[IMPR]: lazy load imageinfo metadata

In case of large pdf/djvu file, a lot of data is transmitted as text
layer is stored as metadata. Lazy load metadata if needed.

Bug: T253591
Change-Id: I742dfb7e0baf22c00698235a87ff805c47e996e9
---
M pywikibot/__init__.py
M tests/site_generators_tests.py
M pywikibot/page/_filepage.py
M pywikibot/site/_apisite.py
M tests/file_tests.py
M pywikibot/data/api/_generators.py
6 files changed, 97 insertions(+), 18 deletions(-)

diff --git a/pywikibot/__init__.py b/pywikibot/__init__.py
index 69bf268..02e7e2f 100644
--- a/pywikibot/__init__.py
+++ b/pywikibot/__init__.py
@@ -72,8 +72,8 @@
     stdout,
     warning,
 )
-from pywikibot.site import APISite, BaseSite
 from pywikibot.time import Timestamp
+from pywikibot.site import APISite, BaseSite
 from pywikibot.tools import PYTHON_VERSION, normalize_username
 
 
diff --git a/pywikibot/data/api/_generators.py b/pywikibot/data/api/_generators.py
index 07f0338..45a1e57 100644
--- a/pywikibot/data/api/_generators.py
+++ b/pywikibot/data/api/_generators.py
@@ -701,7 +701,7 @@
                 and 'protection' in parameters['inprop']):
             append_params(parameters, 'inprop', 'protection')
         append_params(parameters, 'iiprop',
-                      'timestamp|user|comment|url|size|sha1|metadata')
+                      'timestamp|user|comment|url|size|sha1')
         append_params(parameters, 'iilimit', 'max')  # T194233
         parameters['generator'] = generator
         super().__init__(**kwargs)
diff --git a/pywikibot/page/_filepage.py b/pywikibot/page/_filepage.py
index f9347ad..e95da06 100644
--- a/pywikibot/page/_filepage.py
+++ b/pywikibot/page/_filepage.py
@@ -65,6 +65,12 @@
             )
 
     def _load_file_revisions(self, imageinfo) -> None:
+        """
+        Store an Image revision of FilePage (a FileInfo object) in local cache.
+
+        Metadata shall be added lazily to the revision already present
+        in cache.
+        """
         for file_rev in imageinfo:
             # filemissing in API response indicates most fields are missing
             # see https://gerrit.wikimedia.org/r/c/mediawiki/core/+/533482/
@@ -72,8 +78,13 @@
                 pywikibot.warning(
                     f"File '{self.title()}' contains missing revisions")
                 continue
-            file_revision = FileInfo(file_rev)
-            self._file_revisions[file_revision.timestamp] = file_revision
+
+            ts_key = pywikibot.Timestamp.fromISOformat(file_rev['timestamp'])
+            file_revision = self._file_revisions.setdefault(
+                ts_key, FileInfo(file_rev, self))
+
+            # add new imageinfo attributes since last request.
+            file_revision.update(file_rev)
 
     @property
     def latest_file_info(self):
@@ -105,6 +116,20 @@
         oldest_ts = min(self._file_revisions)
         return self._file_revisions[oldest_ts]
 
+    def get_file_info(self, ts) -> dict:
+        """
+        Retrieve and store information of a specific Image rev. of FilePage.
+
+        This function will load also metadata.
+        It is also used as a helper in FileInfo to load metadata lazily.
+
+        :param ts: timestamp of the Image rev. to retrieve
+
+        :return: instance of FileInfo()
+        """
+        self.site.loadimageinfo(self, history=False, timestamp=ts)
+        return self._file_revisions[ts]
+
     def get_file_history(self) -> dict:
         """
         Return the file's version history.
@@ -431,7 +456,7 @@
     Attributes can be retrieved both as self['key'] or self.key.
 
     Following attributes will be returned:
-        - timestamp, user, comment, url, size, sha1, mime, metadata
+        - timestamp, user, comment, url, size, sha1, mime, metadata (lazily)
         - archivename (not for latest revision)
 
     see :meth:`Site.loadimageinfo()
@@ -442,12 +467,23 @@
     .. versionchanged:: 7.7
        raises KeyError instead of AttributeError if FileInfo is used as
        Mapping.
+    .. versionchanged:: 8.6.0
+       Metadata are loaded lazily.
+       Added *filepage* parameter.
     """
 
-    def __init__(self, file_revision) -> None:
+    def __init__(self, file_revision, filepage) -> None:
         """Initiate the class using the dict from ``APISite.loadimageinfo``."""
-        self.__dict__.update(file_revision)
-        self.timestamp = pywikibot.Timestamp.fromISOformat(self.timestamp)
+        self.filepage = filepage
+        self._metadata = None
+        self.update(file_revision)
+
+    def update(self, file_revision):
+        """Update FileInfo with new values."""
+        for k, v in file_revision.items():
+            if k == 'timestamp':
+                v = pywikibot.Timestamp.fromISOformat(v)
+            setattr(self, k, v)
 
     def __getitem__(self, key):
         """Give access to class values by key."""
@@ -464,3 +500,15 @@
     def __eq__(self, other) -> bool:
         """Test if two FileInfo objects are equal."""
         return self.__dict__ == other.__dict__
+
+    @property
+    def metadata(self):
+        """Return metadata."""
+        if self._metadata is None:
+            self.filepage.get_file_info(self.timestamp)
+        return self._metadata
+
+    @metadata.setter
+    def metadata(self, value):
+        """Set metadata."""
+        self._metadata = value
diff --git a/pywikibot/site/_apisite.py b/pywikibot/site/_apisite.py
index 332eada..d3f2652 100644
--- a/pywikibot/site/_apisite.py
+++ b/pywikibot/site/_apisite.py
@@ -1362,27 +1362,35 @@
         history: bool = False,
         url_width: Optional[int] = None,
         url_height: Optional[int] = None,
-        url_param: Optional[str] = None
+        url_param: Optional[str] = None,
+        timestamp: Optional[pywikibot.Timestamp] = None
     ) -> None:
         """Load image info from api and save in page attributes.
 
         The following properties are loaded: ``timestamp``, ``user``,
         ``comment``, ``url``, ``size``, ``sha1``, ``mime``, ``mediatype``,
-        ``metadata``, ``archivename`` and ``bitdepth``. If *url_width*,
-        *url_height* or *url_param* is given, additional properties
-        ``thumbwidth``, ``thumbheight``, ``thumburl`` and
+        ``archivename`` and ``bitdepth``.
+        ``metadata``is loaded only if history is False.
+        If *url_width*, *url_height* or *url_param* is given, additional
+        properties ``thumbwidth``, ``thumbheight``, ``thumburl`` and
         ``responsiveUrls`` are given.
 
         .. note:: Parameters validation and error handling left to the
            API call.
         .. versionchanged:: 8.2
            *mediatype* and *bitdepth* properties were added.
+        .. versionchanged:: 8.6.0
+           Added *timestamp* parameter.
+           Metadata are loaded only if history is False.
         .. seealso:: :api:`Imageinfo`
 
         :param history: if true, return the image's version history
         :param url_width: get info for a thumbnail with given width
         :param url_height: get info for a thumbnail with given height
         :param url_param:  get info for a thumbnail with given param
+        :param timestamp: timestamp of the image's version to retrieve.
+            It has effect only if history is False.
+            If omitted, the latest version will be fetched.
         """
         args = {
             'titles': page.title(with_section=False),
@@ -1391,11 +1399,15 @@
             'iiurlparam': url_param,
             'iiprop': [
                 'timestamp', 'user', 'comment', 'url', 'size', 'sha1', 'mime',
-                'mediatype', 'metadata', 'archivename', 'bitdepth',
+                'mediatype', 'archivename', 'bitdepth',
             ]
         }
         if not history:
             args['total'] = 1
+            args['iiprop'].append('metadata')
+            if timestamp:
+                args['iistart'] = args['iiend'] = timestamp.isoformat()
+
         query = self._generator(api.PropertyGenerator,
                                 type_arg='imageinfo',
                                 **args)
diff --git a/tests/file_tests.py b/tests/file_tests.py
index adf1d92..0457925 100755
--- a/tests/file_tests.py
+++ b/tests/file_tests.py
@@ -229,6 +229,14 @@
         super().setUp()
         self.image = pywikibot.FilePage(self.site, self.file_name)
 
+    def test_lazyload_metadata(self):
+        """Test metadata lazy load."""
+        self.assertTrue(self.image.exists())
+
+        rev = self.image.latest_file_info
+        self.assertIsNone(rev._metadata)
+        self.assertIsNotNone(rev.metadata)
+
     def test_get_file_url(self):
         """Get File url."""
         self.assertTrue(self.image.exists())
diff --git a/tests/site_generators_tests.py b/tests/site_generators_tests.py
index ec63ae4..fd22d31 100755
--- a/tests/site_generators_tests.py
+++ b/tests/site_generators_tests.py
@@ -181,8 +181,7 @@
             'continue': [True],
             'inprop': ['protection'],
             'iilimit': ['max'],
-            'iiprop': ['timestamp', 'user', 'comment', 'url', 'size', 'sha1',
-                       'metadata'],
+            'iiprop': ['timestamp', 'user', 'comment', 'url', 'size', 'sha1'],
             'indexpageids': [True],
             'generator': ['templates'], 'action': ['query'],
             'prop': ['info', 'imageinfo', 'categoryinfo'],
@@ -218,7 +217,7 @@
             'inprop': ['protection'],
             'iilimit': ['max'],
             'iiprop': ['timestamp', 'user', 'comment', 'url', 'size',
-                       'sha1', 'metadata'], 'generator': ['links'],
+                       'sha1'], 'generator': ['links'],
             'prop': ['info', 'imageinfo', 'categoryinfo'],
             'redirects': [False],
         }
@@ -1108,8 +1107,7 @@
         expected_params = {
             'prop': ['info', 'imageinfo', 'categoryinfo'],
             'inprop': ['protection'],
-            'iiprop': ['timestamp', 'user', 'comment', 'url', 'size', 'sha1',
-                       'metadata'],
+            'iiprop': ['timestamp', 'user', 'comment', 'url', 'size', 'sha1'],
             'iilimit': ['max'], 'generator': ['search'], 'action': ['query'],
             'indexpageids': [True], 'continue': [True],
             'gsrnamespace': [0], 'gsrsearch': ['wiki'], 'gsrwhat': ['title']}

