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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.solr.schema;

import org.apache.lucene.search.SortField;
import org.apache.lucene.document.Fieldable;
import org.apache.solr.search.function.ValueSource;
import org.apache.solr.search.function.FloatFieldSource;
import org.apache.solr.search.function.FileFloatSource;
import org.apache.solr.search.QParser;
import org.apache.solr.request.XMLWriter;
import org.apache.solr.request.TextResponseWriter;
import org.apache.solr.common.SolrException;

import java.util.Map;
import java.io.IOException;

/** Get values from an external file instead of the index.
 *
 * keyField will normally be the unique key field, but it doesn't have to be.
 * 
 It's OK to have a keyField value that can't be found in the index
 * It's OK to have some documents without a keyField in the file (defVal is used as the default)
 * It's OK for a keyField value to point to multiple documents (no uniqueness requirement)
 * 
 * valType is a reference to another fieldType to define the value type of this field (must currently be FloatField (float))
 *
 * The format of the external file is simply newline separated keyFieldValue=floatValue.
 * 
Example:
 * 
doc33=1.414
 * 
doc34=3.14159
 * 
doc40=42
 *
 * Solr looks for the external file in the index directory under the name of
 * external_<fieldname> or external_<fieldname>.*
 *
 * 
If any files of the latter pattern appear, the last (after being sorted by name) will be used and previous versions will be deleted.
 * This is to help support systems where one may not be able to overwrite a file (like Windows, if the file is in use).
 * 
If the external file has already been loaded, and it is changed, those changes will not be visible until a commit has been done.
 * 
The external file may be sorted or unsorted by the key field, but it will be substantially slower (untested) if it isn't sorted.
 * Fields of this type may currently only be used as a ValueSource in a FunctionQuery.
 *
 * @version $Id: ExternalFileField.java 587098 2007-10-22 13:53:14Z yonik $
 */
public class ExternalFileField extends FieldType {
  private FieldType ftype;
  private String keyFieldName;
  private IndexSchema schema;
  private float defVal;

  protected void init(IndexSchema schema, Map args) {
    restrictProps(SORT_MISSING_FIRST | SORT_MISSING_LAST);
    String ftypeS = getArg("valType", args);
    if (ftypeS!=null) {
      ftype = schema.getFieldTypes().get(ftypeS);
      if (ftype==null || !(ftype instanceof FloatField)) {
        throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, "Only float (FloatField) is currently supported as external field type.  got " + ftypeS);
      }
    }   
    keyFieldName = args.remove("keyField");
    String defValS = args.remove("defVal");
    defVal = defValS==null ? 0 : Float.parseFloat(defValS);
    this.schema = schema;
  }

  public void write(XMLWriter xmlWriter, String name, Fieldable f) throws IOException {
    throw new UnsupportedOperationException();
  }

  public void write(TextResponseWriter writer, String name, Fieldable f) throws IOException {
    throw new UnsupportedOperationException();
  }

  public SortField getSortField(SchemaField field,boolean reverse) {
    throw new UnsupportedOperationException();
  }

  public ValueSource getValueSource(SchemaField field, QParser parser) {
    // default key field to unique key
    SchemaField keyField = keyFieldName==null ? schema.getUniqueKeyField() : schema.getField(keyFieldName);
    return new FileFloatSource(field, keyField, defVal, parser);
  }


}