// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package datastore

import (
	"encoding/base64"
	"strings"

	"cloud.google.com/go/datastore/internal/gaepb"
	"github.com/golang/protobuf/proto"
)

// decodeGAEKey attempts to decode the given encoded key generated by the
// GAE Datastore package (google.golang.org/appengine/datastore), returning nil
// if the key couldn't be decoded.
func decodeGAEKey(encoded string) *Key {
	// Re-add padding.
	if m := len(encoded) % 4; m != 0 {
		encoded += strings.Repeat("=", 4-m)
	}

	b, err := base64.URLEncoding.DecodeString(encoded)
	if err != nil {
		return nil
	}
	ref := new(gaepb.Reference)
	if err := proto.Unmarshal(b, ref); err != nil {
		return nil
	}
	return gaeProtoToKey(ref)
}

// gaeProtoToKey accepts a GAE Datastore key and converts it to a Cloud Datastore key.
// This is adapted from the "protoToKey" function in the appengine/datastore package.
//
// NOTE(cbro): this is a lossy operation, as GAE Datastore keys include the project/app ID,
// but Cloud Datastore keys do not.
func gaeProtoToKey(r *gaepb.Reference) *Key {
	namespace := r.GetNameSpace()
	var k *Key
	for _, e := range r.Path.Element {
		k = &Key{
			Kind:      e.GetType(),
			Name:      e.GetName(),
			ID:        e.GetId(),
			Parent:    k,
			Namespace: namespace,
		}
	}
	if !k.valid() {
		return nil
	}
	return k
}