# Copyright (c) Facebook, Inc. and its affiliates.
#
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

import unittest
from copy import deepcopy
from dataclasses import dataclass
from typing import Optional

import torch
from fairseq.models.ema import EMA


class DummyModule(torch.nn.Module):
    def __init__(self) -> None:
        """LightningModule for testing purposes

        Args:
            epoch_min_loss_override (int, optional): Pass in an epoch that will be set to the minimum
                validation loss for testing purposes (zero based). If None this is ignored. Defaults to None.
        """
        super().__init__()
        self.layer = torch.nn.Linear(in_features=32, out_features=2)
        self.another_layer = torch.nn.Linear(in_features=2, out_features=2)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.layer(x)
        return self.another_layer(x)


@dataclass
class EMAConfig(object):
    ema_decay: float = 0.99
    ema_start_update: int = 0
    ema_fp32: bool = False
    ema_seed_model: Optional[str] = None


class TestEMAGPU(unittest.TestCase):
    def assertTorchAllClose(self, x, y, atol=1e-8, rtol=1e-5, msg=None):
        diff = x.float() - y.float()
        diff_norm = torch.norm(diff)
        other_norm = torch.norm(y.float())

        if msg is None:
            msg = "|input - other| > {} + {} * |other|".format(
                atol, rtol
            )

        self.assertLessEqual(
            diff_norm,
            atol + rtol * other_norm,
            msg=msg,
        )

    def test_ema(self):
        model = DummyModule()
        optimizer = torch.optim.SGD(model.parameters(), lr=0.01)
        state = deepcopy(model.state_dict())
        config = EMAConfig()
        ema = EMA(model, config)

        # set decay
        ema._set_decay(config.ema_decay)
        self.assertEqual(ema.get_decay(), config.ema_decay)

        # get model
        self.assertEqual(ema.get_model(), ema.model)

        # Since fp32 params is not used, it should be of size 0
        self.assertEqual(len(ema.fp32_params), 0)

        # EMA step
        x = torch.randn(32)
        y = model(x)
        loss = y.sum()
        loss.backward()
        optimizer.step()

        ema.step(model)

        ema_state_dict = ema.get_model().state_dict()

        for key, param in model.state_dict().items():
            prev_param = state[key]
            ema_param = ema_state_dict[key]

            if "version" in key:
                # Do not decay a model.version pytorch param
                continue
            self.assertTorchAllClose(
                ema_param,
                config.ema_decay * prev_param + (1 - config.ema_decay) * param,
            )

        # Since fp32 params is not used, it should be of size 0
        self.assertEqual(len(ema.fp32_params), 0)

        # Load EMA into model
        model2 = DummyModule()
        ema.reverse(model2)

        for key, param in model2.state_dict().items():
            ema_param = ema_state_dict[key]
            self.assertTrue(
                torch.allclose(ema_param, param)
            )

    def test_ema_fp32(self):
        model = DummyModule().half()
        optimizer = torch.optim.SGD(model.parameters(), lr=0.01)
        state = deepcopy(model.state_dict())
        config = EMAConfig(ema_fp32=True)
        ema = EMA(model, config)

        x = torch.randn(32)
        y = model(x.half())
        loss = y.sum()
        loss.backward()
        optimizer.step()

        ema.step(model)

        for key, param in model.state_dict().items():
            prev_param = state[key]
            ema_param = ema.get_model().state_dict()[key]

            if "version" in key:
                # Do not decay a model.version pytorch param
                continue
            self.assertIn(key, ema.fp32_params)

            # EMA update is done in fp32, and hence the EMA param must be
            # closer to the EMA update done in fp32 than in fp16.
            self.assertLessEqual(
                torch.norm(
                    ema_param.float() -
                    (config.ema_decay * prev_param.float() + (1 - config.ema_decay) * param.float()).half().float()
                ),
                torch.norm(
                    ema_param.float() -
                    (config.ema_decay * prev_param + (1 - config.ema_decay) * param).float()
                ),
            )
            self.assertTorchAllClose(
                ema_param,
                (config.ema_decay * prev_param.float() + (1 - config.ema_decay) * param.float()).half(),
            )

    def test_ema_fp16(self):
        model = DummyModule().half()
        optimizer = torch.optim.SGD(model.parameters(), lr=0.01)
        state = deepcopy(model.state_dict())
        config = EMAConfig(ema_fp32=False)
        ema = EMA(model, config)

        # Since fp32 params is not used, it should be of size 0
        self.assertEqual(len(ema.fp32_params), 0)

        x = torch.randn(32)
        y = model(x.half())
        loss = y.sum()
        loss.backward()
        optimizer.step()

        ema.step(model)

        for key, param in model.state_dict().items():
            prev_param = state[key]
            ema_param = ema.get_model().state_dict()[key]

            if "version" in key:
                # Do not decay a model.version pytorch param
                continue

            # EMA update is done in fp16, and hence the EMA param must be
            # closer to the EMA update done in fp16 than in fp32.
            self.assertLessEqual(
                torch.norm(
                    ema_param.float() -
                    (config.ema_decay * prev_param + (1 - config.ema_decay) * param).float()
                ),
                torch.norm(
                    ema_param.float() -
                    (config.ema_decay * prev_param.float() + (1 - config.ema_decay) * param.float()).half().float()
                ),
            )
            self.assertTorchAllClose(
                ema_param,
                config.ema_decay * prev_param + (1 - config.ema_decay) * param,
            )

        # Since fp32 params is not used, it should be of size 0
        self.assertEqual(len(ema.fp32_params), 0)


if __name__ == "__main__":
    unittest.main()
