# Copyright (C) 2012-2013 Aleksey Lim
#
# This program 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.
#
# 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/>.

import os
import gzip
import zlib
import json
import logging
from cStringIO import StringIO
from types import GeneratorType
from os.path import exists, join, dirname, basename, splitext

from sugar_network import toolkit
from sugar_network.toolkit import coroutine, enforce


# Filename suffix to use for sneakernet synchronization files
_SNEAKERNET_SUFFIX = '.sneakernet'

# Leave at leat n bytes in fs whle calling `encode_to_file()`
_SNEAKERNET_RESERVED_SIZE = 1024 * 1024

_logger = logging.getLogger('node.sync')


def decode(stream):
    packet = _PacketsIterator(stream)
    while True:
        packet.next()
        if packet.name == 'last':
            break
        yield packet


def encode(packets, **header):
    return _encode(None, packets, False, header, _EncodingStatus())


def limited_encode(limit, packets, **header):
    return _encode(limit, packets, False, header, _EncodingStatus())


def package_decode(stream):
    stream = _GzipStream(stream)
    package_props = json.loads(stream.readline())

    for packet in decode(stream):
        packet.props.update(package_props)
        yield packet


def package_encode(packets, **header):
    # XXX Only for small amount of data
    # TODO Support real streaming
    buf = StringIO()
    zipfile = gzip.GzipFile(mode='wb', fileobj=buf)

    header['filename'] = toolkit.uuid() + _SNEAKERNET_SUFFIX
    json.dump(header, zipfile)
    zipfile.write('\n')

    for chunk in _encode(None, packets, False, None, _EncodingStatus()):
        zipfile.write(chunk)
    zipfile.close()

    yield buf.getvalue()


def sneakernet_decode(root, node=None, session=None):
    for root, __, files in os.walk(root):
        for filename in files:
            if not filename.endswith(_SNEAKERNET_SUFFIX):
                continue
            zipfile = gzip.open(join(root, filename), 'rb')
            try:
                package_props = json.loads(zipfile.readline())

                if node is not None and package_props.get('src') == node:
                    if package_props.get('session') == session:
                        _logger.debug('Skip session %r sneakernet package',
                                zipfile.name)
                    else:
                        _logger.debug('Remove outdate %r sneakernet package',
                                zipfile.name)
                        os.unlink(zipfile.name)
                    continue

                for packet in decode(zipfile):
                    packet.props.update(package_props)
                    yield packet
            finally:
                zipfile.close()


def sneakernet_encode(packets, root=None, limit=None, path=None, **header):
    if path is None:
        if not exists(root):
            os.makedirs(root)
        filename = toolkit.uuid() + _SNEAKERNET_SUFFIX
        path = toolkit.unique_filename(root, filename)
    else:
        filename = splitext(basename(path))[0] + _SNEAKERNET_SUFFIX
    if 'filename' not in header:
        header['filename'] = filename

    if limit <= 0:
        stat = os.statvfs(dirname(path))
        limit = stat.f_bfree * stat.f_frsize - _SNEAKERNET_RESERVED_SIZE

    _logger.debug('Creating %r sneakernet package, limit=%s header=%r',
            path, limit, header)

    status = _EncodingStatus()
    with file(path, 'wb') as package:
        zipfile = gzip.GzipFile(fileobj=package)
        try:
            json.dump(header, zipfile)
            zipfile.write('\n')

            pos = None
            encoder = _encode(limit, packets, True, None, status)
            while True:
                try:
                    chunk = encoder.send(pos)
                    zipfile.write(chunk)
                    pos = zipfile.fileobj.tell()
                    coroutine.dispatch()
                except StopIteration:
                    break

        except Exception:
            _logger.debug('Emergency removing %r package', path)
            package.close()
            os.unlink(path)
            raise
        else:
            zipfile.close()
            package.flush()
            os.fsync(package.fileno())

    return not status.aborted


class _EncodingStatus(object):

    aborted = False


def _encode(limit, packets, download_blobs, header, status):
    for packet, props, content in packets:
        if status.aborted:
            break

        if props is None:
            props = {}
        if header:
            props.update(header)
        props['packet'] = packet
        pos = (yield json.dumps(props) + '\n') or 0

        if content is None:
            continue

        content = iter(content)
        try:
            record = next(content)

            while True:
                blob = None
                blob_size = 0
                if 'blob' in record:
                    blob = record.pop('blob')
                    blob_size = record['blob_size']

                dump = json.dumps(record) + '\n'
                if not status.aborted and limit is not None and \
                        pos + len(dump) + blob_size > limit:
                    status.aborted = True
                    if not isinstance(content, GeneratorType):
                        raise StopIteration()
                    record = content.throw(StopIteration())
                    continue
                pos = (yield dump) or 0

                if blob is not None:
                    for chunk in blob:
                        pos = (yield chunk) or 0
                        blob_size -= len(chunk)
                    enforce(blob_size == 0, EOFError,
                            'Blob size is not the same as declared')

                record = next(content)
        except StopIteration:
            pass

    yield json.dumps({'packet': 'last'}) + '\n'


class _PacketsIterator(object):

    def __init__(self, stream):
        if not hasattr(stream, 'readline'):
            stream.readline = lambda: toolkit.readline(stream)
        if hasattr(stream, 'seek'):
            self._seek = stream.seek
        self._stream = stream
        self.props = {}
        self._name = None
        self._shift = True

    @property
    def name(self):
        return self._name

    def next(self):
        if self._shift:
            for __ in self:
                pass
        if self._name is None:
            raise EOFError()
        self._shift = True

    def __repr__(self):
        return '<SyncPacket %r>' % self.props

    def __getitem__(self, key):
        return self.props.get(key)

    def __iter__(self):
        blob = None
        while True:
            if blob is not None and blob.size_to_read:
                self._seek(blob.size_to_read, 1)
                blob = None
            record = self._stream.readline()
            if not record:
                self._name = None
                raise EOFError()
            record = json.loads(record)
            if 'packet' in record:
                self._name = record['packet'] or ''
                self.props = record
                self._shift = False
                break
            blob_size = record.get('blob_size')
            if blob_size:
                blob = record['blob'] = _Blob(self._stream, blob_size)
            yield record

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        pass

    # pylint: disable-msg=E0202
    def _seek(self, distance, where):
        while distance:
            chunk = self._stream.read(min(distance, toolkit.BUFFER_SIZE))
            distance -= len(chunk)


class _Blob(object):

    def __init__(self, stream, size):
        self._stream = stream
        self.size_to_read = size

    def read(self, size=toolkit.BUFFER_SIZE):
        chunk = self._stream.read(min(size, self.size_to_read))
        self.size_to_read -= len(chunk)
        return chunk


class _GzipStream(object):

    def __init__(self, stream):
        self._stream = stream
        self._zip = zlib.decompressobj(16 + zlib.MAX_WBITS)
        self._buffer = bytearray()

    def read(self, size):
        while True:
            if size <= len(self._buffer):
                result = self._buffer[:size]
                self._buffer = self._buffer[size:]
                return bytes(result)
            chunk = self._stream.read(size)
            if not chunk:
                result, self._buffer = self._buffer, bytearray()
                return result
            self._buffer += self._zip.decompress(chunk)

    def readline(self):
        return toolkit.readline(self)