fulldump/goconfig

package goconfig

import (
    "bytes"
    "encoding/json"
    "errors"
    "flag"
    "fmt"
    "os"
    "reflect"
    "strings"
    "time"
)

var values = map[string]interface{}{}

type postFillArgs struct {
    item
    Raw *string
}

func FillArgs(c interface{}, args []string) error {
    var f = flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
    f.Usage = func() {}
    f.SetOutput(os.Stdout)

    // Default config flag
    f.String("config", "", "Configuration JSON file")

    post := []postFillArgs{}

    traverse(c, func(i item) {
        name_path := strings.ToLower(strings.Join(i.Path, "."))

        if reflect.TypeOf(time.Duration(0)) == i.Value.Type() {
            value := ""
            f.StringVar(&value, name_path, i.Value.Interface().(time.Duration).String(), i.Usage)

            post = append(post, postFillArgs{
                Raw:  &value,
                item: i,
            })

        } else if reflect.Bool == i.Kind {
            f.BoolVar(i.Ptr.(*bool), name_path, i.Value.Interface().(bool), i.Usage)

        } else if reflect.Float64 == i.Kind {
            f.Float64Var(i.Ptr.(*float64), name_path, i.Value.Interface().(float64), i.Usage)

        } else if reflect.Int64 == i.Kind {
            f.Int64Var(i.Ptr.(*int64), name_path, i.Value.Interface().(int64), i.Usage)

        } else if reflect.Int == i.Kind {
            f.IntVar(i.Ptr.(*int), name_path, i.Value.Interface().(int), i.Usage)

        } else if reflect.String == i.Kind {
            f.StringVar(i.Ptr.(*string), name_path, i.Value.Interface().(string), i.Usage)

        } else if reflect.Uint64 == i.Kind {
            f.Uint64Var(i.Ptr.(*uint64), name_path, i.Value.Interface().(uint64), i.Usage)

        } else if reflect.Uint == i.Kind {
            f.UintVar(i.Ptr.(*uint), name_path, i.Value.Interface().(uint), i.Usage)

        } else if reflect.Slice == i.Kind {

            b, _ := json.Marshal(i.Value.Interface())

            value := ""
            f.StringVar(&value, name_path, string(b), i.Usage)

            post = append(post, postFillArgs{
                Raw:  &value,
                item: i,
            })

        } else {
            panic("Kind `" + i.Kind.String() +
                "` is not supported by goconfig (field `" + i.FieldName + "`)")
        }

    })

    if err := f.Parse(args); err != nil && err == flag.ErrHelp {
        m := bytes.NewBufferString("Usage of goconfig:\n\n")
        f.SetOutput(m)
        f.PrintDefaults()
        return errors.New(m.String())
    }

    // Postprocess flags: unsupported flags needs to be declared as string
    // and parsed later. Here is the place.
    for _, p := range post {
        // Special case for durations
        if reflect.TypeOf(time.Duration(0)) == p.Value.Type() {
            d, err := unmarshalDurationString(*p.Raw)
            if err != nil {
                return fmt.Errorf(
                    "'%s' should be nanoseconds or a time.Duration string: %s",
                    p.FieldName, err.Error(),
                )
            }
            p.Value.SetInt(int64(d))

            continue
        }

        err := json.Unmarshal([]byte(*p.Raw), p.Ptr)
        if err != nil {
            return errors.New(fmt.Sprintf(
                "'%s' should be a JSON array: %s",
                p.FieldName, err.Error(),
            ))
        }
    }

    return nil
}