"""
Unified Error Handling Module

This module provides:
- Custom exception classes for different error types
- Global exception handlers for Flask
- Unified error response format
- Error logging with timestamp, context, and stack trace

Requirements:
    - 8.1: Log errors with timestamp, context, and stack trace
    - 8.5: Gracefully handle critical errors without crashing
"""

import traceback
import logging
from datetime import datetime, timezone
from functools import wraps
from typing import Optional, Dict, Any

from flask import jsonify, request, current_app

# Configure module logger
logger = logging.getLogger(__name__)


# ==================== Error Codes ====================

class ErrorCode:
    """Standardized error codes for the application"""
    # Authentication errors (401)
    AUTHENTICATION_FAILED = 'AUTHENTICATION_FAILED'
    TOKEN_EXPIRED = 'TOKEN_EXPIRED'
    TOKEN_INVALID = 'TOKEN_INVALID'
    
    # Authorization errors (403)
    ACCESS_DENIED = 'ACCESS_DENIED'
    INSUFFICIENT_PERMISSIONS = 'INSUFFICIENT_PERMISSIONS'
    
    # Validation errors (400)
    VALIDATION_ERROR = 'VALIDATION_ERROR'
    MISSING_REQUIRED_FIELD = 'MISSING_REQUIRED_FIELD'
    INVALID_FIELD_FORMAT = 'INVALID_FIELD_FORMAT'
    
    # Resource errors (404)
    RESOURCE_NOT_FOUND = 'RESOURCE_NOT_FOUND'
    USER_NOT_FOUND = 'USER_NOT_FOUND'
    CREDENTIAL_NOT_FOUND = 'CREDENTIAL_NOT_FOUND'
    TASK_NOT_FOUND = 'TASK_NOT_FOUND'
    REPORT_NOT_FOUND = 'REPORT_NOT_FOUND'
    
    # AWS errors
    AWS_CREDENTIAL_INVALID = 'AWS_CREDENTIAL_INVALID'
    AWS_API_ERROR = 'AWS_API_ERROR'
    AWS_RATE_LIMITED = 'AWS_RATE_LIMITED'
    AWS_ACCESS_DENIED = 'AWS_ACCESS_DENIED'
    
    # System errors (500)
    INTERNAL_ERROR = 'INTERNAL_ERROR'
    DATABASE_ERROR = 'DATABASE_ERROR'
    FILE_SYSTEM_ERROR = 'FILE_SYSTEM_ERROR'
    WORKER_ERROR = 'WORKER_ERROR'
    
    # Task errors
    TASK_EXECUTION_ERROR = 'TASK_EXECUTION_ERROR'
    TASK_TIMEOUT = 'TASK_TIMEOUT'
    SCAN_ERROR = 'SCAN_ERROR'
    REPORT_GENERATION_ERROR = 'REPORT_GENERATION_ERROR'


# ==================== Custom Exception Classes ====================

class AppError(Exception):
    """
    Base application error class.
    
    All custom exceptions should inherit from this class.
    Provides consistent error structure with code, message, status_code, and details.
    """
    
    def __init__(
        self,
        message: str,
        code: str = ErrorCode.INTERNAL_ERROR,
        status_code: int = 400,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None
    ):
        super().__init__(message)
        self.message = message
        self.code = code
        self.status_code = status_code
        self.details = details or {}
        self.original_exception = original_exception
        self.timestamp = datetime.now(timezone.utc)
        
        # Capture stack trace if original exception provided
        if original_exception:
            self.stack_trace = traceback.format_exception(
                type(original_exception),
                original_exception,
                original_exception.__traceback__
            )
        else:
            self.stack_trace = traceback.format_stack()
    
    def to_dict(self) -> Dict[str, Any]:
        """Convert error to dictionary for JSON response"""
        error_dict = {
            'code': self.code,
            'message': self.message,
            'timestamp': self.timestamp.isoformat()
        }
        if self.details:
            error_dict['details'] = self.details
        return error_dict
    
    def to_log_dict(self) -> Dict[str, Any]:
        """Convert error to dictionary for logging (includes stack trace)"""
        log_dict = self.to_dict()
        log_dict['status_code'] = self.status_code
        log_dict['stack_trace'] = ''.join(self.stack_trace) if self.stack_trace else None
        return log_dict


class AuthenticationError(AppError):
    """Authentication related errors (401)"""
    
    def __init__(
        self,
        message: str = "Authentication failed",
        code: str = ErrorCode.AUTHENTICATION_FAILED,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None
    ):
        super().__init__(
            message=message,
            code=code,
            status_code=401,
            details=details,
            original_exception=original_exception
        )


class AuthorizationError(AppError):
    """Authorization related errors (403)"""
    
    def __init__(
        self,
        message: str = "Access denied",
        code: str = ErrorCode.ACCESS_DENIED,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None
    ):
        super().__init__(
            message=message,
            code=code,
            status_code=403,
            details=details,
            original_exception=original_exception
        )


class NotFoundError(AppError):
    """Resource not found errors (404)"""
    
    def __init__(
        self,
        message: str = "Resource not found",
        code: str = ErrorCode.RESOURCE_NOT_FOUND,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None
    ):
        super().__init__(
            message=message,
            code=code,
            status_code=404,
            details=details,
            original_exception=original_exception
        )


class ValidationError(AppError):
    """Validation errors (400)"""
    
    def __init__(
        self,
        message: str = "Validation failed",
        code: str = ErrorCode.VALIDATION_ERROR,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None
    ):
        super().__init__(
            message=message,
            code=code,
            status_code=400,
            details=details,
            original_exception=original_exception
        )


class AWSError(AppError):
    """AWS related errors"""
    
    def __init__(
        self,
        message: str = "AWS operation failed",
        code: str = ErrorCode.AWS_API_ERROR,
        status_code: int = 500,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None
    ):
        super().__init__(
            message=message,
            code=code,
            status_code=status_code,
            details=details,
            original_exception=original_exception
        )


class DatabaseError(AppError):
    """Database related errors"""
    
    def __init__(
        self,
        message: str = "Database operation failed",
        code: str = ErrorCode.DATABASE_ERROR,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None
    ):
        super().__init__(
            message=message,
            code=code,
            status_code=500,
            details=details,
            original_exception=original_exception
        )


class TaskError(AppError):
    """Task execution related errors"""
    
    def __init__(
        self,
        message: str = "Task execution failed",
        code: str = ErrorCode.TASK_EXECUTION_ERROR,
        status_code: int = 500,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None,
        task_id: Optional[int] = None
    ):
        if task_id:
            details = details or {}
            details['task_id'] = task_id
        super().__init__(
            message=message,
            code=code,
            status_code=status_code,
            details=details,
            original_exception=original_exception
        )
        self.task_id = task_id


class ScanError(TaskError):
    """Scan operation related errors"""
    
    def __init__(
        self,
        message: str = "Scan operation failed",
        code: str = ErrorCode.SCAN_ERROR,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None,
        task_id: Optional[int] = None,
        service: Optional[str] = None,
        region: Optional[str] = None
    ):
        details = details or {}
        if service:
            details['service'] = service
        if region:
            details['region'] = region
        super().__init__(
            message=message,
            code=code,
            status_code=500,
            details=details,
            original_exception=original_exception,
            task_id=task_id
        )
        self.service = service
        self.region = region


class ReportGenerationError(TaskError):
    """Report generation related errors"""
    
    def __init__(
        self,
        message: str = "Report generation failed",
        code: str = ErrorCode.REPORT_GENERATION_ERROR,
        details: Optional[Dict[str, Any]] = None,
        original_exception: Optional[Exception] = None,
        task_id: Optional[int] = None
    ):
        super().__init__(
            message=message,
            code=code,
            status_code=500,
            details=details,
            original_exception=original_exception,
            task_id=task_id
        )


# ==================== Error Logging Utilities ====================

def log_error(
    error: Exception,
    context: Optional[Dict[str, Any]] = None,
    level: str = 'error'
) -> Dict[str, Any]:
    """
    Log an error with full context and stack trace.
    
    Requirements:
        - 8.1: Log errors with timestamp, context, and stack trace
    
    Args:
        error: The exception to log
        context: Additional context information
        level: Log level ('error', 'warning', 'critical')
    
    Returns:
        Dictionary containing the logged error information
    """
    timestamp = datetime.now(timezone.utc)
    
    # Build error log entry
    log_entry = {
        'timestamp': timestamp.isoformat(),
        'error_type': type(error).__name__,
        'message': str(error),
        'context': context or {}
    }
    
    # Add request context if available
    try:
        if request:
            log_entry['request'] = {
                'method': request.method,
                'path': request.path,
                'remote_addr': request.remote_addr,
                'user_agent': str(request.user_agent) if request.user_agent else None
            }
    except RuntimeError:
        # Outside of request context
        pass
    
    # Add stack trace
    if isinstance(error, AppError):
        log_entry['code'] = error.code
        log_entry['status_code'] = error.status_code
        log_entry['details'] = error.details
        log_entry['stack_trace'] = ''.join(error.stack_trace) if error.stack_trace else None
    else:
        log_entry['stack_trace'] = traceback.format_exc()
    
    # Log at appropriate level
    log_message = f"[{log_entry['error_type']}] {log_entry['message']}"
    if level == 'critical':
        logger.critical(log_message, extra={'error_details': log_entry})
    elif level == 'warning':
        logger.warning(log_message, extra={'error_details': log_entry})
    else:
        logger.error(log_message, extra={'error_details': log_entry})
    
    return log_entry


def create_error_response(
    code: str,
    message: str,
    status_code: int = 400,
    details: Optional[Dict[str, Any]] = None
) -> tuple:
    """
    Create a standardized error response.
    
    Args:
        code: Error code
        message: Human-readable error message
        status_code: HTTP status code
        details: Additional error details
    
    Returns:
        Tuple of (response_json, status_code)
    """
    response = {
        'error': {
            'code': code,
            'message': message,
            'timestamp': datetime.now(timezone.utc).isoformat()
        }
    }
    if details:
        response['error']['details'] = details
    
    return jsonify(response), status_code


# ==================== Error Handler Decorator ====================

def handle_errors(func):
    """
    Decorator to handle errors in route handlers.
    
    Catches exceptions and converts them to appropriate error responses.
    Logs all errors with full context.
    
    Requirements:
        - 8.5: Gracefully handle critical errors without crashing
    """
    @wraps(func)
    def wrapper(*args, **kwargs):
        try:
            return func(*args, **kwargs)
        except AppError as e:
            # Log the error
            log_error(e, context={'handler': func.__name__})
            # Return error response
            return jsonify({'error': e.to_dict()}), e.status_code
        except Exception as e:
            # Log unexpected error
            log_error(e, context={'handler': func.__name__}, level='critical')
            # Return generic error response
            return create_error_response(
                code=ErrorCode.INTERNAL_ERROR,
                message='An unexpected error occurred',
                status_code=500
            )
    return wrapper


# ==================== Global Error Handlers ====================

def register_error_handlers(app):
    """
    Register global error handlers for the Flask app.
    
    Requirements:
        - 8.5: Gracefully handle critical errors without crashing
    """
    
    @app.errorhandler(AppError)
    def handle_app_error(error):
        """Handle custom application errors"""
        log_error(error)
        return jsonify({'error': error.to_dict()}), error.status_code
    
    @app.errorhandler(400)
    def handle_bad_request(error):
        """Handle 400 Bad Request errors"""
        log_entry = log_error(error, context={'type': 'bad_request'}, level='warning')
        return create_error_response(
            code=ErrorCode.VALIDATION_ERROR,
            message='Bad request',
            status_code=400,
            details={'description': str(error.description) if hasattr(error, 'description') else None}
        )
    
    @app.errorhandler(401)
    def handle_unauthorized(error):
        """Handle 401 Unauthorized errors"""
        log_entry = log_error(error, context={'type': 'unauthorized'}, level='warning')
        return create_error_response(
            code=ErrorCode.AUTHENTICATION_FAILED,
            message='Authentication required',
            status_code=401
        )
    
    @app.errorhandler(403)
    def handle_forbidden(error):
        """Handle 403 Forbidden errors"""
        log_entry = log_error(error, context={'type': 'forbidden'}, level='warning')
        return create_error_response(
            code=ErrorCode.ACCESS_DENIED,
            message='Access denied',
            status_code=403
        )
    
    @app.errorhandler(404)
    def handle_not_found(error):
        """Handle 404 Not Found errors"""
        log_entry = log_error(error, context={'type': 'not_found'}, level='warning')
        return create_error_response(
            code=ErrorCode.RESOURCE_NOT_FOUND,
            message='Resource not found',
            status_code=404
        )
    
    @app.errorhandler(405)
    def handle_method_not_allowed(error):
        """Handle 405 Method Not Allowed errors"""
        log_entry = log_error(error, context={'type': 'method_not_allowed'}, level='warning')
        return create_error_response(
            code='METHOD_NOT_ALLOWED',
            message='Method not allowed',
            status_code=405
        )
    
    @app.errorhandler(500)
    def handle_internal_error(error):
        """Handle 500 Internal Server errors"""
        log_entry = log_error(error, context={'type': 'internal_error'}, level='critical')
        return create_error_response(
            code=ErrorCode.INTERNAL_ERROR,
            message='An internal error occurred',
            status_code=500
        )
    
    @app.errorhandler(Exception)
    def handle_unexpected_error(error):
        """
        Handle any unexpected exceptions.
        
        Requirements:
            - 8.5: Gracefully handle critical errors without crashing
        """
        log_entry = log_error(error, context={'type': 'unexpected'}, level='critical')
        return create_error_response(
            code=ErrorCode.INTERNAL_ERROR,
            message='An unexpected error occurred',
            status_code=500
        )


# ==================== Task Error Logging ====================

class TaskErrorLogger:
    """
    Utility class for logging errors associated with tasks.
    
    Requirements:
        - 8.2: Record error details in task record
        - 8.3: Display error logs associated with task
    """
    
    @staticmethod
    def log_task_error(
        task_id: int,
        error: Exception,
        service: Optional[str] = None,
        region: Optional[str] = None,
        context: Optional[Dict[str, Any]] = None
    ) -> None:
        """
        Log an error for a specific task.
        
        Args:
            task_id: The task ID to associate the error with
            error: The exception that occurred
            service: Optional AWS service name
            region: Optional AWS region
            context: Additional context information
        """
        from app import db
        from app.models import TaskLog
        import json
        
        # Build error details
        details = {
            'error_type': type(error).__name__,
            'timestamp': datetime.now(timezone.utc).isoformat()
        }
        
        if service:
            details['service'] = service
        if region:
            details['region'] = region
        if context:
            details['context'] = context
        
        # Add stack trace
        if isinstance(error, AppError):
            details['code'] = error.code
            details['stack_trace'] = ''.join(error.stack_trace) if error.stack_trace else None
        else:
            details['stack_trace'] = traceback.format_exc()
        
        # Create task log entry
        log_entry = TaskLog(
            task_id=task_id,
            level='error',
            message=str(error),
            details=json.dumps(details)
        )
        
        db.session.add(log_entry)
        db.session.commit()
        
        # Also log to application logger
        log_error(error, context={'task_id': task_id, 'service': service, 'region': region})
    
    @staticmethod
    def log_task_warning(
        task_id: int,
        message: str,
        details: Optional[Dict[str, Any]] = None
    ) -> None:
        """Log a warning for a specific task"""
        from app import db
        from app.models import TaskLog
        import json
        
        log_entry = TaskLog(
            task_id=task_id,
            level='warning',
            message=message,
            details=json.dumps(details) if details else None
        )
        
        db.session.add(log_entry)
        db.session.commit()
    
    @staticmethod
    def log_task_info(
        task_id: int,
        message: str,
        details: Optional[Dict[str, Any]] = None
    ) -> None:
        """Log an info message for a specific task"""
        from app import db
        from app.models import TaskLog
        import json
        
        log_entry = TaskLog(
            task_id=task_id,
            level='info',
            message=message,
            details=json.dumps(details) if details else None
        )
        
        db.session.add(log_entry)
        db.session.commit()
    
    @staticmethod
    def get_task_errors(task_id: int) -> list:
        """
        Get all error logs for a specific task.
        
        Requirements:
            - 8.3: Display error logs associated with task
        """
        from app.models import TaskLog
        
        logs = TaskLog.query.filter_by(
            task_id=task_id,
            level='error'
        ).order_by(TaskLog.created_at.desc()).all()
        
        return [log.to_dict() for log in logs]
    
    @staticmethod
    def get_task_logs(
        task_id: int,
        level: Optional[str] = None,
        page: int = 1,
        page_size: int = 20
    ) -> Dict[str, Any]:
        """
        Get paginated logs for a specific task.
        
        Args:
            task_id: The task ID
            level: Optional filter by log level
            page: Page number
            page_size: Number of items per page
        
        Returns:
            Dictionary with logs and pagination info
        """
        from app.models import TaskLog
        
        query = TaskLog.query.filter_by(task_id=task_id)
        
        if level:
            query = query.filter_by(level=level)
        
        query = query.order_by(TaskLog.created_at.desc())
        
        # Paginate
        total = query.count()
        logs = query.offset((page - 1) * page_size).limit(page_size).all()
        
        return {
            'data': [log.to_dict() for log in logs],
            'pagination': {
                'page': page,
                'page_size': page_size,
                'total': total,
                'total_pages': (total + page_size - 1) // page_size
            }
        }