# Some code borrowed from the awesome work: https://github.com/zhuzilin/ring-flash-attention
# Copyright (c) ModelScope Contributors. All rights reserved.
import torch
import torch.distributed as dist
from typing import Optional, Tuple


class RingComm:

    def __init__(self, process_group: dist.ProcessGroup):
        self._process_group = process_group
        self._ops = []
        self.rank = dist.get_rank(self._process_group)
        self.world_size = dist.get_world_size(self._process_group)
        self._reqs = None

        self.send_rank = (self.rank + 1) % self.world_size
        self.recv_rank = (self.rank - 1) % self.world_size

        if process_group is not None:
            self.send_rank = dist.get_global_rank(self._process_group, self.send_rank)
            self.recv_rank = dist.get_global_rank(self._process_group, self.recv_rank)

    def send_recv(self, to_send: torch.Tensor, recv_tensor: Optional[torch.Tensor] = None) -> torch.Tensor:
        if recv_tensor is None:
            res = torch.empty_like(to_send)
        else:
            res = recv_tensor

        send_op = dist.P2POp(dist.isend, to_send, self.send_rank, group=self._process_group)
        recv_op = dist.P2POp(dist.irecv, res, self.recv_rank, group=self._process_group)
        self._ops.append(send_op)
        self._ops.append(recv_op)
        return res

    def commit(self):
        if self._reqs is not None:
            raise RuntimeError('commit called twice')
        self._reqs = dist.batch_isend_irecv(self._ops)

    def wait(self):
        if self._reqs is None:
            raise RuntimeError('wait called before commit')
        for req in self._reqs:
            req.wait()
        self._reqs = None
        self._ops = []

    def send_recv_kv(
        self,
        k: torch.Tensor,
        v: torch.Tensor,
        k_buffer: Optional[torch.Tensor] = None,
        v_buffer: Optional[torch.Tensor] = None,
    ) -> Tuple[torch.Tensor, torch.Tensor]:
        next_k, next_v = self.send_recv(k, k_buffer), self.send_recv(v, v_buffer)
        self.commit()
        return next_k, next_v