###############################################################################
##
##  Copyright (C) 2011-2014 Tavendo GmbH
##
##  Licensed under the Apache License, Version 2.0 (the "License");
##  you may not use this file except in compliance with the License.
##  You may obtain a copy of the License at
##
##      http://www.apache.org/licenses/LICENSE-2.0
##
##  Unless required by applicable law or agreed to in writing, software
##  distributed under the License is distributed on an "AS IS" BASIS,
##  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
##  See the License for the specific language governing permissions and
##  limitations under the License.
##
###############################################################################

from __future__ import absolute_import

__all__ = ("utcnow",
           "parseutc",
           "utcstr",
           "id",
           "newid",
           "rtime",
           "Stopwatch",
           "Tracker",
           "EqualityMixin")


import time
import random
import sys
from datetime import datetime, timedelta
from pprint import pformat
import six
if six.PY3:
    # Python 3
    # noinspection PyShadowingBuiltins
    xrange = range



def utcnow():
   """
   Get current time in UTC as ISO 8601 string.

   :returns: Current time as string in ISO 8601 format.
   :rtype: unicode
   """
   now = datetime.utcnow()
   return now.strftime("%Y-%m-%dT%H:%M:%S.%f")[:-3] + "Z"



def utcstr(ts):
   """
   Format UTC timestamp in ISO 8601 format.

   :param ts: The timestamp to format.
   :type ts: instance of :py:class:`datetime.datetime`

   :returns: Timestamp formatted in ISO 8601 format.
   :rtype: unicode
   """
   if ts:
      return ts.strftime("%Y-%m-%dT%H:%M:%S.%f")[:-3] + "Z"
   else:
      return ts



def parseutc(datestr):
   """
   Parse an ISO 8601 combined date and time string, like i.e. ``"2011-11-23T12:23:00Z"``
   into a UTC datetime instance.

   .. deprecated:: 0.8.12
      Use the **iso8601** module instead (e.g. ``iso8601.parse_date("2014-05-23T13:03:44.123Z")``)

   :param datestr: The datetime string to parse.
   :type datestr: unicode

   :returns: The converted datetime object.
   :rtype: instance of :py:class:`datetime.datetime`
   """
   try:
      return datetime.strptime(datestr, "%Y-%m-%dT%H:%M:%SZ")
   except:
      return None



def id():
   """
   Generate a new random object ID from range **[0, 2**53]**.

   The upper bound **2**53** is chosen since it is the maximum integer that can be
   represented as a IEEE double such that all smaller integers are representable as well.

   Hence, IDs can be safely used with languages that use IEEE double as their
   main (or only) number type (JavaScript, Lua, etc).

   :returns: A random object ID.
   :rtype: int
   """
   return random.randint(0, 9007199254740992)



def newid(len = 16):
   """
   Generate a new random object ID.

   :param len: The length (in chars) of the ID to generate.
   :type len: int

   :returns: A random object ID.
   :rtype: str
   """
   return ''.join([random.choice("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_") for _ in xrange(len)])



## Select the most precise walltime measurement function available
## on the platform
##
if sys.platform.startswith('win'):
   ## On Windows, this function returns wall-clock seconds elapsed since the
   ## first call to this function, as a floating point number, based on the
   ## Win32 function QueryPerformanceCounter(). The resolution is typically
   ## better than one microsecond
   _rtime = time.clock
   _ = _rtime() # this starts wallclock
else:
   ## On Unix-like platforms, this used the first available from this list:
   ## (1) gettimeofday() -- resolution in microseconds
   ## (2) ftime() -- resolution in milliseconds
   ## (3) time() -- resolution in seconds
   _rtime = time.time


rtime = _rtime
"""
Precise wallclock time.

:returns: The current wallclock in seconds. Returned values are only guaranteed
   to be meaningful relative to each other.
:rtype: float
"""


class Stopwatch:
   """
   Stopwatch based on walltime.

   This can be used to do code timing and uses the most precise walltime measurement
   available on the platform. This is a very light-weight object,
   so create/dispose is very cheap.
   """

   def __init__(self, start = True):
      """
      :param start: If ``True``, immediately start the stopwatch.
      :type start: bool
      """
      self._elapsed = 0
      if start:
         self._started = rtime()
         self._running = True
      else:
         self._started = None
         self._running = False

   def elapsed(self):
      """
      Return total time elapsed in seconds during which the stopwatch was running.

      :returns: The elapsed time in seconds.
      :rtype: float
      """
      if self._running:
         now = rtime()
         return self._elapsed + (now - self._started)
      else:
         return self._elapsed

   def pause(self):
      """
      Pauses the stopwatch and returns total time elapsed in seconds during which
      the stopwatch was running.

      :returns: The elapsed time in seconds.
      :rtype: float
      """
      if self._running:
         now = rtime()
         self._elapsed += now - self._started
         self._running = False
         return self._elapsed
      else:
         return self._elapsed

   def resume(self):
      """
      Resumes a paused stopwatch and returns total elapsed time in seconds
      during which the stopwatch was running.

      :returns: The elapsed time in seconds.
      :rtype: float
      """
      if not self._running:
         self._started = rtime()
         self._running = True
         return self._elapsed
      else:
         now = rtime()
         return self._elapsed + (now - self._started)

   def stop(self):
      """
      Stops the stopwatch and returns total time elapsed in seconds during which
      the stopwatch was (previously) running.

      :returns: The elapsed time in seconds.
      :rtype: float
      """
      elapsed = self.pause()
      self._elapsed = 0
      self._started = None
      self._running = False
      return elapsed



class Tracker:
   """
   A key-based statistics tracker.
   """

   def __init__(self, tracker, tracked):
      """
      """
      self.tracker = tracker
      self.tracked = tracked
      self._timings = {}
      self._offset = rtime()
      self._dt_offset = datetime.utcnow()


   def track(self, key):
      """
      Track elapsed for key.

      :param key: Key under which to track the timing.
      :type key: str
      """
      self._timings[key] = rtime()


   def diff(self, startKey, endKey, format = True):
      """
      Get elapsed difference between two previously tracked keys.

      :param startKey: First key for interval (older timestamp).
      :type startKey: str
      :param endKey: Second key for interval (younger timestamp).
      :type endKey: str
      :param format: If ``True``, format computed time period and return string.
      :type format: bool

      :returns: Computed time period in seconds (or formatted string).
      :rtype: float or str
      """
      if endKey in self._timings and startKey in self._timings:
         d = self._timings[endKey] - self._timings[startKey]
         if format:
            if d < 0.00001: # 10us
               s = "%d ns" % round(d * 1000000000.)
            elif d < 0.01: # 10ms
               s = "%d us" % round(d * 1000000.)
            elif d < 10: # 10s
               s = "%d ms" % round(d * 1000.)
            else:
               s = "%d s" % round(d)
            return s.rjust(8)
         else:
            return d
      else:
         if format:
            return "n.a.".rjust(8)
         else:
            return None

   def absolute(self, key):
      """
      Return the UTC wall-clock time at which a tracked event occurred.

      :param key: The key
      :type key: str

      :returns: Timezone-naive datetime.
      :rtype: instance of :py:class:`datetime.datetime`
      """
      elapsed = self[key]
      if elapsed is None:
         raise KeyError("No such key \"%s\"." % elapsed)
      return self._dt_offset + timedelta(seconds=elapsed)


   def __getitem__(self, key):
      if key in self._timings:
         return self._timings[key] - self._offset
      else:
         return None


   def __iter__(self):
      return self._timings.__iter__()


   def __str__(self):
      return pformat(self._timings)



class EqualityMixin:
   """
   Mixing to add equality comparison operators to a class.

   Two objects are identical under this mixin, if and only if:

   1. both object have the same class
   2. all non-private object attributes are equal
   """

   def __eq__(self, other):
      """
      Compare this object to another object for equality.

      :param other: The other object to compare with.
      :type other: obj

      :returns: ``True`` iff the objects are equal.
      :rtype: bool
      """
      if not isinstance(other, self.__class__):
         return False
      # we only want the actual message data attributes (not eg _serialize)
      for k in self.__dict__:
         if not k.startswith('_'):
            if not self.__dict__[k] == other.__dict__[k]:
               return False
      return True
      #return (isinstance(other, self.__class__) and self.__dict__ == other.__dict__)


   def __ne__(self, other):
      """
      Compare this object to another object for inequality.

      :param other: The other object to compare with.
      :type other: obj

      :returns: ``True`` iff the objects are not equal.
      :rtype: bool
      """
      return not self.__eq__(other)
