# Copyright (c) Facebook, Inc. and its affiliates.
# All rights reserved.

# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.

import torch
import torch.nn as nn
from functools import partial

from timm.models.vision_transformer import VisionTransformer, _cfg

__all__ = [
    'vit_small', 
    'vit_base',
    'vit_large',
    'vit_huge',
]


class VisionTransformerMoCo(VisionTransformer):
    def __init__(self, stop_grad_conv1=False, **kwargs):
        super().__init__(**kwargs)
        self.stop_grad_conv1 = stop_grad_conv1

    def forward_features(self, x):
        x = self.patch_embed(x)
        # Add stop-grad after conv1
        if self.stop_grad_conv1:
            x = x.detach()
        cls_token = self.cls_token.expand(x.shape[0], -1, -1)
        if self.dist_token is None:
            x = torch.cat((cls_token, x), dim=1)
        else:
            x = torch.cat((cls_token, self.dist_token.expand(x.shape[0], -1, -1), x), dim=1)
        x = self.pos_drop(x + self.pos_embed)
        x = self.blocks(x)
        x = self.norm(x)
        if self.dist_token is None:
            return self.pre_logits(x[:, 0])
        else:
            return x[:, 0], x[:, 1]


def build_pos_embedding_2d_sincos(grid_size, hidden_dim, temperature):
    grid_h = torch.arange(grid_size, dtype=torch.float32)
    grid_w = torch.arange(grid_size, dtype=torch.float32)
    grid_w, grid_h = torch.meshgrid(grid_w, grid_h)

    assert hidden_dim % 4 == 0, 'Hidden dimension must be an even number for position embedding.'
    pos_dim = hidden_dim // 4
    omega = torch.arange(pos_dim, dtype=torch.float32) / pos_dim
    omega = 1. / (temperature**omega)

    out_w = torch.einsum('m,d->md', [grid_w.flatten(), omega])
    out_h = torch.einsum('m,d->md', [grid_h.flatten(), omega])

    pos_emb = torch.cat([torch.sin(out_w), torch.cos(out_w), torch.sin(out_h), torch.cos(out_h)], dim=1)[:, None, :]

    p = torch.zeros([1, 1, hidden_dim], dtype=torch.float32)
    pos_emb = torch.cat([p, pos_emb], dim=0)
    return pos_emb


def vit_small(**kwargs):
    model = VisionTransformerMoCo(
        patch_size=16, embed_dim=384, depth=12, num_heads=12, mlp_ratio=4, qkv_bias=True,
        norm_layer=partial(nn.LayerNorm, eps=1e-6), **kwargs)
    model.default_cfg = _cfg()
    return model


def vit_base(**kwargs):
    model = VisionTransformerMoCo(
        patch_size=16, embed_dim=768, depth=12, num_heads=12, mlp_ratio=4, qkv_bias=True,
        norm_layer=partial(nn.LayerNorm, eps=1e-6), **kwargs)
    model.default_cfg = _cfg()
    return model


def vit_large(**kwargs):
    model = VisionTransformerMoCo(
        patch_size=16, embed_dim=1024, depth=24, num_heads=16, mlp_ratio=4, qkv_bias=True,
        norm_layer=partial(nn.LayerNorm, eps=1e-6), **kwargs)
    model.default_cfg = _cfg()
    return model


def vit_huge(**kwargs):
    model = VisionTransformerMoCo(
        patch_size=16, embed_dim=1280, depth=32, num_heads=16, mlp_ratio=4, qkv_bias=True,
        norm_layer=partial(nn.LayerNorm, eps=1e-6), **kwargs)
    model.default_cfg = _cfg()
    return model