Improve and clean up modules package to also consider dependencies in prepping phase

modules/modules.go

@@ -4,15 +4,15 @@ package modules
 
 import (
 	"errors"
+	"fmt"
 	"sync"
 
 	"github.com/tevino/abool"
 )
 
 var (
-	modulesLock  sync.Mutex
-	modules      = make(map[string]*Module)
-	modulesOrder []*Module
+	modulesLock sync.Mutex
+	modules     = make(map[string]*Module)
 
 	// ErrCleanExit is returned by Start() when the program is interrupted before starting. This can happen for example, when using the "--help" flag.
 	ErrCleanExit = errors.New("clean exit requested")
@@ -21,14 +21,18 @@ var (
 // Module represents a module.
 type Module struct {
 	Name         string
-	Active       *abool.AtomicBool
+	Prepped      *abool.AtomicBool
+	Started      *abool.AtomicBool
+	Stopped      *abool.AtomicBool
 	inTransition *abool.AtomicBool
 
 	prep  func() error
 	start func() error
 	stop  func() error
 
-	dependencies []string
+	depNames   []string
+	depModules []*Module
+	depReverse []*Module
 }
 
 func dummyAction() error {
@@ -39,12 +43,14 @@ func dummyAction() error {
 func Register(name string, prep, start, stop func() error, dependencies ...string) *Module {
 	newModule := &Module{
 		Name:         name,
-		Active:       abool.NewBool(false),
+		Prepped:      abool.NewBool(false),
+		Started:      abool.NewBool(false),
+		Stopped:      abool.NewBool(false),
 		inTransition: abool.NewBool(false),
 		prep:         prep,
 		start:        start,
 		stop:         stop,
-		dependencies: dependencies,
+		depNames:     dependencies,
 	}
 
 	// replace nil arguments with dummy action
@@ -60,7 +66,72 @@ func Register(name string, prep, start, stop func() error, dependencies ...strin
 
 	modulesLock.Lock()
 	defer modulesLock.Unlock()
-	modulesOrder = append(modulesOrder, newModule)
 	modules[name] = newModule
 	return newModule
 }
+
+func initDependencies() error {
+	for _, m := range modules {
+		for _, depName := range m.depNames {
+
+			// get dependency
+			depModule, ok := modules[depName]
+			if !ok {
+				return fmt.Errorf("modules: module %s declares dependency \"%s\", but this module has not been registered", m.Name, depName)
+			}
+
+			// link together
+			m.depModules = append(m.depModules, depModule)
+			depModule.depReverse = append(depModule.depReverse, m)
+
+		}
+	}
+
+	return nil
+}
+
+// ReadyToPrep returns whether all dependencies are ready for this module to prep.
+func (m *Module) ReadyToPrep() bool {
+	if m.inTransition.IsSet() || m.Prepped.IsSet() {
+		return false
+	}
+
+	for _, dep := range m.depModules {
+		if !dep.Prepped.IsSet() {
+			return false
+		}
+	}
+
+	return true
+}
+
+// ReadyToStart returns whether all dependencies are ready for this module to start.
+func (m *Module) ReadyToStart() bool {
+	if m.inTransition.IsSet() || m.Started.IsSet() {
+		return false
+	}
+
+	for _, dep := range m.depModules {
+		if !dep.Started.IsSet() {
+			return false
+		}
+	}
+
+	return true
+}
+
+// ReadyToStop returns whether all dependencies are ready for this module to stop.
+func (m *Module) ReadyToStop() bool {
+	if !m.Started.IsSet() || m.inTransition.IsSet() || m.Stopped.IsSet() {
+		return false
+	}
+
+	for _, revDep := range m.depReverse {
+		// not ready if a reverse dependency was started, but not yet stopped
+		if revDep.Started.IsSet() && !revDep.Stopped.IsSet() {
+			return false
+		}
+	}
+
+	return true
+}