[postprocessor:metadata] implement 'mode: modify' (#2640)

docs/configuration.rst

@@ -3312,14 +3312,15 @@ Type
 Default
     ``"json"``
 Description
-    Select how to write metadata.
+    Selects how to process metadata.
 
-    * ``"json"``: all metadata using `json.dump()
+    * ``"json"``: write metadata using `json.dump()
       <https://docs.python.org/3/library/json.html#json.dump>`_
-    * ``"tags"``: ``tags`` separated by newlines
-    * ``"custom"``: result of applying `metadata.content-format`_
+    * ``"tags"``: write ``tags`` separated by newlines
+    * ``"custom"``: write the result of applying `metadata.content-format`_
       to a file's metadata dictionary
-    * ``"delete"``: remove metadata entries specified in `metadata.fields`_
+    * ``"modify"``: add or modify metadata entries
+    * ``"delete"``: remove metadata entries
 
 
 metadata.filename
@@ -3411,11 +3412,27 @@ Description
 metadata.fields
 ---------------
 Type
-    ``list`` of ``strings``
+    * ``list`` of ``strings``
+    * ``object`` (`field name` -> `format string`_)
 Example
-    ``["blocked", "watching", "status[creator][name]"]``
+    * .. code:: json
+
+        ["blocked", "watching", "status[creator][name]"]
+
+    * .. code:: json
+
+        {
+            "blocked"         : "***",
+            "watching"        : "\fE 'yes' if watching else 'no'",
+            "status[username]": "{status[creator][name]!l}"
+        }
+
 Description
-    List of metadata field names to remove for ``"mode": "delete"``.
+    * ``"mode": "delete"``:
+        A list of metadata field names to remove.
+    * ``"mode": "modify"``:
+        An object with metadata field names mapping to a `format string`_
+        whose result is assigned to said field name.
 
 
 metadata.content-format

gallery_dl/postprocessor/metadata.py

@@ -30,6 +30,13 @@ class MetadataPP(PostProcessor):
         elif mode == "tags":
             self.write = self._write_tags
             ext = "txt"
+        elif mode == "modify":
+            self.run = self._run_modify
+            self.fields = {
+                name: formatter.parse(value, None, util.identity).format_map
+                for name, value in options.get("fields").items()
+            }
+            ext = None
         elif mode == "delete":
             self.run = self._run_delete
             self.fields = options.get("fields")
@@ -118,6 +125,19 @@ class MetadataPP(PostProcessor):
     def _run_stdout(self, pathfmt):
         self.write(sys.stdout, pathfmt.kwdict)
 
+    def _run_modify(self, pathfmt):
+        kwdict = pathfmt.kwdict
+        for key, func in self.fields.items():
+            obj = kwdict
+            try:
+                while "[" in key:
+                    name, _, key = key.partition("[")
+                    obj = obj[name]
+                    key = key.rstrip("]")
+                obj[key] = func(kwdict)
+            except Exception:
+                pass
+
     def _run_delete(self, pathfmt):
         kwdict = pathfmt.kwdict
         for key in self.fields:

test/test_postprocessor.py

@@ -339,15 +339,39 @@ class MetadataTest(BasePostprocessorTest):
 {"category": "test", "extension": "ext", "filename": "file"}
 """)
 
+    def test_metadata_modify(self):
+        kwdict = {"foo": 0, "bar": {"bax": 1, "bay": 2, "baz": 3}}
+        self._create({
+            "mode": "modify",
+            "fields": {
+                "foo"     : "{filename}-{foo!s}",
+                "foo2"    : "\fE bar['bax'] + 122",
+                "bar[baz]": "{_now}",
+                "bar[ba2]": "test",
+            },
+        }, kwdict)
+        pdict = self.pathfmt.kwdict
+
+        self.assertIsNot(kwdict, pdict)
+        self.assertEqual(pdict["foo"], kwdict["foo"])
+        self.assertEqual(pdict["bar"], kwdict["bar"])
+
+        self._trigger()
+
+        self.assertEqual(pdict["foo"]       , "file-0")
+        self.assertEqual(pdict["foo2"]      , 123)
+        self.assertEqual(pdict["bar"]["ba2"], "test")
+        self.assertIsInstance(pdict["bar"]["baz"], datetime)
+
     def test_metadata_delete(self):
         kwdict = {"foo": 0, "bar": {"bax": 1, "bay": 2, "baz": 3}}
         self._create({"mode": "delete", "fields": ["foo", "bar[baz]"]}, kwdict)
         pdict = self.pathfmt.kwdict
 
+        self.assertIsNot(kwdict, pdict)
         self.assertEqual(pdict["foo"], kwdict["foo"])
         self.assertEqual(pdict["bar"], kwdict["bar"])
 
-        self.assertIsNot(kwdict, pdict)
         del kwdict["foo"]
         del kwdict["bar"]["baz"]