/**
 * 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.hadoop.hive.ql.exec;

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

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.plan.ExprNodeColumnDesc;
import org.apache.hadoop.hive.ql.plan.ExprNodeConstantDesc;
import org.apache.hadoop.hive.ql.plan.ExprNodeDesc;
import org.apache.hadoop.hive.ql.plan.ExprNodeDynamicValueDesc;
import org.apache.hadoop.hive.ql.plan.ExprNodeFieldDesc;
import org.apache.hadoop.hive.ql.plan.ExprNodeGenericFuncDesc;

/**
 * ExprNodeEvaluatorFactory.
 *
 */
public final class ExprNodeEvaluatorFactory {

  private ExprNodeEvaluatorFactory() {
  }

  public static ExprNodeEvaluator get(ExprNodeDesc desc) throws HiveException {
    return get(desc, null);
  }

  public static ExprNodeEvaluator get(ExprNodeDesc desc, Configuration conf) throws HiveException {
    // Constant node
    if (desc instanceof ExprNodeConstantDesc) {
      return new ExprNodeConstantEvaluator((ExprNodeConstantDesc) desc, conf);
    }

    // Column-reference node, e.g. a column in the input row
    if (desc instanceof ExprNodeColumnDesc) {
      return new ExprNodeColumnEvaluator((ExprNodeColumnDesc) desc, conf);
    }
    // Generic Function node, e.g. CASE, an operator or a UDF node
    if (desc instanceof ExprNodeGenericFuncDesc) {
      return new ExprNodeGenericFuncEvaluator((ExprNodeGenericFuncDesc) desc, conf);
    }
    // Field node, e.g. get a.myfield1 from a
    if (desc instanceof ExprNodeFieldDesc) {
      return new ExprNodeFieldEvaluator((ExprNodeFieldDesc) desc, conf);
    }
    // Dynamic value which will be determined during query runtime
    if (desc instanceof ExprNodeDynamicValueDesc) {
      return new ExprNodeDynamicValueEvaluator((ExprNodeDynamicValueDesc) desc, conf);
    }
    throw new RuntimeException(
        "Cannot find ExprNodeEvaluator for the exprNodeDesc = " + desc);
  }

  public static ExprNodeEvaluator[] toCachedEvals(ExprNodeEvaluator[] evals) {
    EvaluatorContext context = new EvaluatorContext();
    for (int i = 0; i < evals.length; i++) {
      if (evals[i] instanceof ExprNodeGenericFuncEvaluator) {
        iterate(evals[i], context);
        if (context.hasReference) {
          evals[i] = new ExprNodeEvaluatorHead(evals[i]);
          context.hasReference = false;
        }
      }
    }
    return evals;
  }

  /**
   * Should be called before eval is initialized
   */
  public static ExprNodeEvaluator toCachedEval(ExprNodeEvaluator eval) {
    if (eval instanceof ExprNodeGenericFuncEvaluator) {
      EvaluatorContext context = new EvaluatorContext();
      iterate(eval, context);
      if (context.hasReference) {
        return new ExprNodeEvaluatorHead(eval);
      }
    }
    // has nothing to be cached
    return eval;
  }

  private static ExprNodeEvaluator iterate(ExprNodeEvaluator eval, EvaluatorContext context) {
    if (!(eval instanceof ExprNodeConstantEvaluator) && eval.isDeterministic()) {
      ExprNodeEvaluator replace = context.getEvaluated(eval);
      if (replace != null) {
        return replace;
      }
    }
    ExprNodeEvaluator[] children = eval.getChildren();
    if (children != null && children.length > 0) {
      for (int i = 0; i < children.length; i++) {
        ExprNodeEvaluator replace = iterate(children[i], context);
        if (replace != null) {
          children[i] = replace;
        }
      }
    }
    return null;
  }

  private static class EvaluatorContext {

    private final Map<ExprNodeDesc.ExprNodeDescEqualityWrapper, ExprNodeEvaluator> cached =
        new HashMap<ExprNodeDesc.ExprNodeDescEqualityWrapper, ExprNodeEvaluator>();

    private boolean hasReference;

    public ExprNodeEvaluator getEvaluated(ExprNodeEvaluator eval) {
      ExprNodeDesc.ExprNodeDescEqualityWrapper key =
          new ExprNodeDesc.ExprNodeDescEqualityWrapper(eval.expr);
      ExprNodeEvaluator prev = cached.get(key);
      if (prev == null) {
        cached.put(key, eval);
        return null;
      }
      hasReference = true;
      return new ExprNodeEvaluatorRef(prev);
    }
  }
}