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/**
 *  Copyright (c) 2011, The Staccato-Commons Team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU Lesser General Public License as published by
 *  the Free Software Foundation; version 3 of the License.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 */
package net.sf.staccatocommons.lang.thunk;

import java.util.Date;
import java.util.concurrent.Callable;

import net.sf.staccatocommons.check.Ensure;
import net.sf.staccatocommons.defs.Thunk;
import net.sf.staccatocommons.defs.function.Function;
import net.sf.staccatocommons.iterators.thriter.internal.ConstantThunk;
import net.sf.staccatocommons.lang.SoftException;
import net.sf.staccatocommons.lang.function.AbstractFunction;
import net.sf.staccatocommons.lang.thunk.internal.DateThunk;
import net.sf.staccatocommons.lang.thunk.internal.FailThunk;
import net.sf.staccatocommons.lang.thunk.internal.NullThunk;
import net.sf.staccatocommons.lang.thunk.internal.UndefinedThunk;
import net.sf.staccatocommons.restrictions.Constant;
import net.sf.staccatocommons.restrictions.check.NonNull;


/**
 * Class factory methods for some common {@link Thunk}s
 * 
 * @author flbulgarelli
 * 
 */
public class Thunks {

  private Thunks() {}

  /**
   * Returns a thunk that returns always the given value
   * 
   * @param 
   * @param value
   *          the value the constant thunk will return as when invoking
   *          {@link Thunk#value()}
   * @return a new thunk
   */
  public static  Thunk constant(A value) {
    return new ConstantThunk(value);

  }

  /**
   * Returns a constant {@link Thunk} that always provides null
   * 
   * @param 
   * @return a constant thunk of nulls
   */
  @Constant
  public static  Thunk null_() {
    return NullThunk.null_();
  }

  /**
   * Returns a {@link Thunk} that provides the current date
   * 
   * @return a constant thunk that provides new Date()
   */
  @Constant
  public static Thunk currentDate() {
    return DateThunk.INSTANCE;
  }

  /**
   * Returns a thunk whose value is retrieved sending {@link Callable#call()} to
   * the given {@link Callable}
   * 
   * @param 
   * @param callable
   * @return a new {@link Thunk} that wraps the given callable
   */
  public static  Thunk from(@NonNull final Callable callable) {
    return new Thunk() {
      public A value() {
        return SoftException.callOrSoften(callable);
      }
    };
  }

  /**
   * Returns a thunk that when evaluated throws a {@link RuntimeException}. This
   * Thunk is said to have an undefined element.
   * 
   * @param 
   * @return a {@link Constant} undefined thunk
   */
  @Constant
  public static  Thunk undefined() {
    return UndefinedThunk.undefined();
  }
  
  /**
   * Answers a {@link Thunk} that, when evaluated, throws an exception with the given 
   * formatted message as {@link Ensure#fail(String, Object...)}
   * 
   * @param message the message
   * @param args the message arguments
   * @return a new {@link Thunk} that fails with the given message 
   */
  public static  Thunk fail(@NonNull String message, Object... args) {
    return new FailThunk(message, args);
  }

  /**
   * Returns a cell that provides not actual value, but a side effect instead,
   * by sending {@link Runnable#run()} to the given runnable
   * 
   * @param runnable
   * @return a new {@link Thunk} that wraps the given {@link Runnable}
   */
  public static Thunk from(@NonNull final Runnable runnable) {
    return new Thunk() {
      public Void value() {
        runnable.run();
        return null;
      }
    };
  }

  /**
   * Returns a {@link Function} that evaluates its Thunk argument
   * 
   * @param 
   * @return a constant {@link Function}
   */
  @Constant
  public static  Function, A> value() {
    return new AbstractFunction, A>() {
      public A apply(Thunk arg) {
        return arg.value();
      }
    };
  }
}