map_params.go

package struct_utils

import (
	"encoding/json"
	"fmt"
	"reflect"
	"strings"
)

//convert fields in a struct to a map of parameters, as if defined in a URL
//we use this mainly for legacy functions that expect params to be defined in a map[string]string
//to convert the new params struct into such a map
func MapParams(data interface{}) map[string]string {
	params := map[string]string{}
	addStructParams(params, reflect.ValueOf(data))
	return params
}

//recursive function
func addStructParams(params map[string]string, structValue reflect.Value) {
	t := structValue.Type()
	if t.Kind() != reflect.Struct {
		return
	}

	for i := 0; i < t.NumField(); i++ {
		tf := t.Field(i)
		//recurse for embedded structs
		if tf.Anonymous {
			addStructParams(params, structValue.Field(i))
		} else {
			jsonTags := strings.Split(t.Field(i).Tag.Get("json"), ",")
			skip := false
			if jsonTags[0] == "-" || jsonTags[0] == "" {
				skip = true
			} else {
				for _, option := range jsonTags[1:] {
					if option == "omitempty" && structValue.Field(i).IsZero() { // ignore the field if omitempty is applicable
						skip = true
					}
				}
			}
			if !skip {
				//lists must be written as JSON lists so they can be unmarshalled
				//jsut because that is how the legacy code did it
				if t.Field(i).Type.Kind() == reflect.Slice {
					jsonValue, _ := json.Marshal(structValue.Field(i).Interface())
					params[jsonTags[0]] = string(jsonValue)
				} else {
					params[jsonTags[0]] = fmt.Sprintf("%v", structValue.Field(i).Interface())
				}
			}
		}
	}
}