"""Tests TDD pour la résolution de device paramétrable (auto/cuda/cpu).

Objectif : basculer OCR/YOLO sur GPU local quand la VRAM est libre, SANS
hardcoder cuda, avec garde-fou VRAM et fallback CPU propre.

Tous les tests mockent `torch.cuda.is_available` et `torch.cuda.mem_get_info`
pour ne PAS dépendre du GPU réel de la machine de CI/dev.
"""

from __future__ import annotations

import importlib
from unittest import mock

import pytest

from core.gpu import device_policy


GB = 1024 ** 3


def _mock_cuda(available: bool, free_gb: float = 0.0, total_gb: float = 12.0):
    """Construit un contexte de mock torch.cuda cohérent.

    free_gb / total_gb sont exprimés en Go ; mem_get_info renvoie des octets.
    """
    free_bytes = int(free_gb * GB)
    total_bytes = int(total_gb * GB)
    return mock.patch.multiple(
        device_policy.torch.cuda,
        is_available=mock.Mock(return_value=available),
        mem_get_info=mock.Mock(return_value=(free_bytes, total_bytes)),
    )


# ── requested="cpu" ─────────────────────────────────────────────────────────

def test_resolve_cpu_explicit_returns_cpu(monkeypatch):
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=12.0):
        assert device_policy.resolve_device("cpu") == "cpu"


# ── requested="cuda" ────────────────────────────────────────────────────────

def test_resolve_cuda_falls_back_to_cpu_when_unavailable(monkeypatch):
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=False):
        assert device_policy.resolve_device("cuda") == "cpu"


def test_resolve_cuda_returns_cuda_when_available(monkeypatch):
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=8.0):
        assert device_policy.resolve_device("cuda") == "cuda"


# ── requested="auto" (défaut) ───────────────────────────────────────────────

def test_resolve_auto_cuda_when_vram_sufficient(monkeypatch):
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=8.0):
        assert device_policy.resolve_device("auto", min_free_gb=2.0) == "cuda"


def test_resolve_auto_cpu_when_vram_insufficient(monkeypatch):
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=1.0):
        assert device_policy.resolve_device("auto", min_free_gb=2.0) == "cpu"


def test_resolve_auto_cpu_when_cuda_unavailable(monkeypatch):
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=False):
        assert device_policy.resolve_device("auto") == "cpu"


def test_resolve_default_is_auto(monkeypatch):
    """Sans argument, le défaut est 'auto'."""
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=8.0):
        assert device_policy.resolve_device() == "cuda"


# ── garde-fou : usage total ne doit pas dépasser le plafond ─────────────────

def test_resolve_auto_cpu_when_switch_would_exceed_total_cap(monkeypatch):
    """Si basculer cuda ferait dépasser le plafond d'usage total (6 Go par
    défaut), on reste CPU même si la VRAM libre dépasse min_free_gb.

    total=12, free=4 → used=8 > cap 6 → CPU.
    """
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=4.0, total_gb=12.0):
        assert device_policy.resolve_device("auto", min_free_gb=2.0,
                                             max_total_gb=6.0) == "cpu"


def test_resolve_auto_cuda_when_under_total_cap(monkeypatch):
    """total=12, free=11 → used=1 < cap 6 et free 11 ≥ min 2 → CUDA."""
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=11.0, total_gb=12.0):
        assert device_policy.resolve_device("auto", min_free_gb=2.0,
                                             max_total_gb=6.0) == "cuda"


# ── mémoire unifiée / grosse carte (DGX GB10) : plafond inapplicable ─────────

def test_resolve_auto_cuda_on_unified_memory_ignores_total_cap(monkeypatch):
    """Mémoire unifiée GB10 : total=121, free=22 → used=99 > cap 6, MAIS total
    > seuil grosse mémoire (24) → plafond ignoré, free 22 ≥ min 2 → CUDA.
    Sans ce comportement, le DGX tomberait à tort sur CPU (régression observée
    au bench GB10 2026-06-08)."""
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=22.0, total_gb=121.0):
        assert device_policy.resolve_device("auto", min_free_gb=2.0,
                                             max_total_gb=6.0) == "cuda"


def test_resolve_auto_cpu_on_large_memory_when_free_too_low(monkeypatch):
    """Grosse mémoire mais free < min → CPU (free reste le garde-fou réel)."""
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with _mock_cuda(available=True, free_gb=1.0, total_gb=121.0):
        assert device_policy.resolve_device("auto", min_free_gb=2.0) == "cpu"


# ── override env RPA_VISION_DEVICE ──────────────────────────────────────────

def test_env_override_cpu_forces_cpu_even_in_auto(monkeypatch):
    monkeypatch.setenv("RPA_VISION_DEVICE", "cpu")
    with _mock_cuda(available=True, free_gb=12.0):
        assert device_policy.resolve_device("auto") == "cpu"
        assert device_policy.resolve_device("cuda") == "cpu"


def test_env_override_cuda_takes_precedence_over_requested_cpu(monkeypatch):
    """L'override env prime sur l'argument requested."""
    monkeypatch.setenv("RPA_VISION_DEVICE", "cuda")
    with _mock_cuda(available=True, free_gb=8.0):
        assert device_policy.resolve_device("cpu") == "cuda"


def test_env_override_cuda_still_falls_back_when_unavailable(monkeypatch):
    monkeypatch.setenv("RPA_VISION_DEVICE", "cuda")
    with _mock_cuda(available=False):
        assert device_policy.resolve_device("auto") == "cpu"


def test_env_override_invalid_value_ignored(monkeypatch):
    """Une valeur env invalide est ignorée (on retombe sur requested)."""
    monkeypatch.setenv("RPA_VISION_DEVICE", "banana")
    with _mock_cuda(available=False):
        assert device_policy.resolve_device("auto") == "cpu"


# ── robustesse : pas de crash si torch.cuda lève ───────────────────────────

def test_resolve_auto_cpu_on_torch_exception(monkeypatch):
    monkeypatch.delenv("RPA_VISION_DEVICE", raising=False)
    with mock.patch.object(
        device_policy.torch.cuda, "is_available",
        side_effect=RuntimeError("driver boom"),
    ):
        assert device_policy.resolve_device("auto") == "cpu"


# ── import-safe : pas d'effet de bord à l'import ───────────────────────────

def test_module_import_is_safe():
    """Réimporter le module ne doit déclencher aucun chargement modèle/GPU."""
    importlib.reload(device_policy)
    assert hasattr(device_policy, "resolve_device")