@@ -184,6 +184,9 @@ def get_filename_question(*, suggested_filename, url, parent=None):
     """
     suggested_filename = utils.sanitize_filename(suggested_filename)
 
+    if url.toDisplayString()[:7] == "file://":
+        return "FILE"
+
     q = usertypes.Question(parent)
     q.title = "Save file to:"
     q.text = "Please enter a location for <b>{}</b>".format(
# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et:

# Copyright 2014-2021 Florian Bruhin (The Compiler) <mail@qutebrowser.org>
#
# This file is part of qutebrowser.
#
# qutebrowser 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.
#
# qutebrowser 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 qutebrowser.  If not, see <https://www.gnu.org/licenses/>.

"""Shared QtWebKit/QtWebEngine code for downloads."""

import re
import sys
import html
import os.path
import collections
import functools
import pathlib
import tempfile
import enum
from typing import Any, Dict, IO, List, MutableSequence, Optional, Union

from PyQt5.QtCore import (pyqtSlot, pyqtSignal, Qt, QObject, QModelIndex,
                          QTimer, QAbstractListModel, QUrl)

from qutebrowser.browser import pdfjs
from qutebrowser.api import cmdutils
from qutebrowser.config import config
from qutebrowser.utils import (usertypes, standarddir, utils, message, log,
                               qtutils, objreg)
from qutebrowser.qt import sip


class ModelRole(enum.IntEnum):

    """Custom download model roles."""

    item = Qt.UserRole


# Remember the last used directory
last_used_directory: Optional[str] = None

# All REFRESH_INTERVAL milliseconds, speeds will be recalculated and downloads
# redrawn.
_REFRESH_INTERVAL = 500


class UnsupportedAttribute:

    """Class which is used to create attributes which are not supported.

    This is used for attributes like "fileobj" for downloads which are not
    supported with QtWebengine.
    """


class UnsupportedOperationError(Exception):

    """Raised when an operation is not supported with the given backend."""


def init():
    """Set the application wide downloads variables."""
    global last_used_directory
    last_used_directory = None

    config.instance.changed.connect(_clear_last_used)


@pyqtSlot()
def shutdown():
    temp_download_manager.cleanup()


@config.change_filter('downloads.location.directory', function=True)
def _clear_last_used():
    global last_used_directory
    last_used_directory = None


def download_dir():
    """Get the download directory to use."""
    directory = config.val.downloads.location.directory
    remember_dir = config.val.downloads.location.remember

    if remember_dir and last_used_directory is not None:
        ddir = last_used_directory
    elif directory is None:
        ddir = standarddir.download()
    else:
        ddir = directory

    try:
        os.makedirs(ddir, exist_ok=True)
    except OSError as e:
        message.error("Failed to create download directory: {}".format(e))

    return ddir


def immediate_download_path(prompt_download_directory=None):
    """Try to get an immediate download path without asking the user.

    If that's possible, we return a path immediately. If not, None is returned.

    Args:
        prompt_download_directory: If this is something else than None, it
                                   will overwrite the
                                   downloads.location.prompt setting.
    """
    if prompt_download_directory is None:
        prompt_download_directory = config.val.downloads.location.prompt

    if not prompt_download_directory:
        return download_dir()

    return None


def _path_suggestion(filename):
    """Get the suggested file path.

    Args:
        filename: The filename to use if included in the suggestion.
    """
    suggestion = config.val.downloads.location.suggestion
    if suggestion == 'path':
        # add trailing '/' if not present
        return os.path.join(download_dir(), '')
    elif suggestion == 'filename':
        return filename
    elif suggestion == 'both':
        return os.path.join(download_dir(), filename)
    else:  # pragma: no cover
        raise ValueError("Invalid suggestion value {}!".format(suggestion))


def create_full_filename(basename, filename):
    """Create a full filename based on the given basename and filename.

    Args:
        basename: The basename to use if filename is a directory.
        filename: The path to a folder or file where you want to save.

    Return:
        The full absolute path, or None if filename creation was not possible.
    """
    basename = utils.sanitize_filename(basename)
    # Filename can be a full path so don't use sanitize_filename on it.
    # Remove chars which can't be encoded in the filename encoding.
    # See https://github.com/qutebrowser/qutebrowser/issues/427
    encoding = sys.getfilesystemencoding()
    filename = utils.force_encoding(filename, encoding)
    if os.path.isabs(filename) and (os.path.isdir(filename) or
                                    filename.endswith(os.sep)):
        # We got an absolute directory from the user, so we save it under
        # the default filename in that directory.
        return os.path.join(filename, basename)
    elif os.path.isabs(filename):
        # We got an absolute filename from the user, so we save it under
        # that filename.
        return filename
    return None


def get_filename_question(*, suggested_filename, url, parent=None):
    """Get a Question object for a download-path.

    Args:
        suggested_filename: The "default"-name that is pre-entered as path.
        url: The URL the download originated from.
        parent: The parent of the question (a QObject).
    """
    suggested_filename = utils.sanitize_filename(suggested_filename)

    q = usertypes.Question(parent)
    q.title = "Save file to:"
    q.text = "Please enter a location for <b>{}</b>".format(
        html.escape(url.toDisplayString()))
    q.url = url.toString(QUrl.RemovePassword | QUrl.FullyEncoded)
    q.mode = usertypes.PromptMode.download
    q.completed.connect(q.deleteLater)
    q.default = _path_suggestion(suggested_filename)
    return q


def transform_path(path):
    r"""Do platform-specific transformations, like changing E: to E:\.

    Returns None if the path is invalid on the current platform.
    """
    if not utils.is_windows:
        return path
    path = utils.expand_windows_drive(path)
    # Drive dependent working directories are not supported, e.g.
    # E:filename is invalid
    if re.search(r'^[A-Z]:[^\\]', path, re.IGNORECASE):
        return None
    # Paths like COM1, ...
    # See https://github.com/qutebrowser/qutebrowser/issues/82
    if pathlib.Path(path).is_reserved():
        return None
    return path


def suggested_fn_from_title(url_path, title=None):
    """Suggest a filename depending on the URL extension and page title.

    Args:
        url_path: a string with the URL path
        title: the page title string

    Return:
        The download filename based on the title, or None if the extension is
        not found in the whitelist (or if there is no page title).
    """
    ext_whitelist = [".html", ".htm", ".php", ""]
    _, ext = os.path.splitext(url_path)

    suggested_fn: Optional[str] = None
    if ext.lower() in ext_whitelist and title:
        suggested_fn = utils.sanitize_filename(title, shorten=True)
        if not suggested_fn.lower().endswith((".html", ".htm")):
            suggested_fn += ".html"
            suggested_fn = utils.sanitize_filename(suggested_fn, shorten=True)

    return suggested_fn


class NoFilenameError(Exception):

    """Raised when we can't find out a filename in DownloadTarget."""


# Where a download should be saved
class _DownloadTarget:

    """Abstract base class for different download targets."""

    def suggested_filename(self):
        """Get the suggested filename for this download target."""
        raise NotImplementedError


class FileDownloadTarget(_DownloadTarget):

    """Save the download to the given file.

    Attributes:
        filename: Filename where the download should be saved.
        force_overwrite: Whether to overwrite the target without
                         prompting the user.
    """

    def __init__(self, filename, force_overwrite=False):
        self.filename = filename
        self.force_overwrite = force_overwrite

    def suggested_filename(self):
        return os.path.basename(self.filename)

    def __str__(self):
        return self.filename


class FileObjDownloadTarget(_DownloadTarget):

    """Save the download to the given file-like object.

    Attributes:
        fileobj: File-like object where the download should be written to.
    """

    def __init__(self, fileobj):
        self.fileobj = fileobj

    def suggested_filename(self):
        try:
            return self.fileobj.name
        except AttributeError:
            raise NoFilenameError

    def __str__(self):
        try:
            return 'file object at {}'.format(self.fileobj.name)
        except AttributeError:
            return 'anonymous file object'


class OpenFileDownloadTarget(_DownloadTarget):

    """Save the download in a temp dir and directly open it.

    Attributes:
        cmdline: The command to use as string. A `{}` is expanded to the
                 filename. None means to use the system's default application.
                 If no `{}` is found, the filename is appended to the cmdline.
    """

    def __init__(self, cmdline=None):
        self.cmdline = cmdline

    def suggested_filename(self):
        raise NoFilenameError

    def __str__(self):
        return 'temporary file'


class PDFJSDownloadTarget(_DownloadTarget):

    """Open the download via PDF.js."""

    def suggested_filename(self):
        raise NoFilenameError

    def __str__(self):
        return 'temporary PDF.js file'


class DownloadItemStats(QObject):

    """Statistics (bytes done, total bytes, time, etc.) about a download.

    Class attributes:
        SPEED_AVG_WINDOW: How many seconds of speed data to average to
                          estimate the remaining time.

    Attributes:
        done: How many bytes there are already downloaded.
        total: The total count of bytes.  None if the total is unknown.
        speed: The current download speed, in bytes per second.
        _speed_avg: A rolling average of speeds.
        _last_done: The count of bytes which where downloaded when calculating
                    the speed the last time.
    """

    SPEED_AVG_WINDOW = 30

    def __init__(self, parent=None):
        super().__init__(parent)
        self.total = None
        self.done = None
        self.speed = 0
        self._last_done = 0
        samples = int(self.SPEED_AVG_WINDOW * (1000 / _REFRESH_INTERVAL))
        self._speed_avg: MutableSequence[float] = collections.deque(maxlen=samples)

    def update_speed(self):
        """Recalculate the current download speed.

        The caller needs to guarantee this is called all _REFRESH_INTERVAL ms.
        """
        if self.done is None:
            # this can happen for very fast downloads, e.g. when actually
            # opening a file
            return
        delta = self.done - self._last_done
        self.speed = delta * 1000 / _REFRESH_INTERVAL
        self._speed_avg.append(self.speed)
        self._last_done = self.done

    def finish(self):
        """Set the download stats as finished."""
        self.done = self.total

    def percentage(self):
        """The current download percentage, or None if unknown."""
        if self.done == self.total:
            return 100
        elif self.total is None:
            return None
        else:
            assert self.done is not None
            return 100 * self.done / self.total

    def remaining_time(self):
        """The remaining download time in seconds, or None."""
        if self.total is None or not self._speed_avg:
            # No average yet or we don't know the total size.
            return None
        remaining_bytes = self.total - self.done
        avg = sum(self._speed_avg) / len(self._speed_avg)
        if avg == 0:
            # Download stalled
            return None
        else:
            return remaining_bytes / avg

    @pyqtSlot('qint64', 'qint64')
    def on_download_progress(self, bytes_done, bytes_total):
        """Update local variables when the download progress changed.

        Args:
            bytes_done: How many bytes are downloaded.
            bytes_total: How many bytes there are to download in total.
        """
        if bytes_total in [0, -1]:  # QtWebEngine, QtWebKit
            bytes_total = None
        self.done = bytes_done
        self.total = bytes_total


class AbstractDownloadItem(QObject):

    """Shared QtNetwork/QtWebEngine part of a download item.

    Attributes:
        done: Whether the download is finished.
        stats: A DownloadItemStats object.
        index: The index of the download in the view.
        successful: Whether the download has completed successfully.
        error_msg: The current error message, or None
        fileobj: The file object to download the file to.
        raw_headers: The headers sent by the server.
        _filename: The filename of the download.
        _dead: Whether the Download has _die()'d.
        _manager: The DownloadManager which started this download.

    Signals:
        data_changed: The downloads metadata changed.
        finished: The download was finished.
        cancelled: The download was cancelled.
        error: An error with the download occurred.
               arg: The error message as string.
        remove_requested: Emitted when the removal of this download was
                          requested.
        pdfjs_requested: Emitted when PDF.js should be opened.
                         arg 1: The filename of the PDF download.
                         arg 2: The original download URL.
    """

    data_changed = pyqtSignal()
    finished = pyqtSignal()
    error = pyqtSignal(str)
    cancelled = pyqtSignal()
    remove_requested = pyqtSignal()
    pdfjs_requested = pyqtSignal(str, QUrl)

    def __init__(self, manager, parent=None):
        super().__init__(parent)
        self._manager = manager
        self.done = False
        self.stats = DownloadItemStats(self)
        self.index = 0
        self.error_msg = None
        self.basename = '???'
        self.successful = False

        self.fileobj: Union[
            UnsupportedAttribute, IO[bytes], None
        ] = UnsupportedAttribute()
        self.raw_headers: Union[
            UnsupportedAttribute, Dict[bytes, bytes]
        ] = UnsupportedAttribute()

        self._filename: Optional[str] = None
        self._dead = False

    def __repr__(self):
        return utils.get_repr(self, basename=self.basename)

    def __str__(self):
        """Get the download as a string.

        Example: foo.pdf [699.2kB/s|0.34|16%|4.253/25.124]
        """
        speed = utils.format_size(self.stats.speed, suffix='B/s')
        down = utils.format_size(self.stats.done, suffix='B')
        perc = self.stats.percentage()
        remaining = self.stats.remaining_time()
        if self.error_msg is None:
            errmsg = ""
        else:
            errmsg = " - {}".format(self.error_msg)

        if all(e is None for e in [perc, remaining, self.stats.total]):
            return ('{index}: {name} [{speed:>10}|{down}]{errmsg}'.format(
                index=self.index, name=self.basename, speed=speed,
                down=down, errmsg=errmsg))

        perc = round(perc)
        if remaining is None:
            remaining = '?'
        else:
            remaining = utils.format_seconds(remaining)
        total = utils.format_size(self.stats.total, suffix='B')
        if self.done:
            return ('{index}: {name} [{perc:>2}%|{total}]{errmsg}'.format(
                index=self.index, name=self.basename, perc=perc,
                total=total, errmsg=errmsg))
        else:
            return ('{index}: {name} [{speed:>10}|{remaining:>5}|{perc:>2}%|'
                    '{down}/{total}]{errmsg}'.format(
                        index=self.index, name=self.basename, speed=speed,
                        remaining=remaining, perc=perc, down=down,
                        total=total, errmsg=errmsg))

    def _do_die(self):
        """Do cleanup steps after a download has died."""
        raise NotImplementedError

    def _die(self, msg):
        """Abort the download and emit an error."""
        assert not self.successful
        # Prevent actions if calling _die() twice.
        #
        # For QtWebKit, this might happen if the error handler correctly
        # connects, and the error occurs in _init_reply between
        # reply.error.connect and the reply.error() check. In this case, the
        # connected error handlers will be called twice, once via the direct
        # error.emit() and once here in _die(). The stacks look like this then:
        #
        #   <networkmanager error.emit> -> on_reply_error -> _die ->
        #   self.error.emit()
        #
        # and
        #
        #   [_init_reply -> <single shot timer> ->] <lambda in _init_reply> ->
        #   self.error.emit()
        #
        # which may lead to duplicate error messages (and failing tests)
        if self._dead:
            return
        self._dead = True
        self._do_die()
        self.error_msg = msg
        self.stats.finish()
        self.error.emit(msg)
        self.done = True
        self.data_changed.emit()

    def get_status_color(self, position):
        """Choose an appropriate color for presenting the download's status.

        Args:
            position: The color type requested, can be 'fg' or 'bg'.
        """
        assert position in ["fg", "bg"]
        start = getattr(config.val.colors.downloads.start, position)
        stop = getattr(config.val.colors.downloads.stop, position)
        system = getattr(config.val.colors.downloads.system, position)
        error = getattr(config.val.colors.downloads.error, position)
        if self.error_msg is not None:
            assert not self.successful
            return error
        elif self.stats.percentage() is None:
            return start
        else:
            return qtutils.interpolate_color(
                start, stop, self.stats.percentage(), system)

    def _do_cancel(self):
        """Actual cancel implementation."""
        raise NotImplementedError

    @pyqtSlot()
    def cancel(self, *, remove_data=True):
        """Cancel the download.

        Args:
            remove_data: Whether to remove the downloaded data.
        """
        assert not self.done
        self._do_cancel()
        log.downloads.debug("cancelled")
        if remove_data:
            self.delete()
        self.done = True
        self.finished.emit()
        self.data_changed.emit()

    @pyqtSlot()
    def remove(self):
        """Remove the download from the model."""
        self.remove_requested.emit()

    def delete(self):
        """Delete the downloaded file."""
        try:
            if self._filename is not None and os.path.exists(self._filename):
                os.remove(self._filename)
                log.downloads.debug("Deleted {}".format(self._filename))
            else:
                log.downloads.debug("Not deleting {}".format(self._filename))
        except OSError:
            log.downloads.exception("Failed to remove partial file")

    @pyqtSlot()
    def retry(self):
        """Retry a failed download."""
        raise NotImplementedError

    @pyqtSlot()
    def try_retry(self):
        """Try to retry a download and show an error if it's unsupported."""
        try:
            self.retry()
        except UnsupportedOperationError as e:
            message.error(str(e))

    def url(self) -> QUrl:
        """Get the download's origin URL."""
        raise NotImplementedError

    def _get_open_filename(self):
        """Get the filename to open a download.

        Returns None if no suitable filename was found.
        """
        raise NotImplementedError

    @pyqtSlot()
    def open_file(self, cmdline=None, open_dir=False):
        """Open the downloaded file.

        Args:
            cmdline: The command to use as string. A `{}` is expanded to the
                     filename. None means to use the system's default
                     application or `downloads.open_dispatcher` if set. If no
                     `{}` is found, the filename is appended to the cmdline.
            open_dir: Specify whether to open the file's directory instead.
        """
        assert self.successful
        filename = self._get_open_filename()
        if filename is None:  # pragma: no cover
            log.downloads.error("No filename to open the download!")
            return
        if open_dir:
            filename = os.path.dirname(filename)
        # By using a singleshot timer, we ensure that we return fast. This
        # is important on systems where process creation takes long, as
        # otherwise the prompt might hang around and cause bugs
        # (see issue #2296)
        QTimer.singleShot(0, lambda: utils.open_file(filename, cmdline))

    def _ensure_can_set_filename(self, filename):
        """Make sure we can still set a filename."""
        raise NotImplementedError

    def _after_set_filename(self):
        """Finish initialization based on self._filename."""
        raise NotImplementedError

    def _ask_confirm_question(self, title, msg, *, custom_yes_action=None):
        """Ask a confirmation question for the download."""
        raise NotImplementedError

    def _ask_create_parent_question(self, title, msg,
                                    force_overwrite, remember_directory):
        """Ask a confirmation question for the parent directory."""
        raise NotImplementedError

    def _set_fileobj(self, fileobj, *, autoclose=True):
        """Set a file object to save the download to.

        Not supported by QtWebEngine.

        Args:
            fileobj: The file object to download to.
            autoclose: Close the file object automatically when it's done.
        """
        raise NotImplementedError

    def _set_tempfile(self, fileobj):
        """Set a temporary file when opening the download."""
        raise NotImplementedError

    def _set_filename(self, filename, *, force_overwrite=False,
                      remember_directory=True):
        """Set the filename to save the download to.

        Args:
            filename: The full filename to save the download to.
                      None: special value to stop the download.
            force_overwrite: Force overwriting existing files.
            remember_directory: If True, remember the directory for future
                                downloads.
        """
        filename = os.path.expanduser(filename)
        self._ensure_can_set_filename(filename)

        self._filename = create_full_filename(self.basename, filename)
        if self._filename is None:
            # We only got a filename (without directory) or a relative path
            # from the user, so we append that to the default directory and
            # try again.
            self._filename = create_full_filename(
                self.basename, os.path.join(download_dir(), filename))

        # At this point, we have a misconfigured XDG_DOWNLOAD_DIR, as
        # download_dir() + filename is still no absolute path.
        # The config value is checked for "absoluteness", but
        # ~/.config/user-dirs.dirs may be misconfigured and a non-absolute path
        # may be set for XDG_DOWNLOAD_DIR
        if self._filename is None:
            message.error(
                "XDG_DOWNLOAD_DIR points to a relative path - please check"
                " your ~/.config/user-dirs.dirs. The download is saved in"
                " your home directory.",
            )
            # fall back to $HOME as download_dir
            self._filename = create_full_filename(self.basename,
                                                  os.path.expanduser('~'))

        dirname = os.path.dirname(self._filename)
        if not os.path.exists(dirname):
            txt = ("<b>{}</b> does not exist. Create it?".
                   format(html.escape(
                       os.path.join(dirname, ""))))
            self._ask_create_parent_question("Create directory?", txt,
                                             force_overwrite,
                                             remember_directory)
        else:
            self._after_create_parent_question(force_overwrite,
                                               remember_directory)

    def _after_create_parent_question(self,
                                      force_overwrite, remember_directory):
        """After asking about parent directory.

        Args:
            force_overwrite: Force overwriting existing files.
            remember_directory: If True, remember the directory for future
                                downloads.
        """
        assert self._filename is not None
        global last_used_directory

        try:
            os.makedirs(os.path.dirname(self._filename), exist_ok=True)
        except OSError as e:
            self._die(e.strerror)

        self.basename = os.path.basename(self._filename)
        if remember_directory:
            last_used_directory = os.path.dirname(self._filename)

        log.downloads.debug("Setting filename to {}".format(self._filename))
        if self._get_conflicting_download():
            txt = ("<b>{}</b> is already downloading. Cancel and "
                   "re-download?".format(html.escape(self._filename)))
            self._ask_confirm_question(
                "Cancel other download?", txt,
                custom_yes_action=self._cancel_conflicting_download)
        elif force_overwrite:
            self._after_set_filename()
        elif os.path.isfile(self._filename):
            # The file already exists, so ask the user if it should be
            # overwritten.
            txt = "<b>{}</b> already exists. Overwrite?".format(
                html.escape(self._filename))
            self._ask_confirm_question("Overwrite existing file?", txt)
        # FIFO, device node, etc. Make sure we want to do this
        elif (os.path.exists(self._filename) and
              not os.path.isdir(self._filename)):
            txt = ("<b>{}</b> already exists and is a special file. Write to "
                   "it anyways?".format(html.escape(self._filename)))
            self._ask_confirm_question("Overwrite special file?", txt)
        else:
            self._after_set_filename()

    def _conflicts_with(self, other: 'AbstractDownloadItem') -> bool:
        """Check if this download conflicts with the other given one."""
        return (
            other is not self and
            other._filename == self._filename and  # pylint: disable=protected-access
            not other.done
        )

    def _get_conflicting_download(self):
        """Return another potential active download with the same name."""
        for download in self._manager.downloads:
            if self._conflicts_with(download):
                return download
        return None

    def _cancel_conflicting_download(self):
        """Cancel any conflicting download and call _after_set_filename."""
        conflicting_download = self._get_conflicting_download()
        if conflicting_download:
            conflicting_download.cancel(remove_data=False)
        self._after_set_filename()

    def _open_if_successful(self, cmdline):
        """Open the downloaded file, but only if it was successful.

        Args:
            cmdline: Passed to DownloadItem.open_file().
        """
        if not self.successful:
            log.downloads.debug("{} finished but not successful, not opening!"
                                .format(self))
            return
        self.open_file(cmdline)

    def _pdfjs_if_successful(self):
        """Open the file via PDF.js if downloading was successful."""
        if not self.successful:
            log.downloads.debug("{} finished but not successful, not opening!"
                                .format(self))
            return

        filename = self._get_open_filename()
        if filename is None:  # pragma: no cover
            log.downloads.error("No filename to open the download!")
            return
        self.pdfjs_requested.emit(os.path.basename(filename),
                                  self.url())

    def set_target(self, target):
        """Set the target for a given download.

        Args:
            target: The DownloadTarget for this download.
        """
        if isinstance(target, FileObjDownloadTarget):
            self._set_fileobj(target.fileobj, autoclose=False)
        elif isinstance(target, FileDownloadTarget):
            self._set_filename(
                target.filename, force_overwrite=target.force_overwrite)
        elif isinstance(target, (OpenFileDownloadTarget, PDFJSDownloadTarget)):
            try:
                fobj = temp_download_manager.get_tmpfile(self.basename)
            except OSError as exc:
                msg = "Download error: {}".format(exc)
                message.error(msg)
                self.cancel()
                return

            if isinstance(target, OpenFileDownloadTarget):
                self.finished.connect(functools.partial(
                    self._open_if_successful, target.cmdline))
            elif isinstance(target, PDFJSDownloadTarget):
                self.finished.connect(self._pdfjs_if_successful)
            else:
                raise utils.Unreachable

            self._set_tempfile(fobj)
        else:  # pragma: no cover
            raise ValueError("Unsupported download target: {}".format(target))


class AbstractDownloadManager(QObject):

    """Backend-independent download manager code.

    Attributes:
        downloads: A list of active DownloadItems.
        _networkmanager: A NetworkManager for generic downloads.

    Signals:
        begin_remove_row: Emitted before downloads are removed.
        end_remove_row: Emitted after downloads are removed.
        begin_insert_row: Emitted before downloads are inserted.
        end_insert_row: Emitted after downloads are inserted.
        data_changed: Emitted when the data of the model changed.
                      The argument is the index of the changed download
    """

    begin_remove_row = pyqtSignal(int)
    end_remove_row = pyqtSignal()
    begin_insert_row = pyqtSignal(int)
    end_insert_row = pyqtSignal()
    data_changed = pyqtSignal(int)

    def __init__(self, parent=None):
        super().__init__(parent)
        self.downloads: List[AbstractDownloadItem] = []
        self._update_timer = usertypes.Timer(self, 'download-update')
        self._update_timer.timeout.connect(self._update_gui)
        self._update_timer.setInterval(_REFRESH_INTERVAL)

    def __repr__(self):
        return utils.get_repr(self, downloads=len(self.downloads))

    @pyqtSlot()
    def _update_gui(self):
        """Periodical GUI update of all items."""
        assert self.downloads
        for dl in self.downloads:
            dl.stats.update_speed()
        self.data_changed.emit(-1)

    @pyqtSlot(str, QUrl)
    def _on_pdfjs_requested(self, filename: str, original_url: QUrl) -> None:
        """Open PDF.js when a download requests it."""
        tabbed_browser = objreg.get('tabbed-browser', scope='window',
                                    window='last-focused')
        tabbed_browser.tabopen(pdfjs.get_main_url(filename, original_url),
                               background=False)

    def _init_item(self, download, auto_remove, suggested_filename):
        """Initialize a newly created DownloadItem."""
        download.cancelled.connect(download.remove)
        download.remove_requested.connect(functools.partial(
            self._remove_item, download))

        delay = config.val.downloads.remove_finished
        if delay > -1:
            download.finished.connect(
                lambda: QTimer.singleShot(delay, download.remove))
        elif auto_remove:
            download.finished.connect(download.remove)

        download.data_changed.connect(
            functools.partial(self._on_data_changed, download))
        download.error.connect(self._on_error)
        download.pdfjs_requested.connect(self._on_pdfjs_requested)

        download.basename = suggested_filename
        idx = len(self.downloads)
        download.index = idx + 1  # "Human readable" index
        self.begin_insert_row.emit(idx)
        self.downloads.append(download)
        self.end_insert_row.emit()

        if not self._update_timer.isActive():
            self._update_timer.start()

    @pyqtSlot(AbstractDownloadItem)
    def _on_data_changed(self, download):
        """Emit data_changed signal when download data changed."""
        try:
            idx = self.downloads.index(download)
        except ValueError:
            # download has been deleted in the meantime
            return
        self.data_changed.emit(idx)

    @pyqtSlot(str)
    def _on_error(self, msg):
        """Display error message on download errors."""
        message.error("Download error: {}".format(msg))

    @pyqtSlot(AbstractDownloadItem)
    def _remove_item(self, download):
        """Remove a given download."""
        if sip.isdeleted(self):
            # https://github.com/qutebrowser/qutebrowser/issues/1242
            return
        try:
            idx = self.downloads.index(download)
        except ValueError:
            # already removed
            return
        self.begin_remove_row.emit(idx)
        del self.downloads[idx]
        self.end_remove_row.emit()
        download.deleteLater()
        self._update_indexes()
        if not self.downloads:
            self._update_timer.stop()
        log.downloads.debug("Removed download {}".format(download))

    def _update_indexes(self):
        """Update indexes of all DownloadItems."""
        for i, d in enumerate(self.downloads, 1):
            d.index = i
        self.data_changed.emit(-1)

    def _init_filename_question(self, question, download):
        """Set up an existing filename question with a download."""
        question.answered.connect(download.set_target)
        question.cancelled.connect(download.cancel)
        download.cancelled.connect(question.abort)
        download.error.connect(question.abort)

    @pyqtSlot()
    def shutdown(self):
        """Cancel all downloads when shutting down."""
        for download in self.downloads:
            if not download.done:
                download.cancel(remove_data=False)


class DownloadModel(QAbstractListModel):

    """A list model showing downloads."""

    def __init__(self, qtnetwork_manager, webengine_manager=None, parent=None):
        super().__init__(parent)
        self._qtnetwork_manager = qtnetwork_manager
        self._webengine_manager = webengine_manager

        qtnetwork_manager.data_changed.connect(
            functools.partial(self._on_data_changed, webengine=False))
        qtnetwork_manager.begin_insert_row.connect(
            functools.partial(self._on_begin_insert_row, webengine=False))
        qtnetwork_manager.begin_remove_row.connect(
            functools.partial(self._on_begin_remove_row, webengine=False))
        qtnetwork_manager.end_insert_row.connect(self.endInsertRows)
        qtnetwork_manager.end_remove_row.connect(self.endRemoveRows)

        if webengine_manager is not None:
            webengine_manager.data_changed.connect(
                functools.partial(self._on_data_changed, webengine=True))
            webengine_manager.begin_insert_row.connect(
                functools.partial(self._on_begin_insert_row, webengine=True))
            webengine_manager.begin_remove_row.connect(
                functools.partial(self._on_begin_remove_row, webengine=True))
            webengine_manager.end_insert_row.connect(self.endInsertRows)
            webengine_manager.end_remove_row.connect(self.endRemoveRows)

    def _all_downloads(self):
        """Combine downloads from both downloaders."""
        if self._webengine_manager is None:
            return self._qtnetwork_manager.downloads[:]
        else:
            return (self._qtnetwork_manager.downloads +
                    self._webengine_manager.downloads)

    def __len__(self):
        return len(self._all_downloads())

    def __iter__(self):
        return iter(self._all_downloads())

    def __getitem__(self, idx):
        return self._all_downloads()[idx]

    def _on_begin_insert_row(self, idx, webengine=False):
        log.downloads.debug("_on_begin_insert_row with idx {}, "
                            "webengine {}".format(idx, webengine))
        if idx == -1:
            self.beginInsertRows(QModelIndex(), 0, -1)
            return

        assert idx >= 0, idx
        if webengine:
            idx += len(self._qtnetwork_manager.downloads)
        self.beginInsertRows(QModelIndex(), idx, idx)

    def _on_begin_remove_row(self, idx, webengine=False):
        log.downloads.debug("_on_begin_remove_row with idx {}, "
                            "webengine {}".format(idx, webengine))
        if idx == -1:
            self.beginRemoveRows(QModelIndex(), 0, -1)
            return

        assert idx >= 0, idx
        if webengine:
            idx += len(self._qtnetwork_manager.downloads)
        self.beginRemoveRows(QModelIndex(), idx, idx)

    def _on_data_changed(self, idx, *, webengine):
        """Called when a downloader's data changed.

        Args:
            start: The first changed index as int.
            end: The last changed index as int, or -1 for all indices.
            webengine: If given, the QtNetwork download length is added to the
                      index.
        """
        if idx == -1:
            start_index = self.index(0, 0)
            end_index = self.last_index()
        else:
            if webengine:
                idx += len(self._qtnetwork_manager.downloads)
            start_index = self.index(idx, 0)
            end_index = self.index(idx, 0)
            qtutils.ensure_valid(start_index)
            qtutils.ensure_valid(end_index)
        self.dataChanged.emit(start_index, end_index)

    def _raise_no_download(self, count):
        """Raise an exception that the download doesn't exist.

        Args:
            count: The index of the download
        """
        if not count:
            raise cmdutils.CommandError("There's no download!")
        raise cmdutils.CommandError("There's no download {}!".format(count))

    @cmdutils.register(instance='download-model', scope='window')
    @cmdutils.argument('count', value=cmdutils.Value.count)
    def download_cancel(self, all_=False, count=0):
        """Cancel the last/[count]th download.

        Args:
            all_: Cancel all running downloads
            count: The index of the download to cancel.
        """
        downloads = self._all_downloads()
        if all_:
            for download in downloads:
                if not download.done:
                    download.cancel()
        else:
            try:
                download = downloads[count - 1]
            except IndexError:
                self._raise_no_download(count)
            if download.done:
                if not count:
                    count = len(self)
                raise cmdutils.CommandError("Download {} is already done!"
                                            .format(count))
            download.cancel()

    @cmdutils.register(instance='download-model', scope='window')
    @cmdutils.argument('count', value=cmdutils.Value.count)
    def download_delete(self, count=0):
        """Delete the last/[count]th download from disk.

        Args:
            count: The index of the download to delete.
        """
        try:
            download = self[count - 1]
        except IndexError:
            self._raise_no_download(count)
        if not download.successful:
            if not count:
                count = len(self)
            raise cmdutils.CommandError("Download {} is not done!"
                                        .format(count))
        download.delete()
        download.remove()
        log.downloads.debug("deleted download {}".format(download))

    @cmdutils.register(instance='download-model', scope='window', maxsplit=0)
    @cmdutils.argument('count', value=cmdutils.Value.count)
    def download_open(self, cmdline: str = None, count: int = 0,
                      dir_: bool = False) -> None:
        """Open the last/[count]th download.

        If no specific command is given, this will use the system's default
        application to open the file.

        Args:
            cmdline: The command which should be used to open the file. A `{}`
                     is expanded to the temporary file name. If no `{}` is
                     present, the filename is automatically appended to the
                     cmdline.
            count: The index of the download to open.
            dir_: Whether to open the file's directory instead.
        """
        try:
            download = self[count - 1]
        except IndexError:
            self._raise_no_download(count)
        if not download.successful:
            if not count:
                count = len(self)
            raise cmdutils.CommandError("Download {} is not done!"
                                        .format(count))
        download.open_file(cmdline, open_dir=dir_)

    @cmdutils.register(instance='download-model', scope='window')
    @cmdutils.argument('count', value=cmdutils.Value.count)
    def download_retry(self, count=0):
        """Retry the first failed/[count]th download.

        Args:
            count: The index of the download to retry.
        """
        if count:
            try:
                download = self[count - 1]
            except IndexError:
                self._raise_no_download(count)
            if download.successful or not download.done:
                raise cmdutils.CommandError("Download {} did not fail!"
                                            .format(count))
        else:
            to_retry = [d for d in self if d.done and not d.successful]
            if not to_retry:
                raise cmdutils.CommandError("No failed downloads!")
            download = to_retry[0]
        download.try_retry()

    def can_clear(self):
        """Check if there are finished downloads to clear."""
        return any(download.done for download in self)

    @cmdutils.register(instance='download-model', scope='window')
    def download_clear(self):
        """Remove all finished downloads from the list."""
        for download in self:
            if download.done:
                download.remove()

    @cmdutils.register(instance='download-model', scope='window')
    @cmdutils.argument('count', value=cmdutils.Value.count)
    def download_remove(self, all_=False, count=0):
        """Remove the last/[count]th download from the list.

        Args:
            all_: Remove all finished downloads.
            count: The index of the download to remove.
        """
        if all_:
            self.download_clear()
        else:
            try:
                download = self[count - 1]
            except IndexError:
                self._raise_no_download(count)
            if not download.done:
                if not count:
                    count = len(self)
                raise cmdutils.CommandError("Download {} is not done!"
                                            .format(count))
            download.remove()

    def running_downloads(self):
        """Return the amount of still running downloads.

        Return:
            The number of unfinished downloads.
        """
        return sum(1 for download in self if not download.done)

    def last_index(self):
        """Get the last index in the model.

        Return:
            A (possibly invalid) QModelIndex.
        """
        idx = self.index(self.rowCount() - 1)
        return idx

    def headerData(self, section, orientation, role=Qt.DisplayRole):
        """Simple constant header."""
        if (section == 0 and orientation == Qt.Horizontal and
                role == Qt.DisplayRole):
            return "Downloads"
        else:
            return ""

    def data(self, index, role):
        """Download data from DownloadManager."""
        if not index.isValid():
            return None

        if index.parent().isValid() or index.column() != 0:
            return None

        item = self[index.row()]
        if role == Qt.DisplayRole:
            data: Any = str(item)
        elif role == Qt.ForegroundRole:
            data = item.get_status_color('fg')
        elif role == Qt.BackgroundRole:
            data = item.get_status_color('bg')
        elif role == ModelRole.item:
            data = item
        elif role == Qt.ToolTipRole:
            if item.error_msg is None:
                data = None
            else:
                return item.error_msg
        else:
            data = None
        return data

    def flags(self, index):
        """Override flags so items aren't selectable.

        The default would be Qt.ItemIsEnabled | Qt.ItemIsSelectable.
        """
        if not index.isValid():
            return Qt.ItemFlags()
        return Qt.ItemIsEnabled | Qt.ItemNeverHasChildren

    def rowCount(self, parent=QModelIndex()):
        """Get count of active downloads."""
        if parent.isValid():
            # We don't have children
            return 0
        return len(self)


class TempDownloadManager:

    """Manager to handle temporary download files.

    The downloads are downloaded to a temporary location and then opened with
    the system standard application. The temporary files are deleted when
    qutebrowser is shutdown.

    Attributes:
        files: A list of NamedTemporaryFiles of downloaded items.
    """

    def __init__(self):
        self.files: MutableSequence[IO[bytes]] = []
        self._tmpdir = None

    def cleanup(self):
        """Clean up any temporary files."""
        if self._tmpdir is not None:
            try:
                self._tmpdir.cleanup()
            except OSError:
                log.misc.exception("Failed to clean up temporary download "
                                   "directory")
            self._tmpdir = None

    def get_tmpdir(self):
        """Return the temporary directory that is used for downloads.

        The directory is created lazily on first access.

        Return:
            The tempfile.TemporaryDirectory that is used.
        """
        if self._tmpdir is None:
            self._tmpdir = tempfile.TemporaryDirectory(
                prefix='qutebrowser-downloads-')
        return self._tmpdir

    def get_tmpfile(self, suggested_name):
        """Return a temporary file in the temporary downloads directory.

        The files are kept as long as qutebrowser is running and automatically
        cleaned up at program exit.

        Args:
            suggested_name: str of the "suggested"/original filename. Used as a
                            suffix, so any file extensions are preserved.

        Return:
            A tempfile.NamedTemporaryFile that should be used to save the file.
        """
        tmpdir = self.get_tmpdir()
        suggested_name = utils.sanitize_filename(suggested_name)
        # Make sure that the filename is not too long
        suggested_name = utils.elide_filename(suggested_name, 50)
        fobj = tempfile.NamedTemporaryFile(dir=tmpdir.name, delete=False,
                                           suffix='_' + suggested_name)
        self.files.append(fobj)
        return fobj


temp_download_manager = TempDownloadManager()

This "magic" value seems quite odd. Why not handle this in `handle_download` before even calling `get_filename_question`?