# protocol.py -- Shared parts of the git protocols
# Copyright (C) 2008 John Carr <john.carr@unrouted.co.uk>
# Copyright (C) 2008-2012 Jelmer Vernooij <jelmer@jelmer.uk>
#
# Dulwich is dual-licensed under the Apache License, Version 2.0 and the GNU
# General Public License as public by the Free Software Foundation; version 2.0
# or (at your option) any later version. You can redistribute it and/or
# modify it under the terms of either of these two licenses.
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# You should have received a copy of the licenses; if not, see
# <http://www.gnu.org/licenses/> for a copy of the GNU General Public License
# and <http://www.apache.org/licenses/LICENSE-2.0> for a copy of the Apache
# License, Version 2.0.
#

"""Generic functions for talking the git smart server protocol."""

from io import BytesIO
from os import (
    SEEK_END,
    )
import socket

import dulwich
from dulwich.errors import (
    HangupException,
    GitProtocolError,
    )

TCP_GIT_PORT = 9418

ZERO_SHA = b"0" * 40

SINGLE_ACK = 0
MULTI_ACK = 1
MULTI_ACK_DETAILED = 2

# pack data
SIDE_BAND_CHANNEL_DATA = 1
# progress messages
SIDE_BAND_CHANNEL_PROGRESS = 2
# fatal error message just before stream aborts
SIDE_BAND_CHANNEL_FATAL = 3

CAPABILITY_DEEPEN_SINCE = b'deepen-since'
CAPABILITY_DEEPEN_NOT = b'deepen-not'
CAPABILITY_DEEPEN_RELATIVE = b'deepen-relative'
CAPABILITY_DELETE_REFS = b'delete-refs'
CAPABILITY_INCLUDE_TAG = b'include-tag'
CAPABILITY_MULTI_ACK = b'multi_ack'
CAPABILITY_MULTI_ACK_DETAILED = b'multi_ack_detailed'
CAPABILITY_NO_DONE = b'no-done'
CAPABILITY_NO_PROGRESS = b'no-progress'
CAPABILITY_OFS_DELTA = b'ofs-delta'
CAPABILITY_QUIET = b'quiet'
CAPABILITY_REPORT_STATUS = b'report-status'
CAPABILITY_SHALLOW = b'shallow'
CAPABILITY_SIDE_BAND = b'side-band'
CAPABILITY_SIDE_BAND_64K = b'side-band-64k'
CAPABILITY_THIN_PACK = b'thin-pack'
CAPABILITY_AGENT = b'agent'
CAPABILITY_SYMREF = b'symref'

# Magic ref that is used to attach capabilities to when
# there are no refs. Should always be ste to ZERO_SHA.
CAPABILITIES_REF = b'capabilities^{}'

COMMON_CAPABILITIES = [
    CAPABILITY_OFS_DELTA,
    CAPABILITY_SIDE_BAND,
    CAPABILITY_SIDE_BAND_64K,
    CAPABILITY_AGENT,
    CAPABILITY_NO_PROGRESS]
KNOWN_UPLOAD_CAPABILITIES = set(COMMON_CAPABILITIES + [
    CAPABILITY_THIN_PACK,
    CAPABILITY_MULTI_ACK,
    CAPABILITY_MULTI_ACK_DETAILED,
    CAPABILITY_INCLUDE_TAG,
    CAPABILITY_DEEPEN_SINCE,
    CAPABILITY_SYMREF,
    CAPABILITY_SHALLOW,
    CAPABILITY_DEEPEN_NOT,
    CAPABILITY_DEEPEN_RELATIVE,
    ])
KNOWN_RECEIVE_CAPABILITIES = set(COMMON_CAPABILITIES + [
    CAPABILITY_REPORT_STATUS])


def agent_string():
    return ('dulwich/%d.%d.%d' % dulwich.__version__).encode('ascii')


def capability_agent():
    return CAPABILITY_AGENT + b'=' + agent_string()


def capability_symref(from_ref, to_ref):
    return CAPABILITY_SYMREF + b'=' + from_ref + b':' + to_ref


def extract_capability_names(capabilities):
    return set(parse_capability(c)[0] for c in capabilities)


def parse_capability(capability):
    parts = capability.split(b'=', 1)
    if len(parts) == 1:
        return (parts[0], None)
    return tuple(parts)


def symref_capabilities(symrefs):
    return [capability_symref(*k) for k in symrefs]


COMMAND_DEEPEN = b'deepen'
COMMAND_SHALLOW = b'shallow'
COMMAND_UNSHALLOW = b'unshallow'
COMMAND_DONE = b'done'
COMMAND_WANT = b'want'
COMMAND_HAVE = b'have'


class ProtocolFile(object):
    """A dummy file for network ops that expect file-like objects."""

    def __init__(self, read, write):
        self.read = read
        self.write = write

    def tell(self):
        pass

    def close(self):
        pass


def pkt_line(data):
    """Wrap data in a pkt-line.

    :param data: The data to wrap, as a str or None.
    :return: The data prefixed with its length in pkt-line format; if data was
        None, returns the flush-pkt ('0000').
    """
    if data is None:
        return b'0000'
    return ('%04x' % (len(data) + 4)).encode('ascii') + data


class Protocol(object):
    """Class for interacting with a remote git process over the wire.

    Parts of the git wire protocol use 'pkt-lines' to communicate. A pkt-line
    consists of the length of the line as a 4-byte hex string, followed by the
    payload data. The length includes the 4-byte header. The special line
    '0000' indicates the end of a section of input and is called a 'flush-pkt'.

    For details on the pkt-line format, see the cgit distribution:
        Documentation/technical/protocol-common.txt
    """

    def __init__(self, read, write, close=None, report_activity=None):
        self.read = read
        self.write = write
        self._close = close
        self.report_activity = report_activity
        self._readahead = None

    def close(self):
        if self._close:
            self._close()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.close()

    def read_pkt_line(self):
        """Reads a pkt-line from the remote git process.

        This method may read from the readahead buffer; see unread_pkt_line.

        :return: The next string from the stream, without the length prefix, or
            None for a flush-pkt ('0000').
        """
        if self._readahead is None:
            read = self.read
        else:
            read = self._readahead.read
            self._readahead = None

        try:
            sizestr = read(4)
            if not sizestr:
                raise HangupException()
            size = int(sizestr, 16)
            if size == 0:
                if self.report_activity:
                    self.report_activity(4, 'read')
                return None
            if self.report_activity:
                self.report_activity(size, 'read')
            pkt_contents = read(size-4)
        except socket.error as e:
            raise GitProtocolError(e)
        else:
            if len(pkt_contents) + 4 != size:
                raise GitProtocolError(
                    'Length of pkt read %04x does not match length prefix %04x'
                    % (len(pkt_contents) + 4, size))
            return pkt_contents

    def eof(self):
        """Test whether the protocol stream has reached EOF.

        Note that this refers to the actual stream EOF and not just a
        flush-pkt.

        :return: True if the stream is at EOF, False otherwise.
        """
        try:
            next_line = self.read_pkt_line()
        except HangupException:
            return True
        self.unread_pkt_line(next_line)
        return False

    def unread_pkt_line(self, data):
        """Unread a single line of data into the readahead buffer.

        This method can be used to unread a single pkt-line into a fixed
        readahead buffer.

        :param data: The data to unread, without the length prefix.
        :raise ValueError: If more than one pkt-line is unread.
        """
        if self._readahead is not None:
            raise ValueError('Attempted to unread multiple pkt-lines.')
        self._readahead = BytesIO(pkt_line(data))

    def read_pkt_seq(self):
        """Read a sequence of pkt-lines from the remote git process.

        :return: Yields each line of data up to but not including the next
            flush-pkt.
        """
        pkt = self.read_pkt_line()
        while pkt:
            yield pkt
            pkt = self.read_pkt_line()

    def write_pkt_line(self, line):
        """Sends a pkt-line to the remote git process.

        :param line: A string containing the data to send, without the length
            prefix.
        """
        try:
            line = pkt_line(line)
            self.write(line)
            if self.report_activity:
                self.report_activity(len(line), 'write')
        except socket.error as e:
            raise GitProtocolError(e)

    def write_file(self):
        """Return a writable file-like object for this protocol."""

        class ProtocolFile(object):

            def __init__(self, proto):
                self._proto = proto
                self._offset = 0

            def write(self, data):
                self._proto.write(data)
                self._offset += len(data)

            def tell(self):
                return self._offset

            def close(self):
                pass

        return ProtocolFile(self)

    def write_sideband(self, channel, blob):
        """Write multiplexed data to the sideband.

        :param channel: An int specifying the channel to write to.
        :param blob: A blob of data (as a string) to send on this channel.
        """
        # a pktline can be a max of 65520. a sideband line can therefore be
        # 65520-5 = 65515
        # WTF: Why have the len in ASCII, but the channel in binary.
        while blob:
            self.write_pkt_line(bytes(bytearray([channel])) + blob[:65515])
            blob = blob[65515:]

    def send_cmd(self, cmd, *args):
        """Send a command and some arguments to a git server.

        Only used for the TCP git protocol (git://).

        :param cmd: The remote service to access.
        :param args: List of arguments to send to remove service.
        """
        self.write_pkt_line(cmd + b" " + b"".join([(a + b"\0") for a in args]))

    def read_cmd(self):
        """Read a command and some arguments from the git client

        Only used for the TCP git protocol (git://).

        :return: A tuple of (command, [list of arguments]).
        """
        line = self.read_pkt_line()
        splice_at = line.find(b" ")
        cmd, args = line[:splice_at], line[splice_at+1:]
        assert args[-1:] == b"\x00"
        return cmd, args[:-1].split(b"\0")


_RBUFSIZE = 8192  # Default read buffer size.


class ReceivableProtocol(Protocol):
    """Variant of Protocol that allows reading up to a size without blocking.

    This class has a recv() method that behaves like socket.recv() in addition
    to a read() method.

    If you want to read n bytes from the wire and block until exactly n bytes
    (or EOF) are read, use read(n). If you want to read at most n bytes from
    the wire but don't care if you get less, use recv(n). Note that recv(n)
    will still block until at least one byte is read.
    """