import traceback as _traceback
import os as _os
from syslog import (LOG_EMERG, LOG_ALERT, LOG_CRIT, LOG_ERR,
                    LOG_WARNING, LOG_NOTICE, LOG_INFO, LOG_DEBUG)
from ._journal import sendv, stream_fd

def _make_line(field, value):
    if isinstance(value, bytes):
        return field.encode('utf-8') + b'=' + value
    else:
        return field + '=' + value

def send(MESSAGE, MESSAGE_ID=None,
         CODE_FILE=None, CODE_LINE=None, CODE_FUNC=None,
         **kwargs):
    r"""Send a message to journald.

    >>> journal.send('Hello world')
    >>> journal.send('Hello, again, world', FIELD2='Greetings!')
    >>> journal.send('Binary message', BINARY=b'\xde\xad\xbe\xef')

    Value of the MESSAGE argument will be used for the MESSAGE= field.

    MESSAGE_ID can be given to uniquely identify the type of message.

    Other parts of the message can be specified as keyword arguments.

    Both MESSAGE and MESSAGE_ID, if present, must be strings, and will
    be sent as UTF-8 to journal. Other arguments can be bytes, in
    which case they will be sent as-is to journal.

    CODE_LINE, CODE_FILE, and CODE_FUNC can be specified to identify
    the caller. Unless at least on of the three is given, values are
    extracted from the stack frame of the caller of send(). CODE_FILE
    and CODE_FUNC must be strings, CODE_LINE must be an integer.

    Other useful fields include PRIORITY, SYSLOG_FACILITY,
    SYSLOG_IDENTIFIER, SYSLOG_PID.
    """

    args = ['MESSAGE=' + MESSAGE]

    if MESSAGE_ID is not None:
        args.append('MESSAGE_ID=' + MESSAGE_ID)

    if CODE_LINE == CODE_FILE == CODE_FUNC == None:
        CODE_FILE, CODE_LINE, CODE_FUNC = \
            _traceback.extract_stack(limit=2)[0][:3]
    if CODE_FILE is not None:
        args.append('CODE_FILE=' + CODE_FILE)
    if CODE_LINE is not None:
        args.append('CODE_LINE={:d}'.format(CODE_LINE))
    if CODE_FUNC is not None:
        args.append('CODE_FUNC=' + CODE_FUNC)

    args.extend(_make_line(key, val) for key, val in kwargs.items())
    return sendv(*args)

def stream(identifier, priority=LOG_DEBUG, level_prefix=False):
    r"""Return a file object wrapping a stream to journal.

    Log messages written to this file as simple newline sepearted
    text strings are written to the journal.

    The file will be line buffered, so messages are actually sent
    after a newline character is written.

    >>> stream = journal.stream('myapp')
    >>> stream
    <open file '<fdopen>', mode 'w' at 0x...>
    >>> stream.write('message...\n')

    will produce the following message in the journal:

    PRIORITY=7
    SYSLOG_IDENTIFIER=myapp
    MESSAGE=message...

    Using the interface with print might be more convinient:

    >>> from __future__ import print_function
    >>> print('message...', file=stream)

    priority is the syslog priority, one of LOG_EMERG, LOG_ALERT,
    LOG_CRIT, LOG_ERR, LOG_WARNING, LOG_NOTICE, LOG_INFO, LOG_DEBUG.

    level_prefix is a boolean. If true, kernel-style log priority
    level prefixes (such as '<1>') are interpreted. See sd-daemon(3)
    for more information.
    """

    fd = stream_fd(identifier, priority, level_prefix)
    return _os.fdopen(fd, 'w', 1)