// Load an extensible section that has a type keyword
func LoadExtensibleSection(app *Application, sectionName string,
	extensions AvailableExtensions, env envconf.Environment,
	configFile ConfigFile) (obj HasConfigStruct, err error) {

	confSection := new(ExtensibleGlobals)

	conf, ok := configFile[sectionName]
	if !ok {
		return nil, fmt.Errorf("Missing section '%s'", sectionName)
	}

	if err = toml.PrimitiveDecode(conf, confSection); err != nil {
		return nil, err
	}
	if err = env.Decode(toEnvName(sectionName), EnvSep, confSection); err != nil {
		return nil, err
	}
	ext, ok := extensions.Get(confSection.Typ)
	if !ok {
		//TODO: Add log info to indicate using "default"
		return nil, fmt.Errorf("No type '%s' available to load for section '%s'",
			confSection.Typ, sectionName)
	}

	obj = ext()
	loadedConfig, err := LoadConfigStruct(sectionName, env, conf, obj)
	if err != nil {
		return nil, err
	}

	err = obj.Init(app, loadedConfig)
	return obj, err
}

// Loads the config for a section supplied, configures the supplied object, and initializes
func LoadConfigForSection(app *Application, sectionName string, obj HasConfigStruct,
	env envconf.Environment, configFile ConfigFile) (err error) {

	conf, ok := configFile[sectionName]
	if !ok {
		return fmt.Errorf("Error loading config file, section: %s", sectionName)
	}
	confStruct := obj.ConfigStruct()
	if confStruct == nil {
		return nil
	}

	if err = toml.PrimitiveDecode(conf, confStruct); err != nil {
		return fmt.Errorf("Unable to decode config for section '%s': %s",
			sectionName, err)
	}

	if err = env.Decode(toEnvName(sectionName), EnvSep, confStruct); err != nil {
		return fmt.Errorf("Invalid environment variable for section '%s': %s",
			sectionName, err)
	}

	err = obj.Init(app, confStruct)
	return
}

func loadEnvConfig(env envconf.Environment, section string,
	app *Application, configable HasConfigStruct) (err error) {

	confStruct := configable.ConfigStruct()
	if err = env.Decode(toEnvName(section), EnvSep, confStruct); err != nil {
		return fmt.Errorf("Error decoding config for section %q: %s",
			section, err)
	}
	return configable.Init(app, confStruct)
}

// Applies environment variable overrides to confStruct and initializes obj
func LoadConfigFromEnvironment(app *Application, sectionName string,
	obj HasInit, env envconf.Environment, confStruct interface{}) (err error) {

	if confStruct == nil {
		return nil
	}
	if err = env.Decode(toEnvName(sectionName), EnvSep, confStruct); err != nil {
		return fmt.Errorf("Invalid environment variable for section '%s': %s",
			sectionName, err)
	}
	return obj.Init(app, confStruct)
}

func LoadConfigStruct(sectionName string, env envconf.Environment,
	config toml.Primitive, configable HasConfigStruct) (
	configStruct interface{}, err error) {

	if configStruct = configable.ConfigStruct(); configStruct == nil {
		return configStruct, nil
	}

	// Global section options
	// SimplePush defines some common parameters
	// that are defined in the ExtensibleGlobals struct.
	// Use reflection to extract the tagged ExtensibleGlobals fields.
	var pg ExtensibleGlobals
	rt := reflect.TypeOf(pg)

	ignoreConfig := make(map[string]interface{}, rt.NumField())
	ignoreEnv := make(map[string]interface{}, rt.NumField())

	for i := 0; i < rt.NumField(); i++ {
		sft := rt.Field(i)
		kname := sft.Tag.Get("toml")
		if len(kname) == 0 {
			kname = sft.Name
		}
		ignoreConfig[kname] = true
		if kname = sft.Tag.Get("env"); len(kname) == 0 {
			kname = sft.Name
		}
		ignoreEnv[toEnvName(sectionName, kname)] = true
	}

	if err = toml.PrimitiveDecodeStrict(config, configStruct, ignoreConfig); err != nil {
		matches := unknownOptionRegex.FindStringSubmatch(err.Error())
		if len(matches) == 2 {
			// We've got an unrecognized config option.
			err = fmt.Errorf("Unknown config setting for section '%s': %s",
				sectionName, matches[1])
		}
		return nil, err
	}

	if err = env.DecodeStrict(toEnvName(sectionName), EnvSep, configStruct, ignoreEnv); err != nil {
		return nil, fmt.Errorf("Invalid environment variable for section '%s': %s",
			sectionName, err)
	}

	return configStruct, nil
}