require proof of turn to use items or shoot

game/game.go

@@ -1,5 +1,11 @@
 package game
 
+import (
+	"errors"
+
+	"git.sunturtle.xyz/studio/shotgun/player"
+)
+
 type Game struct {
 	RNG    RNG
 	PP     [2]Player
@@ -57,14 +63,20 @@ func (g *Game) Opponent() *Player {
 }
 
 // Apply uses an item by index for the current player.
-func (g *Game) Apply(item int) {
+// This may cause the group to end.
+// Returns ErrWrongTurn if id does not correspond to the current player.
+func (g *Game) Apply(id player.ID, item int) error {
 	cur := g.CurrentPlayer()
+	if cur.ID != id {
+		return ErrWrongTurn
+	}
 	if item < 0 || item >= len(cur.Items) {
-		return
+		return errors.New("item index out of bounds")
 	}
 	if cur.Items[item].Apply(g) {
 		cur.Items[item] = ItemNone
 	}
+	return nil
 }
 
 // PopShell removes a shell from the shotgun.
@@ -95,7 +107,12 @@ func (g *Game) Winner() *Player {
 // Shoot fires the shotgun, at the opponent if self is false and at the current
 // player if self is true. Afterward, the round may be over, or the shotgun may
 // be empty.
-func (g *Game) Shoot(self bool) {
+// Returns ErrWrongTurn if id does not correspond to the current player.
+func (g *Game) Shoot(id player.ID, self bool) error {
+	cur := g.CurrentPlayer()
+	if cur.ID != id {
+		return ErrWrongTurn
+	}
 	target := g.Opponent()
 	if self {
 		target = g.CurrentPlayer()
@@ -107,4 +124,7 @@ func (g *Game) Shoot(self bool) {
 	} else if !self {
 		g.Turn++
 	}
+	return nil
 }
+
+var ErrWrongTurn = errors.New("not your turn")