[pp:metadata] implement format strings for 'directory' (#5728)

docs/configuration.rst

@@ -5442,11 +5442,13 @@ Description
 metadata.directory
 ------------------
 Type
-    ``string``
+    * ``string``
+    * ``list`` of ``strings``
 Default
     ``"."``
 Example
-    ``"metadata"``
+    * ``"metadata"``
+    * ``["..", "metadata", "\fF {id // 500 * 500}"]``
 Description
     Directory where metadata files are stored in relative to the
     current target location for file downloads.

gallery_dl/postprocessor/metadata.py

@@ -56,7 +56,13 @@ class MetadataPP(PostProcessor):
             ext = "json"
 
         directory = options.get("directory")
-        if directory:
+        if isinstance(directory, list):
+            self._directory = self._directory_format
+            self._directory_formatters = [
+                formatter.parse(dirfmt, util.NONE).format_map
+                for dirfmt in directory
+            ]
+        elif directory:
             self._directory = self._directory_custom
             sep = os.sep + (os.altsep or "")
             self._metadir = util.expand_path(directory).rstrip(sep) + os.sep
@@ -147,6 +153,16 @@ class MetadataPP(PostProcessor):
     def _directory_custom(self, pathfmt):
         return os.path.join(pathfmt.realdirectory, self._metadir)
 
+    def _directory_format(self, pathfmt):
+        formatters = pathfmt.directory_formatters
+        try:
+            pathfmt.directory_formatters = self._directory_formatters
+            segments = pathfmt.build_directory(pathfmt.kwdict)
+            directory = pathfmt.clean_path(os.sep.join(segments) + os.sep)
+            return os.path.join(pathfmt.realdirectory, directory)
+        finally:
+            pathfmt.directory_formatters = formatters
+
     def _filename(self, pathfmt):
         return (pathfmt.filename or "metadata") + "." + self.extension
 

test/test_postprocessor.py

@@ -440,6 +440,18 @@ class MetadataTest(BasePostprocessorTest):
         path = self.pathfmt.realdirectory + "metadata/file.json"
         m.assert_called_once_with(path, "w", encoding="utf-8")
 
+    def test_metadata_directory_format(self):
+        self._create(
+            {"directory": ["..", "json", "\fF {id // 500 * 500 + 500}"]},
+            {"id": 12345},
+        )
+
+        with patch("builtins.open", mock_open()) as m:
+            self._trigger()
+
+        path = self.pathfmt.realdirectory + "../json/12500/file.ext.json"
+        m.assert_called_once_with(path, "w", encoding="utf-8")
+
     def test_metadata_filename(self):
         self._create({
             "filename"        : "{category}_{filename}_/meta/\n\r.data",