# Copyright The Lightning AI team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from datetime import timedelta
from re import escape
from unittest import mock
from unittest.mock import Mock

import pytest
import torch
import torch.nn as nn

from lightning.fabric.strategies.model_parallel import _is_sharded_checkpoint
from lightning.pytorch import LightningModule
from lightning.pytorch.plugins.environments import LightningEnvironment
from lightning.pytorch.strategies import ModelParallelStrategy
from tests_pytorch.helpers.runif import RunIf


@RunIf(min_torch="2.4")
def test_device_mesh_access():
    strategy = ModelParallelStrategy()
    with pytest.raises(RuntimeError, match="Accessing the device mesh .* not allowed"):
        _ = strategy.device_mesh


@RunIf(min_torch="2.4")
@pytest.mark.parametrize(
    ("num_nodes", "devices", "invalid_dp_size", "invalid_tp_size"),
    [
        (1, 4, 1, 1),
        (1, 4, 2, 3),
        (1, 4, 4, 2),
        (2, 4, 1, 4),
        (2, 4, 2, 1),
    ],
)
def test_validate_device_mesh_dimensions(num_nodes, devices, invalid_dp_size, invalid_tp_size):
    """Test passing sizes that don't multiply to the world size raises an error."""
    strategy = ModelParallelStrategy(
        data_parallel_size=invalid_dp_size,
        tensor_parallel_size=invalid_tp_size,
    )
    strategy._setup_distributed = Mock()
    strategy._accelerator = Mock()
    strategy.cluster_environment = Mock(
        world_size=Mock(return_value=(num_nodes * devices)), local_rank=Mock(return_value=1)
    )
    strategy.parallel_devices = [torch.device("cpu")] * devices
    strategy.num_nodes = num_nodes
    with pytest.raises(RuntimeError, match="multiplied should equal the world size"):
        strategy.setup_environment()


@RunIf(min_torch="2.4")
def test_fsdp_v1_modules_unsupported():
    """Test that the strategy won't allow setting up a module wrapped with the legacy FSDP API."""
    from torch.distributed.fsdp import FullyShardedDataParallel

    class Model(LightningModule):
        def configure_model(self):
            pass

    model = Model()
    model.modules = Mock(return_value=[Mock(spec=FullyShardedDataParallel)])
    strategy = ModelParallelStrategy()
    strategy.model = model
    strategy._lightning_module = model
    strategy._accelerator = Mock()

    with pytest.raises(TypeError, match="only supports the new FSDP2 APIs in PyTorch >= 2.4"):
        strategy.setup(Mock())


@RunIf(min_torch="2.4")
def test_configure_model_required():
    class Model1(LightningModule):
        pass

    class Model2(LightningModule):
        def configure_model(self):
            pass

    model = Model1()
    strategy = ModelParallelStrategy()
    strategy.model = model
    strategy._lightning_module = model
    strategy._accelerator = Mock()
    strategy._parallel_devices = [torch.device("cpu")]

    with pytest.raises(TypeError, match="you are required to override the `configure_model"):
        strategy.setup(Mock())

    model = Model2()
    strategy.model = model
    strategy._lightning_module = model
    strategy.setup(Mock())


@RunIf(min_torch="2.4")
def test_save_checkpoint_storage_options(tmp_path):
    """Test that the strategy does not accept storage options for saving checkpoints."""
    strategy = ModelParallelStrategy()
    with pytest.raises(
        TypeError, match=escape("ModelParallelStrategy.save_checkpoint(..., storage_options=...)` is not")
    ):
        strategy.save_checkpoint(checkpoint=Mock(), filepath=tmp_path, storage_options=Mock())


@RunIf(min_torch="2.4")
@mock.patch("lightning.pytorch.strategies.model_parallel.ModelParallelStrategy.broadcast", lambda _, x: x)
@mock.patch("lightning.fabric.plugins.io.torch_io._atomic_save")
@mock.patch("lightning.pytorch.strategies.model_parallel._remove_checkpoint")
def test_save_checkpoint_path_exists(remove_checkpoint_mock, atomic_save_mock, tmp_path):
    strategy = ModelParallelStrategy(save_distributed_checkpoint=False)

    # save_distributed_checkpoint=False, path exists, path is not a sharded checkpoint: error
    path = tmp_path / "not-empty"
    path.mkdir()
    (path / "file").touch()
    assert not _is_sharded_checkpoint(path)
    with pytest.raises(IsADirectoryError, match="exists and is a directory"):
        strategy.save_checkpoint(Mock(), filepath=path)

    # save_distributed_checkpoint=False, path exists, path is a sharded checkpoint: no error (overwrite)
    path = tmp_path / "sharded-checkpoint"
    path.mkdir()
    (path / "meta.pt").touch()
    assert _is_sharded_checkpoint(path)
    strategy.save_checkpoint(Mock(), filepath=path)
    remove_checkpoint_mock.assert_called_once_with(path)

    # save_distributed_checkpoint=False, path exists, path is a file: no error (overwrite)
    path = tmp_path / "file.pt"
    path.touch()
    atomic_save_mock.reset_mock()
    strategy.save_checkpoint(Mock(), filepath=path)
    atomic_save_mock.assert_called_once()

    strategy = ModelParallelStrategy(save_distributed_checkpoint=True)

    save_mock = mock.patch("torch.distributed.checkpoint.save")

    # save_distributed_checkpoint=True, path exists, path is a folder: no error (overwrite)
    path = tmp_path / "not-empty-2"
    path.mkdir()
    (path / "file").touch()
    with save_mock:
        strategy.save_checkpoint({"state_dict": {}, "optimizer_states": {"": {}}}, filepath=path)
    assert (path / "file").exists()

    # save_distributed_checkpoint=True, path exists, path is a file: no error (overwrite)
    path = tmp_path / "file-2.pt"
    path.touch()
    with save_mock:
        strategy.save_checkpoint({"state_dict": {}, "optimizer_states": {"": {}}}, filepath=path)
    assert path.is_dir()


@RunIf(min_torch="2.4")
@mock.patch("lightning.fabric.strategies.model_parallel._has_dtensor_modules", return_value=True)
def test_load_unknown_checkpoint_type(_, tmp_path):
    """Test that the strategy validates the contents at the checkpoint path."""
    strategy = ModelParallelStrategy()
    strategy.model = Mock()
    strategy._lightning_module = Mock(strict_loading=True)
    path = tmp_path / "empty_dir"  # neither a single file nor a directory with meta file
    path.mkdir()
    with pytest.raises(ValueError, match="does not point to a valid checkpoint"):
        strategy.load_checkpoint(checkpoint_path=path)


@RunIf(min_torch="2.4")
@mock.patch("lightning.pytorch.strategies.model_parallel._setup_device_mesh")
@mock.patch("torch.distributed.init_process_group")
def test_set_timeout(init_process_group_mock, _):
    """Test that the timeout gets passed to the ``torch.distributed.init_process_group`` function."""
    test_timedelta = timedelta(seconds=30)
    strategy = ModelParallelStrategy(timeout=test_timedelta)
    strategy._lightning_module = Mock()
    strategy.parallel_devices = [torch.device("cpu")]
    strategy.cluster_environment = LightningEnvironment()
    strategy.accelerator = Mock()
    strategy.setup_environment()
    process_group_backend = strategy._get_process_group_backend()
    global_rank = strategy.cluster_environment.global_rank()
    world_size = strategy.cluster_environment.world_size()
    init_process_group_mock.assert_called_with(
        process_group_backend,
        rank=global_rank,
        world_size=world_size,
        timeout=test_timedelta,
        device_id=None,
    )


@RunIf(min_torch="2.4")
def test_meta_device_materialization():
    """Test that the `setup()` method materializes meta-device tensors in the LightningModule."""

    class NoResetParameters(nn.Module):
        def __init__(self):
            super().__init__()
            self.weight = nn.Parameter(torch.ones(4, 4))

    class CustomModel(LightningModule):
        def __init__(self):
            super().__init__()
            # nn.Sequential as a parameterless module
            self.layer1 = nn.Sequential(NoResetParameters(), NoResetParameters())
            self.layer2 = nn.Linear(4, 4)
            self.register_buffer("buffer", torch.rand(2))

        def reset_parameters(self):
            self.buffer.fill_(1.0)

        def configure_model(self) -> None:
            pass

    with torch.device("meta"):
        model = CustomModel()
    assert model.layer1[0].weight.is_meta
    assert model.layer2.weight.is_meta
    assert model.buffer.is_meta

    strategy = ModelParallelStrategy()
    strategy._accelerator = Mock()
    strategy._device_mesh = Mock()
    strategy._parallel_devices = [torch.device("cpu")]
    strategy._lightning_module = model
    strategy.model = model

    with pytest.warns(UserWarning, match=r"`reset_parameters\(\)` method for re-initialization: NoResetParameters"):
        strategy.setup(Mock())
    assert all(not p.is_meta for p in model.parameters())
    assert all(not b.is_meta for b in model.buffers())


@RunIf(min_torch="2.4")
def test_align_compiled_param_names_with_module():
    """Test that optimizer state dict keys are aligned with compiled submodule parameter names."""
    from lightning.pytorch.strategies.model_parallel import _align_compiled_param_names_with_module

    class SimpleModule(nn.Module):
        def __init__(self):
            super().__init__()
            self.model = nn.Sequential(nn.Linear(32, 64), nn.ReLU(), nn.Linear(64, 32))

        def forward(self, x):
            return self.model(x)

    # Test with compiled submodule
    m = SimpleModule()
    m.model = torch.compile(m.model)

    # Simulate optimizer state dict without _orig_mod in keys (includes both state and param_groups)
    state_dict = {
        "state": {
            "model.0.weight": {"step": 1},
            "model.0.bias": {"step": 1},
            "model.2.weight": {"step": 1},
            "model.2.bias": {"step": 1},
        },
        "param_groups": [{"params": ["model.0.weight", "model.0.bias", "model.2.weight", "model.2.bias"], "lr": 0.01}],
    }

    result = _align_compiled_param_names_with_module(state_dict, m)

    # Verify state keys now have _orig_mod inserted
    expected_keys = {
        "model._orig_mod.0.weight",
        "model._orig_mod.0.bias",
        "model._orig_mod.2.weight",
        "model._orig_mod.2.bias",
    }
    assert set(result["state"].keys()) == expected_keys

    # Verify param_groups params also have _orig_mod inserted
    assert set(result["param_groups"][0]["params"]) == expected_keys

    # Verify they match the module's named_parameters
    param_names = {name for name, _ in m.named_parameters()}
    assert set(result["state"].keys()) == param_names


@RunIf(min_torch="2.4")
def test_align_compiled_param_names_no_compile():
    """Test that non-compiled modules pass through unchanged."""
    from lightning.pytorch.strategies.model_parallel import _align_compiled_param_names_with_module

    class SimpleModule(nn.Module):
        def __init__(self):
            super().__init__()
            self.model = nn.Sequential(nn.Linear(32, 64), nn.Linear(64, 32))

        def forward(self, x):
            return self.model(x)

    m = SimpleModule()  # Not compiled

    state_dict = {
        "state": {
            "model.0.weight": {"step": 1},
            "model.0.bias": {"step": 1},
        }
    }

    result = _align_compiled_param_names_with_module(state_dict, m)

    # Keys should be unchanged
    assert set(result["state"].keys()) == {"model.0.weight", "model.0.bias"}


@RunIf(min_torch="2.4")
def test_model_parallel_pytorch_save_checkpoint_remote_path(monkeypatch):
    """Regression: a gs:// URL must reach the DCP layer uncorrupted (not gs:/)."""
    from lightning.pytorch.strategies import model_parallel as mp

    strategy = ModelParallelStrategy()
    strategy._save_distributed_checkpoint = True
    monkeypatch.setattr(strategy, "broadcast", lambda x: x)
    monkeypatch.setattr(type(strategy), "global_rank", property(lambda self: 0))

    captured = {}
    monkeypatch.setattr(mp, "_distributed_checkpoint_save", lambda state, path: captured.update(path=path))
    monkeypatch.setattr(mp, "_prepare_directory_checkpoint", lambda p: None)
    monkeypatch.setattr(mp, "_is_checkpoint_dir", lambda p: False)
    monkeypatch.setattr(mp, "_atomic_save", lambda obj, path: captured.update(meta=str(path)))

    checkpoint = {"state_dict": {"w": 1}, "optimizer_states": []}
    strategy.save_checkpoint(checkpoint, "gs://bucket/run/ckpt")
    assert captured["path"] == "gs://bucket/run/ckpt"
    assert captured["meta"] == "gs://bucket/run/ckpt/meta.pt"
