# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

import pytest
import torch

from vllm.utils.math_utils import cdiv
from vllm.v1.attention.ops.triton_decode_attention import decode_attention_fwd


@pytest.mark.parametrize("B", [3, 5])
@pytest.mark.parametrize("L", [1027, 1025])
@pytest.mark.parametrize("H_Q", [32])
@pytest.mark.parametrize("H_KV", [32, 8])
@pytest.mark.parametrize("D_QK", [128, 192, 576])
@pytest.mark.parametrize("D_V", [128, 512])
@pytest.mark.parametrize("CACHE_SIZE", [16384])
@pytest.mark.parametrize("PAGE_SIZE", [1, 16])
def test_decode_attention(B, L, H_Q, H_KV, D_QK, D_V, CACHE_SIZE, PAGE_SIZE):
    assert CACHE_SIZE % PAGE_SIZE == 0
    dtype = torch.bfloat16
    seq_len = L  # This represents the number of tokens already in the sequence
    sm_scale = 1.0 / (D_QK**0.5)
    num_kv_splits = 8

    num_pages_per_batch = cdiv(seq_len, PAGE_SIZE)
    req_to_page = torch.randint(
        0, CACHE_SIZE // PAGE_SIZE, (B, num_pages_per_batch, 1), device="cuda"
    )
    req_to_token = req_to_page * PAGE_SIZE
    req_to_token = req_to_token.expand(B, num_pages_per_batch, PAGE_SIZE)
    req_to_token = req_to_token + torch.arange(PAGE_SIZE, device="cuda").view(1, 1, -1)
    req_to_token = req_to_token.view(B, -1)
    req_to_token = req_to_token[:, :seq_len].contiguous()

    # q represents the new token being generated, one per batch
    q = torch.randn(B, H_Q, D_QK, dtype=dtype, device="cuda")

    # k_buffer and v_buffer represent all previous tokens
    # Page size is 1.
    k_buffer = torch.randn(CACHE_SIZE, H_KV, D_QK, dtype=dtype, device="cuda")
    v_buffer = torch.randn(CACHE_SIZE, H_KV, D_V, dtype=dtype, device="cuda")

    # o will have the same shape as q
    o = torch.zeros(B, H_Q, D_V, dtype=dtype, device="cuda")

    lse = torch.zeros(B, H_Q, dtype=dtype, device="cuda")

    b_seq_len = torch.full((B,), seq_len, device="cuda")

    attn_logits = torch.empty(
        (B, H_Q, num_kv_splits, D_V + 1),
        dtype=torch.float32,
        device="cuda",
    )

    # Call the original implementation.
    decode_attention_fwd(
        q,
        k_buffer,
        v_buffer,
        o,
        lse,
        req_to_token,
        b_seq_len,
        attn_logits,
        num_kv_splits,
        sm_scale,
    )

    # Page size can be larger than 1.
    k_buffer = k_buffer.view(CACHE_SIZE // PAGE_SIZE, PAGE_SIZE, H_KV, D_QK)
    v_buffer = v_buffer.view(CACHE_SIZE // PAGE_SIZE, PAGE_SIZE, H_KV, D_V)

    o1 = torch.zeros_like(o)
    lse1 = torch.zeros_like(lse)

    decode_attention_fwd(
        q,
        k_buffer,
        v_buffer,
        o1,
        lse1,
        req_to_page,
        b_seq_len,
        attn_logits,
        num_kv_splits,
        sm_scale,
        PAGE_SIZE,
    )

    assert torch.allclose(o, o1)


def _quantize_to_fp8(tensor: torch.Tensor):
    """Quantize a BF16 tensor to FP8 e4m3fn with per-tensor scale.

    Returns (fp8_tensor, scale) where:
        fp8_tensor ≈ tensor / scale  (stored as float8_e4m3fn)
        tensor ≈ fp8_tensor.to(float32) * scale  (dequantized)
    """
    amax = tensor.abs().amax()
    # float8_e4m3fn max representable value is 448.0
    scale = (amax / 448.0).clamp(min=1e-12).to(torch.float32)
    fp8_tensor = (
        (tensor.to(torch.float32) / scale).clamp(-448.0, 448.0).to(torch.float8_e4m3fn)
    )
    return fp8_tensor, scale


@pytest.mark.parametrize("B", [3])
@pytest.mark.parametrize("L", [1025])
@pytest.mark.parametrize("H_Q", [32])
@pytest.mark.parametrize("H_KV", [32, 8])
@pytest.mark.parametrize("D_QK", [128, 576])
@pytest.mark.parametrize("D_V", [128, 512])
@pytest.mark.parametrize("CACHE_SIZE", [16384])
@pytest.mark.parametrize("PAGE_SIZE", [1, 16])
def test_decode_attention_fp8(B, L, H_Q, H_KV, D_QK, D_V, CACHE_SIZE, PAGE_SIZE):
    """Test FP8 KV cache path: quantize K/V to FP8, run kernel with scales,
    and compare against BF16 reference output."""
    assert CACHE_SIZE % PAGE_SIZE == 0
    dtype = torch.bfloat16
    seq_len = L
    sm_scale = 1.0 / (D_QK**0.5)
    num_kv_splits = 8

    num_pages_per_batch = cdiv(seq_len, PAGE_SIZE)
    req_to_page = torch.randint(
        0, CACHE_SIZE // PAGE_SIZE, (B, num_pages_per_batch, 1), device="cuda"
    )
    req_to_token = req_to_page * PAGE_SIZE
    req_to_token = req_to_token.expand(B, num_pages_per_batch, PAGE_SIZE)
    req_to_token = req_to_token + torch.arange(PAGE_SIZE, device="cuda").view(1, 1, -1)
    req_to_token = req_to_token.view(B, -1)
    req_to_token = req_to_token[:, :seq_len].contiguous()

    q = torch.randn(B, H_Q, D_QK, dtype=dtype, device="cuda")

    # Create BF16 K/V as reference
    k_bf16 = torch.randn(CACHE_SIZE, H_KV, D_QK, dtype=dtype, device="cuda")
    v_bf16 = torch.randn(CACHE_SIZE, H_KV, D_V, dtype=dtype, device="cuda")

    # --- BF16 reference ---
    o_ref = torch.zeros(B, H_Q, D_V, dtype=dtype, device="cuda")
    lse_ref = torch.zeros(B, H_Q, dtype=dtype, device="cuda")
    attn_logits = torch.empty(
        (B, H_Q, num_kv_splits, D_V + 1), dtype=torch.float32, device="cuda"
    )

    if PAGE_SIZE == 1:
        decode_attention_fwd(
            q,
            k_bf16,
            v_bf16,
            o_ref,
            lse_ref,
            req_to_token,
            b_seq_len=torch.full((B,), seq_len, device="cuda"),
            attn_logits=attn_logits,
            num_kv_splits=num_kv_splits,
            sm_scale=sm_scale,
        )
    else:
        k_paged = k_bf16.view(CACHE_SIZE // PAGE_SIZE, PAGE_SIZE, H_KV, D_QK)
        v_paged = v_bf16.view(CACHE_SIZE // PAGE_SIZE, PAGE_SIZE, H_KV, D_V)
        decode_attention_fwd(
            q,
            k_paged,
            v_paged,
            o_ref,
            lse_ref,
            req_to_page,
            b_seq_len=torch.full((B,), seq_len, device="cuda"),
            attn_logits=attn_logits,
            num_kv_splits=num_kv_splits,
            sm_scale=sm_scale,
            page_size=PAGE_SIZE,
        )

    # --- FP8 path ---
    k_fp8, k_scale = _quantize_to_fp8(k_bf16)
    v_fp8, v_scale = _quantize_to_fp8(v_bf16)

    o_fp8 = torch.zeros(B, H_Q, D_V, dtype=dtype, device="cuda")
    lse_fp8 = torch.zeros(B, H_Q, dtype=dtype, device="cuda")
    attn_logits_fp8 = torch.empty(
        (B, H_Q, num_kv_splits, D_V + 1), dtype=torch.float32, device="cuda"
    )

    if PAGE_SIZE == 1:
        decode_attention_fwd(
            q,
            k_fp8,
            v_fp8,
            o_fp8,
            lse_fp8,
            req_to_token,
            b_seq_len=torch.full((B,), seq_len, device="cuda"),
            attn_logits=attn_logits_fp8,
            num_kv_splits=num_kv_splits,
            sm_scale=sm_scale,
            k_scale=k_scale,
            v_scale=v_scale,
        )
    else:
        k_fp8_paged = k_fp8.view(CACHE_SIZE // PAGE_SIZE, PAGE_SIZE, H_KV, D_QK)
        v_fp8_paged = v_fp8.view(CACHE_SIZE // PAGE_SIZE, PAGE_SIZE, H_KV, D_V)
        decode_attention_fwd(
            q,
            k_fp8_paged,
            v_fp8_paged,
            o_fp8,
            lse_fp8,
            req_to_page,
            b_seq_len=torch.full((B,), seq_len, device="cuda"),
            attn_logits=attn_logits_fp8,
            num_kv_splits=num_kv_splits,
            sm_scale=sm_scale,
            page_size=PAGE_SIZE,
            k_scale=k_scale,
            v_scale=v_scale,
        )

    # FP8 tolerances match test_mla_backends.py test_backend_correctness.
    torch.testing.assert_close(o_ref, o_fp8, atol=5e-1, rtol=1e-2)
