prevent targeting the same object multiple times

1 files changed, 15 insertions, 2 deletions

diff --git a/go/game/targets.go b/go/game/targets.go
index 02f63378..2e29d64e 100644
--- a/go/game/targets.go
+++ b/go/game/targets.go
@@ -1,6 +1,7 @@
 package game
 
 import (
+	"errors"
 	"fmt"
 	"log"
 	"strconv"
@@ -183,7 +184,18 @@ func (d *TargetDesc) requirement() TargetRequirement {
 	}
 }
 
-func (t *Target) AddSelection(sel interface{}) (err error) {
+var (
+	ErrAlreadySelected = errors.New("already selected")
+)
+
+// AddSelection adds an object as selection to the target.
+// If the provided object does not satisfy the target contraint err != nil is returned.
+// Selecting the same object multiple times reaul%s in an error.
+func (t *Target) AddSelection(sel any) (err error) {
+	if slices.Contains(t.sel, sel) {
+		return ErrAlreadySelected
+	}
+
 	if err = t.constraint(sel); err == nil {
 		t.sel = append(t.sel, sel)
 	}
@@ -227,7 +239,8 @@ func (t *Target) CheckSelection(s *LocalState) error {
 	return nil
 }
 
-func (t *Targets) AddSelection(sel interface{}) error { return t.ts[t.idx].AddSelection(sel) }
+// AddSelection adds an object as selection to the current target.
+func (t *Targets) AddSelection(sel any) error { return t.ts[t.idx].AddSelection(sel) }
 
 func (t *Targets) HasSelections() bool {
 	for _, t := range t.ts {