feat: westworldwithwoman. add elsa

chapter-2-state-driven-agent-design/westworldwithwoman/state_wifes_global_state.go

@@ -0,0 +1,50 @@
+package westworldwithwoman
+
+import (
+	"math/rand"
+	"sync"
+)
+
+// wifesGlobalState is Elsa's global state - its Execute runs on
+// every single tick of her state machine, in addition to whatever
+// her current state is doing (see StateMachine.Update). That's what
+// makes it the right place for "does nature call right now" logic:
+// the book says that can happen "during any state and at any time,"
+// which is exactly what a global state is for.
+type wifesGlobalState struct{}
+
+var (
+	wifesGlobalStateInstance *wifesGlobalState
+	wifesGlobalStateOnce     sync.Once
+)
+
+// WifesGlobalState is the Go stand-in for
+// "WifesGlobalState::Instance()".
+func WifesGlobalState() *wifesGlobalState {
+	wifesGlobalStateOnce.Do(func() {
+		wifesGlobalStateInstance = &wifesGlobalState{}
+	})
+	return wifesGlobalStateInstance
+}
+
+var _ State[Elsa] = (*wifesGlobalState)(nil)
+
+// Enter and Exit do nothing - a global state is set once, in
+// NewElsa, and never changed, so these never actually get called.
+// They only exist to satisfy the State[Elsa] interface.
+func (s *wifesGlobalState) Enter(e *Elsa) {}
+func (s *wifesGlobalState) Exit(e *Elsa)  {}
+
+// bathroomCallChance is a 1-in-N chance, per the chapter's "1 in 10
+// chance to change to VisitBathroom state."
+const bathroomCallChance = 10
+
+// Execute rolls the dice every tick. If it comes up, and Elsa isn't
+// already in the bathroom (checked with IsInState, so this can't
+// interrupt a bathroom trip that's already happening), she breaks
+// off into VisitBathroom.
+func (s *wifesGlobalState) Execute(e *Elsa) {
+	if !e.FSM().IsInState(VisitBathroom()) && rand.Intn(bathroomCallChance) == 0 {
+		e.ChangeState(VisitBathroom())
+	}
+}