#!/usr/bin/env python3

import threading
import time

from sfa.util.sfalogging import logger

"""
Callids: a simple mechanism to remember the call ids served so fas
memory-only for now - thread-safe
implemented as a (singleton) hash 'callid'->timestamp
"""

debug = False


class _call_ids_impl (dict):

    _instance = None
    # 5 minutes sounds amply enough
    purge_timeout = 5 * 60
    # when trying to get a lock
    retries = 10
    # in ms
    wait_ms = 100

    def __init__(self):
        self._lock = threading.Lock()

    # the only primitive
    # return True if the callid is unknown, False otherwise
    def already_handled(self, call_id):
        # if not provided in the call...
        if not call_id:
            return False
        has_lock = False
        for attempt in range(_call_ids_impl.retries):
            if debug:
                logger.debug("Waiting for lock (%d)" % attempt)
            if self._lock.acquire(False):
                has_lock = True
                if debug:
                    logger.debug("got lock (%d)" % attempt)
                break
            time.sleep(float(_call_ids_impl.wait_ms) / 1000)
        # in the unlikely event where we can't get the lock
        if not has_lock:
            logger.warning(
                "_call_ids_impl.should_handle_call_id: could not acquire lock")
            return False
        # we're good to go
        if call_id in self:
            self._purge()
            self._lock.release()
            return True
        self[call_id] = time.time()
        self._purge()
        self._lock.release()
        if debug:
            logger.debug("released lock")
        return False

    def _purge(self):
        now = time.time()
        o_keys = []
        for (k, v) in self.items():
            if (now - v) >= _call_ids_impl.purge_timeout:
                o_keys.append(k)
        for k in o_keys:
            if debug:
                logger.debug("Purging call_id %r (%s)" % (
                    k, time.strftime("%H:%M:%S", time.localtime(self[k]))))
            del self[k]
        if debug:
            logger.debug("AFTER PURGE")
            for (k, v) in self.items():
                logger.debug("%s -> %s" %
                             (k, time.strftime("%H:%M:%S", time.localtime(v))))


def Callids():
    if not _call_ids_impl._instance:
        _call_ids_impl._instance = _call_ids_impl()
    return _call_ids_impl._instance