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/*
 * Licensed to Metamarkets Group Inc. (Metamarkets) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. Metamarkets 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 io.druid.java.util.common.parsers;

import com.google.common.base.Function;
import org.mozilla.javascript.Context;
import org.mozilla.javascript.ContextFactory;
import org.mozilla.javascript.ScriptableObject;

import java.util.List;
import java.util.Map;

/**
 */
public class JavaScriptParser implements Parser
{
  private static Function compile(String function)
  {
    final ContextFactory contextFactory = ContextFactory.getGlobal();
    final Context context = contextFactory.enterContext();
    context.setOptimizationLevel(9);

    final ScriptableObject scope = context.initStandardObjects();

    final org.mozilla.javascript.Function fn = context.compileFunction(scope, function, "fn", 1, null);
    Context.exit();

    return new Function()
    {
      public Object apply(Object input)
      {
        // ideally we need a close() function to discard the context once it is not used anymore
        Context cx = Context.getCurrentContext();
        if (cx == null) {
          cx = contextFactory.enterContext();
        }

        final Object res = fn.call(cx, scope, scope, new Object[]{input});
        return res != null ? Context.toObject(res, scope) : null;
      }
    };
  }

  private final Function fn;

  public JavaScriptParser(
      final String function
  )
  {
    this.fn = compile(function);
  }

  public Function getFn()
  {
    return fn;
  }

  @Override
  public Map parse(String input)
  {
    try {
      final Object compiled = fn.apply(input);
      if (!(compiled instanceof Map)) {
        throw new ParseException("JavaScript parsed value must be in {key: value} format!");
      }

      return (Map) compiled;
    }
    catch (Exception e) {
      throw new ParseException(e, "Unable to parse row [%s]", input);
    }
  }

  @Override
  public void setFieldNames(Iterable fieldNames)
  {
    throw new UnsupportedOperationException();
  }

  @Override
  public List getFieldNames()
  {
    throw new UnsupportedOperationException();
  }
}