/*
 * 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 com.google.cloud.firestore.annotation;

import com.google.cloud.firestore.DocumentReference;
import com.google.cloud.firestore.DocumentSnapshot;
import com.google.cloud.firestore.WriteBatch;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Annotation used to mark a POJO property to be automatically populated with the document's ID when
 * the POJO is created from a Cloud Firestore document (for example, via {@link
 * DocumentSnapshot#toObject}).
 *
 * <p>Any of the following will throw a runtime exception:
 *
 * <ul>
 *   <li>This annotation is applied to a property of a type other than String or {@link
 *       DocumentReference}.
 *   <li>This annotation is applied to a property that is not writable (for example, a Java Bean
 *       getter without a backing field).
 *   <li>This annotation is applied to a property with a name that conflicts with a read document
 *       field. For example, if a POJO has a field `firstName` annotated by @DocumentId, and there
 *       is a property from the document named `firstName` as well, an exception is thrown when you
 *       try to read the document into the POJO via {@link DocumentSnapshot#toObject} or {@link
 *       DocumentReference#get}.
 *   <li>
 * </ul>
 *
 * <p>When using a POJO to write to a document (via {@link DocumentReference#set} or @{@link
 * WriteBatch#set}), the property annotated by @DocumentId is ignored, which allows writing the POJO
 * back to any document, even if it's not the origin of the POJO.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
public @interface DocumentId {}
