Implement logic for retrieving component params

This commit will add an interface `GetComponentParams` to
metadata.Manager that returns a map of parameters for the passed in
component.

Also implements the logic for parsing the jsonnet snippet to retrieve
the parameters.

This functionality will later support new commands to list parameters.

metadata/interface.go

@@ -45,6 +45,7 @@ type Manager interface {
 	CreateComponent(name string, text string, params map[string]string, templateType prototype.TemplateType) error
 	LibPaths(envName string) (libPath, envLibPath, envComponentPath, envParamsPath AbsPath)
 	SetComponentParams(component string, params map[string]string) error
+	GetComponentParams(name string) (map[string]string, error)
 	CreateEnvironment(name, uri, namespace string, spec ClusterSpec) error
 	DeleteEnvironment(name string) error
 	GetEnvironments() ([]*Environment, error)
@@ -57,7 +58,6 @@ type Manager interface {
 	// GetPrototype(id string) Protoype
 	// SearchPrototypes(query string) []Protoype
 	// VendorLibrary(uri, version string) error
-	// GetComponentParams(name string) map[string]string
 	// SetEnvironmentParams(component, env string, params map[string]string) error
 	// GetEnvironmentParams(env string) (map[string]map[string]string, error)
 }

metadata/manager.go

@@ -194,6 +194,15 @@ func (m *manager) LibPaths(envName string) (libPath, envLibPath, envComponentPat
 		appendToAbsPath(envPath, path.Base(envName)+".jsonnet"), appendToAbsPath(envPath, componentParamsFile)
 }
 
+func (m *manager) GetComponentParams(component string) (map[string]string, error) {
+	text, err := afero.ReadFile(m.appFS, string(m.componentParamsPath))
+	if err != nil {
+		return nil, err
+	}
+
+	return snippet.GetComponentParams(component, string(text))
+}
+
 func (m *manager) SetComponentParams(component string, params map[string]string) error {
 	text, err := afero.ReadFile(m.appFS, string(m.componentParamsPath))
 	if err != nil {

metadata/snippet/interface.go

@@ -26,6 +26,19 @@ func AppendComponent(component, snippet string, params map[string]string) (strin
 	return appendComponent(component, snippet, params)
 }
 
+// GetComponentParams takes
+//
+//  component: the name of the component to retrieve params for.
+//  snippet: the jsonnet snippet containing the component parameters.
+//
+// and returns a map of key-value param pairs corresponding to that component.
+//
+// An error will be returned if the component is not found in the snippet.
+func GetComponentParams(component, snippet string) (map[string]string, error) {
+	params, _, err := getComponentParams(component, snippet)
+	return params, err
+}
+
 // SetComponentParams takes
 //
 //   component: the name of the new component to be modified.

metadata/snippet/params.go

@@ -148,31 +148,30 @@ func appendComponent(component, snippet string, params map[string]string) (strin
 	return strings.Join(lines, "\n"), nil
 }
 
-func setComponentParams(component, snippet string, params map[string]string) (string, error) {
+func getComponentParams(component, snippet string) (map[string]string, *ast.LocationRange, error) {
 	componentsNode, err := visitComponentsObj(component, snippet)
 	if err != nil {
-		return "", err
+		return nil, nil, err
 	}
 
-	var loc *ast.LocationRange
-	var currentParams map[string]string
-
 	switch n := (*componentsNode).(type) {
 	case *ast.Object:
 		for _, field := range n.Fields {
 			if field.Id != nil && string(*field.Id) == component {
-				currentParams, loc, err = visitComponentParams(field.Expr2)
-				if err != nil {
-					return "", err
-				}
+				return visitComponentParams(field.Expr2)
 			}
 		}
 	default:
-		return "", fmt.Errorf("Expected component node type to be object")
+		return nil, nil, fmt.Errorf("Expected component node type to be object")
 	}
 
-	if loc == nil {
-		return "", fmt.Errorf("Could not find component identifier '%s' when attempting to set params", component)
+	return nil, nil, fmt.Errorf("Could not find component identifier '%s' when attempting to set params", component)
+}
+
+func setComponentParams(component, snippet string, params map[string]string) (string, error) {
+	currentParams, loc, err := getComponentParams(component, snippet)
+	if err != nil {
+		return "", err
 	}
 
 	for k, v := range currentParams {

metadata/snippet/params_test.go

@@ -16,6 +16,7 @@
 package snippet
 
 import (
+	"reflect"
 	"testing"
 )
 
@@ -175,6 +176,96 @@ func TestAppendComponentParams(t *testing.T) {
 	}
 }
 
+func TestGetComponentParams(t *testing.T) {
+	tests := []struct {
+		componentName string
+		jsonnet       string
+		expected      map[string]string
+	}{
+		// Test getting the parameters where there is a single component
+		{
+			"foo",
+			`
+{
+  global: {},
+  components: {
+    foo: {
+      name: "foo",
+      replicas: 1,
+    },
+  },
+}`,
+			map[string]string{"name": `"foo"`, "replicas": "1"},
+		},
+		// Test getting the parameters where there are multiple components
+		{
+			"foo",
+			`
+{
+  global: {},
+  components: {
+    bar: {
+      replicas: 5
+    },
+    foo: {
+      name: "foo",
+      replicas: 1,
+    },
+  },
+}`,
+			map[string]string{"name": `"foo"`, "replicas": "1"},
+		},
+	}
+
+	errors := []struct {
+		componentName string
+		jsonnet       string
+	}{
+		// Test case where component doesn't exist
+		{
+			"baz",
+			`
+{
+  components: {
+    foo: {
+      name: "foo",
+    },
+  },
+}`,
+		},
+		// Test case where components isn't a top level object
+		{
+			"baz",
+			`
+{
+  global: {
+    // User-defined global parameters; accessible to all component and environments, Ex:
+    // replicas: 4,
+		components: {},
+  },
+}`,
+		},
+	}
+
+	for _, s := range tests {
+		params, err := GetComponentParams(s.componentName, s.jsonnet)
+		if err != nil {
+			t.Errorf("Unexpected error\n  input: %v\n  error: %v", s.jsonnet, err)
+		}
+
+		if !reflect.DeepEqual(params, s.expected) {
+			t.Errorf("Wrong conversion\n  expected:%v\n  got:%v", s.expected, params)
+		}
+	}
+
+	for _, e := range errors {
+		params, err := GetComponentParams(e.componentName, e.jsonnet)
+		if err == nil {
+			t.Errorf("Expected error but not found\n  input: %v  got: %v", e, params)
+		}
+	}
+}
+
 func TestSetComponentParams(t *testing.T) {
 	tests := []struct {
 		componentName string