// Copyright 2020 The Gitea Authors. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.

package storage

import (
	"reflect"

	jsoniter "github.com/json-iterator/go"
)

// Mappable represents an interface that can MapTo another interface
type Mappable interface {
	MapTo(v interface{}) error
}

// toConfig will attempt to convert a given configuration cfg into the provided exemplar type.
//
// It will tolerate the cfg being passed as a []byte or string of a json representation of the
// exemplar or the correct type of the exemplar itself
func toConfig(exemplar, cfg interface{}) (interface{}, error) {
	json := jsoniter.ConfigCompatibleWithStandardLibrary

	// First of all check if we've got the same type as the exemplar - if so it's all fine.
	if reflect.TypeOf(cfg).AssignableTo(reflect.TypeOf(exemplar)) {
		return cfg, nil
	}

	// Now if not - does it provide a MapTo function we can try?
	if mappable, ok := cfg.(Mappable); ok {
		newVal := reflect.New(reflect.TypeOf(exemplar))
		if err := mappable.MapTo(newVal.Interface()); err == nil {
			return newVal.Elem().Interface(), nil
		}
		// MapTo has failed us ... let's try the json route ...
	}

	// OK we've been passed a byte array right?
	configBytes, ok := cfg.([]byte)
	if !ok {
		// oh ... it's a string then?
		var configStr string

		configStr, ok = cfg.(string)
		configBytes = []byte(configStr)
	}
	if !ok {
		// hmm ... can we marshal it to json?
		var err error

		configBytes, err = json.Marshal(cfg)
		ok = (err == nil)
	}
	if !ok {
		// no ... we've tried hard enough at this point - throw an error!
		return nil, ErrInvalidConfiguration{cfg: cfg}
	}

	// OK unmarshal the byte array into a new copy of the exemplar
	newVal := reflect.New(reflect.TypeOf(exemplar))
	if err := json.Unmarshal(configBytes, newVal.Interface()); err != nil {
		// If we can't unmarshal it then return an error!
		return nil, ErrInvalidConfiguration{cfg: cfg, err: err}
	}
	return newVal.Elem().Interface(), nil
}