/*
 * 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.solr.handler.dataimport;

import java.lang.invoke.MethodHandles;
import java.util.HashMap;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * <p>
 * A {@link Transformer} which can put values into a column by resolving an expression
 * containing other columns
 * </p>
 * <p>
 * For example:<br>
 * <field column="name" template="${e.lastName}, ${e.firstName}
 * ${e.middleName}" /> will produce the name by combining values from
 * lastName, firstName and middleName fields as given in the template attribute.
 * </p>
 * <p>
 * Refer to <a
 * href="http://wiki.apache.org/solr/DataImportHandler">http://wiki.apache.org/solr/DataImportHandler</a>
 * for more details.
 * </p>
 * <p>
 * <b>This API is experimental and may change in the future.</b>
 *
 *
 * @since solr 1.3
 */
public class TemplateTransformer extends Transformer {

  private static final Logger LOG = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
  private Map<String ,List<String>> templateVsVars = new HashMap<>();

  @Override
  @SuppressWarnings("unchecked")
  public Object transformRow(Map<String, Object> row, Context context) {


    VariableResolver resolver = context.getVariableResolver();
    // Add current row to the copy of resolver map

    for (Map<String, String> map : context.getAllEntityFields()) {
      map.entrySet();
      String expr = map.get(TEMPLATE);
      if (expr == null)
        continue;

      String column = map.get(DataImporter.COLUMN);

      // Verify if all variables can be resolved or not
      boolean resolvable = true;
      List<String> variables = this.templateVsVars.get(expr);
      if(variables == null){
        variables = resolver.getVariables(expr);
        this.templateVsVars.put(expr, variables);
      }
      for (String v : variables) {
        if (resolver.resolve(v) == null) {
          LOG.warn("Unable to resolve variable: " + v
                  + " while parsing expression: " + expr);
          resolvable = false;
        }
      }

      if (!resolvable)
        continue;
      if(variables.size() == 1 && expr.startsWith("${") && expr.endsWith("}")){
        addToRow(column, row, resolver.resolve(variables.get(0)));
      } else {
        addToRow(column, row, resolver.replaceTokens(expr));
      }
    }

    return row;
  }

  private void addToRow(String key, Map<String, Object> row, Object value) {
    Object prevVal = row.get(key);
    if (prevVal != null) {
      if (prevVal instanceof List) {
        ((List) prevVal).add(value);
      } else {
        ArrayList<Object> valList = new ArrayList<Object>();
        valList.add(prevVal);
        valList.add(value);
        row.put(key, valList);
      }
    } else {
      row.put(key, value);
    }
  }
    
  public static final String TEMPLATE = "template";
}