Introduce SimulatorBuilder

[gromacs.git] / src / gromacs / commandline / cmdlinehelpmodule.cpp

/*
 * This file is part of the GROMACS molecular simulation package.
 *
 * Copyright (c) 2012,2013,2014,2015,2016,2017,2018,2019, by the GROMACS development team, led by
 * Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
 * and including many others, as listed in the AUTHORS file in the
 * top-level source directory and at http://www.gromacs.org.
 *
 * GROMACS is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1
 * of the License, or (at your option) any later version.
 *
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 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
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 */
/*! \internal \file
 * \brief
 * Implements gmx::CommandLineHelpModule.
 *
 * \author Teemu Murtola <teemu.murtola@gmail.com>
 * \ingroup module_commandline
 */
#include "gmxpre.h"

#include "cmdlinehelpmodule.h"

#include <memory>
#include <string>
#include <vector>

#include "gromacs/commandline/cmdlinehelpcontext.h"
#include "gromacs/commandline/cmdlinehelpwriter.h"
#include "gromacs/commandline/cmdlineparser.h"
#include "gromacs/onlinehelp/helpformat.h"
#include "gromacs/onlinehelp/helpmanager.h"
#include "gromacs/onlinehelp/helptopic.h"
#include "gromacs/onlinehelp/helpwritercontext.h"
#include "gromacs/options/basicoptions.h"
#include "gromacs/options/options.h"
#include "gromacs/utility/arrayref.h"
#include "gromacs/utility/baseversion.h"
#include "gromacs/utility/exceptions.h"
#include "gromacs/utility/fileredirector.h"
#include "gromacs/utility/gmxassert.h"
#include "gromacs/utility/path.h"
#include "gromacs/utility/programcontext.h"
#include "gromacs/utility/stringstream.h"
#include "gromacs/utility/stringutil.h"
#include "gromacs/utility/textreader.h"
#include "gromacs/utility/textstream.h"
#include "gromacs/utility/textwriter.h"

#include "shellcompletions.h"

namespace gmx
{

namespace
{
class IHelpExport;

/********************************************************************
 * RootHelpTopic declaration
 */

/*! \brief
 * Help topic that forms the root of the help tree for the help subcommand.
 *
 * \ingroup module_commandline
 */
class RootHelpTopic : public AbstractCompositeHelpTopic
{
    public:
        /*! \brief
         * Creates a root help topic.
         *
         * Does not throw.
         */
        explicit RootHelpTopic(const CommandLineHelpModuleImpl &helpModule)
            : helpModule_(helpModule)
        {
        }

        const char *name() const override;
        const char *title() const override { return title_.c_str(); }

        //! Adds a top-level topic and optionally marks it as exported.
        void addTopic(HelpTopicPointer topic, bool bExported)
        {
            if (bExported)
            {
                exportedTopics_.emplace_back(topic->name());
            }
            addSubTopic(std::move(topic));
        }
        //! Exports all the top-level topics with the given exporter.
        void exportHelp(IHelpExport *exporter);

        void writeHelp(const HelpWriterContext &context) const override;

    private:
        // unused because of the writeHelp() override
        std::string helpText() const override { return ""; }

        CommandLineHelpContext createContext(const HelpWriterContext &context) const;

        const CommandLineHelpModuleImpl  &helpModule_;
        std::string                       title_;
        std::vector<std::string>          exportedTopics_;

        GMX_DISALLOW_COPY_AND_ASSIGN(RootHelpTopic);
};

}   // namespace

/********************************************************************
 * CommandLineHelpModuleImpl declaration
 */

class CommandLineHelpModuleImpl
{
    public:
        CommandLineHelpModuleImpl(const IProgramContext            &programContext,
                                  const std::string                &binaryName,
                                  const CommandLineModuleMap       &modules,
                                  const CommandLineModuleGroupList &groups);

        std::unique_ptr<IHelpExport> createExporter(
            const std::string     &format,
            IFileOutputRedirector *redirector);
        void exportHelp(IHelpExport *exporter);

        RootHelpTopic                     rootTopic_;
        const IProgramContext            &programContext_;
        std::string                       binaryName_;
        const CommandLineModuleMap       &modules_;
        const CommandLineModuleGroupList &groups_;

        CommandLineHelpContext           *context_;
        const ICommandLineModule         *moduleOverride_;
        bool                              bHidden_;

        IFileOutputRedirector            *outputRedirector_;

        GMX_DISALLOW_COPY_AND_ASSIGN(CommandLineHelpModuleImpl);
};

namespace
{

/********************************************************************
 * IHelpExport
 */

/*! \brief
 * Callbacks for exporting help information for command-line modules.
 *
 * \ingroup module_commandline
 */
class IHelpExport
{
    public:
        //! Shorthand for a list of modules contained in a group.
        typedef CommandLineModuleGroupData::ModuleList ModuleGroupContents;

        virtual ~IHelpExport() {}

        /*! \brief
         * Called once before exporting individual modules.
         *
         * Can, e.g., open shared output files (e.g., if the output is written
         * into a single file, or if a separate index is required) and write
         * headers into them.
         */
        virtual void startModuleExport() = 0;
        /*! \brief
         * Called to export the help for each module.
         *
         * \param[in] module      Module for which the help should be exported.
         * \param[in] tag         Unique tag for the module (gmx-something).
         * \param[in] displayName Display name for the module (gmx something).
         */
        virtual void exportModuleHelp(
            const ICommandLineModule         &module,
            const std::string                &tag,
            const std::string                &displayName) = 0;
        /*! \brief
         * Called after all modules have been exported.
         *
         * Can close files opened in startModuleExport(), write footers to them
         * etc.
         */
        virtual void finishModuleExport() = 0;

        /*! \brief
         * Called once before exporting module groups.
         *
         * Can, e.g., open a single output file for listing all the groups.
         */
        virtual void startModuleGroupExport() = 0;
        /*! \brief
         * Called to export the help for each module group.
         *
         * \param[in] title    Title for the group.
         * \param[in] modules  List of modules in the group.
         */
        virtual void exportModuleGroup(const char                *title,
                                       const ModuleGroupContents &modules) = 0;
        /*! \brief
         * Called after all module groups have been exported.
         *
         * Can close files opened in startModuleGroupExport(), write footers to them
         * etc.
         */
        virtual void finishModuleGroupExport() = 0;

        /*! \brief
         * Called to export the help for a top-level topic.
         *
         * \param[in] topic   Topic to export.
         */
        virtual void exportTopic(const IHelpTopic &topic) = 0;
};

/********************************************************************
 * RootHelpTopic implementation
 */

struct RootHelpText
{
    static const char        title[];
    static const char *const text[];
};

// These are used for the gmx.1 man page.
// TODO: Do not hardcode them here, but pass them from the outside to make this
// code more generic.
const char        RootHelpText::title[] = "molecular dynamics simulation suite";
const char *const RootHelpText::text[]  = {
    "|Gromacs| is a full-featured suite of programs to perform molecular",
    "dynamics simulations, i.e., to simulate the behavior of systems with",
    "hundreds to millions of particles using Newtonian equations of motion.",
    "It is primarily used for research on proteins, lipids, and polymers, but",
    "can be applied to a wide variety of chemical and biological research",
    "questions.",
};

const char *RootHelpTopic::name() const
{
    return helpModule_.binaryName_.c_str();
}

void RootHelpTopic::exportHelp(IHelpExport *exporter)
{
    std::vector<std::string>::const_iterator topicName;
    for (topicName = exportedTopics_.begin();
         topicName != exportedTopics_.end();
         ++topicName)
    {
        const IHelpTopic *topic = findSubTopic(topicName->c_str());
        GMX_RELEASE_ASSERT(topic != nullptr, "Exported help topic no longer found");
        exporter->exportTopic(*topic);
    }
    // For now, the title is only set for the export to make it not appear in
    // console output, which makes things consistent for 'gmx help' and
    // 'gmx help <command>'.
    title_ = RootHelpText::title;
    exporter->exportTopic(*this);
}

void RootHelpTopic::writeHelp(const HelpWriterContext &context) const
{
    {
        CommandLineCommonOptionsHolder  optionsHolder;
        CommandLineHelpContext          cmdlineContext(createContext(context));
        cmdlineContext.setModuleDisplayName(helpModule_.binaryName_);
        optionsHolder.initOptions();
        Options                    &options = *optionsHolder.options();
        ArrayRef<const char *const> helpText;
        if (context.outputFormat() != eHelpOutputFormat_Console)
        {
            helpText = RootHelpText::text;
        }
        // TODO: Add <command> [<args>] into the synopsis.
        CommandLineHelpWriter(options)
            .setHelpText(helpText)
            .writeHelp(cmdlineContext);
    }
    if (context.outputFormat() == eHelpOutputFormat_Console)
    {
        // TODO: Consider printing a list of "core" commands. Would require someone
        // to determine such a set...
        context.paragraphBreak();
        writeSubTopicList(context,
                          "Additional help is available on the following topics:");
        context.writeTextBlock("To access the help, use '[PROGRAM] help <topic>'.");
        context.writeTextBlock("For help on a command, use '[PROGRAM] help <command>'.");
    }
    else
    {
        // TODO: This should not really end up on the HTML page.
        context.writeTitle(formatString("%s commands", helpModule_.binaryName_.c_str()));
        context.writeTextBlock(
                "The following commands are available. Please refer to their "
                "individual man pages or [TT][PROGRAM] help <command>[tt] "
                "for further details.");
        context.writeTextBlock("");
        context.writeTextBlock(".. include:: /fragments/bytopic-man.rst");
    }
}

CommandLineHelpContext
RootHelpTopic::createContext(const HelpWriterContext &context) const
{
    if (helpModule_.context_ != nullptr)
    {
        return CommandLineHelpContext(*helpModule_.context_);
    }
    else
    {
        return CommandLineHelpContext(context);
    }
}

/********************************************************************
 * CommandsHelpTopic
 */

/*! \brief
 * Help topic for listing the commands.
 *
 * \ingroup module_commandline
 */
class CommandsHelpTopic : public IHelpTopic
{
    public:
        /*! \brief
         * Creates a command list help topic.
         *
         * \param[in]     helpModule Help module to get module information from.
         *
         * Does not throw.
         */
        explicit CommandsHelpTopic(const CommandLineHelpModuleImpl &helpModule)
            : helpModule_(helpModule)
        {
        }

        const char *name() const override { return "commands"; }
        const char *title() const override { return "List of available commands"; }
        bool hasSubTopics() const override { return false; }
        const IHelpTopic *findSubTopic(const char * /*name*/) const override
        {
            return nullptr;
        }

        void writeHelp(const HelpWriterContext &context) const override;

    private:
        const CommandLineHelpModuleImpl &helpModule_;

        GMX_DISALLOW_COPY_AND_ASSIGN(CommandsHelpTopic);
};

void CommandsHelpTopic::writeHelp(const HelpWriterContext &context) const
{
    if (context.outputFormat() != eHelpOutputFormat_Console)
    {
        GMX_THROW(NotImplementedError(
                          "Module list is not implemented for this output format"));
    }
    int maxNameLength = 0;
    const CommandLineModuleMap           &modules = helpModule_.modules_;
    CommandLineModuleMap::const_iterator  module;
    for (module = modules.begin(); module != modules.end(); ++module)
    {
        int nameLength = static_cast<int>(module->first.length());
        if (module->second->shortDescription() != nullptr
            && nameLength > maxNameLength)
        {
            maxNameLength = nameLength;
        }
    }
    context.writeTextBlock(
            "Usage: [PROGRAM] [<options>] <command> [<args>][PAR]"
            "Available commands:");
    TextWriter        &file = context.outputFile();
    TextTableFormatter formatter;
    formatter.addColumn(nullptr, maxNameLength + 1, false);
    formatter.addColumn(nullptr, 72 - maxNameLength, true);
    formatter.setFirstColumnIndent(4);
    for (module = modules.begin(); module != modules.end(); ++module)
    {
        const char *name        = module->first.c_str();
        const char *description = module->second->shortDescription();
        if (description != nullptr)
        {
            formatter.clear();
            formatter.addColumnLine(0, name);
            formatter.addColumnLine(1, description);
            file.writeString(formatter.formatRow());
        }
    }
    context.writeTextBlock(
            "For help on a command, use '[PROGRAM] help <command>'.");
}

/********************************************************************
 * ModuleHelpTopic
 */

/*! \brief
 * Help topic wrapper for a command-line module.
 *
 * This class implements IHelpTopic such that it wraps a
 * ICommandLineModule, allowing subcommand "help <command>"
 * to produce the help for "<command>".
 *
 * \ingroup module_commandline
 */
class ModuleHelpTopic : public IHelpTopic
{
    public:
        //! Constructs a help topic for a specific module.
        ModuleHelpTopic(const ICommandLineModule         &module,
                        const CommandLineHelpModuleImpl  &helpModule)
            : module_(module), helpModule_(helpModule)
        {
        }

        const char *name() const override { return module_.name(); }
        const char *title() const override { return nullptr; }
        bool hasSubTopics() const override { return false; }
        const IHelpTopic *findSubTopic(const char * /*name*/) const override
        {
            return nullptr;
        }
        void writeHelp(const HelpWriterContext &context) const override;

    private:
        const ICommandLineModule         &module_;
        const CommandLineHelpModuleImpl  &helpModule_;

        GMX_DISALLOW_COPY_AND_ASSIGN(ModuleHelpTopic);
};

void ModuleHelpTopic::writeHelp(const HelpWriterContext & /*context*/) const
{
    CommandLineHelpContext context(*helpModule_.context_);
    const char *const      program = helpModule_.binaryName_.c_str();
    context.setModuleDisplayName(formatString("%s %s", program, module_.name()));
    module_.writeHelp(context);
}

/********************************************************************
 * HelpExportReStructuredText
 */

/*! \internal \brief
 * Adds hyperlinks to modules within this binary.
 *
 * \param[in,out] links      Links are added here.
 * \param[in]     helpModule Help module to get module information from.
 * \throws        std::bad_alloc if out of memory.
 *
 * Initializes a HelpLinks object with links to modules defined in
 * \p helpModule.
 *
 * \ingroup module_commandline
 */
void initProgramLinks(HelpLinks *links, const CommandLineHelpModuleImpl &helpModule)
{
    const char *const                    program = helpModule.binaryName_.c_str();
    CommandLineModuleMap::const_iterator module;
    for (module = helpModule.modules_.begin();
         module != helpModule.modules_.end();
         ++module)
    {
        if (module->second->shortDescription() != nullptr)
        {
            std::string linkName("[gmx-" + module->first + "]");
            const char *name = module->first.c_str();
            std::string reference(
                    formatString(":doc:`%s %s <%s-%s>`", program, name, program, name));
            std::string displayName(
                    formatString("[TT]%s %s[tt]", program, name));
            links->addLink(linkName, reference, displayName);
        }
    }
}

/*! \internal \brief
 * Implements export for web pages as reStructuredText.
 *
 * \ingroup module_commandline
 */
class HelpExportReStructuredText : public IHelpExport
{
    public:
        //! Initializes reST exporter.
        HelpExportReStructuredText(
            const CommandLineHelpModuleImpl &helpModule,
            IFileOutputRedirector           *outputRedirector);

        void startModuleExport() override;
        void exportModuleHelp(
            const ICommandLineModule         &module,
            const std::string                &tag,
            const std::string                &displayName) override;
        void finishModuleExport() override;

        void startModuleGroupExport() override;
        void exportModuleGroup(const char                *title,
                               const ModuleGroupContents &modules) override;
        void finishModuleGroupExport() override;

        void exportTopic(const IHelpTopic &topic) override;

    private:
        IFileOutputRedirector          *outputRedirector_;
        const std::string              &binaryName_; //NOLINT(google-runtime-member-string-references)
        HelpLinks                       links_;
        // These never release ownership.
        std::unique_ptr<TextWriter>     indexFile_;
        std::unique_ptr<TextWriter>     manPagesFile_;
};

HelpExportReStructuredText::HelpExportReStructuredText(
        const CommandLineHelpModuleImpl &helpModule,
        IFileOutputRedirector           *outputRedirector)
    : outputRedirector_(outputRedirector),
      binaryName_(helpModule.binaryName_),
      links_(eHelpOutputFormat_Rst)
{
    TextReader   linksFile("links.dat");
    std::string  line;
    linksFile.setTrimTrailingWhiteSpace(true);
    while (linksFile.readLine(&line))
    {
        links_.addLink("[REF]." + line + "[ref]",
                       formatString(":ref:`.%s <%s>`", line.c_str(), line.c_str()),
                       line);
        links_.addLink("[REF]" + line + "[ref]", formatString(":ref:`%s`", line.c_str()), line);
    }
    linksFile.close();
    initProgramLinks(&links_, helpModule);
}

void HelpExportReStructuredText::startModuleExport()
{
    indexFile_ = std::make_unique<TextWriter>(
                outputRedirector_->openTextOutputFile("fragments/byname.rst"));
    indexFile_->writeLine(formatString("* :doc:`%s </onlinehelp/%s>` - %s",
                                       binaryName_.c_str(), binaryName_.c_str(),
                                       RootHelpText::title));
    manPagesFile_ = std::make_unique<TextWriter>(
                outputRedirector_->openTextOutputFile("conf-man.py"));
    manPagesFile_->writeLine("man_pages = [");
}

void HelpExportReStructuredText::exportModuleHelp(
        const ICommandLineModule         &module,
        const std::string                &tag,
        const std::string                &displayName)
{
    TextOutputStreamPointer file
        = outputRedirector_->openTextOutputFile("onlinehelp/" + tag + ".rst");
    TextWriter              writer(file);
    writer.writeLine(formatString(".. _%s:", displayName.c_str()));
    if (displayName == binaryName_ + " mdrun")
    {
        // Make an extra link target for the convenience of
        // MPI-specific documentation
        writer.writeLine(".. _mdrun_mpi:");
    }
    writer.ensureEmptyLine();

    CommandLineHelpContext context(&writer, eHelpOutputFormat_Rst, &links_, binaryName_);
    context.enterSubSection(displayName);
    context.setModuleDisplayName(displayName);
    module.writeHelp(context);

    writer.ensureEmptyLine();
    writer.writeLine(".. only:: man");
    writer.writeLine();
    writer.writeLine("   See also");
    writer.writeLine("   --------");
    writer.writeLine();
    writer.writeLine(formatString("   :manpage:`%s(1)`", binaryName_.c_str()));
    writer.writeLine();
    writer.writeLine("   More information about |Gromacs| is available at <http://www.gromacs.org/>.");
    file->close();

    indexFile_->writeLine(formatString("* :doc:`%s </onlinehelp/%s>` - %s",
                                       displayName.c_str(), tag.c_str(),
                                       module.shortDescription()));
    manPagesFile_->writeLine(
            formatString("    ('onlinehelp/%s', '%s', \"%s\", '', 1),",
                         tag.c_str(), tag.c_str(), module.shortDescription()));
}

void HelpExportReStructuredText::finishModuleExport()
{
    indexFile_->close();
    indexFile_.reset();
    // TODO: Generalize.
    manPagesFile_->writeLine(
            formatString("    ('onlinehelp/%s', '%s', '%s', '', 1)",
                         binaryName_.c_str(), binaryName_.c_str(),
                         RootHelpText::title));
    manPagesFile_->writeLine("]");
    manPagesFile_->close();
    manPagesFile_.reset();
}

void HelpExportReStructuredText::startModuleGroupExport()
{
    indexFile_ = std::make_unique<TextWriter>(
                outputRedirector_->openTextOutputFile("fragments/bytopic.rst"));
    manPagesFile_ = std::make_unique<TextWriter>(
                outputRedirector_->openTextOutputFile("fragments/bytopic-man.rst"));
}

void HelpExportReStructuredText::exportModuleGroup(
        const char                *title,
        const ModuleGroupContents &modules)
{
    indexFile_->ensureEmptyLine();
    indexFile_->writeLine(title);
    indexFile_->writeLine(std::string(std::strlen(title), '^'));
    manPagesFile_->ensureEmptyLine();
    manPagesFile_->writeLine(title);
    manPagesFile_->writeLine(std::string(std::strlen(title), '^'));

    ModuleGroupContents::const_iterator module;
    for (module = modules.begin(); module != modules.end(); ++module)
    {
        const std::string     &tag(module->first);
        std::string            displayName(tag);
        // TODO: This does not work if the binary name would contain a dash,
        // but that is not currently the case.
        const size_t           dashPos = displayName.find('-');
        GMX_RELEASE_ASSERT(dashPos != std::string::npos,
                           "There should always be at least one dash in the tag");
        displayName[dashPos] = ' ';
        indexFile_->writeLine(formatString(":doc:`%s </onlinehelp/%s>`\n  %s",
                                           displayName.c_str(), tag.c_str(),
                                           module->second));
        manPagesFile_->writeLine(formatString(":manpage:`%s(1)`\n  %s",
                                              tag.c_str(),
                                              module->second));
    }
}

void HelpExportReStructuredText::finishModuleGroupExport()
{
    indexFile_->close();
    indexFile_.reset();
    manPagesFile_->close();
    manPagesFile_.reset();
}

void HelpExportReStructuredText::exportTopic(const IHelpTopic &topic)
{
    const std::string       path("onlinehelp/" + std::string(topic.name()) + ".rst");
    TextWriter              writer(outputRedirector_->openTextOutputFile(path));
    CommandLineHelpContext  context(&writer, eHelpOutputFormat_Rst, &links_,
                                    binaryName_);
    HelpManager             manager(topic, context.writerContext());
    manager.writeCurrentTopic();
    writer.close();
}

/********************************************************************
 * HelpExportCompletion
 */

/*! \internal \brief
 * Implements export for command-line completion.
 *
 * \ingroup module_commandline
 */
class HelpExportCompletion : public IHelpExport
{
    public:
        //! Initializes completion exporter.
        explicit HelpExportCompletion(const CommandLineHelpModuleImpl &helpModule);

        void startModuleExport() override;
        void exportModuleHelp(
            const ICommandLineModule         &module,
            const std::string                &tag,
            const std::string                &displayName) override;
        void finishModuleExport() override;

        void startModuleGroupExport() override {}
        void exportModuleGroup(const char                * /*title*/,
                               const ModuleGroupContents & /*modules*/) override {}
        void finishModuleGroupExport() override {}

        void exportTopic(const IHelpTopic & /*topic*/) override {}

    private:
        ShellCompletionWriter    bashWriter_;
        std::vector<std::string> modules_;
};

HelpExportCompletion::HelpExportCompletion(
        const CommandLineHelpModuleImpl &helpModule)
    : bashWriter_(helpModule.binaryName_, eShellCompletionFormat_Bash)
{
}

void HelpExportCompletion::startModuleExport()
{
    bashWriter_.startCompletions();
}

void HelpExportCompletion::exportModuleHelp(
        const ICommandLineModule         &module,
        const std::string                 & /*tag*/,
        const std::string                 & /*displayName*/)
{
    modules_.emplace_back(module.name());
    {
        CommandLineHelpContext context(&bashWriter_);
        // We use the display name to pass the name of the module to the
        // completion writer.
        context.setModuleDisplayName(module.name());
        module.writeHelp(context);
    }
}

void HelpExportCompletion::finishModuleExport()
{
    CommandLineCommonOptionsHolder optionsHolder;
    optionsHolder.initOptions();
    bashWriter_.writeWrapperCompletions(modules_, *optionsHolder.options());
    bashWriter_.finishCompletions();
}

}   // namespace

/********************************************************************
 * CommandLineHelpModuleImpl implementation
 */

CommandLineHelpModuleImpl::CommandLineHelpModuleImpl(
        const IProgramContext            &programContext,
        const std::string                &binaryName,
        const CommandLineModuleMap       &modules,
        const CommandLineModuleGroupList &groups)
    : rootTopic_(*this), programContext_(programContext),
      binaryName_(binaryName), modules_(modules), groups_(groups),
      context_(nullptr), moduleOverride_(nullptr), bHidden_(false),
      outputRedirector_(&defaultFileOutputRedirector())
{
}

std::unique_ptr<IHelpExport>
CommandLineHelpModuleImpl::createExporter(const std::string     &format,
                                          IFileOutputRedirector *redirector)
{
    if (format == "rst")
    {
        return std::unique_ptr<IHelpExport>(
                new HelpExportReStructuredText(*this, redirector));
    }
    else if (format == "completion")
    {
        return std::unique_ptr<IHelpExport>(
                new HelpExportCompletion(*this));
    }
    GMX_THROW(NotImplementedError("This help format is not implemented"));
}

void CommandLineHelpModuleImpl::exportHelp(IHelpExport *exporter)
{
    // TODO: Would be nicer to have the file names supplied by the build system
    // and/or export a list of files from here.
    const char *const program = binaryName_.c_str();

    exporter->startModuleExport();
    CommandLineModuleMap::const_iterator module;
    for (module = modules_.begin(); module != modules_.end(); ++module)
    {
        if (module->second->shortDescription() != nullptr)
        {
            const char *const moduleName = module->first.c_str();
            std::string       tag(formatString("%s-%s", program, moduleName));
            std::string       displayName(formatString("%s %s", program, moduleName));
            exporter->exportModuleHelp(*module->second, tag, displayName);
        }
    }
    exporter->finishModuleExport();

    exporter->startModuleGroupExport();
    CommandLineModuleGroupList::const_iterator group;
    for (group = groups_.begin(); group != groups_.end(); ++group)
    {
        exporter->exportModuleGroup((*group)->title(), (*group)->modules());
    }
    exporter->finishModuleGroupExport();

    rootTopic_.exportHelp(exporter);
}

namespace
{

/********************************************************************
 * ModificationCheckingFileOutputStream
 */

class ModificationCheckingFileOutputStream : public TextOutputStream
{
    public:
        ModificationCheckingFileOutputStream(
            const char                    *path,
            IFileOutputRedirector         *redirector)
            : path_(path), redirector_(redirector)
        {
        }

        void write(const char *str) override { contents_.write(str); }
        void close() override
        {
            const std::string &newContents = contents_.toString();
            // TODO: Redirect these for unit tests.
            if (File::exists(path_, File::returnFalseOnError))
            {
                const std::string originalContents_
                    = TextReader::readFileToString(path_);
                if (originalContents_ == newContents)
                {
                    return;
                }
            }
            TextWriter writer(redirector_->openTextOutputFile(path_));
            writer.writeString(newContents);
        }

    private:
        std::string                     path_;
        StringOutputStream              contents_;
        IFileOutputRedirector          *redirector_;
};

/********************************************************************
 * ModificationCheckingFileOutputRedirector
 */

class ModificationCheckingFileOutputRedirector : public IFileOutputRedirector
{
    public:
        explicit ModificationCheckingFileOutputRedirector(
            IFileOutputRedirector *redirector)
            : redirector_(redirector)
        {
        }

        TextOutputStream &standardOutput() override
        {
            return redirector_->standardOutput();
        }
        TextOutputStreamPointer openTextOutputFile(const char *filename) override
        {
            return TextOutputStreamPointer(
                    new ModificationCheckingFileOutputStream(filename, redirector_));
        }

    private:
        IFileOutputRedirector  *redirector_;
};

}   // namespace

/********************************************************************
 * CommandLineHelpModule
 */

CommandLineHelpModule::CommandLineHelpModule(
        const IProgramContext            &programContext,
        const std::string                &binaryName,
        const CommandLineModuleMap       &modules,
        const CommandLineModuleGroupList &groups)
    : impl_(new Impl(programContext, binaryName, modules, groups))
{
}

CommandLineHelpModule::~CommandLineHelpModule()
{
}

HelpTopicPointer CommandLineHelpModule::createModuleHelpTopic(
        const ICommandLineModule &module) const
{
    return HelpTopicPointer(new ModuleHelpTopic(module, *impl_));
}

void CommandLineHelpModule::addTopic(HelpTopicPointer topic, bool bExported)
{
    impl_->rootTopic_.addTopic(std::move(topic), bExported);
}

void CommandLineHelpModule::setShowHidden(bool bHidden)
{
    impl_->bHidden_ = bHidden;
}

void CommandLineHelpModule::setModuleOverride(
        const ICommandLineModule &module)
{
    impl_->moduleOverride_ = &module;
}

void CommandLineHelpModule::setOutputRedirector(
        IFileOutputRedirector *output)
{
    impl_->outputRedirector_ = output;
}

int CommandLineHelpModule::run(int argc, char *argv[])
{
    // Add internal topics lazily here.
    addTopic(HelpTopicPointer(new CommandsHelpTopic(*impl_)), false);

    const char *const exportFormats[] = { "rst", "completion" };
    std::string       exportFormat;
    Options           options;
    options.addOption(StringOption("export").store(&exportFormat)
                          .enumValue(exportFormats));
    CommandLineParser(&options).allowPositionalArguments(true).parse(&argc, argv);
    if (!exportFormat.empty())
    {
        ModificationCheckingFileOutputRedirector redirector(impl_->outputRedirector_);
        const std::unique_ptr<IHelpExport>       exporter(
                impl_->createExporter(exportFormat, &redirector));
        impl_->exportHelp(exporter.get());
        return 0;
    }

    TextOutputStream      &outputFile = impl_->outputRedirector_->standardOutput();
    TextWriter             writer(&outputFile);
    HelpLinks              links(eHelpOutputFormat_Console);
    initProgramLinks(&links, *impl_);
    CommandLineHelpContext context(&writer, eHelpOutputFormat_Console, &links,
                                   impl_->binaryName_);
    context.setShowHidden(impl_->bHidden_);
    if (impl_->moduleOverride_ != nullptr)
    {
        context.setModuleDisplayName(impl_->programContext_.displayName());
        impl_->moduleOverride_->writeHelp(context);
        return 0;
    }
    impl_->context_ = &context;

    HelpManager helpManager(impl_->rootTopic_, context.writerContext());
    try
    {
        for (int i = 1; i < argc; ++i)
        {
            helpManager.enterTopic(argv[i]);
        }
    }
    catch (const InvalidInputError &ex)
    {
        fprintf(stderr, "%s\n", ex.what());
        return 2;
    }
    helpManager.writeCurrentTopic();
    return 0;
}

void CommandLineHelpModule::writeHelp(const CommandLineHelpContext &context) const
{
    const HelpWriterContext &writerContext = context.writerContext();
    // TODO: Implement.
    if (writerContext.outputFormat() != eHelpOutputFormat_Console)
    {
        return;
    }
    writerContext.writeTextBlock(
            "Usage: [PROGRAM] help [<command>|<topic> [<subtopic> [...]]]");
    // TODO: More information.
}

} // namespace gmx