"""The real engine: SemIf's torch scorers over one resident model. Needs the `model` extra.

Contract: semif-serve.contract.md, INV-3 (fail-closed startup), INV-4 (VRAM cap + OOM),
INV-5 (offline weights). load() is checked on the card at acceptance; the OOM path is
unit-tested against a fake torch (tests/test_engine.py).
"""
from __future__ import annotations

import gc
import logging
import traceback
from typing import Any, Callable

from .config import Settings
from .errors import OutOfMemory, ScoringFailed

log = logging.getLogger("semif_serve.engine")

RELEASE_SLACK_BYTES = 512 * 2**20
WARMUP_ROW = {
    "id": "semif-serve-warmup",
    "state": "The deployment completed at 14:02 UTC. Health checks passed in all three zones.",
    "question": "Is there evidence that the deployment succeeded?",
    "options": [
        {"id": "yes", "description": "The deployment succeeded."},
        {"id": "no", "description": "The deployment did not succeed."},
    ],
}


def _first_line(exc: BaseException) -> str:
    lines = str(exc).splitlines()
    return lines[0] if lines else ""


class TorchEngine:
    def __init__(self, torch: Any, model: Any, tokenizer: Any, metadata: dict, settings: Settings,
                 direct_fn: Callable, shared_fn: Callable, release_above_bytes: int | None = None):
        self._torch, self._model, self._tokenizer = torch, model, tokenizer
        self._metadata, self._settings = metadata, settings
        self._direct, self._shared = direct_fn, shared_fn
        self._release_above = release_above_bytes

    @classmethod
    def load(cls, settings: Settings) -> "TorchEngine":
        import torch
        from semif_phase1.core import load_causal_model
        from semif_phase1.direct import score
        from semif_phase1.shared import score_shared

        if settings.device == "cuda":
            if not torch.cuda.is_available():
                raise RuntimeError("SEMIF_DEVICE=cuda but torch sees no CUDA device")
            major, minor = torch.cuda.get_device_capability(0)
            arch = f"sm_{major}{minor}"
            if arch not in torch.cuda.get_arch_list():            # INV-3: no silent PTX/CPU fallback
                raise RuntimeError(f"torch {torch.__version__} has no kernels for {arch}: {torch.cuda.get_arch_list()}")
            if settings.vram_cap_gib is not None:                  # INV-4: cap BEFORE the weights land
                total = torch.cuda.get_device_properties(0).total_memory
                fraction = settings.vram_cap_gib * 2**30 / total
                if not 0 < fraction <= 1:
                    raise ValueError(f"SEMIF_VRAM_CAP_GIB={settings.vram_cap_gib} does not fit a {total / 2**30:.1f} GiB card")
                torch.cuda.set_per_process_memory_fraction(fraction, 0)
        elif settings.device != "cpu":
            raise ValueError(f"SEMIF_DEVICE must be cuda or cpu, not {settings.device!r}")

        model, tokenizer, metadata = load_causal_model(settings.model, settings.revision, settings.device, "bfloat16")
        placed = next(model.parameters()).device.type
        if placed != settings.device:                              # INV-3
            raise RuntimeError(f"model landed on {placed}, expected {settings.device}")
        engine = cls(torch, model, tokenizer, metadata, settings, direct_fn=score, shared_fn=score_shared)
        engine.direct(WARMUP_ROW)                                  # INV-3: one decision must score
        if settings.device == "cuda":                              # INV-4: the resting footprint
            engine._release_above = torch.cuda.memory_reserved(0) + RELEASE_SLACK_BYTES
        return engine

    def health(self) -> dict:
        info = dict(self._metadata)
        if self._settings.device == "cuda":
            info["device_name"] = self._torch.cuda.get_device_name(0)
            info["allocated_gib"] = round(self._torch.cuda.memory_allocated(0) / 2**30, 2)
            info["reserved_gib"] = round(self._torch.cuda.memory_reserved(0) / 2**30, 2)
        return info

    def _release_burst(self) -> None:
        """INV-4: hand a burst back to the driver so the card's shared headroom (scriberr, the
        vLLM seats) returns after a big request, instead of sitting in torch's cache."""
        if self._release_above is not None and self._torch.cuda.memory_reserved(0) > self._release_above:
            self._torch.cuda.empty_cache()

    def _guard(self, fn, *args):
        try:
            result = fn(*args)
        except ValueError:
            raise                            # validation: SemIf raises it before any GPU work
        except self._torch.cuda.OutOfMemoryError as exc:
            failure, message = OutOfMemory, _first_line(exc) or "CUDA out of memory"
        except Exception as exc:  # noqa: BLE001 — every other failure is released and reported below
            message = _first_line(exc)
            if "out of memory" in message.lower():      # cuBLAS/cuDNN allocation failures
                failure = OutOfMemory
            else:
                failure, message = ScoringFailed, f"{type(exc).__name__}: {message}"
                # Formatted text, not exc_info: a log record that keeps the traceback object alive
                # (pytest's capture handler does; so would any buffering handler) pins the tensors.
                log.error("scorer failed:\n%s", traceback.format_exc())
        else:
            self._release_burst()
            return result
        # INV-4, outside the except block on purpose: the exception's traceback holds the failed
        # scorer's frames, and with them its tensors (the replicated prefix cache). Raising inside
        # the block, or `from exc`, would chain to it and keep GiBs allocated after the response.
        gc.collect()
        self._torch.cuda.empty_cache()
        raise failure(message)

    def direct(self, row: dict) -> dict:
        return self._guard(self._direct, self._model, self._tokenizer, row, self._metadata, self._settings.max_tokens)

    def shared(self, rows: list[dict]) -> tuple[list[dict], dict]:
        return self._guard(self._shared, self._model, self._tokenizer, rows, self._metadata, self._settings.max_tokens)