import asyncio
import pytest

from llmux.vram_manager import VRAMManager, ModelSlot


class FakeBackend:
    """Simulates a backend that tracks load/unload calls."""

    def __init__(self):
        self.loaded = {}
        self.load_count = 0
        self.unload_count = 0

    async def load(self, model_id: str):
        self.loaded[model_id] = True
        self.load_count += 1

    async def unload(self, model_id: str):
        self.loaded.pop(model_id, None)
        self.unload_count += 1


@pytest.fixture
def manager():
    return VRAMManager(total_vram_gb=16.0)


def test_priority_ordering():
    assert ModelSlot.priority_rank("llm") == 0
    assert ModelSlot.priority_rank("tts") == 1
    assert ModelSlot.priority_rank("asr") == 2


@pytest.mark.asyncio
async def test_load_into_empty_vram(manager):
    backend = FakeBackend()
    await manager.load_model("qwen3.5-4b", model_type="llm", vram_gb=4.0, backend=backend)
    assert manager.is_loaded("qwen3.5-4b")
    assert manager.available_vram_gb == pytest.approx(12.0)


@pytest.mark.asyncio
async def test_load_alongside_when_fits(manager):
    backend = FakeBackend()
    await manager.load_model("cohere-transcribe", model_type="asr", vram_gb=4.0, backend=backend)
    await manager.load_model("qwen3.5-4b", model_type="llm", vram_gb=4.0, backend=backend)
    assert manager.is_loaded("cohere-transcribe")
    assert manager.is_loaded("qwen3.5-4b")
    assert manager.available_vram_gb == pytest.approx(8.0)


@pytest.mark.asyncio
async def test_evict_llm_first(manager):
    backend = FakeBackend()
    await manager.load_model("cohere-transcribe", model_type="asr", vram_gb=4.0, backend=backend)
    await manager.load_model("chatterbox-multilingual", model_type="tts", vram_gb=2.0, backend=backend)
    await manager.load_model("qwen3.5-4b", model_type="llm", vram_gb=4.0, backend=backend)
    # 10 GB used. Loading 9B (9GB). Evict LLM (4B), free=12. ASR+TTS+9B=15, fits.
    await manager.load_model("qwen3.5-9b-fp8", model_type="llm", vram_gb=9.0, backend=backend)
    assert not manager.is_loaded("qwen3.5-4b")
    assert manager.is_loaded("cohere-transcribe")
    assert manager.is_loaded("chatterbox-multilingual")
    assert manager.is_loaded("qwen3.5-9b-fp8")


@pytest.mark.asyncio
async def test_evict_cascade_for_large_llm(manager):
    backend = FakeBackend()
    await manager.load_model("cohere-transcribe", model_type="asr", vram_gb=4.0, backend=backend)
    await manager.load_model("chatterbox-multilingual", model_type="tts", vram_gb=2.0, backend=backend)
    await manager.load_model("qwen3.5-4b", model_type="llm", vram_gb=4.0, backend=backend)
    # 10 GB used. gpt-oss-20b needs 12GB. Evict LLM(4)->free=10. Evict TTS(2)->free=12. Load.
    await manager.load_model("gpt-oss-20b", model_type="llm", vram_gb=12.0, backend=backend)
    assert not manager.is_loaded("qwen3.5-4b")
    assert not manager.is_loaded("chatterbox-multilingual")
    assert manager.is_loaded("cohere-transcribe")  # ASR survives if possible
    assert manager.is_loaded("gpt-oss-20b")


@pytest.mark.asyncio
async def test_asr_evicts_llm_not_reversed(manager):
    """When ASR request arrives and LLM is loaded, evict LLM (lower priority)."""
    backend = FakeBackend()
    await manager.load_model("gpt-oss-20b", model_type="llm", vram_gb=13.0, backend=backend)
    # 13GB used, 3GB free. ASR needs 4GB. Must evict LLM.
    await manager.load_model("cohere-transcribe", model_type="asr", vram_gb=4.0, backend=backend)
    assert not manager.is_loaded("gpt-oss-20b")
    assert manager.is_loaded("cohere-transcribe")


@pytest.mark.asyncio
async def test_already_loaded_is_noop(manager):
    backend = FakeBackend()
    await manager.load_model("qwen3.5-4b", model_type="llm", vram_gb=4.0, backend=backend)
    await manager.load_model("qwen3.5-4b", model_type="llm", vram_gb=4.0, backend=backend)
    assert backend.load_count == 1


@pytest.mark.asyncio
async def test_spec_scenario_switch_to_9b(manager):
    backend = FakeBackend()
    await manager.load_model("cohere-transcribe", model_type="asr", vram_gb=4.0, backend=backend)
    await manager.load_model("chatterbox-multilingual", model_type="tts", vram_gb=2.0, backend=backend)
    await manager.load_model("qwen3.5-4b", model_type="llm", vram_gb=4.0, backend=backend)
    await manager.load_model("qwen3.5-9b-fp8", model_type="llm", vram_gb=9.0, backend=backend)
    assert manager.is_loaded("cohere-transcribe")
    assert manager.is_loaded("chatterbox-multilingual")
    assert manager.is_loaded("qwen3.5-9b-fp8")
    assert not manager.is_loaded("qwen3.5-4b")
    assert manager.available_vram_gb == pytest.approx(1.0)


@pytest.mark.asyncio
async def test_get_loaded_models(manager):
    backend = FakeBackend()
    await manager.load_model("cohere-transcribe", model_type="asr", vram_gb=4.0, backend=backend)
    await manager.load_model("qwen3.5-4b", model_type="llm", vram_gb=4.0, backend=backend)
    loaded = manager.get_loaded_models()
    assert set(loaded.keys()) == {"cohere-transcribe", "qwen3.5-4b"}