Simplify state reconciliation and support changing Softnet settings (#364)

* Simplify state reconciliation and support changing Softnet settings

* Remove unused "updateFunc" parameter from syncOnDiskVMs()

* Don't take an address of a loop variable

* ensure → ensures

* updateVMState(): don't forget to update VMState

* Introduce TestSpecUpdateSoftnet integration test

* Update OpenAPI specification to include generation/observedGeneration

internal/worker/fsm.go

@@ -0,0 +1,58 @@
+package worker
+
+import (
+	"fmt"
+
+	v1 "github.com/cirruslabs/orchard/pkg/resource/v1"
+	"github.com/samber/mo"
+)
+
+type Action string
+
+const (
+	ActionIgnore         Action = "ignore"
+	ActionCreate         Action = "create"
+	ActionMonitorPending Action = "monitor-pending"
+	ActionReportRunning  Action = "report-running"
+	ActionMonitorRunning Action = "monitor-running"
+	ActionStop           Action = "stop"
+	ActionFail           Action = "fail"
+	ActionLostTrack      Action = "lost-track"
+	ActionImpossible     Action = "impossible"
+	ActionDelete         Action = "delete"
+)
+
+var transitions = map[mo.Option[v1.VMStatus]]map[mo.Option[v1.VMStatus]]Action{
+	mo.None[v1.VMStatus](): {
+		mo.None[v1.VMStatus]():      ActionIgnore,
+		mo.Some(v1.VMStatusPending): ActionDelete,
+		mo.Some(v1.VMStatusRunning): ActionDelete,
+		mo.Some(v1.VMStatusFailed):  ActionDelete,
+	},
+	mo.Some(v1.VMStatusPending): {
+		mo.None[v1.VMStatus]():      ActionCreate,
+		mo.Some(v1.VMStatusPending): ActionMonitorPending,
+		mo.Some(v1.VMStatusRunning): ActionReportRunning,
+		mo.Some(v1.VMStatusFailed):  ActionFail,
+	},
+	mo.Some(v1.VMStatusRunning): {
+		mo.None[v1.VMStatus]():      ActionLostTrack,
+		mo.Some(v1.VMStatusPending): ActionImpossible,
+		mo.Some(v1.VMStatusRunning): ActionMonitorRunning,
+		mo.Some(v1.VMStatusFailed):  ActionFail,
+	},
+	mo.Some(v1.VMStatusFailed): {
+		mo.None[v1.VMStatus]():      ActionIgnore,
+		mo.Some(v1.VMStatusPending): ActionStop,
+		mo.Some(v1.VMStatusRunning): ActionStop,
+		mo.Some(v1.VMStatusFailed):  ActionIgnore,
+	},
+}
+
+func optionToString[T any](option mo.Option[T]) string {
+	if option.IsNone() {
+		return "None"
+	}
+
+	return fmt.Sprintf("Some(%v)", option.MustGet())
+}