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A set of utilities and tools to speed up and ease programming in Java.
There is a newer version: 0.5
/*
 * (c) 2005 David B. Bracewell
 *
 * 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 com.davidbracewell.collection;

import com.davidbracewell.conversion.Convert;
import com.davidbracewell.conversion.Val;
import com.davidbracewell.io.resource.Resource;
import com.davidbracewell.io.structured.ElementType;
import com.davidbracewell.io.structured.StructuredFormat;
import com.davidbracewell.io.structured.StructuredReader;
import com.davidbracewell.tuple.Tuple2;
import lombok.NonNull;

import java.io.IOException;
import java.util.EnumSet;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

/**
 * Common methods for reading counters from structured files, creating synchronized and unmodifiable wrappers, and
 * creating collectors.
 */
public interface Counters {

  /**
   * Creates a Counter collector that count the items in a string generating a {@link HashMapCounter}.
   *
   * @param  the type parameter
   * @return the collector
   */
  static  Collector, Counter> collector() {
    return new CounterCollector<>();
  }

  /**
   * Creates a Counter collector that count the items in a string generating a Counter using the given supplier.
   *
   * @param       the type parameter
   * @param supplier the supplier to use for creating a counter
   * @return the collector
   */
  static  Collector, Counter> collector(@NonNull Supplier> supplier) {
    return new CounterCollector<>(supplier);
  }

  /**
   * Creates a Counter whose keys are Integers and values are associated value in the given double array.
   *
   * @param array the array
   * @return the counter
   */
  static Counter createVectorCounter(@NonNull double[] array) {
    Counter counter = new HashMapCounter<>();
    for (int i = 0; i < array.length; i++) {
      counter.set(i, array[i]);
    }
    return counter;
  }

  /**
   * Reads a resource in the given {@link StructuredFormat} which is made up of key value pairs where the key is the
   * item in the counter and the value is its count.
   *
   * @param            the item type
   * @param structuredFormat the format of the file being read
   * @param resource         the resource of the file being read
   * @param keyType          the class of the item type
   * @return the counter
   * @throws IOException Something went wrong reading in the counter.
   */
  static  Counter read(@NonNull StructuredFormat structuredFormat, @NonNull Resource resource, @NonNull Class keyType) throws IOException {
    return read(structuredFormat, resource, str -> Convert.convert(str, keyType), HashMapCounter::new);
  }

  /**
   * Reads a resource in the given {@link StructuredFormat} which is made up of key value pairs where the key is the
   * item in the counter and the value is its count.
   *
   * @param            the item type
   * @param structuredFormat the format of the file being read
   * @param resource         the resource of the file being read
   * @param deserializer     Function to turn string representation of key into an item
   * @param supplier         the supplier to use for creating the initial counter
   * @return the counter
   * @throws IOException Something went wrong reading in the counter.
   */
  static  Counter read(@NonNull StructuredFormat structuredFormat, @NonNull Resource resource, @NonNull Function deserializer, @NonNull Supplier> supplier) throws IOException {
    Counter counter = supplier.get();
    try (StructuredReader reader = structuredFormat.createReader(resource)) {
      reader.beginDocument();
      while (reader.peek() != ElementType.END_DOCUMENT) {
        Tuple2 keyValue = reader.nextKeyValue();
        counter.set(deserializer.apply(keyValue.v1), keyValue.v2.asDouble());
      }
      reader.endDocument();
    }
    return counter;
  }

  /**
   * Reads a counter from a CSV file.
   *
   * @param    the item type
   * @param resource the resource that the counter values are written to.
   * @param keyClass the class of the item type
   * @return the counter
   * @throws IOException Something went wrong reading in the counter.
   */
  static  Counter readCSV(@NonNull Resource resource, @NonNull Class keyClass) throws IOException {
    return read(StructuredFormat.CSV, resource, keyClass);
  }

  /**
   * Reads a counter from a Json file.
   *
   * @param    the item type
   * @param resource the resource that the counter values are written to.
   * @param keyClass the class of the item type
   * @return the counter
   * @throws IOException Something went wrong reading in the counter.
   */
  static  Counter readJson(@NonNull Resource resource, @NonNull Class keyClass) throws IOException {
    return read(StructuredFormat.JSON, resource, keyClass);
  }

  /**
   * Wraps a counter making each method call synchronized.
   *
   * @param   the item type
   * @param counter the counter to wrap
   * @return the wrapped counter
   */
  static  Counter synchronizedCounter(@NonNull Counter counter) {
    return new SynchronizedCounter<>(counter);
  }

  /**
   * Wraps a counter making its entries unmodifiable.
   *
   * @param   the item type
   * @param counter the counter to wrap
   * @return the wrapped counter
   */
  static  Counter unmodifiableCounter(@NonNull final Counter counter) {
    return new UnmodifiableCounter<>(counter);
  }

  /**
   * {@link Collector} implementation for Counters.
   *
   * @param  The item type of the Counter
   */
  class CounterCollector implements Collector, Counter> {

    /**
     * The Supplier.
     */
    final Supplier> supplier;

    /**
     * Instantiates a new Counter collector.
     */
    public CounterCollector() {
      this(HashMapCounter::new);
    }

    /**
     * Instantiates a new Counter collector.
     *
     * @param supplier the supplier
     */
    public CounterCollector(Supplier> supplier) {
      this.supplier = supplier;
    }

    @Override
    public BiConsumer, T> accumulator() {
      return Counter::increment;
    }

    @Override
    public Set characteristics() {
      return EnumSet.of(Characteristics.UNORDERED);
    }

    @Override
    public BinaryOperator> combiner() {
      return Counter::merge;
    }

    @Override
    public Function, Counter> finisher() {
      return c -> c;
    }

    @Override
    public Supplier> supplier() {
      return supplier;
    }

  }


}//END OF Counters