# 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/>.

"""Parser for line-based files like histories."""

import os
import os.path
import contextlib
from typing import Sequence

from PyQt5.QtCore import pyqtSlot, pyqtSignal, QObject

from qutebrowser.utils import log, utils, qtutils
from qutebrowser.config import config


class BaseLineParser(QObject):

    """A LineParser without any real data.

    Attributes:
        _configdir: Directory to read the config from, or None.
        _configfile: The config file path.
        _fname: Filename of the config.
        _binary: Whether to open the file in binary mode.

    Signals:
        changed: Emitted when the history was changed.
    """

    changed = pyqtSignal()

    def __init__(self, configdir, fname, *, binary=False, parent=None):
        """Constructor.

        Args:
            configdir: Directory to read the config from.
            fname: Filename of the config file.
            binary: Whether to open the file in binary mode.
            _opened: Whether the underlying file is open
        """
        super().__init__(parent)
        self._configdir = configdir
        self._configfile = os.path.join(self._configdir, fname)
        self._fname = fname
        self._binary = binary
        self._opened = False

    def __repr__(self):
        return utils.get_repr(self, constructor=True,
                              configdir=self._configdir, fname=self._fname,
                              binary=self._binary)

    def _prepare_save(self):
        """Prepare saving of the file.

        Return:
            True if the file should be saved, False otherwise.
        """
        os.makedirs(self._configdir, 0o755, exist_ok=True)
        return True

    def _after_save(self):
        """Log a message after saving is done."""
        log.destroy.debug("Saved to {}".format(self._configfile))

    @contextlib.contextmanager
    def _open(self, mode):
        """Open self._configfile for reading.

        Args:
            mode: The mode to use ('a'/'r'/'w')

        Raises:
            OSError: if the file is already open

        Yields:
            a file object for the config file
        """
        assert self._configfile is not None
        if self._opened:
            raise OSError("Refusing to double-open LineParser.")
        self._opened = True
        try:
            if self._binary:
                # pylint: disable=unspecified-encoding
                with open(self._configfile, mode + 'b') as f:
                    yield f
            else:
                with open(self._configfile, mode, encoding='utf-8') as f:
                    yield f
        finally:
            self._opened = False

    def _write(self, fp, data):
        """Write the data to a file.

        Args:
            fp: A file object to write the data to.
            data: The data to write.
        """
        if not data:
            return
        if self._binary:
            fp.write(b'\n'.join(data))
            fp.write(b'\n')
        else:
            fp.write('\n'.join(data))
            fp.write('\n')

    def save(self):
        """Save the history to disk."""
        raise NotImplementedError

    def clear(self):
        """Clear the contents of the file."""
        raise NotImplementedError


class LineParser(BaseLineParser):

    """Parser for configuration files which are simply line-based.

    Attributes:
        data: A list of lines.
    """

    def __init__(self, configdir, fname, *, binary=False, parent=None):
        """Constructor.

        Args:
            configdir: Directory to read the config from.
            fname: Filename of the config file.
            binary: Whether to open the file in binary mode.
        """
        super().__init__(configdir, fname, binary=binary, parent=parent)
        if not os.path.isfile(self._configfile):
            self.data: Sequence[str] = []
        else:
            log.init.debug("Reading {}".format(self._configfile))
            self._read()

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

    def __getitem__(self, key):
        return self.data[key]

    def _read(self):
        """Read the data from self._configfile."""
        with self._open('r') as f:
            if self._binary:
                self.data = [line.rstrip(b'\n') for line in f]
            else:
                self.data = [line.rstrip('\n') for line in f]

    def save(self):
        """Save the config file."""
        if self._opened:
            raise OSError("Refusing to double-open LineParser.")
        do_save = self._prepare_save()
        if not do_save:
            return
        self._opened = True
        try:
            assert self._configfile is not None
            with qtutils.savefile_open(self._configfile, self._binary) as f:
                self._write(f, self.data)
        finally:
            self._opened = False
        self._after_save()

    def clear(self):
        self.data = []
        self.save()


class LimitLineParser(LineParser):

    """A LineParser with a limited count of lines.

    Attributes:
        _limit: The config option used to limit the maximum number of lines.
    """

    def __init__(self, configdir, fname, *, limit, binary=False, parent=None):
        """Constructor.

        Args:
            configdir: Directory to read the config from, or None.
            fname: Filename of the config file.
            limit: Config option which contains a limit.
            binary: Whether to open the file in binary mode.
        """
        super().__init__(configdir, fname, binary=binary, parent=parent)
        self._limit = limit
        if limit is not None and configdir is not None:
            config.instance.changed.connect(self._cleanup_file)

    def __repr__(self):
        return utils.get_repr(self, constructor=True,
                              configdir=self._configdir, fname=self._fname,
                              limit=self._limit, binary=self._binary)

    @pyqtSlot(str)
    def _cleanup_file(self, option):
        """Delete the file if the limit was changed to 0."""
        assert self._configfile is not None
        if option != self._limit:
            return
        value = config.instance.get(option)
        if value == 0:
            if os.path.exists(self._configfile):
                os.remove(self._configfile)

    def save(self):
        """Save the config file."""
        limit = config.instance.get(self._limit)
        if limit == 0:
            return
        do_save = self._prepare_save()
        if not do_save:
            return
        assert self._configfile is not None
        with qtutils.savefile_open(self._configfile, self._binary) as f:
            self._write(f, self.data[-limit:])
        self._after_save()
