// Licensed to the Software Freedom Conservancy (SFC) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The SFC 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.openqa.selenium.concurrent;

import static java.util.Objects.requireNonNull;

import java.util.Optional;
import org.jspecify.annotations.Nullable;

public final class Lazy<T> {

  private final Object lock = new Object();
  private volatile @Nullable T value;
  private final Supplier<T> supplier;

  private Lazy(Supplier<T> supplier) {
    this.supplier = supplier;
  }

  public Optional<T> getIfInitialized() {
    return value == null ? Optional.empty() : Optional.ofNullable(value);
  }

  public T get() {
    if (value == null) {
      synchronized (lock) {
        if (value == null) {
          try {
            value = supplier.get();
          } catch (RuntimeException e) {
            throw e;
          } catch (Exception e) {
            throw new InitializationException(e);
          }
        }
      }
    }
    return requireNonNull(value);
  }

  public static <T> Lazy<T> lazy(Supplier<T> supplier) {
    return new Lazy<>(supplier);
  }

  @FunctionalInterface
  public interface Supplier<T> {
    T get() throws Exception;
  }

  public static class InitializationException extends RuntimeException {
    public InitializationException(Exception cause) {
      super(cause);
    }
  }
}
