ARIA: set aria-sort on th for sortable columns

- Table: optional col sort_field; th gets aria-sort when col is sorted.
- User index: pass sort_field/sort_order to table, sort_field: :email on email col.

lib/mv_web/components/core_components.ex

@@ -545,6 +545,9 @@ defmodule MvWeb.CoreComponents do
     attr :label, :string
     attr :class, :string
     attr :col_click, :any, doc: "optional column-specific click handler that overrides row_click"
+
+    attr :sort_field, :any,
+      doc: "optional; when equal to table sort_field, aria-sort is set on this th"
   end
 
   slot :action, doc: "the slot for showing user actions in the last table column"
@@ -560,7 +563,13 @@ defmodule MvWeb.CoreComponents do
       <table class="table table-zebra">
         <thead>
           <tr>
-            <th :for={col <- @col} class={Map.get(col, :class)}>{col[:label]}</th>
+            <th
+              :for={col <- @col}
+              class={Map.get(col, :class)}
+              aria-sort={table_th_aria_sort(col, @sort_field, @sort_order)}
+            >
+              {col[:label]}
+            </th>
             <th :for={dyn_col <- @dynamic_cols}>
               <.live_component
                 module={MvWeb.Components.SortHeaderComponent}
@@ -646,6 +655,16 @@ defmodule MvWeb.CoreComponents do
     """
   end
 
+  defp table_th_aria_sort(col, sort_field, sort_order) do
+    col_sort = Map.get(col, :sort_field)
+
+    if not is_nil(col_sort) and col_sort == sort_field and sort_order in [:asc, :desc] do
+      if sort_order == :asc, do: "ascending", else: "descending"
+    else
+      nil
+    end
+  end
+
   @doc """
   Renders a data list.