/*

  * #%L

  * LetBuilder.java - mongodb-async-driver - Allanbank Consulting, Inc.

  * %%

  * Copyright (C) 2011 - 2014 Allanbank Consulting, Inc.

  * %%

  * 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.

  * #L%

  */

 package com.allanbank.mongodb.builder.expression;

 import java.util.ArrayList;

 import java.util.List;

 import com.allanbank.mongodb.bson.DocumentAssignable;

 import com.allanbank.mongodb.bson.Element;

 import com.allanbank.mongodb.bson.element.DocumentElement;

 /**

  * LetBuilder provides a builder for a {@code $let} expression.

  * 

  * @api.yes This class is part of the driver's API. Public and protected members

  *          will be deprecated for at least 1 non-bugfix release (version

  *          numbers are <major>.<minor>.<bugfix>) before being

  *          removed or modified.

  * @copyright 2014, Allanbank Consulting, Inc., All Rights Reserved

  */

 public class LetBuilder {

     /** The fields in the {@code $let} expression. */

     private final List<Element> myFields;

     /**

      * Creates a new MapStage2.

      * 

      * @param firstField

      *            The name of the {@code input} field.

      */

     /* package */LetBuilder(final Element firstField) {

         myFields = new ArrayList<Element>();

         myFields.add(firstField);

     }

     /**

      * Creates the final {@code $let} expression to evaluate.

      * 

      * @param letExpression

      *            The expression to be evaluated with the variables within the

      *            {@code $let} expression.

      * @return The {@link UnaryExpression} for the {@code $let}.

      */

     public UnaryExpression in(final Expression letExpression) {

         return Expressions.let(myFields, letExpression);

     }

     /**

      * Adds a variable to the {@code $let} expression.

      * 

      * @param name

      *            The name of the variable to set.

      * @param document

      *            The document to set the variable to.

      * @return This builder for method call chaining.

      */

     public LetBuilder let(final String name, final DocumentAssignable document) {

         myFields.add(new DocumentElement(name, document.asDocument()));

         return this;

     }

     /**

      * Adds a variable to the {@code $let} expression.

      * 

      * @param name

      *            The name of the variable to set.

      * @param expression

      *            The expression to compute the value for the variable.

      * @return This builder for method call chaining.

      */

     public LetBuilder let(final String name, final Expression expression) {

         myFields.add(expression.toElement(name));

         return this;

     }

 }