/*
 * gtkimcontextime.c
 * Copyright (C) 2003 Takuro Ashie
 * Copyright (C) 2003-2004 Kazuki IWAMOTO
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 *
 */

/*
 *  Please see the following site for the detail of Windows IME API.
 *  http://msdn.microsoft.com/library/default.asp?url=/library/en-us/appendix/hh/appendix/imeimes2_35ph.asp
 */

#ifdef GTK_DISABLE_DEPRECATED
#undef GTK_DISABLE_DEPRECATED
#endif

#include "gtkimcontextimeprivate.h"
#include "gtkimmoduleprivate.h"
#include "gtkroot.h"

#include "imm-extra.h"

#include "gdk/gdkkeysyms.h"
#include "gdk/gdkeventsprivate.h"
#include "gdk/win32/gdkwin32.h"
#include "gtk/gtkimmodule.h"
#include "gtk/deprecated/gtkstylecontextprivate.h"
#include "gtkwidgetprivate.h"

#undef STRICT
#include <pango/pangowin32.h>

/* Determines what happens when focus is lost while preedit is in process. */
typedef enum {
  /* Preedit is committed. */
  GTK_WIN32_IME_FOCUS_BEHAVIOR_COMMIT,
  /* Preedit is discarded. */
  GTK_WIN32_IME_FOCUS_BEHAVIOR_DISCARD,
  /* Preedit follows the cursor (that means it will appear in the widget
   * that receives the focus) */
  GTK_WIN32_IME_FOCUS_BEHAVIOR_FOLLOW,
} GtkWin32IMEFocusBehavior;

struct _GtkIMContextIMEPrivate
{
  /* When pretend_empty_preedit is set to TRUE,
   * gtk_im_context_ime_get_preedit_string() will return an empty string
   * instead of the actual content of ImmGetCompositionStringW().
   *
   * This is necessary because GtkEntry expects the preedit buffer to be
   * cleared before commit() is called, otherwise it leads to an assertion
   * failure in Pango. However, since we emit the commit() signal while
   * handling the WM_IME_COMPOSITION message, the IME buffer will be non-empty,
   * so we temporarily set this flag while emitting the appropriate signals.
   *
   * See also:
   *   https://bugzilla.gnome.org/show_bug.cgi?id=787142
   *   https://gitlab.gnome.org/GNOME/gtk/commit/c255ba68fc2c918dd84da48a472e7973d3c00b03
   */
  gboolean pretend_empty_preedit;
  GtkWin32IMEFocusBehavior focus_behavior;
};


/* GObject class methods */
static void gtk_im_context_ime_dispose    (GObject              *obj);
static void gtk_im_context_ime_finalize   (GObject              *obj);

static void gtk_im_context_ime_set_property (GObject      *object,
                                             guint         prop_id,
                                             const GValue *value,
                                             GParamSpec   *pspec);
static void gtk_im_context_ime_get_property (GObject      *object,
                                             guint         prop_id,
                                             GValue       *value,
                                             GParamSpec   *pspec);

/* GtkIMContext's virtual functions */
static void gtk_im_context_ime_set_client_widget   (GtkIMContext *context,
                                                    GtkWidget    *widget);
static gboolean gtk_im_context_ime_filter_keypress (GtkIMContext   *context,
                                                    GdkEvent       *event);
static void gtk_im_context_ime_reset               (GtkIMContext   *context);
static void gtk_im_context_ime_get_preedit_string  (GtkIMContext   *context,
                                                    char          **str,
                                                    PangoAttrList **attrs,
                                                    int            *cursor_pos);
static void gtk_im_context_ime_focus_in            (GtkIMContext   *context);
static void gtk_im_context_ime_focus_out           (GtkIMContext   *context);
static void gtk_im_context_ime_set_cursor_location (GtkIMContext   *context,
                                                    GdkRectangle   *area);
static void gtk_im_context_ime_set_use_preedit     (GtkIMContext   *context,
                                                    gboolean        use_preedit);

/* GtkIMContextIME's private functions */
static void gtk_im_context_ime_set_preedit_font (GtkIMContext    *context);

static GdkWin32MessageFilterReturn
gtk_im_context_ime_message_filter               (GdkWin32Display *display,
                                                 MSG             *msg,
                                                 int             *ret_valp,
                                                 gpointer         data);

G_DEFINE_TYPE_WITH_CODE (GtkIMContextIME, gtk_im_context_ime, GTK_TYPE_IM_CONTEXT,
    gtk_im_module_ensure_extension_point ();
                         g_io_extension_point_implement (GTK_IM_MODULE_EXTENSION_POINT_NAME,
                                                         g_define_type_id,
                                                         "ime",
                                                         0))

static GdkSurface *
surface_from_widget (GtkIMContext *context)
{
  GtkIMContextIME *context_ime = GTK_IM_CONTEXT_IME (context);
  GtkNative *native;

  if (!context_ime->client_widget)
    return NULL;

  native = gtk_widget_get_native (context_ime->client_widget);
  if (!native)
    return NULL;

  return gtk_native_get_surface (native);
}

static void
after_layout_cb (GtkIMContext *context)
{
  GtkIMContextIME *context_ime = GTK_IM_CONTEXT_IME (context);
  cairo_rectangle_int_t rect;
  GtkNative *native;
  graphene_point_t p;
  double nx, ny;

  native = gtk_widget_get_native (context_ime->client_widget);
  if (!native)
    return;

  /* Compute surface-local coordinates */
  rect = context_ime->cursor_location;

  if (!gtk_widget_compute_point (context_ime->client_widget,
                                 GTK_WIDGET (native),
                                 &GRAPHENE_POINT_INIT (rect.x, rect.y),
                                 &p))
    graphene_point_init (&p, rect.x, rect.y);

  gtk_native_get_surface_transform (native, &nx, &ny);
  rect.x = p.x + nx;
  rect.y = p.y + ny;

  if (context_ime->surface_cursor_location.x != rect.x ||
      context_ime->surface_cursor_location.y != rect.y ||
      context_ime->surface_cursor_location.width != rect.width ||
      context_ime->surface_cursor_location.height != rect.height)
    {
      GdkSurface *surface;
      COMPOSITIONFORM cf;
      HWND hwnd;
      HIMC himc;

      context_ime->surface_cursor_location = rect;

      surface = surface_from_widget (context);
      if (!surface)
        return;

      hwnd = gdk_win32_surface_get_handle (surface);
      himc = ImmGetContext (hwnd);
      if (!himc)
        return;

      cf.dwStyle = CFS_POINT;
      cf.ptCurrentPos.x = context_ime->surface_cursor_location.x;
      cf.ptCurrentPos.y = context_ime->surface_cursor_location.y;
      ImmSetCompositionWindow (himc, &cf);
      ImmReleaseContext (hwnd, himc);
    }
}

static void
on_widget_realize (GtkWidget       *widget,
                   GtkIMContextIME *context)
{
  GdkFrameClock *frame_clock;

  frame_clock = gtk_widget_get_frame_clock (widget);
  if (frame_clock)
    {
      context->after_layout_id =
        g_signal_connect_object (frame_clock, "layout",
                                 G_CALLBACK (after_layout_cb), context,
                                 G_CONNECT_AFTER | G_CONNECT_SWAPPED);
    }
}

static void
on_widget_unrealize (GtkWidget       *widget,
                     GtkIMContextIME *context)
{
  GdkFrameClock *frame_clock;

  frame_clock = gtk_widget_get_frame_clock (context->client_widget);
  g_clear_signal_handler (&context->after_layout_id, frame_clock);
}

static void
gtk_im_context_ime_class_init (GtkIMContextIMEClass *class)
{
  GtkIMContextClass *im_context_class = GTK_IM_CONTEXT_CLASS (class);
  GObjectClass *gobject_class = G_OBJECT_CLASS (class);

  gobject_class->finalize     = gtk_im_context_ime_finalize;
  gobject_class->dispose      = gtk_im_context_ime_dispose;
  gobject_class->set_property = gtk_im_context_ime_set_property;
  gobject_class->get_property = gtk_im_context_ime_get_property;

  im_context_class->set_client_widget   = gtk_im_context_ime_set_client_widget;
  im_context_class->filter_keypress     = gtk_im_context_ime_filter_keypress;
  im_context_class->reset               = gtk_im_context_ime_reset;
  im_context_class->get_preedit_string  = gtk_im_context_ime_get_preedit_string;
  im_context_class->focus_in            = gtk_im_context_ime_focus_in;
  im_context_class->focus_out           = gtk_im_context_ime_focus_out;
  im_context_class->set_cursor_location = gtk_im_context_ime_set_cursor_location;
  im_context_class->set_use_preedit     = gtk_im_context_ime_set_use_preedit;
}

static void
gtk_im_context_ime_init (GtkIMContextIME *context_ime)
{
  context_ime->client_widget          = NULL;
  context_ime->use_preedit            = TRUE;
  context_ime->preediting             = FALSE;
  context_ime->opened                 = FALSE;
  context_ime->focus                  = FALSE;
  context_ime->cursor_location.x      = 0;
  context_ime->cursor_location.y      = 0;
  context_ime->cursor_location.width  = 0;
  context_ime->cursor_location.height = 0;
  context_ime->commit_string          = NULL;

  context_ime->priv = g_new0 (GtkIMContextIMEPrivate, 1);
  context_ime->priv->focus_behavior = GTK_WIN32_IME_FOCUS_BEHAVIOR_COMMIT;
}


static void
gtk_im_context_ime_dispose (GObject *obj)
{
  GtkIMContext *context = GTK_IM_CONTEXT (obj);

  gtk_im_context_ime_set_client_widget (context, NULL);

  G_OBJECT_CLASS (gtk_im_context_ime_parent_class)->dispose (obj);
}


static void
gtk_im_context_ime_finalize (GObject *obj)
{
  GtkIMContextIME *context_ime = GTK_IM_CONTEXT_IME (obj);

  g_clear_pointer (&context_ime->priv, g_free);

  G_OBJECT_CLASS (gtk_im_context_ime_parent_class)->finalize (obj);
}


static void
gtk_im_context_ime_set_property (GObject      *object,
                                 guint         prop_id,
                                 const GValue *value,
                                 GParamSpec   *pspec)
{
  GtkIMContextIME *context_ime = GTK_IM_CONTEXT_IME (object);

  g_return_if_fail (GTK_IS_IM_CONTEXT_IME (context_ime));

  switch (prop_id)
    {
    default:
      break;
    }
}


static void
gtk_im_context_ime_get_property (GObject    *object,
                                 guint       prop_id,
                                 GValue     *value,
                                 GParamSpec *pspec)
{
  GtkIMContextIME *context_ime = GTK_IM_CONTEXT_IME (object);

  g_return_if_fail (GTK_IS_IM_CONTEXT_IME (context_ime));

  switch (prop_id)
    {
    default:
      break;
    }
}


GtkIMContext *
gtk_im_context_ime_new (void)
{
  return g_object_new (GTK_TYPE_IM_CONTEXT_IME, NULL);
}

static void
gtk_im_context_ime_set_client_widget (GtkIMContext *context,
                                      GtkWidget    *widget)
{
  GtkIMContextIME *context_ime;

  g_return_if_fail (GTK_IS_IM_CONTEXT_IME (context));
  context_ime = GTK_IM_CONTEXT_IME (context);

  if (context_ime->client_widget)
    {
      on_widget_unrealize (widget, context_ime);
      g_signal_handlers_disconnect_by_func (context_ime->client_widget,
                                            on_widget_realize,
                                            context);
      g_signal_handlers_disconnect_by_func (context_ime->client_widget,
                                            on_widget_unrealize,
                                            context);

      g_clear_weak_pointer (&context_ime->client_widget);
    }

  context_ime->client_widget = widget;

  if (widget)
    {
      g_object_add_weak_pointer (G_OBJECT (context_ime->client_widget),
                                 (gpointer*) &context_ime->client_widget);

      g_signal_connect (context_ime->client_widget, "realize",
                        G_CALLBACK (on_widget_realize), context);
      g_signal_connect (context_ime->client_widget, "unrealize",
                        G_CALLBACK (on_widget_unrealize), context);
      on_widget_realize (widget, context_ime);
    }
}

static gboolean
gtk_im_context_ime_filter_keypress (GtkIMContext *context,
                                    GdkEvent     *event)
{
  GtkIMContextIME *context_ime;
  char *compose_sequence = NULL;

  g_return_val_if_fail (GTK_IS_IM_CONTEXT_IME (context), FALSE);
  g_return_val_if_fail (event, FALSE);

  context_ime = GTK_IM_CONTEXT_IME (context);

  compose_sequence = gdk_key_event_get_compose_sequence (event);
  if (compose_sequence)
    {
      g_signal_emit_by_name (context_ime, "commit", compose_sequence);
      return TRUE;
    }

  return FALSE;
}

static void
gtk_im_context_ime_reset (GtkIMContext *context)
{
  GtkIMContextIME *context_ime = GTK_IM_CONTEXT_IME (context);
  GdkSurface *surface;
  HWND hwnd;
  HIMC himc;

  surface = surface_from_widget (context);
  if (!surface)
    return;

  hwnd = gdk_win32_surface_get_handle (surface);
  himc = ImmGetContext (hwnd);
  if (!himc)
    return;

  ImmNotifyIME (himc, NI_COMPOSITIONSTR, CPS_CANCEL, 0);

  if (context_ime->preediting)
    {
      context_ime->preediting = FALSE;
      g_signal_emit_by_name (context, "preedit-changed");
    }

  ImmReleaseContext (hwnd, himc);
}


static char *
get_utf8_preedit_string (GtkIMContextIME *context_ime,
                         int  kind,
                         int *pos_ret)
{
  gunichar2 *utf16str = NULL;
  glong size;
  char *utf8str = NULL;
  HWND hwnd;
  HIMC himc;
  int pos = 0;
  GdkSurface *surface;
  GError *error = NULL;

  if (pos_ret)
    *pos_ret = 0;

  surface = surface_from_widget (GTK_IM_CONTEXT (context_ime));

  if (!surface)
    return g_strdup ("");
  hwnd = gdk_win32_surface_get_handle (surface);
  himc = ImmGetContext (hwnd);
  if (!himc)
    return g_strdup ("");

  size = ImmGetCompositionStringW (himc, kind, NULL, 0);

  if (size > 0)
    {
      utf16str = g_malloc (size);

      ImmGetCompositionStringW (himc, kind, utf16str, size);
      utf8str = g_utf16_to_utf8 (utf16str, size / sizeof (gunichar2),
                                 NULL, NULL, &error);
      if (error)
        {
          g_warning ("%s", error->message);
          g_error_free (error);

        }
    }

  if (pos_ret)
    {
      pos = ImmGetCompositionStringW (himc, GCS_CURSORPOS, NULL, 0);
      if (pos < 0 || size < pos)
        {
          g_warning ("ImmGetCompositionString: "
                     "Invalid cursor position!");
          pos = 0;
        }
    }

  if (!utf8str)
    {
      utf8str = g_strdup ("");
      pos = 0;
    }

  if (pos_ret)
    *pos_ret = pos;

  ImmReleaseContext (hwnd, himc);
  g_free (utf16str);

  return utf8str;
}


static PangoAttrList *
get_pango_attr_list (GtkIMContextIME *context_ime, const char *utf8str)
{
  PangoAttrList *attrs = pango_attr_list_new ();
  GdkSurface *surface;
  HWND hwnd;
  HIMC himc;
  guint8 *buf = NULL;

  surface = surface_from_widget (GTK_IM_CONTEXT (context_ime));

  if (!surface)
    return attrs;
  hwnd = gdk_win32_surface_get_handle (surface);
  himc = ImmGetContext (hwnd);
  if (!himc)
    return attrs;

  if (context_ime->preediting)
    {
      const char *schr = utf8str, *echr;
      guint16 f_red, f_green, f_blue, b_red, b_green, b_blue;
      glong len, spos = 0, epos, sidx = 0, eidx;
      PangoAttribute *attr;

      /*
       *  get attributes list of IME.
       */
      len = ImmGetCompositionStringW (himc, GCS_COMPATTR, NULL, 0);
      buf = g_malloc (len);
      ImmGetCompositionStringW (himc, GCS_COMPATTR, buf, len);

      /*
       *  schr and echr are pointer in utf8str.
       */
      for (echr = g_utf8_next_char (utf8str); *schr != '\0';
           echr = g_utf8_next_char (echr))
        {
          /*
           *  spos and epos are buf(attributes list of IME) position by
           *  bytes.
           *  Using the wide-char API, this value is same with UTF-8 offset.
           */
   epos = g_utf8_pointer_to_offset (utf8str, echr);

          /*
           *  sidx and eidx are positions in utf8str by bytes.
           */
          eidx = echr - utf8str;

          /*
           *  convert attributes list to PangoAttriute.
           */
          if (*echr == '\0' || buf[spos] != buf[epos])
            {
              switch (buf[spos])
                {
                case ATTR_TARGET_CONVERTED:
                  attr = pango_attr_underline_new (PANGO_UNDERLINE_DOUBLE);
                  attr->start_index = sidx;
                  attr->end_index = eidx;
                  pango_attr_list_change (attrs, attr);
                  f_red = f_green = f_blue = 0;
                  b_red = b_green = b_blue = 0xffff;
                  break;
                case ATTR_TARGET_NOTCONVERTED:
                  f_red = f_green = f_blue = 0xffff;
                  b_red = b_green = b_blue = 0;
                  break;
                case ATTR_INPUT_ERROR:
                  f_red = f_green = f_blue = 0;
                  b_red = b_green = b_blue = 0x7fff;
                  break;
                default:        /* ATTR_INPUT,ATTR_CONVERTED,ATTR_FIXEDCONVERTED */
                  attr = pango_attr_underline_new (PANGO_UNDERLINE_SINGLE);
                  attr->start_index = sidx;
                  attr->end_index = eidx;
                  pango_attr_list_change (attrs, attr);
                  f_red = f_green = f_blue = 0;
                  b_red = b_green = b_blue = 0xffff;
                }
              attr = pango_attr_foreground_new (f_red, f_green, f_blue);
              attr->start_index = sidx;
              attr->end_index = eidx;
              pango_attr_list_change (attrs, attr);
              attr = pango_attr_background_new (b_red, b_green, b_blue);
              attr->start_index = sidx;
              attr->end_index = eidx;
              pango_attr_list_change (attrs, attr);

              schr = echr;
              spos = epos;
              sidx = eidx;
            }
        }
    }

  ImmReleaseContext (hwnd, himc);
  g_free (buf);

  return attrs;
}


static void
gtk_im_context_ime_get_preedit_string (GtkIMContext   *context,
                                       char          **str,
                                       PangoAttrList **attrs,
                                       int            *cursor_pos)
{
  char *utf8str = NULL;
  int pos = 0;
  GtkIMContextIME *context_ime;

  context_ime = GTK_IM_CONTEXT_IME (context);

  if (!context_ime->focus || context_ime->priv->pretend_empty_preedit)
    utf8str = g_strdup ("");
  else
    utf8str = get_utf8_preedit_string (context_ime, GCS_COMPSTR, &pos);

  if (attrs)
    *attrs = get_pango_attr_list (context_ime, utf8str);

  if (str)
    *str = utf8str;
  else
    utf8str = NULL;

  if (cursor_pos)
    *cursor_pos = pos;
}


static void
gtk_im_context_ime_focus_in (GtkIMContext *context)
{
  GtkIMContextIME *context_ime = GTK_IM_CONTEXT_IME (context);
  GdkSurface *toplevel;
  HWND hwnd;
  HIMC himc;

  toplevel = surface_from_widget (context);

  if (!GDK_IS_SURFACE (toplevel))
    return;

  /* switch current context */
  context_ime->focus = TRUE;

  if (!GDK_IS_SURFACE (toplevel))
    {
      g_warning ("gtk_im_context_ime_focus_in(): "
                 "cannot find toplevel window.");
      return;
    }

  hwnd = gdk_win32_surface_get_handle (toplevel);
  himc = ImmGetContext (hwnd);
  if (!himc)
    return;

  gdk_win32_display_add_filter (GDK_WIN32_DISPLAY (gdk_surface_get_display (toplevel)),
                                gtk_im_context_ime_message_filter, context_ime);

  /* restore preedit context */
  context_ime->opened = ImmGetOpenStatus (himc);

  switch (context_ime->priv->focus_behavior)
    {
      case GTK_WIN32_IME_FOCUS_BEHAVIOR_COMMIT:
      case GTK_WIN32_IME_FOCUS_BEHAVIOR_DISCARD:
        gtk_im_context_ime_reset (context);
        break;

      case GTK_WIN32_IME_FOCUS_BEHAVIOR_FOLLOW:
        {
          gchar *utf8str = get_utf8_preedit_string (context_ime, GCS_COMPSTR, NULL);
          if (utf8str != NULL && strlen(utf8str) > 0)
            {
              GdkFrameClock *frame_clock;

              context_ime->preediting = TRUE;
              frame_clock = gtk_widget_get_frame_clock (context_ime->client_widget);
              if (frame_clock)
                gdk_frame_clock_request_phase (frame_clock, GDK_FRAME_CLOCK_PHASE_LAYOUT);

              g_signal_emit_by_name (context, "preedit-start");
              g_signal_emit_by_name (context, "preedit-changed");
            }
          g_free (utf8str);
        }
        break;
      default:
        g_assert_not_reached ();
        break;
    }

  /* clean */
  ImmReleaseContext (hwnd, himc);
}


static void
gtk_im_context_ime_focus_out (GtkIMContext *context)
{
  GtkIMContextIME *context_ime = GTK_IM_CONTEXT_IME (context);
  gboolean was_preediting;
  GdkSurface *surface;

  surface = surface_from_widget (context);

  if (!GDK_IS_SURFACE (surface))
    return;

  /* switch current context */
  was_preediting = context_ime->preediting;
  context_ime->opened = FALSE;
  context_ime->preediting = FALSE;
  context_ime->focus = FALSE;

  switch (context_ime->priv->focus_behavior)
    {
      case GTK_WIN32_IME_FOCUS_BEHAVIOR_COMMIT:
        if (was_preediting)
          {
            gchar *utf8str = get_utf8_preedit_string (context_ime, GCS_COMPSTR, NULL);

            context_ime->priv->pretend_empty_preedit = TRUE;
            g_signal_emit_by_name (context, "preedit-changed");
            g_signal_emit_by_name (context, "preedit-end");
   g_signal_emit_by_name (context, "commit", utf8str);
            g_signal_emit_by_name (context, "preedit-start");
            g_signal_emit_by_name (context, "preedit-changed");
            context_ime->priv->pretend_empty_preedit = FALSE;
            g_free (utf8str);
          }
        G_GNUC_FALLTHROUGH;
      case GTK_WIN32_IME_FOCUS_BEHAVIOR_DISCARD:
        gtk_im_context_ime_reset (context);

        /* Callbacks triggered by im_context_ime_reset() could set the focus back to our
           context. In that case, we want to exit here. */

        if (context_ime->focus)
          return;

        break;

      case GTK_WIN32_IME_FOCUS_BEHAVIOR_FOLLOW:
        break;

      default:
        g_assert_not_reached ();
    }

  /* remove event filter */
  if (GDK_IS_SURFACE (surface))
    {
      gdk_win32_display_remove_filter (GDK_WIN32_DISPLAY (gdk_surface_get_display (surface)),
                                       gtk_im_context_ime_message_filter,
                                       context_ime);
    }

  if (was_preediting)
    {
      g_warning ("gtk_im_context_ime_focus_out(): "
                 "cannot find toplevel window.");
      g_signal_emit_by_name (context, "preedit-changed");
      g_signal_emit_by_name (context, "preedit-end");
    }
}


static void
gtk_im_context_ime_set_cursor_location (GtkIMContext *context,
                                        GdkRectangle *area)
{
  GtkIMContextIME *context_ime;

  g_return_if_fail (GTK_IS_IM_CONTEXT_IME (context));

  context_ime = GTK_IM_CONTEXT_IME (context);
  if (area)
    context_ime->cursor_location = *area;

  if (context_ime->client_widget)
    {
      GdkFrameClock *frame_clock;

      frame_clock = gtk_widget_get_frame_clock (context_ime->client_widget);
      if (frame_clock)
        gdk_frame_clock_request_phase (frame_clock, GDK_FRAME_CLOCK_PHASE_LAYOUT);
    }
}


static void
gtk_im_context_ime_set_use_preedit (GtkIMContext *context,
                                    gboolean      use_preedit)
{
  GtkIMContextIME *context_ime;

  g_return_if_fail (GTK_IS_IM_CONTEXT_IME (context));
  context_ime = GTK_IM_CONTEXT_IME (context);

  context_ime->use_preedit = use_preedit;
  if (context_ime->preediting)
    {
      GdkSurface *surface;
      HWND hwnd;
      HIMC himc;

      surface = surface_from_widget (context);
      if (!surface)
        return;

      hwnd = gdk_win32_surface_get_handle (surface);
      himc = ImmGetContext (hwnd);
      if (!himc)
        return;

      /* FIXME: What to do? */

      ImmReleaseContext (hwnd, himc);
    }
}


static void
gtk_im_context_ime_set_preedit_font (GtkIMContext *context)
{
  GtkIMContextIME *context_ime;
  HWND hwnd;
  HIMC himc;
  HKL ime = GetKeyboardLayout (0);
  const char *lang;
  gunichar wc;
  PangoContext *pango_context;
  PangoFont *font;
  LOGFONTA *logfont;
  PangoFontDescription *font_desc;
  GtkCssStyle *style;
  GdkSurface *surface;

  g_return_if_fail (GTK_IS_IM_CONTEXT_IME (context));

  context_ime = GTK_IM_CONTEXT_IME (context);

  if (!context_ime->client_widget)
    return;

  surface = surface_from_widget (context);
  if (!surface)
    return;

  hwnd = gdk_win32_surface_get_handle (surface);
  himc = ImmGetContext (hwnd);
  if (!himc)
    return;

  /* set font */
  pango_context = gtk_widget_get_pango_context (context_ime->client_widget);
  if (!pango_context)
    goto ERROR_OUT;

  /* Try to make sure we use a font that actually can show the
   * language in question.
   */

  switch (PRIMARYLANGID (LOWORD (ime)))
    {
    case LANG_JAPANESE:
      lang = "ja"; break;
    case LANG_KOREAN:
      lang = "ko"; break;
    case LANG_CHINESE:
      switch (SUBLANGID (LOWORD (ime)))
 {
 case SUBLANG_CHINESE_TRADITIONAL:
   lang = "zh_TW"; break;
 case SUBLANG_CHINESE_SIMPLIFIED:
   lang = "zh_CN"; break;
 case SUBLANG_CHINESE_HONGKONG:
   lang = "zh_HK"; break;
 case SUBLANG_CHINESE_SINGAPORE:
   lang = "zh_SG"; break;
 case SUBLANG_CHINESE_MACAU:
   lang = "zh_MO"; break;
 default:
   lang = "zh"; break;
 }
      break;
    default:
      lang = ""; break;
    }

  style = gtk_css_node_get_style (gtk_widget_get_css_node (context_ime->client_widget));
  font_desc = gtk_css_style_get_pango_font (style);

  if (lang[0])
    {
      /* We know what language it is. Look for a character, any
       * character, that language needs.
       */
      PangoLanguage *pango_lang = pango_language_from_string (lang);
      PangoFontset *fontset =
        pango_context_load_fontset (pango_context,
                                font_desc,
                                pango_lang);
      gunichar *sample =
 g_utf8_to_ucs4 (pango_language_get_sample_string (pango_lang),
   -1, NULL, NULL, NULL);
      wc = 0x4E00;  /* In all CJK languages? */
      if (sample != NULL)
 {
   int i;

   for (i = 0; sample[i]; i++)
     if (g_unichar_iswide (sample[i]))
       {
  wc = sample[i];
  break;
       }
   g_free (sample);
 }
      font = pango_fontset_get_font (fontset, wc);
      g_object_unref (fontset);
    }
  else
    font = pango_context_load_font (pango_context, font_desc);

  if (!font)
    goto ERROR_OUT;

  logfont = pango_win32_font_logfont (font);
  if (logfont)
    ImmSetCompositionFontA (himc, logfont);

  g_object_unref (font);

ERROR_OUT:
  /* clean */
  ImmReleaseContext (hwnd, himc);
}


static GdkWin32MessageFilterReturn
gtk_im_context_ime_message_filter (GdkWin32Display *display,
                                   MSG             *msg,
                                   int             *ret_valp,
                                   gpointer         data)
{
  GtkIMContext *context;
  GtkIMContextIME *context_ime;
  HWND hwnd;
  HIMC himc;
  GdkSurface *toplevel;
  GdkWin32MessageFilterReturn retval = GDK_WIN32_MESSAGE_FILTER_CONTINUE;

  g_return_val_if_fail (GTK_IS_IM_CONTEXT_IME (data), retval);

  context = GTK_IM_CONTEXT (data);
  context_ime = GTK_IM_CONTEXT_IME (data);
  if (!context_ime->focus)
    return retval;

  toplevel = surface_from_widget (context);
  if (!toplevel)
    return retval;
  if (gdk_win32_surface_get_handle (toplevel) != msg->hwnd)
    return retval;

  hwnd = gdk_win32_surface_get_handle (toplevel);
  himc = ImmGetContext (hwnd);
  if (!himc)
    return retval;

  *ret_valp = 0;

  switch (msg->message)
    {
    case WM_IME_COMPOSITION:
      {
        CANDIDATEFORM cf;
        int wx = 0;
        int wy = 0;
        int scale = 1;

        if (toplevel && context_ime->client_widget)
          {
            GtkNative *native = gtk_native_get_for_surface (toplevel);
            if G_LIKELY (native)
              {
                graphene_point_t p;
                double decor_x = 0.0;
                double decor_y = 0.0;

                if (!gtk_widget_compute_point (context_ime->client_widget,
                                               GTK_WIDGET (native),
                                               &GRAPHENE_POINT_INIT (0, 0), &p))
                  graphene_point_init (&p, 0, 0);

                gtk_native_get_surface_transform (native, &decor_x, &decor_y);
                p.x += decor_x;
                p.y += decor_y;

                wx = (int) p.x;
                wy = (int) p.y;
              }

            scale = gtk_widget_get_scale_factor (context_ime->client_widget);
          }

        cf.dwIndex = 0;
        cf.dwStyle = CFS_EXCLUDE;
        cf.ptCurrentPos.x = (wx + context_ime->cursor_location.x) * scale;
        cf.ptCurrentPos.y = (wy + context_ime->cursor_location.y) * scale;
        cf.rcArea.left = cf.ptCurrentPos.x;
        cf.rcArea.right = cf.rcArea.left + context_ime->cursor_location.width * scale;
        cf.rcArea.top = cf.ptCurrentPos.y;
        cf.rcArea.bottom = cf.rcArea.top + context_ime->cursor_location.height * scale;

        ImmSetCandidateWindow (himc, &cf);

        if ((msg->lParam & GCS_COMPSTR))
          g_signal_emit_by_name (context, "preedit-changed");

        if (msg->lParam & GCS_RESULTSTR)
          {
            gchar *utf8str = get_utf8_preedit_string (context_ime, GCS_RESULTSTR, NULL);

            if (utf8str)
              {
                context_ime->priv->pretend_empty_preedit = TRUE;
                g_signal_emit_by_name (context, "preedit-changed");
                g_signal_emit_by_name (context, "preedit-end");

                g_signal_emit_by_name (context, "commit", utf8str);

                g_signal_emit_by_name (context, "preedit-start");
                g_signal_emit_by_name (context, "preedit-changed");
                context_ime->priv->pretend_empty_preedit = FALSE;

                retval = TRUE;
              }

            g_free (utf8str);
          }

        if (context_ime->use_preedit)
          retval = GDK_WIN32_MESSAGE_FILTER_REMOVE;
      }

      break;

    case WM_IME_STARTCOMPOSITION:
      context_ime->preediting = TRUE;
      gtk_im_context_ime_set_cursor_location (context, NULL);
      g_signal_emit_by_name (context, "preedit-start");
      if (context_ime->use_preedit)
        retval = GDK_WIN32_MESSAGE_FILTER_REMOVE;
      break;

    case WM_IME_ENDCOMPOSITION:
      context_ime->preediting = FALSE;
      g_signal_emit_by_name (context, "preedit-changed");
      g_signal_emit_by_name (context, "preedit-end");

      if (context_ime->use_preedit)
        retval = GDK_WIN32_MESSAGE_FILTER_REMOVE;
      break;

    case WM_IME_NOTIFY:
      switch (msg->wParam)
        {
        case IMN_SETOPENSTATUS:
          context_ime->opened = ImmGetOpenStatus (himc);
          gtk_im_context_ime_set_preedit_font (context);
          break;

        default:
          break;
        }
      break;
    default:
      break;
    }

  ImmReleaseContext (hwnd, himc);
  return retval;
}