json, Value};
use std::collections::HashMap;
use std::sync::Arc;

use super::Engine;
use crate::core::SealMechanism;
use crate::crypto::{CryptoBackend, SymmetricAlgorithm};
use crate::error::{Result, VaultError};
use crate::storage::StorageBackend;

/// Encrypted key version
#[derive(Debug, Clone)]
struct TransitKey {
    name: String,
    versions: HashMap<u64, KeyVersion>,
    current_version: u64,
    min_decrypt_version: u64,
}

/// Individual key version
#[derive(Debug, Clone)]
struct KeyVersion {
    key_material: Vec<u8>,
    #[allow(dead_code)]
    created_at: chrono::DateTime<chrono::Utc>,
}

/// Transit secrets engine for encryption/decryption
pub struct TransitEngine {
    storage: Arc<dyn StorageBackend>,
    crypto: Arc<dyn CryptoBackend>,
    seal: Arc<tokio::sync::Mutex<SealMechanism>>,
    #[allow(dead_code)]
    mount_path: String,
    keys: Arc<tokio::sync::Mutex<HashMap<String, TransitKey>>>,
}

impl TransitEngine {
    /// Create a new Transit engine instance
    pub fn new(
        storage: Arc<dyn StorageBackend>,
        crypto: Arc<dyn CryptoBackend>,
        seal: Arc<tokio::sync::Mutex<SealMechanism>>,
        mount_path: String,
    ) -> Self {
        Self {
            storage,
            crypto,
            seal,
            mount_path,
            keys: Arc::new(tokio::sync::Mutex::new(HashMap::new())),
        }
    }

    /// Get storage key for transit key
    #[allow(dead_code)]
    fn storage_key(&self, key_name: &str) -> String {
        format!("{}keys/{}", self.mount_path, key_name)
    }

    /// Create or update a transit key
    pub async fn create_key(&self, key_name: &str, key_material: Vec<u8>) -> Result<()> {
        let now = chrono::Utc::now();
        let mut keys = self.keys.lock().await;

        if let Some(key) = keys.get_mut(key_name) {
            // Existing key - increment version
            let next_version = key.current_version + 1;
            key.versions.insert(
                next_version,
                KeyVersion {
                    key_material,
                    created_at: now,
                },
            );
            key.current_version = next_version;
        } else {
            // New key - create with version 1
            let mut key = TransitKey {
                name: key_name.to_string(),
                versions: HashMap::new(),
                current_version: 1,
                min_decrypt_version: 1,
            };
            key.versions.insert(
                1,
                KeyVersion {
                    key_material,
                    created_at: now,
                },
            );
            keys.insert(key_name.to_string(), key);
        }

        Ok(())
    }

    /// Encrypt plaintext using the specified key
    pub async fn encrypt(&self, key_name: &str, plaintext: &[u8]) -> Result<String> {
        let keys = self.keys.lock().await;
        let key = keys
            .get(key_name)
            .ok_or_else(|| VaultError::storage(format!("Key not found: {}", key_name)))?;

        let key_version = key
            .versions
            .get(&key.current_version)
            .ok_or_else(|| VaultError::crypto("Key version not found".to_string()))?;

        let key_material = key_version.key_material.clone();
        let current_version = key.current_version;
        drop(keys);

        // Encrypt plaintext using the current key version (lock is dropped before await)
        let ciphertext = self
            .crypto
            .encrypt_symmetric(&key_material, plaintext, SymmetricAlgorithm::Aes256Gcm)
            .await
            .map_err(|e| VaultError::crypto(e.to_string()))?;

        // Format: vault:v{version}:base64_encoded_ciphertext
        let encoded = BASE64.encode(&ciphertext);
        Ok(format!("vault:v{}:{}", current_version, encoded))
    }

    /// Decrypt ciphertext using the appropriate key version
    pub async fn decrypt(&self, key_name: &str, ciphertext_str: &str) -> Result<Vec<u8>> {
        // Parse vault format: vault:v{version}:base64_data
        let parts: Vec<&str> = ciphertext_str.split(':').collect();
        if parts.len() != 3 || parts[0] != "vault" {
            return Err(VaultError::crypto(
                "Invalid vault ciphertext format".to_string(),
            ));
        }

        let version_str = parts[1]
            .strip_prefix('v')
            .ok_or_else(|| VaultError::crypto("Invalid version format".to_string()))?;

        let version: u64 = version_str
            .parse()
            .map_err(|e| VaultError::crypto(format!("Failed to parse version: {}", e)))?;

        let ciphertext = BASE64
            .decode(parts[2])
            .map_err(|e| VaultError::crypto(format!("Failed to decode ciphertext: {}", e)))?;

        let keys = self.keys.lock().await;
        let key = keys
            .get(key_name)
            .ok_or_else(|| VaultError::storage(format!("Key not found: {}", key_name)))?;

        if version < key.min_decrypt_version {
            return Err(VaultError::crypto(format!(
                "Key version {} is below minimum decrypt version {}",
                version, key.min_decrypt_version
            )));
        }

        let key_version = key
            .versions
            .get(&version)
            .ok_or_else(|| VaultError::crypto(format!("Key version {} not found", version)))?;

        let key_material = key_version.key_material.clone();
        drop(keys);

        self.crypto
            .decrypt_symmetric(&key_material, &ciphertext, SymmetricAlgorithm::Aes256Gcm)
            .await
            .map_err(|e| VaultError::crypto(e.to_string()))
    }

    /// Rewrap ciphertext under the current key version
    pub async fn rewrap(&self, key_name: &str, ciphertext_str: &str) -> Result<String> {
        let plaintext = self.decrypt(key_name, ciphertext_str).await?;
        self.encrypt(key_name, &plaintext).await
    }
}

#[async_trait]
impl Engine for TransitEngine {
    fn name(&self) -> &str {
        "transit"
    }

    fn engine_type(&self) -> &str {
        "transit"
    }

    async fn read(&self, path: &str) -> Result<Option<Value>> {
        if let Some(key_name) = path.strip_prefix("keys/") {
            let keys = self.keys.lock().await;
            if let Some(key) = keys.get(key_name) {
                return Ok(Some(json!({
                    "name": key.name,
                    "current_version": key.current_version,
                    "min_decrypt_version": key.min_decrypt_version,
                })));
            }
        }

        Ok(None)
    }

    async fn write(&self, path: &str, data: &Value) -> Result<()> {
        if let Some(key_name) = path.strip_prefix("encrypt/") {
            let plaintext = data
                .get("plaintext")
                .and_then(|v| v.as_str())
                .ok_or_else(|| VaultError::storage("Missing 'plaintext' in request".to_string()))?;

            let _ciphertext = self.encrypt(key_name, plaintext.as_bytes()).await?;
            // Note: In a full implementation, this would return the ciphertext in the response
        } else if let Some(key_name) = path.strip_prefix("decrypt/") {
            let ciphertext = data
                .get("ciphertext")
                .and_then(|v| v.as_str())
                .ok_or_else(|| {
                    VaultError::storage("Missing 'ciphertext' in request".to_string())
                })?;

            let _plaintext = self.decrypt(key_name, ciphertext).await?;
            // Note: In a full implementation, this would return the plaintext in the response
        } else if let Some(key_name) = path.strip_prefix("rewrap/") {
            let ciphertext = data
                .get("ciphertext")
                .and_then(|v| v.as_str())
                .ok_or_else(|| {
                    VaultError::storage("Missing 'ciphertext' in request".to_string())
                })?;

            let _new_ciphertext = self.rewrap(key_name, ciphertext).await?;
            // Note: In a full implementation, this would return the new ciphertext in the response
        }

        Ok(())
    }

    async fn delete(&self, path: &str) -> Result<()> {
        if let Some(key_name) = path.strip_prefix("keys/") {
            let mut keys = self.keys.lock().await;
            keys.remove(key_name);
        }

        Ok(())
    }

    async fn list(&self, prefix: &str) -> Result<Vec<String>> {
        let keys = self.keys.lock().await;
        let mut result = Vec::new();

        for key_name in keys.keys() {
            if key_name.starts_with(prefix) {
                result.push(key_name.clone());
            }
        }

        Ok(result)
    }

    async fn health_check(&self) -> Result<()> {
        self.storage
            .health_check()
            .await
            .map_err(|e| VaultError::storage(e.to_string()))?;

        let seal = self.seal.lock().await;
        if seal.is_sealed() {
            return Err(VaultError::crypto("Vault is sealed".to_string()));
        }

        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::{FilesystemStorageConfig, SealConfig, ShamirSealConfig, StorageConfig};
    use crate::crypto::CryptoRegistry;
    use crate::storage::StorageRegistry;
    use tempfile::TempDir;

    async fn setup_engine() -> Result<(TransitEngine, TempDir)> {
        let temp_dir = TempDir::new().map_err(|e| VaultError::storage(e.to_string()))?;

        let fs_config = FilesystemStorageConfig {
            path: temp_dir.path().to_path_buf(),
        };
        let storage_config = StorageConfig {
            backend: "filesystem".to_string(),
            filesystem: fs_config,
            surrealdb: Default::default(),
            etcd: Default::default(),
            postgresql: Default::default(),
        };

        let storage = StorageRegistry::create(&storage_config).await?;
        let crypto = CryptoRegistry::create("openssl", &Default::default())?;

        let seal_config = SealConfig {
            seal_type: "shamir".to_string(),
            shamir: ShamirSealConfig {
                threshold: 2,
                shares: 3,
            },
            auto_unseal: Default::default(),
        };
        let mut seal = crate::core::SealMechanism::new(&seal_config)?;

        // Initialize and unseal for testing
        let _init_result = seal.init(crypto.as_ref(), storage.as_ref()).await?;

        let seal_arc = Arc::new(tokio::sync::Mutex::new(seal));

        let engine = TransitEngine::new(storage, crypto.clone(), seal_arc, "transit/".to_string());

        Ok((engine, temp_dir))
    }

    #[allow(dead_code)]
    fn mock_key_name() -> String {
        "my-key".to_string()
    }

    #[tokio::test]
    async fn test_transit_encrypt_decrypt() -> Result<()> {
        let (engine, _temp) = setup_engine().await?;

        let plaintext = b"sensitive data";
        engine.create_key("my-key", vec![0x42; 32]).await?;

        let ciphertext = engine.encrypt("my-key", plaintext).await?;
        assert!(ciphertext.starts_with("vault:v"));

        let decrypted = engine.decrypt("my-key", &ciphertext).await?;
        assert_eq!(decrypted, plaintext);

        Ok(())
    }

    #[tokio::test]
    async fn test_transit_key_rotation() -> Result<()> {
        let (engine, _temp) = setup_engine().await?;

        engine.create_key("my-key", vec![0x11; 32]).await?;
        let ct1 = engine.encrypt("my-key", b"data v1").await?;

        // Rotate key
        engine.create_key("my-key", vec![0x22; 32]).await?;
        let ct2 = engine.encrypt("my-key", b"data v2").await?;

        // Should use different versions
        assert!(ct1.contains(":v1:"));
        assert!(ct2.contains(":v2:"));

        Ok(())
    }

    #[tokio::test]
    async fn test_transit_rewrap() -> Result<()> {
        let (engine, _temp) = setup_engine().await?;

        engine.create_key("my-key", vec![0x42; 32]).await?;
        let ct1 = engine.encrypt("my-key", b"test data").await?;

        // Rotate and rewrap
        engine.create_key("my-key", vec![0x99; 32]).await?;
        let ct2 = engine.rewrap("my-key", &ct1).await?;

        // Rewrapped should use new version
        assert!(ct2.contains(":v2:"));

        Ok(())
    }

    #[tokio::test]
    async fn test_transit_invalid_ciphertext() -> Result<()> {
        let (engine, _temp) = setup_engine().await?;

        engine.create_key("my-key", vec![0x42; 32]).await?;

        let result = engine.decrypt("my-key", "invalid:format").await;
        assert!(result.is_err());

        Ok(())
    }

    #[tokio::test]
    async fn test_transit_health_check() -> Result<()> {
        let (engine, _temp) = setup_engine().await?;
        engine.health_check().await?;
        Ok(())
    }
}