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/*
 * Copyright (c) CQSE GmbH
 *
 * 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
 *
 *     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 com.teamscale.commons.lang;

import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

import com.google.common.base.MoreObjects;
import com.google.common.base.MoreObjects.ToStringHelper;
import com.google.common.collect.Iterables;

/**
 * Utilities for working with Guava's {@link ToStringHelper}.
 */
public class ToStringHelpers {

	/**
	 * A reflective variant of {@link MoreObjects#toStringHelper(Object)}.
	 * 
	 * It is significantly slower than its {@code MoreObjects} counterpart, so it should not be used in
	 * performance-critical code.
	 * 
	 * @return a {@link ToStringHelper} with all fields of {@literal self} already
	 *         {@linkplain ToStringHelper#add(String, Object) added}.
	 */
	public static ToStringHelper toReflectiveStringHelper(Object self) {
		if (self == null) {
			return MoreObjects.toStringHelper("null");
		}

		ToStringHelper helper = MoreObjects.toStringHelper(self);
		Class clazz = self.getClass();
		if (clazz.isArray()) {
			return addArrayElements(helper, self);
		}
		if (Iterable.class.isAssignableFrom(clazz)) {
			Object[] array = Iterables.toArray((Iterable) self, Object.class);
			return addArrayElements(helper, array);
		}
		return addInstanceFields(helper, self);
	}

	private static ToStringHelper addArrayElements(ToStringHelper helper, Object array) {
		int length = Array.getLength(array);
		for (int i = 0; i < length; i++) {
			Object element = Array.get(array, i);
			helper.addValue(element);
		}
		return helper;
	}

	private static ToStringHelper addInstanceFields(ToStringHelper helper, Object instance) {
		List allDeclaredFields = getAllProperInstanceFields(instance);
		allDeclaredFields.sort(Comparator.comparing(Field::getName));
		for (Field field : allDeclaredFields) {
			try {
				field.setAccessible(true);
				String name = field.getName();
				Object value = field.get(instance);
				helper.add(name, value);
			} catch (IllegalArgumentException | IllegalAccessException e) {
				// Ignore and proceed on a best-effort basis
				continue;
			}
		}
		return helper;
	}

	/**
	 * @return all proper instance (i.e., not {@code static}) fields of the given object. Fields that
	 *         are only synthesized by the compiler are omitted.
	 */
	private static List getAllProperInstanceFields(Object instance) {
		List declaredFields = new ArrayList<>();

		Class clazz = instance.getClass();
		do {
			for (Field field : clazz.getDeclaredFields()) {
				if (field.isSynthetic()) {
					continue;
				}
				if (Modifier.isStatic(field.getModifiers())) {
					continue;
				}
				declaredFields.add(field);
			}
			clazz = clazz.getSuperclass();
		} while (clazz != null);

		return declaredFields;
	}
}