/*
 * Copyright 2011-2020 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.data.querydsl;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Optional;

import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;

import com.querydsl.core.types.EntityPath;

Simple implementation of EntityPathResolver to lookup a query class by reflection and using the static field of the same type. 
Author:
Oliver Gierke, Jens Schauder/**
 * Simple implementation of {@link EntityPathResolver} to lookup a query class by reflection and using the static field
 * of the same type.
 *
 * @author Oliver Gierke
 * @author Jens Schauder
 */
public class SimpleEntityPathResolver implements EntityPathResolver {

	private static final String NO_CLASS_FOUND_TEMPLATE = "Did not find a query class %s for domain class %s!";
	private static final String NO_FIELD_FOUND_TEMPLATE = "Did not find a static field of the same type in %s!";

	public static final SimpleEntityPathResolver INSTANCE = new SimpleEntityPathResolver("");

	private final String querySuffix;

	
Creates a new SimpleEntityPathResolver with the given query package suffix. 
Params:
querySuffix – must not be null./**
	 * Creates a new {@link SimpleEntityPathResolver} with the given query package suffix.
	 * 
	 * @param querySuffix must not be {@literal null}.
	 */
	public SimpleEntityPathResolver(String querySuffix) {

		Assert.notNull(querySuffix, "Query suffix must not be null!");

		this.querySuffix = querySuffix;
	}

	
Creates an EntityPath instance for the given domain class. Tries to lookup a class matching the naming convention (prepend Q to the simple name of the class, same package) and find a static field of the same type in it. 
Params:
domainClass – 
Returns:
/**
	 * Creates an {@link EntityPath} instance for the given domain class. Tries to lookup a class matching the naming
	 * convention (prepend Q to the simple name of the class, same package) and find a static field of the same type in
	 * it.
	 *
	 * @param domainClass
	 * @return
	 */
	@SuppressWarnings("unchecked")
	public <T> EntityPath<T> createPath(Class<T> domainClass) {

		String pathClassName = getQueryClassName(domainClass);

		try {

			Class<?> pathClass = ClassUtils.forName(pathClassName, domainClass.getClassLoader());

			return getStaticFieldOfType(pathClass)//
					.map(it -> (EntityPath<T>) ReflectionUtils.getField(it, null))//
					.orElseThrow(() -> new IllegalStateException(String.format(NO_FIELD_FOUND_TEMPLATE, pathClass)));

		} catch (ClassNotFoundException e) {
			throw new IllegalArgumentException(String.format(NO_CLASS_FOUND_TEMPLATE, pathClassName, domainClass.getName()),
					e);
		}
	}

	
Returns the first static field of the given type inside the given type.
Params:
type – 
Returns:
/**
	 * Returns the first static field of the given type inside the given type.
	 *
	 * @param type
	 * @return
	 */
	private Optional<Field> getStaticFieldOfType(Class<?> type) {

		for (Field field : type.getDeclaredFields()) {

			boolean isStatic = Modifier.isStatic(field.getModifiers());
			boolean hasSameType = type.equals(field.getType());

			if (isStatic && hasSameType) {
				return Optional.of(field);
			}
		}

		Class<?> superclass = type.getSuperclass();
		return Object.class.equals(superclass) ? Optional.empty() : getStaticFieldOfType(superclass);
	}

	
Returns the name of the query class for the given domain class.
Params:
domainClass – 
Returns:
/**
	 * Returns the name of the query class for the given domain class.
	 *
	 * @param domainClass
	 * @return
	 */
	private String getQueryClassName(Class<?> domainClass) {

		String simpleClassName = ClassUtils.getShortName(domainClass);
		String packageName = domainClass.getPackage().getName();

		return String.format("%s%s.Q%s%s", packageName, querySuffix, getClassBase(simpleClassName),
				domainClass.getSimpleName());
	}

	
Analyzes the short class name and potentially returns the outer class.
Params:
shortName – 
Returns:
/**
	 * Analyzes the short class name and potentially returns the outer class.
	 *
	 * @param shortName
	 * @return
	 */
	private String getClassBase(String shortName) {

		String[] parts = shortName.split("\\.");

		return parts.length < 2 ? "" : parts[0] + "_";
	}
}