config/config.go

package config

import (
	"bytes"
	"io"
	"os"
	"path/filepath"
)

const (
	ConfigEnvPrefix = "CONFIG_ENV_PREFIX"
	ConfigTagEnv    = "env"
)

type Configurator interface {
	SetConfigPath(in string) error
	Load(target interface{}, files ...string) error
	LoadReader(target interface{}, ext string, in io.Reader) error
	Save(target interface{}, file string, overWrite bool) error

	SetEnvPrefix(in string)
}

type config struct {
	configPath string
	// Name of file to look for inside the path
	envPrefix string
}

func New() Configurator {
	return &config{}
}

var _c *config

// SetConfigPath set a path to search for the config file in.
func SetConfigPath(in string) error { return _c.SetConfigPath(in) }
func (c *config) SetConfigPath(in string) error {
	if in != "" {
		absin, err := absPathify(in)
		if nil != err {
			return err
		}

		c.configPath = absin
	}
	return nil
}

// SetEnvPrefix set a prefix to search for the env variable.
func SetEnvPrefix(in string) { _c.SetEnvPrefix(in) }
func (c *config) SetEnvPrefix(in string) {
	if in != "" {
		c.envPrefix = in
	}
}

// Load will unmarshal from configuration file from disk
func Load(target interface{}, files ...string) error {
	return _c.Load(target, files...)
}
func (c *config) Load(target interface{}, files ...string) error {
	filenames := c.getConfigFiles(files...)

	for _, file := range filenames {
		if err := unmarshalFile(target, file); err != nil {
			return err
		}
	}

	return unmarshalTags(target, c.getENVPrefix())
}

// LoadReader will unmarshal from configuration bytes
func LoadReader(target interface{}, ext string, in io.Reader) error {
	return _c.LoadReader(target, ext, in)
}
func (c *config) LoadReader(target interface{}, ext string, in io.Reader) error {
	buf := new(bytes.Buffer)
	buf.ReadFrom(in)

	return unmarshalData(target, ext, buf.Bytes())
}

// Save store to configuration file from disk
func Save(target interface{}, file string, overWrite bool) error {
	return _c.Save(target, file, overWrite)
}
func (c *config) Save(target interface{}, file string, overWrite bool) error {
	return marshalFile(target, file, overWrite)
}

// 1. file
// 2. configPath/file
func (c *config) getConfigFiles(files ...string) []string {
	var results []string

	for _, file := range files {
		// check configuration
		if exists(file) {
			results = append(results, file)
		}
	}

	for _, file := range files {
		// check configuration
		if absin, err := absPathify(filepath.Join(c.configPath, file)); nil == err {
			if exists(absin) {
				results = append(results, absin)
			}
		}
	}

	return results
}

func (c *config) getENVPrefix() string {
	if c.envPrefix == "" {
		if prefix := os.Getenv(ConfigEnvPrefix); prefix != "" {
			return prefix
		}
		return ""
	}
	return c.envPrefix
}