Consolidate hash functions into single implementation

Extract file open/seek/restore logic into _open_for_hashing context
manager and use a single hash loop in compute_blake3_hash for both
file paths and file objects.

Amp-Thread-ID: https://ampcode.com/threads/T-019ccb05-0db1-7206-8bd9-1c2efb898fef
Co-authored-by: Amp <amp@ampcode.com>

Author: luke-mino-altherr

app/assets/services/hashing.py

@@ -1,7 +1,8 @@
 import io
 import os
+from contextlib import contextmanager
 from dataclasses import dataclass
-from typing import IO, Any, Callable
+from typing import IO, Any, Callable, Iterator
 
 from blake3 import blake3
 
@@ -20,6 +21,29 @@ class HashCheckpoint:
     file_size: int = 0
 
 
+@contextmanager
+def _open_for_hashing(fp: str | IO[bytes]) -> Iterator[tuple[IO[bytes], bool]]:
+    """Yield (file_object, is_path) with appropriate setup/teardown."""
+    if hasattr(fp, "read"):
+        seekable = getattr(fp, "seekable", lambda: False)()
+        orig_pos = None
+        if seekable:
+            try:
+                orig_pos = fp.tell()
+                if orig_pos != 0:
+                    fp.seek(0)
+            except io.UnsupportedOperation:
+                orig_pos = None
+        try:
+            yield fp, False
+        finally:
+            if orig_pos is not None:
+                fp.seek(orig_pos)
+    else:
+        with open(os.fspath(fp), "rb") as f:
+            yield f, True
+
+
 def compute_blake3_hash(
     fp: str | IO[bytes],
     chunk_size: int = DEFAULT_CHUNK,
@@ -42,67 +66,30 @@ def compute_blake3_hash(
         (None, checkpoint) on interruption (file paths only), or
         (None, None) on interruption of a file object
     """
-    if hasattr(fp, "read"):
-        digest = _hash_file_obj(fp, chunk_size, interrupt_check)
-        return digest, None
+    if chunk_size <= 0:
+        chunk_size = DEFAULT_CHUNK
 
-    with open(os.fspath(fp), "rb") as f:
-        if checkpoint is not None:
+    with _open_for_hashing(fp) as (f, is_path):
+        if checkpoint is not None and is_path:
             f.seek(checkpoint.bytes_processed)
             h = checkpoint.hasher
             bytes_processed = checkpoint.bytes_processed
         else:
             h = blake3()
             bytes_processed = 0
 
-        if chunk_size <= 0:
-            chunk_size = DEFAULT_CHUNK
-
         while True:
             if interrupt_check is not None and interrupt_check():
-                return None, HashCheckpoint(
-                    bytes_processed=bytes_processed,
-                    hasher=h,
-                )
+                if is_path:
+                    return None, HashCheckpoint(
+                        bytes_processed=bytes_processed,
+                        hasher=h,
+                    )
+                return None, None
             chunk = f.read(chunk_size)
             if not chunk:
                 break
             h.update(chunk)
             bytes_processed += len(chunk)
 
         return h.hexdigest(), None
-
-
-def _hash_file_obj(
-    file_obj: IO,
-    chunk_size: int = DEFAULT_CHUNK,
-    interrupt_check: InterruptCheck | None = None,
-) -> str | None:
-    if chunk_size <= 0:
-        chunk_size = DEFAULT_CHUNK
-
-    seekable = getattr(file_obj, "seekable", lambda: False)()
-    orig_pos = None
-
-    if seekable:
-        try:
-            orig_pos = file_obj.tell()
-            if orig_pos != 0:
-                file_obj.seek(0)
-        except io.UnsupportedOperation:
-            seekable = False
-            orig_pos = None
-
-    try:
-        h = blake3()
-        while True:
-            if interrupt_check is not None and interrupt_check():
-                return None
-            chunk = file_obj.read(chunk_size)
-            if not chunk:
-                break
-            h.update(chunk)
-        return h.hexdigest()
-    finally:
-        if seekable and orig_pos is not None:
-            file_obj.seek(orig_pos)