#!/usr/bin/python3
# coding=utf-8 license=Apache-2.0

"""
Tool to follow caret position reported by applications.

Listens to caret move events and prints and displays the reported positions to
ease debugging apps and toolkits.
"""

import pyatspi

import cairo
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk, GLib


class BaseListener:
    def __init__(self, types):
        self.__types = types

    def __enter__(self):
        for t in self.__types:
            pyatspi.Registry.registerEventListener(self._on_event, t)
        pyatspi.Registry.start()

    def __exit__(self, *args, **kwargs):
        pyatspi.Registry.stop()
        for t in self.__types:
            pyatspi.Registry.deregisterEventListener(self._on_event, t)

    def _on_event(self, event):
        return False


def main(listener):
    try:
        with listener as dummy:
            pass
    except KeyboardInterrupt:
        pass


class Highlight(Gtk.Window):
    """ A overlay to highlight an area on screen.
    TODO: make the window input-less """
    def __init__(self, x, y, w, h):
        super().__init__(type=Gtk.WindowType.POPUP, app_paintable=True)
        self.set_default_size(w, h)
        self.move(x, y)

        self.do_screen_changed(None)

    def do_screen_changed(self, previous_screen):
        screen = self.get_screen()
        visual = screen.get_rgba_visual()
        if visual:
            self.set_visual(visual)

    def do_draw(self, cr):
        cr.set_source_rgba(1, 0, 0, 0.2)
        cr.set_operator(cairo.OPERATOR_SOURCE)
        cr.paint()
        cr.set_source_rgba(1, 0, 0, 0.8)
        alloc = self.get_allocation()
        cr.rectangle(alloc.x, alloc.y, alloc.width, alloc.height)
        cr.stroke()
        return True


class Listener(BaseListener):
    def __init__(self, apps=None):
        super().__init__(types=[
            "object:text-caret-moved",
        ])

        self.apps = [app.casefold() for app in apps] if apps else []

        self.area = None
        self.area_clear_id = 0

    def _update_area(self, extents):
        def clear():
            if self.area:
                self.area.destroy()
                self.area = None
            self.area_clear_id = 0
            return False

        if self.area:
            self.area.destroy()
            GLib.source_remove(self.area_clear_id)
        self.area = Highlight(*extents)
        self.area.show()
        self.area_clear_id = GLib.timeout_add(2000, clear)

    def _on_event(self, event):
        if super()._on_event(event):
            return True

        if event.type != "object:text-caret-moved":
            return False

        if self.apps and event.host_application.name.casefold() not in self.apps:
            return False

        text = event.source.queryText()
        extents = text.getCharacterExtents(event.detail1, pyatspi.DESKTOP_COORDS)

        print(event)
        print("\tx=%s y=%s w=%s h=%s" % extents)

        self._update_area(extents)

        return True


if __name__ == '__main__':
    from sys import argv

    main(Listener(apps=(argv[1:] if len(argv) > 1 else None)))