envoy/common/src/main/java/envoy/data/Config.java

package envoy.data;

import java.io.*;
import java.util.*;
import java.util.function.Function;
import java.util.logging.Level;
import java.util.stream.Collectors;

import envoy.util.EnvoyLog;

/**
 * Manages all application settings that are set during application startup by either loading them
 * from the {@link Properties} file (default values) {@code client.properties} or parsing them from
 * the command line arguments of the application.
 * <p>
 * All items inside the {@code Config} are supposed to either be supplied over default value or over
 * command line argument. Developers that fail to provide default values will be greeted with an
 * error message the next time they try to start Envoy...
 *
 * @author Kai S. K. Engelbart
 * @since Envoy Common v0.1-beta
 */
public class Config {

	protected Map<String, ConfigItem<?>> items = new HashMap<>();

	private boolean modificationDisabled;

	protected Config(String folderName) {
		final var rootDirectory = new File(System.getProperty("user.home"), folderName);
		put("homeDirectory", "home", File::new);
		((ConfigItem<File>) get("homeDirectory")).setValue(rootDirectory);
		put("fileLevelBarrier", "fb", Level::parse);
		put("consoleLevelBarrier", "cb", Level::parse);
	}

	/**
	 * Parses config items from a properties object.
	 *
	 * @param properties the properties object to parse
	 * @since Envoy Common v0.1-beta
	 */
	private void load(Properties properties) {
		items.entrySet().stream().filter(e -> properties.containsKey(e.getKey()))
			.forEach(e -> e.getValue().parse(properties.getProperty(e.getKey())));
	}

	/**
	 * Parses config items from an array of command line arguments.
	 *
	 * @param args the command line arguments to parse
	 * @throws IllegalStateException if a malformed command line argument has been supplied
	 * @since Envoy Common v0.1-beta
	 */
	private void load(String[] args) {
		for (int i = 0; i < args.length; i++)
			for (final ConfigItem<?> item : items.values())
				if (args[i].startsWith("--")) {
					if (args[i].length() == 2)
						throw new IllegalStateException(
							"Malformed command line argument at position " + i + ": " + args[i]);
					final String commandLong = args[i].substring(2);
					if (item.getCommandLong().equals(commandLong)) {
						item.parse(args[++i]);
						break;
					}
				} else if (args[i].startsWith("-")) {
					if (args[i].length() == 1)
						throw new IllegalStateException(
							"Malformed command line argument at position " + i + ": " + args[i]);
					final String commandShort = args[i].substring(1);
					if (item.getCommandShort().equals(commandShort)) {
						item.parse(args[++i]);
						break;
					}
				} else
					throw new IllegalStateException(
						"Malformed command line argument at position " + i + ": " + args[i]);
	}

	/**
	 * Supplies default values from the given .properties file and parses the configuration from an
	 * array of command line arguments.
	 *
	 * @param declaringClass     the class calling this method
	 * @param propertiesFilePath the path to where the .properties file can be found - will be only
	 *                           the file name if it is located directly inside the
	 *                           {@code src/main/resources} folder
	 * @param args               the command line arguments to parse
	 * @throws IllegalStateException if this method is getting called again or if a malformed
	 *                               command line argument has been supplied
	 * @since Envoy Common v0.1-beta
	 */
	public void loadAll(Class<?> declaringClass, String propertiesFilePath, String[] args) {
		if (modificationDisabled)
			throw new IllegalStateException(
				"Cannot change config after isInitialized has been called");

		// Load the defaults from the given .properties file first
		final var properties = new Properties();
		try {
			properties
				.load(declaringClass.getClassLoader().getResourceAsStream(propertiesFilePath));
		} catch (final IOException e) {
			EnvoyLog.getLogger(Config.class).log(Level.SEVERE,
				"An error occurred when reading in the configuration: ",
				e);
		}
		load(properties);

		// Override configuration values with command line arguments
		if (args.length > 0)
			load(args);

		// Check if all configuration values have been initialized
		isInitialized();

		// Disable further editing of the config
		modificationDisabled = true;
	}

	/**
	 * @throws IllegalStateException if a {@link ConfigItem} has not been initialized
	 * @since Envoy Common v0.1-beta
	 */
	private void isInitialized() {
		String uninitialized = items.values().stream().filter(c -> c.get() == null)
			.map(ConfigItem::getCommandLong).collect(Collectors.joining(", "));
		if (!uninitialized.isEmpty())
			throw new IllegalStateException("Config items uninitialized: " + uninitialized);
	}

	/**
	 * @param name the name of the config item to return
	 * @return the config item with the specified name
	 * @since Envoy Common v0.1-beta
	 */
	public ConfigItem<?> get(String name) {
		return items.get(name);
	}

	/**
	 * Shorthand for <br>
	 * {@code items.put(commandName, new ConfigItem<>(commandName, commandShort, parseFunction, defaultValue))}.
	 *
	 * @param <T>           the type of the {@link ConfigItem}
	 * @param commandName   the key for this config item as well as its long name
	 * @param commandShort  the abbreviation of this config item
	 * @param parseFunction the {@code Function<String, T>} that parses the value from a string
	 * @since Envoy Common v0.2-beta
	 */
	protected <T> void put(String commandName, String commandShort,
		Function<String, T> parseFunction) {
		items.put(commandName, new ConfigItem<>(commandName, commandShort, parseFunction));
	}

	/**
	 * @return the directory in which all local files are saves
	 * @since Envoy Client v0.2-beta
	 */
	public File getHomeDirectory() { return (File) items.get("homeDirectory").get(); }

	/**
	 * @return the minimal {@link Level} to log inside the log file
	 * @since Envoy Client v0.2-beta
	 */
	public Level getFileLevelBarrier() { return (Level) items.get("fileLevelBarrier").get(); }

	/**
	 * @return the minimal {@link Level} to log inside the console
	 * @since Envoy Client v0.2-beta
	 */
	public Level getConsoleLevelBarrier() {
		return (Level) items.get("consoleLevelBarrier").get();
	}
}