Implement handlers for stage movement and quest completion

common/stringstack/stringstack.go

@@ -0,0 +1,40 @@
+package stringstack
+
+import (
+	"errors"
+	"sync"
+)
+
+// StringStack is a basic LIFO "stack" for storing strings.
+type StringStack struct {
+	sync.Mutex
+	stack []string
+}
+
+// New creates a new instance of StringStack
+func New() *StringStack {
+	return &StringStack{}
+}
+
+// Push pushes a string onto the stack.
+func (s *StringStack) Push(v string) {
+	s.Lock()
+	defer s.Unlock()
+
+	s.stack = append(s.stack, v)
+}
+
+// Pop pops a string from the stack.
+func (s *StringStack) Pop() (string, error) {
+	s.Lock()
+	defer s.Unlock()
+
+	if len(s.stack) == 0 {
+		return "", errors.New("no items on stack")
+	}
+
+	x := s.stack[len(s.stack)-1]
+	s.stack = s.stack[:len(s.stack)-1]
+
+	return x, nil
+}