fix(scan): make scan tracker totals reflect platforms actually scanned

The scan tracker computed total_platforms and total_roms over every
filesystem platform, ignoring both the selected platforms and the scan
type. For a "new platforms" scan, existing platforms are skipped inside
_identify_platform, so their ROMs never count toward scanned_roms, yet
they were all included in total_roms. This made the tracker wildly
overcount (the whole library instead of just the new platform).

Resolve the platform list before computing totals and, for NEW_PLATFORMS
scans, exclude platforms that already exist in the database so the totals
match what is actually processed.

Fixes #3599

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_0158RJnc7MmAbwRz6Qiyrj5a

backend/endpoints/sockets/scan.py

@@ -699,8 +699,27 @@ async def scan_platforms(
     if MetadataSource.HLTB in metadata_sources:
         meta_hltb_handler.initialize()
 
+    # Resolve the platforms that will actually be scanned. When no platform ids
+    # are provided, every filesystem platform is scanned.
+    platform_list = [
+        platform.fs_slug
+        for s in platform_ids
+        if (platform := db_platform_handler.get_platform(s)) is not None
+    ] or fs_platforms
+    platform_list = sorted(platform_list)
+
+    # A "new platforms" scan skips platforms that already exist in the database,
+    # so they must be excluded from the totals to keep the tracker accurate.
+    platforms_to_scan = platform_list
+    if scan_type == ScanType.NEW_PLATFORMS:
+        platforms_to_scan = [
+            platform_slug
+            for platform_slug in platform_list
+            if db_platform_handler.get_platform_by_fs_slug(platform_slug) is None
+        ]
+
     total_roms = 0
-    for platform_slug in fs_platforms:
+    for platform_slug in platforms_to_scan:
         try:
             total_roms += await fs_rom_handler.count_roms(
                 Platform(fs_slug=platform_slug)
@@ -710,7 +729,7 @@ async def scan_platforms(
 
     await scan_stats.update(
         socket_manager=socket_manager,
-        total_platforms=len(fs_platforms),
+        total_platforms=len(platforms_to_scan),
         total_roms=total_roms,
     )
 
@@ -720,13 +739,6 @@ async def scan_platforms(
         redis_client.delete(STOP_SCAN_FLAG)
 
     try:
-        platform_list = [
-            platform.fs_slug
-            for s in platform_ids
-            if (platform := db_platform_handler.get_platform(s)) is not None
-        ] or fs_platforms
-        platform_list = sorted(platform_list)
-
         if len(platform_list) == 0:
             log.warning(
                 f"{hl(emoji.EMOJI_WARNING, color=LIGHTYELLOW)} No platforms found, verify that the folder structure is right and the volume is mounted correctly."

backend/tests/endpoints/sockets/test_scan.py

@@ -1,9 +1,10 @@
-from unittest.mock import Mock
+from unittest.mock import AsyncMock, MagicMock, Mock
 
 import pytest
 import socketio
 
-from endpoints.sockets.scan import ScanStats, _should_scan_rom
+from endpoints.sockets import scan as scan_module
+from endpoints.sockets.scan import ScanStats, _should_scan_rom, scan_platforms
 from handler.filesystem.roms_handler import FSRomsHandler
 from handler.metadata.base_handler import UniversalPlatformSlug as UPS
 from handler.scan_handler import ScanType
@@ -74,6 +75,89 @@ async def test_merging_scan_stats():
     assert stats.new_firmware == 25
 
 
+class TestScanTotals:
+    """The scan tracker totals must reflect the platforms/roms actually scanned."""
+
+    @pytest.fixture
+    def patched(self, mocker):
+        """Patch the collaborators of scan_platforms so totals can be inspected."""
+        socket_manager = AsyncMock()
+        mocker.patch.object(
+            scan_module, "_get_socket_manager", return_value=socket_manager
+        )
+        mocker.patch.object(
+            scan_module.fs_platform_handler,
+            "get_platforms",
+            AsyncMock(return_value=["existing", "new1", "new2"]),
+        )
+        # Each platform reports 100 roms on disk.
+        mocker.patch.object(
+            scan_module.fs_rom_handler, "count_roms", AsyncMock(return_value=100)
+        )
+        mocker.patch.object(scan_module.meta_gamelist_handler, "clear_cache")
+        mocker.patch.object(
+            scan_module.db_platform_handler, "mark_missing_platforms", return_value=[]
+        )
+        mocker.patch.object(
+            scan_module.db_platform_handler, "get_platforms", return_value=[]
+        )
+        mocker.patch.object(
+            scan_module.db_rom_handler, "invalidate_filter_values_cache"
+        )
+        config = MagicMock()
+        config.GAMELIST_AUTO_EXPORT_ON_SCAN = False
+        config.PEGASUS_AUTO_EXPORT_ON_SCAN = False
+        mocker.patch.object(scan_module.cm, "get_config", return_value=config)
+
+        # Skip the actual per-platform scanning, returning the stats unchanged.
+        async def fake_identify(**kwargs):
+            return kwargs["scan_stats"]
+
+        mocker.patch.object(
+            scan_module, "_identify_platform", side_effect=fake_identify
+        )
+        return socket_manager
+
+    async def test_new_platforms_total_excludes_existing(self, patched, mocker):
+        """NEW_PLATFORMS totals must skip platforms already in the database."""
+
+        def get_by_fs_slug(fs_slug):
+            return MagicMock() if fs_slug == "existing" else None
+
+        mocker.patch.object(
+            scan_module.db_platform_handler,
+            "get_platform_by_fs_slug",
+            side_effect=get_by_fs_slug,
+        )
+
+        result = await scan_platforms(
+            platform_ids=[],
+            metadata_sources=[],
+            scan_type=ScanType.NEW_PLATFORMS,
+        )
+
+        # Only the two new platforms (and their roms) should be counted.
+        assert result.total_platforms == 2
+        assert result.total_roms == 200
+
+    async def test_complete_scan_counts_all_selected(self, patched, mocker):
+        """COMPLETE totals include every filesystem platform being scanned."""
+        mocker.patch.object(
+            scan_module.db_platform_handler,
+            "get_platform_by_fs_slug",
+            return_value=MagicMock(),
+        )
+
+        result = await scan_platforms(
+            platform_ids=[],
+            metadata_sources=[],
+            scan_type=ScanType.COMPLETE,
+        )
+
+        assert result.total_platforms == 3
+        assert result.total_roms == 300
+
+
 class TestShouldScanRom:
     def test_new_platforms_scan_with_no_rom(self):
         """NEW_PLATFORMS should scan when rom is None"""