import pytest
import torch

from mmcv.ops.multi_scale_deform_attn import (
    MultiScaleDeformableAttention, MultiScaleDeformableAttnFunction,
    multi_scale_deformable_attn_pytorch)

_USING_PARROTS = True
try:
    from parrots.autograd import gradcheck
except ImportError:
    from torch.autograd import gradcheck
    _USING_PARROTS = False


def test_forward_multi_scale_deformable_attn_pytorch():
    N, M, D = 1, 2, 2
    Lq, L, P = 2, 2, 2
    shapes = torch.as_tensor([(6, 4), (3, 2)], dtype=torch.long)
    S = sum([(H * W).item() for H, W in shapes])

    torch.manual_seed(3)
    value = torch.rand(N, S, M, D) * 0.01
    sampling_locations = torch.rand(N, Lq, M, L, P, 2)
    attention_weights = torch.rand(N, Lq, M, L, P) + 1e-5
    attention_weights /= attention_weights.sum(
        -1, keepdim=True).sum(
            -2, keepdim=True)

    multi_scale_deformable_attn_pytorch(value.double(), shapes,
                                        sampling_locations.double(),
                                        attention_weights.double()).detach()


@pytest.mark.skipif(
    not torch.cuda.is_available(), reason='requires CUDA support')
def test_forward_equal_with_pytorch_double():
    N, M, D = 1, 2, 2
    Lq, L, P = 2, 2, 2
    shapes = torch.as_tensor([(6, 4), (3, 2)], dtype=torch.long).cuda()
    level_start_index = torch.cat((shapes.new_zeros(
        (1, )), shapes.prod(1).cumsum(0)[:-1]))
    S = sum([(H * W).item() for H, W in shapes])

    torch.manual_seed(3)
    value = torch.rand(N, S, M, D).cuda() * 0.01
    sampling_locations = torch.rand(N, Lq, M, L, P, 2).cuda()
    attention_weights = torch.rand(N, Lq, M, L, P).cuda() + 1e-5
    attention_weights /= attention_weights.sum(
        -1, keepdim=True).sum(
            -2, keepdim=True)
    im2col_step = 2
    output_pytorch = multi_scale_deformable_attn_pytorch(
        value.double(), shapes, sampling_locations.double(),
        attention_weights.double()).detach().cpu()

    output_cuda = MultiScaleDeformableAttnFunction.apply(
        value.double(), shapes, level_start_index, sampling_locations.double(),
        attention_weights.double(), im2col_step).detach().cpu()
    assert torch.allclose(output_cuda, output_pytorch)
    max_abs_err = (output_cuda - output_pytorch).abs().max()
    max_rel_err = ((output_cuda - output_pytorch).abs() /
                   output_pytorch.abs()).max()
    assert max_abs_err < 1e-18
    assert max_rel_err < 1e-15


@pytest.mark.skipif(
    not torch.cuda.is_available(), reason='requires CUDA support')
def test_forward_equal_with_pytorch_float():
    N, M, D = 1, 2, 2
    Lq, L, P = 2, 2, 2
    shapes = torch.as_tensor([(6, 4), (3, 2)], dtype=torch.long).cuda()
    level_start_index = torch.cat((shapes.new_zeros(
        (1, )), shapes.prod(1).cumsum(0)[:-1]))
    S = sum([(H * W).item() for H, W in shapes])

    torch.manual_seed(3)
    value = torch.rand(N, S, M, D).cuda() * 0.01
    sampling_locations = torch.rand(N, Lq, M, L, P, 2).cuda()
    attention_weights = torch.rand(N, Lq, M, L, P).cuda() + 1e-5
    attention_weights /= attention_weights.sum(
        -1, keepdim=True).sum(
            -2, keepdim=True)
    im2col_step = 2
    output_pytorch = multi_scale_deformable_attn_pytorch(
        value, shapes, sampling_locations, attention_weights).detach().cpu()

    output_cuda = MultiScaleDeformableAttnFunction.apply(
        value, shapes, level_start_index, sampling_locations,
        attention_weights, im2col_step).detach().cpu()
    assert torch.allclose(output_cuda, output_pytorch, rtol=1e-2, atol=1e-3)
    max_abs_err = (output_cuda - output_pytorch).abs().max()
    max_rel_err = ((output_cuda - output_pytorch).abs() /
                   output_pytorch.abs()).max()
    assert max_abs_err < 1e-9
    assert max_rel_err < 1e-6


@pytest.mark.skipif(
    not torch.cuda.is_available(), reason='requires CUDA support')
@pytest.mark.parametrize('channels', [
    4,
    30,
    32,
    64,
    71,
    1025,
])
def test_gradient_numerical(channels,
                            grad_value=True,
                            grad_sampling_loc=True,
                            grad_attn_weight=True):

    N, M, _ = 1, 2, 2
    Lq, L, P = 2, 2, 2
    shapes = torch.as_tensor([(6, 4), (3, 2)], dtype=torch.long).cuda()
    level_start_index = torch.cat((shapes.new_zeros(
        (1, )), shapes.prod(1).cumsum(0)[:-1]))
    S = sum([(H * W).item() for H, W in shapes])

    value = torch.rand(N, S, M, channels).cuda() * 0.01
    sampling_locations = torch.rand(N, Lq, M, L, P, 2).cuda()
    attention_weights = torch.rand(N, Lq, M, L, P).cuda() + 1e-5
    attention_weights /= attention_weights.sum(
        -1, keepdim=True).sum(
            -2, keepdim=True)
    im2col_step = 2

    func = MultiScaleDeformableAttnFunction.apply

    value.requires_grad = grad_value
    sampling_locations.requires_grad = grad_sampling_loc
    attention_weights.requires_grad = grad_attn_weight
    if _USING_PARROTS:
        assert gradcheck(
            func, (value.double(), shapes, level_start_index,
                   sampling_locations.double(), attention_weights.double(),
                   im2col_step),
            no_grads=[shapes, level_start_index])
    else:
        assert gradcheck(func, (value.double(), shapes, level_start_index,
                                sampling_locations.double(),
                                attention_weights.double(), im2col_step))


def test_multiscale_deformable_attention():
    with pytest.raises(ValueError):
        # embed_dims must be divisible by num_heads,
        MultiScaleDeformableAttention(
            embed_dims=256,
            num_heads=7,
        )
    with pytest.raises(ValueError):
        # embed_dims must be divisible by num_heads,
        MultiScaleDeformableAttention(
            embed_dims=256,
            num_heads=7,
        )

    MultiScaleDeformableAttention(embed_dims=256, num_heads=8)