Expand configuration with helper methods

Mappings with fallbacks, reverse mappings ...

configuration.go

@@ -1,6 +1,54 @@
 package unipitt
 
+import (
+	"io/ioutil"
+	"log"
+
+	yaml "gopkg.in/yaml.v2"
+)
+
 // Configuration represents the topic name for the MQTT message for a given instance name
 type Configuration struct {
 	Topics map[string]string
 }
+
+// Topic gets a topic (value) for a given name (key). Return the name itself as fallback
+func (c *Configuration) Topic(name string) string {
+	if value, ok := c.Topics[name]; ok {
+		return value
+	}
+	return name
+}
+
+// reverseTopics construct reverse mapping of topics
+func (c *Configuration) reverseTopics() map[string]string {
+	r := make(map[string]string)
+	for key, value := range c.Topics {
+		r[value] = key
+	}
+	return r
+}
+
+// Name reverse mapping of topic for given name. In case nothing is found, just return the topic itself, hoping there's a mapped instance for it
+func (c *Configuration) Name(topic string) string {
+	if name, ok := c.reverseTopics()[topic]; ok {
+		return name
+	}
+	return topic
+}
+
+// configFromFile reads a configuration from a yaml file
+func configFromFile(configFile string) (c Configuration, err error) {
+	f, err := ioutil.ReadFile(configFile)
+	if err != nil {
+		log.Printf("Error reading config file: %s\n", err)
+		return
+	}
+
+	err = yaml.Unmarshal(f, &c)
+	if err != nil {
+		log.Printf("Error unmarshalling the config: %s\n", err)
+		return
+	}
+	return
+}

configuration_test.go

@@ -1,12 +1,14 @@
 package unipitt
 
 import (
+	"io/ioutil"
+	"os"
 	"testing"
 
 	yaml "gopkg.in/yaml.v2"
 )
 
-func TestConfiguration(t *testing.T) {
+func TestConfigurationUnmarshal(t *testing.T) {
 	input := []byte(`
 topics:
   di_1_01: kitchen switch
@@ -33,3 +35,115 @@ topics:
 		}
 	}
 }
+
+func TestConfigurationTopic(t *testing.T) {
+	cases := []struct {
+		Name     string
+		Expected string
+	}{
+		{Name: "foo", Expected: "qux"},
+		{Name: "bar", Expected: "bar"},
+	}
+	c := Configuration{
+		Topics: map[string]string{
+			"foo": "qux",
+		},
+	}
+	for _, testCase := range cases {
+		result := c.Topic(testCase.Name)
+		if result != testCase.Expected {
+			t.Fatalf("Expected result to be %s, got %s\n", testCase.Expected, result)
+		}
+	}
+}
+
+func TestConfigurationName(t *testing.T) {
+	cases := []struct {
+		Topic    string
+		Expected string
+	}{
+		{Topic: "foo", Expected: "qux"},
+		{Topic: "bar", Expected: "bar"},
+	}
+	c := Configuration{
+		Topics: map[string]string{
+			"qux": "foo",
+		},
+	}
+	for _, testCase := range cases {
+		result := c.Name(testCase.Topic)
+		if result != testCase.Expected {
+			t.Fatalf("Expected result to be %s, got %s\n", testCase.Expected, result)
+		}
+	}
+}
+
+func TestConfigFromFileNonExistant(t *testing.T) {
+	_, err := configFromFile("foo")
+	if err == nil {
+		t.Fatalf("Expected an error to occur reading non-existant file, got not none")
+	}
+}
+
+func TestConfigFromFile(t *testing.T) {
+	configFile, err := ioutil.TempFile("", "config")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(configFile.Name())
+
+	content := []byte(`
+topics:
+  di_1_01: kitchen switch
+  do_2_02: living light
+`)
+	if _, err := configFile.Write(content); err != nil {
+		t.Fatal(err)
+	}
+	if err := configFile.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	c, err := configFromFile(configFile.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expected := &Configuration{
+		Topics: map[string]string{
+			"di_1_01": "kitchen switch",
+			"do_2_02": "living light",
+		},
+	}
+
+	for k, v := range expected.Topics {
+		if topic, ok := c.Topics[k]; !ok {
+			t.Errorf("Could not find topic for name %s\n", k)
+		} else if topic != v {
+			t.Errorf("Expected topic to be %s, but got %s\n", v, topic)
+		}
+	}
+
+}
+
+func TestConfigFromFileUnmarshalIssue(t *testing.T) {
+	configFile, err := ioutil.TempFile("", "config")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(configFile.Name())
+
+	content := []byte("foo")
+
+	if _, err := configFile.Write(content); err != nil {
+		t.Fatal(err)
+	}
+	if err := configFile.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = configFromFile(configFile.Name())
+	if err == nil {
+		t.Fatal("Expected an error on unmarshalling, got none")
+	}
+}