fix: backfill transfer download history matching

Fixes #5702

tests/test_transfer_download_history_lookup.py

@@ -0,0 +1,91 @@
+import unittest
+from pathlib import Path
+from types import SimpleNamespace
+
+from app.chain.transfer import TransferChain
+
+
+class FakeDownloadHistoryOper:
+    def __init__(
+        self,
+        histories_by_hash=None,
+        histories_by_path=None,
+        files_by_fullpath=None,
+        files_by_savepath=None,
+    ):
+        self.histories_by_hash = histories_by_hash or {}
+        self.histories_by_path = histories_by_path or {}
+        self.files_by_fullpath = files_by_fullpath or {}
+        self.files_by_savepath = files_by_savepath or {}
+
+    def get_by_hash(self, download_hash: str):
+        return self.histories_by_hash.get(download_hash)
+
+    def get_by_path(self, path: str):
+        return self.histories_by_path.get(path)
+
+    def get_file_by_fullpath(self, fullpath: str):
+        return self.files_by_fullpath.get(fullpath)
+
+    def get_files_by_savepath(self, savepath: str):
+        return self.files_by_savepath.get(savepath, [])
+
+
+class TransferDownloadHistoryLookupTest(unittest.TestCase):
+    def test_resolve_download_history_falls_back_to_parent_download_path(self):
+        expected = SimpleNamespace(download_hash="hash1", downloader="qb")
+        oper = FakeDownloadHistoryOper(
+            histories_by_hash={"hash1": expected},
+            histories_by_path={"/downloads/season-pack": expected},
+        )
+
+        history = TransferChain._resolve_download_history(
+            downloadhis=oper,
+            file_path=Path("/downloads/season-pack/Test.Show.S01E01.mkv"),
+        )
+
+        self.assertIs(history, expected)
+
+    def test_resolve_download_history_falls_back_to_unique_savepath_hash(self):
+        expected = SimpleNamespace(download_hash="hash1", downloader="qb")
+        oper = FakeDownloadHistoryOper(
+            histories_by_hash={"hash1": expected},
+            files_by_savepath={
+                "/downloads/season-pack": [
+                    SimpleNamespace(download_hash="hash1"),
+                    SimpleNamespace(download_hash="hash1"),
+                ]
+            },
+        )
+
+        history = TransferChain._resolve_download_history(
+            downloadhis=oper,
+            file_path=Path("/downloads/season-pack/subs/Test.Show.S01E01.zh.ass"),
+        )
+
+        self.assertIs(history, expected)
+
+    def test_resolve_download_history_skips_ambiguous_savepath_hashes(self):
+        oper = FakeDownloadHistoryOper(
+            histories_by_hash={
+                "hash1": SimpleNamespace(download_hash="hash1", downloader="qb"),
+                "hash2": SimpleNamespace(download_hash="hash2", downloader="tr"),
+            },
+            files_by_savepath={
+                "/downloads/shared": [
+                    SimpleNamespace(download_hash="hash1"),
+                    SimpleNamespace(download_hash="hash2"),
+                ]
+            },
+        )
+
+        history = TransferChain._resolve_download_history(
+            downloadhis=oper,
+            file_path=Path("/downloads/shared/Test.Show.S01E01.mkv"),
+        )
+
+        self.assertIsNone(history)
+
+
+if __name__ == "__main__":
+    unittest.main()