karlch · karlch · Jul 5, 2023 · Feb 25, 2022 · Jan 7, 2023 · Jan 7, 2023
diff --git a/docs/changelog.rst b/docs/changelog.rst
@@ -105,6 +105,11 @@ Changed:
   supported by our testing framework, and 5.11 is out since July 2018. Code will likely
   still work with these versions, but as it is no longer tested, there is no guarantee.
 * The ``shuffle`` setting was moved into the ``sort`` group.
+* Complete refactoring of metadata support. The handler functionality is moved out
+  to the plugin space, allowing for full flexibility in choosing a suitable backend. By
+  default, ``metadata_pyexiv2`` or ``metadata_piexif`` is loaded, if the respective
+  backend is installed. The default behaviour can be overridden by explicitly loading a
+  metadata plugin.
 
 Fixed:
 ^^^^^^

diff --git a/docs/documentation/exif.rst b/docs/documentation/exif.rst
diff --git a/docs/documentation/index.rst b/docs/documentation/index.rst
@@ -10,7 +10,7 @@ The following documents are available:
    getting_started
    commands
    configuration/index
-   exif
+   metadata
    contributing
    migrating
 

diff --git a/docs/documentation/install.rst b/docs/documentation/install.rst
@@ -129,10 +129,9 @@ Dependencies
     - QtSvg (optional for svg support)
 * `PyQt5 <http://www.riverbankcomputing.com/software/pyqt/intro>`_  5.11.3 or newer
 * `setuptools <https://pypi.python.org/pypi/setuptools/>`_ (for installation)
-* `pyexiv2 <https://python3-exiv2.readthedocs.io>`_ (optional for exif support)
-* `piexif <https://pypi.org/project/piexif/>`_ (optional alternative for exif support)
-
-.. include:: pyexiv2.rst
+* `pyexiv2 <https://python3-exiv2.readthedocs.io>`_ (optional for metadata support)
+* `piexif <https://pypi.org/project/piexif/>`_ (optional alternative for metadata
+  support)
 
 Package Names For Distributions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

diff --git a/docs/documentation/metadata.rst b/docs/documentation/metadata.rst
@@ -0,0 +1,144 @@
+Metadata
+========
+
+Vimiv provides optional metadata support. If enabled, then:
+
+#. The ``:metadata`` command and the corresponding ``i``-keybinding is available. It
+   displays the metadata of the current image.
+#. The ``{exif-date-time}`` statusbar module is available. It displays the Exif
+   creation time of the current image.
+#. Metadata is automatically copied from source to destination when writing images to
+   disk.
+
+Vimiv provides full flexibility to users in terms of what metadata backend to use.
+Each backend comes with their advantages and disadvantages, and each user has different
+requirements, as well as different package support. Therefore, vimiv provides metadata
+backends as independent plugins, that can be loaded as one desires. In addition, users
+have the ability to extend vimiv's metadata capabilities using
+:ref:`custom plugins<Plugins>`, as described in
+:ref:`a later section<create_own_plugins>`.
+
+Vimiv comes with two default plugins:
+
+* ``metadata_piexif`` is based on `piexif`_
+* ``metadata_pyexiv2`` is based on `pyexiv2`_
+
+In addition, there are the following user metadata plugins available:
+
+.. _user_metadata_plugins:
+
+.. table:: Overview of user plugins
+   :widths: 20 80
+
+   ===================================================================== ===========
+   Name                                                     Description
+   ===================================================================== ===========
+   `metadata_gexiv2 <https://github.com/jcjgraf/vimiv_metadata-gexiv2>`_  Based on `gexiv2 <https://gitlab.gnome.org/GNOME/gexiv2>`_
+   ===================================================================== ===========
+
+
+Enable Support
+--------------
+
+Metadata plugins are loaded as any other vimiv plugin. To enable one of the default
+plugins, simply list its name in the ``PLUGINS`` section of the configuration file. In
+addition, you need to ensure that the required backend is installed on your system.
+
+To enable a user metadata plugin, first you need to download it, and put it into the
+plugin folder. Afterwards loading is equivalent to the default plugins.
+
+For more information on how to load plugins, please refer to the
+:ref:`plugin section<Plugins>`.
+
+If no metadata plugin is specified, vimiv will load one of the two default plugins, if
+the respective backend is installed. To disable this default behaviour, specify
+``metadata = none`` in the ``PLUGINS`` section.
+
+.. warning::
+
+   Default loading may be dropped in a future version. If you rely on metadata support,
+   we recommend to explicitly specify what backend you want.
+
+.. note::
+   Multiple metadata plugins can be registered at the same time. If they use distinct
+   keys, the value of both is combined in the output of ``:metadata``.
+
+
+Comparison of Different Plugins
+-------------------------------
+
+In short, ``metadata_pyexiv2`` is much more powerful than ``metadata_piexif``, though
+the dependencies are also more involved to install.
+
+.. table:: Comparison of the two libraries
+   :widths: 20 15 20 45
+
+   ======================= =================== ==================== =====================================================================
+   PROPERTY                ``metadata_piexif`` ``metadata_pyexiv2`` Note
+   ======================= =================== ==================== =====================================================================
+   Backend                 `piexif`_           `pyexiv2`_
+   Exif Support            True                True                 pyexiv2 can potentially extract more data for the same image
+   ICMP Support            False               True
+   XMP Suppport            False               True
+   Output Formatting       False               True                 e.g. ``FNumber: 63/10`` vs ``FNumber: F6.3``
+   Supported File Types    JPEG, TIFF          Many common types
+   Ease of installation    Simple              More complicated     pyexiv2 requires some dependencies including the C++ library `exiv2`_
+   ======================= =================== ==================== =====================================================================
+
+We recommend to use ``metadata_pyexiv2`` if the installation of `pyexiv2`_ is not too
+involved on your system and ``metadata_piexif`` as a fallback solution or in case you
+don't need the full power of `pyexiv2`_ and prefer something more lightweight.
+Also consider the list of available
+:ref:`user metadata plugins<user_metadata_plugins>`.
+
+
+Customize Keysets
+-----------------
+
+You can configure the information displayed by the ``:metadata`` command by adding your
+own key sets to the ``METADATA`` section in your configfile like this::
+
+    keys2 = someKey,anotherOne,lastOne
+    keys4 = newKey,oneMore
+
+where the values must be a comma-separated list of valid metadata keys.
+
+In case you are using `pyexiv2`_, you can find a complete overview of valid keys on the
+`exiv2 webpage <https://www.exiv2.org/metadata.html>`_. You can choose any of the Exif,
+IPTC, or XMP keys.
+
+`Piexif`_ uses a simplified form of the key. It does not use the ``Group.Subgroup``
+prefix, which is present in each of `pyexiv2`_'s keys. However, ``metadata_piexif``
+automatically does this truncation, if the provided keys are in the long form.
+
+The ``:metadata-list-keys`` command provides a list of all valid metadata keys, that
+the currently loaded metadata plugins can read. This serves as an easy way to see what
+keys are available in the image.
+
+
+.. _create_own_plugins:
+
+Create Own Plugins
+------------------
+
+One can extend vimiv's metadata capabilities by creating own metadata plugins. This is
+useful if you want to use a different metadata backend.
+
+The rough steps are the following:
+
+#. Create a plugin, that implements the abstract class
+   ``vimiv.imutils.metadata.MetadataPlugin``
+
+   #. Implement all required methods
+
+   #. Optionally, also implement the non-required methods
+
+#. In the plugin's init function, register the plugin using
+   ``vimiv.imutils.metadata.register``
+
+Please see the default metadata plugins for an example implementation.
+
+
+.. _exiv2: https://www.exiv2.org/index.html
+.. _pyexiv2: https://python3-exiv2.readthedocs.io
+.. _piexif: https://pypi.org/project/piexif/
diff --git a/docs/documentation/pyexiv2.rst b/docs/documentation/pyexiv2.rst
diff --git a/pytest.ini b/pytest.ini
@@ -5,9 +5,9 @@ faulthandler_timeout = 30
 markers =
     current: Mark tests during development
     imageformats: Require retrieving images from the web to test additional formats
-    exif: Require exif support
+    metadata: Require metadata support
     piexif: Require piexif
     pyexiv2: Require pyexiv2
-    noexif: Requires exif support NOT to be available
+    nometadata: Requires metadata support NOT to be available
     ci: Run test only on ci
     ci_skip: Skip test on ci
diff --git a/tests/conftest.py b/tests/conftest.py
@@ -12,38 +12,36 @@
 
 import pytest
 
-from vimiv.imutils import exif
+from vimiv.plugins import metadata_pyexiv2, metadata_piexif
 
 
 CI = "CI" in os.environ
 
+HAS_PIEXIF = metadata_piexif.piexif is not None
+HAS_PYEXIV2 = metadata_pyexiv2.pyexiv2 is not None
+HAS_METADATA = HAS_PIEXIF or HAS_PYEXIV2
+
 # fmt: off
 PLATFORM_MARKERS = (
     ("ci", CI, "Only run on ci"),
     ("ci_skip", not CI, "Skipped on ci"),
 )
 
-EXIF_MARKERS = (
-    ("exif", exif.has_exif_support, "Only run with exif support"),
-    ("noexif", not exif.has_exif_support, "Only run without exif support"),
-    ("pyexiv2", exif.pyexiv2 is not None, "Only run with pyexiv2"),
-    ("piexif", exif.piexif is not None, "Only run with piexif"),
+METADATA_MARKERS = (
+    ("metadata", HAS_METADATA, "Only run with metadata support"),
+    ("nometadata", not HAS_METADATA, "Only run without metadata support"),
+    ("piexif", HAS_PIEXIF, "Only run with piexif"),
+    ("pyexiv2", HAS_PYEXIV2, "Only run with pyexiv2"),
 )
 # fmt: on
 
 
-def apply_platform_markers(item):
-    """Apply markers that skip tests depending on the current platform."""
-    apply_markers_helper(item, PLATFORM_MARKERS)
-
-
-def apply_exif_markers(item):
-    """Apply markers that skip tests depending on specific exif support."""
-    if os.path.basename(item.fspath) in ("test_exif.py",):
-        for marker_name in "exif", "pyexiv2", "piexif":
-            marker = getattr(pytest.mark, marker_name)
+def apply_fixture_markers(item, *names):
+    """Helper function to mark all tests using specific fixtures with that mark."""
+    for name in names:
+        marker = getattr(pytest.mark, name)
+        if name in item.fixturenames:
             item.add_marker(marker)
-    apply_markers_helper(item, EXIF_MARKERS)
 
 
 def apply_markers_helper(item, markers):
@@ -60,8 +58,9 @@ def apply_markers_helper(item, markers):
 def pytest_collection_modifyitems(items):
     """Handle custom markers via pytest hook."""
     for item in items:
-        apply_platform_markers(item)
-        apply_exif_markers(item)
+        apply_fixture_markers(item, "piexif", "pyexiv2")
+        apply_markers_helper(item, PLATFORM_MARKERS)
+        apply_markers_helper(item, METADATA_MARKERS)
 
 
 @pytest.fixture
@@ -165,28 +164,17 @@ def tmpdir():
     raise ValueError("Use the 'tmp_path' fixture instead of 'tmpdir'")
 
 
-@pytest.fixture()
-def piexif(monkeypatch):
-    """Pytest fixture to ensure only piexif is available."""
-    monkeypatch.setattr(exif, "pyexiv2", None)
-
-
-@pytest.fixture()
-def noexif(monkeypatch, piexif):
-    """Pytest fixture to ensure no exif library is available."""
-    monkeypatch.setattr(exif, "piexif", None)
-
-
 @pytest.fixture()
 def add_exif_information():
     """Fixture to retrieve a helper function that adds exif content to an image."""
 
     def add_exif_information_impl(path: str, content):
-        assert exif.piexif is not None, "piexif required to add exif information"
-        exif_dict = exif.piexif.load(path)
+        import piexif
+
+        exif_dict = piexif.load(path)
         for ifd, ifd_dict in content.items():
             for key, value in ifd_dict.items():
                 exif_dict[ifd][key] = value
-        exif.piexif.insert(exif.piexif.dump(exif_dict), path)
+        piexif.insert(piexif.dump(exif_dict), path)
 
     return add_exif_information_impl
diff --git a/tests/end2end/features/image/conftest.py b/tests/end2end/features/image/conftest.py
@@ -19,6 +19,7 @@
 
 @pytest.fixture()
 def exif_content():
+    assert piexif is not None, "piexif required create exif information."
     return {
         "0th": {
             piexif.ImageIFD.Make: b"vimiv-testsuite",

diff --git a/tests/end2end/features/image/metadata.feature b/tests/end2end/features/image/metadata.feature
@@ -1,4 +1,4 @@
-@exif
+@metadata
 Feature: Metadata widget displaying image exif information
 
     Scenario: Show metadata widget