import os
import errno
import logging
import ctypes as c
from collections import deque, defaultdict, namedtuple

from edosl0util.headers import (
    PrimaryHeader,
    GROUP_FIRST,
    GROUP_CONTINUING,
    GROUP_LAST,
    GROUP_STANDALONE
)

from edosl0util import headers

LOG = logging.getLogger(__name__)

# Max CCSDS sequence id
MAX_SEQ_ID = 2**14 - 1


class Error(Exception):
    """
    Base stream error.
    """


class PacketTooShort(Error):
    """
    The number of bytes read for a packet does not match the expected length.
    After this error occurs the stream is no longer usable because data offsets
    are no longer reliable.
    """


class NonConsecutiveSeqId(Error):
    """
    Non-consecutive sequence numbers encounterd for apid.
    """


class BasicStream(object):
    """
    Basic packet stream iterator that reads the primary and secondary headers and
    maintains offsets and read sizes.
    """
    Tracker = namedtuple('Tracker', ['h1', 'h2', 'size', 'offset', 'data'])

    def __init__(self, fobj, header_lookup=None, with_data=True):
        self.file = fobj
        self.header_lookup = header_lookup
        self.with_data = with_data
        try:
            self._offset = self.file.tell()
        except IOError as err:  # handle illegal seek for pipes
            if err.errno != errno.ESPIPE:
                raise
            self._offset = 0

    def __iter__(self):
        return self

    def __next__(self):
        return self.next()

    def _read(self, size):
        buf = self.file.read(size)
        if not buf:  # EOF
            raise StopIteration()
        if len(buf) != size:
            raise PacketTooShort(
                'expected to read {:d} bytes, got {:d}'
                .format(size, len(buf)))
        self._offset += size
        return buf

    def read_primary_header(self):
        buf = self._read(headers.PRIMARY_HEADER_SIZE)
        h1 = PrimaryHeader.from_buffer_copy(buf)
        return h1, headers.PRIMARY_HEADER_SIZE

    def read_secondary_header(self, ph):
        H2Impl = self.header_lookup(ph) if self.header_lookup else None
        if H2Impl is None:
            return bytes(), 0
        h2size = c.sizeof(H2Impl)
        buf = self._read(h2size)
        return H2Impl.from_buffer_copy(buf), h2size

    def next(self):
        offset = self._offset
        h1, h1size = self.read_primary_header()
        h2, h2size = self.read_secondary_header(h1)
        # data length includes h2size
        total_size = h1size + h1.data_length_minus1 + 1
        data_size = h1.data_length_minus1 + 1 - h2size
        if self.with_data:
            data = self._read(data_size)
        else:
            data = None
            self.fobj.seek(data_size, os.SEEK_CUR)
        return self.Tracker(h1, h2, total_size, offset, data)


class Packet(object):
    def __init__(self, h1, h2, data, data_size=None, offset=None):
        self.primary_header = h1
        self.secondary_header = h2
        self.data = data
        self.size = data_size
        self.offset = offset
        self.apid = h1.apid
        self.seqid = self.primary_header.source_sequence_count

    def __str__(self):
        return '<Packet apid=%d seqid=%d stamp=%s size=%s offset=%s>' % \
               (self.apid, self.seqid, self.stamp, self.size, self.offset)
    __repr__ = __str__

    @property
    def stamp(self):
        return (
            self.secondary_header and
            hasattr(self.secondary_header, 'timecode') and
            self.secondary_header.timecode.asdatetime() or None)

    @property
    def timestamp(self):
        return (
            self.secondary_header and
            hasattr(self.secondary_header, 'timecode') and
            self.secondary_header.timecode.astimestamp() or None)

    def bytes(self):
        return buffer(self.primary_header) + \
            buffer(self.secondary_header) + self.data

    def is_group(self):
        return self.is_first() or self.is_continuing() or self.is_last()

    def is_first(self):
        return self.primary_header.sequence_grouping == GROUP_FIRST

    def is_continuine(self):
        return self.primary_header.sequence_grouping == GROUP_CONTINUING

    def is_last(self):
        return self.primary_header.sequence_grouping == GROUP_LAST

    def is_standalone(self):
        return self.primary_header.sequence_grouping == GROUP_STANDALONE


class PacketStream(object):
    SEQID_NOTSET = -1

    def __init__(self, data_stream, fail_on_missing=False):
        self._stream = data_stream
        self._seek_cache = deque()
        self._first = None
        self._last = None
        self._apid_info = defaultdict(
            lambda: {'count': 0,
                     'last_seqid': self.SEQID_NOTSET,
                     'num_missing': 0})
        self._fail_on_missing = fail_on_missing

    def __repr__(self):
        filepath = getattr(self.file, 'name', None)
        return '<{} file={}>'.format(self.__class__.__name__, filepath)

    def __iter__(self):
        return self

    # python3
    def __next__(self):
        return self.next()

    @property
    def file(self):
        return self._stream.file

    def push_back(self, packet):
        self._seek_cache.append(packet)

    def next(self):
        # return any items on the seek cache before reading more
        if len(self._seek_cache):
            return self._seek_cache.popleft()
        h1, h2, data_size, offset, data = self._stream.next()
        packet = Packet(h1, h2, data, data_size=data_size, offset=offset)
        have_missing = self._update_info(packet)
        if have_missing and self._fail_on_missing:
            self.push_back(packet)
            raise NonConsecutiveSeqId()
        return packet

    def _update_info(self, packet):
        have_missing = False
        apid = self._apid_info[packet.apid]
        if packet.stamp:
            if self._first is None:
                self._first = packet.stamp
            else:
                self._first = min(packet.stamp, self._first)
            if self._last is None:
                self._last = packet.stamp
            else:
                self._last = max(packet.stamp, self._last)
        apid['count'] += 1
        if apid['last_seqid'] != self.SEQID_NOTSET:
            if packet.seqid > apid['last_seqid']:
                num_missing = packet.seqid - apid['last_seqid'] - 1
            else:
                num_missing = packet.seqid - apid['last_seqid'] + MAX_SEQ_ID
            have_missing = num_missing != apid['num_missing']
            apid['num_missing'] += num_missing
        apid['last_seqid'] = packet.seqid
        return have_missing

    def info(self):
        return self._first, self._last, self._apid_info

    def seek_to(self, stamp, apid=None):
        """
        Seek forward such that the next packet provided will be the first packet
        having a timestamp available in the secondary header >= stamp and apid.
        """
        # seek past partial groups
        packet = self.next()
        while not packet.stamp:
            packet = self.next()

        # seek to first packet => `stamp`
        current_stamp = packet.stamp
        while current_stamp < stamp:
            packet = self.next()
            current_stamp = packet.stamp or current_stamp

        # put back so next packet is the first packet > `stamp`
        self.push_back(packet)

        if apid is not None:
            packet = self.next()
            while packet.apid != apid:
                packet = self.next()
            self.push_back(packet)


def jpss_packet_stream(fobj, **kwargs):
    stream = BasicStream(fobj, headers.jpss_header_lookup)
    return PacketStream(stream, **kwargs)


def aqua_packet_stream(fobj, **kwargs):
    stream = BasicStream(fobj, headers.aqua_header_lookup)
    return PacketStream(stream, **kwargs)