"""
Unit tests for the GPU fallback handler module.

Tests cover automatic fallback to batch_size=1 on GPU errors.
"""

import sys
from unittest.mock import Mock, MagicMock, patch

# Mock torch and transformers before importing
sys_mock = Mock()
sys.modules["torch"] = sys_mock
sys.modules["transformers"] = sys_mock

import pytest

from src.translator.fallback_handler import (
    FallbackHandler,
    FallbackEvent,
    FallbackReason,
)


class MockEngine:
    """Mock translation engine for testing."""

    def __init__(self, fail_on_batch: bool = False, error_msg: str = ""):
        self.fail_on_batch = fail_on_batch
        self.error_msg = error_msg
        self._is_gpu_enabled = True
        self._call_count = 0

    def translate(self, text: str, src_lang: str = "zh", tgt_lang: str = "en", max_length: int = None) -> str:
        return f"Translated: {text}"

    def translate_batch(
        self,
        texts: list,
        src_lang: str = "zh",
        tgt_lang: str = "en",
        batch_size: int = 4,
        max_length: int = None
    ) -> list:
        self._call_count += 1
        # Only fail on first call (with larger batch size), succeed with batch_size=1
        if self.fail_on_batch and batch_size > 1:
            raise RuntimeError(self.error_msg or "CUDA out of memory")
        return [f"Translated: {t}" for t in texts]

    # Use a property with setter for flexibility
    @property
    def is_gpu_enabled(self):
        return self._is_gpu_enabled

    @is_gpu_enabled.setter
    def is_gpu_enabled(self, value):
        self._is_gpu_enabled = value


class TestFallbackEvent:
    """Test cases for FallbackEvent dataclass."""

    def test_create_fallback_event(self):
        """Test creating a fallback event."""
        event = FallbackEvent(
            original_batch_size=4,
            reason=FallbackReason.OUT_OF_MEMORY,
            error_message="CUDA out of memory",
        )

        assert event.original_batch_size == 4
        assert event.reason == FallbackReason.OUT_OF_MEMORY
        assert event.error_message == "CUDA out of memory"

    def test_to_dict(self):
        """Test converting fallback event to dictionary."""
        event = FallbackEvent(
            original_batch_size=4,
            reason=FallbackReason.OUT_OF_MEMORY,
            error_message="CUDA error",
        )

        data = event.to_dict()

        assert data["original_batch_size"] == 4
        assert data["reason"] == "out_of_memory"
        assert data["error_message"] == "CUDA error"
        assert "timestamp" in data
        assert data["recovered"] is False  # default


class TestFallbackHandler:
    """Test cases for FallbackHandler class."""

    def test_init(self):
        """Test FallbackHandler initialization."""
        engine = MockEngine()
        handler = FallbackHandler(engine)

        assert handler.engine == engine
        assert handler.fallback_callback is None
        assert not handler.has_fallback_occurred()

    def test_init_with_callback(self):
        """Test FallbackHandler with callback."""
        engine = MockEngine()
        callback = Mock()
        handler = FallbackHandler(engine, fallback_callback=callback)

        assert handler.fallback_callback == callback

    def test_translate_single(self):
        """Test single text translation (no fallback)."""
        engine = MockEngine()
        handler = FallbackHandler(engine)

        result = handler.translate("Hello")

        assert result == "Translated: Hello"
        assert not handler.has_fallback_occurred()

    def test_translate_batch_success(self):
        """Test successful batch translation."""
        engine = MockEngine()
        handler = FallbackHandler(engine)

        texts = ["Hello", "World"]
        results = handler.translate_batch(texts)

        assert len(results) == 2
        assert results[0] == "Translated: Hello"
        assert results[1] == "Translated: World"
        assert not handler.has_fallback_occurred()

    def test_translate_batch_oom_fallback(self):
        """Test batch translation with OOM fallback."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        handler = FallbackHandler(engine)

        texts = ["Hello", "World"]
        results = handler.translate_batch(texts, batch_size=4)

        assert len(results) == 2
        assert handler.has_fallback_occurred()
        events = handler.get_fallback_events()
        assert len(events) == 1
        assert events[0].reason == FallbackReason.OUT_OF_MEMORY
        assert events[0].original_batch_size == 4
        assert events[0].recovered is True

    def test_translate_batch_cuda_error_fallback(self):
        """Test batch translation with CUDA error fallback."""
        # Create a custom mock that fails on batch_size > 1, succeeds on batch_size=1
        class CustomMockEngine:
            def __init__(self):
                self._gpu = True  # Use different name to avoid property conflict
                self.call_count = 0

            def translate(self, text, src_lang="zh", tgt_lang="en", max_length=None):
                return f"Translated: {text}"

            def translate_batch(self, texts, src_lang="zh", tgt_lang="en", batch_size=4, max_length=None):
                self.call_count += 1
                # Only fail when batch_size > 1
                if batch_size > 1:
                    raise RuntimeError("CUDA error: invalid argument")
                return [f"Translated: {t}" for t in texts]

            @property
            def is_gpu_enabled(self):
                return self._gpu

        engine = CustomMockEngine()
        handler = FallbackHandler(engine)

        texts = ["Hello", "World"]
        results = handler.translate_batch(texts, batch_size=4)

        assert len(results) == 2
        events = handler.get_fallback_events()
        assert events[0].reason == FallbackReason.CUDA_ERROR

    def test_translate_batch_runtime_error_fallback(self):
        """Test batch translation with runtime error fallback."""
        # Create a custom mock that fails on batch_size > 1, succeeds on batch_size=1
        class CustomMockEngine:
            def __init__(self):
                self._gpu = True  # Use different name to avoid property conflict
                self.call_count = 0

            def translate(self, text, src_lang="zh", tgt_lang="en", max_length=None):
                return f"Translated: {text}"

            def translate_batch(self, texts, src_lang="zh", tgt_lang="en", batch_size=4, max_length=None):
                self.call_count += 1
                # Only fail when batch_size > 1
                # Use a message that matches RUNTIME_ERROR pattern
                if batch_size > 1:
                    raise RuntimeError("RuntimeError: CUDA device error")
                return [f"Translated: {t}" for t in texts]

            @property
            def is_gpu_enabled(self):
                return self._gpu

        engine = CustomMockEngine()
        handler = FallbackHandler(engine)

        texts = ["Hello", "World"]
        results = handler.translate_batch(texts, batch_size=4)

        assert len(results) == 2
        events = handler.get_fallback_events()
        assert events[0].reason == FallbackReason.RUNTIME_ERROR

    def test_fallback_callback_invoked(self):
        """Test that fallback callback is invoked."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        callback = Mock()
        handler = FallbackHandler(engine, fallback_callback=callback)

        texts = ["Hello", "World"]
        handler.translate_batch(texts, batch_size=4)

        assert callback.called
        event_arg = callback.call_args[0][0]
        assert isinstance(event_arg, FallbackEvent)
        assert event_arg.reason == FallbackReason.OUT_OF_MEMORY

    def test_no_fallback_for_non_gpu_errors(self):
        """Test that non-GPU errors are not caught."""
        engine = MockEngine(fail_on_batch=True, error_msg="Some other error")
        handler = FallbackHandler(engine)

        texts = ["Hello", "World"]

        with pytest.raises(RuntimeError):
            handler.translate_batch(texts, batch_size=4)

        assert not handler.has_fallback_occurred()

    def test_no_fallback_when_cpu_mode(self):
        """Test that fallback doesn't occur on CPU mode."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        engine.is_gpu_enabled = False  # Use property setter
        handler = FallbackHandler(engine)

        texts = ["Hello", "World"]

        # Should raise the error, not fall back
        with pytest.raises(RuntimeError):
            handler.translate_batch(texts, batch_size=4)

    def test_no_fallback_when_batch_size_is_1(self):
        """Test that fallback doesn't occur when batch_size is already 1."""
        # Use a custom engine that always fails
        engine = Mock()
        engine._is_gpu_enabled = True

        def always_fail(texts, src_lang=None, tgt_lang=None, batch_size=4, max_length=None):
            raise RuntimeError("CUDA out of memory")

        engine.translate = Mock(return_value="Translated: test")
        engine.translate_batch = always_fail

        handler = FallbackHandler(engine)

        texts = ["Hello", "World"]

        # Should raise the error, not fall back (already at batch_size=1)
        with pytest.raises(RuntimeError):
            handler.translate_batch(texts, batch_size=1)

        # Verify no fallback occurred
        assert not handler.has_fallback_occurred()

    def test_fallback_failure_propagates(self):
        """Test that fallback failure is propagated."""
        # Create an engine that fails both in batch and in retry
        engine = Mock()
        engine.is_gpu_enabled = True

        def fail_batch(*args, **kwargs):
            raise RuntimeError("CUDA out of memory")

        engine.translate = Mock(return_value="Translated: test")
        engine.translate_batch = fail_batch

        handler = FallbackHandler(engine)

        texts = ["Hello", "World"]

        with pytest.raises(RuntimeError):
            handler.translate_batch(texts, batch_size=4)

        events = handler.get_fallback_events()
        assert events[0].recovered is False

    def test_get_fallback_summary(self):
        """Test getting fallback summary."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        handler = FallbackHandler(engine)

        # No events initially
        summary = handler.get_fallback_summary()
        assert summary["total_fallbacks"] == 0
        assert summary["successful_recoveries"] == 0

        # Trigger a fallback
        handler.translate_batch(["Hello"], batch_size=4)

        summary = handler.get_fallback_summary()
        assert summary["total_fallbacks"] == 1
        assert summary["successful_recoveries"] == 1
        assert summary["last_event"] is not None

    def test_clear_fallback_history(self):
        """Test clearing fallback history."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        handler = FallbackHandler(engine)

        # Trigger a fallback
        handler.translate_batch(["Hello"], batch_size=4)
        assert handler.has_fallback_occurred()

        # Clear history
        handler.clear_fallback_history()
        assert not handler.has_fallback_occurred()
        assert len(handler.get_fallback_events()) == 0

    def test_get_user_message_with_fallback(self):
        """Test getting user message after fallback."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        handler = FallbackHandler(engine)

        # Before fallback
        assert handler.get_user_message() is None

        # After fallback
        handler.translate_batch(["Hello"], batch_size=4)
        message = handler.get_user_message()
        assert message is not None
        assert "reduced batch size" in message.lower()

    def test_get_user_message_after_failed_recovery(self):
        """Test getting user message after failed recovery."""
        engine = Mock()
        engine.is_gpu_enabled = True
        engine.translate = Mock(return_value="Translated")

        def fail_batch(*args, **kwargs):
            raise RuntimeError("CUDA out of memory")

        engine.translate_batch = fail_batch

        handler = FallbackHandler(engine)

        try:
            handler.translate_batch(["Hello"], batch_size=4)
        except RuntimeError:
            pass

        message = handler.get_user_message()
        assert message is not None
        assert "failed" in message.lower()

    def test_is_recommended_batch_size(self):
        """Test checking recommended batch size."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        handler = FallbackHandler(engine)

        # Before fallback, any size > 1 is recommended
        assert handler.is_recommended_batch_size(4)
        assert not handler.is_recommended_batch_size(1)

        # After fallback, only batch_size=1 is recommended
        handler.translate_batch(["Hello"], batch_size=4)
        assert not handler.is_recommended_batch_size(4)
        assert handler.is_recommended_batch_size(1)

    def test_get_recommended_batch_size(self):
        """Test getting recommended batch size."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        handler = FallbackHandler(engine)

        # Before fallback
        assert handler.get_recommended_batch_size() == 4

        # After fallback
        handler.translate_batch(["Hello"], batch_size=4)
        assert handler.get_recommended_batch_size() == 1

    def test_multiple_fallback_events(self):
        """Test tracking multiple fallback events."""
        engine = MockEngine(fail_on_batch=True, error_msg="CUDA out of memory")
        handler = FallbackHandler(engine)

        # Trigger multiple fallbacks
        for _ in range(3):
            handler.translate_batch(["Hello"], batch_size=4)

        events = handler.get_fallback_events()
        assert len(events) == 3

        summary = handler.get_fallback_summary()
        assert summary["total_fallbacks"] == 3