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A fluent command processing system, in the spirit of POSIX
There is a newer version: 3.0.1
/*
 * Mandate - A flexible annotation-based command parsing and execution system
 * Copyright (C) 2016 Mark Johnson
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */

package pw.stamina.mandate.internal.syntax;

import pw.stamina.mandate.execution.ExecutionContext;
import pw.stamina.mandate.execution.executable.CommandExecutable;
import pw.stamina.mandate.execution.argument.CommandArgument;
import pw.stamina.mandate.parsing.InputParsingException;
import pw.stamina.mandate.syntax.CommandRegistry;
import pw.stamina.mandate.syntax.ExecutableLookup;
import pw.stamina.mandate.syntax.SyntaxComponent;
import pw.stamina.mandate.internal.syntax.component.ImmutableSyntaxComponentDecorator;

import java.util.*;
import java.util.stream.Collectors;

/**
 * @author Mark Johnson
 */
public class SimpleCommandRegistry implements CommandRegistry {

    private final Map registeredCommands = new HashMap<>();

    @Override
    public Set getCommands() {
        return Collections.unmodifiableSet(registeredCommands.values().stream().map(ImmutableSyntaxComponentDecorator::new).collect(Collectors.toSet()));
    }

    @Override
    public void addCommand(final SyntaxComponent component) {
        final SyntaxComponent old;
        if ((old = registeredCommands.get(component.getSyntax())) == null) {
            registeredCommands.put(component.getSyntax(), component);
        } else {
            mergeSyntaxComponent(component, old);
        }
    }

    @Override
    public ExecutableLookup findExecutable(final Deque arguments, final ExecutionContext executionContext) {
        int depth = 0;
        final List consumedArgs = new ArrayList<>();
        SyntaxComponent currentComponent;
        CommandArgument currentArgument;
        if ((currentComponent = registeredCommands.get((currentArgument = arguments.getFirst()).getRaw())) != null) {

            while ((currentArgument = arguments.poll()) != null) {
                consumedArgs.add(currentArgument);
                if (currentComponent.findExecutables().isPresent()) {

                    int lowestConsumed = Integer.MAX_VALUE;
                    InputParsingException lastException = null;
                    for (final CommandExecutable executable : currentComponent.findExecutables().get()) {
                        if (arguments.size() >= executable.minimumArguments() && arguments.size() <= executable.maximumArguments()) {
                            try {
                                executable.validate(arguments, executionContext);
                                return new SimpleExecutableLookup(executable, null);
                            } catch (final InputParsingException e) {
                                lastException = e;
                            }
                        } else {
                            lowestConsumed = lowestConsumed > executable.minimumArguments() ? executable.minimumArguments() : lowestConsumed;
                        }
                    }
                    if (lastException != null) {
                        return new SimpleExecutableLookup(null, lastException);
                    } else if (lowestConsumed != Integer.MAX_VALUE) {
                        depth += lowestConsumed;
                    }
                }
                final Optional tokenLookup;
                if (!arguments.isEmpty() && (tokenLookup = currentComponent.findChild(arguments.getFirst().getRaw())).isPresent()) {
                    depth++;
                    currentComponent = tokenLookup.get();
                } else {
                    consumedArgs.addAll(arguments);
                    if (++depth <= consumedArgs.size()) {
                        return new SimpleExecutableLookup(null, new InputParsingException(String.format("Invalid argument(s) '%s' passed to command '%s'", consumedArgs.subList(depth, consumedArgs.size()), consumedArgs.subList(0, depth))));
                    } else {
                        return new SimpleExecutableLookup(null, new InputParsingException(String.format("Missing %d argument(s) for command '%s'", depth - consumedArgs.size(), consumedArgs)));
                    }
                }
            }
            return new SimpleExecutableLookup(null, new IllegalStateException("No possible arguments available to parse"));
        } else {
            return new SimpleExecutableLookup(null, new InputParsingException(String.format("'%s' is not a valid command", currentArgument)));
        }
    }

    @Override
    public boolean commandPresent(final String command) {
        return registeredCommands.containsKey(command);
    }

    private static void mergeSyntaxComponent(final SyntaxComponent newComponent, final SyntaxComponent oldComponent) {
        Optional lookup;
        newComponent.findExecutables().ifPresent(set -> set.forEach(oldComponent::addExecutable));
        if (newComponent.findChildren().isPresent()) {
            for (final SyntaxComponent component : newComponent.findChildren().get()) {
                if ((lookup = oldComponent.findChild(component.getSyntax())).isPresent()) {
                    mergeSyntaxComponent(component, lookup.get());
                } else {
                    oldComponent.addChild(component);
                }
            }
        }
    }
}