# -*- coding: utf-8 -*-
# Copyright (c) 2024, Songlin Yang, Yu Zhang

from typing import Optional, Tuple

import torch
import triton
import triton.language as tl

from fla.ops.common.chunk_h import chunk_bwd_dh, chunk_fwd_h
from fla.ops.utils import chunk_local_cumsum
from fla.utils import autocast_custom_bwd, autocast_custom_fwd, contiguous


@triton.autotune(
    configs=[
        triton.Config({}, num_warps=4),
    ],
    key=["BT", "BK", "BV"],
)
@triton.heuristics({'USE_OFFSETS': lambda args: args['offsets'] is not None})
@triton.jit
def chunk_simple_gla_fwd_kernel_o(
    q,
    k,
    v,
    h,
    g,
    o,
    offsets,
    indices,
    scale,
    T: tl.constexpr,
    H: tl.constexpr,
    K: tl.constexpr,
    V: tl.constexpr,
    BT: tl.constexpr,
    BK: tl.constexpr,
    BV: tl.constexpr,
    NT: tl.constexpr,
    USE_OFFSETS: tl.constexpr,
    HEAD_FIRST: tl.constexpr
):
    i_v, i_t, i_bh = tl.program_id(0), tl.program_id(1), tl.program_id(2)
    i_b, i_h = i_bh // H, i_bh % H
    if USE_OFFSETS:
        i_tg = i_t
        i_n, i_t = tl.load(indices + i_t * 2).to(tl.int32), tl.load(indices + i_t * 2 + 1).to(tl.int32)
        bos, eos = tl.load(offsets + i_n).to(tl.int32), tl.load(offsets + i_n + 1).to(tl.int32)
        T = eos - bos
        NT = tl.cdiv(T, BT)
    else:
        NT = tl.cdiv(T, BT)
        i_tg = i_b * NT + i_t
        bos, eos = i_b * T, i_b * T + T

    o_i = tl.arange(0, BT)
    m_s = o_i[:, None] >= o_i[None, :]

    b_o = tl.zeros([BT, BV], dtype=tl.float32)
    b_s = tl.zeros([BT, BT], dtype=tl.float32)
    for i_k in range(tl.cdiv(K, BK)):
        if HEAD_FIRST:
            p_q = tl.make_block_ptr(q + i_bh * T*K, (T, K), (K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
            p_k = tl.make_block_ptr(k + i_bh * T*K, (K, T), (1, K), (i_k * BK, i_t * BT), (BK, BT), (0, 1))
            p_h = tl.make_block_ptr(h + (i_bh * NT + i_t) * K*V, (K, V), (V, 1), (i_k * BK, i_v * BV), (BK, BV), (1, 0))
        else:
            p_q = tl.make_block_ptr(q + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
            p_k = tl.make_block_ptr(k + (bos * H + i_h) * K, (K, T), (1, H*K), (i_k * BK, i_t * BT), (BK, BT), (0, 1))
            p_h = tl.make_block_ptr(h + (i_tg * H + i_h) * K*V, (K, V), (V, 1), (i_k * BK, i_v * BV), (BK, BV), (1, 0))
        # [BT, BK]
        b_q = tl.load(p_q, boundary_check=(0, 1))
        # [BK, BT]
        b_k = tl.load(p_k, boundary_check=(0, 1))
        # [BK, BV]
        b_h = tl.load(p_h, boundary_check=(0, 1))
        b_o += tl.dot(b_q, b_h, allow_tf32=False)
        b_s += tl.dot(b_q, b_k, allow_tf32=False)

    if HEAD_FIRST:
        p_g = tl.make_block_ptr(g + i_bh * T, (T,), (1,), (i_t * BT,), (BT,), (0,))
        p_v = tl.make_block_ptr(v + i_bh * T*V, (T, V), (V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
        p_o = tl.make_block_ptr(o + i_bh * T*V, (T, V), (V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
    else:
        p_g = tl.make_block_ptr(g + bos * H + i_h, (T,), (H,), (i_t * BT,), (BT,), (0,))
        p_v = tl.make_block_ptr(v + (bos * H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
        p_o = tl.make_block_ptr(o + (bos * H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
    b_g = tl.load(p_g, boundary_check=(0,))
    b_o = b_o * tl.exp(b_g)[:, None]
    b_s = b_s * tl.exp(b_g[:, None] - b_g[None, :])
    b_s = tl.where(m_s, b_s, 0)

    b_v = tl.load(p_v, boundary_check=(0, 1))
    b_o = (b_o + tl.dot(b_s.to(b_v.dtype), b_v, allow_tf32=False)) * scale
    tl.store(p_o, b_o.to(p_o.dtype.element_ty), boundary_check=(0, 1))


@triton.autotune(
    configs=[
        triton.Config({}, num_warps=4),
        triton.Config({}, num_warps=8)
    ],
    key=["BT", "BK", "BV"],
)
@triton.heuristics({'USE_OFFSETS': lambda args: args['offsets'] is not None})
@triton.jit
def chunk_simple_gla_bwd_kernel_dqkg(
    q,
    k,
    v,
    h,
    g,
    do,
    dh,
    dq,
    dk,
    dg,
    offsets,
    indices,
    scale,
    B: tl.constexpr,
    T: tl.constexpr,
    H: tl.constexpr,
    K: tl.constexpr,
    V: tl.constexpr,
    BT: tl.constexpr,
    BK: tl.constexpr,
    BV: tl.constexpr,
    USE_OFFSETS: tl.constexpr,
    HEAD_FIRST: tl.constexpr
):
    i_k, i_t, i_bh = tl.program_id(0), tl.program_id(1), tl.program_id(2)
    i_b, i_h = i_bh // H, i_bh % H
    if USE_OFFSETS:
        i_tg = i_t
        i_n, i_t = tl.load(indices + i_t * 2).to(tl.int32), tl.load(indices + i_t * 2 + 1).to(tl.int32)
        bos, eos = tl.load(offsets + i_n).to(tl.int32), tl.load(offsets + i_n + 1).to(tl.int32)
        all = T
        T = eos - bos
        NT = tl.cdiv(T, BT)
    else:
        NT = tl.cdiv(T, BT)
        i_tg = i_b * NT + i_t
        bos, eos = i_b * T, i_b * T + T
        all = B * T
    o_i = tl.arange(0, BT)

    if HEAD_FIRST:
        p_g = tl.make_block_ptr(g + i_bh * T, (T,), (1,), (i_t * BT,), (BT,), (0,))
        b_g_last = tl.load(g + i_bh * T + min(i_t * BT + BT, T) - 1)
    else:
        p_g = tl.make_block_ptr(g + bos * H + i_h, (T,), (H,), (i_t * BT,), (BT,), (0,))
        b_g_last = tl.load(g + (bos + min(i_t * BT + BT, T) - 1) * H + i_h)
    b_g = tl.load(p_g, boundary_check=(0,))

    b_dq = tl.zeros([BT, BK], dtype=tl.float32)
    b_dk = tl.zeros([BT, BK], dtype=tl.float32)
    b_ds = tl.zeros([BT, BT], dtype=tl.float32)
    b_dg = tl.zeros([BT,], dtype=tl.float32)
    b_dg_last = tl.zeros([1,], dtype=tl.float32)

    for i_v in range(tl.cdiv(V, BV)):
        if HEAD_FIRST:
            p_v = tl.make_block_ptr(v + i_bh * T*V, (T, V), (V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
            p_do = tl.make_block_ptr(do + i_bh * T*V, (T, V), (V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
            p_h = tl.make_block_ptr(h + (i_bh * NT + i_t) * K*V, (V, K), (1, V), (i_v * BV, i_k * BK), (BV, BK), (0, 1))
            p_dh = tl.make_block_ptr(dh + (i_bh * NT + i_t) * K*V, (V, K), (1, V), (i_v * BV, i_k * BK), (BV, BK), (0, 1))
        else:
            p_v = tl.make_block_ptr(v + (bos*H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
            p_do = tl.make_block_ptr(do + (bos*H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
            p_h = tl.make_block_ptr(h + (i_tg * H + i_h) * K*V, (V, K), (1, V), (i_v * BV, i_k * BK), (BV, BK), (0, 1))
            p_dh = tl.make_block_ptr(dh + (i_tg * H + i_h) * K*V, (V, K), (1, V), (i_v * BV, i_k * BK), (BV, BK), (0, 1))
        # [BT, BV]
        b_v = tl.load(p_v, boundary_check=(0, 1))
        b_do = tl.load(p_do, boundary_check=(0, 1))
        # [BV, BK]
        b_h = tl.load(p_h, boundary_check=(0, 1))
        b_dh = tl.load(p_dh, boundary_check=(0, 1))

        b_dg_last += (tl.sum(b_h * b_dh))
        b_ds += tl.dot(b_do, tl.trans(b_v))
        b_dq += tl.dot(b_do, b_h.to(b_do.dtype))
        b_dk += tl.dot(b_v, b_dh.to(b_v.dtype))

    if HEAD_FIRST:
        p_q = tl.make_block_ptr(q + i_bh * T*K, (T, K), (K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        p_k = tl.make_block_ptr(k + i_bh * T*K, (T, K), (K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        p_dq = tl.make_block_ptr(dq + i_bh * T*K, (T, K), (K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        p_dk = tl.make_block_ptr(dk + i_bh * T*K, (T, K), (K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        p_dg = tl.make_block_ptr(dg + (i_k*B*H + i_bh) * T, (T,), (1,), (i_t * BT,), (BT,), (0,))
    else:
        p_q = tl.make_block_ptr(q + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        p_k = tl.make_block_ptr(k + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BK, BT), (0, 1))
        p_dq = tl.make_block_ptr(dq + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        p_dk = tl.make_block_ptr(dk + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        p_dg = tl.make_block_ptr(dg + (i_k*all + bos) * H + i_h, (T,), (H,), (i_t * BT,), (BT,), (0,))
    b_q = tl.load(p_q, boundary_check=(0, 1))
    b_k = tl.load(p_k, boundary_check=(0, 1))
    b_dg_last *= tl.exp(b_g_last)
    b_dq = b_dq * tl.exp(b_g)[:, None] * scale
    b_dk = b_dk * tl.exp(-b_g + b_g_last)[:, None]
    b_dg_last += tl.sum(b_dk * b_k)
    b_ds = tl.where(o_i[:, None] >= o_i[None, :], b_ds * scale * tl.exp(b_g[:, None] - b_g[None, :]), 0)
    b_ds = b_ds.to(b_k.dtype)
    # [BT, BK]
    b_dq += tl.dot(b_ds, b_k)
    b_dk += tl.dot(tl.trans(b_ds), b_q)
    b_dg += tl.sum(b_q * b_dq - b_k * b_dk, axis=1)
    # (SY 09/21) revcumsum in a separate kernel due to strange triton compiler issue
    # b_dg = tl.dot(tl.where(o_i[:, None] <= o_i[None, :], 1., 0.), b_dg, allow_tf32=False) + b_dg_last)
    b_dg = tl.where(o_i < min(BT, T-i_t*BT) - 1, b_dg, b_dg + b_dg_last)
    tl.store(p_dq, b_dq.to(p_dq.dtype.element_ty), boundary_check=(0, 1))
    tl.store(p_dk, b_dk.to(p_dk.dtype.element_ty), boundary_check=(0, 1))
    tl.store(p_dg, b_dg.to(p_dg.dtype.element_ty), boundary_check=(0,))


@triton.autotune(
    configs=[
        triton.Config({}, num_warps=1),
        triton.Config({}, num_warps=2),
        triton.Config({}, num_warps=4),
        triton.Config({}, num_warps=8),
    ],
    key=["BT", "BK", "BV"],
)
@triton.heuristics({'USE_OFFSETS': lambda args: args['offsets'] is not None})
@triton.jit
def chunk_simple_gla_bwd_kernel_dv(
    q,
    k,
    g,
    do,
    dv,
    dh,
    offsets,
    indices,
    scale,
    T: tl.constexpr,
    H: tl.constexpr,
    K: tl.constexpr,
    V: tl.constexpr,
    BT: tl.constexpr,
    BK: tl.constexpr,
    BV: tl.constexpr,
    USE_OFFSETS: tl.constexpr,
    HEAD_FIRST: tl.constexpr
):
    i_v, i_t, i_bh = tl.program_id(0), tl.program_id(1), tl.program_id(2)
    i_b, i_h = i_bh // H, i_bh % H
    if USE_OFFSETS:
        i_tg = i_t
        i_n, i_t = tl.load(indices + i_t * 2).to(tl.int32), tl.load(indices + i_t * 2 + 1).to(tl.int32)
        bos, eos = tl.load(offsets + i_n).to(tl.int32), tl.load(offsets + i_n + 1).to(tl.int32)
        T = eos - bos
        NT = tl.cdiv(T, BT)
    else:
        NT = tl.cdiv(T, BT)
        i_tg = i_b * NT + i_t
        bos, eos = i_b * T, i_b * T + T

    if HEAD_FIRST:
        b_g = tl.load(g + i_bh * T + i_t * BT + tl.arange(0, BT))
        b_g_last = tl.load(g + i_bh * T + min(i_t * BT + BT, T) - 1)
    else:
        b_g = tl.load(g + (bos + i_t * BT + tl.arange(0, BT)) * H + i_h)
        b_g_last = tl.load(g + (bos + min(i_t * BT + BT, T) - 1) * H + i_h)
    b_dv = tl.zeros([BT, BV], dtype=tl.float32)
    for i_k in range(tl.cdiv(K, BK)):
        if HEAD_FIRST:
            p_k = tl.make_block_ptr(k + i_bh * T*K, (T, K), (K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
            p_dh = tl.make_block_ptr(dh + (i_bh * NT + i_t) * K*V, (K, V), (V, 1), (i_k * BK, i_v * BV), (BK, BV), (1, 0))
        else:
            p_k = tl.make_block_ptr(k + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
            p_dh = tl.make_block_ptr(dh + (i_tg * H + i_h) * K*V, (K, V), (V, 1), (i_k * BK, i_v * BV), (BK, BV), (1, 0))

        # [BT, BK]
        b_k = tl.load(p_k, boundary_check=(0, 1))
        # [BK, BV]
        b_dh = tl.load(p_dh, boundary_check=(0, 1))
        b_dv += tl.dot(b_k, b_dh.to(b_k.dtype)) * tl.exp(-b_g + b_g_last)[:, None]

    b_A = tl.zeros([BT, BT], dtype=tl.float32)
    for i_k in range(tl.cdiv(K, BK)):
        if HEAD_FIRST:
            p_q = tl.make_block_ptr(q + i_bh * T*K, (K, T), (1, K), (i_k * BK, i_t * BT), (BK, BT), (0, 1))
            p_k = tl.make_block_ptr(k + i_bh * T*K, (T, K), (K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        else:
            p_q = tl.make_block_ptr(q + (bos * H + i_h) * K, (K, T), (1, H*K), (i_k * BK, i_t * BT), (BK, BT), (0, 1))
            p_k = tl.make_block_ptr(k + (bos * H + i_h) * K, (T, K), (H*K, 1), (i_t * BT, i_k * BK), (BT, BK), (1, 0))
        b_q = tl.load(p_q, boundary_check=(0, 1))
        b_k = tl.load(p_k, boundary_check=(0, 1))
        b_A += tl.dot(b_k, b_q, allow_tf32=False)

    mask = (tl.arange(0, BT)[:, None] <= tl.arange(0, BT)[None, :]) & (i_t * BT + tl.arange(0, BT) < T)
    b_A = b_A * tl.exp(b_g[None, :] - b_g[:, None]) * scale
    b_A = tl.where(mask, b_A, 0).to(do.dtype.element_ty)

    if HEAD_FIRST:
        p_do = tl.make_block_ptr(do + i_bh * T*V, (T, V), (V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
        p_dv = tl.make_block_ptr(dv + i_bh * T*V, (T, V), (V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
    else:
        p_do = tl.make_block_ptr(do + (bos*H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
        p_dv = tl.make_block_ptr(dv + (bos*H + i_h) * V, (T, V), (H*V, 1), (i_t * BT, i_v * BV), (BT, BV), (1, 0))
    b_do = tl.load(p_do, boundary_check=(0, 1))
    b_dv += tl.dot(b_A, b_do)
    tl.store(p_dv, b_dv.to(p_dv.dtype.element_ty), boundary_check=(0, 1))


def chunk_simple_gla_fwd_o(
    q: torch.Tensor,
    k: torch.Tensor,
    v: torch.Tensor,
    g: torch.Tensor,
    h: torch.Tensor,
    scale: float,
    offsets: Optional[torch.LongTensor] = None,
    indices: Optional[torch.LongTensor] = None,
    head_first: bool = True,
    chunk_size: int = 64
) -> torch.Tensor:
    if head_first:
        B, H, T, K, V = *q.shape, v.shape[-1]
    else:
        B, T, H, K, V = *q.shape, v.shape[-1]
    BT = min(chunk_size, triton.next_power_of_2(T))
    if offsets is None:
        NT = triton.cdiv(T, BT)
    else:
        if indices is None:
            indices = torch.cat([torch.arange(n) for n in triton.cdiv(offsets[1:] - offsets[:-1], BT).tolist()])
            indices = torch.stack([indices.eq(0).cumsum(0) - 1, indices], 1).to(offsets)
        NT = len(indices)
    BK = min(triton.next_power_of_2(K), 64)
    BV = min(triton.next_power_of_2(V), 64)
    NV = triton.cdiv(V, BV)

    o = torch.empty_like(v)
    grid = (NV, NT, B * H)
    chunk_simple_gla_fwd_kernel_o[grid](
        q,
        k,
        v,
        h,
        g,
        o,
        offsets,
        indices,
        scale,
        T=T,
        H=H,
        K=K,
        V=V,
        BT=BT,
        BK=BK,
        BV=BV,
        NT=NT,
        HEAD_FIRST=head_first
    )
    return o


def chunk_simple_gla_bwd_dqkg(
    q: torch.Tensor,
    k: torch.Tensor,
    v: torch.Tensor,
    g: torch.Tensor,
    h: torch.Tensor,
    do: torch.Tensor,
    dh: torch.Tensor,
    scale: float,
    offsets: Optional[torch.LongTensor] = None,
    indices: Optional[torch.LongTensor] = None,
    head_first: bool = True,
    chunk_size: int = 64
) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
    if head_first:
        B, H, T, K, V = *k.shape, v.shape[-1]
    else:
        B, T, H, K, V = *k.shape, v.shape[-1]
    BT = min(chunk_size, triton.next_power_of_2(T))
    if offsets is None:
        NT = triton.cdiv(T, BT)
    else:
        if indices is None:
            indices = torch.cat([torch.arange(n) for n in triton.cdiv(offsets[1:] - offsets[:-1], BT).tolist()])
            indices = torch.stack([indices.eq(0).cumsum(0) - 1, indices], 1).to(offsets)
        NT = len(indices)
    BK = min(triton.next_power_of_2(K), 64)
    BV = min(triton.next_power_of_2(V), 64)
    NK = triton.cdiv(K, BK)

    dq = torch.empty_like(q)
    dk = torch.empty_like(k)
    dg = torch.empty(NK, *g.shape, dtype=torch.float32, device=g.device)
    grid = (NK, NT, B * H)
    chunk_simple_gla_bwd_kernel_dqkg[grid](
        q,
        k,
        v,
        h,
        g,
        do,
        dh,
        dq,
        dk,
        dg,
        offsets,
        indices,
        scale,
        B=B,
        T=T,
        H=H,
        K=K,
        V=V,
        BT=BT,
        BK=BK,
        BV=BV,
        HEAD_FIRST=head_first
    )
    dg = chunk_local_cumsum(dg.sum(0), chunk_size, reverse=True, offsets=offsets, head_first=head_first)
    return dq, dk, dg


def chunk_simple_gla_bwd_dv(
    q: torch.Tensor,
    k: torch.Tensor,
    g: torch.Tensor,
    do: torch.Tensor,
    dh: torch.Tensor,
    scale: float,
    offsets: Optional[torch.LongTensor] = None,
    indices: Optional[torch.LongTensor] = None,
    head_first: bool = True,
    chunk_size: int = 64
) -> torch.Tensor:
    if head_first:
        B, H, T, K, V = *k.shape, do.shape[-1]
    else:
        B, T, H, K, V = *k.shape, do.shape[-1]
    BT = min(chunk_size, triton.next_power_of_2(T))
    if offsets is None:
        NT = triton.cdiv(T, BT)
    else:
        if indices is None:
            indices = torch.cat([torch.arange(n) for n in triton.cdiv(offsets[1:] - offsets[:-1], BT).tolist()])
            indices = torch.stack([indices.eq(0).cumsum(0) - 1, indices], 1).to(offsets)
        NT = len(indices)
    BK = min(triton.next_power_of_2(K), 64)
    BV = min(triton.next_power_of_2(V), 64)
    NV = triton.cdiv(V, BV)

    dv = torch.empty_like(do)
    grid = (NV, NT, B * H)
    chunk_simple_gla_bwd_kernel_dv[grid](
        q,
        k,
        g,
        do,
        dv,
        dh,
        offsets,
        indices,
        scale,
        T=T,
        H=H,
        K=K,
        V=V,
        BT=BT,
        BK=BK,
        BV=BV,
        HEAD_FIRST=head_first
    )
    return dv


def chunk_simple_gla_fwd(
    q: torch.Tensor,
    k: torch.Tensor,
    v: torch.Tensor,
    g: torch.Tensor,
    scale: float,
    initial_state: torch.Tensor,
    output_final_state: bool,
    offsets: Optional[torch.LongTensor] = None,
    indices: Optional[torch.LongTensor] = None,
    head_first: bool = True,
    chunk_size: int = 64
) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
    g = chunk_local_cumsum(g, chunk_size, offsets=offsets, head_first=head_first)
    h, ht = chunk_fwd_h(
        k=k,
        v=v,
        g=g,
        gk=None,
        gv=None,
        h0=initial_state,
        output_final_state=output_final_state,
        states_in_fp32=False,
        offsets=offsets,
        head_first=head_first,
        chunk_size=chunk_size
    )
    o = chunk_simple_gla_fwd_o(
        q=q,
        k=k,
        v=v,
        g=g,
        h=h,
        scale=scale,
        offsets=offsets,
        indices=indices,
        head_first=head_first,
        chunk_size=chunk_size
    )
    return g, o, ht


def chunk_simple_gla_bwd(
    q: torch.Tensor,
    k: torch.Tensor,
    v: torch.Tensor,
    g: torch.Tensor,
    initial_state: torch.Tensor,
    do: torch.Tensor,
    dht: torch.Tensor,
    scale: float,
    offsets: Optional[torch.LongTensor] = None,
    indices: Optional[torch.LongTensor] = None,
    head_first: bool = True,
    chunk_size: int = 64
) -> Tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
    # (SY 09/22) states_in_fp32 seems not affecting the error of dg but for safety, set to True
    h, _ = chunk_fwd_h(
        k=k,
        v=v,
        g=g,
        gk=None,
        gv=None,
        h0=initial_state,
        output_final_state=False,
        states_in_fp32=True,
        offsets=offsets,
        head_first=head_first,
        chunk_size=chunk_size
    )
    dh, dh0 = chunk_bwd_dh(
        q=q,
        k=k,
        v=v,
        g=g,
        gk=None,
        gv=None,
        do=do,
        h0=initial_state,
        dht=dht,
        scale=scale,
        states_in_fp32=True,
        offsets=offsets,
        head_first=head_first,
        chunk_size=chunk_size
    )
    dq, dk, dg = chunk_simple_gla_bwd_dqkg(
        q=q,
        k=k,
        v=v,
        g=g,
        h=h,
        do=do,
        dh=dh,
        scale=scale,
        offsets=offsets,
        indices=indices,
        head_first=head_first,
        chunk_size=chunk_size
    )
    dv = chunk_simple_gla_bwd_dv(
        q=q,
        k=k,
        g=g,
        do=do,
        dh=dh,
        scale=scale,
        offsets=offsets,
        indices=indices,
        head_first=head_first,
        chunk_size=chunk_size
    )
    return dq, dk, dv, dg, dh0


class ChunkSimpleGLAFunction(torch.autograd.Function):

    @staticmethod
    @contiguous
    @autocast_custom_fwd
    def forward(
        ctx,
        q,
        k,
        v,
        g,
        scale,
        initial_state,
        output_final_state,
        offsets,
        head_first
    ):
        T = q.shape[2] if head_first else q.shape[1]
        chunk_size = min(64, triton.next_power_of_2(T))

        # 2-d indices denoting the offsets of chunks in each sequence
        # for example, if the passed `offsets` is [0, 100, 356] and `chunk_size` is 64,
        # then there are 2 and 4 chunks in the 1st and 2nd sequences respectively, and `indices` will be
        # [[0, 0], [0, 1], [1, 0], [1, 1], [1, 2], [1, 3]]
        indices = None
        if offsets is not None:
            indices = torch.cat([torch.arange(n) for n in triton.cdiv(offsets[1:] - offsets[:-1], chunk_size).tolist()])
            indices = torch.stack([indices.eq(0).cumsum(0) - 1, indices], 1).to(offsets)

        g, o, ht = chunk_simple_gla_fwd(
            q=q,
            k=k,
            v=v,
            g=g,
            scale=scale,
            initial_state=initial_state,
            output_final_state=output_final_state,
            offsets=offsets,
            indices=indices,
            head_first=head_first,
            chunk_size=chunk_size
        )
        ctx.save_for_backward(q, k, v, g, initial_state)
        ctx.chunk_size = chunk_size
        ctx.scale = scale
        ctx.offsets = offsets
        ctx.indices = indices
        ctx.head_first = head_first
        return o.to(q.dtype), ht

    @staticmethod
    @contiguous
    @autocast_custom_bwd
    def backward(ctx, do, dht):
        chunk_size, scale, offsets, indices, head_first = ctx.chunk_size, ctx.scale, ctx.offsets, ctx.indices, ctx.head_first
        q, k, v, g, initial_state = ctx.saved_tensors
        dq, dk, dv, dg, dh0 = chunk_simple_gla_bwd(
            q=q,
            k=k,
            v=v,
            g=g,
            initial_state=initial_state,
            do=do,
            dht=dht,
            scale=scale,
            offsets=offsets,
            indices=indices,
            head_first=head_first,
            chunk_size=chunk_size
        )
        return dq.to(q.dtype), dk.to(k.dtype), dv.to(v.dtype), dg.to(g.dtype), None, dh0, None, None, None


def chunk_simple_gla(
    q: torch.Tensor,
    k: torch.Tensor,
    v: torch.Tensor,
    g: torch.Tensor,  # log decay
    scale: Optional[float] = None,
    initial_state: Optional[torch.Tensor] = None,
    output_final_state: bool = False,
    offsets: Optional[torch.LongTensor] = None,
    head_first: bool = True
) -> Tuple[torch.Tensor, torch.Tensor]:
    r"""
    Args:
        q (torch.Tensor):
            queries of shape `[B, H, T, K]` if `head_first=True` else `[B, T, H, K]`.
        k (torch.Tensor):
            keys of shape `[B, H, T, K]` if `head_first=True` else `[B, T, H, K]`.
        v (torch.Tensor):
            values of shape `[B, H, T, V]` if `head_first=True` else `[B, T, H, V]`.
        g (torch.Tensor):
            Forget gates of shape `[B, H, T]` if `head_first=True` else `[B, T, H]`.
            Compared to GLA, the gating is head-wise instead of elementwise.
        scale (Optional[int]):
            Scale factor for the attention scores.
            If not provided, it will default to `1 / sqrt(K)`. Default: `None`.
        initial_state (Optional[torch.Tensor]):
            Initial state of shape `[N, H, K, V]` for `N` input sequences.
            For equal-length input sequences, `N` equals the batch size `B`.
            Default: `None`.
        output_final_state (Optional[bool]):
            Whether to output the final state of shape `[N, H, K, V]`. Default: `False`.
        offsets (Optional[torch.LongTensor]):
            Offsets of shape `[N+1]` defining the bos/eos positions of `N` variable-length sequences in the batch.
            For example,
            if `offsets` is `[0, 1, 3, 6, 10, 15]`, there are `N=5` sequences with lengths 1, 2, 3, 4 and 5 respectively.
            If provided, the inputs are concatenated and the batch size `B` is expected to be 1.
            Default: `None`.
        head_first (Optional[bool]):
            Whether the inputs are in the head-first format, which is not supported for variable-length inputs.
            Default: `True`.

    Returns:
        o (torch.Tensor):
            Outputs of shape `[B, H, T, V]` if `head_first=True` else `[B, T, H, V]`.
        final_state (torch.Tensor):
            Final state of shape `[N, H, K, V]` if `output_final_state=True` else `None`.

    Examples::
        >>> import torch
        >>> import torch.nn.functional as F
        >>> from einops import rearrange
        >>> from fla.ops.simple_gla import chunk_simple_gla
        # inputs with equal lengths
        >>> B, T, H, K, V = 4, 2048, 4, 512, 512
        >>> q = torch.randn(B, T, H, K, device='cuda')
        >>> k = torch.randn(B, T, H, K, device='cuda')
        >>> v = torch.randn(B, T, H, V, device='cuda')
        >>> g = F.logsigmoid(torch.randn(B, T, H, device='cuda'))
        >>> o, ht = chunk_simple_gla(q, k, v, g,
                                     initial_state=None,
                                     output_final_state=True,
                                     head_first=False)
        # for variable-length inputs, the batch size `B` is expected to be 1 and `offsets` is required
        >>> q, k, v, g = map(lambda x: rearrange(x, 'b t ... -> 1 (b t) ...'), (q, k, v, g))
        # for a batch with 4 sequences, offsets with 5 start/end positions are expected
        >>> offsets = q.new_tensor([0, 2048, 4096, 6144, 8192], dtype=torch.long)
        >>> o_var, ht_var = chunk_simple_gla(q, k, v, g,
                                             initial_state=None,
                                             output_final_state=True,
                                             offsets=offsets,
                                             head_first=False)
        >>> assert o.allclose(o_var.view(o.shape))
        >>> assert ht.allclose(ht_var)
    """
    if offsets is not None:
        if q.shape[0] != 1:
            raise ValueError(f"The batch size is expected to be 1 rather than {q.shape[0]} when using `offsets`."
                             f"Please flatten variable-length inputs before processing.")
        if head_first:
            raise RuntimeError("Sequences with variable lengths are not supported for head-first mode")
        if initial_state is not None and initial_state.shape[0] != len(offsets) - 1:
            raise ValueError(f"The number of initial states is expected to be equal to the number of input sequences, "
                             f"i.e., {len(offsets) - 1} rather than {initial_state.shape[0]}.")
    if scale is None:
        scale = k.shape[-1] ** -0.5
    o, final_state = ChunkSimpleGLAFunction.apply(
        q,
        k,
        v,
        g,
        scale,
        initial_state,
        output_final_state,
        offsets,
        head_first
    )
    return o, final_state