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

"""
Testing OssDdp class.
"""

from contextlib import suppress
import copy
import tempfile
from typing import List

import numpy as np
import torch
import torch.distributed as dist
import torch.multiprocessing as mp
from torch.nn import Linear, Sequential
from torch.nn.parallel import DistributedDataParallel as DDP

from fairscale.nn.data_parallel import ShardedDataParallel
from fairscale.optim import OSS
from fairscale.utils.testing import GPT2, skip_if_no_cuda, skip_if_single_gpu


def run_one_step(rank, world_size, backend, device, temp_file_name):
    url = "file://" + temp_file_name
    dist.init_process_group(init_method=url, backend=backend, rank=rank, world_size=world_size)
    if device == torch.device("cuda"):
        torch.cuda.set_device(rank)

    torch.manual_seed(rank)
    np.random.seed(rank)

    def check(broadcast_buffers: bool, grad_accumulation: bool = False) -> None:
        # Any model works. Add one different buffer per rank
        model = Sequential(Linear(2, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3))
        model.register_buffer("test_buffer", torch.ones((1)) * rank)
        model.to(device)

        next(model.parameters()).requires_grad = False  # Test non-trainable parameters

        optimizer = OSS(params=model.parameters(), optim=torch.optim.SGD, lr=0.01, momentum=0.99)
        ddp_model = ShardedDataParallel(model, optimizer, broadcast_buffers=broadcast_buffers)

        def check_same_model_params(same_params: bool):
            # Check that all the params are the same on all ranks
            # This should be true with and without broadcast_buffers, we don't have any real buffer here
            receptacle: List[torch.Tensor] = []

            if dist.get_backend() != "nccl":
                for pg in optimizer.param_groups:
                    for p in pg["params"]:
                        # Check the params
                        receptacle = [p.clone() for _ in range(world_size)] if rank == 0 else []
                        dist.gather(p, receptacle, dst=0)
                        if rank == 0:
                            for sync_p in receptacle[1:]:
                                if same_params:
                                    assert torch.all(torch.eq(receptacle[0], sync_p)), "Models differ in between ranks"
                                else:
                                    assert not torch.all(
                                        torch.eq(receptacle[0], sync_p)
                                    ), "Gradients should not have been synced"

                # Check that all the buffers are in sync (authoritative rank is 0, its buffer is 0)
                if broadcast_buffers:
                    for b in ddp_model.buffers():
                        receptacle = [b.clone() for _ in range(world_size)] if rank == 0 else []
                        dist.gather(b, receptacle, dst=0)
                        if rank == 0:
                            for sync_b in receptacle[1:]:
                                if same_params:
                                    assert torch.all(torch.eq(receptacle[0], sync_b)), "Models differ in between ranks"
                                else:
                                    assert not torch.all(
                                        torch.eq(receptacle[0], sync_b)
                                    ), "Gradients should not have been synced"

                        assert b.cpu().item() == 0.0

        # The model should be synchronized in between the ranks at ShardedDataParallel construction time, check that
        check_same_model_params(same_params=True)

        # Optim loop
        def closure():
            optimizer.zero_grad()

            with ddp_model.no_sync() if grad_accumulation else suppress():
                input_tensor = torch.rand((64, 2)).to(device)
                loss = ddp_model(input_tensor).abs().sum()
                loss.backward()
            return loss

        # The models should stay the same in between the ranks
        for i in range(5):
            _ = optimizer.step(closure=closure)
            # when running on cpu/gloo the "nodes" are not really different
            same_params = device == torch.device("cpu") or grad_accumulation
            check_same_model_params(same_params=same_params)

    check(broadcast_buffers=False)
    check(broadcast_buffers=True)
    check(broadcast_buffers=False, grad_accumulation=True)
    check(broadcast_buffers=True, grad_accumulation=True)
    dist.destroy_process_group()


def run_test(backend, device, world_size=2):
    temp_file_name = tempfile.mkstemp()[1]
    mp.spawn(run_one_step, args=(world_size, backend, device, temp_file_name), nprocs=world_size, join=True)


def test_step_on_cpu():
    run_test(backend=dist.Backend.GLOO, device=torch.device("cpu"), world_size=4)


@skip_if_no_cuda
@skip_if_single_gpu
def test_step_on_gpu():
    run_test(backend=dist.Backend.NCCL, device=torch.device("cuda"))


def run_ddp_parity(rank, world_size, backend, temp_file_name):
    url = "file://" + temp_file_name
    dist.init_process_group(init_method=url, backend=backend, rank=rank, world_size=world_size)

    device = torch.device("cuda")
    torch.cuda.set_device(rank)
    torch.manual_seed(rank)
    np.random.seed(rank)

    # Any model works. Add one different buffer per rank
    model = Sequential(Linear(2, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3))
    model.register_buffer("test_buffer", torch.ones((1)) * rank)
    model.to(device)

    sharded_optimizer = OSS(params=model.parameters(), optim=torch.optim.SGD, lr=1e-3, momentum=0.99)
    sharded_ddp_model = ShardedDataParallel(module=model, sharded_optimizer=sharded_optimizer, broadcast_buffers=True)

    ddp_model_single = copy.deepcopy(model)
    ddp_optimizer = torch.optim.SGD(ddp_model_single.parameters(), lr=1e-3, momentum=0.99)
    ddp_model = DDP(ddp_model_single, device_ids=[rank], broadcast_buffers=True)

    def check_same_model_params():
        for pg, ddp_pg in zip(sharded_optimizer.param_groups, ddp_optimizer.param_groups):
            for p, ddp_p in zip(pg["params"], ddp_pg["params"]):
                assert torch.allclose(
                    p, ddp_p, atol=1e-3
                ), f"Model parameters differ in between DDP and ShardedDDP {p} {ddp_p}"

        for b, ddp_b in zip(sharded_ddp_model.buffers(), ddp_model.buffers()):
            assert torch.allclose(b, ddp_b, atol=1e-3), "Model buffers differ in between DDP and ShardedDDP"

    # The model should be synchronized in between the ranks at construction time, check that
    check_same_model_params()

    # The models should stay the same in between the ranks
    for i in range(20):
        input_tensor = torch.rand((64, 2)).to(device)

        def closure_ddp(input_tensor=input_tensor):
            ddp_optimizer.zero_grad()
            ddp_loss = ddp_model(input_tensor).abs().sum()
            ddp_loss.backward()
            return ddp_loss

        def closure_sharded(input_tensor=input_tensor):
            sharded_optimizer.zero_grad()
            sharded_loss = sharded_ddp_model(input_tensor).abs().sum()
            sharded_loss.backward()
            return sharded_loss

        _ = ddp_optimizer.step(closure=closure_ddp)
        _ = sharded_optimizer.step(closure=closure_sharded)

        check_same_model_params()

    dist.destroy_process_group()


@skip_if_no_cuda
@skip_if_single_gpu
def test_ddp_parity():
    temp_file_name = tempfile.mkstemp()[1]
    world_size = torch.cuda.device_count()
    backend = dist.Backend.NCCL
    mp.spawn(run_ddp_parity, args=(world_size, backend, temp_file_name), nprocs=world_size, join=True)


def run_ddp_parity_two_optim(rank, world_size, backend, temp_file_name):
    url = "file://" + temp_file_name
    dist.init_process_group(init_method=url, backend=backend, rank=rank, world_size=world_size)
    device = torch.device("cuda")
    torch.cuda.set_device(rank)
    torch.manual_seed(rank)
    np.random.seed(rank)  # Any model works. Add one different buffer per rank

    model = Sequential(Linear(2, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3))
    model.register_buffer("test_buffer", torch.ones((1)) * rank)
    model.to(device)
    n_half_params = len(list(model.parameters())) // 2

    sharded_optimizer = OSS(
        params=list(model.parameters())[:n_half_params], optim=torch.optim.SGD, lr=1e-3, momentum=0.99
    )
    sharded_optimizer_2 = OSS(
        params=list(model.parameters())[n_half_params:], optim=torch.optim.SGD, lr=1e-3, momentum=0.99
    )

    sharded_ddp_model = ShardedDataParallel(module=model, sharded_optimizer=sharded_optimizer, broadcast_buffers=True)

    ddp_model_single = copy.deepcopy(model)
    ddp_optimizer = torch.optim.SGD(list(ddp_model_single.parameters())[:n_half_params], lr=1e-3, momentum=0.99)
    ddp_optimizer_2 = torch.optim.SGD(list(ddp_model_single.parameters())[n_half_params:], lr=1e-3, momentum=0.99)
    ddp_model = DDP(ddp_model_single, device_ids=[rank], broadcast_buffers=True)

    def check_same_model_params():
        for pg, ddp_pg in zip(sharded_optimizer.param_groups, ddp_optimizer.param_groups):
            for p, ddp_p in zip(pg["params"], ddp_pg["params"]):
                assert torch.allclose(
                    p, ddp_p, atol=1e-3
                ), f"Model parameters differ in between DDP and ShardedDDP {p} {ddp_p}"
        for b, ddp_b in zip(sharded_ddp_model.buffers(), ddp_model.buffers()):
            assert torch.allclose(b, ddp_b, atol=1e-3), "Model buffers differ in between DDP and ShardedDDP"

    check_same_model_params()  # The models should stay the same in between the ranks

    for i in range(20):
        input_tensor = torch.rand((64, 2)).to(device)

        # Run DDP
        ddp_optimizer.zero_grad()
        ddp_optimizer_2.zero_grad()
        ddp_loss = ddp_model(input_tensor).abs().sum()
        ddp_loss.backward()
        ddp_optimizer.step()
        ddp_optimizer_2.step()

        # Run Sharded
        sharded_optimizer.zero_grad()
        sharded_optimizer_2.zero_grad()
        sharded_loss = sharded_ddp_model(input_tensor).abs().sum()
        sharded_loss.backward()
        sharded_optimizer.step()
        sharded_optimizer_2.step()
        check_same_model_params()

    dist.destroy_process_group()


@skip_if_no_cuda
@skip_if_single_gpu
def test_ddp_parity_two_optim():
    temp_file_name = tempfile.mkstemp()[1]
    world_size = 2
    backend = dist.Backend.NCCL
    mp.spawn(run_ddp_parity_two_optim, args=(world_size, backend, temp_file_name), nprocs=world_size, join=True)


def run_test_two_inputs(rank, world_size, backend, device, temp_file_name):
    url = "file://" + temp_file_name
    dist.init_process_group(init_method=url, backend=backend, rank=rank, world_size=world_size)
    if device == torch.device("cuda"):
        torch.cuda.set_device(rank)

    torch.manual_seed(rank)
    np.random.seed(rank)

    class _DoubleInput(torch.nn.Module):
        def __init__(self):
            super().__init__()
            self.mlp = Sequential(Linear(2, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3))

        def forward(self, x, y):
            x1 = self.mlp(x)
            x2 = self.mlp(y)
            return torch.cat((x1, x2), dim=1)

    model = _DoubleInput().to(device)

    optimizer = OSS(params=model.parameters(), optim=torch.optim.SGD, lr=0.01, momentum=0.99)
    ddp_model = ShardedDataParallel(model, optimizer)

    # Optim loop
    def closure():
        optimizer.zero_grad()
        input_tensor = torch.rand((64, 2)).to(device)
        loss = ddp_model(input_tensor, input_tensor).abs().sum()
        loss.backward()
        return loss

    for i in range(5):
        _ = optimizer.step(closure=closure)

    dist.destroy_process_group()


def test_inputs():
    # Check that the ShardedDDP wrapper accepts tuple(tensors) as inputs
    world_size = 2
    backend = "gloo"
    temp_file_name = tempfile.mkstemp()[1]
    device = "cpu"
    mp.spawn(run_test_two_inputs, args=(world_size, backend, device, temp_file_name), nprocs=world_size, join=True)


def test_ddp_attributes():
    # Check that ShardedDDP exposes the same attributes as Pytorch's DDP
    # - is multi_device_module
    # - device_type

    url = "file://" + tempfile.mkstemp()[1]
    dist.init_process_group(init_method=url, backend="gloo", rank=0, world_size=1)

    model = Sequential(Linear(2, 3), Linear(3, 3))
    optimizer = OSS(params=model.parameters(), optim=torch.optim.SGD, lr=0.01, momentum=0.99)
    ddp_model = ShardedDataParallel(model, optimizer)

    assert hasattr(ddp_model, "is_multi_device_module")
    assert hasattr(ddp_model, "device_type")
    dist.destroy_process_group()


def run_test_ddp_sync_batch_norm(rank, world_size, backend, device, temp_file_name):
    url = "file://" + temp_file_name
    dist.init_process_group(init_method=url, backend=backend, rank=rank, world_size=world_size)

    model = Sequential(Linear(2, 3), torch.nn.BatchNorm1d(3), Linear(3, 3)).to(device)
    model = torch.nn.SyncBatchNorm.convert_sync_batchnorm(model)
    optimizer = OSS(params=model.parameters(), optim=torch.optim.SGD, lr=0.01, momentum=0.99)
    ddp_model = ShardedDataParallel(model, optimizer)

    assert isinstance(model[1], torch.nn.SyncBatchNorm)
    # Ensures sync batch norm handles have been added
    ddp_model(torch.randn(2, 2).to(device))
    dist.destroy_process_group()


@skip_if_no_cuda
@skip_if_single_gpu
def test_ddp_sync_batch_norm():
    # Check that ShardedDDP is compatible with sync batch norm across multiple GPUs
    world_size = 2
    backend = "gloo"
    temp_file_name = tempfile.mkstemp()[1]
    device = "cuda"
    mp.spawn(
        run_test_ddp_sync_batch_norm, args=(world_size, backend, device, temp_file_name), nprocs=world_size, join=True
    )


def run_test_two_optimizers(rank, world_size, backend, device, temp_file_name):
    url = "file://" + temp_file_name
    dist.init_process_group(init_method=url, backend=backend, rank=rank, world_size=world_size)
    if device == torch.device("cuda"):
        torch.cuda.set_device(rank)

    torch.manual_seed(rank)
    np.random.seed(rank)

    class _DoubleInput(torch.nn.Module):
        def __init__(self):
            super().__init__()
            self.mlp = Sequential(Linear(2, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3), Linear(3, 3))

        def forward(self, x, y):
            x1 = self.mlp(x)
            x2 = self.mlp(y)
            return torch.cat((x1, x2), dim=1)

    model = _DoubleInput().to(device)

    parameters = list(model.parameters())
    optimizer_1 = OSS(params=parameters[:-10], optim=torch.optim.SGD, lr=0.01, momentum=0.99)
    optimizer_2 = OSS(params=parameters[-10:], optim=torch.optim.SGD, lr=0.01, momentum=0.99)
    ddp_model = ShardedDataParallel(model, [optimizer_1, optimizer_2])

    # Optim loop
    def closure():
        input_tensor = torch.rand((64, 2)).to(device)
        loss = ddp_model(input_tensor, input_tensor).abs().sum()
        loss.backward()
        return loss

    for i in range(5):
        optimizer_1.zero_grad()
        optimizer_2.zero_grad()

        _ = optimizer_1.step(closure=closure)
        _ = optimizer_2.step(closure=closure)

    dist.destroy_process_group()


def test_two_optimizers():
    # Check that the ShardedDDP wrapper accepts tuple(tensors) as inputs
    world_size = 2
    backend = "gloo"
    temp_file_name = tempfile.mkstemp()[1]
    device = "cpu"
    mp.spawn(run_test_two_optimizers, args=(world_size, backend, device, temp_file_name), nprocs=world_size, join=True)


def run_test_gpt2(rank, world_size, backend, device, temp_file_name):
    INPUT_DIM = 32
    BACH_SIZE = 10
    STEPS = 10

    url = "file://" + temp_file_name
    dist.init_process_group(init_method=url, backend=backend, rank=rank, world_size=world_size)
    if device == torch.device("cuda"):
        torch.cuda.set_device(rank)

    torch.manual_seed(rank)
    np.random.seed(rank)
    model = GPT2(
        embed_dim=512, num_heads=2, num_layers=24, num_positions=INPUT_DIM * INPUT_DIM, num_vocab=512, num_classes=2
    ).to(device)
    optimizer = OSS(params=model.parameters(), optim=torch.optim.SGD, lr=0.01, momentum=0.99)
    ddp_model = ShardedDataParallel(model, optimizer)

    # Optim loop
    def closure():
        optimizer.zero_grad()
        # Force int inputs to prevent the first grad from firing
        input_tensor = torch.randint(10, (BACH_SIZE, INPUT_DIM)).to(device)
        loss = ddp_model(input_tensor).abs().sum()
        loss.backward()
        return loss

    # Check for bucketing overflows
    for i in range(STEPS):
        _ = optimizer.step(closure=closure)

    dist.destroy_process_group()


@skip_if_no_cuda
@skip_if_single_gpu
def test_gpt2():
    # Check that the ShardedDDP wrapper accepts tuple(tensors) as inputs
    world_size = 2
    backend = "gloo"
    temp_file_name = tempfile.mkstemp()[1]
    device = "cuda"
    mp.spawn(run_test_gpt2, args=(world_size, backend, device, temp_file_name), nprocs=world_size, join=True)