"""
Encryption Utility for AegisLM

Provides AES-256 encryption for sensitive fields at rest.
"""

import base64
import hashlib
import os
from typing import Optional, Tuple

from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import padding

from security.secret_manager import get_encryption_key


class EncryptionService:
    """
    AES-256 encryption service for sensitive data at rest.
    
    Uses AES-256-CBC with PKCS7 padding.
    """
    
    _instance: Optional["EncryptionService"] = None
    
    def __new__(cls) -> "EncryptionService":
        """Singleton pattern for encryption service."""
        if cls._instance is None:
            cls._instance = super().__new__(cls)
        return cls._instance
    
    def __init__(self):
        """Initialize the encryption service."""
        if not hasattr(self, "_initialized"):
            self._key = self._derive_key(get_encryption_key())
            self._initialized = True
    
    def _derive_key(self, key_input: str) -> bytes:
        """
        Derive a 256-bit key from the input key.
        
        Args:
            key_input: Input key string
            
        Returns:
            32-byte derived key
        """
        # Use SHA-256 to derive a 32-byte key from the input
        return hashlib.sha256(key_input.encode()).digest()
    
    def _pad(self, data: bytes) -> bytes:
        """
        Pad data using PKCS7 padding.
        
        Args:
            data: Data to pad
            
        Returns:
            Padded data
        """
        padder = padding.PKCS7(algorithms.AES.block_size).padder()
        return padder.update(data) + padder.finalize()
    
    def _unpad(self, data: bytes) -> bytes:
        """
        Remove PKCS7 padding.
        
        Args:
            data: Padded data
            
        Returns:
            Unpadded data
        """
        unpadder = padding.PKCS7(algorithms.AES.block_size).unpadder()
        return unpadder.update(data) + unpadder.finalize()
    
    def encrypt(self, plaintext: str) -> str:
        """
        Encrypt plaintext using AES-256-CBC.
        
        Args:
            plaintext: Plain text to encrypt
            
        Returns:
            Base64-encoded ciphertext (IV + ciphertext)
        """
        # Generate random IV
        iv = os.urandom(16)
        
        # Create cipher
        cipher = Cipher(
            algorithms.AES(self._key),
            modes.CBC(iv),
            backend=default_backend()
        )
        encryptor = cipher.encryptor()
        
        # Pad and encrypt
        padded_data = self._pad(plaintext.encode("utf-8"))
        ciphertext = encryptor.update(padded_data) + encryptor.finalize()
        
        # Combine IV and ciphertext
        combined = iv + ciphertext
        
        # Return base64-encoded result
        return base64.b64encode(combined).decode("utf-8")
    
    def decrypt(self, ciphertext: str) -> str:
        """
        Decrypt ciphertext using AES-256-CBC.
        
        Args:
            ciphertext: Base64-encoded ciphertext (IV + ciphertext)
            
        Returns:
            Decrypted plaintext
        """
        # Decode from base64
        combined = base64.b64decode(ciphertext)
        
        # Extract IV and ciphertext
        iv = combined[:16]
        ciphertext = combined[16:]
        
        # Create cipher
        cipher = Cipher(
            algorithms.AES(self._key),
            modes.CBC(iv),
            backend=default_backend()
        )
        decryptor = cipher.decryptor()
        
        # Decrypt and unpad
        padded_data = decryptor.update(ciphertext) + decryptor.finalize()
        plaintext = self._unpad(padded_data)
        
        return plaintext.decode("utf-8")
    
    def encrypt_bytes(self, data: bytes) -> str:
        """
        Encrypt bytes data.
        
        Args:
            data: Bytes to encrypt
            
        Returns:
            Base64-encoded ciphertext
        """
        return self.encrypt(base64.b64encode(data).decode("utf-8"))
    
    def decrypt_bytes(self, ciphertext: str) -> bytes:
        """
        Decrypt to bytes.
        
        Args:
            ciphertext: Base64-encoded ciphertext
            
        Returns:
            Decrypted bytes
        """
        plaintext = self.decrypt(ciphertext)
        return base64.b64decode(plaintext)


def get_encryption_service() -> EncryptionService:
    """
    Get the singleton encryption service instance.
    
    Returns:
        EncryptionService instance
    """
    return EncryptionService()


# Convenience functions
def encrypt(plaintext: str) -> str:
    """Encrypt plaintext."""
    return get_encryption_service().encrypt(plaintext)


def decrypt(ciphertext: str) -> str:
    """Decrypt ciphertext."""
    return get_encryption_service().decrypt(ciphertext)


# =============================================================================
# Password hashing (using bcrypt)
# =============================================================================

def hash_password(password: str) -> str:
    """
    Hash a password using bcrypt.
    
    Args:
        password: Plain text password
        
    Returns:
        bcrypt hash
    """
    import bcrypt
    return bcrypt.hashpw(password.encode("utf-8"), bcrypt.gensalt()).decode("utf-8")


def verify_password(password: str, hashed: str) -> bool:
    """
    Verify a password against a bcrypt hash.
    
    Args:
        password: Plain text password
        hashed: bcrypt hash
        
    Returns:
        True if password matches
    """
    import bcrypt
    try:
        return bcrypt.checkpw(password.encode("utf-8"), hashed.encode("utf-8"))
    except Exception:
        return False