1 files changed, 86 insertions, 0 deletions
diff --git a/internal/player/hardening_max_inventory_slots_test.go b/internal/player/hardening_max_inventory_slots_test.go
new file mode 100644
index 0000000..8cd9c37
--- /dev/null
+++ b/internal/player/hardening_max_inventory_slots_test.go
@@ -0,0 +1,86 @@
+package player
+
+// Regression coverage for the inventory slot accounting helpers: the capacity
+// is a named constant, FirstFreeSlot stays inside it, and FreeSlots ignores
+// entries a corrupt save can carry that no gameplay path can free.
+
+import "testing"
+
+func TestMaxInventorySlotsMatchesSlotHelpers(t *testing.T) {
+	if MaxInventorySlots != 28 {
+		t.Fatalf("MaxInventorySlots = %d, want 28 (on-disk capacity)", MaxInventorySlots)
+	}
+	p := New("alice")
+	if got := p.FreeSlots(); got != MaxInventorySlots {
+		t.Fatalf("empty inventory free slots = %d, want %d", got, MaxInventorySlots)
+	}
+	if got := p.FirstFreeSlot(); got != 0 {
+		t.Fatalf("empty inventory first free slot = %d, want 0", got)
+	}
+
+	// The last valid slot is addressable, and the first free slot walks up to
+	// the capacity and only then fails.
+	for i := 0; i < MaxInventorySlots-1; i++ {
+		p.SetInvSlot(i, &InventorySlot{ItemID: "rock", Quantity: 1})
+	}
+	if got := p.FirstFreeSlot(); got != MaxInventorySlots-1 {
+		t.Fatalf("first free slot = %d, want %d", got, MaxInventorySlots-1)
+	}
+	if got := p.FreeSlots(); got != 1 {
+		t.Fatalf("free slots = %d, want 1", got)
+	}
+	p.SetInvSlot(MaxInventorySlots-1, &InventorySlot{ItemID: "rock", Quantity: 1})
+	if got := p.FirstFreeSlot(); got != -1 {
+		t.Fatalf("full inventory first free slot = %d, want -1", got)
+	}
+	if got := p.FreeSlots(); got != 0 {
+		t.Fatalf("full inventory free slots = %d, want 0", got)
+	}
+}
+
+// TestFreeSlotsIgnoresInvalidEntries: out-of-range keys (a negative one, and
+// one past the capacity) and nil-valued entries must not consume capacity or
+// drive the count negative, while the valid slots keep counting exactly as
+// before.
+func TestFreeSlotsIgnoresInvalidEntries(t *testing.T) {
+	p := New("alice")
+	p.Inventory = map[int]*InventorySlot{
+		-1:                    {ItemID: "rock", Quantity: 1},
+		MaxInventorySlots:     {ItemID: "rock", Quantity: 1},
+		MaxInventorySlots + 5: {ItemID: "rock", Quantity: 1},
+		3:                     nil, // an explicitly nil entry frees its slot
+		7:                     {ItemID: "rock", Quantity: 1},
+	}
+
+	if got := p.FreeSlots(); got != MaxInventorySlots-1 {
+		t.Fatalf("free slots with invalid entries = %d, want %d", got, MaxInventorySlots-1)
+	}
+	if got := p.FirstFreeSlot(); got != 0 {
+		t.Fatalf("first free slot = %d, want 0", got)
+	}
+
+	// Only valid, non-nil slots are occupied: with every in-range slot filled
+	// the invalid keys must not make the count negative.
+	p.Inventory = make(map[int]*InventorySlot, MaxInventorySlots+2)
+	for i := 0; i < MaxInventorySlots; i++ {
+		p.Inventory[i] = &InventorySlot{ItemID: "rock", Quantity: 1}
+	}
+	p.Inventory[-7] = &InventorySlot{ItemID: "rock", Quantity: 1}
+	p.Inventory[99] = &InventorySlot{ItemID: "rock", Quantity: 1}
+	if got := p.FreeSlots(); got != 0 {
+		t.Fatalf("free slots of a full inventory with stray keys = %d, want 0", got)
+	}
+	if got := p.FirstFreeSlot(); got != -1 {
+		t.Fatalf("first free slot of a full inventory with stray keys = %d, want -1", got)
+	}
+}
+
+func TestFreeSlotsCountsValidSlotsLikeLength(t *testing.T) {
+	p := New("alice")
+	for _, i := range []int{0, 5, 27} {
+		p.SetInvSlot(i, &InventorySlot{ItemID: "rock", Quantity: 1})
+	}
+	if got, want := p.FreeSlots(), MaxInventorySlots-3; got != want {
+		t.Fatalf("free slots = %d, want %d", got, want)
+	}
+}