/*
    * 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 org.apache.maven.model.building;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.List;
  
  import static java.util.Collections.singleton;
  import static org.apache.maven.model.building.ModelProblem.Severity.ERROR;
  import static org.apache.maven.model.building.ModelProblem.Severity.FATAL;
  
  /**
   * 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
   *
   * @param <T> the model type
   */
  public class Result<T> {
  
      /**
       * Success without warnings
       *
       * @param model
       */
      public static <T> Result<T> success(T model) {
          return success(model, Collections.emptyList());
      }
  
      /**
       * Success with warnings
       *
       * @param model
       * @param problems
       */
      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
       */
      public static <T> Result<T> success(T model, Result<?>... results) {
          final List<ModelProblem> problemsList = new ArrayList<>();
  
          for (Result<?> result1 : results) {
              for (ModelProblem modelProblem : result1.getProblems()) {
                  problemsList.add(modelProblem);
              }
          }
  
          return success(model, problemsList);
      }
  
      /**
       * Error with problems describing the cause
       *
       * @param problems
       */
      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.emptyList());
      }
  
      public static <T> Result<T> error(Result<?> result) {
          return error(result.getProblems());
      }
  
      public static <T> Result<T> error(Result<?>... results) {
         final List<ModelProblem> problemsList = new ArrayList<>();
 
         for (Result<?> result1 : results) {
             for (ModelProblem modelProblem : result1.getProblems()) {
                 problemsList.add(modelProblem);
             }
         }
 
         return error(problemsList);
     }
 
     /**
      * Error with partial result and problems describing the cause
      *
      * @param model
      * @param problems
      */
     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
      */
     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
      */
     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
      */
     public static <T> Result<T> addProblems(Result<T> result, Iterable<? extends ModelProblem> problems) {
         Collection<ModelProblem> list = new ArrayList<>();
         for (ModelProblem item : problems) {
             list.add(item);
         }
         for (ModelProblem item : result.getProblems()) {
             list.add(item);
         }
         return new Result<>(result.hasErrors() || hasErrors(problems), result.get(), list);
     }
 
     public static <T> Result<T> addProblems(Result<T> result, Result<?>... results) {
         final List<ModelProblem> problemsList = new ArrayList<>();
 
         for (Result<?> result1 : results) {
             for (ModelProblem modelProblem : result1.getProblems()) {
                 problemsList.add(modelProblem);
             }
         }
         return addProblems(result, problemsList);
     }
 
     /**
      * Turns the given results into a single result by combining problems and models into single collection.
      *
      * @param results
      */
     public static <T> Result<Iterable<T>> newResultSet(Iterable<? extends Result<? extends T>> results) {
         boolean hasErrors = false;
         List<T> modelsList = new ArrayList<>();
         List<ModelProblem> problemsList = new ArrayList<>();
 
         for (Result<? extends T> result : results) {
             modelsList.add(result.get());
 
             for (ModelProblem modelProblem : result.getProblems()) {
                 problemsList.add(modelProblem);
             }
 
             if (result.hasErrors()) {
                 hasErrors = true;
             }
         }
         return new Result<>(hasErrors, (Iterable<T>) modelsList, problemsList);
     }
 
     // helper to determine if problems contain error
     private static boolean hasErrors(Iterable<? extends ModelProblem> problems) {
         for (ModelProblem input : problems) {
             if (input.getSeverity().equals(ERROR) || input.getSeverity().equals(FATAL)) {
                 return true;
             }
         }
         return false;
     }
 
     /**
      * 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;
     }
 }