track previous shell

game/game.go

@@ -16,6 +16,7 @@ type Game struct {
 	HP     int8
 	Damage int8
 	Reveal bool
+	Prev   *bool
 
 	// Backing storage for shells.
 	ShellArray [8]bool
@@ -51,6 +52,7 @@ func (g *Game) StartGroup() {
 	ShuffleSlice(&g.RNG, g.Shells)
 	g.Group++
 	g.Turn = 0
+	g.Prev = nil
 	g.NextTurn()
 }
 
@@ -93,9 +95,9 @@ func (g *Game) Apply(id player.ID, item int) error {
 // This may cause the shotgun to be empty, but does not start the next group
 // if so.
 func (g *Game) PopShell() bool {
-	r := g.Shells[0]
+	g.Prev = &g.Shells[0]
 	g.Shells = g.Shells[1:]
-	return r
+	return *g.Prev
 }
 
 // Empty returns whether the shotgun is empty.