split into separate files

subsystem.go

@@ -0,0 +1,30 @@
+package app
+
+// Subsystem represents a sub-system of the application, with its setup and
+// teardown functions and dependencies.
+type Subsystem struct {
+	name     string
+	setup    setupFn
+	teardown teardownFn
+	depends  []*Subsystem
+}
+
+// SubsystemOpts contains user-exposed options when defining a subsystem.
+type SubsystemOpts struct {
+	// Setup is the setup function for the subsystem.
+	Setup setupFn
+	// Teardown is the teardown function for the subsystem.
+	Teardown teardownFn
+	// Depends is a list of subsystems that this subsystem depends on.
+	Depends []*Subsystem
+}
+
+// NewSubsystem creates a new Subsystem instance with the given name and options.
+func NewSubsystem(name string, opts SubsystemOpts) *Subsystem {
+	return &Subsystem{
+		name:     name,
+		setup:    opts.Setup,
+		teardown: opts.Teardown,
+		depends:  opts.Depends,
+	}
+}