/*
 * Copyright 2012-2020 the original author or authors.
 *
 * Licensed 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
 *
 *      https://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.springframework.boot.gradle.plugin;

import java.io.File;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.Objects;
import java.util.concurrent.Callable;
import java.util.function.Supplier;

import org.gradle.api.InvalidUserDataException;
import org.gradle.api.Project;
import org.gradle.api.file.FileCollection;
import org.gradle.api.plugins.JavaApplication;
import org.gradle.api.provider.Property;

import org.springframework.boot.gradle.dsl.SpringBootExtension;
import org.springframework.boot.loader.tools.MainClassFinder;

/**
 * A {@link Callable} that provides a convention for the project's main class name.
 *
 * @author Andy Wilkinson
 */
final class MainClassConvention implements Callable<String> {

	private static final String SPRING_BOOT_APPLICATION_CLASS_NAME = "org.springframework.boot.autoconfigure.SpringBootApplication";

	private final Project project;

	private final Supplier<FileCollection> classpathSupplier;

	MainClassConvention(Project project, Supplier<FileCollection> classpathSupplier) {
		this.project = project;
		this.classpathSupplier = classpathSupplier;
	}

	@Override
	public String call() throws Exception {
		SpringBootExtension springBootExtension = this.project.getExtensions().findByType(SpringBootExtension.class);
		if (springBootExtension != null) {
			String mainClass = springBootExtension.getMainClass().getOrNull();
			if (mainClass != null) {
				return mainClass;
			}
		}
		String javaApplicationMainClass = getJavaApplicationMainClass();
		return (javaApplicationMainClass != null) ? javaApplicationMainClass : resolveMainClass();
	}

	@SuppressWarnings({ "unchecked", "deprecation" })
	private String getJavaApplicationMainClass() {
		JavaApplication javaApplication = this.project.getConvention().findByType(JavaApplication.class);
		if (javaApplication == null) {
			return null;
		}
		Method getMainClass = findMethod(JavaApplication.class, "getMainClass");
		if (getMainClass != null) {
			try {
				Property<String> mainClass = (Property<String>) getMainClass.invoke(javaApplication);
				return mainClass.getOrElse(null);
			}
			catch (Exception ex) {
				// Continue
			}
		}
		return javaApplication.getMainClassName();
	}

	private static Method findMethod(Class<?> type, String name) {
		for (Method candidate : type.getMethods()) {
			if (candidate.getName().equals(name)) {
				return candidate;
			}
		}
		return null;
	}

	private String resolveMainClass() {
		return this.classpathSupplier.get().filter(File::isDirectory).getFiles().stream().map(this::findMainClass)
				.filter(Objects::nonNull).findFirst().orElseThrow(() -> new InvalidUserDataException(
						"Main class name has not been configured and it could not be resolved"));
	}

	private String findMainClass(File file) {
		try {
			return MainClassFinder.findSingleMainClass(file, SPRING_BOOT_APPLICATION_CLASS_NAME);
		}
		catch (IOException ex) {
			return null;
		}
	}

}
