import torch
import torch.nn as nn
from einops import rearrange

def conv_1x1_bn(inp, oup):
    return nn.Sequential(
        nn.Conv2d(inp, oup, 1, 1, 0, bias=False),
        nn.BatchNorm2d(oup),
        nn.SiLU()
    )

def conv_nxn_bn(inp, oup, kernel_size=3, stride=1):
    return nn.Sequential(
        nn.Conv2d(inp, oup, kernel_size, stride, 1, bias=False),
        nn.BatchNorm2d(oup),
        nn.SiLU()
    )

class PreNorm(nn.Module):
    def __init__(self, dim, fn):
        super().__init__()
        self.norm = nn.LayerNorm(dim)
        self.fn = fn
    def forward(self, x, **kwargs):
        return self.fn(self.norm(x), **kwargs)

class FeedForward(nn.Module):
    def __init__(self, dim, hidden_dim, dropout=0.):
        super().__init__()
        self.net = nn.Sequential(
            nn.Linear(dim, hidden_dim),
            nn.SiLU(),
            nn.Dropout(dropout),
            nn.Linear(hidden_dim, dim),
            nn.Dropout(dropout)
        )
    def forward(self, x):
        return self.net(x)

class Attention(nn.Module):
    def __init__(self, dim, heads=8, dim_head=64, dropout=0.):
        super().__init__()
        inner_dim = dim_head * heads
        project_out = not (heads == 1 and dim_head == dim)

        self.heads = heads
        self.scale = dim_head ** -0.5

        self.attend = nn.Softmax(dim = -1)
        self.to_qkv = nn.Linear(dim, inner_dim * 3, bias = False)

        self.to_out = nn.Sequential(
            nn.Linear(inner_dim, dim),
            nn.Dropout(dropout)
        ) if project_out else nn.Identity()

    def forward(self, x):
        qkv = self.to_qkv(x).chunk(3, dim=-1)
        q, k, v = map(lambda t: rearrange(t, 'b p n (h d) -> b p h n d', h = self.heads), qkv)

        dots = torch.matmul(q, k.transpose(-1, -2)) * self.scale
        attn = self.attend(dots)
        out = torch.matmul(attn, v)
        out = rearrange(out, 'b p h n d -> b p n (h d)')
        return self.to_out(out)

class Transformer(nn.Module):
    def __init__(self, dim, depth, heads, dim_head, mlp_dim, dropout=0.):
        super().__init__()
        self.layers = nn.ModuleList([])
        for _ in range(depth):
            self.layers.append(nn.ModuleList([
                PreNorm(dim, Attention(dim, heads, dim_head, dropout)),
                PreNorm(dim, FeedForward(dim, mlp_dim, dropout))
            ]))
    def forward(self, x):
        for attn, ff in self.layers:
            x = attn(x) + x
            x = ff(x) + x
        return x

class MV2Block(nn.Module):
    def __init__(self, inp, oup, stride=1, expansion=4):
        super().__init__()
        self.stride = stride
        hidden_dim = int(inp * expansion)
        self.use_res_connect = self.stride == 1 and inp == oup

        if expansion == 1:
            self.conv = nn.Sequential(
                nn.Conv2d(hidden_dim, hidden_dim, 3, stride, 1, groups=hidden_dim, bias=False),
                nn.BatchNorm2d(hidden_dim),
                nn.SiLU(),
                nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
                nn.BatchNorm2d(oup),
            )
        else:
            self.conv = nn.Sequential(
                nn.Conv2d(inp, hidden_dim, 1, 1, 0, bias=False),
                nn.BatchNorm2d(hidden_dim),
                nn.SiLU(),
                nn.Conv2d(hidden_dim, hidden_dim, 3, stride, 1, groups=hidden_dim, bias=False),
                nn.BatchNorm2d(hidden_dim),
                nn.SiLU(),
                nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
                nn.BatchNorm2d(oup),
            )

    def forward(self, x):
        if self.use_res_connect:
            return x + self.conv(x)
        else:
            return self.conv(x)

class MobileViTBlock(nn.Module):
    def __init__(self, dim, depth, channel, kernel_size, patch_size, mlp_dim, dropout=0.):
        super().__init__()
        self.ph, self.pw = patch_size

        self.conv1 = conv_nxn_bn(channel, channel, kernel_size)
        self.conv2 = conv_1x1_bn(channel, dim)

        self.transformer = Transformer(dim, depth, 1, 32, mlp_dim, dropout)

        self.conv3 = conv_1x1_bn(dim, channel)
        self.conv4 = conv_nxn_bn(2 * channel, channel, kernel_size)
    
    def forward(self, x):
        y = x.clone()

        x = self.conv1(x)
        x = self.conv2(x)
        
        _, _, h, w = x.shape
        x = rearrange(x, 'b d (h ph) (w pw) -> b (ph pw) (h w) d', ph=self.ph, pw=self.pw)
        x = self.transformer(x)
        x = rearrange(x, 'b (ph pw) (h w) d -> b d (h ph) (w pw)', h=h//self.ph, w=w//self.pw, ph=self.ph, pw=self.pw)

        x = self.conv3(x)
        x = torch.cat((x, y), 1)
        x = self.conv4(x)
        return x

class MobileViTv3_Small(nn.Module):
    def __init__(self, image_size=(224, 224), num_classes=10):
        super().__init__()
        ih, iw = image_size
        ph, pw = 2, 2
        
        dims = [144, 192, 240]
        channels = [16, 32, 64, 64, 96, 96, 128, 128, 160, 160, 640]
        
        self.conv1 = conv_nxn_bn(3, channels[0], stride=2)

        self.mv2 = nn.ModuleList([])
        self.mv2.append(MV2Block(channels[0], channels[1], 1, 4))
        self.mv2.append(MV2Block(channels[1], channels[2], 2, 4))
        self.mv2.append(MV2Block(channels[2], channels[3], 1, 4))
        self.mv2.append(MV2Block(channels[3], channels[4], 2, 4))
        
        self.mvit = nn.ModuleList([])
        self.mvit.append(MobileViTBlock(dims[0], 2, channels[5], 3, (ph, pw), int(dims[0]*2)))
        
        self.mv2_2 = nn.ModuleList([])
        self.mv2_2.append(MV2Block(channels[5], channels[6], 2, 4))
        
        self.mvit_2 = nn.ModuleList([])
        self.mvit_2.append(MobileViTBlock(dims[1], 4, channels[7], 3, (ph, pw), int(dims[1]*2)))
        
        self.mv2_3 = nn.ModuleList([])
        self.mv2_3.append(MV2Block(channels[7], channels[8], 2, 4))
        
        self.mvit_3 = nn.ModuleList([])
        self.mvit_3.append(MobileViTBlock(dims[2], 3, channels[9], 3, (ph, pw), int(dims[2]*2)))
        
        self.conv2 = conv_1x1_bn(channels[9], channels[10])
        self.pool = nn.AdaptiveAvgPool2d((1, 1))
        self.fc = nn.Linear(channels[10], num_classes)

    def forward(self, x):
        x = self.conv1(x)
        for conv in self.mv2: x = conv(x)
        for m in self.mvit: x = m(x)
        for conv in self.mv2_2: x = conv(x)
        for m in self.mvit_2: x = m(x)
        for conv in self.mv2_3: x = conv(x)
        for m in self.mvit_3: x = m(x)
        x = self.conv2(x)
        x = self.pool(x).view(-1, x.shape[1])
        return self.fc(x)