Initial project snapshot

backend/internal/modules/sessionbroker/state_machine.go

@@ -0,0 +1,44 @@
+package sessionbroker
+
+import (
+	"fmt"
+
+	sessioncontracts "github.com/example/remote-access-platform/backend/pkg/contracts/session"
+)
+
+var allowedTransitions = map[sessioncontracts.State]map[sessioncontracts.State]struct{}{
+	sessioncontracts.StateStarting: {
+		sessioncontracts.StateActive:     {},
+		sessioncontracts.StateFailed:     {},
+		sessioncontracts.StateTerminated: {},
+	},
+	sessioncontracts.StateActive: {
+		sessioncontracts.StateDetached:     {},
+		sessioncontracts.StateReconnecting: {},
+		sessioncontracts.StateFailed:       {},
+		sessioncontracts.StateTerminated:   {},
+	},
+	sessioncontracts.StateDetached: {
+		sessioncontracts.StateReconnecting: {},
+		sessioncontracts.StateTerminated:   {},
+		sessioncontracts.StateFailed:       {},
+	},
+	sessioncontracts.StateReconnecting: {
+		sessioncontracts.StateActive:     {},
+		sessioncontracts.StateDetached:   {},
+		sessioncontracts.StateFailed:     {},
+		sessioncontracts.StateTerminated: {},
+	},
+}
+
+func validateTransition(from, to sessioncontracts.State) error {
+	if from == to {
+		return nil
+	}
+	if allowed, ok := allowedTransitions[from]; ok {
+		if _, ok := allowed[to]; ok {
+			return nil
+		}
+	}
+	return fmt.Errorf("invalid session state transition: %s -> %s", from, to)
+}