Plugin.ActionBar: New class added for plugins that use action bars

po/POTFILES.in

@@ -92,6 +92,7 @@ src/client/folder-list/folder-list-search-branch.vala
 src/client/folder-list/folder-list-special-grouping.vala
 src/client/folder-list/folder-list-tree.vala
 src/client/plugin/plugin-account.vala
+src/client/plugin/plugin-action-bar.vala
 src/client/plugin/plugin-actionable.vala
 src/client/plugin/plugin-application.vala
 src/client/plugin/plugin-composer.vala

src/client/meson.build

@@ -113,6 +113,7 @@ client_vala_sources = files(
   'folder-list/folder-list-special-grouping.vala',
 
   'plugin/plugin-account.vala',
+  'plugin/plugin-action-bar.vala',
   'plugin/plugin-actionable.vala',
   'plugin/plugin-application.vala',
   'plugin/plugin-composer.vala',

src/client/plugin/plugin-action-bar.vala

@@ -0,0 +1,184 @@
+/*
+ * Copyright © 2020 Michael Gratton <mike@vee.net>
+ *
+ * This software is licensed under the GNU Lesser General Public License
+ * (version 2.1 or later). See the COPYING file in this distribution.
+ */
+
+/**
+ * Enables plugins to display an action bar.
+ *
+ * Action bars are horizontal containers for buttons, menu buttons and
+ * labels that can be added individually or in groups, at the start,
+ * centre, or end of the bar. These interface items are added by
+ * creating an appropriate {@link Item} instance and calling {@link
+ * append_item}.
+ *
+ * The {@link Actionable} instances added to the action bar must have
+ * their actions registered either globally for the application using
+ * {@link Application.register_action} or locally for a specific UI
+ * element, for example using {@link Composer.register_action}.
+ */
+public class Plugin.ActionBar : Geary.BaseObject {
+
+
+    /**
+     * Determines the position of a widget added to an action bar.
+     *
+     * @see append_item
+     */
+    public enum Position {
+        /**
+         * The widget is added at the start of the action bar.
+         *
+         * The start of the bar is the left side in locales with
+         * left-to-right writing direction, and the right side in
+         * right-to-left locales.
+         */
+        START,
+
+        /** The widget is added in the centre of the action bar. */
+        CENTRE,
+
+        /**
+         * The widget is added at the end of the action bar.
+         *
+         * The end of the bar is the right side in locales with
+         * left-to-right writing direction, and the left side in
+         * right-to-left locales.
+         */
+        END;
+    }
+
+
+    /** Denotes an object that can be added to an action bar. */
+    public interface Item: GLib.Object {
+
+    }
+
+    /** A text label item for an action bar. */
+    public class LabelItem: GLib.Object, Item {
+
+
+        public string text { get; private set; }
+
+        /** Constructs a text label item for an action bar. */
+        public LabelItem(string text) {
+            this.text = text;
+        }
+
+    }
+
+    /** A button item for an action bar. */
+    public class ButtonItem: GLib.Object, Item {
+
+
+        public Actionable action { get; private set; }
+
+
+        /** Constructs a button item for an action bar. */
+        public ButtonItem(Actionable action) {
+            this.action = action;
+        }
+
+    }
+
+    /** A menu for an action bar. */
+    public class MenuItem: GLib.Object, Item {
+
+
+        public string label { get; private set; }
+        public GLib.MenuModel menu { get; private set; }
+
+
+        /** Constructs a menu item for an action bar. */
+        public MenuItem(string label, GLib.MenuModel menu) {
+            this.label = label;
+            this.menu = menu;
+        }
+
+    }
+
+    /**
+     * A group of items for an action bar.
+     *
+     * Groups will be displayed in a way that indicates they are
+     * related, for example as pill buttons. Items in the group are
+     * laid out in the same direction as the current locale's writing
+     * direction.
+     */
+    public class GroupItem: GLib.Object, Item {
+
+
+        private Gee.List<Item> items = new Gee.LinkedList<Item>();
+
+
+        /** Constructs a button item for an action bar. */
+        public GroupItem(Gee.Collection<Item>? items = null) {
+            if (items != null) {
+                this.items.add_all(items);
+            }
+        }
+
+        /** Appends an item to end of the group. */
+        public void append_item(Item item) {
+            this.items.add(item);
+        }
+
+        /** Returns a read-only list of items in the group. */
+        public Gee.List<Item> get_items() {
+            return this.items.read_only_view;
+        }
+
+    }
+
+
+    private Gee.List<Item> start_items = new Gee.LinkedList<Item>();
+    private Gee.List<Item> centre_items = new Gee.LinkedList<Item>();
+    private Gee.List<Item> end_items = new Gee.LinkedList<Item>();
+
+
+    /** Constructs a new, empty action bar. */
+    public ActionBar() {
+    }
+
+    /**
+     * Appends an item to the action bar in the given location.
+     *
+     * Items at the same position are laid out in the same direction
+     * as the current locale's writing direction.
+     */
+    public void append_item(Item item, Position item_position) {
+        switch (item_position) {
+        case START:
+            this.start_items.add(item);
+            break;
+        case CENTRE:
+            this.centre_items.add(item);
+            break;
+        case END:
+            this.end_items.add(item);
+            break;
+        }
+    }
+
+    /** Returns a read-only list of items at the given position. */
+    public Gee.List<Item> get_items(Position item_position) {
+        Gee.List<Item>? items = null;
+        switch (item_position) {
+        case START:
+            items = this.start_items.read_only_view;
+            break;
+
+        case CENTRE:
+            items = this.centre_items.read_only_view;
+            break;
+
+        case END:
+            items = this.end_items.read_only_view;
+            break;
+        }
+        return items;
+    }
+
+}