/*
 * Copyright 2002-2019 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.core.log;

import java.util.function.Supplier;

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * A simple log message type for use with Commons Logging, allowing
 * for convenient lazy resolution of a given {@link Supplier} instance
 * (typically bound to a Java 8 lambda expression) or a printf-style
 * format string ({@link String#format})in its {@link #toString()}.
 *
 * @author Juergen Hoeller
 * @since 5.2
 * @see #of(Supplier)
 * @see #format(String, Object)
 * @see #format(String, Object...)
 * @see org.apache.commons.logging.Log#fatal(Object)
 * @see org.apache.commons.logging.Log#error(Object)
 * @see org.apache.commons.logging.Log#warn(Object)
 * @see org.apache.commons.logging.Log#info(Object)
 * @see org.apache.commons.logging.Log#debug(Object)
 * @see org.apache.commons.logging.Log#trace(Object)
 */
public abstract class LogMessage implements CharSequence {

	@Nullable
	private String result;


	@Override
	public int length() {
		return toString().length();
	}

	@Override
	public char charAt(int index) {
		return toString().charAt(index);
	}

	@Override
	public CharSequence subSequence(int start, int end) {
		return toString().subSequence(start, end);
	}

	/**
	 * This will be called by the logging provider, potentially once
	 * per log target (therefore locally caching the result here).
	 */
	@Override
	public String toString() {
		if (this.result == null) {
			this.result = buildString();
		}
		return this.result;
	}

	abstract String buildString();


	/**
	 * Build a lazily resolving message from the given supplier.
	 * @param supplier the supplier (typically bound to a Java 8 lambda expression)
	 * @see #toString()
	 */
	public static LogMessage of(Supplier<? extends CharSequence> supplier) {
		return new SupplierMessage(supplier);
	}

	/**
	 * Build a lazily formatted message from the given format string and argument.
	 * @param format the format string (following {@link String#format} rules)
	 * @param arg1 the argument
	 * @see String#format(String, Object...)
	 */
	public static LogMessage format(String format, Object arg1) {
		return new FormatMessage1(format, arg1);
	}

	/**
	 * Build a lazily formatted message from the given format string and arguments.
	 * @param format the format string (following {@link String#format} rules)
	 * @param arg1 the first argument
	 * @param arg2 the second argument
	 * @see String#format(String, Object...)
	 */
	public static LogMessage format(String format, Object arg1, Object arg2) {
		return new FormatMessage2(format, arg1, arg2);
	}

	/**
	 * Build a lazily formatted message from the given format string and arguments.
	 * @param format the format string (following {@link String#format} rules)
	 * @param arg1 the first argument
	 * @param arg2 the second argument
	 * @param arg3 the third argument
	 * @see String#format(String, Object...)
	 */
	public static LogMessage format(String format, Object arg1, Object arg2, Object arg3) {
		return new FormatMessage3(format, arg1, arg2, arg3);
	}

	/**
	 * Build a lazily formatted message from the given format string and arguments.
	 * @param format the format string (following {@link String#format} rules)
	 * @param arg1 the first argument
	 * @param arg2 the second argument
	 * @param arg3 the third argument
	 * @param arg4 the fourth argument
	 * @see String#format(String, Object...)
	 */
	public static LogMessage format(String format, Object arg1, Object arg2, Object arg3, Object arg4) {
		return new FormatMessage4(format, arg1, arg2, arg3, arg4);
	}

	/**
	 * Build a lazily formatted message from the given format string and varargs.
	 * @param format the format string (following {@link String#format} rules)
	 * @param args the varargs array (costly, prefer individual arguments)
	 * @see String#format(String, Object...)
	 */
	public static LogMessage format(String format, Object... args) {
		return new FormatMessageX(format, args);
	}


	private static final class SupplierMessage extends LogMessage {

		private Supplier<? extends CharSequence> supplier;

		SupplierMessage(Supplier<? extends CharSequence> supplier) {
			Assert.notNull(supplier, "Supplier must not be null");
			this.supplier = supplier;
		}

		@Override
		String buildString() {
			return this.supplier.get().toString();
		}
	}


	private static abstract class FormatMessage extends LogMessage {

		protected final String format;

		FormatMessage(String format) {
			Assert.notNull(format, "Format must not be null");
			this.format = format;
		}
	}


	private static final class FormatMessage1 extends FormatMessage {

		private final Object arg1;

		FormatMessage1(String format, Object arg1) {
			super(format);
			this.arg1 = arg1;
		}

		@Override
		protected String buildString() {
			return String.format(this.format, this.arg1);
		}
	}


	private static final class FormatMessage2 extends FormatMessage {

		private final Object arg1;

		private final Object arg2;

		FormatMessage2(String format, Object arg1, Object arg2) {
			super(format);
			this.arg1 = arg1;
			this.arg2 = arg2;
		}

		@Override
		String buildString() {
			return String.format(this.format, this.arg1, this.arg2);
		}
	}


	private static final class FormatMessage3 extends FormatMessage {

		private final Object arg1;

		private final Object arg2;

		private final Object arg3;

		FormatMessage3(String format, Object arg1, Object arg2, Object arg3) {
			super(format);
			this.arg1 = arg1;
			this.arg2 = arg2;
			this.arg3 = arg3;
		}

		@Override
		String buildString() {
			return String.format(this.format, this.arg1, this.arg2, this.arg3);
		}
	}


	private static final class FormatMessage4 extends FormatMessage {

		private final Object arg1;

		private final Object arg2;

		private final Object arg3;

		private final Object arg4;

		FormatMessage4(String format, Object arg1, Object arg2, Object arg3, Object arg4) {
			super(format);
			this.arg1 = arg1;
			this.arg2 = arg2;
			this.arg3 = arg3;
			this.arg4 = arg4;
		}

		@Override
		String buildString() {
			return String.format(this.format, this.arg1, this.arg2, this.arg3, this.arg4);
		}
	}


	private static final class FormatMessageX extends FormatMessage {

		private final Object[] args;

		FormatMessageX(String format, Object... args) {
			super(format);
			this.args = args;
		}

		@Override
		String buildString() {
			return String.format(this.format, this.args);
		}
	}

}
