"""
Base Service Layer

This module provides base service classes for implementing business logic.
All services should inherit from these base classes.
"""

from typing import Optional, Dict, Any, List, TypeVar, Generic
from abc import ABC, abstractmethod
import logging
from datetime import datetime
from contextlib import contextmanager

from ..config.settings import Settings, get_settings
from ..repositories.base import BaseRepository, RepositoryException

logger = logging.getLogger(__name__)

T = TypeVar('T')


class ServiceException(Exception):
    """Base exception for service layer errors"""
    pass


class ValidationError(ServiceException):
    """Raised when validation fails"""
    def __init__(self, message: str, errors: Optional[Dict[str, Any]] = None):
        super().__init__(message)
        self.errors = errors or {}


class BusinessRuleViolation(ServiceException):
    """Raised when a business rule is violated"""
    pass


class ResourceNotFoundError(ServiceException):
    """Raised when a requested resource is not found"""
    pass


class ResourceConflictError(ServiceException):
    """Raised when there's a conflict with existing resources"""
    pass


class BaseService(ABC):
    """
    Base service class providing common functionality for all services.

    Services encapsulate business logic and coordinate between repositories,
    external services, and other components.
    """

    def __init__(self, settings: Optional[Settings] = None):
        """
        Initialize service.

        Args:
            settings: Application settings
        """
        self.settings = settings or get_settings()
        self._logger = logging.getLogger(self.__class__.__name__)

    @property
    def logger(self) -> logging.Logger:
        """Get logger for this service"""
        return self._logger

    def log_info(self, message: str, **kwargs):
        """Log info message with context"""
        self._logger.info(message, extra=kwargs)

    def log_error(self, message: str, error: Optional[Exception] = None, **kwargs):
        """Log error message with context"""
        if error:
            self._logger.error(f"{message}: {str(error)}", exc_info=True, extra=kwargs)
        else:
            self._logger.error(message, extra=kwargs)

    def log_warning(self, message: str, **kwargs):
        """Log warning message with context"""
        self._logger.warning(message, extra=kwargs)

    def log_debug(self, message: str, **kwargs):
        """Log debug message with context"""
        self._logger.debug(message, extra=kwargs)

    @contextmanager
    def handle_errors(self, operation: str = "operation"):
        """
        Context manager for handling service errors.

        Args:
            operation: Description of the operation being performed

        Usage:
            with self.handle_errors("creating user"):
                # Service logic here
                pass
        """
        try:
            yield
        except ValidationError:
            raise
        except BusinessRuleViolation:
            raise
        except ResourceNotFoundError:
            raise
        except ResourceConflictError:
            raise
        except RepositoryException as e:
            self.log_error(f"Repository error during {operation}", e)
            raise ServiceException(f"Database error during {operation}: {str(e)}")
        except Exception as e:
            self.log_error(f"Unexpected error during {operation}", e)
            raise ServiceException(f"Unexpected error during {operation}: {str(e)}")

    def validate_required_fields(self, data: Dict[str, Any], required_fields: List[str]):
        """
        Validate that required fields are present and not empty.

        Args:
            data: Data dictionary to validate
            required_fields: List of required field names

        Raises:
            ValidationError: If validation fails
        """
        errors = {}
        for field in required_fields:
            if field not in data or data[field] is None:
                errors[field] = f"{field} is required"
            elif isinstance(data[field], str) and not data[field].strip():
                errors[field] = f"{field} cannot be empty"

        if errors:
            raise ValidationError("Validation failed", errors)

    def validate_field_types(self, data: Dict[str, Any], field_types: Dict[str, type]):
        """
        Validate field types.

        Args:
            data: Data dictionary to validate
            field_types: Dictionary mapping field names to expected types

        Raises:
            ValidationError: If validation fails
        """
        errors = {}
        for field, expected_type in field_types.items():
            if field in data and data[field] is not None:
                if not isinstance(data[field], expected_type):
                    errors[field] = f"{field} must be of type {expected_type.__name__}"

        if errors:
            raise ValidationError("Type validation failed", errors)

    def validate_field_values(self, data: Dict[str, Any], field_validators: Dict[str, callable]):
        """
        Validate field values using custom validators.

        Args:
            data: Data dictionary to validate
            field_validators: Dictionary mapping field names to validator functions

        Raises:
            ValidationError: If validation fails
        """
        errors = {}
        for field, validator in field_validators.items():
            if field in data and data[field] is not None:
                try:
                    if not validator(data[field]):
                        errors[field] = f"{field} validation failed"
                except Exception as e:
                    errors[field] = str(e)

        if errors:
            raise ValidationError("Value validation failed", errors)

    def sanitize_input(self, data: Dict[str, Any]) -> Dict[str, Any]:
        """
        Sanitize input data.

        Args:
            data: Input data to sanitize

        Returns:
            Sanitized data
        """
        sanitized = {}
        for key, value in data.items():
            if isinstance(value, str):
                # Strip whitespace
                value = value.strip()
                # Remove null bytes
                value = value.replace('\x00', '')
            sanitized[key] = value
        return sanitized

    def audit_log(
        self,
        action: str,
        entity_type: str,
        entity_id: Optional[Any] = None,
        user: Optional[str] = None,
        details: Optional[Dict[str, Any]] = None
    ):
        """
        Create an audit log entry.

        Args:
            action: Action performed (e.g., "create", "update", "delete")
            entity_type: Type of entity affected
            entity_id: ID of the affected entity
            user: User who performed the action
            details: Additional details about the action
        """
        log_entry = {
            "timestamp": datetime.utcnow().isoformat(),
            "action": action,
            "entity_type": entity_type,
            "entity_id": entity_id,
            "user": user,
            "details": details
        }
        self.log_info(f"Audit: {action} {entity_type}", **log_entry)


class CRUDService(BaseService, Generic[T]):
    """
    Base service class for CRUD operations.

    This class provides standard CRUD operations with business logic validation.
    """

    def __init__(
        self,
        repository: BaseRepository[T],
        settings: Optional[Settings] = None
    ):
        """
        Initialize CRUD service.

        Args:
            repository: Repository for data access
            settings: Application settings
        """
        super().__init__(settings)
        self.repository = repository

    def create(
        self,
        data: Dict[str, Any],
        user: Optional[str] = None,
        validate: bool = True
    ) -> T:
        """
        Create a new entity.

        Args:
            data: Entity data
            user: User performing the action
            validate: Whether to validate data

        Returns:
            Created entity

        Raises:
            ValidationError: If validation fails
            ServiceException: If creation fails
        """
        with self.handle_errors("creating entity"):
            if validate:
                self.validate_create(data)

            # Sanitize input
            data = self.sanitize_input(data)

            # Create entity
            entity = self._create_entity_from_data(data)
            entity = self.repository.create(entity)

            # Audit log
            self.audit_log(
                action="create",
                entity_type=entity.__class__.__name__,
                entity_id=entity.id,
                user=user,
                details={"data": data}
            )

            return entity

    def update(
        self,
        id: Any,
        data: Dict[str, Any],
        user: Optional[str] = None,
        validate: bool = True,
        partial: bool = True
    ) -> T:
        """
        Update an existing entity.

        Args:
            id: Entity ID
            data: Update data
            user: User performing the action
            validate: Whether to validate data
            partial: Whether this is a partial update

        Returns:
            Updated entity

        Raises:
            ResourceNotFoundError: If entity not found
            ValidationError: If validation fails
            ServiceException: If update fails
        """
        with self.handle_errors("updating entity"):
            # Get existing entity
            entity = self.repository.get(id)
            if not entity:
                raise ResourceNotFoundError(f"Entity with id {id} not found")

            if validate:
                self.validate_update(data, entity, partial)

            # Sanitize input
            data = self.sanitize_input(data)

            # Update entity
            self._update_entity_from_data(entity, data)
            entity = self.repository.update(entity)

            # Audit log
            self.audit_log(
                action="update",
                entity_type=entity.__class__.__name__,
                entity_id=entity.id,
                user=user,
                details={"data": data}
            )

            return entity

    def delete(
        self,
        id: Any,
        user: Optional[str] = None,
        soft: bool = True
    ) -> bool:
        """
        Delete an entity.

        Args:
            id: Entity ID
            user: User performing the action
            soft: Whether to perform soft delete

        Returns:
            True if deleted successfully

        Raises:
            ResourceNotFoundError: If entity not found
            ServiceException: If deletion fails
        """
        with self.handle_errors("deleting entity"):
            # Get existing entity
            entity = self.repository.get(id)
            if not entity:
                raise ResourceNotFoundError(f"Entity with id {id} not found")

            # Validate deletion
            self.validate_delete(entity)

            # Delete entity
            if soft and hasattr(entity, 'soft_delete'):
                entity.soft_delete()
                self.repository.update(entity)
                action = "soft_delete"
            else:
                self.repository.delete(entity)
                action = "delete"

            # Audit log
            self.audit_log(
                action=action,
                entity_type=entity.__class__.__name__,
                entity_id=id,
                user=user
            )

            return True

    def get(self, id: Any) -> Optional[T]:
        """
        Get an entity by ID.

        Args:
            id: Entity ID

        Returns:
            Entity or None if not found
        """
        with self.handle_errors("getting entity"):
            return self.repository.get(id)

    def get_or_404(self, id: Any) -> T:
        """
        Get an entity by ID or raise error.

        Args:
            id: Entity ID

        Returns:
            Entity

        Raises:
            ResourceNotFoundError: If entity not found
        """
        entity = self.get(id)
        if not entity:
            raise ResourceNotFoundError(f"Entity with id {id} not found")
        return entity

    def list(
        self,
        filters: Optional[Dict[str, Any]] = None,
        page: int = 1,
        page_size: int = 20,
        order_by: Optional[str] = None,
        order_desc: bool = False
    ) -> Dict[str, Any]:
        """
        List entities with pagination.

        Args:
            filters: Filter criteria
            page: Page number (1-based)
            page_size: Number of items per page
            order_by: Field to order by
            order_desc: Whether to order descending

        Returns:
            Dictionary with items and pagination info
        """
        with self.handle_errors("listing entities"):
            # Calculate offset
            offset = (page - 1) * page_size

            # Get total count
            total = self.repository.count(**(filters or {}))

            # Get items
            items = self.repository.find_all(
                filters=filters,
                limit=page_size,
                offset=offset,
                order_by=order_by,
                order_desc=order_desc
            )

            # Calculate pagination info
            total_pages = (total + page_size - 1) // page_size

            return {
                "items": items,
                "pagination": {
                    "page": page,
                    "page_size": page_size,
                    "total": total,
                    "total_pages": total_pages,
                    "has_next": page < total_pages,
                    "has_prev": page > 1
                }
            }

    def search(
        self,
        query: str,
        fields: List[str],
        filters: Optional[Dict[str, Any]] = None,
        page: int = 1,
        page_size: int = 20
    ) -> Dict[str, Any]:
        """
        Search entities.

        Args:
            query: Search query
            fields: Fields to search in
            filters: Additional filters
            page: Page number
            page_size: Number of items per page

        Returns:
            Search results with pagination
        """
        # This is a basic implementation - override in specific services
        # for more sophisticated search functionality
        combined_filters = filters or {}

        # Add search to filters (basic implementation)
        if query and fields:
            # This would need to be implemented based on your database
            # For now, we'll just use the first field
            combined_filters[fields[0]] = {"ilike": query}

        return self.list(
            filters=combined_filters,
            page=page,
            page_size=page_size
        )

    # Abstract methods to be implemented by subclasses

    @abstractmethod
    def validate_create(self, data: Dict[str, Any]):
        """Validate data for entity creation"""
        pass

    @abstractmethod
    def validate_update(self, data: Dict[str, Any], entity: T, partial: bool = True):
        """Validate data for entity update"""
        pass

    def validate_delete(self, entity: T):
        """Validate entity deletion - override if needed"""
        pass

    @abstractmethod
    def _create_entity_from_data(self, data: Dict[str, Any]) -> T:
        """Create entity instance from data"""
        pass

    @abstractmethod
    def _update_entity_from_data(self, entity: T, data: Dict[str, Any]):
        """Update entity instance from data"""
        pass