ProBKernel.java

package de.prob2.jupyter;

import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.nio.charset.StandardCharsets;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Properties;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Function;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

import com.google.common.base.MoreObjects;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.Singleton;

import de.prob.animator.ReusableAnimator;
import de.prob.animator.domainobjects.ErrorItem;
import de.prob.exception.ProBError;
import de.prob.scripting.ClassicalBFactory;
import de.prob.statespace.AnimationSelector;
import de.prob.statespace.StateSpace;
import de.prob.statespace.Trace;
import de.prob2.jupyter.commands.AssertCommand;
import de.prob2.jupyter.commands.BrowseCommand;
import de.prob2.jupyter.commands.BsymbCommand;
import de.prob2.jupyter.commands.CheckCommand;
import de.prob2.jupyter.commands.ConstantsCommand;
import de.prob2.jupyter.commands.DotCommand;
import de.prob2.jupyter.commands.EvalCommand;
import de.prob2.jupyter.commands.ExecCommand;
import de.prob2.jupyter.commands.FindCommand;
import de.prob2.jupyter.commands.GotoCommand;
import de.prob2.jupyter.commands.GroovyCommand;
import de.prob2.jupyter.commands.HelpCommand;
import de.prob2.jupyter.commands.InitialiseCommand;
import de.prob2.jupyter.commands.LetCommand;
import de.prob2.jupyter.commands.LoadCellCommand;
import de.prob2.jupyter.commands.LoadFileCommand;
import de.prob2.jupyter.commands.ModelCheckCommand;
import de.prob2.jupyter.commands.PrefCommand;
import de.prob2.jupyter.commands.PrettyPrintCommand;
import de.prob2.jupyter.commands.RenderCommand;
import de.prob2.jupyter.commands.ShowCommand;
import de.prob2.jupyter.commands.SolveCommand;
import de.prob2.jupyter.commands.StatsCommand;
import de.prob2.jupyter.commands.TableCommand;
import de.prob2.jupyter.commands.TimeCommand;
import de.prob2.jupyter.commands.TraceCommand;
import de.prob2.jupyter.commands.TypeCommand;
import de.prob2.jupyter.commands.UnletCommand;
import de.prob2.jupyter.commands.VersionCommand;

import io.github.spencerpark.jupyter.kernel.BaseKernel;
import io.github.spencerpark.jupyter.kernel.LanguageInfo;
import io.github.spencerpark.jupyter.kernel.ReplacementOptions;
import io.github.spencerpark.jupyter.kernel.display.DisplayData;
import io.github.spencerpark.jupyter.kernel.display.mime.MIMEType;

import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Singleton
public final class ProBKernel extends BaseKernel {
	/**
	 * Inner class for safe lazy loading of the build info.
	 */
	private static final class BuildInfo {
		static final Properties buildInfo;
		static {
			buildInfo = new Properties();
			try (final Reader reader = new InputStreamReader(
				ProBKernel.class.getResourceAsStream("/de/prob2/jupyter/build.properties"),
				StandardCharsets.UTF_8
			)) {
				buildInfo.load(reader);
			} catch (final IOException e) {
				throw new AssertionError("Failed to load build info", e);
			}
		}
	}
	
	private static final class SplitCommandCall {
		private final @NotNull PositionedString name;
		private final @NotNull PositionedString argString;
		
		private SplitCommandCall(@NotNull final PositionedString name, @NotNull final PositionedString argString) {
			this.name = name;
			this.argString = argString;
		}
		
		private @NotNull PositionedString getName() {
			return this.name;
		}
		
		private @NotNull PositionedString getArgString() {
			return this.argString;
		}
		
		@Override
		public String toString() {
			return MoreObjects.toStringHelper(this)
				.add("name", this.getName())
				.add("argString", this.getArgString())
				.toString();
		}
	}
	
	private static final @NotNull Logger LOGGER = LoggerFactory.getLogger(ProBKernel.class);
	
	private static final @NotNull Pattern COMMAND_PATTERN = Pattern.compile("\\s*(\\:[^\\s]*)(?:\\h*(.*))?", Pattern.DOTALL);
	private static final @NotNull Pattern MACHINE_CODE_PATTERN = Pattern.compile("MACHINE\\W.*", Pattern.DOTALL);
	private static final @NotNull Pattern BSYMB_COMMAND_PATTERN = Pattern.compile("\\\\([a-z]+)");
	private static final @NotNull Pattern LATEX_FORMULA_PATTERN = Pattern.compile("(\\$\\$?)([^\\$]+)\\1");
	
	private static final @NotNull Collection<@NotNull Class<? extends Command>> COMMAND_CLASSES = Collections.unmodifiableList(Arrays.asList(
		AssertCommand.class,
		BrowseCommand.class,
		BsymbCommand.class,
		CheckCommand.class,
		ConstantsCommand.class,
		DotCommand.class,
		EvalCommand.class,
		ExecCommand.class,
		FindCommand.class,
		GotoCommand.class,
		GroovyCommand.class,
		HelpCommand.class,
		InitialiseCommand.class,
		LetCommand.class,
		LoadCellCommand.class,
		LoadFileCommand.class,
		ModelCheckCommand.class,
		PrefCommand.class,
		PrettyPrintCommand.class,
		RenderCommand.class,
		ShowCommand.class,
		SolveCommand.class,
		StatsCommand.class,
		TableCommand.class,
		TimeCommand.class,
		TraceCommand.class,
		TypeCommand.class,
		UnletCommand.class,
		VersionCommand.class
	));
	
	private static final @NotNull Map<@NotNull String, @NotNull String> BSYMB_COMMAND_DEFINITIONS;
	static {
		final Map<String, String> map = new HashMap<>();
		map.put("bfalse", "\\newcommand{\\bfalse}{\\mathord\\bot}");
		map.put("btrue", "\\newcommand{\\btrue}{\\mathord\\top}");
		map.put("limp", "\\newcommand{\\limp}{\\mathbin\\Rightarrow}");
		map.put("leqv", "\\newcommand{\\leqv}{\\mathbin\\Leftrightarrow}");
		map.put("qdot", "\\newcommand{\\qdot}{\\mathord{\\mkern1mu\\cdot\\mkern1mu}}");
		map.put("defi", "\\newcommand{\\defi}{\\mathrel{≙}}");
		map.put("pow", "\\newcommand{\\pow}{\\mathop{\\mathbb P\\hbox{}}\\nolimits}");
		map.put("pown", "\\newcommand{\\pown}{\\mathop{\\mathbb P_1}\\nolimits}");
		map.put("cprod", "\\newcommand{\\cprod}{\\mathbin\\times}");
		map.put("bunion", "\\newcommand{\\bunion}{\\mathbin{\\mkern1mu\\cup\\mkern1mu}}");
		map.put("binter", "\\newcommand{\\binter}{\\mathbin{\\mkern1mu\\cap\\mkern1mu}}");
		map.put("union", "\\newcommand{\\union}{\\mathop{\\mathrm{union}}\\nolimits}");
		map.put("inter", "\\newcommand{\\inter}{\\mathop{\\mathrm{inter}}\\nolimits}");
		map.put("Union", "\\newcommand{\\Union}{\\bigcup\\nolimits}");
		map.put("Inter", "\\newcommand{\\Inter}{\\bigcap\\nolimits}");
		map.put("emptyset", "\\renewcommand{\\emptyset}{\\mathord\\varnothing}");
		map.put("rel", "\\newcommand{\\rel}{\\mathbin{<\\mkern-10mu-\\mkern-10mu>}}");
		map.put("trel", "\\newcommand{\\trel}{\\mathbin{<\\mkern-6mu<\\mkern-10mu-\\mkern-10mu>}}");
		map.put("srel", "\\newcommand{\\srel}{\\mathbin{<\\mkern-10mu-\\mkern-10mu>\\mkern-6mu>}}");
		map.put("strel", "\\newcommand{\\strel}{\\mathbin{<\\mkern-6mu<\\mkern-10mu-\\mkern-10mu>\\mkern-6mu>}}");
		map.put("dom", "\\newcommand{\\dom}{\\mathop{\\mathrm{dom}}\\nolimits}");
		map.put("ran", "\\newcommand{\\ran}{\\mathop{\\mathrm{ran}}\\nolimits}");
		map.put("fcomp", "\\newcommand{\\fcomp}{\\mathbin;}");
		map.put("bcomp", "\\newcommand{\\bcomp}{\\circ}");
		map.put("id", "\\newcommand{\\id}{\\mathop{\\mathrm{id}}\\nolimits}");
		map.put("domres", "\\newcommand{\\domres}{\\mathbin◁}");
		map.put("domsub", "\\newcommand{\\domsub}{\\mathbin⩤}");
		map.put("ranres", "\\newcommand{\\ranres}{\\mathbin▷}");
		map.put("ransub", "\\newcommand{\\ransub}{\\mathbin⩥}");
		map.put("ovl", "\\newcommand{\\ovl}{\\mathbin{<\\mkern-11mu+}}");
		map.put("dprod", "\\newcommand{\\dprod}{\\mathbin\\otimes}");
		map.put("prjone", "\\newcommand{\\prjone}{\\mathop{\\mathrm{prj}_1}\\nolimits}");
		map.put("prjtwo", "\\newcommand{\\prjtwo}{\\mathop{\\mathrm{prj}_2}\\nolimits}");
		map.put("pprod", "\\newcommand{\\pprod}{\\mathbin\\mid}");
		map.put("pfun", "\\newcommand{\\pfun}{\\mathbin↦}");
		map.put("tfun", "\\newcommand{\\tfun}{\\mathbin→}");
		map.put("pinj", "\\newcommand{\\pinj}{\\mathbin⤔}");
		map.put("tinj", "\\newcommand{\\tinj}{\\mathbin↣}");
		map.put("psur", "\\newcommand{\\psur}{\\mathbin⤅}");
		map.put("tsur", "\\newcommand{\\tsur}{\\mathbin↠}");
		map.put("tbij", "\\newcommand{\\tbij}{\\mathbin⤖}");
		map.put("nat", "\\newcommand{\\nat}{\\mathord{\\mathbb N}}");
		map.put("natn", "\\newcommand{\\natn}{\\mathord{\\mathbb N_1}}");
		map.put("intg", "\\newcommand{\\intg}{\\mathord{\\mathbb Z}}");
		map.put("upto", "\\newcommand{\\upto}{\\mathbin{.\\mkern1mu.}}");
		map.put("finite", "\\newcommand{\\finite}{\\mathop{\\mathrm{finite}}\\nolimits}");
		map.put("card", "\\newcommand{\\card}{\\mathop{\\mathrm{card}}\\nolimits}");
		map.put("upred", "\\newcommand{\\upred}{\\mathop{\\mathrm{pred}}\\nolimits}");
		map.put("usucc", "\\newcommand{\\usucc}{\\mathop{\\mathrm{succ}}\\nolimits}");
		map.put("expn", "\\newcommand{\\expn}{\\mathbin{\\widehat{\\mkern1em}}}");
		map.put("Bool", "\\newcommand{\\Bool}{\\mathord{\\mathrm{BOOL}}}");
		map.put("bool", "\\newcommand{\\bool}{\\mathop{\\mathrm{bool}}\\nolimits}");
		map.put("bcmeq", "\\newcommand{\\bcmeq}{\\mathrel{:\\mkern1mu=}}");
		map.put("bcmin", "\\newcommand{\\bcmin}{\\mathrel{:\\mkern1mu\\in}}");
		map.put("bcmsuch", "\\newcommand{\\bcmsuch}{\\mathrel{:\\mkern1mu\\mid}}");
		BSYMB_COMMAND_DEFINITIONS = Collections.unmodifiableMap(map);
	}
	
	private final @NotNull AnimationSelector animationSelector;
	private final @NotNull ReusableAnimator animator;
	
	private final @NotNull Map<@NotNull String, @NotNull Command> commands;
	private final @NotNull AtomicReference<@Nullable Thread> currentEvalThread;
	private final @NotNull Map<@NotNull String, @NotNull String> variables;
	
	private @NotNull Path currentMachineDirectory;
	
	@Inject
	private ProBKernel(final @NotNull Injector injector, final @NotNull ClassicalBFactory classicalBFactory, final @NotNull AnimationSelector animationSelector, final @NotNull ReusableAnimator animator) {
		super();
		
		this.setShouldReplaceStdStreams(false);
		
		this.animationSelector = animationSelector;
		this.animator = animator;
		
		this.commands = COMMAND_CLASSES.stream()
			.map(injector::getInstance)
			.collect(Collectors.toMap(Command::getName, cmd -> cmd));
		
		this.currentEvalThread = new AtomicReference<>(null);
		this.variables = new HashMap<>();
		
		this.switchMachine(Paths.get(""), stateSpace -> {
			classicalBFactory.create("(initial Jupyter machine)", "MACHINE repl END").loadIntoStateSpace(stateSpace);
			return new Trace(stateSpace);
		});
		this.currentMachineDirectory = Paths.get("");
	}
	
	private static @NotNull Properties getBuildInfo() {
		return ProBKernel.BuildInfo.buildInfo;
	}
	
	public static @NotNull String getVersion() {
		return getBuildInfo().getProperty("version");
	}
	
	public static @NotNull String getCommit() {
		return getBuildInfo().getProperty("commit");
	}
	
	public @NotNull Map<@NotNull String, @NotNull Command> getCommands() {
		return Collections.unmodifiableMap(this.commands);
	}
	
	public @NotNull Map<@NotNull String, @NotNull String> getVariables() {
		return this.variables;
	}
	
	public @NotNull Path getCurrentMachineDirectory() {
		return this.currentMachineDirectory;
	}
	
	public void setCurrentMachineDirectory(final @NotNull Path currentMachineDirectory) {
		this.currentMachineDirectory = currentMachineDirectory;
	}
	
	public void unloadMachine() {
		final Trace oldTrace = this.animationSelector.getCurrentTrace();
		if (oldTrace != null) {
			assert oldTrace.getStateSpace() == this.animator.getCurrentStateSpace();
			this.animationSelector.changeCurrentAnimation(null);
			oldTrace.getStateSpace().kill();
		}
		this.setCurrentMachineDirectory(Paths.get(""));
	}
	
	public void switchMachine(final @NotNull Path machineDirectory, final @NotNull Function<@NotNull StateSpace, @NotNull Trace> newTraceCreator) {
		this.unloadMachine();
		final StateSpace newStateSpace = this.animator.createStateSpace();
		try {
			this.animationSelector.changeCurrentAnimation(newTraceCreator.apply(newStateSpace));
		} catch (final RuntimeException e) {
			newStateSpace.kill();
			throw e;
		}
		this.setCurrentMachineDirectory(machineDirectory);
	}
	
	@Override
	public @NotNull String getBanner() {
		return "ProB Interactive Expression and Predicate Evaluator (on Jupyter)\nType \":help\" for more information.";
	}
	
	@Override
	public @NotNull List<LanguageInfo.@NotNull Help> getHelpLinks() {
		return Collections.singletonList(new LanguageInfo.Help("ProB User Manual", "https://www3.hhu.de/stups/prob/index.php/User_Manual"));
	}
	
	private static @NotNull String addBsymbDefinitions(final @NotNull String markdown) {
		final StringBuilder defs = new StringBuilder();
		final Matcher matcher = BSYMB_COMMAND_PATTERN.matcher(markdown);
		while (matcher.find()) {
			defs.append(BSYMB_COMMAND_DEFINITIONS.getOrDefault(matcher.group(1), ""));
		}
		
		if (defs.length() > 0) {
			// Find the first LaTeX formula in the output and add the definitions to it.
			final Matcher latexFormulaMatcher = LATEX_FORMULA_PATTERN.matcher(markdown);
			if (latexFormulaMatcher.find()) {
				// We do this manually instead of using Matcher.replaceFirst to prevent backslashes from being processed.
				return markdown.substring(0, latexFormulaMatcher.start())
					+ latexFormulaMatcher.group(1)
					+ defs
					+ latexFormulaMatcher.group(2)
					+ latexFormulaMatcher.group(1)
					+ markdown.substring(latexFormulaMatcher.end());
			} else {
				// No LaTeX formula found, add an extra one at the start.
				// This can produce an unwanted empty line at the start, so we avoid this method if possible.
				return "$" + defs + "$\n\n" + markdown;
			}
		} else {
			// No definitions needed, so don't modify the output.
			return markdown;
		}
	}
	
	private static @NotNull String addAllBsymbDefinitions() {
		final StringBuilder defs = new StringBuilder("$");
		BSYMB_COMMAND_DEFINITIONS.forEach((k, v) -> {
			defs.append(v);
		});
		defs.append("\\text{All bsymb.sty definitions have been loaded.}$");
		return defs.toString();
	}
	
	private @Nullable DisplayData executeCommand(final @NotNull PositionedString name, final @NotNull PositionedString argString) {
		final Command command = this.getCommands().get(name.getValue());
		if (command == null) {
			throw new NoSuchCommandException(name.getValue());
		}
		final DisplayData result;
		try {
			result = command.run(CommandUtils.parseArgs(command.getParameters(), argString));
		} catch (final UserErrorException e) {
			throw new CommandExecutionException(name.getValue(), e);
		}
		
		if (result != null && result.hasDataForType(MIMEType.TEXT_MARKDOWN)) {
			final String markdown = (String)result.getData(MIMEType.TEXT_MARKDOWN);
			if (command instanceof BsymbCommand) {
				result.putMarkdown(addAllBsymbDefinitions());
			} else {
				// Add definitions for any used bsymb LaTeX commands to Markdown output.
				result.putMarkdown(addBsymbDefinitions(markdown));
			}
		}
		
		return result;
	}
	
	private static boolean isMachineCode(final @NotNull String code) {
		return MACHINE_CODE_PATTERN.matcher(code).matches();
	}
	
	/**
	 * Preprocess the given input by ensuring that it starts with a command name.
	 * If a command name is already present,
	 * the input is returned unchanged.
	 * Otherwise,
	 * an appropriate command is added based on the type of input.
	 * 
	 * @param code the input code to preprocess
	 * @return the input with a command name prefixed if necessary
	 */
	private static @NotNull PositionedString preprocessInput(final @NotNull PositionedString code) {
		final Matcher commandMatcher = COMMAND_PATTERN.matcher(code.getValue());
		final String prefix;
		if (commandMatcher.matches()) {
			// The input already includes a command, so no prefix needs to be added.
			prefix = "";
		} else if (isMachineCode(code.getValue())) {
			// The input appears to be a machine, add a command to load it.
			prefix = "::load\n";
		} else {
			// By default, assume that the input is an expression that should be evaluated.
			prefix = ":eval ";
		}
		// Add the prefix and adjust the start position.
		// This means that the characters from the prefix (if any) will have negative positions,
		// but the characters from the real source code will have the same positions as before.
		return new PositionedString(prefix + code.getValue(), code.getStartPosition() - prefix.length());
	}
	
	/**
	 * Split the given input into a command name and argument string.
	 * The input must include a command name,
	 * which should be ensured by passing it through {@link #preprocessInput(PositionedString)} first.
	 * 
	 * @param code the input, which must contain a command name
	 * @return the input split into a command name and argument string
	 */
	private static @NotNull SplitCommandCall splitCommand(final @NotNull PositionedString code) {
		final Matcher commandMatcher = COMMAND_PATTERN.matcher(code.getValue());
		if (!commandMatcher.matches()) {
			throw new AssertionError("Preprocessed input does not include a command - this should not happen");
		}
		final PositionedString name = code.substring(commandMatcher.start(1), commandMatcher.end(1));
		final PositionedString argString;
		if (commandMatcher.group(2) == null) {
			argString = code.substring(code.getValue().length());
		} else {
			argString = code.substring(commandMatcher.start(2), commandMatcher.end(2));
		}
		return new SplitCommandCall(name, argString);
	}
	
	private @Nullable DisplayData evalInternal(final @NotNull PositionedString code) {
		final SplitCommandCall split = splitCommand(preprocessInput(code));
		return this.executeCommand(split.getName(), split.getArgString());
	}
	
	@Override
	public @Nullable DisplayData eval(final String expr) {
		assert expr != null;
		
		this.currentEvalThread.set(Thread.currentThread());
		
		try {
			return evalInternal(new PositionedString(expr, 0));
		} finally {
			this.currentEvalThread.set(null);
		}
	}
	
	private static @Nullable DisplayData inspectCommandArguments(final @NotNull Command command, final @NotNull PositionedString argString, final int at) {
		final SplitResult split = CommandUtils.splitArgs(command.getParameters(), argString, at);
		if (split.getParameterAtPosition().isPresent()) {
			final Optional<Inspector> inspector = command.getParameterInspectors().getInspectorForParameter(split.getParameterAtPosition().get());
			if (inspector.isPresent()) {
				final List<PositionedString> argsAtPosition = split.getArguments().get(split.getParameterAtPosition().get());
				assert !argsAtPosition.isEmpty();
				final PositionedString lastArgument = argsAtPosition.get(argsAtPosition.size() - 1);
				return inspector.get().inspect(lastArgument.getValue(), at - lastArgument.getStartPosition());
			} else {
				return null;
			}
		} else {
			return null;
		}
	}
	
	private @Nullable DisplayData inspectInternal(final @NotNull PositionedString code, final int at) {
		final SplitCommandCall split = splitCommand(preprocessInput(code));
		if (this.getCommands().containsKey(split.getName().getValue())) {
			final Command command = this.getCommands().get(split.getName().getValue());
			if (at <= split.getName().getEndPosition()) {
				// The cursor is somewhere in the command name, show help text for the command.
				return command.renderHelp();
			} else {
				// The cursor is somewhere in the command arguments, ask the command to inspect.
				return inspectCommandArguments(command, split.getArgString(), at);
			}
		} else {
			// Invalid command, can't inspect.
			return null;
		}
	}
	
	@Override
	public @Nullable DisplayData inspect(final @NotNull String code, final int at, final boolean extraDetail) {
		// Note: We ignore the extraDetail parameter, because in practice it is always false. This is because the inspect_request messages sent by Jupyter Notebook always have their detail_level set to 0.
		return this.inspectInternal(new PositionedString(code, 0), at);
	}
	
	private static @NotNull ReplacementOptions offsetReplacementOptions(final @NotNull ReplacementOptions replacements, final int offset) {
		return new ReplacementOptions(
			replacements.getReplacements(),
			replacements.getSourceStart() + offset,
			replacements.getSourceEnd() + offset
		);
	}
	
	private static @Nullable ReplacementOptions completeCommandArguments(final @NotNull Command command, final @NotNull PositionedString argString, final int at) {
		final SplitResult split = CommandUtils.splitArgs(command.getParameters(), argString, at);
		
		final Parameter<?> parameterToComplete;
		final PositionedString argumentToComplete;
		if (split.getParameterAtPosition().isPresent()) {
			// If any arguments were split,
			// use the last parameter for completion.
			parameterToComplete = split.getParameterAtPosition().get();
			final List<PositionedString> argsAtPosition = split.getArguments().get(parameterToComplete);
			assert !argsAtPosition.isEmpty();
			argumentToComplete = argsAtPosition.get(argsAtPosition.size() - 1);
		} else if (!command.getParameters().getPositionalParameters().isEmpty()) {
			// Special case: if the command has parameters,
			// but argument splitting stopped before any arguments were split,
			// perform completion on the first parameter and an empty string at the cursor.
			parameterToComplete = command.getParameters().getPositionalParameters().get(0);
			argumentToComplete = new PositionedString("", at);
		} else {
			// Command has no parameters,
			// so completion in the arguments is not possible.
			return null;
		}
		
		final Optional<Completer> completer = command.getParameterCompleters().getCompleterForParameter(parameterToComplete);
		if (completer.isPresent()) {
			final ReplacementOptions replacements = completer.get().complete(argumentToComplete.getValue(), at - argumentToComplete.getStartPosition());
			return replacements == null ? null : offsetReplacementOptions(replacements, argumentToComplete.getStartPosition());
		} else {
			return null;
		}
	}
	
	private @Nullable ReplacementOptions completeInternal(final @NotNull PositionedString code, final int at) {
		final SplitCommandCall split = splitCommand(preprocessInput(code));
		if (at <= split.getName().getEndPosition()) {
			// The cursor is somewhere in the command name, provide command completions.
			final String prefix = split.getName().substring(0, at - split.getName().getStartPosition()).getValue();
			return new ReplacementOptions(
				this.getCommands().keySet().stream().filter(s -> s.startsWith(prefix)).sorted().collect(Collectors.toList()),
				split.getName().getStartPosition(),
				split.getName().getEndPosition()
			);
		} else {
			// The cursor is somewhere in the command arguments, ask the command to provide completions.
			if (this.getCommands().containsKey(split.getName().getValue())) {
				return completeCommandArguments(this.getCommands().get(split.getName().getValue()), split.getArgString(), at);
			} else {
				// Invalid command, can't provide any completions.
				return null;
			}
		}
	}
	
	@Override
	public @Nullable ReplacementOptions complete(final @NotNull String code, final int at) {
		return this.completeInternal(new PositionedString(code, 0), at);
	}
	
	@Override
	public String isComplete(final String code) {
		final Matcher commandMatcher = COMMAND_PATTERN.matcher(code);
		if (commandMatcher.matches() && commandMatcher.group(1).startsWith("::")) {
			return code.endsWith("\n") ? IS_COMPLETE_MAYBE : "";
		} else {
			// TODO Support line continuation for normal commands
			return IS_COMPLETE_MAYBE;
		}
	}
	
	@Override
	public @NotNull LanguageInfo getLanguageInfo() {
		return new LanguageInfo.Builder("prob")
			.mimetype("text/x-prob2-jupyter-repl")
			.fileExtension(".prob")
			.codemirror("prob2_jupyter_repl")
			.build();
	}
	
	@Override
	public void onShutdown(final boolean isRestarting) {
		this.animationSelector.getCurrentTrace().getStateSpace().kill();
	}
	
	@Override
	public void interrupt() {
		final Thread evalThread = this.currentEvalThread.get();
		if (evalThread != null) {
			evalThread.interrupt();
		}
		this.animationSelector.getCurrentTrace().getStateSpace().sendInterrupt();
	}
	
	private @NotNull List<@NotNull String> formatErrorSource(final @NotNull List<@NotNull String> sourceLines, final @NotNull ErrorItem.Location location) {
		if (sourceLines.isEmpty()) {
			return Collections.singletonList(this.errorStyler.primary("// Source code not known"));
		}
		
		final List<String> out = new ArrayList<>();
		if (location.getStartLine() < 1 || location.getStartLine() > sourceLines.size()) {
			out.add(this.errorStyler.secondary(String.format("Error start line %d out of bounds (1..%d)", location.getStartLine(), sourceLines.size())));
			return out;
		}
		if (location.getEndLine() < 1 || location.getEndLine() > sourceLines.size()) {
			out.add(this.errorStyler.secondary(String.format("Error end line %d out of bounds (1..%d)", location.getEndLine(), sourceLines.size())));
			return out;
		}
		final List<String> errorLines = sourceLines.subList(location.getStartLine()-1, location.getEndLine());
		assert !errorLines.isEmpty();
		final String firstLine = errorLines.get(0);
		final String lastLine = errorLines.get(errorLines.size() - 1);
		if (location.getStartColumn() < 0 || location.getStartColumn() > firstLine.length()) {
			out.add(this.errorStyler.secondary(String.format("Error start column %d out of bounds (0..%d)", location.getStartColumn(), firstLine.length()-1)));
			return out;
		}
		if (location.getEndColumn() < 0 || location.getEndColumn() > lastLine.length()) {
			out.add(this.errorStyler.secondary(String.format("Error end column %d out of bounds (0..%d)", location.getEndColumn(), lastLine.length()-1)));
			return out;
		}
		if (errorLines.size() == 1) {
			out.add(
				this.errorStyler.primary(firstLine.substring(0, location.getStartColumn()))
				+ this.errorStyler.highlight(firstLine.substring(location.getStartColumn(), location.getEndColumn()))
				+ this.errorStyler.primary(firstLine.substring(location.getEndColumn()))
			);
		} else {
			out.add(
				this.errorStyler.primary(firstLine.substring(0, location.getStartColumn()))
				+ this.errorStyler.highlight(firstLine.substring(location.getStartColumn()))
			);
			errorLines.subList(1, errorLines.size()-1).stream().map(this.errorStyler::highlight).collect(Collectors.toCollection(() -> out));
			out.add(
				this.errorStyler.highlight(lastLine.substring(0, location.getEndColumn()))
				+ this.errorStyler.primary(lastLine.substring(location.getEndColumn()))
			);
		}
		return out;
	}
	
	@Override
	public @NotNull List<@NotNull String> formatError(final Exception e) {
		try {
			LOGGER.warn("Exception while executing command from user", e);
			if (e instanceof UserErrorException) {
				return this.errorStyler.secondaryLines(String.valueOf(e.getMessage()));
			} else if (e instanceof ProBError || e instanceof WithSourceCodeException) {
				final List<String> sourceLines;
				final ProBError proBError;
				if (e instanceof WithSourceCodeException) {
					sourceLines = Arrays.asList(((WithSourceCodeException)e).getSourceCode().split("\n"));
					proBError = ((WithSourceCodeException)e).getCause();
				} else {
					sourceLines = Collections.emptyList();
					proBError = (ProBError)e;
				}
				final List<String> out = new ArrayList<>(Arrays.asList((
					this.errorStyler.primary("Error from ProB: ")
					+ this.errorStyler.secondary(String.valueOf(proBError.getOriginalMessage()))
				).split("\n")));
				if (proBError.getErrors() == null) {
					// If the errors list is null rather than empty, don't show the "no error messages" message.
					// (This matches the normal behavior of ProBError.)
				} else if (proBError.getErrors().isEmpty()) {
					out.addAll(this.errorStyler.primaryLines("ProB returned no error messages.\n"));
				} else {
					if (proBError.getErrors().size() > 1) {
						out.addAll(this.errorStyler.primaryLines(proBError.getErrors().size() + " errors:\n"));
					}
					for (final ErrorItem error : proBError.getErrors()) {
						out.addAll(this.errorStyler.secondaryLines(error.toString()));
						for (final ErrorItem.Location location : error.getLocations()) {
							out.addAll(formatErrorSource(sourceLines, location));
						}
					}
				}
				return out;
			} else {
				return this.errorStyler.secondaryLines(e.toString());
			}
		} catch (final RuntimeException e2) {
			LOGGER.error("Exception in error formatting", e2);
			throw e2;
		}
	}
	
	public @NotNull String insertLetVariables(final @NotNull String code) {
		return CommandUtils.insertLetVariables(code, this.getVariables());
	}
}