from rest_framework import permissions

class IsOwnerOrReadOnly(permissions.BasePermission):
    """
    Owners can edit, others have read-only access.
    """
    def has_object_permission(self, request, view, obj):
        if request.method in permissions.SAFE_METHODS:
            return True
        # obj.user is FK to User, compare with request.user
        return obj.user == request.user


class IsPublicReadOnly(permissions.BasePermission):
    """
    Read-only if public or owner, write only for owner.
    """
    def has_object_permission(self, request, view, obj):
        if request.method in permissions.SAFE_METHODS:
            return obj.is_public or obj.user == request.user
        return obj.user == request.user


class CollectionShared(permissions.BasePermission):
    """
    Allow full access if user is in shared_with of collection(s) or owner,
    read-only if public or shared_with,
    write only if owner or shared_with.
    """
    def has_object_permission(self, request, view, obj):
        user = request.user
        if not user or not user.is_authenticated:
            # Anonymous: only read public
            return request.method in permissions.SAFE_METHODS and obj.is_public

        # Check if user is in shared_with of any collections related to the obj
        # If obj is a Collection itself:
        if hasattr(obj, 'shared_with'):
            if obj.shared_with.filter(id=user.id).exists():
                return True

        # If obj is a Location (has collections M2M)
        if hasattr(obj, 'collections'):
            # Check if user is in shared_with of any related collection
            shared_collections = obj.collections.filter(shared_with=user)
            if shared_collections.exists():
                return True

        # Read permission if public or owner
        if request.method in permissions.SAFE_METHODS:
            return obj.is_public or obj.user == user

        # Write permission only if owner or shared user via collections
        if obj.user == user:
            return True

        if hasattr(obj, 'collections'):
            if obj.collections.filter(shared_with=user).exists():
                return True

        # Default deny
        return False


class IsOwnerOrSharedWithFullAccess(permissions.BasePermission):
    """
    Permission class that provides access control based on ownership and sharing.
    
    Access Rules:
    - Object owners have full access (read/write)
    - Users shared via collections have full access (read/write)
    - Collection owners have full access to objects in their collections
    - Users with direct sharing have full access
    - Anonymous users get read-only access to public objects
    - Authenticated users get read-only access to public objects
    
    Supports multiple sharing patterns:
    - obj.collections (many-to-many collections)
    - obj.collection (single collection foreign key)
    - obj.shared_with (direct sharing many-to-many)
    - obj.is_public (public access flag)
    """
    
    def has_object_permission(self, request, view, obj):
        """
        Check if the user has permission to access the object.
        
        Args:
            request: The HTTP request
            view: The view being accessed
            obj: The object being accessed
            
        Returns:
            bool: True if access is granted, False otherwise
        """
        user = request.user
        is_safe_method = request.method in permissions.SAFE_METHODS
        
        # Anonymous users only get read access to public objects
        if not user or not user.is_authenticated:
            return is_safe_method and getattr(obj, 'is_public', False)
        
        # Owner always has full access
        if self._is_owner(obj, user):
            return True
        
        # Check collection-based access (both ownership and sharing)
        if self._has_collection_access(obj, user):
            return True
        
        # Check direct sharing
        if self._has_direct_sharing_access(obj, user):
            return True
        
        # For safe methods, check if object is public
        if is_safe_method and getattr(obj, 'is_public', False):
            return True
        
        return False
    
    def _is_owner(self, obj, user):
        """
        Check if the user is the owner of the object.
        
        Args:
            obj: The object to check
            user: The user to check ownership for
            
        Returns:
            bool: True if user owns the object
        """
        return hasattr(obj, 'user') and obj.user == user
    
    def _has_collection_access(self, obj, user):
        """
        Check if user has access via collections (either as owner or shared user).
        
        Handles both many-to-many collections and single collection foreign keys.
        
        Args:
            obj: The object to check
            user: The user to check access for
            
        Returns:
            bool: True if user has collection-based access
        """
        # Check many-to-many collections (obj.collections)
        if hasattr(obj, 'collections'):
            collections = obj.collections.all()
            if collections.exists():
                # User is shared with any collection containing this object
                if collections.filter(shared_with=user).exists():
                    return True
                # User owns any collection containing this object
                if collections.filter(user=user).exists():
                    return True
        
        # Check single collection foreign key (obj.collection)
        if hasattr(obj, 'collection') and obj.collection:
            collection = obj.collection
            # User is shared with the collection
            if hasattr(collection, 'shared_with') and collection.shared_with.filter(id=user.id).exists():
                return True
            # User owns the collection
            if hasattr(collection, 'user') and collection.user == user:
                return True
        
        return False
    
    def _has_direct_sharing_access(self, obj, user):
        """
        Check if user has direct sharing access to the object.
        
        Args:
            obj: The object to check
            user: The user to check access for
            
        Returns:
            bool: True if user has direct sharing access
        """
        return (hasattr(obj, 'shared_with') and 
                obj.shared_with.filter(id=user.id).exists())
    
    def has_permission(self, request, view):
        """
        Check if the user has permission to access the view.
        
        This is called before has_object_permission and provides a way to
        deny access at the view level (e.g., for unauthenticated users).
        
        Args:
            request: The HTTP request
            view: The view being accessed
            
        Returns:
            bool: True if access is granted at the view level
        """
        # Allow authenticated users and anonymous users for safe methods
        # Individual object permissions are handled in has_object_permission
        return (request.user and request.user.is_authenticated) or \
               request.method in permissions.SAFE_METHODS