NumberHelper.java

/**
 * Copyright (c) 2012-2015 Edgar Espina
 *
 * This file is part of Handlebars.java.
 *
 * Licensed 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.github.jknack.handlebars.helper;

import static org.apache.commons.lang3.Validate.notNull;

import java.io.IOException;

import com.github.jknack.handlebars.Handlebars;
import com.github.jknack.handlebars.Helper;
import com.github.jknack.handlebars.Options;

/**
 * Commons number function helpers.
 *
 * @author https://github.com/Jarlakxen
 */
public enum NumberHelper implements Helper<Object> {

  /**
   * You can use the isEven helper to return a value only if the first argument
   * is even. Otherwise return null.
   *
   * <li class="{{isEven value "leftBox"}}">
   *
   * If value is 2, the output will be "leftBox".
   *
   */
  isEven {
    @Override
    public CharSequence safeApply(final Number value, final Options options) {
      return isEven(value) ? options.param(0, "even") : null;
    }
  },

  /**
   * You can use the isOdd helper to return a value only if the first argument
   * is odd. Otherwise return null.
   *
   * <li class="{{isOdd value "rightBox"}}">
   *
   * If value is 3, the output will be "rightBox".
   *
   */
  isOdd {
    @Override
    public CharSequence safeApply(final Number value, final Options options) {
      return !isEven(value) ? options.param(0, "odd") : null;
    }
  },

  /**
   * You can use the stripes helper to return different value if the passed
   * argument is odd or even.
   *
   * <tr class="{{stripes value "row-even" "row-odd"}}">
   *
   * If value is 2, the output will be "row-even".
   *
   */
  stripes {
    @Override
    public CharSequence safeApply(final Number value, final Options options) {
      return isEven(value) ? options.param(0, "even") : options.param(1, "odd");
    }
  };

  @Override
  public Object apply(final Object context, final Options options)
      throws IOException {
    if (context instanceof Number) {
      return safeApply((Number) context, options);
    }
    return null;
  }

  /**
   * Apply the helper to the context.
   *
   * @param value
   *        The context object (param=0).
   * @param options
   *        The options object.
   * @return A string result.
   */
  protected abstract CharSequence safeApply(final Number value,
      final Options options);

  /**
   * Apply the helper to the context.
   *
   * @param value
   *        The number value.
   * @return true is even, false is odd
   */
  protected boolean isEven(final Number value) {
    return value.intValue() % 2 == 0;
  }

  /**
   * Register the helper in a handlebars instance.
   *
   * @param handlebars
   *        A handlebars object. Required.
   */
  public void registerHelper(final Handlebars handlebars) {
    notNull(handlebars, "The handlebars is required.");
    handlebars.registerHelper(this.name(), this);
  }

  /**
   * Register all the number helpers.
   *
   * @param handlebars
   *        The helper's owner. Required.
   */
  public static void register(final Handlebars handlebars) {
    notNull(handlebars, "A handlebars object is required.");
    NumberHelper[] helpers = values();
    for (NumberHelper helper : helpers) {
      helper.registerHelper(handlebars);
    }
  }
}