feat: export lyrics default to sidecar path

lrcfetch/lrc.py

@@ -5,6 +5,9 @@ Description: Shared LRC time-tag utilities
 """
 
 import re
+from pathlib import Path
+from typing import Optional
+from urllib.parse import unquote
 
 from .models import CacheStatus
 
@@ -93,3 +96,31 @@ def detect_sync_status(text: str) -> CacheStatus:
     return (
         CacheStatus.SUCCESS_SYNCED if is_synced(text) else CacheStatus.SUCCESS_UNSYNCED
     )
+
+
+def get_audio_path(audio_url: str, ensure_exists: bool = False) -> Optional[Path]:
+    """Convert file:// URL to Path, return None if invalid or (if ensure_exists) file doesn't exist."""
+    if not audio_url.startswith("file://"):
+        return None
+    file_path = unquote(audio_url.replace("file://", "", 1))
+    path = Path(file_path)
+    if ensure_exists and not path.exists():
+        return None
+    return path
+
+
+def get_sidecar_path(
+    audio_url: str, ensure_audio_exists: bool = False, ensure_exists: bool = False
+) -> Optional[Path]:
+    """Given a file:// URL, return the corresponding .lrc sidecar path.
+
+    If ensure_audio_exists is True, return None if the audio file does not exist.
+    If ensure_exists is True, return None if the .lrc file does not exist.
+    """
+    audio_path = get_audio_path(audio_url, ensure_exists=ensure_audio_exists)
+    if not audio_path:
+        return None
+    lrc_path = audio_path.with_suffix(".lrc")
+    if ensure_exists and not lrc_path.exists():
+        return None
+    return lrc_path