"""
Copyright (c) 2021, Alibaba Group;
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.
"""

import time
import torch


class CudaEventTimer(object):
    """Borrowed from Deepspeed"""
    def __init__(self, start_event: torch.cuda.Event, end_event: torch.cuda.Event):
        self.start_event = start_event
        self.end_event = end_event

    def get_elapsed_msec(self):
        #torch.cuda.current_stream().wait_event(self.end_event)
        self.end_event.synchronize()
        return self.start_event.elapsed_time(self.end_event)


class Timer:
    def __init__(self, use_host_timer=False):
        self.started_ = False
        self.use_host_timer = use_host_timer
        self.start_event = None
        self.start_time = 0.0

    def start(self):
        """Start the timer."""
        assert not self.started_, f"timer has already been started"
        if self.use_host_timer:
            self.start_time = time.time()
        else:
            self.start_event = torch.cuda.Event(enable_timing=True)
            self.start_event.record()
        self.started_ = True

    def stop(self):
        """Stop the timer."""
        assert self.started_, "timer is not started"
        self.started_ = False
        if self.use_host_timer:
            end_time = time.time()
            return (end_time - self.start_time) * 1000
        else:
            end_event = torch.cuda.Event(enable_timing=True)
            end_event.record()
            event_timer = CudaEventTimer(self.start_event, end_event)
            self.start_event = None
            return event_timer.get_elapsed_msec()