fix: add basic "Show Totals" feature for main index grids

subclass must define what to display

src/wuttaweb/templates/grids/vue_template.mako

@@ -328,6 +328,7 @@
 
   const ${grid.vue_component} = {
       template: '#${grid.vue_tagname}-template',
+      mixins: [WuttaRequestMixin],
       computed: {
 
           recordCount() {
@@ -658,8 +659,13 @@
                   // fetch new data
                   params.filter = true
                   this.fetchData(params)
+                  ## nb. this is used for "show totals" feature in master/index template
+                  this.appliedFiltersHook()
               },
 
+              ## nb. for now each grid can have "just one" (or no) hook
+              appliedFiltersHook() {},
+
               getFilterParams() {
                   const params = {}
                   for (let filter of this.filters) {

src/wuttaweb/templates/master/index.mako

@@ -31,6 +31,30 @@
   ${parent.modify_vue_vars()}
   <script>
 
+    % if master.has_grid_totals:
+
+        ${grid.vue_component}Data.gridTotalsHTML = ""
+        ${grid.vue_component}Data.gridTotalsFetching = false
+
+        ${grid.vue_component}.methods.gridTotalsFetch = function() {
+            this.gridTotalsFetching = true
+
+            const url = "${url(f'{route_prefix}.fetch_grid_totals')}"
+            this.wuttaGET(url, {}, response => {
+                this.gridTotalsHTML = response.data.totals_html
+                this.gridTotalsFetching = false
+            }, response => {
+                this.gridTotalsFetching = false
+            })
+        }
+
+        ${grid.vue_component}.methods.appliedFiltersHook = function() {
+            this.gridTotalsHTML = ""
+            this.gridTotalsFetching = false
+        }
+
+    % endif
+
     % if master.deletable_bulk and master.has_perm('delete_bulk'):
 
         ${grid.vue_component}Data.deleteResultsSubmitting = false

src/wuttaweb/views/master.py

@@ -193,6 +193,13 @@ class MasterView(View):  # pylint: disable=too-many-public-methods
 
        This is optional; see also :meth:`get_grid_columns()`.
 
+    .. attribute:: has_grid_totals
+
+       Boolean indicating whether the main grid supports a "Show
+       Totals" feature; this is false by default.
+
+       See also :meth:`fetch_grid_totals()`.
+
     .. attribute:: checkable
 
        Boolean indicating whether the grid should expose per-row
@@ -481,6 +488,7 @@ class MasterView(View):  # pylint: disable=too-many-public-methods
     # features
     listable = True
     has_grid = True
+    has_grid_totals = False
     checkable = False
     filterable = True
     filter_defaults = None
@@ -586,6 +594,42 @@ class MasterView(View):  # pylint: disable=too-many-public-methods
 
         return self.render_to_response("index", context)
 
+    def fetch_grid_totals(self):
+        """
+        Should return the "totals info" for the main grid, if
+        applicable.  Only relevant when :attr:`has_grid_totals` is
+        true.
+
+        This method is called "on demand" from the client side; totals
+        are not calculated / shown by default when a grid is first
+        displayed on the page.
+
+        Subclass should override this method to calculate and return
+        the customized info.  Default logic within the template is
+        expecting a ``totals_html`` key within the dict; this will be
+        rendered as-is on the page.  For instance::
+
+           def fetch_grid_totals(self):
+
+               from webhelpers2.html import HTML
+
+               # get current data set from grid
+               # nb. this will be filtered and sorted but *not*
+               # paginated; we want to include all results.
+               grid = self.make_model_grid(paginated=False)
+               rows = grid.get_visible_data()
+
+               # calculate total
+               foo_total = sum([row.foo_amount for row in rows])
+
+               # render as <span> tag
+               html = HTML.tag("span", c=f"Foo Total: {foo_total:0.2f}")
+               return {"totals_html": html}
+
+        :returns: Dict of totals info.
+        """
+        return {"totals_html": "TODO: totals go here"}
+
     ##############################
     # create methods
     ##############################
@@ -2612,7 +2656,7 @@ class MasterView(View):  # pylint: disable=too-many-public-methods
 
     def make_model_grid(
         self, session=None, **kwargs
-    ):  # pylint: disable=too-many-branches
+    ):  # pylint: disable=too-many-branches,too-many-statements
         """
         Create and return a :class:`~wuttaweb.grids.base.Grid`
         instance for use with the :meth:`index()` view.
@@ -2678,6 +2722,29 @@ class MasterView(View):  # pylint: disable=too-many-public-methods
         if "tools" not in kwargs:
             tools = []
 
+            # show totals
+            if self.has_grid_totals:
+                button = self.make_button(
+                    "{{ gridTotalsFetching ? 'Working, please wait...' : 'Show Totals' }}",
+                    icon_left="calculator",
+                    **{
+                        "v-if": "!gridTotalsHTML.length",
+                        ":disabled": "gridTotalsFetching",
+                        "@click": "gridTotalsFetch()",
+                    },
+                )
+                display = HTML.tag(
+                    "div",
+                    class_="control",
+                    style="margin: 0 0.5rem;",
+                    **{
+                        "v-if": "gridTotalsHTML.length",
+                        "v-html": "gridTotalsHTML",
+                    },
+                )
+                wrapper = HTML.tag("div", c=[button, display])
+                tools.append(("show-totals", wrapper))
+
             # delete-bulk
             if self.deletable_bulk and self.has_perm("delete_bulk"):
                 tools.append(("delete-results", self.delete_bulk_make_button()))
@@ -4310,6 +4377,21 @@ class MasterView(View):  # pylint: disable=too-many-public-methods
                 f"Browse / search {model_title_plural}",
             )
 
+            # grid totals
+            if cls.has_grid_totals:
+                config.add_route(
+                    f"{route_prefix}.fetch_grid_totals",
+                    f"{url_prefix}/fetch-grid-totals",
+                    request_method="GET",
+                )
+                config.add_view(
+                    cls,
+                    attr="fetch_grid_totals",
+                    route_name=f"{route_prefix}.fetch_grid_totals",
+                    permission=f"{permission_prefix}.list",
+                    renderer="json",
+                )
+
         # create
         if cls.creatable:
             config.add_route(f"{route_prefix}.create", f"{url_prefix}/new")

tests/views/test_master.py

@@ -34,6 +34,7 @@ class TestMasterView(WebTestCase):
             model_key="uuid",
             deletable_bulk=True,
             has_autocomplete=True,
+            has_grid_totals=True,
             downloadable=True,
             executable=True,
             configurable=True,
@@ -694,6 +695,15 @@ class TestMasterView(WebTestCase):
                 grid = view.make_model_grid(session=self.session)
                 self.assertEqual(grid.tools, {})
 
+            # "show totals" tool added when applicable
+            with patch.multiple(
+                mod.MasterView, model_class=model.Setting, has_grid_totals=True
+            ):
+                view = self.make_view()
+                grid = view.make_model_grid(session=self.session)
+                self.assertEqual(len(grid.tools), 1)
+                self.assertIn("show-totals", grid.tools)
+
             # delete-results tool added if master/perms allow
             with patch.multiple(
                 mod.MasterView,
@@ -763,6 +773,16 @@ class TestMasterView(WebTestCase):
             self.assertEqual(len(data), 1)
             self.assertIs(data[0], setting)
 
+    def test_fetch_grid_totals(self):
+        view = self.make_view()
+        # with patch.object(view, "has_grid_totals", new=True):
+
+        # nb. default logic just returns generic stub info
+        totals = view.fetch_grid_totals()
+        self.assertIsInstance(totals, dict)
+        self.assertIn("totals_html", totals)
+        self.assertEqual(totals["totals_html"], "TODO: totals go here")
+
     def test_configure_grid(self):
         model = self.app.model