#include "parser.hpp"

#include <sstream>

#include <components/debug/debuglog.hpp>
#include <components/files/conversion.hpp>
#include <components/misc/strings/algorithm.hpp>

#include <filesystem>
#include <fstream>

#include <Base64.h>

void Settings::SettingsFileParser::loadSettingsFile(
    const std::filesystem::path& file, CategorySettingValueMap& settings, bool base64Encoded, bool overrideExisting)
{
    mFile = file;
    std::ifstream fstream;
    fstream.open(file);
    auto stream = std::ref<std::istream>(fstream);

    std::istringstream decodedStream;
    if (base64Encoded)
    {
        std::string base64String(std::istreambuf_iterator<char>(fstream), {});
        std::string decodedString;
        auto result = Base64::Base64::Decode(base64String, decodedString);
        if (!result.empty())
            fail("Could not decode Base64 file: " + result);
        // Move won't do anything until C++20, but won't hurt to do it anyway.
        decodedStream.str(std::move(decodedString));
        stream = std::ref<std::istream>(decodedStream);
    }

    Log(Debug::Info) << "Loading settings file: " << file;
    std::string currentCategory;
    mLine = 0;
    while (!stream.get().eof() && !stream.get().fail())
    {
        ++mLine;
        std::string line;
        std::getline(stream.get(), line);

        size_t i = 0;
        if (!skipWhiteSpace(i, line))
            continue;

        if (line[i] == '#') // skip comment
            continue;

        if (line[i] == '[')
        {
            size_t end = line.find(']', i);
            if (end == std::string::npos)
                fail("unterminated category");

            currentCategory = line.substr(i + 1, end - (i + 1));
            Misc::StringUtils::trim(currentCategory);
            i = end + 1;
        }

        if (!skipWhiteSpace(i, line))
            continue;

        if (currentCategory.empty())
            fail("empty category name");

        size_t settingEnd = line.find('=', i);
        if (settingEnd == std::string::npos)
            fail("unterminated setting name");

        std::string setting = line.substr(i, (settingEnd - i));
        Misc::StringUtils::trim(setting);

        size_t valueBegin = settingEnd + 1;
        std::string value = line.substr(valueBegin);
        Misc::StringUtils::trim(value);

        if (overrideExisting)
            settings[std::make_pair(currentCategory, setting)] = std::move(value);
        else if (settings.insert(std::make_pair(std::make_pair(currentCategory, setting), value)).second == false)
            fail(std::string("duplicate setting: [" + currentCategory + "] " + setting));
    }
}

void Settings::SettingsFileParser::saveSettingsFile(
    const std::filesystem::path& file, const CategorySettingValueMap& settings)
{
    using CategorySettingStatusMap = std::map<CategorySetting, bool>;

    // No options have been written to the file yet.
    CategorySettingStatusMap written;
    for (auto it = settings.begin(); it != settings.end(); ++it)
    {
        written[it->first] = false;
    }

    // Have we substantively changed the settings file?
    bool changed = false;

    // Were there any lines at all in the file?
    bool existing = false;

    // Is an entirely blank line queued to be added?
    bool emptyLineQueued = false;

    // The category/section we're currently in.
    std::string currentCategory;

    // Open the existing settings.cfg file to copy comments.  This might not be the same file
    // as the output file if we're copying the setting from the default settings.cfg for the
    // first time.  A minor change in API to pass the source file might be in order here.
    std::ifstream istream;
    istream.open(file);

    // Create a new string stream to write the current settings to.  It's likely that the
    // input file and the output file are the same, so this stream serves as a temporary file
    // of sorts.  The setting files aren't very large so there's no performance issue.
    std::stringstream ostream;

    // For every line in the input file...
    while (!istream.eof() && !istream.fail())
    {
        std::string line;
        std::getline(istream, line);

        // The current character position in the line.
        size_t i = 0;

        // An empty line was queued.
        if (emptyLineQueued)
        {
            emptyLineQueued = false;
            // We're still going through the current category, so we should copy it.
            if (currentCategory.empty() || istream.eof() || line[i] != '[')
                ostream << std::endl;
        }

        // Don't add additional newlines at the end of the file otherwise.
        if (istream.eof())
            continue;

        // Queue entirely blank lines to add them if desired.
        if (!skipWhiteSpace(i, line))
        {
            emptyLineQueued = true;
            continue;
        }

        // There were at least some comments in the input file.
        existing = true;

        // Copy comments.
        if (line[i] == '#')
        {
            ostream << line << std::endl;
            continue;
        }

        // Category heading.
        if (line[i] == '[')
        {
            size_t end = line.find(']', i);
            // This should never happen unless the player edited the file while playing.
            if (end == std::string::npos)
            {
                ostream << "# unterminated category: " << line << std::endl;
                changed = true;
                continue;
            }

            if (!currentCategory.empty())
            {
                // Ensure that all options in the current category have been written.
                for (CategorySettingStatusMap::iterator mit = written.begin(); mit != written.end(); ++mit)
                {
                    if (mit->second == false && mit->first.first == currentCategory)
                    {
                        Log(Debug::Verbose) << "Added new setting: [" << currentCategory << "] " << mit->first.second
                                            << " = " << settings.at(mit->first);
                        ostream << mit->first.second << " = " << settings.at(mit->first) << std::endl;
                        mit->second = true;
                        changed = true;
                    }
                }
                // Add an empty line after the last option in a category.
                ostream << std::endl;
            }

            // Update the current category.
            currentCategory = line.substr(i + 1, end - (i + 1));
            Misc::StringUtils::trim(currentCategory);

            // Write the (new) current category to the file.
            ostream << "[" << currentCategory << "]" << std::endl;
            // Log(Debug::Verbose) << "Wrote category: " << currentCategory;

            // A setting can apparently follow the category on an input line.  That's rather
            // inconvenient, since it makes it more likely to have duplicative sections,
            // which our algorithm doesn't like.  Do the best we can.
            i = end + 1;
        }

        // Truncate trailing whitespace, since we're changing the file anayway.
        if (!skipWhiteSpace(i, line))
            continue;

        // If we've found settings before the first category, something's wrong.  This
        // should never happen unless the player edited the file while playing, since
        // the loadSettingsFile() logic rejects it.
        if (currentCategory.empty())
        {
            ostream << "# empty category name: " << line << std::endl;
            changed = true;
            continue;
        }

        // Which setting was at this location in the input file?
        size_t settingEnd = line.find('=', i);
        // This should never happen unless the player edited the file while playing.
        if (settingEnd == std::string::npos)
        {
            ostream << "# unterminated setting name: " << line << std::endl;
            changed = true;
            continue;
        }
        std::string setting = line.substr(i, (settingEnd - i));
        Misc::StringUtils::trim(setting);

        // Get the existing value so we can see if we've changed it.
        size_t valueBegin = settingEnd + 1;
        std::string value = line.substr(valueBegin);
        Misc::StringUtils::trim(value);

        // Construct the setting map key to determine whether the setting has already been
        // written to the file.
        CategorySetting key = std::make_pair(currentCategory, setting);
        CategorySettingStatusMap::iterator finder = written.find(key);

        // Settings not in the written map are definitely invalid.  Currently, this can only
        // happen if the player edited the file while playing, because loadSettingsFile()
        // will accept anything and pass it along in the map, but in the future, we might
        // want to handle invalid settings more gracefully here.
        if (finder == written.end())
        {
            ostream << "# invalid setting: " << line << std::endl;
            changed = true;
            continue;
        }

        // Write the current value of the setting to the file.  The key must exist in the
        // settings map because of how written was initialized and finder != end().
        ostream << setting << " = " << settings.at(key) << std::endl;
        // Mark that setting as written.
        finder->second = true;
        // Did we really change it?
        if (value != settings.at(key))
        {
            Log(Debug::Verbose) << "Changed setting: [" << currentCategory << "] " << setting << " = "
                                << settings.at(key);
            changed = true;
        }
        // No need to write the current line, because we just emitted a replacement.

        // Curiously, it appears that comments at the ends of lines with settings are not
        // allowed, and the comment becomes part of the value.  Was that intended?
    }

    // We're done with the input stream file.
    istream.close();

    // Ensure that all options in the current category have been written.  We must complete
    // the current category at the end of the file before moving on to any new categories.
    for (CategorySettingStatusMap::iterator mit = written.begin(); mit != written.end(); ++mit)
    {
        if (mit->second == false && mit->first.first == currentCategory)
        {
            Log(Debug::Verbose) << "Added new setting: [" << mit->first.first << "] " << mit->first.second << " = "
                                << settings.at(mit->first);
            ostream << mit->first.second << " = " << settings.at(mit->first) << std::endl;
            mit->second = true;
            changed = true;
        }
    }

    // If there was absolutely nothing in the file (or more likely the file didn't
    // exist), start the newly created file with a helpful comment.
    if (!existing)
    {
        const std::string filename = Files::pathToUnicodeString(file.filename());
        ostream << "# This is the OpenMW user '" << filename << "' file.  This file only contains" << std::endl;
        ostream << "# explicitly changed settings.  If you would like to revert a setting" << std::endl;
        ostream << "# to its default, simply remove it from this file." << std::endl;

        if (filename == "settings.cfg")
        {
            ostream << "# For available settings, see the file 'files/settings-default.cfg' in our source repo or the "
                       "documentation at:"
                    << std::endl;
            ostream << "#" << std::endl;
            ostream << "#   https://openmw.readthedocs.io/en/master/reference/modding/settings/index.html" << std::endl;
        }
        else if (filename == "openmw-cs.cfg")
        {
            ostream << "# For available settings, see the file 'apps/opencs/model/prefs/values.hpp' in our source repo."
                    << std::endl;
        }
    }

    // We still have one more thing to do before we're completely done writing the file.
    // It's possible that there are entirely new categories, or that the input file had
    // disappeared completely, so we need ensure that all settings are written to the file
    // regardless of those issues.
    for (CategorySettingStatusMap::iterator mit = written.begin(); mit != written.end(); ++mit)
    {
        // If the setting hasn't been written yet.
        if (mit->second == false)
        {
            // If the catgory has changed, write a new category header.
            if (mit->first.first != currentCategory)
            {
                currentCategory = mit->first.first;
                Log(Debug::Verbose) << "Created new setting section: " << mit->first.first;
                ostream << std::endl;
                ostream << "[" << currentCategory << "]" << std::endl;
            }
            Log(Debug::Verbose) << "Added new setting: [" << mit->first.first << "] " << mit->first.second << " = "
                                << settings.at(mit->first);
            // Then write the setting.  No need to mark it as written because we're done.
            ostream << mit->first.second << " = " << settings.at(mit->first) << std::endl;
            changed = true;
        }
    }

    // Now install the newly written file in the requested place.
    if (changed)
    {
        Log(Debug::Info) << "Updating settings file: " << file;
        std::ofstream ofstream;
        ofstream.open(file);
        ofstream << ostream.rdbuf();
        ofstream.close();
    }
}

bool Settings::SettingsFileParser::skipWhiteSpace(size_t& i, std::string& str)
{
    while (i < str.size() && std::isspace(str[i], std::locale::classic()))
    {
        ++i;
    }
    return i < str.size();
}

[[noreturn]] void Settings::SettingsFileParser::fail(const std::string& message)
{
    std::stringstream error;
    error << "Error on line " << mLine << " in " << Files::pathToUnicodeString(mFile) << ":\n" << message;
    throw std::runtime_error(error.str());
}