"""Route small TP all-gathers through the RoCEnante one-shot kernel (DSV41_ROCE_GATHER=<max bytes per rank>).

The SG17 overlay builds the runtime with max_gather_bytes=0, so every all-gather (draft logits /
markov gathers, a few per step) still goes to NCCL. The runtime's slots are max(max_size, gather)
wide, so any shard up to max_size fits without re-sizing; the gather launcher and the padded
scratch are prepared here, before CUDA graph capture. Byte copy: outputs are bit-identical.
"""
import logging
import os

logger = logging.getLogger(__name__)


def install(module):
    cls = module.PyNcclCommunicator
    limit = int(os.environ.get('DSV41_ROCE_GATHER', '0') or 0)
    orig_init, orig_gather = cls.__init__, cls.all_gather

    def __init__(self, *args, **kwargs):
        orig_init(self, *args, **kwargs)
        roce = getattr(self, 'roce', None)
        if roce is None or limit <= 0:
            return
        roce.max_gather_bytes = min(limit, roce._slot_bytes)
        roce.prepare((), padded_gather=True)
        self._roce_gather_logged = False
        logger.info('DSV41_ROCE_GATHER ready: max %d bytes per rank', roce.max_gather_bytes)

    def all_gather(self, output_tensor, input_tensor, sizes=None):
        roce = getattr(self, 'roce', None)
        if (roce is not None and not self.disabled and sizes is None and roce.max_gather_bytes > 0
                and output_tensor.is_contiguous()
                and output_tensor.numel() == input_tensor.numel() * self.world_size
                and roce.should_all_gather(input_tensor, 0)):
            out = output_tensor.view(self.world_size * input_tensor.shape[0], *input_tensor.shape[1:]) \
                if input_tensor.dim() > 0 else output_tensor
            roce.all_gather(input_tensor, dim=0, out=out, stream=self._resolve_stream())
            if not self._roce_gather_logged:
                logger.info('DSV41_ROCE_GATHER route rank=%d dtype=%s bytes=%d', self.rank,
                            input_tensor.dtype, input_tensor.numel() * input_tensor.element_size())
                self._roce_gather_logged = True
            return
        return orig_gather(self, output_tensor, input_tensor, sizes)

    cls.__init__, cls.all_gather = __init__, all_gather