001/*
002 * SPDX-License-Identifier: Apache-2.0
003 *
004 * Copyright 2025-2026 The Enola <https://enola.dev> Authors
005 *
006 * Licensed under the Apache License, Version 2.0 (the "License");
007 * you may not use this file except in compliance with the License.
008 * You may obtain a copy of the License at
009 *
010 *     https://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package dev.enola.common;
019
020import org.jspecify.annotations.Nullable;
021
022import java.util.function.Function;
023
024public final class SuccessOrError<T> {
025
026    public static <T> SuccessOrError<T> success(T success) {
027        return new SuccessOrError<T>(success, null);
028    }
029
030    public static <T> SuccessOrError<T> error(String errorMessage) {
031        return new SuccessOrError<T>(null, errorMessage);
032    }
033
034    private final @Nullable T success;
035    private final @Nullable String errorMessage;
036
037    private SuccessOrError(@Nullable T success, @Nullable String errorMessage) {
038        this.success = success;
039        this.errorMessage = errorMessage;
040        if (success == null && errorMessage == null) throw new IllegalArgumentException();
041    }
042
043    public <X> X map(Function<T, X> successFunction, Function<String, X> errorFunction) {
044        if (success != null) return successFunction.apply(success);
045        else if (errorMessage != null) return errorFunction.apply(errorMessage);
046        throw new IllegalStateException();
047    }
048}