import torch
import torch.nn as nn
import torch.nn.functional as F
from timm.models.layers import DropPath

class BiMultiHeadAttention(nn.Module):
    def __init__(self, v_dim, l_dim, embed_dim, num_heads, dropout=0.1, cfg=None):
        super(BiMultiHeadAttention, self).__init__()

        self.embed_dim = embed_dim
        self.num_heads = num_heads
        self.head_dim = embed_dim // num_heads
        self.v_dim = v_dim
        self.l_dim = l_dim

        assert (
            self.head_dim * self.num_heads == self.embed_dim
        ), f"embed_dim must be divisible by num_heads (got `embed_dim`: {self.embed_dim} and `num_heads`: {self.num_heads})."
        self.scale = self.head_dim ** (-0.5)
        self.dropout = dropout

        self.v_proj = nn.Linear(self.v_dim, self.embed_dim)
        self.l_proj = nn.Linear(self.l_dim, self.embed_dim)
        self.values_l_proj = nn.Linear(self.l_dim, self.embed_dim)

        self.out_v_proj = nn.Linear(self.embed_dim, self.v_dim)

        self.stable_softmax_2d = True
        self.clamp_min_for_underflow = True
        self.clamp_max_for_overflow = True

        self._reset_parameters()

    def _shape(self, tensor: torch.Tensor, seq_len: int, bsz: int):
        return tensor.view(bsz, seq_len, self.num_heads, self.head_dim).transpose(1, 2).contiguous()

    def _reset_parameters(self):
        nn.init.xavier_uniform_(self.v_proj.weight)
        self.v_proj.bias.data.fill_(0)
        nn.init.xavier_uniform_(self.l_proj.weight)
        self.l_proj.bias.data.fill_(0)
        nn.init.xavier_uniform_(self.values_l_proj.weight)
        self.values_l_proj.bias.data.fill_(0)
        nn.init.xavier_uniform_(self.out_v_proj.weight)
        self.out_v_proj.bias.data.fill_(0)

    def forward(self, v, l, attention_mask_v=None, attention_mask_l=None):
        bsz, tgt_len, _ = v.size()

        query_states = self.v_proj(v) * self.scale
        key_states = self._shape(self.l_proj(l), -1, bsz)
        value_l_states = self._shape(self.values_l_proj(l), -1, bsz)

        proj_shape = (bsz * self.num_heads, -1, self.head_dim)
        query_states = self._shape(query_states, tgt_len, bsz).view(*proj_shape)
        key_states = key_states.view(*proj_shape)
        value_l_states = value_l_states.view(*proj_shape)

        src_len = key_states.size(1)
        attn_weights = torch.bmm(query_states, key_states.transpose(1, 2))  # bs*nhead, nimg, ntxt

        if attn_weights.size() != (bsz * self.num_heads, tgt_len, src_len):
            raise ValueError(
                f"Attention weights should be of size {(bsz * self.num_heads, tgt_len, src_len)}, but is {attn_weights.size()}"
            )

        if self.stable_softmax_2d:
            attn_weights = attn_weights - attn_weights.max()

        if self.clamp_min_for_underflow:
            attn_weights = torch.clamp(
                attn_weights, min=-50000
            )  # Do not increase -50000, data type half has quite limited range
        if self.clamp_max_for_overflow:
            attn_weights = torch.clamp(
                attn_weights, max=50000
            )  # Do not increase 50000, data type half has quite limited range

        attn_weights_v = attn_weights.softmax(dim=-1)
        attn_probs_v = F.dropout(attn_weights_v, p=self.dropout, training=self.training)
        attn_output_v = torch.bmm(attn_probs_v, value_l_states)
        if attn_output_v.size() != (bsz * self.num_heads, tgt_len, self.head_dim):
            raise ValueError(
                f"`attn_output_v` should be of size {(bsz, self.num_heads, tgt_len, self.head_dim)}, but is {attn_output_v.size()}"
            )

        attn_output_v = attn_output_v.view(bsz, self.num_heads, tgt_len, self.head_dim)
        attn_output_v = attn_output_v.transpose(1, 2)
        attn_output_v = attn_output_v.reshape(bsz, tgt_len, self.embed_dim)
        attn_output_v = self.out_v_proj(attn_output_v)

        return attn_output_v


# Bi-Direction MHA (text->image, image->text)
class BiAttentionBlock(nn.Module):
    def __init__(
        self,
        v_dim,
        l_dim,
        embed_dim,
        num_heads,
        dropout=0.1,
        drop_path=0.0,
        cfg=None,
    ):
        super(BiAttentionBlock, self).__init__()

        # pre layer norm
        self.layer_norm_v = nn.LayerNorm(v_dim)
        self.layer_norm_l = nn.LayerNorm(l_dim)
        self.attn = BiMultiHeadAttention(
            v_dim=v_dim, l_dim=l_dim, embed_dim=embed_dim, num_heads=num_heads, dropout=dropout
        )

        # add layer scale for training stability
        self.drop_path = DropPath(drop_path) if drop_path > 0.0 else nn.Identity()

    def forward(self, v, l, attention_mask_v=None, attention_mask_l=None):
        v = self.layer_norm_v(v)
        l = self.layer_norm_l(l)
        delta_v = self.attn(
            v, l, attention_mask_v=attention_mask_v, attention_mask_l=attention_mask_l
        )
        delta_v = self.drop_path(delta_v)

        return delta_v