# Adapted from OpenSora

# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.
# --------------------------------------------------------
# References:
# OpenSora: https://github.com/hpcaitech/Open-Sora
# --------------------------------------------------------

import functools
import math
from typing import Optional

import torch
import torch.nn as nn
import torch.nn.functional as F
import torch.utils.checkpoint
from einops import rearrange
from timm.models.vision_transformer import Mlp

approx_gelu = lambda: nn.GELU(approximate="tanh")


class LlamaRMSNorm(nn.Module):
    def __init__(self, hidden_size, eps=1e-6):
        """
        LlamaRMSNorm is equivalent to T5LayerNorm
        """
        super().__init__()
        self.weight = nn.Parameter(torch.ones(hidden_size))
        self.variance_epsilon = eps

    def forward(self, hidden_states):
        input_dtype = hidden_states.dtype
        hidden_states = hidden_states.to(torch.float32)
        variance = hidden_states.pow(2).mean(-1, keepdim=True)
        hidden_states = hidden_states * torch.rsqrt(variance + self.variance_epsilon)
        return self.weight * hidden_states.to(input_dtype)


def get_layernorm(hidden_size: torch.Tensor, eps: float, affine: bool):
    return nn.LayerNorm(hidden_size, eps, elementwise_affine=affine)


def t2i_modulate(x, shift, scale):
    return x * (1 + scale) + shift


# ===============================================
# General-purpose Layers
# ===============================================


class PatchEmbed3D(nn.Module):
    """Video to Patch Embedding.

    Args:
        patch_size (int): Patch token size. Default: (2,4,4).
        in_chans (int): Number of input video channels. Default: 3.
        embed_dim (int): Number of linear projection output channels. Default: 96.
        norm_layer (nn.Module, optional): Normalization layer. Default: None
    """

    def __init__(
        self,
        patch_size=(2, 4, 4),
        in_chans=3,
        embed_dim=96,
        norm_layer=None,
        flatten=True,
    ):
        super().__init__()
        self.patch_size = patch_size
        self.flatten = flatten

        self.in_chans = in_chans
        self.embed_dim = embed_dim

        self.proj = nn.Conv3d(in_chans, embed_dim, kernel_size=patch_size, stride=patch_size)
        if norm_layer is not None:
            self.norm = norm_layer(embed_dim)
        else:
            self.norm = None

    def forward(self, x):
        """Forward function."""
        # padding
        _, _, D, H, W = x.size()
        if W % self.patch_size[2] != 0:
            x = F.pad(x, (0, self.patch_size[2] - W % self.patch_size[2]))
        if H % self.patch_size[1] != 0:
            x = F.pad(x, (0, 0, 0, self.patch_size[1] - H % self.patch_size[1]))
        if D % self.patch_size[0] != 0:
            x = F.pad(x, (0, 0, 0, 0, 0, self.patch_size[0] - D % self.patch_size[0]))

        x = self.proj(x)  # (B C T H W)
        if self.norm is not None:
            D, Wh, Ww = x.size(2), x.size(3), x.size(4)
            x = x.flatten(2).transpose(1, 2)
            x = self.norm(x)
            x = x.transpose(1, 2).view(-1, self.embed_dim, D, Wh, Ww)
        if self.flatten:
            x = x.flatten(2).transpose(1, 2)  # BCTHW -> BNC
        return x


class Attention(nn.Module):
    def __init__(
        self,
        dim: int,
        num_heads: int = 8,
        qkv_bias: bool = False,
        qk_norm: bool = False,
        attn_drop: float = 0.0,
        proj_drop: float = 0.0,
        norm_layer: nn.Module = LlamaRMSNorm,
        enable_flash_attn: bool = False,
        rope=None,
        qk_norm_legacy: bool = False,
    ) -> None:
        super().__init__()
        assert dim % num_heads == 0, "dim should be divisible by num_heads"
        self.dim = dim
        self.num_heads = num_heads
        self.head_dim = dim // num_heads
        self.scale = self.head_dim**-0.5
        self.enable_flash_attn = enable_flash_attn

        self.qkv = nn.Linear(dim, dim * 3, bias=qkv_bias)
        self.q_norm = norm_layer(self.head_dim) if qk_norm else nn.Identity()
        self.k_norm = norm_layer(self.head_dim) if qk_norm else nn.Identity()
        self.qk_norm_legacy = qk_norm_legacy
        self.attn_drop = nn.Dropout(attn_drop)
        self.proj = nn.Linear(dim, dim)
        self.proj_drop = nn.Dropout(proj_drop)

        self.rope = False
        if rope is not None:
            self.rope = True
            self.rotary_emb = rope

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        B, N, C = x.shape
        # flash attn is not memory efficient for small sequences, this is empirical
        enable_flash_attn = self.enable_flash_attn and (N > B)
        qkv = self.qkv(x)
        qkv_shape = (B, N, 3, self.num_heads, self.head_dim)

        qkv = qkv.view(qkv_shape).permute(2, 0, 3, 1, 4)
        q, k, v = qkv.unbind(0)
        if self.qk_norm_legacy:
            # WARNING: this may be a bug
            if self.rope:
                q = self.rotary_emb(q)
                k = self.rotary_emb(k)
            q, k = self.q_norm(q), self.k_norm(k)
        else:
            q, k = self.q_norm(q), self.k_norm(k)
            if self.rope:
                q = self.rotary_emb(q)
                k = self.rotary_emb(k)

        if enable_flash_attn:
            from flash_attn import flash_attn_func

            # (B, #heads, N, #dim) -> (B, N, #heads, #dim)
            q = q.permute(0, 2, 1, 3)
            k = k.permute(0, 2, 1, 3)
            v = v.permute(0, 2, 1, 3)
            x = flash_attn_func(
                q,
                k,
                v,
                dropout_p=self.attn_drop.p if self.training else 0.0,
                softmax_scale=self.scale,
            )
        else:
            dtype = q.dtype
            q = q * self.scale
            attn = q @ k.transpose(-2, -1)  # translate attn to float32
            attn = attn.to(torch.float32)
            attn = attn.softmax(dim=-1)
            attn = attn.to(dtype)  # cast back attn to original dtype
            attn = self.attn_drop(attn)
            x = attn @ v

        x_output_shape = (B, N, C)
        if not enable_flash_attn:
            x = x.transpose(1, 2)
        x = x.reshape(x_output_shape)
        x = self.proj(x)
        x = self.proj_drop(x)
        return x


class MultiHeadCrossAttention(nn.Module):
    def __init__(self, d_model, num_heads, attn_drop=0.0, proj_drop=0.0):
        super(MultiHeadCrossAttention, self).__init__()
        assert d_model % num_heads == 0, "d_model must be divisible by num_heads"

        self.d_model = d_model
        self.num_heads = num_heads
        self.head_dim = d_model // num_heads

        self.q_linear = nn.Linear(d_model, d_model)
        self.kv_linear = nn.Linear(d_model, d_model * 2)
        self.attn_drop = nn.Dropout(attn_drop)
        self.proj = nn.Linear(d_model, d_model)
        self.proj_drop = nn.Dropout(proj_drop)

    def forward(self, x, cond, mask=None):
        # query/value: img tokens; key: condition; mask: if padding tokens
        B, N, C = x.shape

        q = self.q_linear(x).view(1, -1, self.num_heads, self.head_dim)
        kv = self.kv_linear(cond).view(1, -1, 2, self.num_heads, self.head_dim)
        k, v = kv.unbind(2)

        attn_bias = None
        # TODO: support torch computation
        import xformers.ops

        if mask is not None:
            attn_bias = xformers.ops.fmha.BlockDiagonalMask.from_seqlens([N] * B, mask)
        x = xformers.ops.memory_efficient_attention(q, k, v, p=self.attn_drop.p, attn_bias=attn_bias)

        x = x.view(B, -1, C)
        x = self.proj(x)
        x = self.proj_drop(x)
        return x


class T2IFinalLayer(nn.Module):
    """
    The final layer of PixArt.
    """

    def __init__(self, hidden_size, num_patch, out_channels, d_t=None, d_s=None):
        super().__init__()
        self.norm_final = nn.LayerNorm(hidden_size, elementwise_affine=False, eps=1e-6)
        self.linear = nn.Linear(hidden_size, num_patch * out_channels, bias=True)
        self.scale_shift_table = nn.Parameter(torch.randn(2, hidden_size) / hidden_size**0.5)
        self.out_channels = out_channels
        self.d_t = d_t
        self.d_s = d_s

    def t_mask_select(self, x_mask, x, masked_x, T, S):
        # x: [B, (T, S), C]
        # mased_x: [B, (T, S), C]
        # x_mask: [B, T]
        x = rearrange(x, "B (T S) C -> B T S C", T=T, S=S)
        masked_x = rearrange(masked_x, "B (T S) C -> B T S C", T=T, S=S)
        x = torch.where(x_mask[:, :, None, None], x, masked_x)
        x = rearrange(x, "B T S C -> B (T S) C")
        return x

    def forward(self, x, t, x_mask=None, t0=None, T=None, S=None):
        if T is None:
            T = self.d_t
        if S is None:
            S = self.d_s
        shift, scale = (self.scale_shift_table[None] + t[:, None]).chunk(2, dim=1)
        x = t2i_modulate(self.norm_final(x), shift, scale)
        if x_mask is not None:
            shift_zero, scale_zero = (self.scale_shift_table[None] + t0[:, None]).chunk(2, dim=1)
            x_zero = t2i_modulate(self.norm_final(x), shift_zero, scale_zero)
            x = self.t_mask_select(x_mask, x, x_zero, T, S)
        x = self.linear(x)
        return x


# ===============================================
# Embedding Layers for Timesteps and Class Labels
# ===============================================


class TimestepEmbedder(nn.Module):
    """
    Embeds scalar timesteps into vector representations.
    """

    def __init__(self, hidden_size, frequency_embedding_size=256):
        super().__init__()
        self.mlp = nn.Sequential(
            nn.Linear(frequency_embedding_size, hidden_size, bias=True),
            nn.SiLU(),
            nn.Linear(hidden_size, hidden_size, bias=True),
        )
        self.frequency_embedding_size = frequency_embedding_size

    @staticmethod
    def timestep_embedding(t, dim, max_period=10000):
        """
        Create sinusoidal timestep embeddings.
        :param t: a 1-D Tensor of N indices, one per batch element.
                          These may be fractional.
        :param dim: the dimension of the output.
        :param max_period: controls the minimum frequency of the embeddings.
        :return: an (N, D) Tensor of positional embeddings.
        """
        # https://github.com/openai/glide-text2im/blob/main/glide_text2im/nn.py
        half = dim // 2
        freqs = torch.exp(-math.log(max_period) * torch.arange(start=0, end=half, dtype=torch.float32) / half)
        freqs = freqs.to(device=t.device)
        args = t[:, None].float() * freqs[None]
        embedding = torch.cat([torch.cos(args), torch.sin(args)], dim=-1)
        if dim % 2:
            embedding = torch.cat([embedding, torch.zeros_like(embedding[:, :1])], dim=-1)
        return embedding

    def forward(self, t, dtype):
        t_freq = self.timestep_embedding(t, self.frequency_embedding_size)
        if t_freq.dtype != dtype:
            t_freq = t_freq.to(dtype)
        t_emb = self.mlp(t_freq)
        return t_emb


class SizeEmbedder(TimestepEmbedder):
    """
    Embeds scalar timesteps into vector representations.
    """

    def __init__(self, hidden_size, frequency_embedding_size=256):
        super().__init__(hidden_size=hidden_size, frequency_embedding_size=frequency_embedding_size)
        self.mlp = nn.Sequential(
            nn.Linear(frequency_embedding_size, hidden_size, bias=True),
            nn.SiLU(),
            nn.Linear(hidden_size, hidden_size, bias=True),
        )
        self.frequency_embedding_size = frequency_embedding_size
        self.outdim = hidden_size

    def forward(self, s, bs):
        if s.ndim == 1:
            s = s[:, None]
        assert s.ndim == 2
        if s.shape[0] != bs:
            s = s.repeat(bs // s.shape[0], 1)
            assert s.shape[0] == bs
        b, dims = s.shape[0], s.shape[1]
        s = rearrange(s, "b d -> (b d)")
        s_freq = self.timestep_embedding(s, self.frequency_embedding_size).to(self.dtype)
        s_emb = self.mlp(s_freq)
        s_emb = rearrange(s_emb, "(b d) d2 -> b (d d2)", b=b, d=dims, d2=self.outdim)
        return s_emb

    @property
    def dtype(self):
        return next(self.parameters()).dtype


class CaptionEmbedder(nn.Module):
    """
    Embeds class labels into vector representations. Also handles label dropout for classifier-free guidance.
    """

    def __init__(
        self,
        in_channels,
        hidden_size,
        uncond_prob,
        act_layer=nn.GELU(approximate="tanh"),
        token_num=120,
    ):
        super().__init__()
        self.y_proj = Mlp(
            in_features=in_channels,
            hidden_features=hidden_size,
            out_features=hidden_size,
            act_layer=act_layer,
            drop=0,
        )
        self.register_buffer(
            "y_embedding",
            torch.randn(token_num, in_channels) / in_channels**0.5,
        )
        self.uncond_prob = uncond_prob

    def token_drop(self, caption, force_drop_ids=None):
        """
        Drops labels to enable classifier-free guidance.
        """
        if force_drop_ids is None:
            drop_ids = torch.rand(caption.shape[0]).cuda() < self.uncond_prob
        else:
            drop_ids = force_drop_ids == 1
        caption = torch.where(drop_ids[:, None, None, None], self.y_embedding, caption)
        return caption

    def forward(self, caption, train, force_drop_ids=None):
        if train:
            assert caption.shape[2:] == self.y_embedding.shape
        use_dropout = self.uncond_prob > 0
        if (train and use_dropout) or (force_drop_ids is not None):
            caption = self.token_drop(caption, force_drop_ids)
        caption = self.y_proj(caption)
        return caption


class PositionEmbedding2D(nn.Module):
    def __init__(self, dim: int) -> None:
        super().__init__()
        self.dim = dim
        assert dim % 4 == 0, "dim must be divisible by 4"
        half_dim = dim // 2
        inv_freq = 1.0 / (10000 ** (torch.arange(0, half_dim, 2).float() / half_dim))
        self.register_buffer("inv_freq", inv_freq, persistent=False)

    def _get_sin_cos_emb(self, t: torch.Tensor):
        out = torch.einsum("i,d->id", t, self.inv_freq)
        emb_cos = torch.cos(out)
        emb_sin = torch.sin(out)
        return torch.cat((emb_sin, emb_cos), dim=-1)

    @functools.lru_cache(maxsize=512)
    def _get_cached_emb(
        self,
        device: torch.device,
        dtype: torch.dtype,
        h: int,
        w: int,
        scale: float = 1.0,
        base_size: Optional[int] = None,
    ):
        grid_h = torch.arange(h, device=device) / scale
        grid_w = torch.arange(w, device=device) / scale
        if base_size is not None:
            grid_h *= base_size / h
            grid_w *= base_size / w
        grid_h, grid_w = torch.meshgrid(
            grid_w,
            grid_h,
            indexing="ij",
        )  # here w goes first
        grid_h = grid_h.t().reshape(-1)
        grid_w = grid_w.t().reshape(-1)
        emb_h = self._get_sin_cos_emb(grid_h)
        emb_w = self._get_sin_cos_emb(grid_w)
        return torch.concat([emb_h, emb_w], dim=-1).unsqueeze(0).to(dtype)

    def forward(
        self,
        x: torch.Tensor,
        h: int,
        w: int,
        scale: Optional[float] = 1.0,
        base_size: Optional[int] = None,
    ) -> torch.Tensor:
        return self._get_cached_emb(x.device, x.dtype, h, w, scale, base_size)