Trying out Cobra and Viper for Go

testingviper.go

package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"os"
	"reflect"

	"github.com/spf13/cobra"
	"github.com/spf13/viper"
)

var configFile string
var someFloat64 float64
var someNumber int
var someString string

// Main command
var TestCmd = &cobra.Command{
	Use:   "testviper",
	Short: "explore how viper & cobra works",
	Long:  `HACK THE PLANET HACK THE PLANET HACK THE PLANET`,
	Run: func(cmd *cobra.Command, args []string) {
		InitializeConfig()
	},
}

// Variable used to get around initialization loop
var testCmdV *cobra.Command

func InitializeDefaultSettings() {
	fmt.Println("InitializeDefaultSettings")

	// Command line config should inform Viper defaults when possible
	float64Flag, _ := testCmdV.PersistentFlags().GetFloat64("float")
	numberFlag, _ := testCmdV.PersistentFlags().GetInt("number")
	stringFlag, _ := testCmdV.PersistentFlags().GetString("string")

	fmt.Println("SomeFloat", reflect.TypeOf(float64Flag))
	fmt.Println("SomeNumber", reflect.TypeOf(numberFlag))
	fmt.Println("SomeString", reflect.TypeOf(stringFlag))

	viper.SetDefault("SomeFloat", float64Flag)
	viper.SetDefault("SomeNumber", numberFlag)
	viper.SetDefault("SomeString", stringFlag)
}

// Interesting that Viper has facilities for reading but none for writing
func CreateConfig() error {
	j, jerr := json.MarshalIndent(viper.AllSettings(), "", "    ")
	if jerr != nil {
		fmt.Println("jerr:", jerr.Error())
		return jerr
	}

	err := ioutil.WriteFile(configFile, j, 0644)
	if err != nil {
		fmt.Println("ERROR: ", err)
		return err
	}

	return nil
}

func InitializeConfig() {
	// Initialize defaults
	InitializeDefaultSettings()

	// Read default from config
	viper.SetConfigFile(configFile)
	err := viper.ReadInConfig()
	if err != nil {
		// No config. Create default
		cErr := CreateConfig()
		if cErr != nil {
			// Couldn't write config. Bail.
			os.Exit(-1)
		}
	}

	// Check for command line overrides of config
	if testCmdV.PersistentFlags().Lookup("float").Changed {
		viper.Set("SomeFloat", someFloat64)
	}
	if testCmdV.PersistentFlags().Lookup("number").Changed {
		viper.Set("SomeNumber", someNumber)
	}
	if testCmdV.PersistentFlags().Lookup("string").Changed {
		viper.Set("SomeString", someString)
	}
}

func init() {
	TestCmd.PersistentFlags().Float64VarP(&someFloat64, "float", "f", 42, "just some float64")
	TestCmd.PersistentFlags().IntVarP(&someNumber, "number", "n", 42, "just some number")
	TestCmd.PersistentFlags().StringVarP(&someString, "string", "s", "weeee", "just some string")
	TestCmd.PersistentFlags().StringVarP(&configFile, "config", "c", "config.json", "filename for storing config as json")

	testCmdV = TestCmd
}

func main() {
	TestCmd.Execute()

	fmt.Println("SomeFloat", reflect.TypeOf(viper.Get("SomeFloat")))
	fmt.Println("SomeNumber", reflect.TypeOf(viper.GetInt("SomeNumber")))
	fmt.Println("SomeString", reflect.TypeOf(viper.Get("SomeString")))

	fmt.Printf("Float64: %f\n", viper.Get("SomeFloat"))
	fmt.Printf("Number:  %d\n", viper.GetInt("SomeNumber"))
	fmt.Printf("String:  %s\n", viper.Get("SomeString"))
	fmt.Printf("Config:  %s\n", configFile)
}