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/*
 * 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.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.queries.function.FunctionValues;
import org.apache.lucene.queries.function.ValueSource;
import org.apache.lucene.search.SortField;

/**
 * A {@link ValueSource} which evaluates a {@link Expression} given the context of an {@link Bindings}.
 */
@SuppressWarnings({"rawtypes", "unchecked"})
final class ExpressionValueSource extends ValueSource {
  final ValueSource variables[];
  final Expression expression;
  final boolean needsScores;

  ExpressionValueSource(Bindings bindings, Expression expression) {
    if (bindings == null) throw new NullPointerException();
    if (expression == null) throw new NullPointerException();
    this.expression = expression;
    variables = new ValueSource[expression.variables.length];
    boolean needsScores = false;
    for (int i = 0; i < variables.length; i++) {
      ValueSource source = bindings.getValueSource(expression.variables[i]);
      if (source instanceof ScoreValueSource) {
        needsScores = true;
      } else if (source instanceof ExpressionValueSource) {
        if (((ExpressionValueSource)source).needsScores()) {
          needsScores = true;
        }
      } else if (source == null) {
        throw new RuntimeException("Internal error. Variable (" + expression.variables[i] + ") does not exist.");
      }
      variables[i] = source;
    }
    this.needsScores = needsScores;
  }

  @Override
  public FunctionValues getValues(Map context, LeafReaderContext readerContext) throws IOException {
    Map valuesCache = (Map)context.get("valuesCache");
    if (valuesCache == null) {
      valuesCache = new HashMap<>();
      context = new HashMap(context);
      context.put("valuesCache", valuesCache);
    }
    FunctionValues[] externalValues = new FunctionValues[expression.variables.length];

    for (int i = 0; i < variables.length; ++i) {
      String externalName = expression.variables[i];
      FunctionValues values = valuesCache.get(externalName);
      if (values == null) {
        values = variables[i].getValues(context, readerContext);
        if (values == null) {
          throw new RuntimeException("Internal error. External (" + externalName + ") does not exist.");
        }
        valuesCache.put(externalName, values);
      }
      externalValues[i] = values;
    }

    return new ExpressionFunctionValues(this, expression, externalValues);
  }

  @Override
  public SortField getSortField(boolean reverse) {
    return new ExpressionSortField(expression.sourceText, this, reverse);
  }

  @Override
  public String description() {
    return "expr(" + expression.sourceText + ")";
  }
  
  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result
        + ((expression == null) ? 0 : expression.hashCode());
    result = prime * result + (needsScores ? 1231 : 1237);
    result = prime * result + Arrays.hashCode(variables);
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj) {
      return true;
    }
    if (obj == null) {
      return false;
    }
    if (getClass() != obj.getClass()) {
      return false;
    }
    ExpressionValueSource other = (ExpressionValueSource) obj;
    if (expression == null) {
      if (other.expression != null) {
        return false;
      }
    } else if (!expression.equals(other.expression)) {
      return false;
    }
    if (needsScores != other.needsScores) {
      return false;
    }
    if (!Arrays.equals(variables, other.variables)) {
      return false;
    }
    return true;
  }

  boolean needsScores() {
    return needsScores;
  }
}