Group menu items into per-category submenus

Parse the Categories key from .desktop files and have the renderer
emit one <menu> submenu per category (via xmerl), with items sorted
within each; entries in multiple categories appear in each submenu,
and uncategorized entries fall into a catch-all "Other" submenu.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

3 files changed, 72 insertions, 41 deletions

diff --git a/src/er_xdg_pipe_menu.app.src b/src/er_xdg_pipe_menu.app.src
index 7013bc7..1649ec3 100644
--- a/src/er_xdg_pipe_menu.app.src
+++ b/src/er_xdg_pipe_menu.app.src
@@ -5,7 +5,8 @@
     {mod, {er_xdg_pipe_menu_app, []}},
     {applications, [
         kernel,
-        stdlib
+        stdlib,
+        xmerl
     ]},
     {env, []},
     {modules, []},
diff --git a/src/er_xdg_pipe_menu_desktop_entry.erl b/src/er_xdg_pipe_menu_desktop_entry.erl
index bbd2594..9a71013 100644
--- a/src/er_xdg_pipe_menu_desktop_entry.erl
+++ b/src/er_xdg_pipe_menu_desktop_entry.erl
@@ -3,8 +3,9 @@
 %%
 %% Reads the `[Desktop Entry]' group of a desktop entry file and
 %% extracts the fields needed to build a menu item: `Name', `Exec'
-%% and (optionally) `Icon'. Other groups (e.g. `[Desktop Action ...]')
-%% and localized keys (e.g. `Name[fr]') are ignored.
+%% and (optionally) `Icon' and `Categories'. Other groups (e.g.
+%% `[Desktop Action ...]') and localized keys (e.g. `Name[fr]') are
+%% ignored.
 %% @end
 %%%-------------------------------------------------------------------
 
@@ -16,7 +17,7 @@
 
 -define(GROUP, <<"Desktop Entry">>).
 -define(WANTED_KEYS, [
-    <<"Name">>, <<"Exec">>, <<"Icon">>, <<"NoDisplay">>, <<"Hidden">>, <<"Type">>
+    <<"Name">>, <<"Exec">>, <<"Icon">>, <<"Categories">>, <<"NoDisplay">>, <<"Hidden">>, <<"Type">>
 ]).
 -define(FIELD_CODES, "fFuUdDnNickvm").
 
@@ -99,11 +100,20 @@ to_entry(Fields) ->
                         name = Name,
                         exec = strip_field_codes(Exec),
                         icon = maps:get(<<"Icon">>, Fields, undefined),
+                        categories = parse_categories(maps:get(<<"Categories">>, Fields, undefined)),
                         hidden = is_hidden(Fields)
                     }}
             end
     end.
 
+%% `Categories' is a `;'-separated list, conventionally with a
+%% trailing separator (e.g. `Utility;Development;'); empty segments
+%% from that trailing separator (or repeated ones) are dropped.
+parse_categories(undefined) ->
+    [];
+parse_categories(Bin) ->
+    [C || C <- binary:split(Bin, <<";">>, [global]), C =/= <<>>].
+
 %% Niche variations (e.g. a Type-less override dropped into
 %% ~/.local/share/applications) are left to be special-cased there
 %% rather than accounted for here.
diff --git a/src/er_xdg_pipe_menu_renderer.erl b/src/er_xdg_pipe_menu_renderer.erl
index fafed45..f89d868 100644
--- a/src/er_xdg_pipe_menu_renderer.erl
+++ b/src/er_xdg_pipe_menu_renderer.erl
@@ -2,9 +2,13 @@
 %% @doc Renders parsed desktop entries as an Openbox pipe menu.
 %%
 %% Given a list of `#desktop_entry{}' records, produces the XML that
-%% Openbox expects on stdout from a pipe menu: one `<item>' per
-%% visible entry (entries with `hidden = true' are dropped), sorted
-%% case-insensitively by name, each wrapping an `Execute' action.
+%% Openbox expects on stdout from a pipe menu: one `<menu>' submenu
+%% per category, each containing an `<item>' per visible entry in
+%% that category (entries with `hidden = true' are dropped). An entry
+%% belonging to several categories appears in each of their submenus;
+%% an entry with no categories is placed in a catch-all `Other'
+%% submenu. Categories are sorted case-insensitively, and entries
+%% within a submenu are sorted case-insensitively by name.
 %% @end
 %%%-------------------------------------------------------------------
 
@@ -14,45 +18,61 @@
 
 -export([render/1]).
 
+-define(OTHER_CATEGORY, <<"Other">>).
+
 -spec render([#desktop_entry{}]) -> binary().
 render(Entries) ->
     Visible = [E || E <- Entries, not E#desktop_entry.hidden],
-    Sorted = lists:sort(fun by_name/2, Visible),
-    iolist_to_binary([
-        <<"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n">>,
-        <<"<openbox_pipe_menu>\n">>,
-        [render_item(E) || E <- Sorted],
-        <<"</openbox_pipe_menu>\n">>
-    ]).
+    Grouped = group_by_category(Visible),
+    Categories = lists:sort(fun category_lt/2, maps:keys(Grouped)),
+    Menu = {openbox_pipe_menu, [], submenus_content(Categories, Grouped)},
+    Xml = xmerl:export_simple(
+        [Menu],
+        xmerl_xml,
+        [{prolog, ["<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"]}]
+    ),
+    iolist_to_binary([Xml, "\n"]).
+
+group_by_category(Entries) ->
+    lists:foldl(fun add_entry_to_categories/2, #{}, Entries).
+
+add_entry_to_categories(#desktop_entry{categories = []} = E, Acc) ->
+    add_entry_to_category(?OTHER_CATEGORY, E, Acc);
+add_entry_to_categories(#desktop_entry{categories = Cats} = E, Acc) ->
+    lists:foldl(fun(Cat, Acc0) -> add_entry_to_category(Cat, E, Acc0) end, Acc, Cats).
+
+add_entry_to_category(Cat, E, Acc) ->
+    maps:update_with(Cat, fun(Es) -> [E | Es] end, [E], Acc).
+
+category_lt(A, B) -> string:lowercase(A) =< string:lowercase(B).
 
 by_name(#desktop_entry{name = A}, #desktop_entry{name = B}) ->
     string:lowercase(A) =< string:lowercase(B).
 
-render_item(#desktop_entry{name = Name, exec = Exec, icon = Icon}) ->
-    [
-        <<"  <item label=\"">>,
-        escape_attr(Name),
-        <<"\"">>,
-        icon_attr(Icon),
-        <<">\n">>,
-        <<"    <action name=\"Execute\">\n">>,
-        <<"      <command>">>,
-        escape_text(Exec),
-        <<"</command>\n">>,
-        <<"    </action>\n">>,
-        <<"  </item>\n">>
-    ].
-
-icon_attr(undefined) -> <<>>;
-icon_attr(Icon) -> [<<" icon=\"">>, escape_attr(Icon), <<"\"">>].
-
-%% Attribute values additionally need '"' escaped; text content doesn't.
-escape_attr(Bin) -> escape(Bin, [{<<"\"">>, <<"&quot;">>}]).
-escape_text(Bin) -> escape(Bin, []).
-
-escape(Bin, Extra) ->
-    lists:foldl(
-        fun({Pat, Repl}, Acc) -> binary:replace(Acc, Pat, Repl, [global]) end,
-        Bin,
-        [{<<"&">>, <<"&amp;">>}, {<<"<">>, <<"&lt;">>}, {<<">">>, <<"&gt;">>} | Extra]
+submenus_content(Categories, Grouped) ->
+    lists:foldr(
+        fun(Cat, Acc) -> ["\n  ", submenu_element(Cat, Grouped) | Acc] end, ["\n"], Categories
     ).
+
+submenu_element(Cat, Grouped) ->
+    Entries = lists:sort(fun by_name/2, maps:get(Cat, Grouped)),
+    {menu, [{id, Cat}, {label, Cat}], items_content(Entries)}.
+
+items_content(Entries) ->
+    lists:foldr(fun(E, Acc) -> ["\n    ", item_element(E) | Acc] end, ["\n  "], Entries).
+
+item_element(#desktop_entry{name = Name, exec = Exec, icon = Icon}) ->
+    {item, item_attrs(Name, Icon), [
+        "\n      ",
+        {action, [{name, <<"Execute">>}], [
+            "\n        ",
+            {command, [], [text(Exec)]},
+            "\n      "
+        ]},
+        "\n    "
+    ]}.
+
+item_attrs(Name, undefined) -> [{label, Name}];
+item_attrs(Name, Icon) -> [{label, Name}, {icon, Icon}].
+
+text(Bin) -> unicode:characters_to_list(Bin).