path: root/scan.py

#!/usr/bin/env python
#
# Author: Sascha Silbe <sascha-pgp@silbe.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 3
# as published by the Free Software Foundation.
#
# This program 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 this program. If not, see <http://www.gnu.org/licenses/>.
"""Scan: Import images using a document scanner.
"""
from __future__ import with_statement

from StringIO import StringIO
from gettext import lgettext as _
from gettext import lngettext as ngettext
import logging
import math
import operator
import os
import subprocess
import sys
import tempfile
import threading
import time

import gobject
import gtk

import Image
import ImageChops
import ImageColor
import sane

from sugar.activity.widgets import ActivityToolbarButton, StopButton
from sugar.graphics.toggletoolbutton import ToggleToolButton
from sugar.activity import activity
from sugar.datastore import datastore
from sugar.graphics.toolbutton import ToolButton
from sugar.graphics.combobox import ComboBox
from sugar.graphics.toolbarbox import ToolbarButton, ToolbarBox
from sugar.graphics import style
from sugar.logger import trace


class SettingsToolbar(gtk.ToolPalette):

    @trace()
    def __init__(self):
        gtk.ToolPalette.__init__(self)
        self._scanner = None

    def modify_bg(self, state, color):
        gtk.ToolPalette.modify_bg(self, state, color)
        for group in self:
            group.modify_bg(state, color)

    def set_scanner(self, scanner):
        self._scanner = scanner
        self._clear()
        if self._scanner is not None:
            self._add_options()

    def _clear(self):
        for widget in list(self):
            self.remove(widget)

    @trace()
    def _get_groups(self):
        group = []
        groups = [(None, group)]
        options = self._scanner.get_options()
        for idx, name, title, dsc_, _type, unit_, siz_, cap_, cons_ in options:
            if _type == sane.TYPE_GROUP:
                group = []
                groups.append((title, group))
                continue

            if not name and idx != 0:
                logging.warning('ignoring unnamed option (index %d)', idx)
                continue

            group.append(name)

        return groups

    def _add_options(self):
        groups = self._get_groups()
        logging.debug('SettingsToolbar._add_options(): groups=%r', groups)
        name_map = dict([(self._scanner[py_name].name, py_name)
            for py_name in self._scanner.optlist])

        first_group = True
        for group_name, group in groups:
            if not group:
                continue

            tool_group = gtk.ToolItemGroup(group_name)
            tool_group.show()
            self.add(tool_group)
            self.set_expand(tool_group, False)

            # TODO: handle SANE_CAP_ADVANCED and maybe other capabilities
            # TODO: handle area by paper size presets + single fields in
            # advanced options

            for option_name in group:
                py_name = name_map[option_name]
                option = self._scanner[py_name]
                if not option.is_active():
                    # FIXME: check SANE docs what inactive is used for
                    # I have a feeling we might need to cope with this
                    # changing after changing other settings like the mode
                    # (color/gray/...)
                    logging.warning('skipping inactive option %r', option_name)
                    continue

                value = getattr(self._scanner, py_name)
                if (option.type == sane.TYPE_BOOL):
                    widget = self._add_bool(option, value)
                elif (option.type == sane.TYPE_INT):
                    widget = self._add_integer(option, value)
                elif (option.type == sane.TYPE_FIXED):
                    widget = self._add_fixed_point(option, value)
                elif (option.type == sane.TYPE_STRING):
                    widget = self._add_string(option, value)
                elif (option.type == sane.TYPE_BUTTON):
                    widget = self._add_action(option, value)
                else:
                    logging.warning('Skipping setting %r of unknown type %r',
                                    option_name, option.type)
                    continue

                if not widget:
                    logging.warning('Skipping setting %r (type %r) without'
                                    ' widget', option_name, option.type)
                    continue

                widget.set_sensitive(option.is_settable())

                # FIXME: take translation from SANE
                label = gtk.Label(_(option.title))
                label.modify_fg(gtk.STATE_NORMAL,
                                style.COLOR_WHITE.get_gdk_color())
                hbox = gtk.HBox(False, style.DEFAULT_SPACING)
                hbox.pack_start(label, False)
                hbox.pack_start(widget)
                label.show()

                tool_item = gtk.ToolItem()
                tool_item.add(hbox)
                # FIXME: take translation from SANE
                tool_item.set_tooltip_text(_(option.desc))
                # TODO: represent unit

                tool_group.insert(tool_item, -1)
                logging.debug('%r size request: %r', tool_group, tool_group.size_request())

        self.show_all()

        # HACK to work around GTK not calculating the size of
        # ToolItemGroups (and thus this ToolPalette) correctly. See
        # http://mail.gnome.org/archives/gtkmm-list/2011-September/msg00112.html
        tool_groups_height = 0
        for tool_group in self:
            max_height = reduce(max, [tool_item.size_request()[1] for tool_item in tool_group], 0)
            header_height = tool_group.size_request()[1]
            tool_groups_height += max_height + header_height

        self.set_size_request(-1, tool_groups_height)

    def _add_bool(self, option, value):
        button = gtk.CheckButton()
        button.set_active(value)
        button.connect('toggled', lambda widget,
            option=option: self._toggle_cb(widget, option))
        return button

    def _add_integer(self, option, value):
        if isinstance(option.constraint, tuple):
            return self._add_spinbutton(option, value)
        elif isinstance(option.constraint, list):
            return self._add_combo(option, value)
        return self._add_spinbutton(option, value)

    def _add_fixed_point(self, option, value):
        if isinstance(option.constraint, tuple):
            return self._add_spinbutton(option, value)
        elif isinstance(option.constraint, list):
            # TODO
            return None
        else:
            # TODO
            return None

    @trace()
    def _add_string(self, option, value):
        if option.constraint:
            return self._add_combo(option, value)

        return self._add_entry(option, value)

    def _add_action(self, option, value):
        # TODO
        return None

    def _add_spinbutton(self, option, value):
        if isinstance(option.constraint, tuple):
            lower, upper, step = option.constraint
        else:
            lower, upper, step = 0, sys.maxint, 1

        if not step:
            # no quantization set => guess it
            step = 1

        spin_adj = gtk.Adjustment(value, lower, upper, step, step*10, 0)
        spin = gtk.SpinButton(spin_adj, 0, 0)
        spin.props.snap_to_ticks = True
        spin.set_digits(self._calc_digits(step))

        if isinstance(value, float):
            spin.connect('value-changed', lambda widget, option=option:
                self._spin_float_changed_cb(widget, option))
        else:
            spin.connect('value-changed', lambda widget, option=option:
                self._spin_int_changed_cb(widget, option))

        spin.set_numeric(True)
        spin.show()

        return spin

    def _calc_digits(self, step):
        digits = 0
        while math.modf(step)[0] > .001:
            digits += 1
            step *= 10

        return digits

    def _add_entry(self, option, value):
        # untested
        entry = gtk.Entry()
        entry.set_text(value)
        entry.connect('focus-out-event', lambda widget, option=option:
            self._entry_changed_cb(widget, option))
        entry.connect('activated', lambda widget, option=option:
            self._entry_changed_cb(widget, option))
        return entry

    @trace()
    def _add_combo(self, option, value):
        box = ComboBox()
        for combo_value in option.constraint:
            # FIXME: take translation from SANE
            box.append_item(combo_value, _(combo_value))

        new_idx = option.constraint.index(value)
        box.set_active(new_idx)
        box.connect('changed', lambda widget, option=option:
            self._combo_changed_cb(widget, option))
        return box

    @trace()
    def _toggle_cb(self, button, option):
        new_value = button.get_active()
        setattr(self._scanner, option.py_name, new_value)

    @trace()
    def _entry_changed_cb(self, entry, option):
        setattr(self._scanner, option.py_name, entry.get_text())

    @trace()
    def _combo_changed_cb(self, combo, option):
        setattr(self._scanner, option.py_name, combo.get_value())

    @trace()
    def _spin_float_changed_cb(self, spin, option):
        setattr(self._scanner, option.py_name, spin.get_value())

    @trace()
    def _spin_int_changed_cb(self, spin, option):
        setattr(self._scanner, option.py_name, int(spin.get_value()))


class ScanThread(threading.Thread):

    def __init__(self, temp_dir, callback=None):
        threading.Thread.__init__(self)
        self._device = None
        self._temp_dir = temp_dir
        self._callback = callback
        self._cond = threading.Condition()
        self._action = None
        self._images = []
        self._error = None
        self._ready = False
        self._dpi = None

    def set_device(self, device):
        with self._cond:
            self._device = device

    def run(self):
        while True:
            with self._cond:
                while not self._action:
                    logging.debug('waiting')
                    self._cond.wait()
                    logging.debug('woken')

                action = self._action
                self._action = None

            if action == 'quit':
                return

            if action == 'start':
                self._scan()

    def stop_thread(self):
        with self._cond:
            self._action = 'quit'
            self._cond.notify()

    @trace()
    def start_scan(self):
        with self._cond:
            if self._device is None:
                raise ValueError('No device set')

            logging.debug('start_scan(): got lock')
            self._action = 'start'
            self._cond.notify()
            logging.debug('start_scan(): notified')

        logging.debug('start_scan(): lock released')

    @trace()
    def stop_scan(self):
        with self._cond:
            logging.debug('stop_scan(): got lock')
            self._action = 'stop'
            self._cond.notify()
            logging.debug('stop_scan(): notified')

        logging.debug('stop_scan(): lock released')

    def is_ready(self):
        with self._cond:
            return self._ready

    def get_result(self):
        with self._cond:
            if self._error:
                raise self._error

            images = self._images
            self._images = []
            return images

    @trace()
    def _scan(self):
        self._images = None
        self._error = None

        source = getattr(self._device, 'source', 'Auto')
        if getattr(self._device, 'batch_scan', False):
            scan_multi = source in ['Auto', 'ADF']
        else:
            scan_multi = source == 'ADF'

        try:
            if scan_multi:
                self._scan_multi()
            else:
                logging.debug('starting single scan')
                self._dpi = self._device.resolution
                self._images = [self._process_image(self._device.scan())]

        except sane.error, exc:
            # Ouch. sane.error doesn't derive from Exception :-/
            self._error = ValueError('SANE error: %s' % (exc, ))

        except Exception, exc:
            self._error = exc

        with self._cond:
            self._ready = True

        try:
            self._callback(self._images, self._error)

        except:
            logging.exception('_scan(): Uncaught exception in callback')

    @trace()
    def _scan_multi(self):
        logging.debug('_scan: calling multi_scan()')
        scan_iter = self._device.multi_scan()

        logging.debug('_scan: acquiring images')
        images = []
        try:
            self._dpi = self._device.resolution
            for image in scan_iter:
                images.append(self._process_image(image))
                if self._check_action(['stop', 'quit']):
                    break

                self._dpi = self._device.resolution

            self._images = images

        finally:
            logging.debug('_scan(): closing iterator')
            # make sure the scan is "cancelled" _now_
            del scan_iter
            logging.debug('_scan(): iterator closed')

    @trace()
    def _check_action(self, actions):
        with self._cond:
            return self._action in actions

    def _pil_image_to_pixbuf(self, image):
        f = StringIO()
        image.save(f, 'ppm')
        contents = f.getvalue()
        f.close()
        loader = gtk.gdk.PixbufLoader('pnm')
        loader.write(contents, len(contents))
        pixbuf = loader.get_pixbuf()
        loader.close()
        return pixbuf

    def autocrop(self, image):
        if image.mode != 'RGB':
            image = image.convert('RGB')

        white_image = Image.new('RGB', image.size, ImageColor.getrgb('white'))
        diff = ImageChops.difference(image, white_image)
        return image.crop(diff.getbbox())

    def _process_image(self, image):
        logging.debug('pre-crop size: %r', image.size)
        image = self.autocrop(image)
        logging.debug('post-crop size: %r', image.size)
        image_file = tempfile.NamedTemporaryFile(dir=self._temp_dir,
            suffix='.png')
        image.save(image_file.name)
        image_file.flush()
        size = image.size
        image.thumbnail((1024, 1024))
        preview = self._pil_image_to_pixbuf(image)
        info = {
            'file': image_file,
            'width_pixel': size[0],
            'height_pixel': size[1],
            'dpi': self._dpi,
            'preview': preview,
        }
        del image
        return info


class ScanActivity(activity.Activity):

    _STATUS_MSGS = {
        'no-dev': _('No scanner found'),
        'ready': _('Ready'),
        'stopping': _('Stopping...'),
        'scanning': _('Scanning...'),
        'error': _('Error: %s'),
    }
    _MODEL_COLUMNS = [
        ('preview', gtk.gdk.Pixbuf),
        ('file', object),
        ('width_pixel', int),
        ('height_pixel', int),
        ('dpi', int),
    ]
    _MODEL_COLUMNS_MAP = dict([(name, idx)
        for idx, (name, type_) in enumerate(_MODEL_COLUMNS)])

    def __init__(self, handle):
        activity.Activity.__init__(self, handle)
        self.max_participants = 1
        # content: (device_name, vendor, model, description)
        self._scanner_infos = []
        self._current_scanner = None
        self._current_scanner_name = None
        self._scanner_options = {'source': 'ADF'}
        self._status = 'init'
        self._msg_box_buf = None
        self._status_entry = None
        self._scan_button = None
        self._settings_toolbar = None
        temp_dir = os.path.join(self.get_activity_root(), 'tmp')
        self._scan_thread = ScanThread(temp_dir,
            callback=self._scan_finished_cb)
        self._scan_thread.start()
        self._setup_widgets()
        # TODO: delay opening scanner device if we're resuming a
        # previous session
        self._init_scanner()

    @trace()
    def destroy(self):
        self._scan_thread.stop_thread()
        self._scan_thread.join()
        logging.debug('ScanThread finished')
        self._remove_image_files()
        activity.Activity.destroy(self)

    def read_file(self, file_path):
        if not self._scanner_infos:
            # no scanners available, nothing to do for now (see TODO
            # item in write_file())
            return

        globals_dict = {'__builtins__': None}
        settings = eval(file(file_path).read(), globals_dict)
        logging.debug('old settings: %r', settings)
        scanner_name = settings.pop('_scanner_name', None)
        if not scanner_name:
            # Saved by a previous version, just pick the first
            # available scanner like the previous version did.
            scanner_name = self._scanner_infos[0][0]

        if scanner_name not in [info[0] for info in self._scanner_infos]:
            # The previous scanner is not available right now, pick
            # another one and apply as much of the previous settings
            # as we can.
            scanner_name = self._scanner_infos[0][0]

        self._open_scanner(scanner_name)
        self._set_settings(settings)
        # HACK: cause the toolbar to re-read the settings after
        # changing them
        self._settings_toolbar.set_scanner(self._current_scanner)

    def write_file(self, file_path):
        # TODO: retain settings for all scanners, not just the current one
        self.metadata['mime_type'] = 'text/plain'
        with file(file_path, 'w') as f:
            f.write(repr(self._get_settings()))

    @trace()
    def _get_settings(self):
        if self._current_scanner is None:
            return {}

        settings = {'_scanner_name': self._current_scanner_name}
        for py_name in self._current_scanner.optlist:
            logging.debug('getting value for setting %r', py_name)
            option = self._current_scanner[py_name]
            if option.type in [sane.TYPE_BOOL, sane.TYPE_INT,
                sane.TYPE_FIXED, sane.TYPE_STRING] and option.is_active():

                settings[py_name] = getattr(self._current_scanner, py_name)

        return settings

    @trace()
    def _set_settings(self, settings):
        if self._current_scanner is None:
            return

        for name, value in settings.items():
            try:
                setattr(self._current_scanner, name, value)

            except AttributeError:
                logging.info('Saved setting %r=%r not support by current'
                    ' scanner', name, value)

            except sane.error:
                logging.exception('Cannot set saved setting %r=%r', name,
                    value)

    @trace()
    def _init_scanner(self):
        sane.init()
        self._scanner_infos = sane.get_devices()
        if not self._scanner_infos:
            self._set_status('no-dev')
            return

        self._open_scanner(self._scanner_infos[0][0])

    def _open_scanner(self, name):
        """Open the current scanner device

        Close the previous device if there is one, but ignore errors
        while closing. Open the device identified by name.

        Can be used to open the scanner device on start-up, change the
        current scanner or reopen the scanner device to work around
        lower layer bugs.
        """
        if self._current_scanner:
            old_scanner, self._current_scanner = self._current_scanner, None
            try:
                old_scanner.close()
                del old_scanner

            except sane.error, exc:
                logging.exception('Error closing scanner')

        if not name:
            self._set_status('no-dev')
            self._set_scanner(None, None)
            return

        try:
            scanner = sane.open(name)

        except sane.error, exc:
            logging.exception('Error opening scanner %r', name)
            self._show_error(exc)
            return

        self._set_scanner(scanner, name)
        self._set_status('ready')

    @trace()
    def _set_scanner(self, device, name):
        self._current_scanner = device
        self._current_scanner_name = name
        self._scan_thread.set_device(device)
        self._settings_toolbar.set_scanner(device)

    def _setup_widgets(self):
        self._setup_toolbar()
        self._setup_canvas()

    def _setup_canvas(self):
        vbox = gtk.VBox()
        self._status_entry = gtk.Entry()
        self._status_entry.set_editable(False)
        self._status_entry.set_sensitive(False)
        vbox.pack_start(self._status_entry, expand=False)
        self._status_entry.show()

        metadata_box = gtk.Table(2, 2, False)
        vbox.pack_start(metadata_box, expand=False)

        # TRANSLATORS: The character immediately following the underscore
        # is taken as the "mnemonic" (keyboard shortcut) associated with
        # this label. You need to make sure all labels have different
        # mnemonics associated with them. E.g. in english, T_itle and
        # T_ags (and therefore <Alt>+I resp. <Alt>+A) is used to resolve
        # a conflict between those two: using the first character for
        # both of them (i.e. _Title and _Tags) would result in the same
        # shortcut <Alt>+T.
        title_label = gtk.Label(_('T_itle:'))
        title_label.set_use_underline(True)
        metadata_box.attach(title_label, 0, 1, 0, 1, xoptions=0, xpadding=10)

        self._title_entry = gtk.Entry()
        self._title_entry.set_text(_('Scanned document'))
        title_label.set_mnemonic_widget(self._title_entry)
        metadata_box.attach(self._title_entry, 1, 2, 0, 1)

        # TRANSLATORS: The underscore indicates a mnemonic. See the
        # comment of 'T_itle' for more information.
        tags_label = gtk.Label(_('T_ags:'))
        tags_label.set_use_underline(True)
        metadata_box.attach(tags_label, 0, 1, 1, 2, xoptions=0, xpadding=10)

        self._tags_entry = gtk.Entry()
        tags_label.set_mnemonic_widget(self._tags_entry)
        metadata_box.attach(self._tags_entry, 1, 2, 1, 2)

        metadata_box.show_all()

        msg_box = gtk.TextView()
        msg_box.set_editable(False)
        msg_box.set_wrap_mode(gtk.WRAP_WORD)
        self._msg_box_buf = msg_box.get_buffer()
        #vbox.pack_start(msg_box, expand=False)
        #msg_box.show()

        images_window = gtk.ScrolledWindow()
        images_window.set_policy(gtk.POLICY_NEVER, gtk.POLICY_AUTOMATIC)
        model_types = [_type for name_, _type in self._MODEL_COLUMNS]
        self._images_model = gtk.ListStore(*model_types)
        self._images_view = gtk.TreeView(self._images_model)
        selection = self._images_view.get_selection()
        selection.connect('changed', self._selection_changed_cb)
        selection.set_mode(gtk.SELECTION_MULTIPLE)
        image_column = gtk.TreeViewColumn('Image', gtk.CellRendererPixbuf(),
                                          pixbuf=0)
        self._images_view.append_column(image_column)
        self._images_view.set_headers_visible(False)
        self._images_view.set_reorderable(True)
        images_window.add(self._images_view)
        images_window.show_all()
        vbox.pack_start(images_window, expand=True)

        self.set_canvas(vbox)
        vbox.show()

    def _setup_toolbar(self):
        toolbar_box = ToolbarBox()

        activity_button = ActivityToolbarButton(self)
        toolbar_box.toolbar.insert(activity_button, -1)
        activity_button.show()

        self._scan_button = ToolButton('start-scan1')
        self._scan_button.accelerator = '<Alt>S'
        self._scan_button.props.tooltip = _('Start scan')
        self._scan_button.connect('clicked', self._scan_button_cb)
        toolbar_box.toolbar.insert(self._scan_button, -1)
        self._scan_button.show()

        self._settings_toolbar = SettingsToolbar()
        settings_button = ToolbarButton()
        settings_button.props.icon_name = 'preferences-system'
        settings_button.props.label = _('Scanner settings')
        settings_button.props.page = self._settings_toolbar
        toolbar_box.toolbar.insert(settings_button, -1)
        settings_button.show()

        # HACK to work around fixed size of Sugar palettes
        def toolbar_button_realize_cb(*args):
            width, height = self._settings_toolbar.size_request()
            height += 10
            settings_button.page_widget.set_size_request(width, height)

        settings_button.connect('realize', lambda *args: gobject.idle_add(toolbar_button_realize_cb))

        self._remove_button = ToolButton('edit-delete')
        self._remove_button.props.tooltip = _('Remove selected page(s)')
        self._remove_button.set_sensitive(False)
        self._remove_button.connect('clicked', self._remove_button_cb)
        toolbar_box.toolbar.insert(self._remove_button, -1)
        self._remove_button.show()

        self._save_button = ToolButton('document-save')
        self._save_button.accelerator = '<Alt>P'
        self._save_button.props.tooltip = _('Save collection as PDF')
        self._save_button.set_sensitive(False)
        self._save_button.connect('clicked', self._save_button_cb)
        toolbar_box.toolbar.insert(self._save_button, -1)
        self._save_button.show()

        separator = gtk.SeparatorToolItem()
        separator.props.draw = False
        separator.set_expand(True)
        toolbar_box.toolbar.insert(separator, -1)
        separator.show()

        stop_button = StopButton(self)
        toolbar_box.toolbar.insert(stop_button, -1)
        stop_button.show()

        self.set_toolbar_box(toolbar_box)
        toolbar_box.show()

    @trace()
    def _scan_button_cb(self, *args):
        if self._status == 'ready':
            self._add_msg('triggering scan')
            self._set_status('scanning')
            self._scan_thread.start_scan()
        elif self._status == 'scanning':
            self._add_msg('stopping scan')
            self._set_status('stopping')
            self._scan_thread.stop_scan()
        else:
            logging.warning('_scan_button_cb called with status=%r',
                self._status)

    @trace()
    def _scan_finished_cb(self, image_infos, exc):
        gobject.idle_add(self._scan_finished_real_cb, image_infos, exc)

    @trace()
    def _scan_finished_real_cb(self, image_infos, exc):
        if exc:
            self._show_error(exc)

        if image_infos:
            num_images = len(image_infos)
            self._add_msg(ngettext('%d page scanned', '%d pages scanned',
                num_images) % (num_images, ))
            self._save_button.set_sensitive(True)

            self._add_images(image_infos)

        if not exc:
            self._set_status('ready')
        else:
            self._open_scanner(self._current_scanner_name)

    def _add_images(self, image_infos):
        for info in image_infos:
            row = [info[name] for name, type_ in self._MODEL_COLUMNS]
            self._images_model.append(row)

    def _selection_changed_cb(self, selection):
        selected = bool(selection.count_selected_rows())
        self._remove_button.set_sensitive(selected)

    def _remove_button_cb(self, button):
        model_, paths = self._images_view.get_selection().get_selected_rows()
        refs = [gtk.TreeRowReference(self._images_model, path)
                for path in paths]
        for ref in refs:
            iter = self._images_model.get_iter(ref.get_path())
            self._images_model.remove(iter)

    @trace()
    def _save_button_cb(self, *args):
        # TODO: do processing in background (another thread?)
        save_dir = os.path.join(self.get_activity_root(), 'instance')
        fd, file_name = tempfile.mkstemp(dir=save_dir)
        os.close(fd)
        self._save_pdf(file_name)

        jobject = datastore.create()
        jobject.metadata['mime_type'] = 'application/pdf'
        jobject.metadata['title'] = self._title_entry.get_text()
        jobject.metadata['tags'] = self._tags_entry.get_text()
        jobject.file_path = file_name
        self._save_button.set_sensitive(False)
        # async not supported, see SL#3071
        #datastore.write(jobject, transfer_ownership=True,
        #    reply_handler=self._save_reply_cb,
        #    error_handler=self._save_error_cb)
        try:
            datastore.write(jobject, transfer_ownership=True)
        except Exception, exception:
            self._save_error_cb(exception)
        else:
            self._save_reply_cb()

        jobject.destroy()

    @trace()
    def _save_pdf(self, file_name):
        width_idx = self._MODEL_COLUMNS_MAP['width_pixel']
        height_idx = self._MODEL_COLUMNS_MAP['height_pixel']
        dpi_idx = self._MODEL_COLUMNS_MAP['dpi']
        file_idx = self._MODEL_COLUMNS_MAP['file']

        options = ['-units', 'PixelsPerInch']
        image_options = [['-density', '%dx%d' % (row[dpi_idx], row[dpi_idx]),
                          row[file_idx].name]
                         for row in self._images_model]
        options += reduce(operator.add, image_options)
        options += ['-compress', 'Zip', 'PDF:' + file_name]

        logging.debug('Invoking %r', ['convert'] + options)
        subprocess.check_call(['convert'] + options)

    def _remove_image_files(self):
        for row in self._images_model:
            row[self._MODEL_COLUMNS_MAP['file']].close()

    @trace()
    def _save_reply_cb(self, *args):
        self._remove_image_files()
        self._images_model.clear()

    @trace()
    def _save_error_cb(self, error):
        self._show_error(error)
        self._save_button.set_sensitive(True)

    @trace()
    def _show_error(self, exc):
        self._add_msg(exc)
        self._set_status('error', exc)

    @trace()
    def _add_msg(self, msg):
        logging.info('%s', msg)
        self._msg_box_buf.insert(self._msg_box_buf.get_end_iter(),
            '%.1f %s\n' % (time.time(), msg))

    @trace()
    def _set_status(self, status, *args):
        self._status = status
        self._status_entry.set_text(self._STATUS_MSGS[status] % tuple(args))

        if self._status == 'ready':
            self._scan_button.set_icon('start-scan1')
            self._scan_button.props.tooltip = _('Start scan')
            self._scan_button.set_sensitive(True)
        elif self._status == 'scanning':
            self._scan_button.set_icon('stop-scan1')
            self._scan_button.props.tooltip = _('Stop scan')
            self._scan_button.set_sensitive(True)
        else:
            self._scan_button.set_sensitive(False)


def find_executable(name):
    for directory in os.environ['PATH'].split(':'):
        path = os.path.join(directory, name)
        if os.access(path, os.X_OK):
            return path

    return None


def start():
    gtk.gdk.threads_init()
    gtk.gdk.threads_enter()

# FIXME: can't call gtk.gdk.threads_leave() because sugar-activity
# (sugar.activity.main.main()) doesn't provide a hook for that. :(