/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.lucene.expressions;


import java.util.HashMap;
import java.util.Map;

import org.apache.lucene.search.DoubleValuesSource;
import org.apache.lucene.search.SortField;

/**
 * Simple class that binds expression variable names to {@link SortField}s
 * or other {@link Expression}s.
 * <p>
 * Example usage:
 * <pre class="prettyprint">
 *   SimpleBindings bindings = new SimpleBindings();
 *   // document's text relevance score
 *   bindings.add(new SortField("_score", SortField.Type.SCORE));
 *   // integer NumericDocValues field
 *   bindings.add(new SortField("popularity", SortField.Type.INT));
 *   // another expression
 *   bindings.add("recency", myRecencyExpression);
 *   
 *   // create a sort field in reverse order
 *   Sort sort = new Sort(expr.getSortField(bindings, true));
 * </pre>
 * 
 * @lucene.experimental
 */
public final class SimpleBindings extends Bindings {
  final Map<String,Object> map = new HashMap<>();
  
  /** Creates a new empty Bindings */
  public SimpleBindings() {}
  
  /** 
   * Adds a SortField to the bindings.
   * <p>
   * This can be used to reference a DocValuesField, a field from
   * FieldCache, the document's score, etc. 
   */
  public void add(SortField sortField) {
    map.put(sortField.getField(), sortField);
  }

  /**
   * Bind a {@link DoubleValuesSource} directly to the given name.
   */
  public void add(String name, DoubleValuesSource source) { map.put(name, source); }
  
  /** 
   * Adds an Expression to the bindings.
   * <p>
   * This can be used to reference expressions from other expressions. 
   */
  public void add(String name, Expression expression) {
    map.put(name, expression);
  }
  
  @Override
  public DoubleValuesSource getDoubleValuesSource(String name) {
    Object o = map.get(name);
    if (o == null) {
      throw new IllegalArgumentException("Invalid reference '" + name + "'");
    } else if (o instanceof Expression) {
      return ((Expression)o).getDoubleValuesSource(this);
    } else if (o instanceof DoubleValuesSource) {
      return ((DoubleValuesSource) o);
    }
    SortField field = (SortField) o;
    switch(field.getType()) {
      case INT:
        return DoubleValuesSource.fromIntField(field.getField());
      case LONG:
        return DoubleValuesSource.fromLongField(field.getField());
      case FLOAT:
        return DoubleValuesSource.fromFloatField(field.getField());
      case DOUBLE:
        return DoubleValuesSource.fromDoubleField(field.getField());
      case SCORE:
        return DoubleValuesSource.SCORES;
      default:
        throw new UnsupportedOperationException(); 
    }
  }
  
  /** 
   * Traverses the graph of bindings, checking there are no cycles or missing references 
   * @throws IllegalArgumentException if the bindings is inconsistent 
   */
  public void validate() {
    for (Object o : map.values()) {
      if (o instanceof Expression) {
        Expression expr = (Expression) o;
        try {
          expr.getDoubleValuesSource(this);
        } catch (StackOverflowError e) {
          throw new IllegalArgumentException("Recursion Error: Cycle detected originating in (" + expr.sourceText + ")");
        }
      }
    }
  }
}