# Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
#
# This source code is licensed under the BSD license found in the
# LICENSE file in the root directory of this source tree.


from dataclasses import replace
from enum import Enum
from functools import partial
from typing import Any, Iterable, List, Optional, Set, Tuple, Union

import torch

from ..common import get_operator, register_operator
from . import attn_bias
from .attn_bias import (
    AttentionBias,
    BlockDiagonalCausalLocalAttentionFromBottomRightMask,
    BlockDiagonalCausalLocalAttentionMask,
    BlockDiagonalCausalMask,
    BlockDiagonalCausalWithOffsetPaddedKeysMask,
    BlockDiagonalMask,
    LowerTriangularFromBottomRightLocalAttentionMask,
    LowerTriangularFromBottomRightMask,
    LowerTriangularMask,
    LowerTriangularMaskWithTensorBias,
)
from .common import (
    _attn_bias_apply,
    AttentionBwOpBase,
    AttentionFwOpBase,
    check_lastdim_alignment_stride1,
    Context,
    Gradients,
    Inputs,
)
from .torch_attention_compat import is_pt_cutlass_compatible


def _uses_tensorcores(sm: int, is_half: bool) -> bool:
    if sm >= 80:
        return True
    if sm >= 70:
        return is_half
    return False


def _minimum_gemm_alignment(inp: Inputs) -> int:
    if inp.device.type != "cuda":
        return 1
    cap = torch.cuda.get_device_capability(inp.device)
    sm = cap[0] * 10 + cap[1]
    bits_per_scalar = {torch.float: 32, torch.half: 16, torch.bfloat16: 16}[
        inp.query.dtype
    ]
    uses_tensorcores = _uses_tensorcores(sm, bits_per_scalar == 16)
    matmul_alignment_mn = 1
    if sm >= 80:
        matmul_alignment_mn = 4
    if uses_tensorcores:
        matmul_alignment_mn = max(matmul_alignment_mn, 128 // bits_per_scalar)
    return matmul_alignment_mn


def _get_seqlen_info(
    inp: Inputs,
) -> Tuple[Optional[torch.Tensor], Optional[torch.Tensor], int, int]:
    attn_bias = inp.attn_bias
    if isinstance(
        attn_bias, (BlockDiagonalMask, BlockDiagonalCausalWithOffsetPaddedKeysMask)
    ):
        assert attn_bias.k_seqinfo.seqstart.device == inp.query.device
        seqstart_k = attn_bias.k_seqinfo.seqstart
        seqstart_q = attn_bias.q_seqinfo.seqstart
        max_seqlen_q = attn_bias.q_seqinfo.max_seqlen
        max_seqlen_k = attn_bias.k_seqinfo.max_seqlen
    else:
        seqstart_k = None
        seqstart_q = None
        max_seqlen_q = -1
        max_seqlen_k = -1

    return seqstart_k, seqstart_q, max_seqlen_q, max_seqlen_k


def _get_tensor_bias(
    attn_bias: Optional[Union[torch.Tensor, AttentionBias]],
) -> Optional[torch.Tensor]:
    if isinstance(attn_bias, LowerTriangularMaskWithTensorBias):
        return attn_bias._bias
    if isinstance(attn_bias, torch.Tensor):
        return attn_bias
    return None


def _check_bias_alignment(
    reasons: List[str], attn_bias: Optional[Union[torch.Tensor, AttentionBias]]
) -> None:
    attn_bias_tensor = _get_tensor_bias(attn_bias)
    if attn_bias_tensor is not None:
        alignment = 128 // torch.finfo(attn_bias_tensor.dtype).bits
        show_padding_hint = False
        for d in range(attn_bias_tensor.ndim - 1):
            if attn_bias_tensor.stride(d) % alignment != 0:
                reasons.append(
                    f"attn_bias.stride(-2) % {alignment} != 0 (attn_bias.stride() = {attn_bias_tensor.stride()})"
                )
                show_padding_hint = True
        if show_padding_hint:
            reasons.append(
                """\
HINT: To use an `attn_bias` with a sequence length that is not a multiple of 8, \
you need to ensure memory is aligned by slicing a bigger tensor. \
Example: use `attn_bias = torch.zeros([1, 1, 5, 8])[:,:,:,:5]` instead of `torch.zeros([1, 1, 5, 5])`"""
            )
        # We can have stride=0 sometimes if dimension=1
        if attn_bias_tensor.stride(-1) > 1:
            reasons.append(
                f"attn_bias.stride(-1) > 1 (attn_bias.stride() = {attn_bias_tensor.stride()}) - "
                "you should call `.contiguous()` on the bias"
            )


class _CustomMaskType(int, Enum):
    """
    (Matches CustomMaskType in C++.)
    """

    NoCustomMask = 0
    CausalFromTopLeft = 1
    CausalFromBottomRight = 2


def _custom_mask_type(bias: Optional[Union[torch.Tensor, AttentionBias]]) -> int:
    if isinstance(
        bias,
        (
            LowerTriangularMask,
            BlockDiagonalCausalMask,
            BlockDiagonalCausalLocalAttentionMask,
        ),
    ):
        return int(_CustomMaskType.CausalFromTopLeft)
    if isinstance(
        bias,
        (
            LowerTriangularFromBottomRightMask,
            LowerTriangularFromBottomRightLocalAttentionMask,
            attn_bias.BlockDiagonalCausalFromBottomRightMask,
            BlockDiagonalCausalWithOffsetPaddedKeysMask,
            BlockDiagonalCausalLocalAttentionFromBottomRightMask,
        ),
    ):
        return int(_CustomMaskType.CausalFromBottomRight)
    return int(_CustomMaskType.NoCustomMask)


@register_operator
class FwOp(AttentionFwOpBase):
    """xFormers' MHA kernel based on CUTLASS.
    Supports a large number of settings (including without TensorCores, f32 ...)
    and GPUs as old as P100 (Sm60)
    """

    OPERATOR = (
        get_operator("aten", "_efficient_attention_forward")
        if is_pt_cutlass_compatible()
        else None
    )
    CUDA_MAXIMUM_COMPUTE_CAPABILITY = (9, 0)
    SUPPORTED_DEVICES: Set[str] = {"cuda"}
    SUPPORTED_DTYPES: Set[torch.dtype] = {torch.float, torch.half, torch.bfloat16}
    SUPPORTED_MAX_K = 65536
    SUPPORTED_ATTN_BIAS_TYPES: Iterable[Any] = (
        type(None),
        torch.Tensor,
        LowerTriangularMask,
        LowerTriangularFromBottomRightMask,
        LowerTriangularFromBottomRightLocalAttentionMask,
        LowerTriangularMaskWithTensorBias,
        BlockDiagonalMask,
        BlockDiagonalCausalMask,
        BlockDiagonalCausalWithOffsetPaddedKeysMask,
        attn_bias.BlockDiagonalCausalFromBottomRightMask,
        attn_bias.BlockDiagonalCausalLocalAttentionMask,
        BlockDiagonalCausalLocalAttentionFromBottomRightMask,
    )
    SUPPORTS_DROPOUT = True
    SUPPORTS_CUSTOM_SCALE = True
    SUPPORTS_DIFFERENT_VALUE_EMBED = True
    SUPPORTS_BMGHK = True
    VARLEN_LSE_PACKED = False
    NAME = "cutlassF-pt"

    _TEST_K: List[int] = [
        32,  # 64x64 kernel
        128,  # 64x128 kernel
        256,  # 64x128 with accumulation in gmem
    ]

    @classmethod
    def apply(
        cls, inp: Inputs, needs_gradient: bool
    ) -> Tuple[torch.Tensor, Optional[Context]]:
        if type(inp.attn_bias) not in FwOp.SUPPORTED_ATTN_BIAS_TYPES:
            raise NotImplementedError("Unsupported attn_bias type")
        if inp.query.ndim in [3, 4]:
            return cls.apply_bmhk(inp, needs_gradient=needs_gradient)
        assert inp.query.ndim == 5, f"query has shape {inp.query.shape}"
        ctx: Optional[Context] = None
        # XXX: Hackfix for BMGHK with H=1
        # In that case we don't want to run G different streams because it adds
        # some overhead
        if inp.query.ndim == 5 and inp.query.shape[3] == 1:
            slice_op = partial(torch.squeeze, dim=3)
            inp = replace(
                inp,
                query=slice_op(inp.query),
                key=slice_op(inp.key),
                value=slice_op(inp.value),
                attn_bias=_attn_bias_apply(
                    inp.attn_bias, partial(torch.squeeze, dim=2)
                ),
            )
            out, ctx = cls.apply_bmhk(inp, needs_gradient=needs_gradient)
            out = out.unsqueeze(3)
            if ctx is not None:
                ctx = replace(ctx, lse=ctx.lse.unsqueeze(1), out=out)
            return out, ctx

        # Workaround until this is properly implemented in C++
        # run each head group in a different stream
        n_groups = inp.key.shape[2]
        main_stream = torch.cuda.current_stream()
        streams = [main_stream] + [
            torch.cuda.Stream(device=inp.query.device) for _ in range(n_groups - 1)
        ]
        outs = []
        for group, stream in enumerate(streams):
            stream.wait_stream(main_stream)
            with torch.cuda.stream(stream):
                query = inp.query[:, :, group]
                key = inp.key[:, :, group]
                value = inp.value[:, :, group]
                bias = _attn_bias_apply(
                    inp.attn_bias, partial(torch.select, dim=1, index=group)
                )
                outs.append(
                    cls.apply_bmhk(
                        replace(inp, query=query, key=key, value=value, attn_bias=bias),
                        needs_gradient=needs_gradient,
                    )
                )
        for s in streams[1:]:
            main_stream.wait_stream(s)
        out = torch.stack([o[0] for o in outs], dim=2)
        if needs_gradient:
            ctx = Context(
                out=out,
                lse=torch.stack([o[1].lse for o in outs], dim=1),  # type: ignore
                op_bw=outs[0][1].op_bw,  # type: ignore
            )
        return out, ctx

    @classmethod
    def apply_bmhk(
        cls, inp: Inputs, needs_gradient: bool
    ) -> Tuple[torch.Tensor, Optional[Context]]:
        if type(inp.attn_bias) not in FwOp.SUPPORTED_ATTN_BIAS_TYPES:
            raise NotImplementedError("Unsupported attn_bias type")
        seqstart_k, seqstart_q, max_seqlen_q, max_seqlen_k = _get_seqlen_info(inp)
        out, lse, rng_seed, rng_offset, _, _ = cls.OPERATOR(
            query=inp.query,
            key=inp.key,
            value=inp.value,
            bias=_get_tensor_bias(inp.attn_bias),
            cu_seqlens_q=seqstart_q,
            cu_seqlens_k=seqstart_k,
            max_seqlen_q=max_seqlen_q,
            max_seqlen_k=max_seqlen_k,
            dropout_p=inp.p,
            compute_log_sumexp=needs_gradient,
            custom_mask_type=_custom_mask_type(inp.attn_bias),
            scale=inp.scale,
            seqlen_k=(
                inp.attn_bias.k_seqinfo.seqlen
                if isinstance(
                    inp.attn_bias, BlockDiagonalCausalWithOffsetPaddedKeysMask
                )
                else None
            ),
            window_size=(
                inp.attn_bias._window_size
                if isinstance(
                    inp.attn_bias,
                    (
                        BlockDiagonalCausalLocalAttentionMask,
                        BlockDiagonalCausalLocalAttentionFromBottomRightMask,
                        LowerTriangularFromBottomRightLocalAttentionMask,
                    ),
                )
                else None
            ),
        )
        ctx: Optional[Context] = None
        if needs_gradient:
            ctx = Context(out=out, lse=lse)
            if inp.p != 0:
                # cutlass forward is only compatible with cutlass backward if
                # dropout is used (because of the way RNG states are passed and the
                # way random numbers are generated during backward)
                ctx.rng_state = (rng_seed, rng_offset)
                ctx.op_bw = BwOp
        return out, ctx

    @classmethod
    def not_supported_reasons(cls, d: Inputs) -> List[str]:
        reasons = super(FwOp, cls).not_supported_reasons(d)
        matmul_alignment_mn = _minimum_gemm_alignment(d)
        check_lastdim_alignment_stride1(reasons, "query", d.query, matmul_alignment_mn)
        check_lastdim_alignment_stride1(reasons, "value", d.value, matmul_alignment_mn)
        _check_bias_alignment(reasons, d.attn_bias)
        return reasons


@register_operator
class BwOp(AttentionBwOpBase):
    __doc__ = FwOp.__doc__

    OPERATOR = (
        get_operator("aten", "_efficient_attention_backward")
        if is_pt_cutlass_compatible()
        else None
    )
    CUDA_MAXIMUM_COMPUTE_CAPABILITY = FwOp.CUDA_MAXIMUM_COMPUTE_CAPABILITY
    SUPPORTED_DEVICES = FwOp.SUPPORTED_DEVICES
    SUPPORTED_DTYPES = FwOp.SUPPORTED_DTYPES
    SUPPORTED_MAX_K = FwOp.SUPPORTED_MAX_K
    SUPPORTED_ATTN_BIAS_TYPES: Iterable[Any] = (
        type(None),
        torch.Tensor,
        LowerTriangularMask,
        LowerTriangularFromBottomRightMask,
        # TODO: Still some infs/nans in the BW pass for
        # local + causal
        # LowerTriangularFromBottomRightLocalAttentionMask,
        # TODO: Fix handling of gradient through the fMHA autograd function
        # LowerTriangularMaskWithTensorBias,
        BlockDiagonalMask,
        BlockDiagonalCausalMask,
        attn_bias.BlockDiagonalCausalFromBottomRightMask,
        attn_bias.BlockDiagonalCausalLocalAttentionMask,
    )
    SUPPORTS_ATTN_BIAS_GRAD = True
    SUPPORTS_DROPOUT = FwOp.SUPPORTS_DROPOUT
    SUPPORTS_CUSTOM_SCALE = FwOp.SUPPORTS_CUSTOM_SCALE
    SUPPORTS_DIFFERENT_VALUE_EMBED = FwOp.SUPPORTS_DIFFERENT_VALUE_EMBED
    VARLEN_LSE_PACKED = False
    NAME = "cutlassB-pt"

    _TEST_K: List[int] = [
        32,  # 64x64 kernel
        128,  # 64x128/128x128 kernel
        256,  # 64x128 with accumulation in gmem
    ]

    @classmethod
    def not_supported_reasons(cls, d: Inputs) -> List[str]:
        reasons = super(BwOp, cls).not_supported_reasons(d)
        matmul_alignment_mn = _minimum_gemm_alignment(d)

        check_lastdim_alignment_stride1(reasons, "query", d.query, matmul_alignment_mn)
        check_lastdim_alignment_stride1(reasons, "key", d.key, matmul_alignment_mn)
        check_lastdim_alignment_stride1(reasons, "value", d.value, matmul_alignment_mn)
        _check_bias_alignment(reasons, d.attn_bias)
        attn_bias_tensor = _get_tensor_bias(d.attn_bias)

        # Backprop of gradient through broadcasted bias is not supported
        if attn_bias_tensor is not None and attn_bias_tensor.requires_grad:
            # Don't forget that inputs are either in BMK or BMHK!
            if d.query.ndim == 3 and attn_bias_tensor.ndim == 3:
                expected_bias_shape = (*d.query.shape[:2], d.key.shape[1])
            else:
                # bias is B H Mq Mk
                expected_bias_shape = (
                    d.query.shape[0],
                    d.query.shape[2] if d.query.ndim == 4 else 1,
                    d.query.shape[1],
                    d.key.shape[1],
                )
            if tuple(attn_bias_tensor.shape) != expected_bias_shape:
                reasons.append(
                    "Broadcasting the `attn_bias` tensor is not supported "
                    f"(shape: {tuple(attn_bias_tensor.shape)}"
                    f"/ expected: {expected_bias_shape})"
                )
        return reasons

    @classmethod
    def apply(cls, ctx: Context, inp: Inputs, grad: torch.Tensor) -> Gradients:
        if type(inp.attn_bias) not in BwOp.SUPPORTED_ATTN_BIAS_TYPES:
            raise NotImplementedError("Unsupported attn_bias type")

        seqstart_k, seqstart_q, max_seqlen_q, max_seqlen_k = _get_seqlen_info(inp)
        dtype = inp.query.dtype

        rng_seed = rng_offset = torch.Tensor()
        if inp.p != 0.0:
            assert ctx.rng_state is not None
            rng_seed, rng_offset = ctx.rng_state
        tensor_bias = _get_tensor_bias(inp.attn_bias)

        force_pad_inf = torch.cuda.get_device_capability(inp.query.device) == (7, 5)
        (grad_q, grad_k, grad_v, grad_bias) = cls.OPERATOR(
            grad.to(dtype),
            inp.query,
            inp.key,
            inp.value,
            bias=tensor_bias,
            bias_requires_grad=(
                tensor_bias.requires_grad if tensor_bias is not None else False
            ),
            cu_seqlens_q=seqstart_q,
            cu_seqlens_k=seqstart_k,
            max_seqlen_q=max_seqlen_q,
            max_seqlen_k=max_seqlen_k,
            logsumexp=ctx.get_padded_lse(32, force_pad_inf=force_pad_inf),
            out=ctx.out.to(dtype),
            dropout_p=inp.p,
            # if not using dropout, seed and offset are irrelevant but still expected
            # in function signature so just pass 0
            # seed and offset could be None if a different FW op other than cutlass
            # was used.
            philox_seed=rng_seed,
            philox_offset=rng_offset,
            custom_mask_type=_custom_mask_type(inp.attn_bias),
            scale=inp.scale,
            num_splits_key=None,  # Let C++ determine it
            window_size=(
                inp.attn_bias._window_size
                if isinstance(
                    inp.attn_bias,
                    (
                        BlockDiagonalCausalLocalAttentionMask,
                        BlockDiagonalCausalLocalAttentionFromBottomRightMask,
                        LowerTriangularFromBottomRightLocalAttentionMask,
                    ),
                )
                else None
            ),
        )

        # c++/CUDA implementation returns an uninitialized tensor if bias doesn't
        # require grad
        if not (
            isinstance(inp.attn_bias, torch.Tensor) and inp.attn_bias.requires_grad
        ):
            grad_bias = None

        return Gradients(dq=grad_q, dk=grad_k, dv=grad_v, db=grad_bias)
