user API for export plot plugin (#1657)

* user API for export plot plugin
* default to png when no extension provided in filename

CHANGES.rst

@@ -12,9 +12,9 @@ New Features
   in Jy [#1564]
 
 - User-friendly API access to plugins, with exposed functionality for:  line analysis, gaussian
-  smooth, moment maps, compass, collapse, metadata, slice, plot options, model fitting, and links
-  control.
-  [#1401, #1642, #1643, #1636, #1641, #1634, #1635, #1637, #1658, #1640]
+  smooth, moment maps, compass, collapse, metadata, slice, plot options, model fitting, links
+  control, and export plot.
+  [#1401, #1642, #1643, #1636, #1641, #1634, #1635, #1637, #1658, #1640, #1657]
 
 - Line Lists show which medium the catalog wavelengths were measured in,
   in accordance to the metadata entry. Lists without medium information

jdaviz/configs/default/plugins/export_plot/export_plot.py

@@ -1,23 +1,61 @@
 from jdaviz.core.registries import tray_registry
 from jdaviz.core.template_mixin import PluginTemplateMixin, ViewerSelectMixin
+from jdaviz.core.user_api import PluginUserApi
 
 __all__ = ['ExportViewer']
 
 
 @tray_registry('g-export-plot', label="Export Plot")
 class ExportViewer(PluginTemplateMixin, ViewerSelectMixin):
+    """
+    See the :ref:`Export Plot Plugin Documentation <imviz-export-plot>` for more details.
+
+    Only the following attributes and methods are available through the
+    :ref:`public plugin API <plugin-apis>`:
+
+    * :meth:`~jdaviz.core.template_mixin.PluginTemplateMixin.show`
+    * :meth:`~jdaviz.core.template_mixin.PluginTemplateMixin.open_in_tray`
+    * :meth:`save_figure`
+    """
     template_file = __file__, "export_plot.vue"
 
+    @property
+    def user_api(self):
+        return PluginUserApi(self, expose=('save_figure',))
+
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
-    def vue_save_figure(self, filetype):
+    def save_figure(self, filename=None, filetype=None):
         """
-        Callback for save figure events in the front end viewer toolbars. Uses
-        the bqplot.Figure save methods.
+        Save the figure to an image with a provided filename or through an interactive save dialog.
+
+        Parameters
+        ----------
+        filename : str or `None`
+            Filename to autopopulate the save dialog.
+        filetype : {'png', 'svg', `None`}
+            Filetype (PNG or SVG).  If `None`, will default based on filename or to PNG.
+
         """
+        if filetype is None:
+            if filename is not None and '.' in filename:
+                filetype = filename.split('.')[-1]
+            else:
+                # default to png
+                filetype = 'png'
+
         viewer = self.viewer.selected_obj
         if filetype == "png":
-            viewer.figure.save_png()
+            viewer.figure.save_png(filename)
         elif filetype == "svg":
-            viewer.figure.save_svg()
+            viewer.figure.save_svg(filename)
+        else:
+            raise NotImplementedError(f"filetype={filetype} not supported")
+
+    def vue_save_figure(self, filetype):
+        """
+        Callback for save figure events in the front end viewer toolbars. Uses
+        the bqplot.Figure save methods.
+        """
+        self.save_figure(filetype=filetype)