# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
import random
from collections.abc import Iterable
from dataclasses import dataclass
from typing import Any

import pytest
import torch
from tqdm import tqdm

from tests.evals.gsm8k.gsm8k_eval import _build_gsm8k_prompts, evaluate_gsm8k_offline
from tests.utils import (
    get_attn_backend_list_based_on_platform,
    large_gpu_mark,
    multi_gpu_marks,
    multi_gpu_only,
    single_gpu_only,
)
from vllm import LLM, SamplingParams
from vllm.assets.base import VLLM_S3_BUCKET_URL
from vllm.assets.image import VLM_IMAGES_DIR
from vllm.benchmarks.datasets import InstructCoderDataset
from vllm.config import VllmConfig, replace
from vllm.distributed import cleanup_dist_env_and_memory
from vllm.engine.arg_utils import EngineArgs
from vllm.platforms import current_platform
from vllm.v1.metrics.reader import Metric

MTP_SIMILARITY_RATE = 0.8


class AsyncSchedulingNotEnabledError(AssertionError):
    """Raised when async_scheduling is expected to be True for draft_model
    spec decode but is False. Tracked in:
    https://github.com/vllm-project/vllm/issues/38929
    """


def _skip_if_insufficient_gpus_for_tp(tp_size: int):
    """Skip test if available GPUs < tp_size on ROCm."""
    available_gpus = torch.accelerator.device_count()
    if available_gpus < tp_size:
        pytest.skip(
            f"Test requires {tp_size} GPUs, but only {available_gpus} available"
        )


Messages = list[dict[str, Any]]


def get_test_prompts(mm_enabled: bool, num_prompts: int = 100) -> list[Messages]:
    prompt_types = ["repeat", "gsm8k"]
    if mm_enabled:
        prompt_types.append("mm")
    prompts: list[Messages] = []

    num_repeat_prompts = num_prompts // len(prompt_types)
    if mm_enabled:
        num_gsm8k_prompts = num_prompts // len(prompt_types)
        num_mm_prompts = num_prompts - num_repeat_prompts - num_gsm8k_prompts
    else:
        num_mm_prompts = 0
        num_gsm8k_prompts = num_prompts - num_repeat_prompts

    # Generate a mixed batch of prompts, some of which can be easily
    # predicted by n-gram matching and some which likely cannot.
    random.seed(0)
    for _ in range(num_repeat_prompts):
        word_choices = ["test", "temp", "hello", "where"]
        word = random.choice(word_choices)
        prompts.append(
            [
                {
                    "role": "user",
                    "content": f"""
        please repeat the word '{word}' 10 times.
        give no other output than the word at least ten times in a row,
        in lowercase with spaces between each word and without quotes.
        """,
                }
            ]
        )
    prompts.extend(
        [{"role": "user", "content": prompt}]
        for prompt in _build_gsm8k_prompts(
            num_questions=num_gsm8k_prompts, num_shots=5
        )[0]
    )
    for _ in range(num_mm_prompts):
        placeholders = [
            {
                "type": "image_url",
                "image_url": {
                    "url": f"{VLLM_S3_BUCKET_URL}/{VLM_IMAGES_DIR}/stop_sign.jpg"
                },
            }
        ]
        prompt = [
            *placeholders,
            {"type": "text", "text": "The meaning of the image is"},
        ]
        prompts.append([{"role": "user", "content": prompt}])

    return prompts


def get_instruct_coder_messages(n: int) -> list[Messages]:
    dataset = InstructCoderDataset(
        dataset_path="likaixin/InstructCoder", dataset_split="train"
    )
    prompts: Iterable[str] = dataset.sample_prompts(n=n)
    return [[{"role": "user", "content": prompt}] for prompt in prompts]


@pytest.fixture
def sampling_config():
    return greedy_sampling()


def greedy_sampling() -> SamplingParams:
    return SamplingParams(temperature=0, max_tokens=10, ignore_eos=False)


def stochastic_sampling() -> SamplingParams:
    return SamplingParams(temperature=1.0, max_tokens=10, ignore_eos=False)


@pytest.fixture
def model_name():
    return "meta-llama/Llama-3.1-8B-Instruct"


def evaluate_llm_for_gsm8k(llm: LLM, expected_accuracy_threshold: float = 0.70) -> None:
    """Evaluate the LLM on GSM8K and check that accuracy is above a sanity threshold.

    The default threshold assumes the LLM uses the same target model as the "model_name"
    fixture, with max model len == 4096. Precomputed reference value is 75% to 80%
    on GSM8K with greedy decoding, so we check that it's above a sanity threshold of 70%
    to verify that the model is correct.
    """
    if expected_accuracy_threshold <= 0.0:
        print("Skipping GSM8K evaluation")
        return
    results = evaluate_gsm8k_offline(llm)
    accuracy = results["accuracy"]
    print(f"GSM8K accuracy: {accuracy:.3f}")
    assert accuracy >= expected_accuracy_threshold, (
        f"Expected GSM8K accuracy >= {expected_accuracy_threshold}, got {accuracy:.3f}"
    )


@pytest.fixture(autouse=True)
def reset_torch_dynamo():
    """Reset torch dynamo cache before each test"""
    yield
    # Cleanup after test
    torch._dynamo.reset()


@pytest.mark.parametrize(
    "speculative_config",
    [
        {
            "method": "ngram",
            "prompt_lookup_max": 5,
            "prompt_lookup_min": 3,
            "num_speculative_tokens": 3,
        },
        {
            "method": "suffix",
            "suffix_decoding_max_spec_factor": 2.0,
        },
    ],
)
@single_gpu_only
@large_gpu_mark(min_gb=20)
def test_ngram_and_suffix_correctness(
    speculative_config: dict,
    model_name: str,
):
    spec_llm = LLM(
        model=model_name,
        speculative_config=speculative_config,
        max_model_len=4096,
    )
    evaluate_llm_for_gsm8k(spec_llm)
    del spec_llm
    torch.accelerator.empty_cache()
    cleanup_dist_env_and_memory()


@pytest.mark.parametrize("async_scheduling", [True], ids=["async"])
@single_gpu_only
@large_gpu_mark(min_gb=20)
def test_ngram_gpu_default_with_async_scheduling(
    async_scheduling: bool,
):
    """
    Test ngram_gpu speculative decoding (k=3) correctness with and without
    async scheduling, validated via GSM8K accuracy.
    Uses Qwen/Qwen3-8B (ref GSM8K accuracy: 87%-92%).
    """
    qwen3_model = "Qwen/Qwen3-8B"
    spec_llm = LLM(
        model=qwen3_model,
        speculative_config={
            "method": "ngram_gpu",
            "prompt_lookup_max": 3,
            "prompt_lookup_min": 2,
            "num_speculative_tokens": 2,
        },
        max_model_len=4096,
        async_scheduling=async_scheduling,
    )
    # Assert the resolved async_scheduling config matches what was requested.
    assert (
        spec_llm.llm_engine.vllm_config.scheduler_config.async_scheduling
        == async_scheduling
    )
    evaluate_llm_for_gsm8k(spec_llm, expected_accuracy_threshold=0.8)
    del spec_llm
    cleanup_dist_env_and_memory()


@single_gpu_only
@large_gpu_mark(min_gb=20)
def test_suffix_decoding_acceptance(
    monkeypatch: pytest.MonkeyPatch,
    sampling_config: SamplingParams,
    model_name: str,
):
    """
    Check that suffix decoding caching takes effect and improves acceptance
    lengths and acceptance rates over multiple runs of the same prompts.
    """
    test_prompts = get_test_prompts(mm_enabled=False)

    spec_llm = LLM(
        model=model_name,
        speculative_config={
            "method": "suffix",
            "suffix_decoding_max_spec_factor": 2.0,
            "suffix_decoding_max_cached_requests": 1000,
        },
        max_model_len=1024,
        disable_log_stats=False,
    )

    # Run several times and check that the accepted tokens increase.
    num_draft = []
    num_accept = []
    for i in range(10):  # Run multiple times to warm up the cache.
        spec_llm.chat(test_prompts, sampling_config)
        # Collect draft and acceptance stats.
        metrics = spec_llm.get_metrics()
        for metric in metrics:
            if metric.name == "vllm:spec_decode_num_draft_tokens":
                num_draft.append(metric.value)
            if metric.name == "vllm:spec_decode_num_accepted_tokens":
                num_accept.append(metric.value)

    # Calculate the acceptance rates for the first and last runs.
    first_accept_tokens = num_accept[0]
    first_draft_tokens = num_draft[0]
    first_accept_rate = first_accept_tokens / first_draft_tokens

    # Take the diff since the stats are cumulative.
    last_accept_tokens = num_accept[-1] - num_accept[-2]
    last_draft_tokens = num_draft[-1] - num_draft[-2]
    last_accept_rate = last_accept_tokens / last_draft_tokens

    # Expect the acceptance length to improve.
    assert first_accept_tokens < last_accept_tokens

    # Expect the acceptance rate to improve.
    assert first_accept_rate < last_accept_rate

    # Heuristic: expect at least 80.0% acceptance rate at the end.
    assert last_accept_rate > 0.80

    del spec_llm
    torch.accelerator.empty_cache()
    cleanup_dist_env_and_memory()


@pytest.mark.parametrize(
    ["model_path", "expected_accuracy_threshold"],
    [
        ("RedHatAI/Llama-3.1-8B-Instruct-speculator.eagle3", 0.7),  # ref: 75%-80%
        ("RedHatAI/Qwen3-8B-speculator.eagle3", 0.8),  # ref: 87%-92%
    ],
    ids=["llama3_eagle3_speculator", "qwen3_eagle3_speculator"],
)
@single_gpu_only
@large_gpu_mark(min_gb=24)
def test_speculators_model_integration(
    monkeypatch: pytest.MonkeyPatch,
    sampling_config: SamplingParams,
    model_path: str,
    expected_accuracy_threshold: float,
):
    """
    Test that speculators models work with the simplified integration.

    This verifies the `vllm serve <speculator-model>` use case where
    speculative config is automatically detected from the model config
    without requiring explicit --speculative-config argument.

    Tests:
    1. Speculator model is correctly detected
    2. Verifier model is extracted from speculator config
    3. Speculative decoding is automatically enabled
    4. Text generation works correctly
    5. GSM8k accuracy of the model passes a sanity check when speculative decoding on
    6. Output matches reference (non-speculative) generation
    """
    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")

    # Generate test prompts
    test_prompts = get_test_prompts(mm_enabled=False)

    # First run: Direct speculator model (simplified integration)
    spec_llm = LLM(model=model_path, max_model_len=4096)
    evaluate_llm_for_gsm8k(
        spec_llm, expected_accuracy_threshold=expected_accuracy_threshold
    )
    spec_outputs = spec_llm.chat(test_prompts, sampling_config)

    # Verify speculative config was auto-detected
    assert spec_llm.llm_engine.vllm_config.speculative_config is not None, (
        f"Speculative config should be auto-detected for {model_path}"
    )

    spec_config = spec_llm.llm_engine.vllm_config.speculative_config
    assert spec_config.num_speculative_tokens > 0, (
        f"Expected positive speculative tokens, "
        f"got {spec_config.num_speculative_tokens}"
    )

    # Verify draft model is set to the speculator model
    assert spec_config.model == model_path, (
        f"Draft model should be {model_path}, got {spec_config.model}"
    )

    # Extract verifier model for reference run
    verifier_model = spec_llm.llm_engine.vllm_config.model_config.model

    del spec_llm
    torch.accelerator.empty_cache()
    cleanup_dist_env_and_memory()

    # Second run: Reference without speculative decoding
    ref_llm = LLM(model=verifier_model, max_model_len=4096)
    ref_outputs = ref_llm.chat(test_prompts, sampling_config)
    del ref_llm
    torch.accelerator.empty_cache()
    cleanup_dist_env_and_memory()

    # Compare outputs
    matches = sum(
        1
        for ref, spec in zip(ref_outputs, spec_outputs)
        if ref.outputs[0].text == spec.outputs[0].text
    )

    # Heuristic: expect at least 66% of prompts to match exactly
    assert matches >= int(0.66 * len(ref_outputs)), (
        f"Only {matches}/{len(ref_outputs)} outputs matched. "
        f"Expected at least {int(0.66 * len(ref_outputs))} matches."
    )


def _run_eagle_correctness(
    monkeypatch: pytest.MonkeyPatch,
    sampling_config: SamplingParams,
    model_setup: tuple[str, str, str, int],
    mm_enabled: bool,
    expected_accuracy_threshold: float,
    enable_chunked_prefill: bool,
    model_impl: str,
    attn_backend: str,
):
    """
    Compare the outputs of an original LLM and a speculative LLM
    which should be the same when using eagle speculative decoding.
    """
    if attn_backend == "TREE_ATTN":
        pytest.skip(
            "TREE_ATTN is flaky in the test disable for now until it can be "
            "resolved (see https://github.com/vllm-project/vllm/issues/22922)"
        )
    if model_impl == "transformers":
        import transformers
        from packaging.version import Version

        installed = Version(transformers.__version__)
        required = Version("5.0.0")
        if installed < required:
            pytest.skip(
                "Eagle3 with the Transformers modeling backend requires "
                f"transformers>={required}, but got {installed}"
            )

    test_prompts = get_test_prompts(mm_enabled)

    if "Llama-4-Scout" in model_setup[1] and attn_backend == "FLASH_ATTN":
        if current_platform.is_rocm():
            print(
                "FLASH_ATTN for spec_decode not supported on "
                "ROCm currently. Changing to FLEX_ATTENTION backend."
            )
            attention_config = {"backend": "FLEX_ATTENTION"}
        else:
            attention_config = None
    else:
        attention_config = {"backend": attn_backend}

    if attn_backend == "TRITON_ATTN" and not current_platform.is_rocm():
        pytest.skip(
            "TRITON_ATTN does not support "
            "multi-token eagle spec decode on current platform"
        )

    with monkeypatch.context() as m:
        m.setenv("VLLM_MLA_DISABLE", "1")

        if attn_backend == "ROCM_AITER_FA" and current_platform.is_rocm():
            if "deepseek" in model_setup[1].lower():
                m.setenv("VLLM_ROCM_USE_AITER", "1")
                m.delenv("VLLM_MLA_DISABLE", raising=False)
                attention_config = {"backend": "TRITON_MLA"}
            else:
                m.setenv("VLLM_ROCM_USE_AITER", "1")

        method, model_name, spec_model_name, tp_size = model_setup
        _skip_if_insufficient_gpus_for_tp(tp_size)

        max_model_len = 2048
        max_num_batched_tokens = 128 if enable_chunked_prefill else max_model_len

        ref_llm = LLM(
            model=model_name,
            max_model_len=max_model_len,
            tensor_parallel_size=tp_size,
            attention_config=attention_config,
        )
        evaluate_llm_for_gsm8k(
            ref_llm, expected_accuracy_threshold=expected_accuracy_threshold
        )
        ref_outputs = ref_llm.chat(test_prompts, sampling_config)
        del ref_llm
        torch.accelerator.empty_cache()
        cleanup_dist_env_and_memory()

        spec_llm = LLM(
            model=model_name,
            trust_remote_code=True,
            tensor_parallel_size=tp_size,
            speculative_config={
                "method": method,
                "model": spec_model_name,
                "num_speculative_tokens": 3,
                "max_model_len": max_model_len,
            },
            max_model_len=max_model_len,
            max_num_batched_tokens=max_num_batched_tokens,
            enable_chunked_prefill=enable_chunked_prefill,
            model_impl=model_impl,
            attention_config=attention_config,
        )
        # EAGLE/EAGLE3 supports async scheduling; assert it is active by default.
        assert spec_llm.llm_engine.vllm_config.scheduler_config.async_scheduling
        evaluate_llm_for_gsm8k(
            spec_llm, expected_accuracy_threshold=expected_accuracy_threshold
        )
        spec_outputs = spec_llm.chat(test_prompts, sampling_config)
        matches = 0
        misses = 0
        for ref_output, spec_output in zip(ref_outputs, spec_outputs):
            if ref_output.outputs[0].text == spec_output.outputs[0].text:
                matches += 1
            else:
                misses += 1
                print(f"ref_output: {ref_output.outputs[0].text}")
                print(f"spec_output: {spec_output.outputs[0].text}")

        assert matches > int(0.6 * len(ref_outputs))
        del spec_llm
        torch.accelerator.empty_cache()
        cleanup_dist_env_and_memory()


@single_gpu_only
@pytest.mark.parametrize(
    [
        "model_setup",
        "mm_enabled",
        "enable_chunked_prefill",
        "model_impl",
        "expected_accuracy_threshold",
    ],
    [
        (
            (
                "eagle",
                "eagle618/deepseek-v3-random",
                "eagle618/eagle-deepseek-v3-random",
                1,
            ),
            False,
            False,
            "auto",
            0.0,
        ),
    ],
    ids=["deepseek_eagle"],
)
@pytest.mark.parametrize("attn_backend", get_attn_backend_list_based_on_platform())
def test_eagle_correctness_light(
    monkeypatch: pytest.MonkeyPatch,
    sampling_config: SamplingParams,
    model_setup: tuple[str, str, str, int],
    mm_enabled: bool,
    expected_accuracy_threshold: float,
    enable_chunked_prefill: bool,
    model_impl: str,
    attn_backend: str,
):
    _run_eagle_correctness(
        monkeypatch,
        sampling_config,
        model_setup,
        mm_enabled,
        expected_accuracy_threshold,
        enable_chunked_prefill,
        model_impl,
        attn_backend,
    )


@single_gpu_only
@large_gpu_mark(min_gb=24)
@pytest.mark.parametrize(
    [
        "model_setup",
        "mm_enabled",
        "enable_chunked_prefill",
        "model_impl",
        "expected_accuracy_threshold",
    ],
    [
        (
            ("eagle3", "Qwen/Qwen3-8B", "AngelSlim/Qwen3-8B_eagle3", 1),
            False,
            False,
            "auto",
            0.8,
        ),
        pytest.param(
            ("eagle3", "Qwen/Qwen3-8B", "AngelSlim/Qwen3-8B_eagle3", 1),
            False,
            False,
            "transformers",
            0.8,
            # TODO(hmellor): figure out why memory usage is so high
            marks=pytest.mark.skip(
                reason="Feature is experimental and uses too much memory in CI",
            ),
        ),
        pytest.param(
            (
                "eagle3",
                "Qwen/Qwen3-VL-8B-Instruct",
                "taobao-mnn/Qwen3-VL-8B-Instruct-Eagle3",
                1,
            ),
            False,
            False,
            "auto",
            0.8,
            marks=pytest.mark.skip(
                reason="architecture of its eagle3 is LlamaForCausalLMEagle3"
            ),
        ),
        pytest.param(
            (
                "eagle3",
                "Qwen/Qwen2.5-VL-7B-Instruct",
                "Rayzl/qwen2.5-vl-7b-eagle3-sgl",
                1,
            ),
            False,
            False,
            "auto",
            0.7,
            marks=pytest.mark.skip(
                reason="Skipping due to its head_dim not being a multiple of 32"
            ),
        ),
        (
            (
                "eagle3",
                "meta-llama/Llama-3.1-8B-Instruct",
                "yuhuili/EAGLE3-LLaMA3.1-Instruct-8B",
                1,
            ),
            False,
            False,
            "auto",
            0.7,
        ),
    ],
    ids=[
        "qwen3_eagle3",
        "qwen3_eagle3-transformers",
        "qwen3_vl_eagle3",
        "qwen2_5_vl_eagle3",
        "llama3_eagle3",
    ],
)
@pytest.mark.parametrize("attn_backend", get_attn_backend_list_based_on_platform())
def test_eagle_correctness_medium(
    monkeypatch: pytest.MonkeyPatch,
    sampling_config: SamplingParams,
    model_setup: tuple[str, str, str, int],
    mm_enabled: bool,
    expected_accuracy_threshold: float,
    enable_chunked_prefill: bool,
    model_impl: str,
    attn_backend: str,
):
    _run_eagle_correctness(
        monkeypatch,
        sampling_config,
        model_setup,
        mm_enabled,
        expected_accuracy_threshold,
        enable_chunked_prefill,
        model_impl,
        attn_backend,
    )


@pytest.mark.parametrize(
    [
        "model_setup",
        "mm_enabled",
        "enable_chunked_prefill",
        "model_impl",
        "expected_accuracy_threshold",
    ],
    [
        pytest.param(
            (
                "eagle",
                "meta-llama/Llama-3.1-8B-Instruct",
                "yuhuili/EAGLE-LLaMA3.1-Instruct-8B",
                1,
            ),
            False,
            True,
            "auto",
            0.7,
            marks=large_gpu_mark(min_gb=40),
            id="llama3_eagle",
        ),
        pytest.param(
            (
                "eagle",
                "meta-llama/Llama-4-Scout-17B-16E-Instruct",
                "morgendave/EAGLE-Llama-4-Scout-17B-16E-Instruct",
                4,
            ),
            False,
            False,
            "auto",
            0.8,
            marks=[*multi_gpu_marks(num_gpus=4), large_gpu_mark(min_gb=40)],
            id="llama4_eagle",
        ),
        pytest.param(
            (
                "eagle",
                "meta-llama/Llama-4-Scout-17B-16E-Instruct",
                "morgendave/EAGLE-Llama-4-Scout-17B-16E-Instruct",
                4,
            ),
            True,
            True,
            "auto",
            0.8,
            marks=[*multi_gpu_marks(num_gpus=4), large_gpu_mark(min_gb=80)],
            id="llama4_eagle_mm",
        ),
    ],
)
@pytest.mark.parametrize("attn_backend", get_attn_backend_list_based_on_platform())
def test_eagle_correctness_heavy(
    monkeypatch: pytest.MonkeyPatch,
    sampling_config: SamplingParams,
    model_setup: tuple[str, str, str, int],
    mm_enabled: bool,
    expected_accuracy_threshold: float,
    enable_chunked_prefill: bool,
    model_impl: str,
    attn_backend: str,
):
    _run_eagle_correctness(
        monkeypatch,
        sampling_config,
        model_setup,
        mm_enabled,
        expected_accuracy_threshold,
        enable_chunked_prefill,
        model_impl,
        attn_backend,
    )


@pytest.mark.parametrize(
    ["model_setup", "mm_enabled", "expected_accuracy_threshold"],
    [
        (("mtp", "XiaomiMiMo/MiMo-7B-Base", 1), False, 0.5),  # ref: 65%-70%
        (("mtp", "ZixiQi/DeepSeek-V3-4layers-MTP-FP8", 1), False, 0.0),  # dummy model
    ],
    ids=["mimo", "deepseek"],
)
@single_gpu_only
@large_gpu_mark(min_gb=20)
def test_mtp_correctness(
    monkeypatch: pytest.MonkeyPatch,
    sampling_config: SamplingParams,
    model_setup: tuple[str, str, int],
    mm_enabled: bool,
    expected_accuracy_threshold: float,
):
    """
    Compare the outputs of a original LLM and a speculative LLM
    which should be the same when using MTP speculative decoding. Due to some variance
    in the engine, it is possible for some outputs to differ, so we expect that at least
    6/10 output tokens match exactly, and that the GSM8k accuracy is above a precomputed
    reference threshold for each model.
    """
    # Generate test prompts inside the function instead of using fixture
    test_prompts = get_test_prompts(mm_enabled)
    with monkeypatch.context() as m:
        m.setenv("VLLM_MLA_DISABLE", "1")

        method, model_name, tp_size = model_setup
        _skip_if_insufficient_gpus_for_tp(tp_size)

        attn_backend = "TRITON_ATTN" if current_platform.is_rocm() else "auto"
        ref_llm = LLM(
            model=model_name,
            max_model_len=2048,
            tensor_parallel_size=tp_size,
            trust_remote_code=True,
            attention_backend=attn_backend,
        )
        ref_outputs = ref_llm.chat(test_prompts, sampling_config)
        evaluate_llm_for_gsm8k(
            ref_llm, expected_accuracy_threshold=expected_accuracy_threshold
        )
        del ref_llm
        torch.accelerator.empty_cache()
        cleanup_dist_env_and_memory()

        spec_llm = LLM(
            model=model_name,
            trust_remote_code=True,
            tensor_parallel_size=tp_size,
            speculative_config={
                "method": method,
                "num_speculative_tokens": 1,
                "max_model_len": 2048,
            },
            max_model_len=2048,
            attention_backend=attn_backend,
        )
        # MTP supports async scheduling; assert it is active by default.
        assert spec_llm.llm_engine.vllm_config.scheduler_config.async_scheduling
        evaluate_llm_for_gsm8k(
            spec_llm, expected_accuracy_threshold=expected_accuracy_threshold
        )
        spec_outputs = spec_llm.chat(test_prompts, sampling_config)
        matches = 0
        misses = 0
        for ref_output, spec_output in zip(ref_outputs, spec_outputs):
            if ref_output.outputs[0].text == spec_output.outputs[0].text:
                matches += 1
            else:
                misses += 1
                print(f"ref_output: {ref_output.outputs[0].text}")
                print(f"spec_output: {spec_output.outputs[0].text}")

        # Heuristic: expect at least 80% of the prompts to match exactly
        # Upon failure, inspect the outputs to check for inaccuracy.
        assert matches > int(MTP_SIMILARITY_RATE * len(ref_outputs))
        del spec_llm
        torch.accelerator.empty_cache()
        cleanup_dist_env_and_memory()


@dataclass
class ArgsTest:
    target_model: str
    draft_model: str
    sampling_config: SamplingParams
    num_speculative_tokens: int
    expected_acceptance_rate: float
    expected_acceptance_len: float
    expected_gsm8k_accuracy: float = 0.0  # skip by default
    # Defaults
    enforce_eager: bool = True
    parallel_drafting: bool = False
    target_tensor_parallel_size: int = 1
    draft_tensor_parallel_size: int = 1
    max_model_len: int = 2048
    gpu_memory_utilization: float = 0.5
    dataset: str = "test_prompts"
    num_prompts: int = 100


cases = [
    # Same model for draft and target, greedy sampling.
    ArgsTest(
        target_model="Qwen/Qwen3-0.6B",
        draft_model="Qwen/Qwen3-0.6B",
        sampling_config=greedy_sampling(),
        num_speculative_tokens=3,  # K
        expected_acceptance_len=0.98 * (3 + 1),  # epsilon discount of K + 1
        expected_acceptance_rate=0.98,  # slight epsilon
        expected_gsm8k_accuracy=0.25,  # ref: 35-40%
    ),
    # Smaller draft model, stochastic sampling.
    ArgsTest(
        target_model="Qwen/Qwen3-1.7B",
        draft_model="Qwen/Qwen3-0.6B",
        sampling_config=stochastic_sampling(),
        num_speculative_tokens=3,
        expected_acceptance_len=3.4,  # ref: 3.7
        expected_acceptance_rate=0.80,  # ref: 0.90
        expected_gsm8k_accuracy=0.5,  # ref: 60%. Note gsm8k always runs greedy sampling
    ),
]


@pytest.mark.parametrize("args", cases)
@pytest.mark.parametrize("enforce_eager", [True, False])
@single_gpu_only
# TODO: Fix async_scheduling & engine initialization issues - see https://github.com/vllm-project/vllm/issues/38929
@pytest.mark.xfail(
    raises=AsyncSchedulingNotEnabledError,
    reason="draft_model does not yet enable async_scheduling: issue #38929",
)
def test_draft_model_correctness(args: ArgsTest, enforce_eager: bool):
    args.enforce_eager = enforce_eager
    assert_draft_model_correctness(args)


@single_gpu_only
# TODO: Fix async_scheduling and engine initialization issues - see https://github.com/vllm-project/vllm/issues/38929
@pytest.mark.xfail(
    raises=AsyncSchedulingNotEnabledError,
    reason="draft_model does not yet enable async_scheduling: issue #38929",
)
def test_draft_model_realistic_example():
    args = ArgsTest(
        target_model="Qwen/Qwen3-1.7B",
        draft_model="Qwen/Qwen3-0.6B",
        dataset="likaixin/InstructCoder",
        num_speculative_tokens=3,
        sampling_config=greedy_sampling(),
        enforce_eager=False,
        expected_acceptance_len=2.6,  # ref: 2.86
        expected_acceptance_rate=0.5,  # ref: 0.62
    )
    assert_draft_model_correctness(args)


@single_gpu_only
# TODO: Fix async_scheduling and engine initialization issues - see https://github.com/vllm-project/vllm/issues/38929
@pytest.mark.xfail(
    raises=AsyncSchedulingNotEnabledError,
    reason="draft_model does not yet enable async_scheduling: issue #38929",
)
def test_draft_model_parallel_drafting():
    args = ArgsTest(
        target_model="Qwen/Qwen3-1.7B",
        draft_model="amd/PARD-Qwen3-0.6B",
        dataset="likaixin/InstructCoder",
        num_speculative_tokens=3,
        sampling_config=greedy_sampling(),
        parallel_drafting=True,
        enforce_eager=False,
        expected_acceptance_len=2.3,  # ref: 2.52
        expected_acceptance_rate=0.4,  # ref: 0.51
    )
    assert_draft_model_correctness(args)


@pytest.mark.parametrize(
    "models",
    [
        # target_model,         draft_model
        ("Qwen/Qwen3-1.7B-FP8", "Qwen/Qwen3-0.6B"),  # target quantized
        ("Qwen/Qwen3-1.7B", "Qwen/Qwen3-0.6B-FP8"),  # draft quantized
    ],
    ids=["target_quantized", "draft_quantized"],
)
@pytest.mark.parametrize("enforce_eager", [True, False])
@single_gpu_only
# TODO: Fix async_scheduling and engine initialization issues - see https://github.com/vllm-project/vllm/issues/38929
@pytest.mark.xfail(
    raises=AsyncSchedulingNotEnabledError,
    reason="draft_model does not yet enable async_scheduling: issue #38929",
)
def test_draft_model_quantization(models: tuple[str, str], enforce_eager: bool):
    tgt_model, draft_model = models
    sd_case = ArgsTest(
        target_model=tgt_model,
        draft_model=draft_model,
        **some_high_acceptance_metrics(),
        enforce_eager=enforce_eager,
    )
    assert_draft_model_correctness(sd_case)


@multi_gpu_only(num_gpus=2)
# TODO: Fix async_scheduling and engine initialization issues - see https://github.com/vllm-project/vllm/issues/38929
@pytest.mark.xfail(
    raises=AsyncSchedulingNotEnabledError,
    reason="draft_model does not yet enable async_scheduling: issue #38929",
)
def test_draft_model_tensor_parallelism():
    """Ensure spec decode works when running with TP > 1."""
    _skip_if_insufficient_gpus_for_tp(2)
    sd_case = ArgsTest(
        target_model="Qwen/Qwen3-1.7B",
        target_tensor_parallel_size=2,
        draft_model="Qwen/Qwen3-0.6B",
        draft_tensor_parallel_size=2,
        **some_high_acceptance_metrics(),
        enforce_eager=False,
        expected_gsm8k_accuracy=0.5,
    )
    assert_draft_model_correctness(sd_case)


@multi_gpu_only(num_gpus=2)
def test_draft_model_engine_args_tensor_parallelism():
    """Ensure the vllm_config for the draft model is created correctly,
    and independently of the target model (quantization, TP, etc.)"""
    _skip_if_insufficient_gpus_for_tp(2)

    engine_args = EngineArgs(
        model="Qwen/Qwen3-1.7B-FP8",  # <<< tgt quantized
        tensor_parallel_size=2,
        speculative_config={
            "model": "Qwen/Qwen3-0.6B",  # <<< draft not quantized
            "method": "draft_model",
            "num_speculative_tokens": 3,
            "draft_tensor_parallel_size": 1,  # <<< valid arg name
        },
    )
    target_config: VllmConfig = engine_args.create_engine_config()
    assert target_config.parallel_config.tensor_parallel_size == 2
    assert target_config.quant_config.get_name() == "fp8"

    speculative_config = target_config.speculative_config
    draft_config: VllmConfig = replace(
        target_config,
        quant_config=None,
        parallel_config=replace(
            speculative_config.draft_parallel_config,
            rank=target_config.parallel_config.rank,
        ),
        model_config=speculative_config.draft_model_config,
    )
    assert draft_config.parallel_config.tensor_parallel_size == 1
    assert draft_config.quant_config is None


def _apply_draft_moe_backend(vllm_config: VllmConfig) -> VllmConfig:
    """Replicate SpecDecodeBaseProposer._create_draft_vllm_config logic
    so we can test it without instantiating a full proposer."""
    spec_cfg = vllm_config.speculative_config
    if spec_cfg.moe_backend is not None:
        return replace(
            vllm_config,
            kernel_config=replace(
                vllm_config.kernel_config,
                moe_backend=spec_cfg.moe_backend,
            ),
        )
    return vllm_config


def test_draft_model_moe_backend_override():
    """When moe_backend is set in speculative_config, the draft VllmConfig
    should use it while the target keeps its own setting."""
    engine_args = EngineArgs(
        model="Qwen/Qwen3-1.7B",
        tensor_parallel_size=1,
        moe_backend="flashinfer_trtllm",
        speculative_config={
            "model": "Qwen/Qwen3-0.6B",
            "method": "draft_model",
            "num_speculative_tokens": 3,
            "moe_backend": "triton",
        },
    )
    tgt_config: VllmConfig = engine_args.create_engine_config()
    assert tgt_config.kernel_config.moe_backend == "flashinfer_trtllm"
    assert tgt_config.speculative_config.moe_backend == "triton"

    draft_config = _apply_draft_moe_backend(tgt_config)
    assert draft_config.kernel_config.moe_backend == "triton"
    # Target config must be unaffected.
    assert tgt_config.kernel_config.moe_backend == "flashinfer_trtllm"


def test_draft_model_moe_backend_inherits_target():
    """When moe_backend is not set in speculative_config, the draft should
    inherit the target's moe_backend."""
    engine_args = EngineArgs(
        model="Qwen/Qwen3-1.7B",
        tensor_parallel_size=1,
        moe_backend="flashinfer_cutlass",
        speculative_config={
            "model": "Qwen/Qwen3-0.6B",
            "method": "draft_model",
            "num_speculative_tokens": 3,
        },
    )
    tgt_config: VllmConfig = engine_args.create_engine_config()
    assert tgt_config.kernel_config.moe_backend == "flashinfer_cutlass"
    assert tgt_config.speculative_config.moe_backend is None

    draft_config = _apply_draft_moe_backend(tgt_config)
    assert draft_config.kernel_config.moe_backend == "flashinfer_cutlass"
    assert draft_config is tgt_config


def test_draft_model_moe_backend_default_auto():
    """When neither target nor draft set moe_backend explicitly, both should
    default to 'auto'."""
    engine_args = EngineArgs(
        model="Qwen/Qwen3-1.7B",
        tensor_parallel_size=1,
        speculative_config={
            "model": "Qwen/Qwen3-0.6B",
            "method": "draft_model",
            "num_speculative_tokens": 3,
        },
    )
    tgt_config: VllmConfig = engine_args.create_engine_config()
    assert tgt_config.kernel_config.moe_backend == "auto"
    assert tgt_config.speculative_config.moe_backend is None

    draft_config = _apply_draft_moe_backend(tgt_config)
    assert draft_config.kernel_config.moe_backend == "auto"
    assert draft_config is tgt_config


def test_draft_model_engine_args_rejects_invalid_tp_argname():
    """The user should pass "draft_tensor_parallel_size" rather than
    "tensor_parallel_size". We enforce this with validation."""

    engine_args = EngineArgs(
        model="Qwen/Qwen3-1.7B",
        tensor_parallel_size=1,
        speculative_config={
            "model": "Qwen/Qwen3-0.6B",
            "method": "draft_model",
            "num_speculative_tokens": 3,
            "tensor_parallel_size": 1,  # <<< invalid arg name
        },
    )
    with pytest.raises(ValueError):
        engine_args.create_engine_config()


def assert_draft_model_correctness(args: ArgsTest):
    """Compare the outputs using and not using speculative decoding.
    In the greedy decoding case, the outputs must match EXACTLY."""
    test_prompts: list[Messages] = get_messages(
        dataset=args.dataset, n=args.num_prompts
    )

    spec_llm = LLM(
        model=args.target_model,
        speculative_config={
            "model": args.draft_model,
            "method": "draft_model",
            "num_speculative_tokens": args.num_speculative_tokens,
            "max_model_len": args.max_model_len,
            "enforce_eager": args.enforce_eager,
            "draft_tensor_parallel_size": args.draft_tensor_parallel_size,
            "parallel_drafting": args.parallel_drafting,
        },
        max_num_seqs=100,  # limit cudagraph capture runtime
        max_model_len=args.max_model_len,
        gpu_memory_utilization=args.gpu_memory_utilization,
        tensor_parallel_size=args.target_tensor_parallel_size,
        enforce_eager=args.enforce_eager,
        disable_log_stats=False,  # enables get_metrics()
    )

    # we don't check the outputs, only check the metrics
    spec_llm.chat(test_prompts, args.sampling_config)
    metrics = spec_llm.get_metrics()
    acceptance_rate: float = compute_acceptance_rate(metrics)
    acceptance_len: float = compute_acceptance_len(metrics)

    # Need to evaluate after getting metrics to avoid polluting the AR
    evaluate_llm_for_gsm8k(
        spec_llm, expected_accuracy_threshold=args.expected_gsm8k_accuracy
    )

    print(
        f"spec-decode: target={args.target_model}, draft={args.draft_model}, "
        f"temperature={args.sampling_config.temperature:.2f}, "
        f"acceptance_rate={acceptance_rate:.2f}, "
        f"acceptance_len={acceptance_len:.2f}, "
    )

    assert acceptance_rate >= args.expected_acceptance_rate
    assert acceptance_len >= args.expected_acceptance_len
    # draft_model supports async scheduling; assert it is active by default.
    # Raise AsyncSchedulingNotEnabledError (a subclass of AssertionError) so that
    # @pytest.mark.xfail(raises=AsyncSchedulingNotEnabledError) catches only this
    # specific failure — leaving all other assertion failures (e.g. correctness or
    # acceptance-rate checks above) visible as real test failures.
    has_async = spec_llm.llm_engine.vllm_config.scheduler_config.async_scheduling
    del spec_llm  # CLEANUP
    torch.accelerator.empty_cache()
    cleanup_dist_env_and_memory()
    if not has_async:
        raise AsyncSchedulingNotEnabledError(
            "Expected async_scheduling=True for draft_model spec decode, got False."
            " See https://github.com/vllm-project/vllm/issues/38929"
        )


def get_messages(dataset: str, n: int) -> list[Messages]:
    if dataset == "test_prompts":
        return get_test_prompts(mm_enabled=False, num_prompts=n)
    elif dataset == "likaixin/InstructCoder":
        return get_instruct_coder_messages(n=n)
    else:
        raise NotImplementedError(f"Dataset '{dataset}' not implemented")


def some_high_acceptance_metrics() -> dict:
    return {
        "sampling_config": greedy_sampling(),
        "num_speculative_tokens": 3,
        "expected_acceptance_len": 3.4,  # ref: 3.75
        "expected_acceptance_rate": 0.8,  # ref: 0.9
    }


def compute_acceptance_rate(
    metrics: list[Metric], prev_metrics: list[Metric] | None = None
) -> float:
    name2metric = {metric.name: metric for metric in metrics}
    n_draft_toks = name2metric["vllm:spec_decode_num_draft_tokens"].value
    if n_draft_toks == 0:
        return float("nan")
    n_accepted_toks = name2metric["vllm:spec_decode_num_accepted_tokens"].value
    if prev_metrics is not None:
        prev_name2metric = {metric.name: metric for metric in prev_metrics}
        n_draft_toks -= prev_name2metric["vllm:spec_decode_num_draft_tokens"].value
        n_accepted_toks -= prev_name2metric[
            "vllm:spec_decode_num_accepted_tokens"
        ].value
        if n_draft_toks <= 0:
            return float("nan")
    return n_accepted_toks / n_draft_toks


def compute_acceptance_len(
    metrics: list[Metric], prev_metrics: list[Metric] | None = None
) -> float:
    name2metric = {metric.name: metric for metric in metrics}
    n_drafts = name2metric["vllm:spec_decode_num_drafts"].value
    n_accepted_toks = name2metric["vllm:spec_decode_num_accepted_tokens"].value
    if n_drafts == 0:
        return 1
    if prev_metrics is not None:
        prev_name2metric = {metric.name: metric for metric in prev_metrics}
        n_drafts -= prev_name2metric["vllm:spec_decode_num_drafts"].value
        n_accepted_toks -= prev_name2metric[
            "vllm:spec_decode_num_accepted_tokens"
        ].value
        if n_drafts <= 0:
            return 1
    return 1 + (n_accepted_toks / n_drafts)


# Datasets in the format used in DFlash validations
def load_and_process_dataset(data_name: str):
    from datasets import load_dataset

    if data_name == "gsm8k":
        dataset = load_dataset("openai/gsm8k", "main", split="test")
        prompt_fmt = (
            "{question}\nPlease reason step by step,"
            " and put your final answer within \\boxed{{}}."
        )
        dataset = dataset.map(lambda x: {"turns": [prompt_fmt.format(**x)]})
    elif data_name == "mt-bench":
        dataset = load_dataset("HuggingFaceH4/mt_bench_prompts", split="train")
        dataset = dataset.map(lambda x: {"turns": x["prompt"]})
    elif data_name == "humaneval":
        dataset = load_dataset("openai/openai_humaneval", split="test")
        prompt_fmt = (
            "Write a solution to the following problem and make sure"
            " that it passes the tests:\n```python\n{prompt}\n```"
        )
        dataset = dataset.map(lambda x: {"turns": [prompt_fmt.format(**x)]})

    return dataset


@pytest.fixture
def dflash_config():
    target_model = "Qwen/Qwen3-8B"
    draft_model = "z-lab/Qwen3-8B-DFlash-b16"

    return dict(
        model=target_model,
        trust_remote_code=True,
        speculative_config={
            "method": "dflash",
            "model": draft_model,
            "num_speculative_tokens": 16,
            "max_model_len": 32768,
        },
        max_model_len=32768,
        max_num_seqs=128,
        gpu_memory_utilization=0.85,
        enforce_eager=False,
        disable_log_stats=False,
    )


def test_dflash_acceptance_rates(dflash_config):
    """
    E2E test for DFlash (block diffusion) speculative decoding.
    Runs acceptance rate validation on GSM8k, MT-Bench, and HumanEval
    comparing against baseline results from the paper (Table 1).
    See https://github.com/z-lab/dflash/blob/main/benchmark_sglang.py for methodology.
    """
    spec_llm = LLM(**dflash_config)

    max_prompts_per_dataset = 200  # mt-bench has 80, humaneval has 164, truncates gsm8k

    # All scores from Table 1 in https://arxiv.org/pdf/2602.06036
    expected_acceptance_lengths = {
        "mt-bench": 4.24,
        "humaneval": 6.50,
        "gsm8k": 6.54 * 0.95,  # runs with a subset of prompts so extra wide tol here
    }

    tokenizer = spec_llm.get_tokenizer()
    for dataset_name, expected_len in expected_acceptance_lengths.items():
        dataset = load_and_process_dataset(dataset_name)
        prev_metrics = None
        acceptance_lengths = []
        for i in tqdm(
            range(min(max_prompts_per_dataset, len(dataset))),
            desc=f"Processing {dataset_name}",
        ):
            user_content = dataset[i]["turns"][0]
            prompt_text = tokenizer.apply_chat_template(
                [{"role": "user", "content": user_content}],
                tokenize=False,
                add_generation_prompt=True,
                enable_thinking=False,
            )

            # Temp=0, MaxTokens=2048 from the paper
            spec_llm.generate(
                [prompt_text],
                SamplingParams(temperature=0, max_tokens=2048),
                use_tqdm=False,
            )
            current_metrics = spec_llm.get_metrics()
            acceptance_len = compute_acceptance_len(current_metrics, prev_metrics)
            prev_metrics = current_metrics
            acceptance_lengths.append(acceptance_len)

        mean_acceptance_length = sum(acceptance_lengths) / len(acceptance_lengths)
        expected_len = expected_len * 0.9
        print(
            f"DFlash acceptance_len for {dataset_name}: {mean_acceptance_length:.2f}"
            f" (expected at least {expected_len:.2f})"
        )

        assert mean_acceptance_length >= expected_len, (
            f"DFlash acceptance_len for {dataset_name} is below expected threshold:"
            f"{mean_acceptance_length:.2f} < {expected_len:.2f}"
        )

    del spec_llm
    torch.accelerator.empty_cache()
    cleanup_dist_env_and_memory()


def test_dflash_correctness(dflash_config):
    """
    E2E test for DFlash (block diffusion) speculative decoding.
    Ensures output correctness on GSM8k, with cudagraphs and batching on.
    """
    spec_llm = LLM(**dflash_config)

    # Evaluate GSM8k accuracy (Qwen3-8B ref: ~87-92% on GSM8k)
    evaluate_llm_for_gsm8k(spec_llm, expected_accuracy_threshold=0.8)

    current_metrics = spec_llm.get_metrics()
    acceptance_len = compute_acceptance_len(current_metrics)

    # AR is thoroughly validated in test_dflash_acceptance_rates, in a manner consistent
    # with the DFlash paper. However, that test measures AL per-request and thus runs
    # with a batch size of 1. To ensure that AL does not collapse with large batch sizes
    # we enforce a baseline on the AL over the full lm-eval-style GSM8k test.
    expected_len = 3.5  # Measured is 3.9 to 4.0
    print(f"DFlash GSM8k correctness test got AL {acceptance_len}")
    assert acceptance_len >= expected_len, (
        "DFlash correctness check failed with"
        f" {acceptance_len=}, expected at least {expected_len}"
    )

    del spec_llm
    torch.accelerator.empty_cache()
    cleanup_dist_env_and_memory()
