Implement HasDependencies interface and Provider (#6)

depresolve.go

@@ -115,26 +115,6 @@ func (d dependencyNode) SpecificationName() SpecificationName {
 
 type dependencyGraph []dependencyNode
 
-//// merge Allows merging this dependency graph with another one and returns the result.
-//func (g dependencyGraph) merge(o dependencyGraph) dependencyGraph {
-//	var lookup = make(map[SpecificationName]bool)
-//	var merge []dependencyNode
-//
-//	for _, node := range g {
-//		merge = append(merge, node)
-//		lookup[node.SpecificationName()] = true
-//	}
-//
-//	for _, node := range o {
-//		if _, found := lookup[node.SpecificationName()]; found {
-//			continue
-//		}
-//		merge = append(merge, node)
-//	}
-//
-//	return newDependencyGraph(merge...)
-//}
-
 func newDependencyGraph(specifications ...dependencyNode) dependencyGraph {
 	return append(dependencyGraph{}, specifications...)
 }
@@ -214,3 +194,27 @@ func (g dependencyGraph) resolve() (ResolvedDependencies, error) {
 
 	return resolved, nil
 }
+
+// HasDependencies is an interface that can be implemented by specifications
+// that define their dependencies from their field values.
+// This interface can be used in conjunction with the HasDependenciesProvider
+// to easily resolve dependencies.
+type HasDependencies interface {
+	Specification
+	Dependencies() []SpecificationName
+}
+
+type HasDependenciesProvider struct{}
+
+func (h HasDependenciesProvider) Supports(s Specification) bool {
+	_, ok := s.(HasDependencies)
+	return ok
+}
+
+func (h HasDependenciesProvider) Provide(s Specification) []SpecificationName {
+	d, ok := s.(HasDependencies)
+	if !ok {
+		return nil
+	}
+	return d.Dependencies()
+}

depresolve_test.go

@@ -243,3 +243,82 @@ func TestDependencyResolutionProcessor_Name(t *testing.T) {
 	p := DependencyResolutionProcessor{}
 	assert.NotEqual(t, "", p.Name())
 }
+
+type hasDependencySpec struct {
+	source       Source
+	dependencies []SpecificationName
+}
+
+func (h *hasDependencySpec) Name() SpecificationName {
+	return "spec"
+}
+
+func (h *hasDependencySpec) Type() SpecificationType {
+	return "spec"
+}
+
+func (h *hasDependencySpec) Description() string {
+	return "description"
+}
+
+func (h *hasDependencySpec) Source() Source {
+	return h.source
+}
+
+func (h *hasDependencySpec) SetSource(s Source) {
+	h.source = s
+}
+
+func (h *hasDependencySpec) Dependencies() []SpecificationName {
+	return h.dependencies
+}
+
+func TestHasDependenciesProvider_Supports(t *testing.T) {
+	tests := []struct {
+		name  string
+		given Specification
+		then  bool
+	}{
+		{
+			name:  "GIVEN specification not implementing HasDependencies THEN return false",
+			given: &GenericSpecification{},
+			then:  false,
+		},
+		{
+			name:  "GIVEN specification implementing HasDependencies THEN return false",
+			given: &hasDependencySpec{},
+			then:  true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			h := HasDependenciesProvider{}
+			assert.Equal(t, tt.then, h.Supports(tt.given))
+		})
+	}
+}
+
+func TestHasDependenciesProvider_Provide(t *testing.T) {
+	tests := []struct {
+		name  string
+		given Specification
+		then  []SpecificationName
+	}{
+		{
+			name:  "GIVEN specification not implementing HasDependencies THEN return nil",
+			given: &GenericSpecification{},
+			then:  nil,
+		},
+		{
+			name:  "GIVEN specification implementing HasDependencies THEN return dependencies",
+			given: &hasDependencySpec{dependencies: []SpecificationName{"spec1"}},
+			then:  []SpecificationName{"spec1"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			h := HasDependenciesProvider{}
+			assert.Equal(t, tt.then, h.Provide(tt.given))
+		})
+	}
+}

util.go

@@ -10,7 +10,7 @@ import (
 // done, it returns nil.
 //
 // This function is useful for early exits in long-running or blocking
-// operations when you want  to respond to context cancellations in a clean
+// operations when you then  to respond to context cancellations in a clean
 // and consistent manner.
 func CheckContextDone(ctx context.Context) error {
 	select {