basicmachines-co-basic-memory/src/basic_memory/services/entity_service.py

"""Service for managing entities in the database."""

from datetime import datetime
from pathlib import Path
from typing import List, Optional, Sequence, Tuple, Union

import frontmatter
import yaml
from loguru import logger
from sqlalchemy.exc import IntegrityError


from basic_memory.config import ProjectConfig, BasicMemoryConfig
from basic_memory.file_utils import (
    has_frontmatter,
    parse_frontmatter,
    remove_frontmatter,
    dump_frontmatter,
)
from basic_memory.markdown import EntityMarkdown
from basic_memory.markdown.entity_parser import EntityParser, normalize_frontmatter_metadata
from basic_memory.markdown.utils import entity_model_from_markdown, schema_to_markdown
from basic_memory.models import Entity as EntityModel
from basic_memory.models import Observation, Relation
from basic_memory.models.knowledge import Entity
from basic_memory.repository import ObservationRepository, RelationRepository
from basic_memory.repository.project_repository import ProjectRepository
from basic_memory.repository.entity_repository import EntityRepository
from basic_memory.schemas import Entity as EntitySchema
from basic_memory.schemas.base import Permalink
from basic_memory.schemas.response import (
    DirectoryMoveResult,
    DirectoryMoveError,
    DirectoryDeleteResult,
    DirectoryDeleteError,
)
from basic_memory.services import BaseService, FileService
from basic_memory.services.exceptions import (
    EntityAlreadyExistsError,
    EntityCreationError,
    EntityNotFoundError,
)
from basic_memory.services.link_resolver import LinkResolver
from basic_memory.services.search_service import SearchService
from basic_memory.utils import build_canonical_permalink


class EntityService(BaseService[EntityModel]):
    """Service for managing entities in the database."""

    def __init__(
        self,
        entity_parser: EntityParser,
        entity_repository: EntityRepository,
        observation_repository: ObservationRepository,
        relation_repository: RelationRepository,
        file_service: FileService,
        link_resolver: LinkResolver,
        search_service: Optional[SearchService] = None,
        app_config: Optional[BasicMemoryConfig] = None,
    ):
        super().__init__(entity_repository)
        self.observation_repository = observation_repository
        self.relation_repository = relation_repository
        self.entity_parser = entity_parser
        self.file_service = file_service
        self.link_resolver = link_resolver
        self.search_service = search_service
        self.app_config = app_config
        self._project_permalink: Optional[str] = None

    async def detect_file_path_conflicts(
        self, file_path: str, skip_check: bool = False
    ) -> List[Entity]:
        """Detect potential file path conflicts for a given file path.

        This checks for entities with similar file paths that might cause conflicts:
        - Case sensitivity differences (Finance/file.md vs finance/file.md)
        - Character encoding differences
        - Hyphen vs space differences
        - Unicode normalization differences

        Args:
            file_path: The file path to check for conflicts
            skip_check: If True, skip the check and return empty list (optimization for bulk operations)

        Returns:
            List of entities that might conflict with the given file path
        """
        if skip_check:
            return []

        from basic_memory.utils import detect_potential_file_conflicts

        conflicts = []

        # Get all existing file paths
        all_entities = await self.repository.find_all()
        existing_paths = [entity.file_path for entity in all_entities]

        # Use the enhanced conflict detection utility
        conflicting_paths = detect_potential_file_conflicts(file_path, existing_paths)

        # Find the entities corresponding to conflicting paths
        for entity in all_entities:
            if entity.file_path in conflicting_paths:
                conflicts.append(entity)

        return conflicts

    async def resolve_permalink(
        self,
        file_path: Permalink | Path,
        markdown: Optional[EntityMarkdown] = None,
        skip_conflict_check: bool = False,
    ) -> str:
        """Get or generate unique permalink for an entity.

        Priority:
        1. If markdown has permalink and it's not used by another file -> use as is
        2. If markdown has permalink but it's used by another file -> make unique
        3. For existing files, keep current permalink from db
        4. Generate new unique permalink from file path

        Enhanced to detect and handle character-related conflicts.

        Note: Uses lightweight repository methods that skip eager loading of
        observations and relations for better performance during bulk operations.
        """
        file_path_str = Path(file_path).as_posix()

        # Check for potential file path conflicts before resolving permalink
        conflicts = await self.detect_file_path_conflicts(
            file_path_str, skip_check=skip_conflict_check
        )
        if conflicts:
            logger.warning(
                f"Detected potential file path conflicts for '{file_path_str}': "
                f"{[entity.file_path for entity in conflicts]}"
            )

        # If markdown has explicit permalink, try to validate it
        if markdown and markdown.frontmatter.permalink:
            desired_permalink = markdown.frontmatter.permalink
            # Use lightweight method - we only need to check file_path
            existing_file_path = await self.repository.get_file_path_for_permalink(
                desired_permalink
            )

            # If no conflict or it's our own file, use as is
            if not existing_file_path or existing_file_path == file_path_str:
                return desired_permalink

        # For existing files, try to find current permalink
        # Use lightweight method - we only need the permalink
        existing_permalink = await self.repository.get_permalink_for_file_path(file_path_str)
        if existing_permalink:
            return existing_permalink

        # New file - generate permalink
        if markdown and markdown.frontmatter.permalink:
            desired_permalink = markdown.frontmatter.permalink
        else:
            # Trigger: generating a permalink for a new file
            # Why: canonical permalinks may require project prefix for global addressing
            # Outcome: include project slug when enabled in config
            include_project = True
            if self.app_config:
                include_project = self.app_config.permalinks_include_project

            project_permalink = None
            # Trigger: project-prefixed permalinks are enabled
            # Why: we need the project slug to build the canonical permalink
            # Outcome: fetch and cache the project's permalink
            if include_project:
                project_permalink = await self._get_project_permalink()

            desired_permalink = build_canonical_permalink(
                project_permalink, file_path_str, include_project=include_project
            )

        # Make unique if needed - enhanced to handle character conflicts
        # Use lightweight existence check instead of loading full entity
        permalink = desired_permalink
        suffix = 1
        while await self.repository.permalink_exists(permalink):
            permalink = f"{desired_permalink}-{suffix}"
            suffix += 1
            logger.debug(f"creating unique permalink: {permalink}")

        return permalink

    async def _get_project_permalink(self) -> Optional[str]:
        """Get and cache the current project's permalink."""
        if self._project_permalink is not None:
            return self._project_permalink

        project_id = self.repository.project_id
        if project_id is None:  # pragma: no cover
            return None  # pragma: no cover

        project_repository = ProjectRepository(self.repository.session_maker)
        project = await project_repository.get_by_id(project_id)
        if project:
            self._project_permalink = project.permalink
        return self._project_permalink

    def _build_frontmatter_markdown(
        self, title: str, note_type: str, permalink: str
    ) -> EntityMarkdown:
        """Build a minimal EntityMarkdown object for permalink resolution."""
        from basic_memory.markdown.schemas import EntityFrontmatter

        frontmatter_metadata = {
            "title": title,
            "type": note_type,
            "permalink": permalink,
        }
        frontmatter_obj = EntityFrontmatter(metadata=frontmatter_metadata)
        return EntityMarkdown(
            frontmatter=frontmatter_obj,
            content="",
            observations=[],
            relations=[],
        )

    async def create_or_update_entity(self, schema: EntitySchema) -> Tuple[EntityModel, bool]:
        """Create new entity or update existing one.
        Returns: (entity, is_new) where is_new is True if a new entity was created
        """
        logger.debug(
            f"Creating or updating entity: {schema.file_path}, permalink: {schema.permalink}"
        )

        # Try to find existing entity using strict resolution (no fuzzy search)
        # This prevents incorrectly matching similar file paths like "Node A.md" and "Node C.md"
        existing = await self.link_resolver.resolve_link(schema.file_path, strict=True)
        if not existing and schema.permalink:
            existing = await self.link_resolver.resolve_link(schema.permalink, strict=True)

        if existing:
            logger.debug(f"Found existing entity: {existing.file_path}")
            return await self.update_entity(existing, schema), False
        else:
            # Create new entity
            return await self.create_entity(schema), True

    async def create_entity(self, schema: EntitySchema) -> EntityModel:
        """Create a new entity and write to filesystem."""
        logger.debug(f"Creating entity: {schema.title}")

        # Get file path and ensure it's a Path object
        file_path = Path(schema.file_path)

        if await self.file_service.exists(file_path):
            raise EntityAlreadyExistsError(
                f"file for entity {schema.directory}/{schema.title} already exists: {file_path}"
            )

        # Parse content frontmatter to check for user-specified permalink and note_type
        content_markdown = None
        if schema.content and has_frontmatter(schema.content):
            content_frontmatter = parse_frontmatter(schema.content)

            # If content has type, use it to override the schema note_type
            if "type" in content_frontmatter:
                schema.note_type = content_frontmatter["type"]

            if "permalink" in content_frontmatter:
                content_markdown = self._build_frontmatter_markdown(
                    schema.title, schema.note_type, content_frontmatter["permalink"]
                )

        # Get unique permalink (prioritizing content frontmatter) unless disabled
        if self.app_config and self.app_config.disable_permalinks:
            # Use empty string as sentinel to indicate permalinks are disabled
            # The permalink property will return None when it sees empty string
            schema._permalink = ""
        else:
            # Generate and set permalink
            permalink = await self.resolve_permalink(file_path, content_markdown)
            schema._permalink = permalink

        post = await schema_to_markdown(schema)

        # write file
        final_content = dump_frontmatter(post)
        checksum = await self.file_service.write_file(file_path, final_content)

        # parse entity from content we just wrote (avoids re-reading file for cloud compatibility)
        entity_markdown = await self.entity_parser.parse_markdown_content(
            file_path=file_path,
            content=final_content,
        )

        # create entity and relations
        entity = await self.upsert_entity_from_markdown(file_path, entity_markdown, is_new=True)

        # Set final checksum to mark complete
        return await self.repository.update(entity.id, {"checksum": checksum})

    async def update_entity(self, entity: EntityModel, schema: EntitySchema) -> EntityModel:
        """Update an entity's content and metadata."""
        logger.debug(
            f"Updating entity with permalink: {entity.permalink} content-type: {schema.content_type}"
        )

        # Convert file path string to Path
        file_path = Path(entity.file_path)

        # Read existing content via file_service (for cloud compatibility)
        existing_content = await self.file_service.read_file_content(file_path)
        existing_markdown = await self.entity_parser.parse_markdown_content(
            file_path=file_path,
            content=existing_content,
        )

        # Parse content frontmatter to check for user-specified permalink and note_type
        content_markdown = None
        if schema.content and has_frontmatter(schema.content):
            content_frontmatter = parse_frontmatter(schema.content)

            # If content has type, use it to override the schema note_type
            if "type" in content_frontmatter:
                schema.note_type = content_frontmatter["type"]

            if "permalink" in content_frontmatter:
                content_markdown = self._build_frontmatter_markdown(
                    schema.title, schema.note_type, content_frontmatter["permalink"]
                )

        # Check if we need to update the permalink based on content frontmatter (unless disabled)
        new_permalink = entity.permalink  # Default to existing
        if self.app_config and not self.app_config.disable_permalinks:
            if content_markdown and content_markdown.frontmatter.permalink:
                # Resolve permalink with the new content frontmatter
                resolved_permalink = await self.resolve_permalink(file_path, content_markdown)
                if resolved_permalink != entity.permalink:
                    new_permalink = resolved_permalink
                    # Update the schema to use the new permalink
                    schema._permalink = new_permalink

        # Create post with new content from schema
        post = await schema_to_markdown(schema)

        # Merge new metadata with existing metadata
        existing_markdown.frontmatter.metadata.update(post.metadata)

        # Always ensure the permalink in the metadata is the canonical one from the database.
        # The schema_to_markdown call above uses EntitySchema.permalink which computes a
        # non-prefixed permalink (e.g., "test/note"). The metadata merge on the previous line
        # would overwrite the project-prefixed permalink (e.g., "project/test/note") stored
        # in the existing file. Setting it unconditionally preserves the correct value.
        existing_markdown.frontmatter.metadata["permalink"] = new_permalink

        # Create a new post with merged metadata
        merged_post = frontmatter.Post(post.content, **existing_markdown.frontmatter.metadata)

        # write file
        final_content = dump_frontmatter(merged_post)
        checksum = await self.file_service.write_file(file_path, final_content)

        # parse entity from content we just wrote (avoids re-reading file for cloud compatibility)
        entity_markdown = await self.entity_parser.parse_markdown_content(
            file_path=file_path,
            content=final_content,
        )

        # update entity and relations
        entity = await self.upsert_entity_from_markdown(file_path, entity_markdown, is_new=False)

        # Set final checksum to match file
        entity = await self.repository.update(entity.id, {"checksum": checksum})

        return entity

    async def fast_write_entity(
        self,
        schema: EntitySchema,
        external_id: Optional[str] = None,
    ) -> EntityModel:
        """Write file and upsert a minimal entity row for fast responses."""
        logger.debug(
            "Fast-writing entity",
            title=schema.title,
            external_id=external_id,
            content_type=schema.content_type,
        )

        # --- Identity & File Path ---
        existing = await self.repository.get_by_external_id(external_id) if external_id else None

        # Trigger: external_id already exists
        # Why: avoid duplicate entities when title-derived paths change
        # Outcome: update in-place and keep the existing file path
        file_path = Path(existing.file_path) if existing else Path(schema.file_path)

        if not existing and await self.file_service.exists(file_path):
            raise EntityAlreadyExistsError(
                f"file for entity {schema.directory}/{schema.title} already exists: {file_path}"
            )

        # --- Frontmatter Overrides ---
        content_markdown = None
        if schema.content and has_frontmatter(schema.content):
            content_frontmatter = parse_frontmatter(schema.content)

            if "type" in content_frontmatter:
                schema.note_type = content_frontmatter["type"]

            if "permalink" in content_frontmatter:
                content_markdown = self._build_frontmatter_markdown(
                    schema.title, schema.note_type, content_frontmatter["permalink"]
                )

        # --- Permalink Resolution ---
        if self.app_config and self.app_config.disable_permalinks:
            schema._permalink = ""
        else:
            if existing and not (content_markdown and content_markdown.frontmatter.permalink):
                schema._permalink = existing.permalink or await self.resolve_permalink(
                    file_path, skip_conflict_check=True
                )
            else:
                schema._permalink = await self.resolve_permalink(
                    file_path, content_markdown, skip_conflict_check=True
                )

        # --- File Write ---
        post = await schema_to_markdown(schema)
        final_content = dump_frontmatter(post)
        checksum = await self.file_service.write_file(file_path, final_content)

        # --- Minimal DB Upsert ---
        metadata = normalize_frontmatter_metadata(post.metadata or {})
        entity_metadata = {k: v for k, v in metadata.items() if v is not None}
        update_data = {
            "title": schema.title,
            "note_type": schema.note_type,
            "file_path": file_path.as_posix(),
            "content_type": schema.content_type,
            "entity_metadata": entity_metadata or None,
            "permalink": schema.permalink,
            "checksum": checksum,
            "updated_at": datetime.now().astimezone(),
        }

        if existing:
            updated = await self.repository.update(existing.id, update_data)
            if not updated:
                raise ValueError(f"Failed to update entity in database: {existing.id}")
            return updated

        create_data = dict(update_data)
        if external_id is not None:
            create_data["external_id"] = external_id
        return await self.repository.create(create_data)

    async def fast_edit_entity(
        self,
        entity: EntityModel,
        operation: str,
        content: str,
        section: Optional[str] = None,
        find_text: Optional[str] = None,
        expected_replacements: int = 1,
    ) -> EntityModel:
        """Edit an entity quickly and defer full indexing to background."""
        logger.debug(f"Fast editing entity: {entity.external_id}, operation: {operation}")

        # --- File Edit ---
        file_path = Path(entity.file_path)
        current_content, _ = await self.file_service.read_file(file_path)
        new_content = self.apply_edit_operation(
            current_content, operation, content, section, find_text, expected_replacements
        )
        checksum = await self.file_service.write_file(file_path, new_content)

        # --- Frontmatter Overrides ---
        update_data = {
            "checksum": checksum,
            "updated_at": datetime.now().astimezone(),
        }
        content_markdown = None
        if has_frontmatter(new_content):
            content_frontmatter = parse_frontmatter(new_content)

            if "title" in content_frontmatter:
                update_data["title"] = content_frontmatter["title"]
            if "type" in content_frontmatter:
                update_data["note_type"] = content_frontmatter["type"]

            if "permalink" in content_frontmatter:
                content_markdown = self._build_frontmatter_markdown(
                    update_data.get("title", entity.title),
                    update_data.get("note_type", entity.note_type),
                    content_frontmatter["permalink"],
                )

            metadata = normalize_frontmatter_metadata(content_frontmatter or {})
            update_data["entity_metadata"] = {k: v for k, v in metadata.items() if v is not None}

        # --- Permalink Resolution ---
        if self.app_config and self.app_config.disable_permalinks:
            update_data["permalink"] = None
        elif content_markdown and content_markdown.frontmatter.permalink:
            update_data["permalink"] = await self.resolve_permalink(
                file_path, content_markdown, skip_conflict_check=True
            )

        updated = await self.repository.update(entity.id, update_data)
        if not updated:
            raise ValueError(f"Failed to update entity in database: {entity.id}")
        return updated

    async def reindex_entity(self, entity_id: int) -> None:
        """Parse file content and rebuild observations/relations/search for an entity."""
        entity = await self.repository.find_by_id(entity_id)
        if not entity:
            raise EntityNotFoundError(f"Entity not found: {entity_id}")

        # --- Full Parse ---
        file_path = Path(entity.file_path)
        content = await self.file_service.read_file_content(file_path)
        entity_markdown = await self.entity_parser.parse_markdown_content(
            file_path=file_path,
            content=content,
        )

        # --- DB Reindex ---
        updated = await self.upsert_entity_from_markdown(file_path, entity_markdown, is_new=False)
        checksum = await self.file_service.compute_checksum(file_path)
        updated = await self.repository.update(updated.id, {"checksum": checksum})
        if not updated:
            raise ValueError(f"Failed to update entity in database: {entity.id}")

        # --- Search Reindex ---
        if self.search_service:
            await self.search_service.index_entity_data(updated, content=content)

    async def delete_entity(self, permalink_or_id: str | int) -> bool:
        """Delete entity and its file."""
        logger.debug(f"Deleting entity: {permalink_or_id}")

        try:
            # Get entity first for file deletion
            if isinstance(permalink_or_id, str):
                entity = await self.get_by_permalink(permalink_or_id)
            else:
                entities = await self.get_entities_by_id([permalink_or_id])
                if len(entities) != 1:  # pragma: no cover
                    logger.error(
                        "Entity lookup error", entity_id=permalink_or_id, found_count=len(entities)
                    )
                    raise ValueError(
                        f"Expected 1 entity with ID {permalink_or_id}, got {len(entities)}"
                    )
                entity = entities[0]

            # Delete from search index first (if search_service is available)
            if self.search_service:
                await self.search_service.handle_delete(entity)

            # Delete file
            await self.file_service.delete_entity_file(entity)

            # Delete from DB (this will cascade to observations/relations)
            return await self.repository.delete(entity.id)

        except EntityNotFoundError:
            logger.info(f"Entity not found: {permalink_or_id}")
            return True  # Already deleted

    async def get_by_permalink(self, permalink: str) -> EntityModel:
        """Get entity by type and name combination."""
        logger.debug(f"Getting entity by permalink: {permalink}")
        db_entity = await self.repository.get_by_permalink(permalink)
        if not db_entity:
            raise EntityNotFoundError(f"Entity not found: {permalink}")
        return db_entity

    async def get_entities_by_id(self, ids: List[int]) -> Sequence[EntityModel]:
        """Get specific entities and their relationships."""
        logger.debug(f"Getting entities: {ids}")
        return await self.repository.find_by_ids(ids)

    async def get_entities_by_permalinks(self, permalinks: List[str]) -> Sequence[EntityModel]:
        """Get specific nodes and their relationships."""
        logger.debug(f"Getting entities permalinks: {permalinks}")
        return await self.repository.find_by_permalinks(permalinks)

    async def delete_entity_by_file_path(self, file_path: Union[str, Path]) -> None:
        """Delete entity by file path."""
        await self.repository.delete_by_file_path(str(file_path))

    async def create_entity_from_markdown(
        self, file_path: Path, markdown: EntityMarkdown
    ) -> EntityModel:
        """Create entity and observations only.

        Creates the entity with null checksum to indicate sync not complete.
        Relations will be added in second pass.

        Uses UPSERT approach to handle permalink/file_path conflicts cleanly.
        """
        logger.debug(f"Creating entity: {markdown.frontmatter.title} file_path: {file_path}")
        model = entity_model_from_markdown(
            file_path, markdown, project_id=self.repository.project_id
        )

        # Mark as incomplete because we still need to add relations
        model.checksum = None

        # Use UPSERT to handle conflicts cleanly
        try:
            return await self.repository.upsert_entity(model)
        except Exception as e:
            logger.error(f"Failed to upsert entity for {file_path}: {e}")
            raise EntityCreationError(f"Failed to create entity: {str(e)}") from e

    async def update_entity_and_observations(
        self, file_path: Path, markdown: EntityMarkdown
    ) -> EntityModel:
        """Update entity fields and observations.

        Updates everything except relations and sets null checksum
        to indicate sync not complete.
        """
        logger.debug(f"Updating entity and observations: {file_path}")

        db_entity = await self.repository.get_by_file_path(file_path.as_posix())

        # Clear observations for entity
        await self.observation_repository.delete_by_fields(entity_id=db_entity.id)

        # add new observations
        observations = [
            Observation(
                project_id=self.observation_repository.project_id,
                entity_id=db_entity.id,
                content=obs.content,
                category=obs.category,
                context=obs.context,
                tags=obs.tags,
            )
            for obs in markdown.observations
        ]
        await self.observation_repository.add_all(observations)

        # update values from markdown
        db_entity = entity_model_from_markdown(file_path, markdown, db_entity)

        # checksum value is None == not finished with sync
        db_entity.checksum = None

        # update entity
        return await self.repository.update(
            db_entity.id,
            db_entity,
        )

    async def upsert_entity_from_markdown(
        self,
        file_path: Path,
        markdown: EntityMarkdown,
        *,
        is_new: bool,
    ) -> EntityModel:
        """Create/update entity and relations from parsed markdown."""
        if is_new:
            created = await self.create_entity_from_markdown(file_path, markdown)
        else:
            created = await self.update_entity_and_observations(file_path, markdown)
        return await self.update_entity_relations(created.file_path, markdown)

    async def update_entity_relations(
        self,
        path: str,
        markdown: EntityMarkdown,
    ) -> EntityModel:
        """Update relations for entity"""
        logger.debug(f"Updating relations for entity: {path}")

        db_entity = await self.repository.get_by_file_path(path)

        # Clear existing relations first
        await self.relation_repository.delete_outgoing_relations_from_entity(db_entity.id)

        # Batch resolve all relation targets in parallel
        if markdown.relations:
            import asyncio

            # Create tasks for all relation lookups
            # Use strict=True to disable fuzzy search - only exact matches should create resolved relations
            # This ensures forward references (links to non-existent entities) remain unresolved (to_id=NULL)
            lookup_tasks = [
                self.link_resolver.resolve_link(rel.target, strict=True)
                for rel in markdown.relations
            ]

            # Execute all lookups in parallel
            resolved_entities = await asyncio.gather(*lookup_tasks, return_exceptions=True)

            # Process results and create relation records
            relations_to_add = []
            for rel, resolved in zip(markdown.relations, resolved_entities):
                # Handle exceptions from gather and None results
                target_entity: Optional[Entity] = None
                if not isinstance(resolved, Exception):
                    # Type narrowing: resolved is Optional[Entity] here, not Exception
                    target_entity = resolved  # type: ignore

                # if the target is found, store the id
                target_id = target_entity.id if target_entity else None
                # if the target is found, store the title, otherwise add the target for a "forward link"
                target_name = target_entity.title if target_entity else rel.target

                # Create the relation
                relation = Relation(
                    project_id=self.relation_repository.project_id,
                    from_id=db_entity.id,
                    to_id=target_id,
                    to_name=target_name,
                    relation_type=rel.type,
                    context=rel.context,
                )
                relations_to_add.append(relation)

            # Batch insert all relations
            if relations_to_add:
                try:
                    await self.relation_repository.add_all(relations_to_add)
                except IntegrityError:
                    # Some relations might be duplicates - fall back to individual inserts
                    logger.debug("Batch relation insert failed, trying individual inserts")
                    for relation in relations_to_add:
                        try:
                            await self.relation_repository.add(relation)
                        except IntegrityError:
                            # Unique constraint violation - relation already exists
                            logger.debug(
                                f"Skipping duplicate relation {relation.relation_type} from {db_entity.permalink}"
                            )
                            continue

        return await self.repository.get_by_file_path(path)

    async def edit_entity(
        self,
        identifier: str,
        operation: str,
        content: str,
        section: Optional[str] = None,
        find_text: Optional[str] = None,
        expected_replacements: int = 1,
    ) -> EntityModel:
        """Edit an existing entity's content using various operations.

        Args:
            identifier: Entity identifier (permalink, title, etc.)
            operation: The editing operation (append, prepend, find_replace, replace_section)
            content: The content to add or use for replacement
            section: For replace_section operation - the markdown header
            find_text: For find_replace operation - the text to find and replace
            expected_replacements: For find_replace operation - expected number of replacements (default: 1)

        Returns:
            The updated entity model

        Raises:
            EntityNotFoundError: If the entity cannot be found
            ValueError: If required parameters are missing for the operation or replacement count doesn't match expected
        """
        logger.debug(f"Editing entity: {identifier}, operation: {operation}")

        # Find the entity using the link resolver with strict mode for destructive operations
        entity = await self.link_resolver.resolve_link(identifier, strict=True)
        if not entity:
            raise EntityNotFoundError(f"Entity not found: {identifier}")

        # Read the current file content
        file_path = Path(entity.file_path)
        current_content, _ = await self.file_service.read_file(file_path)

        # Apply the edit operation
        new_content = self.apply_edit_operation(
            current_content, operation, content, section, find_text, expected_replacements
        )

        # Write the updated content back to the file
        checksum = await self.file_service.write_file(file_path, new_content)

        # Parse the content we just wrote (avoids re-reading file for cloud compatibility)
        entity_markdown = await self.entity_parser.parse_markdown_content(
            file_path=file_path,
            content=new_content,
        )

        # Update entity and its relationships
        entity = await self.upsert_entity_from_markdown(file_path, entity_markdown, is_new=False)

        # Set final checksum to match file
        entity = await self.repository.update(entity.id, {"checksum": checksum})

        return entity

    def apply_edit_operation(
        self,
        current_content: str,
        operation: str,
        content: str,
        section: Optional[str] = None,
        find_text: Optional[str] = None,
        expected_replacements: int = 1,
    ) -> str:
        """Apply the specified edit operation to the current content."""

        if operation == "append":
            # Ensure proper spacing
            if current_content and not current_content.endswith("\n"):
                return current_content + "\n" + content
            return current_content + content  # pragma: no cover

        elif operation == "prepend":
            # Handle frontmatter-aware prepending
            return self._prepend_after_frontmatter(current_content, content)

        elif operation == "find_replace":
            if not find_text:
                raise ValueError("find_text is required for find_replace operation")
            if not find_text.strip():
                raise ValueError("find_text cannot be empty or whitespace only")

            # Count actual occurrences
            actual_count = current_content.count(find_text)

            # Validate count matches expected
            if actual_count != expected_replacements:
                if actual_count == 0:
                    raise ValueError(f"Text to replace not found: '{find_text}'")
                else:
                    raise ValueError(
                        f"Expected {expected_replacements} occurrences of '{find_text}', "
                        f"but found {actual_count}"
                    )

            return current_content.replace(find_text, content)

        elif operation == "replace_section":
            if not section:
                raise ValueError("section is required for replace_section operation")
            if not section.strip():
                raise ValueError("section cannot be empty or whitespace only")
            return self.replace_section_content(current_content, section, content)

        else:
            raise ValueError(f"Unsupported operation: {operation}")

    def replace_section_content(
        self, current_content: str, section_header: str, new_content: str
    ) -> str:
        """Replace content under a specific markdown section header.

        This method uses a simple, safe approach: when replacing a section, it only
        replaces the immediate content under that header until it encounters the next
        header of ANY level. This means:

        - Replacing "# Header" replaces content until "## Subsection" (preserves subsections)
        - Replacing "## Section" replaces content until "### Subsection" (preserves subsections)
        - More predictable and safer than trying to consume entire hierarchies

        Args:
            current_content: The current markdown content
            section_header: The section header to find and replace (e.g., "## Section Name")
            new_content: The new content to replace the section with (should not include the header itself)

        Returns:
            The updated content with the section replaced

        Raises:
            ValueError: If multiple sections with the same header are found
        """
        # Normalize the section header (ensure it starts with #)
        if not section_header.startswith("#"):
            section_header = "## " + section_header

        # Strip duplicate header from new_content if present (fix for issue #390)
        # LLMs sometimes include the section header in their content, which would create duplicates
        new_content_lines = new_content.lstrip().split("\n")
        if new_content_lines and new_content_lines[0].strip() == section_header.strip():
            # Remove the duplicate header line
            new_content = "\n".join(new_content_lines[1:]).lstrip()

        # First pass: count matching sections to check for duplicates
        lines = current_content.split("\n")
        matching_sections = []

        for i, line in enumerate(lines):
            if line.strip() == section_header.strip():
                matching_sections.append(i)

        # Handle multiple sections error
        if len(matching_sections) > 1:
            raise ValueError(
                f"Multiple sections found with header '{section_header}'. "
                f"Section replacement requires unique headers."
            )

        # If no section found, append it
        if len(matching_sections) == 0:
            logger.info(f"Section '{section_header}' not found, appending to end of document")
            separator = "\n\n" if current_content and not current_content.endswith("\n\n") else ""
            return current_content + separator + section_header + "\n" + new_content

        # Replace the single matching section
        result_lines = []
        section_line_idx = matching_sections[0]

        i = 0
        while i < len(lines):
            line = lines[i]

            # Check if this is our target section header
            if i == section_line_idx:
                # Add the section header and new content
                result_lines.append(line)
                result_lines.append(new_content)
                i += 1

                # Skip the original section content until next header or end
                while i < len(lines):
                    next_line = lines[i]
                    # Stop consuming when we hit any header (preserve subsections)
                    if next_line.startswith("#"):
                        # We found another header - continue processing from here
                        break
                    i += 1
                # Continue processing from the next header (don't increment i again)
                continue

            # Add all other lines (including subsequent sections)
            result_lines.append(line)
            i += 1

        return "\n".join(result_lines)

    def _prepend_after_frontmatter(self, current_content: str, content: str) -> str:
        """Prepend content after frontmatter, preserving frontmatter structure."""

        # Check if file has frontmatter
        if has_frontmatter(current_content):
            try:
                # Parse and separate frontmatter from body
                frontmatter_data = parse_frontmatter(current_content)
                body_content = remove_frontmatter(current_content)

                # Prepend content to the body
                if content and not content.endswith("\n"):
                    new_body = content + "\n" + body_content
                else:
                    new_body = content + body_content

                # Reconstruct file with frontmatter + prepended body
                yaml_fm = yaml.dump(frontmatter_data, sort_keys=False, allow_unicode=True)
                return f"---\n{yaml_fm}---\n\n{new_body.strip()}"

            except Exception as e:  # pragma: no cover
                logger.warning(
                    f"Failed to parse frontmatter during prepend: {e}"
                )  # pragma: no cover
                # Fall back to simple prepend if frontmatter parsing fails  # pragma: no cover

        # No frontmatter or parsing failed - do simple prepend  # pragma: no cover
        if content and not content.endswith("\n"):  # pragma: no cover
            return content + "\n" + current_content  # pragma: no cover
        return content + current_content  # pragma: no cover

    async def move_entity(
        self,
        identifier: str,
        destination_path: str,
        project_config: ProjectConfig,
        app_config: BasicMemoryConfig,
    ) -> EntityModel:
        """Move entity to new location with database consistency.

        Args:
            identifier: Entity identifier (title, permalink, or memory:// URL)
            destination_path: New path relative to project root
            project_config: Project configuration for file operations
            app_config: App configuration for permalink update settings

        Returns:
            Success message with move details

        Raises:
            EntityNotFoundError: If the entity cannot be found
            ValueError: If move operation fails due to validation or filesystem errors
        """
        logger.debug(f"Moving entity: {identifier} to {destination_path}")

        # 1. Resolve identifier to entity with strict mode for destructive operations
        entity = await self.link_resolver.resolve_link(identifier, strict=True)
        if not entity:
            raise EntityNotFoundError(f"Entity not found: {identifier}")

        current_path = entity.file_path
        old_permalink = entity.permalink

        # 2. Validate destination path format first
        if not destination_path or destination_path.startswith("/") or not destination_path.strip():
            raise ValueError(f"Invalid destination path: {destination_path}")

        # 3. Validate paths
        # NOTE: In tenantless/cloud mode, we cannot rely on local filesystem paths.
        # Use FileService for existence checks and moving.
        if not await self.file_service.exists(current_path):
            raise ValueError(f"Source file not found: {current_path}")

        if await self.file_service.exists(destination_path):
            raise ValueError(f"Destination already exists: {destination_path}")

        try:
            # 4. Ensure destination directory if needed (no-op for S3)
            await self.file_service.ensure_directory(Path(destination_path).parent)

            # 5. Move physical file via FileService (filesystem rename or cloud move)
            await self.file_service.move_file(current_path, destination_path)
            logger.info(f"Moved file: {current_path} -> {destination_path}")

            # 6. Prepare database updates
            updates = {"file_path": destination_path}

            # 7. Update permalink if configured or if entity has null permalink (unless disabled)
            if not app_config.disable_permalinks and (
                app_config.update_permalinks_on_move or old_permalink is None
            ):
                # Generate new permalink from destination path
                new_permalink = await self.resolve_permalink(destination_path)

                # Update frontmatter with new permalink
                await self.file_service.update_frontmatter(
                    destination_path, {"permalink": new_permalink}
                )

                updates["permalink"] = new_permalink
                if old_permalink is None:
                    logger.info(
                        f"Generated permalink for entity with null permalink: {new_permalink}"
                    )
                else:
                    logger.info(f"Updated permalink: {old_permalink} -> {new_permalink}")

            # 8. Recalculate checksum
            new_checksum = await self.file_service.compute_checksum(destination_path)
            updates["checksum"] = new_checksum

            # 9. Update database
            updated_entity = await self.repository.update(entity.id, updates)
            if not updated_entity:
                raise ValueError(f"Failed to update entity in database: {entity.id}")

            return updated_entity

        except Exception as e:
            # Rollback: try to restore original file location if move succeeded
            try:
                if await self.file_service.exists(
                    destination_path
                ) and not await self.file_service.exists(current_path):
                    await self.file_service.move_file(destination_path, current_path)
                    logger.info(f"Rolled back file move: {destination_path} -> {current_path}")
            except Exception as rollback_error:  # pragma: no cover
                logger.error(f"Failed to rollback file move: {rollback_error}")

            # Re-raise the original error with context
            raise ValueError(f"Move failed: {str(e)}") from e

    async def move_directory(
        self,
        source_directory: str,
        destination_directory: str,
        project_config: ProjectConfig,
        app_config: BasicMemoryConfig,
    ) -> DirectoryMoveResult:
        """Move all entities in a directory to a new location.

        This operation moves all files within a source directory to a destination
        directory, updating database records and search indexes. The operation
        tracks successes and failures individually to provide detailed feedback.

        Args:
            source_directory: Source directory path relative to project root
            destination_directory: Destination directory path relative to project root
            project_config: Project configuration for file operations
            app_config: App configuration for permalink update settings

        Returns:
            DirectoryMoveResult with counts and details of moved files

        Raises:
            ValueError: If source directory is empty or destination conflicts exist
        """

        logger.info(f"Moving directory: {source_directory} -> {destination_directory}")

        # Normalize directory paths (remove trailing slashes)
        source_directory = source_directory.strip("/")
        destination_directory = destination_directory.strip("/")

        # Find all entities in the source directory
        entities = await self.repository.find_by_directory_prefix(source_directory)

        if not entities:
            logger.warning(f"No entities found in directory: {source_directory}")
            return DirectoryMoveResult(
                total_files=0,
                successful_moves=0,
                failed_moves=0,
                moved_files=[],
                errors=[],
            )

        # Track results
        moved_files: list[str] = []
        errors: list[DirectoryMoveError] = []
        successful_moves = 0
        failed_moves = 0

        # Process each entity
        for entity in entities:
            try:
                # Calculate new path by replacing source prefix with destination
                old_path = entity.file_path
                # Replace only the first occurrence of the source directory prefix
                if old_path.startswith(f"{source_directory}/"):
                    new_path = old_path.replace(
                        f"{source_directory}/", f"{destination_directory}/", 1
                    )
                else:  # pragma: no cover
                    # Entity is directly in the source directory (shouldn't happen with prefix match)
                    new_path = f"{destination_directory}/{old_path}"

                # Move the individual entity
                await self.move_entity(
                    identifier=entity.file_path,
                    destination_path=new_path,
                    project_config=project_config,
                    app_config=app_config,
                )

                moved_files.append(new_path)
                successful_moves += 1
                logger.debug(f"Moved entity: {old_path} -> {new_path}")

            except Exception as e:  # pragma: no cover
                failed_moves += 1
                errors.append(DirectoryMoveError(path=entity.file_path, error=str(e)))
                logger.error(f"Failed to move entity {entity.file_path}: {e}")

        logger.info(
            f"Directory move complete: {successful_moves} succeeded, {failed_moves} failed "
            f"(source={source_directory}, dest={destination_directory})"
        )

        return DirectoryMoveResult(
            total_files=len(entities),
            successful_moves=successful_moves,
            failed_moves=failed_moves,
            moved_files=moved_files,
            errors=errors,
        )

    async def delete_directory(
        self,
        directory: str,
    ) -> DirectoryDeleteResult:
        """Delete all entities in a directory.

        This operation deletes all files within a directory, updating database
        records and search indexes. The operation tracks successes and failures
        individually to provide detailed feedback.

        Args:
            directory: Directory path relative to project root

        Returns:
            DirectoryDeleteResult with counts and details of deleted files
        """
        logger.info(f"Deleting directory: {directory}")

        # Normalize directory path (remove trailing slashes)
        directory = directory.strip("/")

        # Find all entities in the directory
        entities = await self.repository.find_by_directory_prefix(directory)

        if not entities:
            logger.warning(f"No entities found in directory: {directory}")
            return DirectoryDeleteResult(
                total_files=0,
                successful_deletes=0,
                failed_deletes=0,
                deleted_files=[],
                errors=[],
            )

        # Track results
        deleted_files: list[str] = []
        errors: list[DirectoryDeleteError] = []
        successful_deletes = 0
        failed_deletes = 0

        # Process each entity
        for entity in entities:
            try:
                file_path = entity.file_path

                # Delete the entity (this handles file deletion and database cleanup)
                deleted = await self.delete_entity(entity.id)

                if deleted:
                    deleted_files.append(file_path)
                    successful_deletes += 1
                    logger.debug(f"Deleted entity: {file_path}")
                else:  # pragma: no cover
                    failed_deletes += 1
                    errors.append(
                        DirectoryDeleteError(path=file_path, error="Delete returned False")
                    )
                    logger.warning(f"Delete returned False for entity: {file_path}")

            except Exception as e:  # pragma: no cover
                failed_deletes += 1
                errors.append(DirectoryDeleteError(path=entity.file_path, error=str(e)))
                logger.error(f"Failed to delete entity {entity.file_path}: {e}")

        logger.info(
            f"Directory delete complete: {successful_deletes} succeeded, {failed_deletes} failed "
            f"(directory={directory})"
        )

        return DirectoryDeleteResult(
            total_files=len(entities),
            successful_deletes=successful_deletes,
            failed_deletes=failed_deletes,
            deleted_files=deleted_files,
            errors=errors,
        )