/*
    * Entreri, an entity-component framework in Java
    *
    * Copyright (c) 2013, Michael Ludwig
    * All rights reserved.
    *
    * Redistribution and use in source and binary forms, with or without modification,
    * are permitted provided that the following conditions are met:
    *
   *     Redistributions of source code must retain the above copyright notice,
   *         this list of conditions and the following disclaimer.
   *     Redistributions in binary form must reproduce the above copyright notice,
   *         this list of conditions and the following disclaimer in the
   *         documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
   * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
   * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
   * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  package com.lhkbob.entreri.task;
  
  import com.lhkbob.entreri.Component;
  import com.lhkbob.entreri.EntitySystem;
  
  import java.util.Collections;
  import java.util.Set;
  
  /**
   * Timers is a utility class that provides factory methods for creating Tasks that report
   * {@link ElapsedTimeResult} for use with other tasks that might have time-dependent
   * behavior.
   *
   * @author Michael Ludwig
   */
  public final class Timers {
      private Timers() {
      }
  
      /**
       * <p/>
       * Create a new Task that reports an {@link ElapsedTimeResult} with the provided fixed
       * time delta. It is generally recommended for this task to be one of the first to
       * execute within a job.
       * <p/>
       * The created task always reports the fixed time delta, regardless of true elapsed
       * time between invocations, and performs no other action.
       *
       * @param dt The fixed time delta to always report
       *
       * @return Return a task that measures and reports a fixed delta
       *
       * @throws IllegalArgumentException if dt is less than or equal to zero
       */
      public static Task fixedDelta(double dt) {
          if (dt <= 0) {
              throw new IllegalArgumentException("Fixed delta must be positive: " + dt);
          }
          return new FixedDeltaTask(dt);
      }
  
      /**
       * <p/>
       * Create a new Task that reports an {@link ElapsedTimeResult} with the elapsed time
       * since the start of the task's last invocation. It is generally recommended for this
       * task to be one of the first to execute within a job.
       * <p/>
       * The created task always reports the measured elapsed time and performs no other
       * action.
       *
       * @return Return a task that measures and reports delta time
       */
      public static Task measuredDelta() {
          return new MeasuredDeltaTask();
      }
  
      /*
       * Task that reports the same delta each invocation, even if it does equal
       * the elapsed wall time
       */
      private static class FixedDeltaTask implements Task, ParallelAware {
          private final ElapsedTimeResult delta;
  
          public FixedDeltaTask(double dt) {
              delta = new ElapsedTimeResult(dt);
          }
  
          @Override
          public Task process(EntitySystem system, Job job) {
              job.report(delta);
              return null;
          }
  
         @Override
         public void reset(EntitySystem system) {
             // do nothing
         }
 
         @Override
         public Set<Class<? extends Component>> getAccessedComponents() {
             return Collections.emptySet();
         }
 
         @Override
         public boolean isEntitySetModified() {
             return false;
         }
     }
 
     /*
      * Task that measures the time delta from its last invocation
      */
     private static class MeasuredDeltaTask implements Task, ParallelAware {
         private long lastStart = -1L;
 
         @Override
         public Task process(EntitySystem system, Job job) {
             long now = System.nanoTime();
             if (lastStart <= 0) {
                 job.report(new ElapsedTimeResult(0));
             } else {
                 job.report(new ElapsedTimeResult((now - lastStart) / 1e9));
             }
             lastStart = now;
 
             return null;
         }
 
         @Override
         public void reset(EntitySystem system) {
             // do nothing
         }
 
         @Override
         public Set<Class<? extends Component>> getAccessedComponents() {
             return Collections.emptySet();
         }
 
         @Override
         public boolean isEntitySetModified() {
             return false;
         }
     }
 }