text: ////////////////////////////////////////////////////////////////////////////////
  //
  // Copyright 2016 - 2021, Thomas Lauf, Paul Beckingham, Federico Hernandez.
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included
  // in all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  // OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  // THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  // SOFTWARE.
  //
  // https://www.opensource.org/licenses/mit-license.php
  //
  ////////////////////////////////////////////////////////////////////////////////
  
  #include <cmake.h>
  #include <cassert>
  #include <commands.h>
  #include <format.h>
  #include <timew.h>
  #include <iostream>
  #include <stdlib.h>
  #include <IntervalFilterAllWithIds.h>
  #include <IntervalFilterAllInRange.h>
  #include <IntervalFilterFirstOf.h>
  
  ////////////////////////////////////////////////////////////////////////////////
  int CmdTag (
    const CLI& cli,
    Rules& rules,
    Database& database,
    Journal& journal)
  {
    const bool verbose = rules.getBoolean ("verbose");
  
    // Gather IDs and TAGs.
    std::set <int> ids = cli.getIds ();
    std::vector<std::string> tags = cli.getTags ();
  
    if (tags.empty ())
    {
      throw std::string ("At least one tag must be specified. See 'timew help tag'.");
    }
  
    journal.startTransaction ();
  
    flattenDatabase (database, rules);
    std::vector <Interval> intervals;
  
    if (ids.empty ())
    {
      IntervalFilterFirstOf filtering {std::make_shared <IntervalFilterAllInRange> (Range {})};
      auto latest = getTracked (database, rules, filtering);
  
      if (latest.empty ())
      {
        throw std::string ("There is no active time tracking.");
      }
      else if (!latest.at (0).is_open ())
      {
        throw std::string ("At least one ID must be specified. See 'timew help tag'.");
      }
  
      intervals = latest;
    }
    else
    {
      auto filtering = IntervalFilterAllWithIds (ids);
      intervals = getTracked (database, rules, filtering);
  
      if (intervals.size () != ids.size ())
      {
        for (auto& id: ids)
        {
          bool found = false;
  
          for (auto& interval: intervals)
          {
            if (interval.id == id)
            {
              found = true;
              break;
            }
          }
          if (!found)
          {
            throw format ("ID '@{1}' does not correspond to any tracking.", id);
          }
        }
      }
    }
  
    // Apply tags to intervals.
    for (const auto& interval : intervals)
    {
      Interval modified {interval};
  
      for (auto& tag : tags)
      {
        modified.tag (tag);
      }
  
      database.modifyInterval (interval, modified, verbose);
  
      if (verbose)
      {
        std::cout << "Added " << joinQuotedIfNeeded (" ", tags) << " to @" << interval.id << '\n';
      }
    }
  
    journal.endTransaction ();
  
    return 0;
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  