cfg/main.go

package main

import (
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/pelletier/go-toml/v2"
	"github.com/philandstuff/dhall-golang/v6"
	"github.com/tailscale/hujson"
	"go.jolheiser.com/nixfig"
	"gopkg.in/yaml.v3"
)

func maine() error {
	var unmarshal func([]byte, any) error
	var marshal func(any) ([]byte, error)

	fs := flag.NewFlagSet("cfg", flag.ExitOnError)
	fromFunc := func(s string) error {
		switch strings.ToLower(s) {
		case "json", "jsonc":
			unmarshal = func(b []byte, a any) error {
				b, err := hujson.Standardize(b)
				if err != nil {
					return err
				}
				return json.Unmarshal(b, a)
			}
		case "yaml":
			unmarshal = yaml.Unmarshal
		case "toml":
			unmarshal = toml.Unmarshal
		case "dhall":
			unmarshal = dhall.Unmarshal
		case "nix":
			unmarshal = nixfig.Unmarshal
		default:
			return fmt.Errorf("unknown format %q", s)
		}
		return nil
	}
	fs.Func("from", "The format to convert from", fromFunc)
	fs.Func("f", "--from", fromFunc)
	toFunc := func(s string) error {
		switch strings.ToLower(s) {
		case "json", "jsonc":
			marshal = func(a any) ([]byte, error) {
				return json.MarshalIndent(a, "", "\t")
			}
		case "yaml":
			marshal = yaml.Marshal
		case "toml":
			marshal = toml.Marshal
		case "nix":
			marshal = nixfig.Marshal
		default:
			return fmt.Errorf("unknown format %q", s)
		}
		return nil
	}
	fs.Func("to", "The format to convert to", toFunc)
	fs.Func("t", "--to", toFunc)
	if err := fs.Parse(os.Args[1:]); err != nil {
		return err
	}

	if fs.NArg() < 1 {
		return errors.New("cfg requires at least an input file")
	}

	in := fs.Arg(0)
	if unmarshal == nil {
		if err := fromFunc(strings.TrimPrefix(filepath.Ext(fs.Arg(0)), ".")); err != nil {
			return err
		}
	}

	out := os.Stdout
	if fs.NArg() > 1 {
		fi, err := os.Create(fs.Arg(1))
		if err != nil {
			return err
		}
		defer fi.Close()
		out = fi

		if marshal == nil {
			if err := toFunc(strings.TrimPrefix(filepath.Ext(fs.Arg(1)), ".")); err != nil {
				return err
			}
		}
	} else if marshal == nil {
		marshal = json.Marshal
	}

	var data any

	inData, err := os.ReadFile(in)
	if err != nil {
		return err
	}

	if err := unmarshal(inData, &data); err != nil {
		return err
	}

	outData, err := marshal(data)
	if err != nil {
		return err
	}

	if _, err := out.Write(outData); err != nil {
		return err
	}

	return nil
}

func main() {
	if err := maine(); err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
}