"""
JWT Authentication Service

Provides JWT token generation, validation, and authentication decorators.
"""
import jwt
from datetime import datetime, timedelta, timezone
from functools import wraps
from typing import Optional, Tuple, Dict, Any

from flask import request, current_app, g

from app import db
from app.models import User
from app.errors import AuthenticationError, AuthorizationError


class AuthService:
    """Service for handling JWT authentication"""
    
    @staticmethod
    def generate_access_token(user: User) -> str:
        """Generate a JWT access token for a user"""
        now = datetime.now(timezone.utc)
        expires = now + current_app.config['JWT_ACCESS_TOKEN_EXPIRES']
        payload = {
            'user_id': user.id,
            'username': user.username,
            'role': user.role,
            'type': 'access',
            'exp': expires,
            'iat': now
        }
        return jwt.encode(
            payload,
            current_app.config['JWT_SECRET_KEY'],
            algorithm='HS256'
        )
    
    @staticmethod
    def generate_refresh_token(user: User) -> str:
        """Generate a JWT refresh token for a user"""
        now = datetime.now(timezone.utc)
        expires = now + current_app.config['JWT_REFRESH_TOKEN_EXPIRES']
        payload = {
            'user_id': user.id,
            'type': 'refresh',
            'exp': expires,
            'iat': now
        }
        return jwt.encode(
            payload,
            current_app.config['JWT_SECRET_KEY'],
            algorithm='HS256'
        )
    
    @staticmethod
    def generate_tokens(user: User) -> Dict[str, str]:
        """Generate both access and refresh tokens"""
        return {
            'access_token': AuthService.generate_access_token(user),
            'refresh_token': AuthService.generate_refresh_token(user)
        }
    
    @staticmethod
    def decode_token(token: str) -> Dict[str, Any]:
        """
        Decode and validate a JWT token
        
        Raises:
            AuthenticationError: If token is invalid or expired
        """
        try:
            payload = jwt.decode(
                token,
                current_app.config['JWT_SECRET_KEY'],
                algorithms=['HS256']
            )
            return payload
        except jwt.ExpiredSignatureError:
            raise AuthenticationError(
                message="Token has expired",
                details={"reason": "token_expired"}
            )
        except jwt.InvalidTokenError as e:
            raise AuthenticationError(
                message="Invalid token",
                details={"reason": "invalid_token"}
            )
    
    @staticmethod
    def get_token_from_header() -> Optional[str]:
        """Extract JWT token from Authorization header"""
        auth_header = request.headers.get('Authorization', '')
        if auth_header.startswith('Bearer '):
            return auth_header[7:]
        return None
    
    @staticmethod
    def get_current_user() -> Optional[User]:
        """Get the current authenticated user from the request"""
        token = AuthService.get_token_from_header()
        if not token:
            return None
        
        try:
            payload = AuthService.decode_token(token)
            if payload.get('type') != 'access':
                return None
            
            user = db.session.get(User, payload['user_id'])
            if user and user.is_active:
                return user
            return None
        except AuthenticationError:
            return None
    
    @staticmethod
    def authenticate(username: str, password: str) -> Tuple[User, Dict[str, str]]:
        """
        Authenticate a user with username and password
        
        Returns:
            Tuple of (User, tokens dict)
            
        Raises:
            AuthenticationError: If credentials are invalid
        """
        user = User.query.filter_by(username=username).first()
        
        if not user or not user.check_password(password):
            raise AuthenticationError(
                message="Invalid username or password",
                details={"reason": "invalid_credentials"}
            )
        
        if not user.is_active:
            raise AuthenticationError(
                message="User account is disabled",
                details={"reason": "account_disabled"}
            )
        
        tokens = AuthService.generate_tokens(user)
        return user, tokens
    
    @staticmethod
    def refresh_access_token(refresh_token: str) -> Dict[str, str]:
        """
        Generate a new access token using a refresh token
        
        Returns:
            Dict with new access_token
            
        Raises:
            AuthenticationError: If refresh token is invalid
        """
        payload = AuthService.decode_token(refresh_token)
        
        if payload.get('type') != 'refresh':
            raise AuthenticationError(
                message="Invalid token type",
                details={"reason": "not_refresh_token"}
            )
        
        user = db.session.get(User, payload['user_id'])
        if not user or not user.is_active:
            raise AuthenticationError(
                message="User not found or inactive",
                details={"reason": "user_invalid"}
            )
        
        return {
            'access_token': AuthService.generate_access_token(user)
        }


def login_required(f):
    """Decorator to require authentication for a route"""
    @wraps(f)
    def decorated_function(*args, **kwargs):
        token = AuthService.get_token_from_header()
        
        if not token:
            raise AuthenticationError(
                message="Authentication required",
                details={"reason": "missing_token"}
            )
        
        payload = AuthService.decode_token(token)
        
        if payload.get('type') != 'access':
            raise AuthenticationError(
                message="Invalid token type",
                details={"reason": "not_access_token"}
            )
        
        user = db.session.get(User, payload['user_id'])
        if not user:
            raise AuthenticationError(
                message="User not found",
                details={"reason": "user_not_found"}
            )
        
        if not user.is_active:
            raise AuthenticationError(
                message="User account is disabled",
                details={"reason": "account_disabled"}
            )
        
        # Store user in flask g object for access in route
        g.current_user = user
        return f(*args, **kwargs)
    
    return decorated_function


def get_current_user_from_context() -> User:
    """Get the current user from Flask g context (use after login_required)"""
    return getattr(g, 'current_user', None)


def admin_required(f):
    """
    Decorator to require admin role for a route.
    Must be used after @login_required.
    """
    @wraps(f)
    def decorated_function(*args, **kwargs):
        token = AuthService.get_token_from_header()
        
        if not token:
            raise AuthenticationError(
                message="Authentication required",
                details={"reason": "missing_token"}
            )
        
        payload = AuthService.decode_token(token)
        
        if payload.get('type') != 'access':
            raise AuthenticationError(
                message="Invalid token type",
                details={"reason": "not_access_token"}
            )
        
        user = db.session.get(User, payload['user_id'])
        if not user:
            raise AuthenticationError(
                message="User not found",
                details={"reason": "user_not_found"}
            )
        
        if not user.is_active:
            raise AuthenticationError(
                message="User account is disabled",
                details={"reason": "account_disabled"}
            )
        
        if user.role != 'admin':
            raise AuthorizationError(
                message="Admin access required",
                details={"reason": "insufficient_permissions", "required_role": "admin"}
            )
        
        g.current_user = user
        return f(*args, **kwargs)
    
    return decorated_function


def power_user_required(f):
    """
    Decorator to require power_user or admin role for a route.
    Must be used after @login_required.
    """
    @wraps(f)
    def decorated_function(*args, **kwargs):
        token = AuthService.get_token_from_header()
        
        if not token:
            raise AuthenticationError(
                message="Authentication required",
                details={"reason": "missing_token"}
            )
        
        payload = AuthService.decode_token(token)
        
        if payload.get('type') != 'access':
            raise AuthenticationError(
                message="Invalid token type",
                details={"reason": "not_access_token"}
            )
        
        user = db.session.get(User, payload['user_id'])
        if not user:
            raise AuthenticationError(
                message="User not found",
                details={"reason": "user_not_found"}
            )
        
        if not user.is_active:
            raise AuthenticationError(
                message="User account is disabled",
                details={"reason": "account_disabled"}
            )
        
        if user.role not in ['admin', 'power_user']:
            raise AuthorizationError(
                message="Power user or admin access required",
                details={"reason": "insufficient_permissions", "required_role": "power_user"}
            )
        
        g.current_user = user
        return f(*args, **kwargs)
    
    return decorated_function


def check_resource_access(user: User, resource_owner_id: int) -> bool:
    """
    Check if a user has access to a resource based on ownership.
    
    - Admin: Can access all resources
    - Power User: Can access all resources
    - User: Can only access their own resources
    
    Args:
        user: The current user
        resource_owner_id: The ID of the resource owner
        
    Returns:
        True if access is allowed, False otherwise
    """
    if user.role in ['admin', 'power_user']:
        return True
    return user.id == resource_owner_id


def check_credential_access(user: User, credential_id: int) -> bool:
    """
    Check if a user has access to a specific credential.
    
    - Admin: Can access all credentials
    - Power User: Can access all credentials
    - User: Can only access assigned credentials
    
    Args:
        user: The current user
        credential_id: The ID of the credential
        
    Returns:
        True if access is allowed, False otherwise
    """
    if user.role in ['admin', 'power_user']:
        return True
    
    # Check if credential is assigned to user
    from app.models import UserCredential
    assignment = UserCredential.query.filter_by(
        user_id=user.id,
        credential_id=credential_id
    ).first()
    
    return assignment is not None


def get_accessible_credentials(user: User):
    """
    Get list of credentials accessible to a user.
    
    - Admin/Power User: All credentials
    - User: Only assigned credentials
    
    Args:
        user: The current user
        
    Returns:
        Query for accessible credentials
    """
    from app.models import AWSCredential, UserCredential
    
    if user.role in ['admin', 'power_user']:
        return AWSCredential.query.filter_by(is_active=True)
    
    # Get only assigned credentials for regular users
    return AWSCredential.query.join(UserCredential).filter(
        UserCredential.user_id == user.id,
        AWSCredential.is_active == True
    )


def get_accessible_reports(user: User):
    """
    Get list of reports accessible to a user.
    
    - Admin/Power User: All reports
    - User: Only their own reports
    
    Args:
        user: The current user
        
    Returns:
        Query for accessible reports
    """
    from app.models import Report, Task
    
    if user.role in ['admin', 'power_user']:
        return Report.query
    
    # Get only reports from user's own tasks
    return Report.query.join(Task).filter(Task.created_by == user.id)