feat: cfg

Signed-off-by: jolheiser <john.olheiser@gmail.com>

example/example.dhall

@@ -0,0 +1,7 @@
+let name = "jolheiser"
+
+in  { username = name
+    , home = "/home/${name}"
+    , admins = [ name, "admin" ]
+    , email = "${name}@example.com"
+    }

example/example.json

@@ -0,0 +1,9 @@
+{
+	"admins": [
+		"jolheiser",
+		"admin"
+	],
+	"email": "jolheiser@example.com",
+	"home": "/home/jolheiser",
+	"username": "jolheiser"
+}

example/example.jsonc

@@ -0,0 +1,10 @@
+{
+	"admins": [
+		"jolheiser",
+		"admin"
+	],
+	"email": "jolheiser@example.com",
+	"home": "/home/jolheiser",
+	// The user!
+	"username": "jolheiser",
+}

example/example.nix

@@ -0,0 +1 @@
+{ admins = [ "jolheiser" "admin" ]; email = "jolheiser@example.com"; home = "/home/jolheiser"; username = "jolheiser"; }

example/example.toml

@@ -0,0 +1,4 @@
+admins = ['jolheiser', 'admin']
+email = 'jolheiser@example.com'
+home = '/home/jolheiser'
+username = 'jolheiser'

example/example.yaml

@@ -0,0 +1,6 @@
+admins:
+    - jolheiser
+    - admin
+email: jolheiser@example.com
+home: /home/jolheiser
+username: jolheiser

go.mod

@@ -0,0 +1,16 @@
+module go.jolheiser.com/cfg
+
+go 1.22.3
+
+require (
+	github.com/pelletier/go-toml/v2 v2.2.2
+	github.com/philandstuff/dhall-golang/v6 v6.0.2
+	github.com/tailscale/hujson v0.0.0-20221223112325-20486734a56a
+	go.jolheiser.com/nixfig v0.0.0-20231129190849-8b2170b2ecda
+	gopkg.in/yaml.v3 v3.0.1
+)
+
+require (
+	github.com/fxamacker/cbor/v2 v2.2.1-0.20200511212021-28e39be4a84f // indirect
+	github.com/x448/float16 v0.8.4 // indirect
+)

go.sum

@@ -0,0 +1,83 @@
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main.go

@@ -0,0 +1,129 @@
+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)
+	}
+}