project-kyoku/core/shared/core/timeline.h

#pragma once

#include <vector>
#include <memory>
#include <algorithm>

#include "tools/mathutils.h"
#include "core/note.h"

template <class TNote, class = std::enable_if_t<std::is_base_of<Note, TNote>::value>>
class Timeline
{
public:
    explicit Timeline() :
        _current_offset(0)
    {}

    typedef typename std::vector<TNote*>::const_iterator Iterator;

    void setNotes(const std::vector<TNote*>& notes, const microsec& visibility)
    {
        _visibility_offset = visibility;
        _timeline = std::move(notes);

        _top_note = _timeline.begin();
        expire(_first_visible_note);
        expire(_last_visible_note);
        expire(_active_note);

        fetchVisibleNotes();
    }

    inline void clear()
    {
        for (auto& note : _timeline)
            delete note;

        _timeline.clear();
    }

    void update(const microsec& offset)
    {
        _current_offset = offset;

        checkCurrentActiveNote();
        checkForNextActiveNote();
        updateVisibleSprites(_current_offset);
    }

    void drawVisibleNotes() const
    {
        if (nothingToDraw())
            return;

        std::for_each(_first_visible_note, _last_visible_note,
                      [](const auto& note)
                      {
                          note->draw();
                      });
    }

    void fetchVisibleNotes()
    {
        findLastVisibleNote(_current_offset);
        findFirstVisibleNote();
    }

    void findLastVisibleNote(const microsec& music_offset)
    {
        Iterator note_iterator = _top_note;
        while (isVisiblyClose(note_iterator, music_offset))
        {
            if (nothingToDraw())
                _first_visible_note = note_iterator;

            auto note = *note_iterator;

            if (!note->isInGame())
                note->putToGame(music_offset);

            ++note_iterator;
        }

        _last_visible_note = note_iterator;
    }

    void findFirstVisibleNote()
    {
        if (nothingToDraw())
            return;

        auto note_iterator = _first_visible_note;
        while (note_iterator != _last_visible_note)
        {
            auto note = *note_iterator;
            if (note->shouldRemove())
                ++_first_visible_note;

            ++note_iterator;
        }
    }

    inline Iterator getActiveNote() noexcept
    {
        return _active_note;
    }

    inline bool isExpired(const Iterator& iterator) const
    {
        return iterator == _timeline.end();
    }

    inline void expire(Iterator& iterator)
    {
        iterator = _timeline.end();
    }

private:
    std::vector<microsec> _input_intervals;
    std::vector<TNote*> _timeline;
    microsec _visibility_offset;
    microsec _current_offset;

    void updateVisibleSprites(const microsec& music_offset)
    {
        if (nothingToDraw())
            return;

        std::for_each(_first_visible_note, _last_visible_note,
                      [&music_offset](const auto& note)
                      {
                          note->update(music_offset);
                      });
    }

    void checkCurrentActiveNote()
    {
        if (isExpired(_active_note))
            return;

        auto note = *_active_note;

        if (!note->isActive())
        {
            expire(_active_note);
            ++_top_note;
        }
    }

    void checkForNextActiveNote()
    {
        if (!isExpired(_active_note))
            return;

        auto top_note = *_top_note;
        if (top_note->isActive())
            _active_note = _top_note;
    }

    inline bool isVisiblyClose(const Iterator& iterator, const microsec& music_offset) const
    {
        return ((*iterator)->offset() - _visibility_offset) <= music_offset;
    }

    inline bool nothingToDraw() const noexcept
    {
        return isExpired(_first_visible_note);
    }

    /* Difference between top and active note is that
     * top note is the note handling input right now
     * OR it's the closest note from current music offset
     * position, not necessarily active. A note stops being top only
     * after dying or being tapped by player, even if it's already
     * past her perfect offset.
     *
     * Meanwhile active note is the note which is currently handling
     *     player input for grade.
     *
     * An active note is always top note but a top note
     *    is not always active note.
     *                                         */

    Iterator _top_note;
    Iterator _active_note;
    Iterator _last_visible_note;
    Iterator _first_visible_note;
};