Add transparent library health engine

tests/test_health.py

@@ -0,0 +1,56 @@
+from pathlib import Path
+
+from serato_doctor.health import analyze_health
+from serato_doctor.models.library import Library
+from serato_doctor.models.reference import TrackReference
+from serato_doctor.models.track import DiskTrack
+
+
+def reference(filename):
+    return TrackReference(
+        Path("Test.crate"), Path("/old/House") / filename, filename
+    )
+
+
+def track(filename, folder="House"):
+    path = Path("/new") / folder / filename
+    return DiskTrack(path, filename, 100, path.suffix.lower())
+
+
+def test_health_report_exposes_each_metric():
+    library = Library.build(
+        [
+            reference("Found.mp3"),
+            reference("Conflict.mp3"),
+            reference("Absent.mp3"),
+        ],
+        [
+            track("Found.mp3"),
+            track("Conflict 2.mp3"),
+            track("Conflict 2.mp3", "Backup"),
+            track("Unused.mp3"),
+        ],
+    )
+
+    report = analyze_health(library)
+
+    assert report.score == 33.3
+    assert report.score_basis == (
+        "Resolved crate references / total crate references"
+    )
+    assert report.total_references == 3
+    assert report.healthy_references == 1
+    assert report.missing_references == 2
+    assert report.unique_missing_filenames == 2
+    assert report.disk_tracks == 4
+    assert report.duplicate_filename_groups == 1
+    assert report.duplicate_files == 1
+    assert report.unused_tracks == 3
+    assert report.suggested_matches == 1
+
+
+def test_empty_library_has_no_health_score():
+    report = analyze_health(Library.build([], []))
+
+    assert report.score is None
+    assert report.total_references == 0