/*
 * 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
 *
 * @author bbusjaeger
 * @param <T>
 */
public class Result<T> {

    /**
     * Success without warnings
     *
     * @param model
     */
    public static <T> Result<T> success(T model) {
        return success(model, Collections.<ModelProblem>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.<ModelProblem>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;
    }
}
