from re import compile
from typing import Optional
from djbdns.common import *

# The regex to match dnscache log lines.
dnscache_log_re = compile(fr'({timestamp_pat}) (\w+)(.*)')


def decode_client(words : list, i : int):
    r"""
    Helper function to decode the client field in a dnscache log
    entry.

    There are two possible formats for the client field,

      1. clientip:clientport, used by tcpopen/tcpclose entries,
      2. clientip:clientport:id, used by "query" entries.

    We convert each part from hex to decimal, and in the second
    format, separate the packet id from the client information.

    Parameters
    ----------

    words : list
        The ``words`` list (a list of fields) from
        :func:`handle_dnscache_log`.

    i : int
        The index of the client field within ``words``

    Returns
    -------

    Nothing; the ``i``th entry in the ``words`` list is modified
    in-place.

    Examples
    --------

        >>> words = ["foo", "bar", "7f000001:9253", "quux"]
        >>> decode_client(words, 2)
        >>> words
        ['foo', 'bar', '127.0.0.1:37459', 'quux']

        >>> words = ["foo", "7f000001:a3db:4fb9", "bar", "quux"]
        >>> decode_client(words, 1)
        >>> words
        ['foo', '127.0.0.1:41947 (id 20409)', 'bar', 'quux']

    """
    chunks = words[i].split(":")

    ip = convert_ip(chunks[0])
    port = int(chunks[1], 16)
    words[i] = f"{ip}:{port}"

    if len(chunks) == 3:
        # For a "query" entry's clientip:clientport:id field.
        id = int(chunks[2], 16)
        words[i] += f" (id {id})"

def decode_ip(words : list, i : int):
    r"""
    Helper function to decode the ip field in a dnscache log
    entry.

    A single "serverip" field is present in the lame, nodata,
    nxdomain, and rr entry types. We convert it from hex to decimal.

    Parameters
    ----------

    words : list
        The ``words`` list (a list of fields) from
        :func:`handle_dnscache_log`.

    i : int
        The index of the ip field within ``words``

    Returns
    -------

    Nothing; the ``i``th entry in the ``words`` list is modified
    in-place.

    Examples
    --------

        >>> words = ["foo", "bar", "7f000001", "quux"]
        >>> decode_ip(words, 2)
        >>> words
        ['foo', 'bar', '127.0.0.1', 'quux']

        >>> words = ["foo", "00000000000000000000ffff7f000001", "bar", "quux"]
        >>> decode_ip(words, 1)
        >>> words
        ['foo', '0000:0000:0000:0000:0000:ffff:7f00:0001', 'bar', 'quux']
    """
    words[i] = convert_ip(words[i])

def decode_ttl(words : list, i : int):
    r"""
    Helper function to decode the ttl field in a dnscache log
    entry.

    A single "ttl" field is present in the nodata, nxdomain, and
    rr entry types. We prefix it with "TTL=" so that its meaning
    is clear in the human-readable logs.

    Parameters
    ----------

    words : list
        The ``words`` list (a list of fields) from
        :func:`handle_dnscache_log`.

    i : int
        The index of the ttl field within ``words``

    Returns
    -------

    Nothing; the ``i``th entry in the ``words`` list is modified
    in-place.

    Examples
    --------

        >>> words = ["c0a80101", "20865", "1", "www.example.com.", "5db8d822"]
        >>> decode_ttl(words, 1)
        >>> words
        ['c0a80101', 'TTL=20865', '1', 'www.example.com.', '5db8d822']

    """
    words[i] = f"TTL={words[i]}"

def decode_serial(words : list, i : int):
    r"""
    Helper function to decode the serial field in a dnscache log
    entry.

    A single "serial" field is present in the drop and query entry
    types. It's already in decimal; we simply prefix it with a hash.

    Parameters
    ----------

    words : list
        The ``words`` list (a list of fields) from
        :func:`handle_dnscache_log`.

    i : int
        The index of the serial field within ``words``

    Returns
    -------

    Nothing; the ``i``th entry in the ``words`` list is modified
    in-place.

    Examples
    --------

        >>> words = ["1", "7f000001:a3db:4fb9", "1", "www.example.com."]
        >>> decode_serial(words, 0)
        >>> words
        ['#1', '7f000001:a3db:4fb9', '1', 'www.example.com.']

    """
    words[i] = f"#{words[i]}"

def decode_type(words : list, i : int):
    qt = words[i]
    words[i] = query_type.get(int(qt), qt)

def handle_dnscache_log(line : str) -> Optional[str]:
    r"""
    Handle a single log line if it matches the ``dnscache_log_re`` regex.

    Parameters
    ----------

    line : string
        The log line that might match ``dnscache_log_re``.

    Returns
    -------

    Either the human-readable string if the log line was handled (that
    is, if it was really a dnscache log line), or ``None`` if it was
    not.

    Examples
    --------

        >>> line = "2022-09-15 18:37:33.863805500 query 1 7f000001:a3db:4fb9 1 www.example.com."
        >>> handle_dnscache_log(line)
        '2022-09-15 18:37:33.863805500 query #1 127.0.0.1:41947 (id 20409) a www.example.com.'

        >>> line = "2022-09-15 18:37:33.863874500 tx 0 1 www.example.com. . c0a80101"
        >>> handle_dnscache_log(line)
        '2022-09-15 18:37:33.863874500 tx g=0 a www.example.com. . 192.168.1.1'

        >>> line = "2022-09-15 18:37:33.878529500 rr c0a80101 20865 1 www.example.com. 5db8d822"
        >>> handle_dnscache_log(line)
        '2022-09-15 18:37:33.878529500 rr 192.168.1.1 TTL=20865 a www.example.com. 93.184.216.34'

        >>> line = "2022-09-15 18:37:33.878532500 stats 1 43 1 0"
        >>> handle_dnscache_log(line)
        '2022-09-15 18:37:33.878532500 stats count=1 motion=43 udp-active=1 tcp-active=0'

        >>> line = "2022-09-15 18:37:33.878602500 sent 1 49"
        >>> handle_dnscache_log(line)
        '2022-09-15 18:37:33.878602500 sent #1 49'

        >>> line = "this line is nonsense"
        >>> handle_dnscache_log(line)

    """
    match = dnscache_log_re.match(line)
    if not match:
        return None

    (timestamp, event, data) = match.groups()

    words = data.split()
    if event == "cached":
        if words[0] not in ("cname", "ns", "nxdomain"):
            decode_type(words, 0)

    elif event == "drop":
        decode_serial(words, 0)

    elif event == "lame":
        decode_ip(words, 0)

    elif event == "nodata":
        decode_ip(words, 0)
        decode_ttl(words, 1)
        decode_type(words, 2)

    elif event == "nxdomain":
        decode_ip(words, 0)
        decode_ttl(words, 1)

    elif event == "query":
        decode_serial(words, 0)
        decode_client(words, 1)
        decode_type(words, 2)

    elif event == "rr":
        decode_ip(words, 0)
        decode_ttl(words, 1)
        if words[2] not in ("cname", "mx", "ns", "ptr", "soa"):
            decode_type(words, 2)
            if words[2] == "a":         # decode answer to an A query
                decode_ip(words, 4)
            if words[2] == "txt":       # text record
                response = words[4]
                if response.endswith("..."):
                    ellipsis = "..."
                    response = response[0:-3]
                else:
                    ellipsis = ""
                length = int(response[0:2], 16)
                chars = []
                for i in range(1, len(response)//2):
                    chars.append(chr(int(response[2*i : (2*i)+2], 16)))
                txt = "".join(chars)
                words[4] = f"{length}:\"{txt}{ellipsis}\""

    elif event == "sent":
        decode_serial(words, 0)

    elif event == "stats":
        words[0] = f"count={words[0]}"
        words[1] = f"motion={words[1]}"
        words[2] = f"udp-active={words[2]}"
        words[3] = f"tcp-active={words[3]}"

    elif event == "tx":
        words[0] = f"g={words[0]}"
        decode_type(words, 1)
        # words[2] = name
        # words[3] = control (domain for which these servers are believed
        #            to be authoritative)
        for i in range(4, len(words)):
            decode_ip(words, i)

    elif event in ("tcpopen", "tcpclose"):
        decode_client(words, 0)

    # Reconstitute "data" (i.e. everything after the timestamp and the
    # event) from "words", which was originally obtained by splitting
    # "data".
    data = " ".join(words)
    return f"{timestamp} {event} {data}"