feat(scanner): replace file writes with DB persistence for series

- SerieScanner.scan() now calls _persist_serie_to_db() instead of serie.save_to_file()
- Added _sync_episodes_to_db() helper to handle episode CRUD during sync
- EpisodeService gains delete_by_series() for targeted episode deletion
- SerieList gains add_to_db() async method for DB-based series addition
- test_serie_scanner_db_writes.py covers create/update/preserve/sync scenarios
- DATABASE.md updated with Series Persistence Flow section

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

docs/DATABASE.md

@@ -509,6 +509,85 @@ After verifying database schema supports all fields, file-based storage can be r
 
 ---
 
+## 12. Series Persistence Flow
+
+When a directory scan discovers or updates series, the scanner persists data to the database instead of writing to disk files.
+
+### Scan Flow
+
+```
+Scan Directory
+    │
+    ▼
+Find MP4 Files → Extract Serie Key
+    │
+    ▼
+Check DB for Existing Series (by key)
+    │
+    ├─── EXISTS ──────────────────────► Update Series Metadata
+    │                                        │
+    │                                        ▼
+    │                                 Sync Episodes to DB
+    │                                      │
+    │◄──────────────────────────────────────┘
+    │
+    └─── NEW ───────────────────────────► Create New Series Record
+                                             │
+                                             ▼
+                                      Create Episode Records
+                                             │
+                                             ▼
+                                      Return to Scan Loop
+```
+
+### Key Methods
+
+**SerieScanner._persist_serie_to_db()**
+- Called after `get_missing_episodes_and_season()` computes episodeDict
+- Uses `AnimeSeriesService.get_by_key()` to check if series exists
+- If exists: calls `AnimeSeriesService.update()` + `_sync_episodes_to_db()`
+- If new: calls `AnimeSeriesService.create()` + creates episodes
+
+**SerieScanner._sync_episodes_to_db()**
+- Gets existing episodes from DB via `EpisodeService.get_by_series()`
+- Compares with new episodeDict
+- Removes episodes no longer missing (unless `is_downloaded=True`)
+- Adds new missing episodes
+- Preserves `is_downloaded=True` episodes when removing missing ones
+
+**SerieList.add_to_db()**
+- Used when adding a new discovered series via API
+- Creates filesystem folder + database record + episode records
+
+### Episode Sync Logic
+
+```python
+# For each episode in DB but not in new episodeDict:
+if episode.is_downloaded:
+    # Keep - file exists, don't remove
+    pass
+else:
+    # Remove - no longer missing
+    EpisodeService.delete()
+
+# For each episode in new episodeDict but not in DB:
+# Add as new missing episode
+EpisodeService.create(is_downloaded=False)
+```
+
+### Transaction Handling
+
+- DB operations use their own session with commit/rollback
+- If DB write fails, error is logged and scan continues
+- File-based `save_to_file()` no longer called during scan
+
+### Migration Path
+
+1. v2.x: Scanner writes to both DB (primary) and files (fallback)
+2. v3.0: Scanner writes only to DB, file methods removed
+
+---
+
 ## 13. Database Location
 
 | Environment | Default Location                                  |

src/core/SerieScanner.py

@@ -10,6 +10,7 @@ Note:
 """
 from __future__ import annotations
 
+import asyncio
 import logging
 import os
 import re
@@ -24,7 +25,7 @@ from src.core.exceptions.Exceptions import MatchNotFoundError, NoKeyFoundExcepti
 from src.core.providers.base_provider import Loader
 
 from src.server.database.connection import get_sync_session
-from src.server.database.service import AnimeSeriesService
+from src.server.database.service import AnimeSeriesService, EpisodeService
 
 logger = logging.getLogger(__name__)
 error_logger = logging.getLogger("error")
@@ -208,6 +209,106 @@ class SerieScanner:
         """Reinitialize the series dictionary (keyed by serie.key)."""
         self.keyDict: dict[str, Serie] = {}
 
+    async def _persist_serie_to_db(self, serie: Serie) -> None:
+        """Persist serie to database (create or update).
+
+        Args:
+            serie: Serie domain object to persist
+        """
+        try:
+            from src.server.database.connection import get_async_session_factory
+
+            session_factory = get_async_session_factory()
+            db = session_factory()
+            try:
+                existing = await AnimeSeriesService.get_by_key(db, serie.key)
+                if existing:
+                    await AnimeSeriesService.update(
+                        db, existing.id,
+                        name=serie.name,
+                        folder=serie.folder,
+                        year=serie.year
+                    )
+                    await self._sync_episodes_to_db(db, existing.id, serie.episodeDict)
+                else:
+                    anime_series = await AnimeSeriesService.create(
+                        db=db,
+                        key=serie.key,
+                        name=serie.name,
+                        site=serie.site,
+                        folder=serie.folder,
+                        year=serie.year
+                    )
+                    for season, eps in serie.episodeDict.items():
+                        for ep in eps:
+                            await EpisodeService.create(
+                                db=db,
+                                series_id=anime_series.id,
+                                season=season,
+                                episode_number=ep
+                            )
+                await db.commit()
+                logger.debug(
+                    "Persisted serie '%s' (key=%s) to database",
+                    serie.name, serie.key
+                )
+            except Exception as e:
+                await db.rollback()
+                logger.error(
+                    "Failed to persist serie '%s' to DB: %s",
+                    serie.key, e, exc_info=True
+                )
+                raise
+            finally:
+                await db.close()
+        except Exception as e:
+            logger.error(
+                "Could not persist serie '%s' to DB (DB unavailable?): %s",
+                serie.key, e
+            )
+
+    async def _sync_episodes_to_db(
+        self, db, series_id: int, episode_dict: dict[int, list[int]]
+    ) -> None:
+        """Sync episodes to database, preserving downloaded flags.
+
+        Adds missing episodes, removes episodes no longer missing,
+        and preserves is_downloaded=True episodes.
+
+        Args:
+            db: Async database session
+            series_id: Database ID of the series
+            episode_dict: Dict mapping season -> list of episode numbers
+        """
+        existing_episodes = await EpisodeService.get_by_series(db, series_id)
+        existing_map = {
+            (ep.season, ep.episode_number): ep for ep in existing_episodes
+        }
+        new_keys = set()
+        for season, eps in episode_dict.items():
+            for ep_num in eps:
+                new_keys.add((season, ep_num))
+        for (season, ep_num), ep in existing_map.items():
+            if (season, ep_num) not in new_keys:
+                if ep.is_downloaded:
+                    logger.debug(
+                        "Preserving downloaded episode S%02dE%02d for series_id=%d",
+                        season, ep_num, series_id
+                    )
+                else:
+                    await EpisodeService.delete_by_series(
+                        db, series_id, season, ep_num
+                    )
+        for season, eps in episode_dict.items():
+            for ep_num in eps:
+                if (season, ep_num) not in existing_map:
+                    await EpisodeService.create(
+                        db=db,
+                        series_id=series_id,
+                        season=season,
+                        episode_number=ep_num
+                    )
+
     def get_total_to_scan(self) -> int:
         """Get the total number of folders to scan.
         
@@ -329,10 +430,16 @@ class SerieScanner:
                         )
                         serie.episodeDict = missing_episodes
                         serie.folder = folder
-                        data_path = os.path.join(
+
-                            self.directory, folder, 'data'
+                        # Persist to database (async)
-                        )
+                        try:
-                        serie.save_to_file(data_path)
+                            asyncio.run(self._persist_serie_to_db(serie))
+                        except Exception as e:
+                            logger.warning(
+                                "DB persistence failed for '%s', "
+                                "continuing without DB: %s",
+                                serie.key, e
+                            )
 
                         # Store by key (primary identifier), not folder
                         if serie.key in self.keyDict:

src/core/entities/SerieList.py

@@ -1,15 +1,17 @@
 """Utilities for loading and managing stored anime series metadata.
 
 This module provides the SerieList class for managing collections of anime
-series metadata. It uses file-based storage only.
+series metadata. It uses file-based storage as fallback when database
+is not available.
 
 Note:
-    This module is part of the core domain layer and has no database
+    This module is part of the core domain layer. Database operations
-    dependencies. All database operations are handled by the service layer.
+    are handled by the service layer via add_to_db().
 """
 
 from __future__ import annotations
 
+import asyncio
 import logging
 import os
 import warnings
@@ -106,6 +108,76 @@ class SerieList:
         
         return anime_path
 
+    async def add_to_db(self, serie: Serie) -> bool:
+        """Persist a new series to the database.
+
+        Creates the filesystem folder using serie.folder, then persists
+        the series metadata to the database.
+
+        Args:
+            serie: The Serie instance to add
+
+        Returns:
+            True if successful, False otherwise
+        """
+        try:
+            from src.server.database.connection import get_async_session_factory
+            from src.server.database.service import AnimeSeriesService, EpisodeService
+
+            folder_name = serie.folder
+            anime_path = os.path.join(self.directory, folder_name)
+            os.makedirs(anime_path, exist_ok=True)
+
+            session_factory = get_async_session_factory()
+            db = session_factory()
+            try:
+                existing = await AnimeSeriesService.get_by_key(db, serie.key)
+                if existing:
+                    logger.debug(
+                        "Series '%s' (key=%s) already exists in DB, skipping",
+                        serie.name, serie.key
+                    )
+                    return True
+
+                anime_series = await AnimeSeriesService.create(
+                    db=db,
+                    key=serie.key,
+                    name=serie.name,
+                    site=serie.site,
+                    folder=folder_name,
+                    year=serie.year
+                )
+                for season, eps in serie.episodeDict.items():
+                    for ep in eps:
+                        await EpisodeService.create(
+                            db=db,
+                            series_id=anime_series.id,
+                            season=season,
+                            episode_number=ep
+                        )
+                await db.commit()
+                self.keyDict[serie.key] = serie
+                logger.info(
+                    "Persisted series '%s' to database",
+                    serie.name
+                )
+                return True
+            except Exception as e:
+                await db.rollback()
+                logger.error(
+                    "Failed to persist series '%s' to DB: %s",
+                    serie.key, e, exc_info=True
+                )
+                return False
+            finally:
+                await db.close()
+        except Exception as e:
+            logger.error(
+                "Could not add series '%s' to DB (DB unavailable?): %s",
+                serie.key, e
+            )
+            return False
+
     def contains(self, key: str) -> bool:
         """
         Return True when a series identified by ``key`` already exists.

src/server/database/service.py

@@ -662,6 +662,33 @@ class EpisodeService:
         )
         return result.rowcount > 0
 
+    @staticmethod
+    async def delete_by_series(
+        db: AsyncSession,
+        series_id: int,
+        season: int,
+        episode_number: int,
+    ) -> bool:
+        """Delete episode by series ID, season, and episode number.
+
+        Args:
+            db: Database session
+            series_id: Foreign key to AnimeSeries
+            season: Season number
+            episode_number: Episode number within season
+
+        Returns:
+            True if deleted, False if not found
+        """
+        result = await db.execute(
+            delete(Episode).where(
+                Episode.series_id == series_id,
+                Episode.season == season,
+                Episode.episode_number == episode_number,
+            )
+        )
+        return result.rowcount > 0
+
     @staticmethod
     async def delete_by_series_and_episode(
         db: AsyncSession,

tests/unit/test_serie_scanner.py

@@ -75,10 +75,10 @@ class TestSerieScannerInitialization:
 class TestSerieScannerScan:
     """Test file-based scan operations."""
 
-    def test_file_based_scan_works(
+    def test_scan_persists_to_db(
         self, temp_directory, mock_loader, sample_serie
     ):
-        """Test file-based scan works properly."""
+        """Test scan persists series to database."""
         scanner = SerieScanner(temp_directory, mock_loader)
 
         with patch.object(scanner, 'get_total_to_scan', return_value=1):
@@ -100,12 +100,15 @@ class TestSerieScannerScan:
                         return_value=({1: [2, 3]}, "aniworld.to")
                     ):
                         with patch.object(
-                            sample_serie, 'save_to_file'
+                            scanner, '_persist_serie_to_db'
-                        ) as mock_save:
+                        ) as mock_persist:
                             scanner.scan()
 
-                            # Verify file was saved
+                            # Verify DB persistence was called
-                            mock_save.assert_called_once()
+                            mock_persist.assert_called_once()
+                            # Check the serie passed matches
+                            call_args = mock_persist.call_args
+                            assert call_args[0][0].key == "attack-on-titan"
 
     def test_keydict_populated_after_scan(
         self, temp_directory, mock_loader, sample_serie

tests/unit/test_serie_scanner_db_writes.py

@@ -0,0 +1,225 @@
+"""Tests for SerieScanner DB persistence functionality."""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+from src.core.entities.series import Serie
+from src.core.SerieScanner import SerieScanner
+
+
+@pytest.fixture
+def mock_session_factory():
+    """Create a mock async session factory."""
+    mock_session = AsyncMock()
+    mock_session_factory = MagicMock(return_value=mock_session)
+    return mock_session_factory, mock_session
+
+
+@pytest.fixture
+def sample_serie():
+    """Create a sample Serie for testing."""
+    return Serie(
+        key="attack-on-titan",
+        name="Attack on Titan",
+        site="aniworld.to",
+        folder="Attack on Titan (2013)",
+        episodeDict={1: [1, 2, 3], 2: [1, 2]},
+        year=2013
+    )
+
+
+class TestPersistSerieToDb:
+    """Test _persist_serie_to_db method."""
+
+    @pytest.mark.asyncio
+    async def test_creates_new_series_when_not_exists(
+        self, mock_session_factory, sample_serie
+    ):
+        """Verify new series is created in DB."""
+        mock_factory, mock_session = mock_session_factory
+
+        with patch(
+            "src.server.database.connection.get_async_session_factory",
+            return_value=mock_factory
+        ):
+            with patch(
+                "src.server.database.service.AnimeSeriesService.get_by_key",
+                return_value=None
+            ):
+                mock_anime_series = MagicMock()
+                mock_anime_series.id = 1
+                with patch(
+                    "src.server.database.service.AnimeSeriesService.create",
+                    return_value=mock_anime_series
+                ):
+                    scanner = SerieScanner("/tmp", MagicMock())
+                    await scanner._persist_serie_to_db(sample_serie)
+
+                    from src.server.database.service import AnimeSeriesService
+                    AnimeSeriesService.create.assert_called_once()
+                    call_kwargs = AnimeSeriesService.create.call_args[1]
+                    assert call_kwargs["key"] == "attack-on-titan"
+                    assert call_kwargs["name"] == "Attack on Titan"
+
+    @pytest.mark.asyncio
+    async def test_updates_existing_series(self, mock_session_factory, sample_serie):
+        """Verify existing series is updated."""
+        mock_factory, mock_session = mock_session_factory
+
+        mock_existing = MagicMock()
+        mock_existing.id = 42
+        mock_existing.key = "attack-on-titan"
+
+        scanner = SerieScanner("/tmp", MagicMock())
+
+        with patch(
+            "src.server.database.connection.get_async_session_factory",
+            return_value=mock_factory
+        ):
+            with patch(
+                "src.server.database.service.AnimeSeriesService.get_by_key",
+                return_value=mock_existing
+            ):
+                with patch(
+                    "src.server.database.service.AnimeSeriesService.update",
+                    new_callable=AsyncMock
+                ) as mock_update:
+                    with patch.object(
+                        scanner,
+                        "_sync_episodes_to_db",
+                        new_callable=AsyncMock
+                    ):
+                        await scanner._persist_serie_to_db(sample_serie)
+
+                        mock_update.assert_called_once()
+                        call_args = mock_update.call_args[0]
+                        assert call_args[1] == 42  # series_id
+
+
+class TestSyncEpisodesToDb:
+    """Test _sync_episodes_to_db method."""
+
+    @pytest.mark.asyncio
+    async def test_preserves_downloaded_episodes(self):
+        """Verify downloaded episodes are not removed even when no longer missing."""
+        mock_session = AsyncMock()
+
+        # S01E1 was downloaded (file exists), S01E2 was missing but file now exists
+        # Both are no longer in episode_dict
+        existing_eps = [
+            MagicMock(id=1, season=1, episode_number=1, is_downloaded=True),
+            MagicMock(id=2, season=1, episode_number=2, is_downloaded=True),
+        ]
+
+        with patch(
+            "src.server.database.service.EpisodeService.get_by_series",
+            return_value=existing_eps
+        ):
+            with patch(
+                "src.server.database.service.EpisodeService.delete_by_series",
+                new_callable=AsyncMock
+            ) as mock_delete:
+                scanner = SerieScanner("/tmp", MagicMock())
+                # Neither S01E1 nor S01E2 are missing now
+                await scanner._sync_episodes_to_db(
+                    mock_session, 1, {}  # No episodes missing
+                )
+
+                # Neither should be deleted since both are downloaded
+                mock_delete.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_removes_missing_episodes_when_no_longer_missing(self):
+        """Verify episodes removed from DB if file now exists."""
+        mock_session = AsyncMock()
+
+        existing_eps = [
+            MagicMock(id=1, season=1, episode_number=1, is_downloaded=False),
+            MagicMock(id=2, season=1, episode_number=2, is_downloaded=False),
+        ]
+
+        with patch(
+            "src.server.database.service.EpisodeService.get_by_series",
+            return_value=existing_eps
+        ):
+            with patch(
+                "src.server.database.service.EpisodeService.delete_by_series",
+                new_callable=AsyncMock
+            ) as mock_delete:
+                with patch(
+                    "src.server.database.service.EpisodeService.create",
+                    new_callable=AsyncMock
+                ):
+                    scanner = SerieScanner("/tmp", MagicMock())
+                    await scanner._sync_episodes_to_db(
+                        mock_session, 1, {1: [1]}  # Only S01E01 now missing
+                    )
+
+                    # S01E02 should be deleted since no longer missing
+                    mock_delete.assert_called_once()
+
+    @pytest.mark.asyncio
+    async def test_adds_new_missing_episodes(self):
+        """Verify new missing episodes are added."""
+        mock_session = AsyncMock()
+
+        existing_eps = [
+            MagicMock(id=1, season=1, episode_number=1, is_downloaded=False),
+        ]
+
+        with patch(
+            "src.server.database.service.EpisodeService.get_by_series",
+            return_value=existing_eps
+        ):
+            with patch(
+                "src.server.database.service.EpisodeService.create",
+                new_callable=AsyncMock
+            ) as mock_create:
+                scanner = SerieScanner("/tmp", MagicMock())
+                await scanner._sync_episodes_to_db(
+                    mock_session, 1, {1: [1, 2, 3]}  # S01E01, S01E02, S01E03
+                )
+
+                # S01E02 and S01E03 should be created
+                assert mock_create.call_count == 2
+
+
+class TestPersistSerieToDbErrorHandling:
+    """Test error handling in _persist_serie_to_db."""
+
+    @pytest.mark.asyncio
+    async def test_logs_error_when_db_unavailable(self, sample_serie):
+        """Verify DB unavailability is logged but doesn't crash."""
+        with patch(
+            "src.server.database.connection.get_async_session_factory",
+            side_effect=RuntimeError("DB not initialized")
+        ):
+            scanner = SerieScanner("/tmp", MagicMock())
+            # Should not raise
+            await scanner._persist_serie_to_db(sample_serie)
+
+    @pytest.mark.asyncio
+    async def test_rollback_on_failure(self, mock_session_factory, sample_serie):
+        """Verify rollback on DB failure."""
+        mock_factory, mock_session = mock_session_factory
+
+        mock_existing = MagicMock()
+        mock_existing.id = 1
+
+        with patch(
+            "src.server.database.connection.get_async_session_factory",
+            return_value=mock_factory
+        ):
+            with patch(
+                "src.server.database.service.AnimeSeriesService.get_by_key",
+                return_value=mock_existing
+            ):
+                with patch(
+                    "src.server.database.service.AnimeSeriesService.update",
+                    side_effect=Exception("DB error")
+                ):
+                    scanner = SerieScanner("/tmp", MagicMock())
+                    # Should not raise but should rollback
+                    await scanner._persist_serie_to_db(sample_serie)
+                    mock_session.rollback.assert_called_once()