/*
    This file is part of darktable,
    Copyright (C) 2020-2023 darktable developers.

    darktable is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    darktable is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with darktable.  If not, see <http://www.gnu.org/licenses/>.
*/

/** a class to manage a collection of zoomable thumbnails for culling
 * or full preview.  */

#include "dtgtk/culling.h"
#include "common/collection.h"
#include "common/debug.h"
#include "common/selection.h"
#include "control/control.h"
#include "gui/gtk.h"
#include "views/view.h"

#define FULL_PREVIEW_IN_MEMORY_LIMIT 9
#define ZOOM_MAX 100000.0f

static inline float _absmul(float a, float b)
{
  return a > b ? a / b : b / a;
}

static inline int _get_max_in_memory_images()
{
  const int max_in_memory_images =
    dt_conf_get_int("plugins/lighttable/preview/max_in_memory_images");
  return MIN(max_in_memory_images, FULL_PREVIEW_IN_MEMORY_LIMIT);
}

static void _list_remove_thumb(gpointer user_data)
{
  dt_thumbnail_t *thumb = (dt_thumbnail_t *)user_data;
  gtk_container_remove(GTK_CONTAINER(gtk_widget_get_parent(thumb->w_main)), thumb->w_main);
  dt_thumbnail_destroy(thumb);
}

// get imgid from rowid
static dt_imgid_t _thumb_get_imgid(int rowid)
{
  dt_imgid_t id = NO_IMGID;
  sqlite3_stmt *stmt;
  gchar *query = g_strdup_printf
    ("SELECT imgid"
     " FROM memory.collected_images"
     " WHERE rowid=%d", rowid);
  DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
  if(sqlite3_step(stmt) == SQLITE_ROW)
  {
    id = sqlite3_column_int(stmt, 0);
  }
  g_free(query);
  sqlite3_finalize(stmt);
  return id;
}
// get rowid from imgid
static int _thumb_get_rowid(dt_imgid_t imgid)
{
  dt_imgid_t id = NO_IMGID;
  sqlite3_stmt *stmt;
  gchar *query = g_strdup_printf
    ("SELECT rowid"
     " FROM memory.collected_images"
     " WHERE imgid=%d", imgid);
  DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
  if(sqlite3_step(stmt) == SQLITE_ROW)
  {
    id = sqlite3_column_int(stmt, 0);
  }
  g_free(query);
  sqlite3_finalize(stmt);
  return id;
}

// compute thumb_size, thumbs_per_row and rows for the current widget size
// return TRUE if something as changed (or forced) FALSE otherwise
static gboolean _compute_sizes(dt_culling_t *table, const gboolean force)
{
  gboolean ret = FALSE; // return value to show if something as changed
  GtkAllocation allocation;
  gtk_widget_get_allocation(table->widget, &allocation);

  if(allocation.width <= 20 || allocation.height <= 20)
  {
    table->view_width = allocation.width;
    table->view_height = allocation.height;
    return FALSE;
  }

  // check the offset
  if(table->list)
  {
    dt_thumbnail_t *th = table->list->data;
    if(th->imgid != table->offset_imgid || th->display_focus != table->focus)
      ret = TRUE;
  }
  else if(dt_is_valid_imgid(table->offset_imgid))
    ret = TRUE;

  if(table->mode == DT_CULLING_MODE_CULLING)
  {
    const int npr = dt_view_lighttable_get_zoom(darktable.view_manager);

    if(force || allocation.width != table->view_width
       || allocation.height != table->view_height
       || npr != table->thumbs_count)
    {
      table->thumbs_count = npr;
      table->view_width = allocation.width;
      table->view_height = allocation.height;
      ret = TRUE;
    }
  }
  else if(table->mode == DT_CULLING_MODE_PREVIEW)
  {
    if(force
       || allocation.width != table->view_width
       || allocation.height != table->view_height)
    {
      table->thumbs_count = 1;
      table->view_width = allocation.width;
      table->view_height = allocation.height;
      ret = TRUE;
    }
  }
  return ret;
}

// set mouse_over_id to thumb under mouse or to first thumb
static void _thumbs_refocus(dt_culling_t *table)
{
  dt_imgid_t overid = NO_IMGID;

  if(table->mouse_inside)
  {
    // the exact position of the mouse
    int x = -1;
    int y = -1;
    gdk_window_get_origin(gtk_widget_get_window(table->widget), &x, &y);
    x = table->pan_x - x;
    y = table->pan_y - y;

    // which thumb is under the mouse ?
    for(GList *l = table->list; l; l = g_list_next(l))
    {
      dt_thumbnail_t *th = l->data;
      if(th->x <= x && th->x + th->width > x && th->y <= y && th->y + th->height > y)
      {
        overid = th->imgid;
        break;
      }
    }
  }

  // if overid not valid, we use the offset image
  if(!dt_is_valid_imgid(overid))
  {
    overid = table->offset_imgid;
  }

  // and we set the overid
  dt_control_set_mouse_over_id(overid);
}

static void _thumbs_move(dt_culling_t *table, const int move)
{
  if(move == 0) return;
  int new_offset = table->offset;
  // we sanintize the values to be sure to stay in the allowed collection
  if(move < 0)
  {
    if(table->navigate_inside_selection)
    {
      sqlite3_stmt *stmt;
      // clang-format off
      gchar *query = g_strdup_printf
        ("SELECT m.rowid FROM memory.collected_images as m, main.selected_images as s"
         " WHERE m.imgid=s.imgid AND m.rowid<=%d"
         " ORDER BY m.rowid DESC LIMIT 1 OFFSET %d",
         table->offset, -1 * move);
      // clang-format on
      DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
      if(sqlite3_step(stmt) == SQLITE_ROW)
      {
        new_offset = sqlite3_column_int(stmt, 0);
      }
      else
      {
        // if we are here, that means we don't have enough space to
        // move as wanted. So we move to first position
        g_free(query);
        sqlite3_finalize(stmt);
        // clang-format off
        query = g_strdup_printf
          ("SELECT m.rowid FROM memory.collected_images as m, main.selected_images as s"
           " WHERE m.imgid=s.imgid"
           " ORDER BY m.rowid LIMIT 1");
        // clang-format on
        DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
        if(sqlite3_step(stmt) == SQLITE_ROW)
        {
          new_offset = sqlite3_column_int(stmt, 0);
        }
      }
      g_free(query);
      sqlite3_finalize(stmt);
      if(new_offset == table->offset)
      {
        dt_control_log(_("you have reached the start of your selection"));
        return;
      }
    }
    else
    {
      new_offset = MAX(1, table->offset + move);
      if(new_offset == table->offset)
      {
        dt_control_log(_("you have reached the start of your collection"));
        return;
      }
    }
  }
  else
  {
    if(table->navigate_inside_selection)
    {
      sqlite3_stmt *stmt;
      // clang-format off
      gchar *query = g_strdup_printf
        ("SELECT COUNT(m.rowid)"
         " FROM memory.collected_images as m, main.selected_images as s"
         " WHERE m.imgid=s.imgid AND m.rowid>%d",
         table->offset);
      // clang-format on
      DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
      int nb_after = 0;
      if(sqlite3_step(stmt) == SQLITE_ROW)
      {
        nb_after = sqlite3_column_int(stmt, 0);
      }
      g_free(query);
      sqlite3_finalize(stmt);

      if(nb_after >= table->thumbs_count)
      {
        const int delta = MIN(nb_after + 1 - table->thumbs_count, move);
        // clang-format off
        query = g_strdup_printf
          ("SELECT m.rowid FROM memory.collected_images as m, main.selected_images as s"
           " WHERE m.imgid=s.imgid AND m.rowid>=%d"
           " ORDER BY m.rowid LIMIT 1 OFFSET %d",
           table->offset, delta);
        // clang-format on
        DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
        if(sqlite3_step(stmt) == SQLITE_ROW)
        {
          new_offset = sqlite3_column_int(stmt, 0);
        }
        g_free(query);
        sqlite3_finalize(stmt);
      }

      if(new_offset == table->offset)
      {
        dt_control_log(_("you have reached the end of your selection"));
        return;
      }
    }
    else
    {
      sqlite3_stmt *stmt;
      // clang-format off
      gchar *query = g_strdup_printf
        ("SELECT COUNT(m.rowid)"
         " FROM memory.collected_images as m"
         " WHERE m.rowid>%d",
         table->offset);
      // clang-format on
      DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
      if(sqlite3_step(stmt) == SQLITE_ROW)
      {
        const int nb = sqlite3_column_int(stmt, 0);
        if(nb >= table->thumbs_count)
        {
          new_offset = table->offset + MIN(nb + 1 - table->thumbs_count, move);
        }
      }
      g_free(query);
      sqlite3_finalize(stmt);
      if(new_offset == table->offset)
      {
        dt_control_log(_("you have reached the end of your collection"));
        return;
      }
    }
  }

  if(new_offset != table->offset)
  {
    table->offset = new_offset;
    dt_culling_full_redraw(table, TRUE);
    _thumbs_refocus(table);
  }
}

static void _set_table_zoom_ratio(dt_culling_t *table, dt_thumbnail_t *th)
{
  table->zoom_ratio = dt_thumbnail_get_zoom_ratio(th);
}

static void _get_root_offset(GtkWidget *w_image_box,
                             const float x_root,
                             const float y_root,
                             int *x_offset,
                             int *y_offset)
{
  gdk_window_get_origin(gtk_widget_get_window(w_image_box), x_offset, y_offset);
  *x_offset = x_root - *x_offset;
  *y_offset = y_root - *y_offset;
}

static gboolean _zoom_and_shift(dt_thumbnail_t *th,
                                const int x_offset,
                                const int y_offset,
                                const float zoom_delta)
{
  const float zd = CLAMP(th->zoom + zoom_delta, 1.0f, th->zoom_100);
  if(zd == th->zoom)
    return FALSE; // delta_zoom did not change this thumbnail's zoom factor

  const float z_ratio = zd / th->zoom;
  th->zoom = zd;

  int posx = x_offset;
  int posy = y_offset;

  const int iw = gtk_widget_get_allocated_width(th->w_image);
  const int ih = gtk_widget_get_allocated_height(th->w_image);

  // we center the zoom around cursor position
  if(posx >= 0 && posy >= 0)
  {
    // we take in account that the image may be smaller that the imagebox
    posx -= (gtk_widget_get_allocated_width(th->w_image_box) - iw) / 2;
    posy -= (gtk_widget_get_allocated_height(th->w_image_box) - ih) / 2;
  }

  // we change the value. Values will be sanitized in the drawing event
  th->zoomx = posx - (posx - th->zoomx) * z_ratio;
  th->zoomy = posy - (posy - th->zoomy) * z_ratio;

  dt_thumbnail_image_refresh(th);

  return TRUE;
}

static gboolean _zoom_to_x_root(dt_thumbnail_t *th,
                                const float x_root,
                                const float y_root,
                                const float zoom_delta)
{
  int x_offset = 0;
  int y_offset = 0;

  _get_root_offset(th->w_image_box, x_root, y_root, &x_offset, &y_offset);

  return _zoom_and_shift(th, x_offset, y_offset, zoom_delta);
}

static gboolean _zoom_to_center(dt_thumbnail_t *th,
                                const float zoom_delta)
{
  const float zd = CLAMP(th->zoom + zoom_delta, 1.0f, th->zoom_100);
  if(zd == th->zoom)
    return FALSE; // delta_zoom did not change this thumbnail's zoom factor

  const float z_ratio = zd / th->zoom;
  th->zoom = zd;
  // we center the zoom around center of the shown image
  int iw = 0;
  int ih = 0;
  gtk_widget_get_size_request(th->w_image_box, &iw, &ih);
  th->zoomx = fmaxf(iw - th->img_width * z_ratio,
                    fminf(0.0f, iw / 2.0 - (iw / 2.0 - th->zoomx) * z_ratio));
  th->zoomy = fmaxf(ih - th->img_height * z_ratio,
                    fminf(0.0f, ih / 2.0 - (ih / 2.0 - th->zoomy) * z_ratio));

  dt_thumbnail_image_refresh(th);

  return TRUE;
}

static gboolean _thumbs_zoom_add(dt_culling_t *table,
                                 const float zoom_delta,
                                 const float x_root,
                                 const float y_root, int state)
{
  const int max_in_memory_images = _get_max_in_memory_images();
  if(table->mode == DT_CULLING_MODE_CULLING && table->thumbs_count > max_in_memory_images)
  {
    dt_control_log(_("zooming is limited to %d images"), max_in_memory_images);
    return TRUE;
  }

  // we ensure the zoom 100 is computed for all images
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    dt_thumbnail_get_zoom100(th);
  }

  if(!g_list_shorter_than(table->list, 2))  // at least two images?
  {
    // CULLING with multiple images
    // if shift+ctrl, we only change the current image
    if(dt_modifiers_include(state, GDK_SHIFT_MASK))
    {
      const dt_imgid_t mouseid = dt_control_get_mouse_over_id();
      for(GList *l = table->list; l; l = g_list_next(l))
      {
        dt_thumbnail_t *th = l->data;
        if(th->imgid == mouseid)
        {
          if(_zoom_to_x_root(th, x_root, y_root, zoom_delta))
            _set_table_zoom_ratio(table, th);
          break;
        }
      }
    }
    else
    {
      const dt_imgid_t mouseid = dt_control_get_mouse_over_id();
      int x_offset = 0;
      int y_offset = 0;
      gboolean to_pointer = FALSE;

      // get the offset for the image under the cursor
      for(GList *l = table->list; l; l = g_list_next(l))
      {
        dt_thumbnail_t *th = l->data;
        if(th->imgid == mouseid)
        {
          _get_root_offset(th->w_image_box, x_root, y_root, &x_offset, &y_offset);
          to_pointer = TRUE;
          break;
        }
      }

      // apply the offset to all images
      for(GList *l = table->list; l; l = g_list_next(l))
      {
        dt_thumbnail_t *th = l->data;
        if(to_pointer == TRUE ? _zoom_and_shift(th, x_offset, y_offset, zoom_delta)
                              : _zoom_to_center(th, zoom_delta))
          _set_table_zoom_ratio(table, th);
      }
    }
  }
  else if(table->list)
  {
    // FULL PREVIEW or CULLING with 1 image
    dt_thumbnail_t *th = table->list->data;
    if(_zoom_to_x_root(th, x_root, y_root, zoom_delta))
      _set_table_zoom_ratio(table, th);
  }

  return TRUE;
}

static void _zoom_thumb_fit(dt_thumbnail_t *th)
{
  th->zoom = 1.0;
  th->zoomx = 0;
  th->zoomy = 0;
  dt_thumbnail_image_refresh(th);
}

static gboolean _zoom_thumb_max(dt_thumbnail_t *th,
                                const float x_root,
                                const float y_root)
{
  dt_thumbnail_get_zoom100(th);
  return _zoom_to_x_root(th, x_root, y_root, ZOOM_MAX);
}

// toggle zoom max / zoom fit of image currently having mouse over id
static void _toggle_zoom_current(dt_culling_t *table,
                                 const float x_root,
                                 const float y_root)
{
  const dt_imgid_t id = dt_control_get_mouse_over_id();
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    if(th->imgid == id)
    {
      if(th->zoom_100 < 1.0 || th->zoom < th->zoom_100)
        _zoom_thumb_max(th, x_root, y_root);
      else
        _zoom_thumb_fit(th);
      break;
    }
  }
}

// toggle zoom max / zoom fit of all images in culling table
static void _toggle_zoom_all(dt_culling_t *table,
                             const float x_root,
                             const float y_root)
{
  gboolean zmax = TRUE;
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    if(th->zoom_100 < 1.0 || th->zoom < th->zoom_100)
    {
      zmax = FALSE;
      break;
    }
  }

  if(zmax)
    dt_culling_zoom_fit(table);
  else
    _thumbs_zoom_add(table, ZOOM_MAX, x_root, y_root, 0);
}

static gboolean _event_scroll(GtkWidget *widget,
                              GdkEvent *event,
                              gpointer user_data)
{
  GdkEventScroll *e = (GdkEventScroll *)event;
  dt_culling_t *table = (dt_culling_t *)user_data;
  int delta;

  if(dt_gui_get_scroll_unit_delta(e, &delta))
  {
    if(dt_modifiers_include(e->state, GDK_CONTROL_MASK))
    {
      // zooming
      const float zoom_delta = delta < 0 ? 0.5f : -0.5f;
      _thumbs_zoom_add(table, zoom_delta, e->x_root, e->y_root, e->state);
    }
    else
    {
      const int move = delta < 0 ? -1 : 1;
      _thumbs_move(table, move);
    }
  }
  return TRUE;
}

static gboolean _event_draw(GtkWidget *widget, cairo_t *cr, gpointer user_data)
{
  if(!GTK_IS_CONTAINER(gtk_widget_get_parent(widget))) return TRUE;

  // we render the background (can be visible if before first image /
  // after last image)
  GtkStyleContext *context = gtk_widget_get_style_context(widget);
  gtk_render_background(context, cr, 0, 0, gtk_widget_get_allocated_width(widget),
                        gtk_widget_get_allocated_height(widget));

  // but we don't really want to draw something, this is just to know
  // when the widget is really ready
  dt_culling_t *table = (dt_culling_t *)user_data;
  dt_culling_full_redraw(table, FALSE);
  return FALSE; // let's propagate this event
}

static gboolean _event_leave_notify(GtkWidget *widget,
                                    GdkEventCrossing *event,
                                    gpointer user_data)
{
  dt_culling_t *table = (dt_culling_t *)user_data;
  // if the leaving cause is the hide of the widget, no mouseover change
  if(!gtk_widget_is_visible(widget))
  {
    table->mouse_inside = FALSE;
    return FALSE;
  }

  // if we leave thumbtable in favour of an inferior (a thumbnail)
  // it's not a real leave !  same if this is not a mouse move action
  // (shortcut that activate a button for example)
  if(event->detail == GDK_NOTIFY_INFERIOR || event->mode == GDK_CROSSING_GTK_GRAB
     || event->mode == GDK_CROSSING_GRAB)
    return FALSE;

  table->mouse_inside = FALSE;
  dt_control_set_mouse_over_id(NO_IMGID);
  return TRUE;
}

static gboolean _event_enter_notify(GtkWidget *widget,
                                    GdkEventCrossing *event,
                                    gpointer user_data)
{
  // we only handle the case where we enter thumbtable from an
  // inferior (a thumbnail) this is when the mouse enter an "empty"
  // area of thumbtable
  if(event->detail != GDK_NOTIFY_INFERIOR) return FALSE;

  dt_control_set_mouse_over_id(NO_IMGID);
  return TRUE;
}

static gboolean _event_button_press(GtkWidget *widget,
                                    GdkEventButton *event,
                                    gpointer user_data)
{
  dt_culling_t *table = (dt_culling_t *)user_data;

  if(event->button == GDK_BUTTON_PRIMARY && event->type == GDK_BUTTON_PRESS)
  {
    // make sure any edition field loses the focus
    gtk_widget_grab_focus(dt_ui_center(darktable.gui->ui));
  }

  if(event->button == GDK_BUTTON_MIDDLE)
  {
    // if shift is pressed, we work only with image hovered
    if(dt_modifier_is(event->state, GDK_SHIFT_MASK))
      _toggle_zoom_current(table, event->x_root, event->y_root);
    else
      _toggle_zoom_all(table, event->x_root, event->y_root);
    return TRUE;
  }

  const dt_imgid_t id = dt_control_get_mouse_over_id();

  if(dt_is_valid_imgid(id) && event->button == GDK_BUTTON_PRIMARY && event->type == GDK_2BUTTON_PRESS)
  {
    dt_view_manager_switch(darktable.view_manager, "darkroom");
    return TRUE;
  }

  table->pan_x = event->x_root;
  table->pan_y = event->y_root;
  table->panning = TRUE;
  return TRUE;
}

static gboolean _event_motion_notify(GtkWidget *widget,
                                     GdkEventMotion *event,
                                     gpointer user_data)
{
  dt_culling_t *table = (dt_culling_t *)user_data;
  table->mouse_inside = TRUE;
  if(!table->panning)
  {
    table->pan_x = event->x_root;
    table->pan_y = event->y_root;
    return FALSE;
  }

  // get the max zoom of all images
  const int max_in_memory_images = _get_max_in_memory_images();
  if(table->mode == DT_CULLING_MODE_CULLING
     && table->thumbs_count > max_in_memory_images)
    return FALSE;

  float fz = 1.0f;
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    fz = fmaxf(fz, th->zoom);
  }

  if(table->panning && fz > 1.0f)
  {
    const double x = event->x_root;
    const double y = event->y_root;
    // we want the images to stay in the screen
    const float scale = darktable.gui->ppd_thb / darktable.gui->ppd;
    const float valx = (x - table->pan_x) * scale;
    const float valy = (y - table->pan_y) * scale;

    if(dt_modifier_is(event->state, GDK_SHIFT_MASK))
    {
      const dt_imgid_t mouseid = dt_control_get_mouse_over_id();
      for(GList *l = table->list; l; l = g_list_next(l))
      {
        dt_thumbnail_t *th = l->data;
        if(th->imgid == mouseid)
        {
          th->zoomx += valx;
          th->zoomy += valy;
          break;
        }
      }
    }
    else
    {
      for(GList *l = table->list; l; l = g_list_next(l))
      {
        dt_thumbnail_t *th = l->data;
        th->zoomx += valx;
        th->zoomy += valy;
      }
    }
    // sanitize specific positions of individual images
    for(GList *l = table->list; l; l = g_list_next(l))
    {
      dt_thumbnail_t *th = l->data;
      int iw = 0;
      int ih = 0;
      gtk_widget_get_size_request(th->w_image, &iw, &ih);
      const int mindx = iw * darktable.gui->ppd_thb - th->img_width;
      const int mindy = ih * darktable.gui->ppd_thb - th->img_height;
      if(th->zoomx > 0) th->zoomx = 0;
      if(th->zoomx < mindx) th->zoomx = mindx;
      if(th->zoomy > 0) th->zoomy = 0;
      if(th->zoomy < mindy) th->zoomy = mindy;
    }

    table->pan_x = x;
    table->pan_y = y;
  }

  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    dt_thumbnail_image_refresh_position(th);
  }
  return TRUE;
}

static gboolean _event_button_release(GtkWidget *widget,
                                      GdkEventButton *event,
                                      gpointer user_data)
{
  dt_culling_t *table = (dt_culling_t *)user_data;
  table->panning = FALSE;

  const dt_imgid_t overid = dt_control_get_mouse_over_id();

  // if the act_on algorithm need a specific culling "selection",
  // we use a very simple culling-specific selection
  if(dt_act_on_use_culling_selection()
     && dt_is_valid_imgid(overid)
     && event->button == GDK_BUTTON_PRIMARY)
  {
    const dt_imgid_t old_sel = table->selection;
    if(table->selection == overid)
    {
      // this image is already selected
      // so we deselect it
      table->selection = NO_IMGID;
    }
    else
      table->selection = overid;

    // now we update the thumbnail class to reflect the selected state
    for(GList *l = table->list; l; l = g_list_next(l))
    {
      dt_thumbnail_t *th = l->data;
      if (th->imgid == old_sel)
      {
        dt_gui_remove_class(th->w_main, "dt_culling_selected");
        gtk_widget_queue_draw(th->w_main);
      }
      else if(th->imgid == table->selection)
      {
        dt_gui_add_class(th->w_main, "dt_culling_selected");
        gtk_widget_queue_draw(th->w_main);
      }
    }

    // and we reset the cache
    dt_act_on_reset_cache(TRUE);
    dt_act_on_reset_cache(FALSE);
  }

  return TRUE;
}

// called each time the preference change, to update specific parts
static void _dt_pref_change_callback(gpointer instance,
                                     gpointer user_data)
{
  if(!user_data) return;
  dt_culling_t *table = (dt_culling_t *)user_data;

  // adjust the act_on algo class if needed
  dt_act_on_set_class(table->widget);

  dt_culling_full_redraw(table, TRUE);

  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    th->overlay_timeout_duration = dt_conf_get_int("plugins/lighttable/overlay_timeout");
    dt_thumbnail_reload_infos(th);
    const float zoom_ratio = th->zoom_100 > 1 ? th->zoom / th->zoom_100 : table->zoom_ratio;
    dt_thumbnail_resize(th, th->width, th->height, TRUE, zoom_ratio);
  }
  dt_get_sysresource_level();
  dt_opencl_update_settings();
  dt_configure_ppd_dpi(darktable.gui);
}

static void _dt_selection_changed_callback(gpointer instance, gpointer user_data)
{
  if(!user_data) return;
  dt_culling_t *table = (dt_culling_t *)user_data;
  if(!gtk_widget_get_visible(table->widget)) return;

  // if we are in selection synchronisation mode, we exit this mode
  if(table->selection_sync) table->selection_sync = FALSE;

  // if we are in dynamic mode, zoom = selection count
  if(table->mode == DT_CULLING_MODE_CULLING
     && dt_view_lighttable_get_layout(darktable.view_manager)
        == DT_LIGHTTABLE_LAYOUT_CULLING_DYNAMIC)
  {
    sqlite3_stmt *stmt;
    int sel_count = 0;
    // clang-format off
    DT_DEBUG_SQLITE3_PREPARE_V2
      (dt_database_get(darktable.db),
       "SELECT count(*)"
       " FROM memory.collected_images AS col, main.selected_images as sel"
       " WHERE col.imgid=sel.imgid",
       -1, &stmt, NULL);
    // clang-format on
    if(sqlite3_step(stmt) == SQLITE_ROW) sel_count = sqlite3_column_int(stmt, 0);
    sqlite3_finalize(stmt);
    const int nz = (sel_count <= 1)
      ? dt_conf_get_int("plugins/lighttable/culling_num_images")
      : sel_count;

    dt_view_lighttable_set_zoom(darktable.view_manager, nz);
  }
  // if we navigate only in the selection we just redraw to ensure no
  // unselected image is present
  if(table->navigate_inside_selection)
  {
    dt_culling_full_redraw(table, TRUE);
    _thumbs_refocus(table);
  }
}

static void _dt_profile_change_callback(gpointer instance,
                                        const int type,
                                        gpointer user_data)
{
  if(!user_data) return;
  dt_culling_t *table = (dt_culling_t *)user_data;
  if(!gtk_widget_get_visible(table->widget)) return;

  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    dt_thumbnail_image_refresh(th);
  }
}

// this is called each time mouse_over id change
static void _dt_mouse_over_image_callback(gpointer instance, gpointer user_data)
{
  if(!user_data) return;
  dt_culling_t *table = (dt_culling_t *)user_data;
  if(!gtk_widget_get_visible(table->widget)) return;

  const dt_imgid_t imgid = dt_control_get_mouse_over_id();

  // we crawl over all images to find the right one
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    // if needed, the change mouseover value of the thumb
    if(th->mouse_over != (th->imgid == imgid))
      dt_thumbnail_set_mouseover(th, (th->imgid == imgid));
  }
}

static void _dt_filmstrip_change(gpointer instance,
                                 const dt_imgid_t imgid,
                                 gpointer user_data)
{
  if(!user_data || !dt_is_valid_imgid(imgid)) return;
  dt_culling_t *table = (dt_culling_t *)user_data;
  if(!gtk_widget_get_visible(table->widget)) return;

  table->offset = _thumb_get_rowid(imgid);
  dt_culling_full_redraw(table, TRUE);
  _thumbs_refocus(table);
}

// get the class name associated with the overlays mode
static gchar *_thumbs_get_overlays_class(dt_thumbnail_overlay_t over)
{
  switch(over)
  {
    case DT_THUMBNAIL_OVERLAYS_NONE:
      return g_strdup("dt_overlays_none");
    case DT_THUMBNAIL_OVERLAYS_HOVER_EXTENDED:
      return g_strdup("dt_overlays_hover_extended");
    case DT_THUMBNAIL_OVERLAYS_ALWAYS_NORMAL:
      return g_strdup("dt_overlays_always");
    case DT_THUMBNAIL_OVERLAYS_ALWAYS_EXTENDED:
      return g_strdup("dt_overlays_always_extended");
    case DT_THUMBNAIL_OVERLAYS_MIXED:
      return g_strdup("dt_overlays_mixed");
    case DT_THUMBNAIL_OVERLAYS_HOVER_BLOCK:
      return g_strdup("dt_overlays_hover_block");
    default:
      return g_strdup("dt_overlays_hover");
  }
}

dt_culling_t *dt_culling_new(dt_culling_mode_t mode)
{
  dt_culling_t *table = calloc(1, sizeof(dt_culling_t));
  table->mode = mode;
  table->zoom_ratio = IMG_TO_FIT;
  table->widget = gtk_layout_new(NULL, NULL);
  table->selection = NO_IMGID;
  dt_gui_add_class(table->widget, "dt_fullview");
  dt_act_on_set_class(table->widget);
  // TODO dt_gui_add_help_link(table->widget, "lighttable_filemanager");

  // overlays
  gchar *otxt = g_strdup_printf("plugins/lighttable/overlays/culling/%d", table->mode);
  table->overlays = dt_conf_get_int(otxt);
  g_free(otxt);

  gchar *cl0 = _thumbs_get_overlays_class(table->overlays);
  dt_gui_add_class(table->widget, cl0);
  free(cl0);

  otxt = g_strdup_printf("plugins/lighttable/overlays/culling_block_timeout/%d",
                         table->mode);
  table->overlays_block_timeout = 2;
  if(!dt_conf_key_exists(otxt))
    table->overlays_block_timeout = dt_conf_get_int("plugins/lighttable/overlay_timeout");
  else
    table->overlays_block_timeout = dt_conf_get_int(otxt);
  g_free(otxt);

  otxt = g_strdup_printf("plugins/lighttable/tooltips/culling/%d", table->mode);
  table->show_tooltips = dt_conf_get_bool(otxt);
  g_free(otxt);

  // set widget signals
  gtk_widget_set_events(table->widget,
                        GDK_EXPOSURE_MASK | GDK_POINTER_MOTION_MASK
                        | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK
                        | GDK_STRUCTURE_MASK
                        | GDK_ENTER_NOTIFY_MASK | GDK_LEAVE_NOTIFY_MASK);
  gtk_widget_set_app_paintable(table->widget, TRUE);
  gtk_widget_set_can_focus(table->widget, TRUE);

  g_signal_connect(G_OBJECT(table->widget), "scroll-event",
                   G_CALLBACK(_event_scroll), table);
  g_signal_connect(G_OBJECT(table->widget), "draw",
                   G_CALLBACK(_event_draw), table);
  g_signal_connect(G_OBJECT(table->widget), "leave-notify-event",
                   G_CALLBACK(_event_leave_notify), table);
  g_signal_connect(G_OBJECT(table->widget), "enter-notify-event",
                   G_CALLBACK(_event_enter_notify), table);
  g_signal_connect(G_OBJECT(table->widget), "button-press-event",
                   G_CALLBACK(_event_button_press), table);
  g_signal_connect(G_OBJECT(table->widget), "motion-notify-event",
                   G_CALLBACK(_event_motion_notify), table);
  g_signal_connect(G_OBJECT(table->widget), "button-release-event",
                   G_CALLBACK(_event_button_release), table);

  // we register globals signals
  DT_CONTROL_SIGNAL_CONNECT(DT_SIGNAL_MOUSE_OVER_IMAGE_CHANGE, _dt_mouse_over_image_callback, table);
  DT_CONTROL_SIGNAL_CONNECT(DT_SIGNAL_CONTROL_PROFILE_USER_CHANGED, _dt_profile_change_callback, table);
  DT_CONTROL_SIGNAL_CONNECT(DT_SIGNAL_PREFERENCES_CHANGE, _dt_pref_change_callback, table);
  DT_CONTROL_SIGNAL_CONNECT(DT_SIGNAL_VIEWMANAGER_THUMBTABLE_ACTIVATE, _dt_filmstrip_change, table);
  DT_CONTROL_SIGNAL_CONNECT(DT_SIGNAL_SELECTION_CHANGED, _dt_selection_changed_callback, table);

  g_object_ref(table->widget);

  return table;
}

// initialize offset, ... values
// to be used when reentering culling
void dt_culling_init(dt_culling_t *table,
                     const int fallback_offset,
                     const dt_lighttable_culling_restriction_t restriction)
{
  /** HOW it works :
   *
   * For the first image :
   *  act_on main image or fallback_offset if no image
   *
   * For the automatic detection of navigation in selection :
   *  culling dynamic mode                       => OFF (whatever the restriction value)
   *  first image in selection AND selection > 1 => ON
   *  otherwise                                  => OFF
   *
   * For the selection following :
   *  culling dynamic mode                                    => OFF
   *  first image(s) == selection && selection is continuous  => ON
   */

  // init values
  table->navigate_inside_selection = FALSE;
  table->selection_sync = FALSE;
  table->zoom_ratio = IMG_TO_FIT;
  table->view_width = 0; // in order to force a full redraw

  if(restriction == DT_LIGHTTABLE_CULLING_RESTRICTION_SELECTION)
    table->navigate_inside_selection = TRUE;

  // reset remaining zooming values if any
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *thumb = l->data;
    thumb->zoom = 1.0f;
    thumb->zoomx = 0.0;
    thumb->zoomy = 0.0;
    thumb->img_surf_dirty = TRUE;
  }

  const gboolean culling_dynamic
      = (table->mode == DT_CULLING_MODE_CULLING
         && dt_view_lighttable_get_layout(darktable.view_manager)
            == DT_LIGHTTABLE_LAYOUT_CULLING_DYNAMIC);

  // get first id
  dt_imgid_t first_id = dt_act_on_get_main_image();

  // if no new offset is available until now, we continue with the fallback one
  if(!dt_is_valid_imgid(first_id))
    first_id = _thumb_get_imgid(fallback_offset);

  // if this also fails we start at the beginning of the collection
  if(!dt_is_valid_imgid(first_id))
  {
    first_id = _thumb_get_imgid(1);
  }

  if(!dt_is_valid_imgid(first_id))
  {
    // Collection probably empty?
    return;
  }

  // selection count
  int sel_count = 0;
  sqlite3_stmt *stmt;
  // clang-format off
  DT_DEBUG_SQLITE3_PREPARE_V2
    (dt_database_get(darktable.db),
     "SELECT count(*)"
     " FROM memory.collected_images AS col, main.selected_images as sel"
     " WHERE col.imgid=sel.imgid",
     -1, &stmt, NULL);
  // clang-format on
  if(sqlite3_step(stmt) == SQLITE_ROW)
    sel_count = sqlite3_column_int(stmt, 0);
  sqlite3_finalize(stmt);

  // special culling dynamic mode
  if(culling_dynamic)
  {
    if(sel_count == 0)
    {
      dt_control_log(_("no image selected!"));
      first_id = NO_IMGID;
    }
    table->navigate_inside_selection = TRUE;
    table->offset = _thumb_get_rowid(first_id);
    table->offset_imgid = first_id;
    return;
  }

  // is first_id inside selection ?
  gboolean inside = FALSE;
  // clang-format off
  gchar *query = g_strdup_printf
    ("SELECT col.imgid"
     " FROM memory.collected_images AS col, main.selected_images AS sel"
     " WHERE col.imgid=sel.imgid AND col.imgid=%d",
     first_id);
  // clang-format on
  DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
  if(sqlite3_step(stmt) == SQLITE_ROW) inside = TRUE;
  sqlite3_finalize(stmt);
  g_free(query);

  if(table->mode == DT_CULLING_MODE_PREVIEW)
  {
    if(restriction == DT_LIGHTTABLE_CULLING_RESTRICTION_AUTO)
      table->navigate_inside_selection = (sel_count > 1 && inside);
    table->selection_sync = (sel_count == 1 && inside);
  }
  else if(table->mode == DT_CULLING_MODE_CULLING)
  {
    const int zoom = dt_view_lighttable_get_zoom(darktable.view_manager);
    // we first determine if we synchronize the selection with culling images
    table->selection_sync = FALSE;
    if(sel_count == 1 && inside)
      table->selection_sync = TRUE;
    else if(sel_count == zoom && inside)
    {
      // we ensure that the selection is continuous
      // clang-format off
      DT_DEBUG_SQLITE3_PREPARE_V2
        (dt_database_get(darktable.db),
         "SELECT MIN(rowid), MAX(rowid)"
         " FROM memory.collected_images AS col, main.selected_images as sel"
         " WHERE col.imgid=sel.imgid",
         -1, &stmt, NULL);
      // clang-format on
      if(sqlite3_step(stmt) == SQLITE_ROW)
      {
        if(sqlite3_column_int(stmt, 0) + sel_count - 1 == sqlite3_column_int(stmt, 1))
        {
          table->selection_sync = TRUE;
        }
      }
      sqlite3_finalize(stmt);
    }

    // we now determine if we limit culling images to the selection
    if(restriction == DT_LIGHTTABLE_CULLING_RESTRICTION_AUTO)
      table->navigate_inside_selection = (!table->selection_sync && inside);
  }

  table->offset = _thumb_get_rowid(first_id);
  table->offset_imgid = first_id;
}

static void _thumbs_prefetch(dt_culling_t *table)
{
  if(!table->list) return;

  // get the mip level by using the max image size actually shown
  int maxw = 0;
  int maxh = 0;
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    maxw = MAX(maxw, th->width);
    maxh = MAX(maxh, th->height);
  }
  dt_mipmap_size_t mip =
    dt_mipmap_cache_get_matching_size(maxw, maxh);

  // prefetch next image
  gchar *query;
  sqlite3_stmt *stmt;
  dt_thumbnail_t *last = g_list_last(table->list)->data;
  if(table->navigate_inside_selection)
  {
    // clang-format off
    query = g_strdup_printf
      ("SELECT m.imgid"
       " FROM memory.collected_images AS m, main.selected_images AS s"
       " WHERE m.imgid = s.imgid"
       "   AND m.rowid > %d"
       " ORDER BY m.rowid "
       " LIMIT 1",
       last->rowid);
    // clang-format on
  }
  else
  {
    // clang-format off
    query = g_strdup_printf
      ("SELECT m.imgid"
       " FROM memory.collected_images AS m "
       " WHERE m.rowid > %d"
       " ORDER BY m.rowid "
       " LIMIT 1",
       last->rowid);
    // clang-format on
  }
  DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
  if(sqlite3_step(stmt) == SQLITE_ROW)
  {
    const dt_imgid_t id = sqlite3_column_int(stmt, 0);
    if(dt_is_valid_imgid(id))
      dt_mipmap_cache_get(NULL, id, mip, DT_MIPMAP_PREFETCH, 'r');
  }
  sqlite3_finalize(stmt);
  g_free(query);

  // prefetch previous image
  dt_thumbnail_t *prev = (table->list)->data;
  if(table->navigate_inside_selection)
  {
    // clang-format off
    query = g_strdup_printf
      ("SELECT m.imgid"
       " FROM memory.collected_images AS m, main.selected_images AS s"
       " WHERE m.imgid = s.imgid"
       "   AND m.rowid < %d"
       " ORDER BY m.rowid DESC "
       " LIMIT 1",
       prev->rowid);
    // clang-format on
  }
  else
  {
    // clang-format off
    query = g_strdup_printf
      ("SELECT m.imgid"
       " FROM memory.collected_images AS m"
       " WHERE m.rowid < %d"
       " ORDER BY m.rowid DESC "
       " LIMIT 1",
       prev->rowid);
    // clang-format on
  }
  DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
  if(sqlite3_step(stmt) == SQLITE_ROW)
  {
    const dt_imgid_t id = sqlite3_column_int(stmt, 0);
    if(dt_is_valid_imgid(id))
      dt_mipmap_cache_get(NULL, id, mip, DT_MIPMAP_PREFETCH, 'r');
  }
  sqlite3_finalize(stmt);
}

static gboolean _thumbs_recreate_list_at(dt_culling_t *table,
                                         const int offset)
{
  gchar *query = NULL;
  sqlite3_stmt *stmt;

  int nw = 40;
  int nh = 40;

  // get width/height before the list is destroyed
  if(table->list)
  {
    dt_thumbnail_t *th_model = table->list->data;
    nw = th_model->width;
    nh = th_model->height;
  }

  // let's create a hashtable of table->list in order to speddup search in next loop
  GHashTable *htable = g_hash_table_new_full(g_int_hash, g_int_equal, NULL, _list_remove_thumb);
  for(const GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    g_hash_table_insert(htable, &th->imgid, (gpointer)th);
  }
  g_list_free(table->list);
  table->list = NULL;

  if(table->navigate_inside_selection)
  {
    // in this mode, we have "gaps" between rowid because of unselected images
    // if some case, there isn't enough select images *after* the offset
    // in this case, we need to try to take some image before the offset
    // the "dynamic" field "newrow" below is taking care of that

    // clang-format off
    query = g_strdup_printf
      ("SELECT i1, i2, i3, i2, newrow"
       " FROM (SELECT m.rowid AS i1, m.imgid AS i2, b.aspect_ratio AS i3,"
       "              (CASE WHEN m.rowid >= %d"
       "                 THEN m.rowid"
       "                 ELSE (SELECT MAX(rowid) FROM memory.collected_images) + %d - m.rowid"
       "               END) AS newrow"
       "       FROM memory.collected_images AS m, main.selected_images AS s, images AS b"
       "       WHERE m.imgid = b.id AND m.imgid = s.imgid"
       "       ORDER BY newrow"
       "       LIMIT %d)"
       " ORDER BY i1",
       offset, offset, table->thumbs_count);
    // clang-format on
  }
  else
  {
    // clang-format off
    query = g_strdup_printf
      ("SELECT m.rowid, m.imgid, b.aspect_ratio, s.imgid"
       " FROM (SELECT rowid, imgid "
       "       FROM memory.collected_images "
       "       WHERE rowid < %d + %d "
       "       ORDER BY rowid DESC "
       "       LIMIT %d) AS m "
       " LEFT JOIN main.selected_images AS s"
       "   ON m.imgid=s.imgid,"
       " images AS b"
       " WHERE m.imgid = b.id "
       " ORDER BY m.rowid",
       offset, table->thumbs_count, table->thumbs_count);
    // clang-format on
  }

  DT_DEBUG_SQLITE3_PREPARE_V2(dt_database_get(darktable.db), query, -1, &stmt, NULL);
  while(sqlite3_step(stmt) == SQLITE_ROW)
  {
    const int nrow = sqlite3_column_int(stmt, 0);
    const dt_imgid_t nid = sqlite3_column_int(stmt, 1);
    const gboolean selected = (nid == sqlite3_column_int(stmt, 3));

    // first, we search if the thumb is already here
    dt_thumbnail_t *thumb = (dt_thumbnail_t *)g_hash_table_lookup(htable, &nid);
    if(thumb)
    {
      g_hash_table_steal(htable, &nid);
      thumb->rowid = nrow; // this may have changed
      thumb->display_focus = table->focus;
      table->list = g_list_prepend(table->list, thumb);
    }
    else
    {
      // we create a completely new thumb we set its size to the thumb
      // it replace in the list if any otherwise we set it to
      // something > 0 to trigger draw events
      if(table->mode == DT_CULLING_MODE_PREVIEW ||
         (table->mode == DT_CULLING_MODE_CULLING && table->thumbs_count == 1))
      {
        nw = table->view_width;
        nh = table->view_height;
      }

      const dt_thumbnail_container_t container = table->mode == DT_CULLING_MODE_PREVIEW
        ? DT_THUMBNAIL_CONTAINER_PREVIEW
        : DT_THUMBNAIL_CONTAINER_CULLING;

      thumb = dt_thumbnail_new(nw,
                               nh,
                               table->zoom_ratio,
                               nid,
                               nrow,
                               table->overlays,
                               container,
                               table->show_tooltips,
                               selected);

      thumb->display_focus = table->focus;
      thumb->sel_mode = DT_THUMBNAIL_SEL_MODE_DISABLED;
      float aspect_ratio = sqlite3_column_double(stmt, 2);
      if(!aspect_ratio || aspect_ratio < 0.0001f)
      {
        aspect_ratio = dt_image_set_aspect_ratio(nid, FALSE);
        // if an error occurs, let's use 1:1 value
        if(aspect_ratio < 0.0001f) aspect_ratio = 1.0f;
      }
      thumb->aspect_ratio = aspect_ratio;
      table->list = g_list_prepend(table->list, thumb);
    }
    // if it's the offset, we record the imgid
    if(nrow == table->offset) table->offset_imgid = nid;
  }
  // list was built in reverse order, so un-reverse it
  table->list = g_list_reverse(table->list);
  // clean up all remaining thumbnails
  g_hash_table_destroy(htable);

  // and we ensure that we have the right offset
  if(table->list)
  {
    dt_thumbnail_t *thumb = table->list->data;
    table->offset_imgid = thumb->imgid;
    table->offset = _thumb_get_rowid(thumb->imgid);
  }
  return TRUE;
}

static gboolean _thumbs_compute_positions(dt_culling_t *table)
{
  // This code computes sizes and positions of thumbnails in culling view mode
  if(!table->list) return FALSE;

  // if we have only 1 image, it should take the entire screen
  if(g_list_is_singleton(table->list))
  {
    dt_thumbnail_t *thumb = table->list->data;
    thumb->width = table->view_width;
    thumb->height = table->view_height;
    thumb->x = 0;
    thumb->y = 0;
    return TRUE;
  }

  // initialize horizontal and vertical spacing distance between
  // thumbnails with lowest value possible. Will be scaled up later.
  const int spacing = 1;

  // reinit size and positions of each thumbnail, remember size from
  // biggest thumbnail, calculate average thumbnail ratio
  int max_thumb_height = 0;

  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *thumb = l->data;
    const float aspect_ratio = thumb->aspect_ratio;
    thumb->width = (gint)(sqrtf(aspect_ratio) * 100);
    thumb->height = (gint)(1 / sqrtf(aspect_ratio) * 100);
    thumb->x = thumb->y = 0;

    max_thumb_height = MAX(max_thumb_height, thumb->height);
  }

  // Vertical image stacking:
  //  Vertical stacking is only allowed if the height of the biggest thumbnail is more than the height
  //  of 2 or more thumbs combined.
  //  for example: we have three images and image 2 is higher than heights of image 1 and 3 combined
  //  [  1  ] | 2 |                                                | 2 |
  //  [  3  ] | 2 |      instead of this placement -->    [  1  ]  | 2 |  [  3  ]
  //          | 2 |                                                | 2 |
  // in this case, images 1 and 3 would be stacked in one slot and image 2 will be placed in a new slot alone.
  // if all images have similar heights, they will not be stacked and placed in separate slots.

  // Note: Stacking only make sense for images in the same row as the portrait image.
  //       The algorithm does not check for this so unnecessary stacking can occur.

  GList *slots = NULL;
  int max_slot_heigth = 0;
  int avg_thumb_width = 0;

  // loop through all thumbs
  int thumb_counter = 0;
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *thumb = l->data;
    GList *slot_iter = slots;

    thumb_counter++;
    avg_thumb_width += (thumb->width - avg_thumb_width) / (float)thumb_counter;

    // loop through newly created slots to check for available space
    for(; slot_iter; slot_iter = slot_iter->next)
    {
      GList *slot = (GList *)slot_iter->data;
      int slot_heigth = 0;

      // loop through thumbnails in slot
      for(GList *slot_thumb_iter = slot;
          slot_thumb_iter;
          slot_thumb_iter = g_list_next(slot_thumb_iter))
      {
        dt_thumbnail_t *slot_thumb = slot_thumb_iter->data;
        slot_heigth = slot_heigth + slot_thumb->height + spacing;
      }
      slot_heigth -= spacing;

      // Add thumbnail to slot if the slot height after adding the thumbnail
      // doesn't exceed the height of the highest thumbnail
      if(slot_heigth + spacing + thumb->height < max_thumb_height)
      {
        slot_iter->data = g_list_append(slot, thumb);
        max_slot_heigth =
          MAX(max_slot_heigth, slot_heigth + spacing + thumb->height);
        break;
      }
    }
    // Otherwise, create a new slot with only this thumbnail
    if(!slot_iter)
    {
      slots = g_list_prepend(slots, g_list_prepend(NULL, thumb));
      max_slot_heigth = MAX(max_slot_heigth, thumb->height);
    }
  }
  slots = g_list_reverse(slots);  // list was built in reverse order, so un-reverse it
  const int number_of_slots = g_list_length(slots);

  // finished assigning thumbnails to slots
  // we also know max slot height, so we can now scale all slots to this height
  // and then calculate average slot height and width
  int slot_counter = 0;
  float avg_slot_aspect_r = 0.0f;
  int total_slot_width = 0;
  int avg_slot_width = 0;

  for(GList *slot_iter = slots;
      slot_iter;
      slot_iter = g_list_next(slot_iter))
  {
    slot_counter++;

    GList *slot = (GList *)slot_iter->data;
    int slot_heigth = 0;
    int scaled_slot_height = 0;
    int scaled_slot_width = 0;

    // calculate current slot height for upscaling
    for(GList *slot_thumb_iter = slot;
      slot_thumb_iter;
      slot_thumb_iter = g_list_next(slot_thumb_iter))
    {
      const dt_thumbnail_t *thumb = slot_thumb_iter->data;
      slot_heigth += thumb->height + spacing;
    }
    slot_heigth -= spacing;

    // apply scaling to even out heights
    for(GList *slot_thumb_iter = slot;
      slot_thumb_iter;
      slot_thumb_iter = g_list_next(slot_thumb_iter))
    {
      dt_thumbnail_t *thumb = slot_thumb_iter->data;
      float stack_heigth_factor =
        (max_slot_heigth) / (float)slot_heigth;

      if(number_of_slots == 2)
      {
        // limit scaling factor to 20% if only two images are displayed so that slight differences are corrected
        // but portrait and landscape orientation are displayed at similar sizes
        stack_heigth_factor = MIN(stack_heigth_factor, 1.2);
      }
      else
      {
        // limit scaling so that width does not increase to more than twice the average thumbnail width
        stack_heigth_factor = MIN(stack_heigth_factor, 2 * avg_thumb_width / (float)thumb->width);
      }
      thumb->height *= stack_heigth_factor;
      thumb->width *= stack_heigth_factor;

      // calculate new slot height and width
      scaled_slot_width = MAX(scaled_slot_width, thumb->width);
      scaled_slot_height += thumb->height + spacing;
    }
    scaled_slot_height -= spacing;
    total_slot_width += scaled_slot_width + spacing;

    // iterative formula to calculate average slot ratio and width
    avg_slot_aspect_r += (scaled_slot_width/(float)scaled_slot_height - avg_slot_aspect_r) / (float)slot_counter;
    avg_slot_width += (scaled_slot_width - avg_slot_width) / (float)thumb_counter;
  }
  total_slot_width -= spacing;

  // variables to hold vertical and horizontal width of all thumbnails after their final placement
  unsigned int planned_total_width = total_slot_width;
  unsigned int planned_total_height = max_thumb_height;

  const float screen_aspect_r = table->view_width / (float)table->view_height;
  int row_cnt = 1;
  int row_cnt_tmp = 1;

  float deviation = _absmul(planned_total_width / (float)planned_total_height, screen_aspect_r);
  float deviation_tmp = deviation;

  do {
    row_cnt = row_cnt_tmp;
    deviation = deviation_tmp;
    planned_total_width = total_slot_width / (float) row_cnt;
    planned_total_height = row_cnt * max_slot_heigth;

    if(planned_total_width / (float)planned_total_height > screen_aspect_r)
      row_cnt_tmp = row_cnt + 1;
    else
      row_cnt_tmp = row_cnt - 1;

    if(row_cnt_tmp == 0 || row_cnt_tmp > slot_counter)
      break;

    const float planned_total_width_tmp = total_slot_width / (float) row_cnt_tmp;
    const int planned_total_height_tmp = row_cnt_tmp * max_slot_heigth;

    deviation_tmp = _absmul(planned_total_width_tmp / (float)planned_total_height_tmp, screen_aspect_r);

  } while(deviation_tmp < deviation);

  int total_height = 0;
  int total_width = 0;

  // create a nested list to hold all thumbnails in their final placement in rows
  GList *rows = g_list_append(NULL, NULL);
  {
    int row_y = 0;
    int thumb_x = 0;
    int row_heigth = 0;
    const int row_width_limit = planned_total_width;

    // work with one slot at a time
    for(GList *slot_iter = slots; slot_iter; slot_iter = g_list_next(slot_iter))
    {
      GList *slot = (GList *)slot_iter->data;

      // Calculate max width and total height of thumbs in the slot so that all thumbs can be centered within the slot
      int slot_max_thumb_width = 0;
      int slot_total_heigth = 0;
      for(GList *slot_thumb_iter = slot;
          slot_thumb_iter;
          slot_thumb_iter = g_list_next(slot_thumb_iter))
      {
        const dt_thumbnail_t *thumb = slot_thumb_iter->data;
        slot_max_thumb_width = MAX(slot_max_thumb_width, thumb->width);
        slot_total_heigth = slot_total_heigth + thumb->height + spacing;
      }
      // don't include bottom spacing in height calculation
      slot_total_heigth -= spacing;

      // if slot is about to be placed outside of allocated horizontal space, place the slot in a new row
      //  we allow for 20% thumbnail width tolerance to account for the influence of images with mixed aspect ratios in the math
      gboolean create_new_row = FALSE;

      // if the row limit is exceeded by more than 60% of a slot place it in the next row
      //  unless this is the last thumbnail and squeezing it into the current row results
      //  in a better placement ratio than opening a new row.
      if(thumb_x + 0.4 * slot_max_thumb_width > row_width_limit)
      {
        create_new_row = TRUE;

        if(!slot_iter->next)
        {
          const float ratio_same_row = _absmul(
            MAX(total_width, (thumb_x + slot_max_thumb_width)) / (float)MAX(total_height, row_y + slot_total_heigth),
            table->view_width / (float)table->view_height
          );
          const float ratio_new_row = _absmul(
            MAX(total_width, slot_max_thumb_width) / (float)(total_height + slot_total_heigth),
            table->view_width / (float)table->view_height
          );

          if(ratio_new_row > ratio_same_row)
            create_new_row = FALSE;
        }
      }

      if(create_new_row)
      {
        thumb_x = 0;
        row_y += row_heigth;
        row_heigth = 0;
        rows = g_list_append(rows, 0);
        rows = rows->next; // keep rows pointing at last element to
                           // avoid quadratic runtime
      }

      int thumb_y = row_y;

      // loop through all images assigned to a slot and calculate their placement
      //  place all of them within the same row
      for(GList *slot_thumb_iter = slot;
          slot_thumb_iter;
          slot_thumb_iter = g_list_next(slot_thumb_iter))
      {
        dt_thumbnail_t *thumb = slot_thumb_iter->data;
        thumb->x = thumb_x + (slot_max_thumb_width - thumb->width) / 2; // x position should be horizontally centered within the slot
        thumb->y = thumb_y;                                // y position starts at 0
        thumb_y += thumb->height + spacing;               // and is increased by the height of the thumb + spacing of spacing for placing the next image of the slot
      }
      rows->data = g_list_append(rows->data, slot); // append slot to row
      row_heigth = MAX(row_heigth, thumb_y - row_y);
      total_height = MAX(total_height, thumb_y);        // update total height of all thumbs combined as we fill column by column with thumbnails
      thumb_x += slot_max_thumb_width + spacing;
      total_width = MAX(total_width, thumb_x);          // update total width of all thumbs combined as we fill column by column with thumbnails
    }
    total_width -= spacing;
    g_list_free(slots);
    slots = NULL;
  }
  total_height -= spacing;

  rows = g_list_first(rows); // rows points at the last element of the
                             // constructed list, so move it back to
                             // the start


  // loop through all thumbnails to apply offsets for final positioning
  // loop through rows
  for(const GList *row_iter = rows; row_iter; row_iter = g_list_next(row_iter))
  {
    GList *row = (GList *)row_iter->data;
    int row_width = 0;
    int row_heigth = 0;
    int xoff = 0;
    int yoff = 0;

    // loop through slots of the row
    for(GList *slot_iter = row;
        slot_iter;
        slot_iter = g_list_next(slot_iter))
    {
      GList *slot = (GList *)slot_iter->data;
      int slot_heigth = 0;

      // loop through thumbs of the slot
      // to calculate slot height and update row width and height
      // which is used for xoffset of row and yoffset of individual thumbs
      for(GList *slot_thumb_iter = slot;
        slot_thumb_iter;
        slot_thumb_iter = g_list_next(slot_thumb_iter))
      {
        const dt_thumbnail_t *thumb = slot_thumb_iter->data;
        row_width = MAX(row_width, thumb->x + thumb->width + spacing);
        slot_heigth += thumb->height + spacing;
      }
      slot_heigth -= spacing;
      row_heigth = MAX(row_heigth, slot_heigth);
    }
    row_width -= spacing;
    xoff = (total_width - row_width) / 2;

    // loop through all slots and thumbs again to apply offset
    for(GList *slot_iter = row;
        slot_iter;
        slot_iter = g_list_next(slot_iter))
    {
      GList *slot = (GList *)slot_iter->data;

      // calculate vertical offset
      int slot_heigth = 0;
      for(GList *slot_thumb_iter = slot;
        slot_thumb_iter;
        slot_thumb_iter = g_list_next(slot_thumb_iter))
      {
        const dt_thumbnail_t *thumb = slot_thumb_iter->data;
        slot_heigth += thumb->height + spacing;
      }
      slot_heigth -= spacing;
      yoff = (row_heigth - slot_heigth) / 2;

      // Apply vertical and horizontal offsets
      for(GList *slot_thumb_iter = slot; slot_thumb_iter; slot_thumb_iter = g_list_next(slot_thumb_iter))
      {
        dt_thumbnail_t *thumb = slot_thumb_iter->data;
        thumb->x += xoff;
        thumb->y += yoff;
      }
      g_list_free(slot);
    }
    g_list_free(row);
  }
  g_list_free(rows);

  float factor = (table->view_width) / (float)total_width;
  if(factor * total_height > table->view_height)
    factor = (table->view_height) / (float)total_height;

  const int xoff = (table->view_width - total_width * factor) / 2;
  const int yoff = (table->view_height - total_height * factor) / 2;

  // scale everything to match the size of your screen
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *thumb = l->data;
    thumb->width  = thumb->width * factor;
    thumb->height = thumb->height * factor;
    thumb->x      = thumb->x * factor + xoff;
    thumb->y      = thumb->y * factor + yoff;

    dt_print(DT_DEBUG_LIGHTTABLE,
      "[culling_placement] thumb_id=%d, x=%d, y=%d, width=%d, height=%d"
             " - table_width=%d, table_height=%d",
             thumb->imgid, thumb->x, thumb->y, thumb->width, thumb->height,
             table->view_width, table->view_height);
  }

  // we save the current first id
  dt_conf_set_int("plugins/lighttable/culling_last_id", table->offset_imgid);

  return TRUE;
}

void dt_culling_update_active_images_list(dt_culling_t *table)
{
  // we erase the list of active images
  g_slist_free(darktable.view_manager->active_images);
  darktable.view_manager->active_images = NULL;

  // and we effectively move and resize thumbs
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *thumb = l->data;
    // we update the active images list
    darktable.view_manager->active_images =
      g_slist_append(darktable.view_manager->active_images,
                     GINT_TO_POINTER(thumb->imgid));
  }

  DT_CONTROL_SIGNAL_RAISE(DT_SIGNAL_ACTIVE_IMAGES_CHANGE);
}

// recreate the list of thumbs if needed and recomputes sizes and positions if needed
void dt_culling_full_redraw(dt_culling_t *table, const gboolean force)
{
  if(!gtk_widget_get_visible(table->widget) && !force) return;
  // first, we see if we need to do something
  if(!_compute_sizes(table, force)) return;
  const double start = dt_get_debug_wtime();

  // we store first image zoom and pos for new ones
  float old_zx = 0.0;
  float old_zy = 0.0;
  int old_margin_x = 0;
  int old_margin_y = 0;
  if(table->list)
  {
    dt_thumbnail_t *thumb = table->list->data;
    old_zx = thumb->zoomx;
    old_zy = thumb->zoomy;
    old_margin_x = gtk_widget_get_margin_start(thumb->w_image_box);
    old_margin_y = gtk_widget_get_margin_top(thumb->w_image_box);
  }
  // we recreate the list of images
  _thumbs_recreate_list_at(table, table->offset);

  // we compute the sizes and positions of thumbs
  _thumbs_compute_positions(table);

  // we erase the list of active images
  g_slist_free(darktable.view_manager->active_images);
  darktable.view_manager->active_images = NULL;

  // and we effectively move and resize thumbs
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *thumb = l->data;
    // we set the overlays timeout
    thumb->overlay_timeout_duration = table->overlays_block_timeout;
    // we add or move the thumb at the right position
    if(!gtk_widget_get_parent(thumb->w_main))
    {
      gtk_widget_set_margin_start(thumb->w_image_box, old_margin_x);
      gtk_widget_set_margin_top(thumb->w_image_box, old_margin_y);
      // and we resize the thumb
      dt_thumbnail_resize(thumb, thumb->width, thumb->height, FALSE, table->zoom_ratio);
      gtk_layout_put(GTK_LAYOUT(table->widget), thumb->w_main, thumb->x, thumb->y);
      thumb->zoomx = old_zx;
      thumb->zoomy = old_zy;
    }
    else
    {
      gtk_layout_move(GTK_LAYOUT(table->widget), thumb->w_main, thumb->x, thumb->y);
      // and we resize the thumb
      const float zoom_ratio = thumb->zoom_100 > 1
        ? thumb->zoom / thumb->zoom_100
        : IMG_TO_FIT;
      dt_thumbnail_resize(thumb, thumb->width, thumb->height, FALSE, zoom_ratio);
    }

    // we update the active images list
    darktable.view_manager->active_images
        = g_slist_append(darktable.view_manager->active_images,
                         GINT_TO_POINTER(thumb->imgid));
  }

  DT_CONTROL_SIGNAL_RAISE(DT_SIGNAL_ACTIVE_IMAGES_CHANGE);

  // if the selection should follow active images
  if(table->selection_sync)
  {
    // deactivate selection_change event
    table->select_desactivate = TRUE;
    // deselect all
    DT_DEBUG_SQLITE3_EXEC(dt_database_get(darktable.db),
                          "DELETE FROM main.selected_images",
                          NULL, NULL, NULL);
    // select all active images
    GList *ls = NULL;
    for(GList *l = table->list; l; l = g_list_next(l))
    {
      dt_thumbnail_t *thumb = l->data;
      ls = g_list_prepend(ls, GINT_TO_POINTER(thumb->imgid));
    }
    ls = g_list_reverse(ls);  // list was built in reverse order, so un-reverse it
    dt_selection_select_list(darktable.selection, ls);
    g_list_free(ls);
    // reactivate selection_change event
    table->select_desactivate = FALSE;
  }

  // we prefetch next/previous images
  _thumbs_prefetch(table);

  // ensure that no hidden image as the focus or is selected
  const dt_imgid_t overid = dt_control_get_mouse_over_id();
  if(dt_is_valid_imgid(overid) || dt_is_valid_imgid(table->selection))
  {
    gboolean in_list_over = FALSE;
    gboolean in_list_sel = FALSE;
    for(GList *l = table->list; l; l = g_list_next(l))
    {
      dt_thumbnail_t *thumb = l->data;
      if(thumb->imgid == overid)
      {
        in_list_over = TRUE;
        if(in_list_sel || !dt_is_valid_imgid(table->selection))
          break;
      }
      if(thumb->imgid == table->selection)
      {
        in_list_sel = TRUE;
        if(in_list_over || !dt_is_valid_imgid(overid))
          break;
      }
    }
    if(dt_is_valid_imgid(overid) && !in_list_over)
      dt_control_set_mouse_over_id(NO_IMGID);
    if(dt_is_valid_imgid(table->selection) && !in_list_sel)
    {
      table->selection = NO_IMGID;
      // and we reset the cache
      dt_act_on_reset_cache(TRUE);
      dt_act_on_reset_cache(FALSE);
    }
  }

  dt_print(DT_DEBUG_LIGHTTABLE | DT_DEBUG_PERF,
           "[dt_culling_full_redraw] done in %0.04f sec", dt_get_wtime() - start);

  if(darktable.unmuted & DT_DEBUG_CACHE) dt_mipmap_cache_print();
}

gboolean dt_culling_key_move(dt_culling_t *table, dt_culling_move_t move)
{
  int val = 0;
  switch(move)
  {
    case DT_CULLING_MOVE_LEFT:
    case DT_CULLING_MOVE_UP:
      val = -1;
      break;
    case DT_CULLING_MOVE_RIGHT:
    case DT_CULLING_MOVE_DOWN:
      val = 1;
      break;
    case DT_CULLING_MOVE_PAGEUP:
      val = -1 * table->thumbs_count;
      break;
    case DT_CULLING_MOVE_PAGEDOWN:
      val = table->thumbs_count;
      break;
    case DT_CULLING_MOVE_START:
      val = -1 * INT_MAX;
      break;
    case DT_CULLING_MOVE_END:
      val = INT_MAX;
      break;
    default:
      val = 0;
      break;
  }
  _thumbs_move(table, val);
  return TRUE;
}

void dt_culling_change_offset_image(dt_culling_t *table, dt_imgid_t imgid)
{
  table->offset = _thumb_get_rowid(imgid);
  dt_culling_full_redraw(table, TRUE);
  _thumbs_refocus(table);
}

void dt_culling_zoom_max(dt_culling_t *table)
{
  float x = 0;
  float y = 0;
  if(table->mode == DT_CULLING_MODE_PREVIEW && table->list)
  {
    dt_thumbnail_t *th = table->list->data;
    x = gtk_widget_get_allocated_width(th->w_image_box) / 2.0;
    y = gtk_widget_get_allocated_height(th->w_image_box) / 2.0;
  }
  _thumbs_zoom_add(table, ZOOM_MAX, x, y, 0);
}

void dt_culling_zoom_fit(dt_culling_t *table)
{
  table->zoom_ratio = IMG_TO_FIT;
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    _zoom_thumb_fit((dt_thumbnail_t *)l->data);
  }
}

// change the type of overlays that should be shown
void dt_culling_set_overlays_mode(dt_culling_t *table, dt_thumbnail_overlay_t over)
{
  if(!table) return;
  gchar *txt = g_strdup_printf("plugins/lighttable/overlays/culling/%d", table->mode);
  dt_conf_set_int(txt, over);
  g_free(txt);
  gchar *cl0 = _thumbs_get_overlays_class(table->overlays);
  gchar *cl1 = _thumbs_get_overlays_class(over);

  dt_gui_remove_class(table->widget, cl0);
  dt_gui_add_class(table->widget, cl1);

  txt = g_strdup_printf("plugins/lighttable/overlays/culling_block_timeout/%d",
                        table->mode);
  int timeout = 2;
  if(!dt_conf_key_exists(txt))
    timeout = dt_conf_get_int("plugins/lighttable/overlay_timeout");
  else
    timeout = dt_conf_get_int(txt);
  g_free(txt);

  txt = g_strdup_printf("plugins/lighttable/tooltips/culling/%d", table->mode);
  table->show_tooltips = dt_conf_get_bool(txt);
  g_free(txt);

  // we need to change the overlay content if we pass from normal to
  // extended overlays this is not done on the fly with css to avoid
  // computing extended msg for nothing and to reserve space if needed
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    dt_thumbnail_set_overlay(th, over, timeout);
    th->tooltip = table->show_tooltips;
    // and we resize the bottom area
    const float zoom_ratio = th->zoom_100 > 1
      ? th->zoom / th->zoom_100
      : table->zoom_ratio;
    dt_thumbnail_resize(th, th->width, th->height, TRUE, zoom_ratio);
  }

  table->overlays = over;
  g_free(cl0);
  g_free(cl1);
}

// force the overlays to be shown
void dt_culling_force_overlay(dt_culling_t *table, const gboolean force)
{
  if(!table) return;

  int timeout = -1;

  gchar *txt = g_strdup_printf("plugins/lighttable/overlays/culling/%d", table->mode);
  dt_thumbnail_overlay_t over = dt_conf_get_int(txt);
  g_free(txt);
  gchar *cl0 = _thumbs_get_overlays_class(DT_THUMBNAIL_OVERLAYS_HOVER_BLOCK);
  gchar *cl1 = _thumbs_get_overlays_class(over);

  if(!force)
  {
    dt_gui_remove_class(table->widget, cl0);
    dt_gui_add_class(table->widget, cl1);

    txt = g_strdup_printf("plugins/lighttable/overlays/culling_block_timeout/%d",
                          table->mode);
    timeout = 2;
    if(!dt_conf_key_exists(txt))
      timeout = dt_conf_get_int("plugins/lighttable/overlay_timeout");
    else
      timeout = dt_conf_get_int(txt);
    g_free(txt);
  }
  else
  {
    dt_gui_remove_class(table->widget, cl1);
    dt_gui_add_class(table->widget, cl0);
    over = DT_THUMBNAIL_OVERLAYS_HOVER_BLOCK;
  }

  g_free(cl0);
  g_free(cl1);

  // we need to change the overlay content if we pass from normal to
  // extended overlays this is not done on the fly with css to avoid
  // computing extended msg for nothing and to reserve space if needed
  for(GList *l = table->list; l; l = g_list_next(l))
  {
    dt_thumbnail_t *th = l->data;
    dt_thumbnail_set_overlay(th, over, timeout);
    // and we resize the bottom area
    const float zoom_ratio = th->zoom_100 > 1
      ? th->zoom / th->zoom_100
      : table->zoom_ratio;
    dt_thumbnail_resize(th, th->width, th->height, TRUE, zoom_ratio);
  }

  table->overlays = over;
}

// clang-format off
// modelines: These editor modelines have been set for all relevant files by tools/update_modelines.py
// vim: shiftwidth=2 expandtab tabstop=2 cindent
// kate: tab-indents: off; indent-width 2; replace-tabs on; indent-mode cstyle; remove-trailing-spaces modified;
// clang-format on
