Implement Regex Rules backend functionality for path mapping

- Add CompiledRegexRules dataclass for all four processing stages
- Update _compile_regex_rules to support both legacy (pattern/replacement)
  and new (search/replace) field names with proper empty string handling
- Add _compile_path_mapping_rules helper function
- Update _write_results to apply post-processing rules:
  - local_result.m3u8 with local_post rules
  - remote_result.m3u8 with remote_post rules
  - base_next.m3u8 unprocessed (normalized sync result)
- Update merge_playlists and _sync_single_playlist to pass compiled_rules
- Update sync_all_playlists to implement full processing flow:
  1. Detect REGEX mode from path_mapping config
  2. Apply local_pre rules to local playlists before sync
  3. Apply remote_pre rules to remote playlists before sync
  4. Perform sync/merge
  5. Apply post rules to results for respective outputs

Co-authored-by: Koha9 <36852125+Koha9@users.noreply.github.com>

app/utils/playlist_merge.py

@@ -40,6 +40,15 @@ class PlaylistSyncResult:
     output_dir: str
 
 
+@dataclass
+class CompiledRegexRules:
+    """Holds compiled regex rules for all four processing stages."""
+    local_pre: list[tuple[re.Pattern[str], str]]
+    local_post: list[tuple[re.Pattern[str], str]]
+    remote_pre: list[tuple[re.Pattern[str], str]]
+    remote_post: list[tuple[re.Pattern[str], str]]
+
+
 def load_paths(text: str) -> list[str]:
     """Normalize playlist text into a list of absolute paths.
 
@@ -72,12 +81,21 @@ def save_paths(paths: Sequence[str]) -> str:
 
 
 def _compile_regex_rules(rules: Sequence[dict[str, str]]) -> list[tuple[re.Pattern[str], str]]:
+    """Compile regex rules into pattern/replacement pairs.
+    
+    Supports both legacy format (pattern/replacement) and new format (search/replace).
+    """
     compiled: list[tuple[re.Pattern[str], str]] = []
     for rule in rules:
-        pattern = rule.get("pattern")
+        # Support both legacy (pattern/replacement) and new (search/replace) field names
+        # Use explicit None checks to allow empty strings as valid values
+        pattern = rule.get("pattern") if rule.get("pattern") is not None else rule.get("search")
         if not pattern:
             continue
-        replacement = rule.get("replacement", "")
+        # For replacement, empty string is a valid value (for deletion)
+        replacement = rule.get("replacement") if rule.get("replacement") is not None else rule.get("replace")
+        if replacement is None:
+            replacement = ""
         try:
             compiled.append((re.compile(pattern), replacement))
         except re.error as exc:
@@ -234,9 +252,31 @@ def _merge_chunks(
     return chunks
 
 
-def _write_results(merged_lines: Sequence[str], folder: str) -> None:
+def _write_results(
-    _save_playlist_to_folder("local_result.m3u8", merged_lines, folder)
+    merged_lines: Sequence[str], 
-    _save_playlist_to_folder("remote_result.m3u8", merged_lines, folder)
+    folder: str,
+    compiled_rules: CompiledRegexRules | None = None
+) -> None:
+    """Write sync results to the test folder.
+    
+    If compiled_rules is provided with post-processing rules:
+    - local_result.m3u8: merged_lines processed with local_post rules
+    - remote_result.m3u8: merged_lines processed with remote_post rules
+    - base_next.m3u8: unprocessed merged_lines (normalized sync result)
+    """
+    # Apply post-processing regex rules if provided
+    if compiled_rules and compiled_rules.local_post:
+        local_lines = _apply_compiled_rules_to_paths(merged_lines, compiled_rules.local_post)
+    else:
+        local_lines = list(merged_lines)
+    
+    if compiled_rules and compiled_rules.remote_post:
+        remote_lines = _apply_compiled_rules_to_paths(merged_lines, compiled_rules.remote_post)
+    else:
+        remote_lines = list(merged_lines)
+    
+    _save_playlist_to_folder("local_result.m3u8", local_lines, folder)
+    _save_playlist_to_folder("remote_result.m3u8", remote_lines, folder)
     _save_playlist_to_folder("base_next.m3u8", merged_lines, folder)
 
 
@@ -379,12 +419,16 @@ def merge_playlists(
     remote_text: str,
     strategy: ConflictResolutionStrategy = ConflictResolutionStrategy.LOCAL_PRIORITY,
     test_folder: str = TEST_PLAYLIST_DIR,
+    compiled_rules: CompiledRegexRules | None = None,
 ) -> MergeResult:
     """Merge playlists using diff3 and resolve conflicts per strategy.
 
     The base, local, and remote normalized playlists are saved into ``test_folder``
     for inspection. The merged playlist is also stored twice to simulate the
     versions intended for local save and cloud upload.
+    
+    If compiled_rules is provided, post-processing regex rules will be applied
+    to the results before writing.
     """
 
     base_paths, local_paths, remote_paths = _normalize_inputs(
@@ -420,7 +464,7 @@ def merge_playlists(
             merged_lines, base_paths, local_paths, remote_paths
         )
 
-    _write_results(merged_lines, test_folder)
+    _write_results(merged_lines, test_folder, compiled_rules)
 
     return MergeResult(merged_paths=merged_lines, conflicts=conflicts)
 
@@ -517,6 +561,7 @@ def _sync_single_playlist(
     remote_text: str,
     playlist_folder: str,
     remote_present: bool,
+    compiled_rules: CompiledRegexRules | None = None,
 ) -> PlaylistSyncResult:
     local_present = local_text is not None
     local_text = local_text or ""
@@ -535,7 +580,7 @@ def _sync_single_playlist(
             base_text, local_text, remote_text, playlist_folder
         )
         merged_lines = list(local_paths)
-        _write_results(merged_lines, playlist_folder)
+        _write_results(merged_lines, playlist_folder, compiled_rules)
         return PlaylistSyncResult(playlist, merged_lines, [], "synced", playlist_folder)
 
     if mode == SyncMode.REMOTE_FORCE:
@@ -547,7 +592,7 @@ def _sync_single_playlist(
             base_text, local_text, remote_text, playlist_folder
         )
         merged_lines = list(remote_paths)
-        _write_results(merged_lines, playlist_folder)
+        _write_results(merged_lines, playlist_folder, compiled_rules)
         return PlaylistSyncResult(playlist, merged_lines, [], "synced", playlist_folder)
 
     if mode not in (SyncMode.MERGE_LOCAL_PRIMARY, SyncMode.MERGE_REMOTE_PRIMARY):
@@ -565,6 +610,7 @@ def _sync_single_playlist(
         remote_text=remote_text,
         strategy=merge_strategy,
         test_folder=playlist_folder,
+        compiled_rules=compiled_rules,
     )
 
     if not merge_result.merged_paths and (not local_present or not remote_present):
@@ -578,13 +624,48 @@ def _sync_single_playlist(
     )
 
 
+def _compile_path_mapping_rules(path_mapping: dict) -> CompiledRegexRules:
+    """Compile regex rules from path_mapping config for all four processing stages."""
+    regex_config = path_mapping.get("regex", {})
+    return CompiledRegexRules(
+        local_pre=_compile_regex_rules(regex_config.get("local_pre", [])),
+        local_post=_compile_regex_rules(regex_config.get("local_post", [])),
+        remote_pre=_compile_regex_rules(regex_config.get("remote_pre", [])),
+        remote_post=_compile_regex_rules(regex_config.get("remote_post", [])),
+    )
+
+
 def sync_all_playlists(
     local_dir: str, mode: SyncMode, test_folder: str = TEST_PLAYLIST_DIR
 ) -> list[PlaylistSyncResult]:
-    """Synchronize all playlists that can be matched by name."""
+    """Synchronize all playlists that can be matched by name.
+    
+    When path_mapping mode is REGEX, the following processing flow is applied:
+    1. local_pre rules are applied to local playlists before sync
+    2. remote_pre rules are applied to remote playlists before sync
+    3. Sync/merge is performed
+    4. local_post rules are applied to results before writing to local_result.m3u8
+    5. remote_post rules are applied to results before writing to remote_result.m3u8
+    """
 
     server_config.load()
-    compiled_rules = _compile_regex_rules(server_config.path_rules)
+    
+    # Check if we should use the new path_mapping REGEX mode
+    path_mapping = server_config.path_mapping
+    use_regex_mode = path_mapping.get("mode") == "REGEX"
+    
+    # Compile rules based on the mode
+    compiled_rules: CompiledRegexRules | None = None
+    legacy_compiled_rules: list[tuple[re.Pattern[str], str]] = []
+    
+    if use_regex_mode:
+        compiled_rules = _compile_path_mapping_rules(path_mapping)
+        logger.info("Using REGEX mode for path mapping with 4 rule groups")
+    else:
+        # Use legacy path_rules for backward compatibility
+        legacy_compiled_rules = _compile_regex_rules(server_config.path_rules)
+        logger.info("Using legacy path_rules for preprocessing")
+    
     _ensure_test_dir(test_folder)
     logger.info(f"Syncing playlists to test folder: {test_folder}")
     local_playlists = _load_local_playlists(local_dir)
@@ -613,15 +694,28 @@ def sync_all_playlists(
             remote_text = snapshot_remote_text
             remote_present = bool(remote_text.strip()) or remote_exists
 
+        if use_regex_mode and compiled_rules:
+            # Apply pre-processing rules for REGEX mode
+            # base_text doesn't need pre-processing as it's the normalized state
+            if local_text is not None and compiled_rules.local_pre:
+                local_text = preprocess_playlist_text(
+                    local_text, [], compiled_rules.local_pre
+                )
+            if remote_text and compiled_rules.remote_pre:
+                remote_text = preprocess_playlist_text(
+                    remote_text, [], compiled_rules.remote_pre
+                )
+        else:
+            # Use legacy preprocessing for all texts
             base_text = preprocess_playlist_text(
-            base_text, server_config.path_rules, compiled_rules
+                base_text, server_config.path_rules, legacy_compiled_rules
             )
             remote_text = preprocess_playlist_text(
-            remote_text, server_config.path_rules, compiled_rules
+                remote_text, server_config.path_rules, legacy_compiled_rules
             )
             if local_text is not None:
                 local_text = preprocess_playlist_text(
-                local_text, server_config.path_rules, compiled_rules
+                    local_text, server_config.path_rules, legacy_compiled_rules
                 )
 
         # Treat missing remote text as absent playlist.
@@ -633,6 +727,7 @@ def sync_all_playlists(
             remote_text=remote_text,
             playlist_folder=playlist_folder,
             remote_present=remote_present,
+            compiled_rules=compiled_rules if use_regex_mode else None,
         )
         results.append(result)