Randomize starter decks presentation

data/objects/choose_deck_controller.cfg

@@ -252,10 +252,26 @@
 			where selected_deck = lib.citadel.preferences[if(starter, 'selected_starter_deck', 'selected_custom_deck')]
 			)
 		] where decks_sorted = if (starter,
-			// Assume starter decks will always be carefully
-			// crafted with at least 50 cards each.
-			sort(values(decks), [a.custom_sort] < [b.custom_sort]),
-			sort(
+			rotate_decks(
+				//   Assume starter decks will always be
+				// carefully crafted with at least 50 cards
+				// each.
+				sort(
+					values(decks),
+					[a.custom_sort] < [b.custom_sort]),
+				//   There are nine deck widgets in the panel,
+				// only eight are rotating because one of them
+				// always stays in the middle. There are only
+				// eight rotations.
+				mensis_domini % 8
+			)
+			//   This formula guarantees year over year continuity
+			// until `int` overflow.
+			where mensis_domini = year * 12 + month
+			where month = now.month
+			where year = now.year
+			where now = time()
+			, sort(
 				filter(values(decks), size(value.cards) >= 50),
 				[a.creation_time, a.name] <
 					[b.creation_time, b.name])
@@ -267,6 +283,36 @@
 		])
 		",
 
+		//   This is a quick and dirty list rotator with no careful
+		// thinking of performance. Do NOT use it unless for lists
+		// known to be ALWAYS small.
+		rotate_decks: "def
+			([Deck] decks, int positions) -> [Deck]
+			if (positions < 1,
+				decks,
+				rotate_decks(
+					single_decks_rotation(decks),
+					positions - 1))
+		",
+
+		//   Helps `rotate_decks(([Deck], int) -> [Deck])`.
+		single_decks_rotation: "def
+			([Deck] decks) -> [Deck]
+//			dump(
+//				[
+//					'single_decks_rotation',
+//					map(decks, value.custom_sort),
+//					map(returning, value.custom_sort)
+//				], returning)
+//			where returning =
+			//   Clockwise rotation of 9 decks forming a mosaic.
+			[
+				decks[3], decks[0], decks[1], decks[6],
+				decks[4], decks[2], decks[7], decks[8],
+				decks[5]
+			] asserting size(decks) = 9
+		",
+
 		create_objects: "def() ->commands [
 			spawn('combo_label_controller', {
 				xpos: x + lib.gui.py(int(228*scaling)),