Rework the preset menu system to permit submenus.

To do this, I've completely replaced the API between mid-end and front
end, so any downstream front end maintainers will have to do some
rewriting of their own (sorry). I've done the necessary work in all
five of the front ends I keep in-tree here - Windows, GTK, OS X,
Javascript/Emscripten, and Java/NestedVM - and I've done it in various
different styles (as each front end found most convenient), so that
should provide a variety of sample code to show downstreams how, if
they should need it.

I've left in the old puzzle back-end API function to return a flat
list of presets, so for the moment, all the puzzle backends are
unchanged apart from an extra null pointer appearing in their
top-level game structure. In a future commit I'll actually use the new
feature in a puzzle; perhaps in the further future it might make sense
to migrate all the puzzles to the new API and stop providing back ends
with two alternative ways of doing things, but this seemed like enough
upheaval for one day.

osx.m

@@ -426,6 +426,9 @@ struct frontend {
     NSView **cfg_controls;
     int cfg_ncontrols;
     NSTextField *status;
+    struct preset_menu *preset_menu;
+    NSMenuItem **preset_menu_items;
+    int n_preset_menu_items;
 }
 - (id)initWithGame:(const game *)g;
 - (void)dealloc;
@@ -540,6 +543,8 @@ struct frontend {
     int w, h;
 
     ourgame = g;
+    preset_menu = NULL;
+    preset_menu_items = NULL;
 
     fe.window = self;
 
@@ -618,6 +623,7 @@ struct frontend {
 	[fe.colours[i] release];
     }
     sfree(fe.colours);
+    sfree(preset_menu_items);
     midend_free(me);
     [super dealloc];
 }
@@ -847,54 +853,99 @@ struct frontend {
 
 - (void)clearTypeMenu
 {
+    int i;
+
     while ([typemenu numberOfItems] > 1)
 	[typemenu removeItemAtIndex:0];
     [[typemenu itemAtIndex:0] setState:NSOffState];
+
+    for (i = 0; i < n_preset_menu_items; i++)
+        preset_menu_items[i] = NULL;
 }
 
 - (void)updateTypeMenuTick
 {
-    int i, total, n;
+    int i, n;
 
-    total = [typemenu numberOfItems];
     n = midend_which_preset(me);
-    if (n < 0)
-	n = total - 1;		       /* that's always where "Custom" lives */
-    for (i = 0; i < total; i++)
-	[[typemenu itemAtIndex:i] setState:(i == n ? NSOnState : NSOffState)];
+
+    for (i = 0; i < n_preset_menu_items; i++)
+        if (preset_menu_items[i])
+            [preset_menu_items[i] setState:(i == n ? NSOnState : NSOffState)];
+
+    /*
+     * The Custom menu item is always right at the bottom of the
+     * Type menu.
+     */
+    [[typemenu itemAtIndex:[typemenu numberOfItems]-1]
+             setState:(n < 0 ? NSOnState : NSOffState)];
+}
+
+- (void)populateTypeMenu:(NSMenu *)nsmenu from:(struct preset_menu *)menu
+{
+    int i;
+
+    /*
+     * We process the entries in reverse order so that (in the
+     * top-level Type menu at least) we don't disturb the 'Custom'
+     * item which remains fixed even when we change back and forth
+     * between puzzle type windows.
+     */
+    for (i = menu->n_entries; i-- > 0 ;) {
+        struct preset_menu_entry *entry = &menu->entries[i];
+        NSMenuItem *item;
+
+        if (entry->params) {
+            DataMenuItem *ditem;
+            ditem = [[[DataMenuItem alloc]
+                        initWithTitle:[NSString stringWithUTF8String:
+                                                    entry->title]
+                               action:NULL keyEquivalent:@""]
+                       autorelease];
+
+            [ditem setTarget:self];
+            [ditem setAction:@selector(presetGame:)];
+            [ditem setPayload:entry->params];
+
+            preset_menu_items[entry->id] = ditem;
+
+            item = ditem;
+        } else {
+            NSMenu *nssubmenu;
+
+            item = [[[NSMenuItem alloc]
+                        initWithTitle:[NSString stringWithUTF8String:
+                                                    entry->title]
+                               action:NULL keyEquivalent:@""]
+                       autorelease];
+            nssubmenu = newmenu(entry->title);
+            [item setSubmenu:nssubmenu];
+
+            [self populateTypeMenu:nssubmenu from:entry->submenu];
+        }
+
+        [item setEnabled:YES];
+        [nsmenu insertItem:item atIndex:0];
+    }
 }
 
 - (void)becomeKeyWindow
 {
-    int n;
-
     [self clearTypeMenu];
 
     [super becomeKeyWindow];
 
-    n = midend_num_presets(me);
+    if (!preset_menu) {
+        int i;
+        preset_menu = midend_get_presets(me, &n_preset_menu_items);
+        preset_menu_items = snewn(n_preset_menu_items, NSMenuItem *);
+        for (i = 0; i < n_preset_menu_items; i++)
+            preset_menu_items[i] = NULL;
+    }
 
-    if (n > 0) {
+    if (preset_menu->n_entries > 0) {
 	[typemenu insertItem:[NSMenuItem separatorItem] atIndex:0];
-	while (n--) {
-	    char *name;
-	    game_params *params;
-	    DataMenuItem *item;
-
-	    midend_fetch_preset(me, n, &name, &params);
-
-	    item = [[[DataMenuItem alloc]
-		     initWithTitle:[NSString stringWithUTF8String:name]
-		     action:NULL keyEquivalent:@""]
-		    autorelease];
-
-	    [item setEnabled:YES];
-	    [item setTarget:self];
-	    [item setAction:@selector(presetGame:)];
-	    [item setPayload:params];
-
-	    [typemenu insertItem:item atIndex:0];
-	}
+        [self populateTypeMenu:typemenu from:preset_menu];
     }
 
     [self updateTypeMenuTick];