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from cuda import cuda, cudart


class GpuTimer:
    def __init__(self) -> None:
        self.events = [
            cuda.cuEventCreate(cuda.CUevent_flags.CU_EVENT_DEFAULT)[1],
            cuda.cuEventCreate(cuda.CUevent_flags.CU_EVENT_DEFAULT)[1],
        ]

    def start(self, stream=cuda.CUstream(0)):
        (err,) = cuda.cuEventRecord(self.events[0], stream)
        if err != cuda.CUresult.CUDA_SUCCESS:
            raise RuntimeError("CUDA Error %s" % str(err))

    def stop(self, stream=cuda.CUstream(0)):
        (err,) = cuda.cuEventRecord(self.events[1], stream)
        if err != cuda.CUresult.CUDA_SUCCESS:
            raise RuntimeError("CUDA Error %s" % str(err))
        pass

    def stop_and_wait(self, stream=cuda.CUstream(0)):
        self.stop(stream)
        if stream:
            (err,) = cuda.cuStreamSynchronize(stream)
            if err != cuda.CUresult.CUDA_SUCCESS:
                raise RuntimeError("CUDA Error %s" % str(err))
        else:
            (err,) = cudart.cudaDeviceSynchronize()
            if err != cuda.CUresult.CUDA_SUCCESS:
                raise RuntimeError("CUDA Error %s" % str(err))

    def duration(self, iterations=1):
        err, duration = cuda.cuEventElapsedTime(self.events[0], self.events[1])
        if err != cuda.CUresult.CUDA_SUCCESS:
            raise RuntimeError("CUDA Error %s" % str(err))
        return duration / float(iterations)
