"""Pure runtime configuration and ZeroGPU-safe PEFT loading helpers."""

from __future__ import annotations

import re
import warnings
from collections.abc import Mapping
from collections.abc import Callable
from dataclasses import dataclass
from typing import Any


DEFAULT_ADAPTER_REVISION = "3702c6cbc8d0bef2327e4c16d72d061247c2bbf2"
DEFAULT_BASE_MODEL_ID = "Qwen/Qwen3-0.6B"
DEFAULT_BASE_REVISION = "c1899de289a04d12100db370d81485cdf75e47ca"
DEFAULT_GPU_SIZE = "large"
DEFAULT_GPU_DURATION_SECONDS = 60
DEFAULT_MAX_INPUT_TOKENS = 512
DEFAULT_MAX_NEW_TOKENS = 256

_COMMIT_SHA_RE = re.compile(r"[0-9a-f]{40}")


@dataclass(frozen=True)
class AppSettings:
    """Validated settings needed by the model runtime."""

    model_id: str
    model_revision: str
    base_model_id: str
    base_model_revision: str
    gpu_size: str
    gpu_duration_seconds: int
    max_input_tokens: int
    max_new_tokens: int


def _text(
    environ: Mapping[str, str],
    name: str,
    default: str = "",
) -> str:
    return (environ.get(name) or default).strip()


def _bounded_int(
    environ: Mapping[str, str],
    name: str,
    default: int,
    minimum: int,
    maximum: int,
) -> int:
    raw_value = _text(environ, name, str(default))
    try:
        value = int(raw_value)
    except ValueError as exc:
        raise RuntimeError(f"{name} must be an integer.") from exc
    if not minimum <= value <= maximum:
        raise RuntimeError(f"{name} must be between {minimum} and {maximum}.")
    return value


def load_app_settings(environ: Mapping[str, str]) -> AppSettings:
    """Resolve required values and apply safe defaults to every optional value."""

    if not _text(environ, "HF_TOKEN"):
        raise RuntimeError(
            "HF_TOKEN is not set. Add it to .env or Space Settings > Secrets."
        )

    model_id = _text(environ, "MODEL_ID")
    legacy_model_id = _text(environ, "MEDEL_ID")
    if not model_id and legacy_model_id:
        model_id = legacy_model_id
        warnings.warn(
            "MEDEL_ID is a supported compatibility alias; rename it to MODEL_ID.",
            RuntimeWarning,
            stacklevel=2,
        )
    if not model_id:
        raise RuntimeError(
            "MODEL_ID is not set. Add it to .env or Space Settings > Variables."
        )

    model_revision = _text(
        environ,
        "MODEL_REVISION",
        DEFAULT_ADAPTER_REVISION,
    )
    base_model_id = _text(environ, "BASE_MODEL_ID", DEFAULT_BASE_MODEL_ID)
    base_model_revision = _text(
        environ,
        "BASE_MODEL_REVISION",
        DEFAULT_BASE_REVISION,
    )
    for name, revision in (
        ("MODEL_REVISION", model_revision),
        ("BASE_MODEL_REVISION", base_model_revision),
    ):
        if _COMMIT_SHA_RE.fullmatch(revision) is None:
            raise RuntimeError(f"{name} must be a pinned 40-character commit SHA.")

    gpu_size = _text(environ, "GPU_SIZE", DEFAULT_GPU_SIZE)
    if gpu_size not in {"large", "xlarge"}:
        raise RuntimeError("GPU_SIZE must be either 'large' or 'xlarge'.")

    return AppSettings(
        model_id=model_id,
        model_revision=model_revision,
        base_model_id=base_model_id,
        base_model_revision=base_model_revision,
        gpu_size=gpu_size,
        gpu_duration_seconds=_bounded_int(
            environ,
            "GPU_DURATION_SECONDS",
            DEFAULT_GPU_DURATION_SECONDS,
            1,
            300,
        ),
        max_input_tokens=_bounded_int(
            environ,
            "MAX_INPUT_TOKENS",
            DEFAULT_MAX_INPUT_TOKENS,
            128,
            1024,
        ),
        max_new_tokens=_bounded_int(
            environ,
            "MAX_NEW_TOKENS",
            DEFAULT_MAX_NEW_TOKENS,
            32,
            256,
        ),
    )


def load_peft_adapter_on_cpu(
    peft_model_type: Any,
    base_model: Any,
    *,
    model_id: str,
    model_revision: str,
) -> Any:
    """Deserialize adapter tensors on CPU before ZeroGPU's root CUDA transfer.

    ZeroGPU exposes CUDA emulation during module initialization. Without an
    explicit device, PEFT infers CUDA and asks safetensors to allocate on a real
    GPU before a GPU lease exists. Loading on CPU avoids that native CUDA path;
    the caller must then move the complete model to the selected runtime device.
    """

    return peft_model_type.from_pretrained(
        base_model,
        model_id,
        revision=model_revision,
        is_trainable=False,
        torch_device="cpu",
    )


def require_zero_gpu_execution(
    environ: Mapping[str, str],
    *,
    server_pid: int,
    current_pid: int,
    cuda_available: bool,
    model_device_type: str,
    cuda_probe: Callable[[], None],
) -> bool:
    """Fail closed unless a hosted request is executing on a ZeroGPU worker.

    The ``spaces.GPU`` runtime invokes the decorated task in a forked worker
    after acquiring a real GPU. CUDA is emulated in the long-lived server
    process, so ``torch.cuda.is_available()`` alone is not sufficient proof.
    A distinct PID plus a successful CUDA operation verifies the execution
    boundary without preventing local CPU/MPS development.
    """

    is_space = bool((environ.get("SPACE_ID") or "").strip())
    is_zero_gpu = (environ.get("SPACES_ZERO_GPU") or "").lower() in {
        "1",
        "t",
        "true",
    }
    if not is_zero_gpu:
        if is_space:
            raise RuntimeError("This Space must run on ZeroGPU hardware.")
        return False
    if current_pid == server_pid:
        raise RuntimeError("Request did not enter a ZeroGPU GPU worker.")
    if not cuda_available or model_device_type != "cuda":
        raise RuntimeError("ZeroGPU worker does not expose the model on CUDA.")

    cuda_probe()
    return True