# Copyright (c) 2026 LightSeek Foundation
#
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# furnished to do so, subject to the following conditions:
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# The above copyright notice and this permission notice shall be included in
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# SOFTWARE.

from __future__ import annotations

from typing import TYPE_CHECKING

from tokenspeed_kernel.platform import current_platform

from tokenspeed.runtime.sampling.backends.base import (
    DEFAULT_RANDOM_SEED,
    SamplingBackend,
    SamplingBackendConfig,
)

if TYPE_CHECKING:
    from tokenspeed.runtime.utils.server_args import ServerArgs


_BACKEND_REGISTRY: dict[str, type[SamplingBackend]] = {}


def _get_default_backend_name() -> str:
    if current_platform().is_nvidia:
        return "flashinfer"
    return "greedy"


def _resolve_backend_name(server_args: ServerArgs) -> str:
    return server_args.sampling_backend or _get_default_backend_name()


def register_backend(name: str, cls: type[SamplingBackend]) -> None:
    _BACKEND_REGISTRY[name] = cls


def create_sampling_backend(
    server_args: ServerArgs,
    *,
    max_bs: int,
    max_draft_tokens_per_req: int,
    device: str,
    random_seed: int = DEFAULT_RANDOM_SEED,
    max_req_pool_size: int = 0,
    vocab_size: int = 0,
    tp_group: tuple[int, ...] | None = None,
) -> SamplingBackend:
    # Trigger concrete-backend registration on first use.
    from tokenspeed.runtime.sampling.backends import flashinfer as _fi  # noqa: F401
    from tokenspeed.runtime.sampling.backends import (  # noqa: F401
        flashinfer_full as _ff,
    )
    from tokenspeed.runtime.sampling.backends import greedy as _g  # noqa: F401
    from tokenspeed.runtime.sampling.backends import triton as _t  # noqa: F401
    from tokenspeed.runtime.sampling.backends import triton_full as _tf  # noqa: F401

    name = _resolve_backend_name(server_args)
    if name not in _BACKEND_REGISTRY:
        raise ValueError(
            f"Unknown sampling backend: {name!r}. "
            f"Available: {list(_BACKEND_REGISTRY)}"
        )
    cls = _BACKEND_REGISTRY[name]

    return cls(
        SamplingBackendConfig.from_server_args(
            server_args,
            max_bs=max_bs,
            max_draft_tokens_per_req=max_draft_tokens_per_req,
            device=device,
            random_seed=random_seed,
            max_req_pool_size=max_req_pool_size,
            vocab_size=vocab_size,
            tp_group=tp_group,
        )
    )