package bjc.utils.cli;

import java.util.TreeMap;
import java.util.function.BiConsumer;
import java.util.function.Consumer;

import bjc.utils.funcdata.FunctionalMap;
import bjc.utils.funcdata.IMap;

import org.eclipse.jdt.annotation.Nullable;

/**
 * A general command mode, with a customizable set of commands
 * 
 * There is a small set of commands which is handled by default. The first
 * is 'list', which lists all the commands the user can input. The second
 * is 'alias', which allows the user to bind a new name to a command
 * 
 * @author ben
 *
 */
public class GenericCommandMode implements ICommandMode {
	/*
	 * Contains the commands this mode handles
	 */
	private IMap<String, ICommand>			commandHandlers;
	private IMap<String, ICommand>			defaultHandlers;

	// Contains help topics without an associated command
	private IMap<String, ICommandHelp>		helpTopics;

	// The action to execute upon encountering an unknown command
	private BiConsumer<String, String[]>	unknownCommandHandler;

	// The functions to use for input/output
	private Consumer<String>				errorOutput;
	private Consumer<String>				normalOutput;

	// The name of this command mode, or null if it is unnamed
	private String							modeName;

	// The custom prompt to use, or null if none is specified
	private String							customPrompt;

	/**
	 * Create a new generic command mode
	 * 
	 * @param normalOutput
	 *            The function to use for normal output
	 * @param errorOutput
	 *            The function to use for error output
	 */
	public GenericCommandMode(Consumer<String> normalOutput,
			Consumer<String> errorOutput) {
		if (normalOutput == null) {
			throw new NullPointerException(
					"Normal output source must be non-null");
		} else if (errorOutput == null) {
			throw new NullPointerException(
					"Error output source must be non-null");
		}

		this.normalOutput = normalOutput;
		this.errorOutput = errorOutput;

		// Initialize handler maps so that they sort in alphabetical order
		commandHandlers = new FunctionalMap<>(new TreeMap<>());
		defaultHandlers = new FunctionalMap<>(new TreeMap<>());
		helpTopics = new FunctionalMap<>(new TreeMap<>());

		setupDefaultCommands();
	}

	/**
	 * Add an alias to an existing command
	 * 
	 * @param commandName
	 *            The name of the command to add an alias for
	 * @param aliasName
	 *            The new alias for the command
	 * 
	 * @throws IllegalArgumentException
	 *             if the specified command doesn't have a bound handler,
	 *             or if the alias name already has a bound value
	 */
	public void addCommandAlias(String commandName, String aliasName) {
		if (commandName == null) {
			throw new NullPointerException(
					"Command name must not be null");
		} else if (aliasName == null) {
			throw new NullPointerException("Alias name must not be null");
		} else if (!commandHandlers.containsKey(commandName)
				&& !defaultHandlers.containsKey(commandName)) {
			throw new IllegalArgumentException(
					"Cannot alias non-existant command '" + commandName
							+ "'");
		} else if (commandHandlers.containsKey(aliasName)
				|| defaultHandlers.containsKey(aliasName)) {
			throw new IllegalArgumentException("Cannot bind alias '"
					+ aliasName + "' to a command with a bound handler");
		} else {
			ICommand aliasedCommand;

			if (defaultHandlers.containsKey(commandName)) {
				aliasedCommand = defaultHandlers.get(commandName)
						.aliased();
			} else {
				aliasedCommand = commandHandlers.get(commandName)
						.aliased();
			}

			commandHandlers.put(aliasName, aliasedCommand);
		}
	}

	/**
	 * Add a command to this command mode
	 * 
	 * @param command
	 *            The name of the command to add
	 * @param handler
	 *            The handler to use for the specified command
	 * 
	 * @throws IllegalArgumentException
	 *             if the specified command already has a handler
	 *             registered
	 */
	public void addCommandHandler(String command, ICommand handler) {
		if (command == null) {
			throw new NullPointerException("Command must not be null");
		} else if (handler == null) {
			throw new NullPointerException("Handler must not be null");
		} else if (canHandle(command)) {
			throw new IllegalArgumentException("Command " + command
					+ " already has a handler registered");
		} else {
			commandHandlers.put(command, handler);
		}
	}

	/**
	 * Add a help topic to this command mode that isn't tied to a command
	 * 
	 * @param topicName
	 *            The name of the topic
	 * @param topic
	 *            The contents of the topic
	 */
	public void addHelpTopic(String topicName, ICommandHelp topic) {
		helpTopics.put(topicName, topic);
	}

	// -------------------------------------------------------------------------
	/*
	 * Default command builders
	 */
	// -------------------------------------------------------------------------

	private GenericCommand buildAliasCommand() {
		return new GenericCommand((args) -> {
			doAliasCommands(args);

			return this;
		}, "alias\tAlias one command to another",
				"Gives a command another name it can be invoked by. Invoke"
						+ " with two arguments: the name of the command to alias"
						+ "followed by the name of the alias to give that command.");
	}

	private GenericCommand buildClearCommands() {
		return new GenericCommand((args) -> {
			errorOutput.accept(
					"ERROR: This console doesn't support screen clearing");

			return this;
		}, "clear\tClear the screen",
				"Clears the screen of all the text on it,"
						+ " and prints a new prompt.");
	}

	private GenericCommand buildExitCommand() {
		return new GenericCommand((args) -> {
			errorOutput.accept(
					"ERROR: This console doesn't support auto-exiting");

			return this;
		}, "exit\tExit the console",
				"First prompts the user to make sure they want to exit,"
						+ " and if they affirm it, it immediately exits");
	}

	private GenericCommand buildHelpCommand() {
		return new GenericCommand((args) -> {
			if (args == null || args.length == 0) {
				// Invoke general help
				doHelpSummary();
			} else {
				// Invoke help for a command
				doHelpCommand(args[0]);
			}

			return this;
		}, "help\tConsult the help system",
				"Consults the internal help system."
						+ " Invoked in two different ways. Invoking with no arguments"
						+ " causes all the topics you can ask for details on to be list,"
						+ " while invoking with the name of a topic will print the entry"
						+ " for that topic");
	}

	private GenericCommand buildListCommand() {
		return new GenericCommand((args) -> {
			doListCommands();

			return this;
		}, "list\tList available command",
				"Lists all of the commands available in this mode,"
						+ " as well as the commands that are valid in any mode.");
	}

	@Override
	public boolean canHandle(String command) {
		return commandHandlers.containsKey(command)
				|| defaultHandlers.containsKey(command);
	}

	// -------------------------------------------------------------------------
	/*
	 * Implement default commands
	 */
	// -------------------------------------------------------------------------

	private void doAliasCommands(String[] args) {
		if (args.length != 2) {
			errorOutput.accept("ERROR: Alias requires two arguments. "
					+ "The command name, and the alias for that command");
		} else {
			String commandName = args[0];
			String aliasName = args[1];

			if (!canHandle(commandName)) {
				errorOutput.accept("ERROR: '" + commandName
						+ "' is not a valid command.");
			} else if (canHandle(aliasName)) {
				errorOutput.accept("ERROR: Cannot overwrite command '"
						+ aliasName + "'");
			} else {
				addCommandAlias(commandName, aliasName);
			}
		}
	}

	private void doHelpCommand(String commandName) {
		if (commandHandlers.containsKey(commandName)) {
			normalOutput.accept("\n" + commandHandlers.get(commandName)
					.getHelp().getDescription());
		} else if (defaultHandlers.containsKey(commandName)) {
			normalOutput.accept("\n" + defaultHandlers.get(commandName)
					.getHelp().getDescription());
		} else if (helpTopics.containsKey(commandName)) {
			normalOutput.accept(
					"\n" + helpTopics.get(commandName).getDescription());
		} else {
			errorOutput
					.accept("ERROR: I'm sorry, but there is no help available for '"
							+ commandName + "'");
		}
	}

	private void doHelpSummary() {
		normalOutput.accept(
				"Help topics for this command mode are as follows:\n");
		if (commandHandlers.getSize() > 0) {
			commandHandlers.forEachValue((command) -> {
				if (!command.isAlias()) {
					normalOutput.accept(
							"\t" + command.getHelp().getSummary() + "\n");
				}
			});
		} else {
			normalOutput.accept("\tNone available\n");
		}

		normalOutput.accept(
				"\nHelp topics available in all command modes are as follows\n");
		if (defaultHandlers.getSize() > 0) {
			defaultHandlers.forEachValue((command) -> {
				if (!command.isAlias()) {
					normalOutput.accept(
							"\t" + command.getHelp().getSummary() + "\n");
				}
			});
		} else {
			normalOutput.accept("\tNone available\n");
		}

		normalOutput.accept(
				"\nHelp topics not associated with a command are as follows\n");
		if (helpTopics.getSize() > 0) {
			helpTopics.forEachValue((topic) -> {
				normalOutput.accept("\t" + topic.getSummary() + "\n");
			});
		} else {
			normalOutput.accept("\tNone available\n");
		}
	}

	private void doListCommands() {
		normalOutput.accept(
				"The available commands for this mode are as follows:\n");

		commandHandlers.keyList().forEach((commandName) -> {
			normalOutput.accept("\t" + commandName);
		});

		normalOutput.accept(
				"\nThe following commands are available in all modes:\n");

		defaultHandlers.keyList().forEach((commandName) -> {
			normalOutput.accept("\t" + commandName);
		});

		normalOutput.accept("\n");
	}

	@Override
	public String getCustomPrompt() {
		if (customPrompt != null) {
			return customPrompt;
		}

		return ICommandMode.super.getCustomPrompt();
	}

	@Override
	public String getName() {
		if (modeName != null) {
			return modeName;
		}

		return ICommandMode.super.getName();
	}

	@Override
	public boolean isCustomPromptEnabled() {
		return customPrompt != null;
	}

	@Override
	public ICommandMode process(String command, String[] args) {
		normalOutput.accept("\n");

		if (defaultHandlers.containsKey(command)) {
			return defaultHandlers.get(command).getHandler().handle(args);
		} else if (commandHandlers.containsKey(command)) {
			return commandHandlers.get(command).getHandler().handle(args);
		} else {
			if (args != null) {
				errorOutput.accept("ERROR: Unrecognized command " + command
						+ String.join(" ", args));
			} else {
				errorOutput
						.accept("ERROR: Unrecognized command " + command);
			}

			if (unknownCommandHandler == null) {
				throw new UnsupportedOperationException(
						"Command " + command + " is invalid.");
			}

			unknownCommandHandler.accept(command, args);
		}

		return this;
	}

	/**
	 * Set the custom prompt for this mode
	 * 
	 * @param prompt
	 *            The custom prompt for this mode, or null to disable the
	 *            custom prompt
	 */
	public void setCustomPrompt(@Nullable String prompt) {
		customPrompt = prompt;
	}

	/**
	 * Set the name of this mode
	 * 
	 * @param name
	 *            The desired name of this mode, or null to use the default
	 *            name
	 */
	public void setModeName(@Nullable String name) {
		modeName = name;
	}

	/**
	 * Set the handler to use for unknown commands
	 * 
	 * @param handler
	 *            The handler to use for unknown commands, or null to throw
	 *            on unknown commands
	 */
	public void setUnknownCommandHandler(
			@Nullable BiConsumer<String, String[]> handler) {
		if (handler == null) {
			throw new NullPointerException("Handler must not be null");
		}

		unknownCommandHandler = handler;
	}

	private void setupDefaultCommands() {
		defaultHandlers.put("list", buildListCommand());

		defaultHandlers.put("alias", buildAliasCommand());

		defaultHandlers.put("help", buildHelpCommand());

		addCommandAlias("help", "man");

		// Add commands handled in a upper layer.

		// TODO figure out a place to put commands that apply across all
		// modes, but only apply to a specific application
		defaultHandlers.put("clear", buildClearCommands());

		defaultHandlers.put("exit", buildExitCommand());
	}
}