import logging

import requests

from borgmatic.hooks import monitor

logger = logging.getLogger(__name__)

MONITOR_STATE_TO_HEALTHCHECKS = {
    monitor.State.START: 'start',
    monitor.State.FINISH: None,  # Healthchecks doesn't append to the URL for the finished state.
    monitor.State.FAIL: 'fail',
}

PAYLOAD_TRUNCATION_INDICATOR = '...\n'
PAYLOAD_LIMIT_BYTES = 10 * 1024 - len(PAYLOAD_TRUNCATION_INDICATOR)


class Forgetful_buffering_handler(logging.Handler):
    '''
    A buffering log handler that stores log messages in memory, and throws away messages (oldest
    first) once a particular capacity in bytes is reached.
    '''

    def __init__(self, byte_capacity):
        super().__init__()

        self.byte_capacity = byte_capacity
        self.byte_count = 0
        self.buffer = []
        self.forgot = False

    def emit(self, record):
        message = record.getMessage() + '\n'
        self.byte_count += len(message)
        self.buffer.append(message)

        while self.byte_count > self.byte_capacity and self.buffer:
            self.byte_count -= len(self.buffer[0])
            self.buffer.pop(0)
            self.forgot = True


def format_buffered_logs_for_payload():
    '''
    Get the handler previously added to the root logger, and slurp buffered logs out of it to
    send to Healthchecks.
    '''
    try:
        buffering_handler = next(
            handler
            for handler in logging.getLogger().handlers
            if isinstance(handler, Forgetful_buffering_handler)
        )
    except StopIteration:
        # No handler means no payload.
        return ''

    payload = ''.join(message for message in buffering_handler.buffer)

    if buffering_handler.forgot:
        return PAYLOAD_TRUNCATION_INDICATOR + payload

    return payload


def ping_monitor(ping_url_or_uuid, config_filename, state, dry_run):
    '''
    Ping the given Healthchecks URL or UUID, modified with the monitor.State. Use the given
    configuration filename in any log entries. If this is a dry run, then don't actually ping
    anything.
    '''
    if state is monitor.State.START:
        # Add a handler to the root logger that stores in memory the most recent logs emitted. That
        # way, we can send them all to Healthchecks upon a finish or failure state.
        logging.getLogger().addHandler(Forgetful_buffering_handler(PAYLOAD_LIMIT_BYTES))
        payload = ''

    ping_url = (
        ping_url_or_uuid
        if ping_url_or_uuid.startswith('http')
        else 'https://hc-ping.com/{}'.format(ping_url_or_uuid)
    )
    dry_run_label = ' (dry run; not actually pinging)' if dry_run else ''

    healthchecks_state = MONITOR_STATE_TO_HEALTHCHECKS.get(state)
    if healthchecks_state:
        ping_url = '{}/{}'.format(ping_url, healthchecks_state)

    logger.info(
        '{}: Pinging Healthchecks {}{}'.format(config_filename, state.name.lower(), dry_run_label)
    )
    logger.debug('{}: Using Healthchecks ping URL {}'.format(config_filename, ping_url))

    if state in (monitor.State.FINISH, monitor.State.FAIL):
        payload = format_buffered_logs_for_payload()

    if not dry_run:
        logging.getLogger('urllib3').setLevel(logging.ERROR)
        requests.post(ping_url, data=payload.encode('utf-8'))
