# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et:

# Copyright 2014-2019 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 <http://www.gnu.org/licenses/>.

"""Functions related to ad blocking."""

import io
import os.path
import functools
import posixpath
import zipfile
import logging
import typing
import pathlib

from PyQt5.QtCore import QUrl

from qutebrowser.api import (cmdutils, hook, config, message, downloads,
                             interceptor, apitypes)


logger = logging.getLogger('misc')
_host_blocker = typing.cast('HostBlocker', None)


def _guess_zip_filename(zf: zipfile.ZipFile) -> str:
    """Guess which file to use inside a zip file."""
    files = zf.namelist()
    if len(files) == 1:
        return files[0]
    else:
        for e in files:
            if posixpath.splitext(e)[0].lower() == 'hosts':
                return e
    raise FileNotFoundError("No hosts file found in zip")


def get_fileobj(byte_io: typing.IO[bytes]) -> typing.IO[bytes]:
    """Get a usable file object to read the hosts file from."""
    byte_io.seek(0)  # rewind downloaded file
    if zipfile.is_zipfile(byte_io):
        byte_io.seek(0)  # rewind what zipfile.is_zipfile did
        zf = zipfile.ZipFile(byte_io)
        filename = _guess_zip_filename(zf)
        byte_io = zf.open(filename, mode='r')
    else:
        byte_io.seek(0)  # rewind what zipfile.is_zipfile did
    return byte_io


def _is_whitelisted_url(url: QUrl) -> bool:
    """Check if the given URL is on the adblock whitelist."""
    for pattern in config.val.content.host_blocking.whitelist:
        if pattern.matches(url):
            return True
    return False


class _FakeDownload(downloads.TempDownload):

    """A download stub to use on_download_finished with local files."""

    def __init__(self,  # pylint: disable=super-init-not-called
                 fileobj: typing.IO[bytes]) -> None:
        self.fileobj = fileobj
        self.successful = True


class HostBlocker:

    """Manage blocked hosts based from /etc/hosts-like files.

    Attributes:
        _blocked_hosts: A set of blocked hosts.
        _config_blocked_hosts: A set of blocked hosts from ~/.config.
        _in_progress: The DownloadItems which are currently downloading.
        _done_count: How many files have been read successfully.
        _local_hosts_file: The path to the blocked-hosts file.
        _config_hosts_file: The path to a blocked-hosts in ~/.config
        _has_basedir: Whether a custom --basedir is set.
    """

    def __init__(self, *, data_dir: pathlib.Path, config_dir: pathlib.Path,
                 has_basedir: bool = False) -> None:
        self._has_basedir = has_basedir
        self._blocked_hosts = set()  # type: typing.Set[str]
        self._config_blocked_hosts = set()  # type: typing.Set[str]
        self._in_progress = []  # type: typing.List[downloads.TempDownload]
        self._done_count = 0

        self._local_hosts_file = str(data_dir / 'blocked-hosts')
        self.update_files()

        self._config_hosts_file = str(config_dir / 'blocked-hosts')

    def _is_blocked(self, request_url: QUrl,
                    first_party_url: QUrl = None) -> bool:
        """Check whether the given request is blocked."""
        if first_party_url is not None and not first_party_url.isValid():
            first_party_url = None

        if not config.get('content.host_blocking.enabled',
                          url=first_party_url):
            return False

        host = request_url.host()
        return ((host in self._blocked_hosts or
                 host in self._config_blocked_hosts) and
                not _is_whitelisted_url(request_url))

    def filter_request(self, info: interceptor.Request) -> None:
        """Block the given request if necessary."""
        if self._is_blocked(request_url=info.request_url,
                            first_party_url=info.first_party_url):
            logger.info("Request to {} blocked by host blocker."
                        .format(info.request_url.host()))
            info.block()

    def _read_hosts_file(self, filename: str, target: typing.Set[str]) -> bool:
        """Read hosts from the given filename.

        Args:
            filename: The file to read.
            target: The set to store the hosts in.

        Return:
            True if a read was attempted, False otherwise
        """
        if not os.path.exists(filename):
            return False

        try:
            with open(filename, 'r', encoding='utf-8') as f:
                for line in f:
                    target.add(line.strip())
        except (OSError, UnicodeDecodeError):
            logger.exception("Failed to read host blocklist!")

        return True

    def read_hosts(self) -> None:
        """Read hosts from the existing blocked-hosts file."""
        self._blocked_hosts = set()

        self._read_hosts_file(self._config_hosts_file,
                              self._config_blocked_hosts)

        found = self._read_hosts_file(self._local_hosts_file,
                                      self._blocked_hosts)

        if not found:
            if (config.val.content.host_blocking.lists and
                    not self._has_basedir and
                    config.val.content.host_blocking.enabled):
                message.info("Run :adblock-update to get adblock lists.")

    def adblock_update(self) -> None:
        """Update the adblock block lists."""
        self._read_hosts_file(self._config_hosts_file,
                              self._config_blocked_hosts)
        self._blocked_hosts = set()
        self._done_count = 0
        for url in config.val.content.host_blocking.lists:
            if url.scheme() == 'file':
                filename = url.toLocalFile()
                if os.path.isdir(filename):
                    for entry in os.scandir(filename):
                        if entry.is_file():
                            self._import_local(entry.path)
                else:
                    self._import_local(filename)
            else:
                download = downloads.download_temp(url)
                self._in_progress.append(download)
                download.finished.connect(
                    functools.partial(self._on_download_finished, download))

    def _import_local(self, filename: str) -> None:
        """Adds the contents of a file to the blocklist.

        Args:
            filename: path to a local file to import.
        """
        try:
            fileobj = open(filename, 'rb')
        except OSError as e:
            message.error("adblock: Error while reading {}: {}".format(
                filename, e.strerror))
            return
        download = _FakeDownload(fileobj)
        self._in_progress.append(download)
        self._on_download_finished(download)

    def _parse_line(self, raw_line: bytes) -> bool:
        """Parse a line from a host file.

        Args:
            raw_line: The bytes object to parse.

        Returns:
            True if parsing succeeded, False otherwise.
        """
        if raw_line.startswith(b'#'):
            # Ignoring comments early so we don't have to care about
            # encoding errors in them.
            return True

        try:
            line = raw_line.decode('utf-8')
        except UnicodeDecodeError:
            logger.error("Failed to decode: {!r}".format(raw_line))
            return False

        # Remove comments
        try:
            hash_idx = line.index('#')
            line = line[:hash_idx]
        except ValueError:
            pass

        line = line.strip()
        # Skip empty lines
        if not line:
            return True

        parts = line.split()
        if len(parts) == 1:
            # "one host per line" format
            hosts = [parts[0]]
        else:
            # /etc/hosts format
            hosts = parts[1:]

        for host in hosts:
            if ('.' in host and
                    not host.endswith('.localdomain') and
                    host != '0.0.0.0'):
                self._blocked_hosts.add(host)

        return True

    def _merge_file(self, byte_io: io.BytesIO) -> None:
        """Read and merge host files.

        Args:
            byte_io: The BytesIO object of the completed download.
        """
        error_count = 0
        line_count = 0
        try:
            f = get_fileobj(byte_io)
        except (OSError, zipfile.BadZipFile, zipfile.LargeZipFile,
                LookupError) as e:
            message.error("adblock: Error while reading {}: {} - {}".format(
                byte_io.name, e.__class__.__name__, e))
            return

        for line in f:
            line_count += 1
            ok = self._parse_line(line)
            if not ok:
                error_count += 1

        logger.debug("{}: read {} lines".format(byte_io.name, line_count))
        if error_count > 0:
            message.error("adblock: {} read errors for {}".format(
                error_count, byte_io.name))

    def _on_lists_downloaded(self) -> None:
        """Install block lists after files have been downloaded."""
        with open(self._local_hosts_file, 'w', encoding='utf-8') as f:
            for host in sorted(self._blocked_hosts):
                f.write(host + '\n')
            message.info("adblock: Read {} hosts from {} sources.".format(
                len(self._blocked_hosts), self._done_count))

    def update_files(self) -> None:
        """Update files when the config changed."""
        if not config.val.content.host_blocking.lists:
            try:
                os.remove(self._local_hosts_file)
            except FileNotFoundError:
                pass
            except OSError as e:
                logger.exception("Failed to delete hosts file: {}".format(e))

    def _on_download_finished(self, download: downloads.TempDownload) -> None:
        """Check if all downloads are finished and if so, trigger reading.

        Arguments:
            download: The finished download.
        """
        self._in_progress.remove(download)
        if download.successful:
            self._done_count += 1
            try:
                self._merge_file(download.fileobj)
            finally:
                download.fileobj.close()
        if not self._in_progress:
            try:
                self._on_lists_downloaded()
            except OSError:
                logger.exception("Failed to write host block list!")


@cmdutils.register()
def adblock_update() -> None:
    """Update the adblock block lists.

    This updates `~/.local/share/qutebrowser/blocked-hosts` with downloaded
    host lists and re-reads `~/.config/qutebrowser/blocked-hosts`.
    """
    # FIXME: As soon as we can register instances again, we should move this
    # back to the class.
    _host_blocker.adblock_update()


@hook.config_changed('content.host_blocking.lists')
def on_config_changed() -> None:
    _host_blocker.update_files()


@hook.init()
def init(context: apitypes.InitContext) -> None:
    """Initialize the host blocker."""
    global _host_blocker
    _host_blocker = HostBlocker(data_dir=context.data_dir,
                                config_dir=context.config_dir,
                                has_basedir=context.args.basedir is not None)
    _host_blocker.read_hosts()
    interceptor.register(_host_blocker.filter_request)
