package internal

import (

	"reflect"

	"strings"

)

// RemainingKeys will inspect a struct and compare it to a map. Any struct

// field that does not have a JSON tag that matches a key in the map or

// a matching lower-case field in the map will be returned as an extra.

//

// This is useful for determining the extra fields returned in response bodies

// for resources that can contain an arbitrary or dynamic number of fields.

func RemainingKeys(s interface{}, m map[string]interface{}) (extras map[string]interface{}) {

	extras = make(map[string]interface{})

	for k, v := range m {

		extras[k] = v

	}

	valueOf := reflect.ValueOf(s)

	typeOf := reflect.TypeOf(s)

	for i := 0; i < valueOf.NumField(); i++ {

		field := typeOf.Field(i)

		lowerField := strings.ToLower(field.Name)

		delete(extras, lowerField)

		if tagValue := field.Tag.Get("json"); tagValue != "" && tagValue != "-" {

			delete(extras, tagValue)

		}

	}

	return

}