package envoy.data;

import java.io.File;
import java.io.IOException;
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
 * {@code client.properties} or parsing them from the command line arguments of
 * the application.<br>
 * <br>
 * Project: <strong>envoy-client</strong><br>
 * File: <strong>Config.java</strong><br>
 * Created: <strong>12 Oct 2019</strong><br>
 *
 * @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, true);
		((ConfigItem<File>) get("homeDirectory")).setValue(rootDirectory);
		put("fileLevelBarrier", "fb", Level::parse, true);
		put("consoleLevelBarrier", "cb", Level::parse, true);
	}

	/**
	 * 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 mandatory configuration values have been initialized
		isInitialized();
		// Disable further editing of the config
		modificationDisabled = true;
	}

	/**
	 * @throws IllegalStateException if a mandatory {@link ConfigItem} has not been
	 *                               initialized
	 * @since Envoy Common v0.1-beta
	 */
	private void isInitialized() {
		if (items.values().stream().filter(ConfigItem::isMandatory).map(ConfigItem::get).anyMatch(Objects::isNull))
			throw new IllegalStateException("config item(s) has/ have not been initialized:" + items.values()
				.stream()
				.filter(configItem -> configItem.isMandatory() && configItem.get() == null)
				.map(ConfigItem::getCommandLong)
				.collect(Collectors.toSet()));
	}

	/**
	 * @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, mandatory))}.
	 *
	 * @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
	 * @param mandatory     indicated that this config item must be initialized with
	 *                      a non-null value
	 * @since Envoy Common v0.2-beta
	 */
	protected <T> void put(String commandName, String commandShort, Function<String, T> parseFunction, boolean mandatory) {
		items.put(commandName, new ConfigItem<>(commandName, commandShort, parseFunction, mandatory));
	}

	/**
	 * Shorthand for <br>
	 * {@code put(commandName, commandShort, parseFunction, false)}.
	 *
	 * @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) {
		put(commandName, commandShort, parseFunction, false);
	}

	/**
	 * @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(); }

}