// For license of this file, see <project-root-folder>/LICENSE.md.

#include "core/messagesmodel.h"

#include "core/messagesmodelcache.h"
#include "database/databasefactory.h"
#include "database/databasequeries.h"
#include "definitions/definitions.h"
#include "miscellaneous/application.h"
#include "miscellaneous/iconfactory.h"
#include "miscellaneous/skinfactory.h"
#include "miscellaneous/textfactory.h"
#include "services/abstract/recyclebin.h"
#include "services/abstract/serviceroot.h"

#include <QPainter>
#include <QPainterPath>
#include <QSqlError>
#include <QSqlField>

#include <cmath>

MessagesModel::MessagesModel(QObject* parent)
  : QSqlQueryModel(parent), m_cache(new MessagesModelCache(this)), m_messageHighlighter(MessageHighlighter::NoHighlighting),
  m_customDateFormat(QString()), m_selectedItem(nullptr), m_itemHeight(-1), m_displayFeedIcons(false) {
  setupFonts();
  setupIcons();
  setupHeaderData();
  updateDateFormat();
  updateFeedIconsDisplay();
  loadMessages(nullptr);
}

MessagesModel::~MessagesModel() {
  qDebugNN << LOGSEC_MESSAGEMODEL << "Destroying MessagesModel instance.";
}

void MessagesModel::setupIcons() {
  m_favoriteIcon = qApp->icons()->fromTheme(QSL("mail-mark-important"));
  m_readIcon = qApp->icons()->fromTheme(QSL("mail-mark-read"));
  m_unreadIcon = qApp->icons()->fromTheme(QSL("mail-mark-unread"));
  m_enclosuresIcon = qApp->icons()->fromTheme(QSL("mail-attachment"));

  for (int i = int(MSG_SCORE_MIN); i <= int(MSG_SCORE_MAX); i += 10) {
    m_scoreIcons.append(generateIconForScore(double(i)));
  }
}

QIcon MessagesModel::generateIconForScore(double score) {
  QPixmap pix(64, 64);
  QPainter paint(&pix);

  paint.setRenderHint(QPainter::RenderHint::Antialiasing);

  int level = std::min(MSG_SCORE_MAX, std::max(MSG_SCORE_MIN, std::floor(score / 10.0)));
  QPainterPath path;

  path.addRoundedRect(QRectF(2, 2, 60, 60), 5, 5);

  QPen pen(Qt::GlobalColor::black, 2);

  paint.setPen(pen);
  paint.fillPath(path, Qt::GlobalColor::white);
  paint.drawPath(path);

#if QT_VERSION >= 0x050D00 // Qt >= 5.13.0
  path.clear();
#else
  path = QPainterPath();
#endif

  paint.setPen(Qt::GlobalColor::transparent);

  int bar_height = 6 * level;

  path.addRoundedRect(QRectF(2, 64 - bar_height - 2, 60, bar_height), 5, 5);
  paint.fillPath(path, QColor::fromHsv(int(score), 200, 230));

  return pix;
}

MessagesModelCache* MessagesModel::cache() const {
  return m_cache;
}

void MessagesModel::repopulate() {
  m_cache->clear();
  setQuery(selectStatement(), m_db);

  if (lastError().isValid()) {
    qCriticalNN << LOGSEC_MESSAGEMODEL << "Error when setting new msg view query: '" << lastError().text() << "'.";
    qCriticalNN << LOGSEC_MESSAGEMODEL << "Used SQL select statement: '" << selectStatement() << "'.";
  }

  while (canFetchMore()) {
    fetchMore();
  }

  qDebugNN << LOGSEC_MESSAGEMODEL
           << "Repopulated model, SQL statement is now:\n"
           << QUOTE_W_SPACE_DOT(selectStatement());
}

bool MessagesModel::setData(const QModelIndex& index, const QVariant& value, int role) {
  Q_UNUSED(role)
  m_cache->setData(index, value, record(index.row()));
  return true;
}

void MessagesModel::setupFonts() {
  QFont fon;

  fon.fromString(qApp->settings()->value(GROUP(Messages), Messages::ListFont, Application::font("MessagesView").toString()).toString());

  m_normalFont = fon;
  m_boldFont = m_normalFont;
  m_boldFont.setBold(true);
  m_normalStrikedFont = m_normalFont;
  m_boldStrikedFont = m_boldFont;
  m_normalStrikedFont.setStrikeOut(true);
  m_boldStrikedFont.setStrikeOut(true);

  m_itemHeight = qApp->settings()->value(GROUP(GUI), SETTING(GUI::HeightRowMessages)).toInt();

  if (m_itemHeight > 0) {
    m_boldFont.setPixelSize(int(m_itemHeight * 0.6));
    m_normalFont.setPixelSize(int(m_itemHeight * 0.6));
    m_boldStrikedFont.setPixelSize(int(m_itemHeight * 0.6));
    m_normalStrikedFont.setPixelSize(int(m_itemHeight * 0.6));
  }
}

void MessagesModel::loadMessages(RootItem* item) {
  m_selectedItem = item;

  if (item == nullptr) {
    setFilter(QSL(DEFAULT_SQL_MESSAGES_FILTER));
  }
  else {
    if (!item->getParentServiceRoot()->loadMessagesForItem(item, this)) {
      setFilter(QSL(DEFAULT_SQL_MESSAGES_FILTER));
      qCriticalNN << LOGSEC_MESSAGEMODEL
                  << "Loading of messages from item '"
                  << item->title() << "' failed.";
      qApp->showGuiMessage(Notification::Event::GeneralEvent,
                           tr("Loading of articles from item '%1' failed.").arg(item->title()),
                           tr("Loading of articles failed, maybe messages could not be downloaded."),
                           QSystemTrayIcon::MessageIcon::Critical,
                           true);
    }
  }

  repopulate();
}

bool MessagesModel::setMessageImportantById(int id, RootItem::Importance important) {
  for (int i = 0; i < rowCount(); i++) {
    int found_id = data(i, MSG_DB_ID_INDEX, Qt::EditRole).toInt();

    if (found_id == id) {
      bool set = setData(index(i, MSG_DB_IMPORTANT_INDEX), int(important));

      if (set) {
        emit dataChanged(index(i, 0), index(i, MSG_DB_CUSTOM_HASH_INDEX));
      }

      return set;
    }
  }

  return false;
}

void MessagesModel::highlightMessages(MessagesModel::MessageHighlighter highlight) {
  m_messageHighlighter = highlight;
  emit layoutAboutToBeChanged();
  emit layoutChanged();
}

int MessagesModel::messageId(int row_index) const {
  return data(row_index, MSG_DB_ID_INDEX, Qt::EditRole).toInt();
}

RootItem::Importance MessagesModel::messageImportance(int row_index) const {
  return RootItem::Importance(data(row_index, MSG_DB_IMPORTANT_INDEX, Qt::EditRole).toInt());
}

RootItem* MessagesModel::loadedItem() const {
  return m_selectedItem;
}

void MessagesModel::updateDateFormat() {
  if (qApp->settings()->value(GROUP(Messages), SETTING(Messages::UseCustomDate)).toBool()) {
    m_customDateFormat = qApp->settings()->value(GROUP(Messages), SETTING(Messages::CustomDateFormat)).toString();
  }
  else {
    m_customDateFormat = QString();
  }
}

void MessagesModel::updateFeedIconsDisplay() {
  m_displayFeedIcons = qApp->settings()->value(GROUP(Messages), SETTING(Messages::DisplayFeedIconsInList)).toBool();
}

void MessagesModel::reloadWholeLayout() {
  emit layoutAboutToBeChanged();
  emit layoutChanged();
}

Message MessagesModel::messageAt(int row_index) const {
  return Message::fromSqlRecord(m_cache->containsData(row_index) ? m_cache->record(row_index) : record(row_index));
}

void MessagesModel::setupHeaderData() {
  m_headerData <<

    /*: Tooltip for ID of message.*/ tr("Id") <<

    /*: Tooltip for "read" column in msg list.*/ tr("Read") <<

    /*: Tooltip for "important" column in msg list.*/ tr("Important") <<

    /*: Tooltip for "deleted" column in msg list.*/ tr("Deleted") <<

    /*: Tooltip for "pdeleted" column in msg list.*/ tr("Permanently deleted") <<

    /*: Tooltip for custom ID of feed of message.*/ tr("Feed ID") <<

    /*: Tooltip for title of message.*/ tr("Title") <<

    /*: Tooltip for url of message.*/ tr("Url") <<

    /*: Tooltip for author of message.*/ tr("Author") <<

    /*: Tooltip for creation date of message.*/ tr("Date") <<

    /*: Tooltip for contents of message.*/ tr("Contents") <<

    /*: Tooltip for attachments of message.*/ tr("Attachments") <<

    /*: Tooltip for score of message.*/ tr("Score") <<

    /*: Tooltip for account ID of message.*/ tr("Account ID") <<

    /*: Tooltip for custom ID of message.*/ tr("Custom ID") <<

    /*: Tooltip for custom hash string of message.*/ tr("Custom hash") <<

    /*: Tooltip for name of feed for message.*/ tr("Feed") <<

    /*: Tooltip for indication of presence of enclosures.*/ tr("Has enclosures");

  m_tooltipData
    << tr("ID of the article.")
    << tr("Is article read?")
    << tr("Is article important?")
    << tr("Is article deleted?")
    << tr("Is article permanently deleted from recycle bin?")
    << tr("ID of feed which this article belongs to.")
    << tr("Title of the article.")
    << tr("Url of the article.")
    << tr("Author of the article.")
    << tr("Creation date of the article.")
    << tr("Contents of the article.")
    << tr("List of attachments.")
    << tr("Score of the article.")
    << tr("Account ID of the article.")
    << tr("Custom ID of the article")
    << tr("Custom hash of the article.")
    << tr("Custom ID of feed of the article.")
    << tr("Indication of enclosures presence within the article.");
}

Qt::ItemFlags MessagesModel::flags(const QModelIndex& index) const {
  Q_UNUSED(index)
  return Qt::ItemIsSelectable | Qt::ItemIsEnabled | Qt::ItemIsEditable | Qt::ItemNeverHasChildren;
}

QList<Message> MessagesModel::messagesAt(const QList<int>& row_indices) const {
  QList<Message> msgs; msgs.reserve(row_indices.size());

  for (int idx : row_indices) {
    msgs << messageAt(idx);
  }

  return msgs;
}

QVariant MessagesModel::data(int row, int column, int role) const {
  return data(index(row, column), role);
}

QVariant MessagesModel::data(const QModelIndex& idx, int role) const {
  // This message is not in cache, return real data from live query.
  switch (role) {
    // Human readable data for viewing.
    case Qt::ItemDataRole::DisplayRole: {
      int index_column = idx.column();

      if (index_column == MSG_DB_DCREATED_INDEX) {
        QDateTime dt = TextFactory::parseDateTime(QSqlQueryModel::data(idx, role).value<qint64>()).toLocalTime();

        if (m_customDateFormat.isEmpty()) {
          return QLocale().toString(dt, QLocale::FormatType::ShortFormat);
        }
        else {
          return dt.toString(m_customDateFormat);
        }
      }
      else if (index_column == MSG_DB_CONTENTS_INDEX) {
        // Do not display full contents here.
        QString contents = data(idx, Qt::EditRole).toString().mid(0, 64).simplified() + QL1S("...");

        return contents;
      }
      else if (index_column == MSG_DB_AUTHOR_INDEX) {
        const QString author_name = QSqlQueryModel::data(idx, role).toString();

        return author_name.isEmpty() ? QSL("-") : author_name;
      }
      else if (index_column != MSG_DB_IMPORTANT_INDEX &&
               index_column != MSG_DB_READ_INDEX &&
               index_column != MSG_DB_HAS_ENCLOSURES &&
               index_column != MSG_DB_SCORE_INDEX) {
        return QSqlQueryModel::data(idx, role);
      }
      else {
        return QVariant();
      }
    }

    case LOWER_TITLE_ROLE:
      return m_cache->containsData(idx.row())
          ? m_cache->data(idx).toString().toLower()
          : QSqlQueryModel::data(idx, Qt::ItemDataRole::EditRole).toString().toLower();

    case Qt::ItemDataRole::EditRole:
      return m_cache->containsData(idx.row())
          ? m_cache->data(idx)
          : QSqlQueryModel::data(idx, role);

    case Qt::ItemDataRole::ToolTipRole: {
      if (!qApp->settings()->value(GROUP(Feeds), SETTING(Feeds::EnableTooltipsFeedsMessages)).toBool()) {
        return QVariant();
      }
      else {
        if (idx.column() == MSG_DB_SCORE_INDEX) {
          return data(idx, Qt::ItemDataRole::EditRole);
        }
        else {
          return data(idx, Qt::ItemDataRole::DisplayRole);
        }
      }
    }

    case Qt::ItemDataRole::FontRole: {
      QModelIndex idx_read = index(idx.row(), MSG_DB_READ_INDEX);
      QVariant data_read = data(idx_read, Qt::ItemDataRole::EditRole);
      const bool is_bin = qobject_cast<RecycleBin*>(loadedItem()) != nullptr;
      bool is_deleted;

      if (is_bin) {
        QModelIndex idx_del = index(idx.row(), MSG_DB_PDELETED_INDEX);

        is_deleted = data(idx_del, Qt::ItemDataRole::EditRole).toBool();
      }
      else {
        QModelIndex idx_del = index(idx.row(), MSG_DB_DELETED_INDEX);

        is_deleted = data(idx_del, Qt::ItemDataRole::EditRole).toBool();
      }

      const bool striked = is_deleted;

      if (data_read.toBool()) {
        return striked ? m_normalStrikedFont : m_normalFont;
      }
      else {
        return striked ? m_boldStrikedFont : m_boldFont;
      }
    }

    case Qt::ItemDataRole::ForegroundRole:
      switch (m_messageHighlighter) {
        case MessageHighlighter::HighlightImportant: {
          QModelIndex idx_important = index(idx.row(), MSG_DB_IMPORTANT_INDEX);
          QVariant dta = m_cache->containsData(idx_important.row()) ? m_cache->data(idx_important) : QSqlQueryModel::data(idx_important);

          return dta.toInt() == 1 ? qApp->skins()->currentSkin().m_colorPalette[Skin::PaletteColors::Highlight] : QVariant();
        }

        case MessageHighlighter::HighlightUnread: {
          QModelIndex idx_read = index(idx.row(), MSG_DB_READ_INDEX);
          QVariant dta = m_cache->containsData(idx_read.row()) ? m_cache->data(idx_read) : QSqlQueryModel::data(idx_read);

          return dta.toInt() == 0 ? qApp->skins()->currentSkin().m_colorPalette[Skin::PaletteColors::Highlight] : QVariant();
        }

        case MessageHighlighter::NoHighlighting:
        default:
          return QVariant();
      }

    case Qt::ItemDataRole::DecorationRole: {
      const int index_column = idx.column();

      if (index_column == MSG_DB_READ_INDEX) {
        if (m_displayFeedIcons && m_selectedItem != nullptr) {
          QModelIndex idx_feedid = index(idx.row(), MSG_DB_FEED_CUSTOM_ID_INDEX);
          QVariant dta = m_cache->containsData(idx_feedid.row())
                           ? m_cache->data(idx_feedid)
                           : QSqlQueryModel::data(idx_feedid);
          QString feed_custom_id = dta.toString();
          auto acc = m_selectedItem->getParentServiceRoot()->feedIconForMessage(feed_custom_id);

          if (acc.isNull()) {
            return qApp->icons()->fromTheme(QSL("application-rss+xml"));
          }
          else {
            return acc;
          }
        }
        else {
          QModelIndex idx_read = index(idx.row(), MSG_DB_READ_INDEX);
          QVariant dta = m_cache->containsData(idx_read.row()) ? m_cache->data(idx_read) : QSqlQueryModel::data(idx_read);

          return dta.toInt() == 1 ? m_readIcon : m_unreadIcon;
        }
      }
      else if (index_column == MSG_DB_IMPORTANT_INDEX) {
        QModelIndex idx_important = index(idx.row(), MSG_DB_IMPORTANT_INDEX);
        QVariant dta = m_cache->containsData(idx_important.row()) ? m_cache->data(idx_important) : QSqlQueryModel::data(idx_important);

        return dta.toInt() == 1 ? m_favoriteIcon : QVariant();
      }
      else if (index_column == MSG_DB_HAS_ENCLOSURES) {
        QModelIndex idx_important = index(idx.row(), MSG_DB_HAS_ENCLOSURES);
        QVariant dta = QSqlQueryModel::data(idx_important);

        return dta.toBool() ? m_enclosuresIcon : QVariant();
      }
      else if (index_column == MSG_DB_SCORE_INDEX) {
        QVariant dta = QSqlQueryModel::data(idx);
        int level = std::min(MSG_SCORE_MAX, std::max(MSG_SCORE_MIN, std::floor(dta.toDouble() / 10.0)));

        return m_scoreIcons.at(level);
      }
      else {
        return QVariant();
      }
    }

    default:
      return QVariant();
  }
}

bool MessagesModel::setMessageRead(int row_index, RootItem::ReadStatus read) {
  if (data(row_index, MSG_DB_READ_INDEX, Qt::EditRole).toInt() == int(read)) {
    // Read status is the same is the one currently set.
    // In that case, no extra work is needed.
    return true;
  }

  Message message = messageAt(row_index);

  if (!m_selectedItem->getParentServiceRoot()->onBeforeSetMessagesRead(m_selectedItem, QList<Message>() << message, read)) {
    // Cannot change read status of the item. Abort.
    return false;
  }

  // Rewrite "visible" data in the model.
  bool working_change = setData(index(row_index, MSG_DB_READ_INDEX), int(read));

  if (!working_change) {
    // If rewriting in the model failed, then cancel all actions.
    qDebug("Setting of new data to the model failed for message read change.");
    return false;
  }

  if (DatabaseQueries::markMessagesReadUnread(m_db, QStringList() << QString::number(message.m_id), read)) {
    return m_selectedItem->getParentServiceRoot()->onAfterSetMessagesRead(m_selectedItem, QList<Message>() << message, read);
  }
  else {
    return false;
  }
}

bool MessagesModel::setMessageReadById(int id, RootItem::ReadStatus read) {
  for (int i = 0; i < rowCount(); i++) {
    int found_id = data(i, MSG_DB_ID_INDEX, Qt::EditRole).toInt();

    if (found_id == id) {
      bool set = setData(index(i, MSG_DB_READ_INDEX), int(read));

      if (set) {
        emit dataChanged(index(i, 0), index(i, MSG_DB_CUSTOM_HASH_INDEX));
      }

      return set;
    }
  }

  return false;
}

bool MessagesModel::switchMessageImportance(int row_index) {
  const QModelIndex target_index = index(row_index, MSG_DB_IMPORTANT_INDEX);
  const RootItem::Importance current_importance = (RootItem::Importance) data(target_index, Qt::EditRole).toInt();
  const RootItem::Importance next_importance = current_importance == RootItem::Importance::Important
                                               ? RootItem::Importance::NotImportant
                                               : RootItem::Importance::Important;
  const Message message = messageAt(row_index);
  const QPair<Message, RootItem::Importance> pair(message, next_importance);

  if (!m_selectedItem->getParentServiceRoot()->onBeforeSwitchMessageImportance(m_selectedItem,
                                                                               QList<QPair<Message, RootItem::Importance>>() << pair)) {
    return false;
  }

  // Rewrite "visible" data in the model.
  const bool working_change = setData(target_index, int(next_importance));

  if (!working_change) {
    // If rewriting in the model failed, then cancel all actions.
    qDebugNN << LOGSEC_MESSAGEMODEL << "Setting of new data to the model failed for message importance change.";
    return false;
  }

  // Commit changes.
  if (DatabaseQueries::markMessageImportant(m_db, message.m_id, next_importance)) {
    emit dataChanged(index(row_index, 0), index(row_index, MSG_DB_FEED_CUSTOM_ID_INDEX), QVector<int>() << Qt::FontRole);

    return m_selectedItem->getParentServiceRoot()->onAfterSwitchMessageImportance(m_selectedItem,
                                                                                  QList<QPair<Message, RootItem::Importance>>() << pair);
  }
  else {
    return false;
  }
}

bool MessagesModel::switchBatchMessageImportance(const QModelIndexList& messages) {
  QStringList message_ids; message_ids.reserve(messages.size());
  QList<QPair<Message, RootItem::Importance>> message_states; message_states.reserve(messages.size());

  // Obtain IDs of all desired messages.
  for (const QModelIndex& message : messages) {
    const Message msg = messageAt(message.row());

    RootItem::Importance message_importance = messageImportance((message.row()));

    message_states.append(QPair<Message, RootItem::Importance>(msg, message_importance == RootItem::Importance::Important
                                                               ? RootItem::Importance::NotImportant
                                                               : RootItem::Importance::Important));
    message_ids.append(QString::number(msg.m_id));
    QModelIndex idx_msg_imp = index(message.row(), MSG_DB_IMPORTANT_INDEX);

    setData(idx_msg_imp, message_importance == RootItem::Importance::Important
            ? int(RootItem::Importance::NotImportant)
            : int(RootItem::Importance::Important));
  }

  reloadWholeLayout();

  if (!m_selectedItem->getParentServiceRoot()->onBeforeSwitchMessageImportance(m_selectedItem, message_states)) {
    return false;
  }

  if (DatabaseQueries::switchMessagesImportance(m_db, message_ids)) {
    return m_selectedItem->getParentServiceRoot()->onAfterSwitchMessageImportance(m_selectedItem, message_states);
  }
  else {
    return false;
  }
}

bool MessagesModel::setBatchMessagesDeleted(const QModelIndexList& messages) {
  QStringList message_ids; message_ids.reserve(messages.size());
  QList<Message> msgs; msgs.reserve(messages.size());

  // Obtain IDs of all desired messages.
  for (const QModelIndex& message : messages) {
    const Message msg = messageAt(message.row());

    msgs.append(msg);
    message_ids.append(QString::number(msg.m_id));

    if (qobject_cast<RecycleBin*>(m_selectedItem) != nullptr) {
      setData(index(message.row(), MSG_DB_PDELETED_INDEX), 1);
    }
    else {
      setData(index(message.row(), MSG_DB_DELETED_INDEX), 1);
    }
  }

  reloadWholeLayout();

  if (!m_selectedItem->getParentServiceRoot()->onBeforeMessagesDelete(m_selectedItem, msgs)) {
    return false;
  }

  bool deleted;

  if (m_selectedItem->kind() != RootItem::Kind::Bin) {
    deleted = DatabaseQueries::deleteOrRestoreMessagesToFromBin(m_db, message_ids, true);
  }
  else {
    deleted = DatabaseQueries::permanentlyDeleteMessages(m_db, message_ids);
  }

  if (deleted) {
    return m_selectedItem->getParentServiceRoot()->onAfterMessagesDelete(m_selectedItem, msgs);
  }
  else {
    return false;
  }
}

bool MessagesModel::setBatchMessagesRead(const QModelIndexList& messages, RootItem::ReadStatus read) {
  QStringList message_ids; message_ids.reserve(messages.size());
  QList<Message> msgs; msgs.reserve(messages.size());

  // Obtain IDs of all desired messages.
  for (const QModelIndex& message : messages) {
    Message msg = messageAt(message.row());

    msgs.append(msg);
    message_ids.append(QString::number(msg.m_id));
    setData(index(message.row(), MSG_DB_READ_INDEX), int(read));
  }

  reloadWholeLayout();

  if (!m_selectedItem->getParentServiceRoot()->onBeforeSetMessagesRead(m_selectedItem, msgs, read)) {
    return false;
  }

  if (DatabaseQueries::markMessagesReadUnread(m_db, message_ids, read)) {
    return m_selectedItem->getParentServiceRoot()->onAfterSetMessagesRead(m_selectedItem, msgs, read);
  }
  else {
    return false;
  }
}

bool MessagesModel::setBatchMessagesRestored(const QModelIndexList& messages) {
  QStringList message_ids; message_ids.reserve(messages.size());
  QList<Message> msgs; msgs.reserve(messages.size());

  // Obtain IDs of all desired messages.
  for (const QModelIndex& message : messages) {
    const Message msg = messageAt(message.row());

    msgs.append(msg);
    message_ids.append(QString::number(msg.m_id));
    setData(index(message.row(), MSG_DB_PDELETED_INDEX), 0);
    setData(index(message.row(), MSG_DB_DELETED_INDEX), 0);
  }

  reloadWholeLayout();

  if (!m_selectedItem->getParentServiceRoot()->onBeforeMessagesRestoredFromBin(m_selectedItem, msgs)) {
    return false;
  }

  if (DatabaseQueries::deleteOrRestoreMessagesToFromBin(m_db, message_ids, false)) {
    return m_selectedItem->getParentServiceRoot()->onAfterMessagesRestoredFromBin(m_selectedItem, msgs);
  }
  else {
    return false;
  }
}

QVariant MessagesModel::headerData(int section, Qt::Orientation orientation, int role) const {
  Q_UNUSED(orientation)

  switch (role) {
    case Qt::DisplayRole:

      // Display textual headers for all columns except "read" and
      // "important" and "has enclosures" columns.
      if (section != MSG_DB_READ_INDEX &&
          section != MSG_DB_IMPORTANT_INDEX &&
          section != MSG_DB_SCORE_INDEX &&
          section != MSG_DB_HAS_ENCLOSURES) {
        return m_headerData.at(section);
      }
      else {
        return QVariant();
      }

    case Qt::ToolTipRole:
      return m_tooltipData.at(section);

    case Qt::EditRole:
      return m_headerData.at(section);

    // Display icons for "read" and "important" columns.
    case Qt::DecorationRole: {
      switch (section) {
        case MSG_DB_HAS_ENCLOSURES:
          return m_enclosuresIcon;

        case MSG_DB_READ_INDEX:
          return m_readIcon;

        case MSG_DB_IMPORTANT_INDEX:
          return m_favoriteIcon;

        case MSG_DB_SCORE_INDEX:
          return m_scoreIcons.at(5);

        default:
          return QVariant();
      }
    }

    default:
      return QVariant();
  }
}
