package org.apache.maven.model.building;
   
   /*
    * 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.
   */
  
  import static com.google.common.base.Predicates.in;
  import static com.google.common.collect.Iterables.any;
  import static com.google.common.collect.Iterables.concat;
  import static com.google.common.collect.Iterables.transform;
  import static java.util.Collections.singleton;
  import static java.util.EnumSet.of;
  import static org.apache.maven.model.building.ModelProblem.Severity.ERROR;
  import static org.apache.maven.model.building.ModelProblem.Severity.FATAL;
  
  import java.util.Arrays;
  import java.util.Collections;
  
  import org.apache.maven.model.building.ModelProblem.Severity;
  
  import com.google.common.base.Function;
  import com.google.common.base.Predicates;
  import com.google.common.collect.Iterables;
  
  /**
   * There are various forms of results that are represented by this class:
   * <ol>
   * <li>success - in which case only the model field is set
   * <li>success with warnings - model field + non-error model problems
   * <li>error - no model, but diagnostics
   * <li>error - (partial) model and diagnostics
   * </ol>
   * Could encode these variants as subclasses, but kept in one for now
   * 
   * @author bbusjaeger
   * @param <T>
   */
  public class Result<T>
  {
  
      /**
       * Success without warnings
       * 
       * @param model
       * @return
       */
      public static <T> Result<T> success( T model )
      {
          return success( model, Collections.<ModelProblem>emptyList() );
      }
  
      /**
       * Success with warnings
       * 
       * @param model
       * @param problems
       * @return
       */
      public static <T> Result<T> success( T model, Iterable<? extends ModelProblem> problems )
      {
          assert !hasErrors( problems );
          return new Result<>( false, model, problems );
      }
  
      /**
       * Success with warnings
       * 
       * @param model
       * @param results
       * @return
       */
      public static <T> Result<T> success( T model, Result<?>... results )
      {
          return success( model, Iterables.concat( Iterables.transform( Arrays.asList( results ), GET_PROBLEMS ) ) );
      }
  
      /**
       * Error with problems describing the cause
       *
       * @param problems
       * @return
       */
      public static <T> Result<T> error( Iterable<? extends ModelProblem> problems )
      {
         return error( null, problems );
     }
 
     public static <T> Result<T> error( T model )
     {
         return error( model, Collections.<ModelProblem>emptyList() );
     }
 
     public static <T> Result<T> error( Result<?> result )
     {
         return error( result.getProblems() );
     }
 
     public static <T> Result<T> error( Result<?>... results )
     {
         return error( Iterables.concat( Iterables.transform( Arrays.asList( results ), GET_PROBLEMS ) ) );
     }
 
     /**
      * Error with partial result and problems describing the cause
      *
      * @param model
      * @param problems
      * @return
      */
     public static <T> Result<T> error( T model, Iterable<? extends ModelProblem> problems )
     {
         return new Result<>( true, model, problems );
     }
 
     /**
      * New result - determine whether error or success by checking problems for errors
      * 
      * @param model
      * @param problems
      * @return
      */
     public static <T> Result<T> newResult( T model, Iterable<? extends ModelProblem> problems )
     {
         return new Result<>( hasErrors( problems ), model, problems );
     }
 
     /**
      * New result consisting of given result and new problem. Convenience for newResult(result.get(),
      * concat(result.getProblems(),problems)).
      * 
      * @param result
      * @param problem
      * @return
      */
     public static <T> Result<T> addProblem( Result<T> result, ModelProblem problem )
     {
         return addProblems( result, singleton( problem ) );
     }
 
     /**
      * New result that includes the given
      *
      * @param result
      * @param problems
      * @return
      */
     public static <T> Result<T> addProblems( Result<T> result, Iterable<? extends ModelProblem> problems )
     {
         return new Result<>( result.hasErrors() || hasErrors( problems ), result.get(), concat( result.getProblems(),
                                                                                                  problems ) );
     }
 
     public static <T> Result<T> addProblems( Result<T> result, Result<?>... results )
     {
         return addProblems( result, Iterables.concat( Iterables.transform( Arrays.asList( results ), GET_PROBLEMS ) ) );
     }
 
     /**
      * Turns the given results into a single result by combining problems and models into single collection.
      * 
      * @param results
      * @return
      */
     public static <T> Result<Iterable<T>> newResultSet( Iterable<? extends Result<? extends T>> results )
     {
         final boolean hasErrors = any( transform( results, new Function<Result<?>, Boolean>()
         {
             @Override
             public Boolean apply( Result<?> input )
             {
                 return input.hasErrors();
             }
         } ), Predicates.equalTo( true ) );
         final Iterable<T> models = transform( results, new Function<Result<? extends T>, T>()
         {
             @Override
             public T apply( Result<? extends T> input )
             {
                 return input.get();
             }
         } );
         final Iterable<ModelProblem> problems = concat( transform( results, GET_PROBLEMS ) );
         return new Result<>( hasErrors, models, problems );
     }
 
     // helper to determine if problems contain error
     private static boolean hasErrors( Iterable<? extends ModelProblem> problems )
     {
         return any( transform( problems, new Function<ModelProblem, Severity>()
         {
             @Override
             public Severity apply( ModelProblem input )
             {
                 return input.getSeverity();
             }
         } ), in( of( ERROR, FATAL ) ) );
     }
 
     /**
      * Class definition
      */
 
     private final boolean errors;
 
     private final T value;
 
     private final Iterable<? extends ModelProblem> problems;
 
     private Result( boolean errors, T model, Iterable<? extends ModelProblem> problems )
     {
         this.errors = errors;
         this.value = model;
         this.problems = problems;
     }
 
     public Iterable<? extends ModelProblem> getProblems()
     {
         return problems;
     }
 
     public T get()
     {
         return value;
     }
 
     public boolean hasErrors()
     {
         return errors;
     }
 
     private static final Function<Result<?>, Iterable<? extends ModelProblem>> GET_PROBLEMS =
         new Function<Result<?>, Iterable<? extends ModelProblem>>()
         {
             @Override
             public Iterable<? extends ModelProblem> apply( Result<?> input )
             {
                 return input.getProblems();
             }
         };
 }