feat: bootstrap NAS music deduper

am_deduper/hashing.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+import hashlib
+from pathlib import Path
+
+from .constants import FAST_HASH_CHUNK
+
+
+def fast_hash(path: Path) -> str:
+    """Hash size + first/last 64 KiB; used only as a candidate key."""
+    size = path.stat().st_size
+    with path.open("rb") as f:
+        head = f.read(FAST_HASH_CHUNK)
+        if size > FAST_HASH_CHUNK:
+            f.seek(max(0, size - FAST_HASH_CHUNK))
+        tail = f.read(FAST_HASH_CHUNK)
+    h = hashlib.sha256()
+    h.update(str(size).encode())
+    h.update(b"\0")
+    h.update(head)
+    h.update(b"\0")
+    h.update(tail)
+    return h.hexdigest()
+
+
+def sha256(path: Path, chunk_size: int = 1024 * 1024) -> str:
+    h = hashlib.sha256()
+    with path.open("rb") as f:
+        while True:
+            chunk = f.read(chunk_size)
+            if not chunk:
+                break
+            h.update(chunk)
+    return h.hexdigest()