# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.
# --------------------------------------------------------
# References:
# PixArt: https://github.com/PixArt-alpha/PixArt-alpha
# Latte:  https://github.com/Vchitect/Latte
# DiT:    https://github.com/facebookresearch/DiT/tree/main
# GLIDE:  https://github.com/openai/glide-text2im
# MAE:    https://github.com/facebookresearch/mae/blob/main/models_mae.py
# --------------------------------------------------------

import math

import numpy as np
import torch
import torch.distributed as dist
import torch.nn as nn
import torch.nn.functional as F
import torch.utils.checkpoint
import xformers.ops
from einops import rearrange
from timm.models.vision_transformer import Mlp

from opensora.acceleration.communications import all_to_all, split_forward_gather_backward
from opensora.acceleration.parallel_states import get_sequence_parallel_group

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


def get_layernorm(hidden_size: torch.Tensor, eps: float, affine: bool, use_kernel: bool):
    if use_kernel:
        try:
            from apex.normalization import FusedLayerNorm

            return FusedLayerNorm(hidden_size, elementwise_affine=affine, eps=eps)
        except ImportError:
            raise RuntimeError("FusedLayerNorm not available. Please install apex.")
    else:
        return nn.LayerNorm(hidden_size, eps, elementwise_affine=affine)


def modulate(norm_func, x, shift, scale):
    # Suppose x is (B, N, D), shift is (B, D), scale is (B, D)
    dtype = x.dtype
    x = norm_func(x.to(torch.float32)).to(dtype)
    x = x * (scale.unsqueeze(1) + 1) + shift.unsqueeze(1)
    x = x.to(dtype)
    return x


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 = nn.LayerNorm,
        enable_flashattn: 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_flashattn = enable_flashattn

        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.attn_drop = nn.Dropout(attn_drop)
        self.proj = nn.Linear(dim, dim)
        self.proj_drop = nn.Dropout(proj_drop)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        B, N, C = x.shape
        qkv = self.qkv(x)
        qkv_shape = (B, N, 3, self.num_heads, self.head_dim)
        if self.enable_flashattn:
            qkv_permute_shape = (2, 0, 1, 3, 4)
        else:
            qkv_permute_shape = (2, 0, 3, 1, 4)
        qkv = qkv.view(qkv_shape).permute(qkv_permute_shape)
        q, k, v = qkv.unbind(0)
        q, k = self.q_norm(q), self.k_norm(k)
        if self.enable_flashattn:
            from flash_attn import flash_attn_func

            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 self.enable_flashattn:
            x = x.transpose(1, 2)
        x = x.reshape(x_output_shape)
        x = self.proj(x)
        x = self.proj_drop(x)
        return x


class SeqParallelAttention(Attention):
    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 = nn.LayerNorm,
        enable_flashattn: bool = False,
    ) -> None:
        super().__init__(
            dim=dim,
            num_heads=num_heads,
            qkv_bias=qkv_bias,
            qk_norm=qk_norm,
            attn_drop=attn_drop,
            proj_drop=proj_drop,
            norm_layer=norm_layer,
            enable_flashattn=enable_flashattn,
        )

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        B, N, C = x.shape  # for sequence parallel here, the N is a local sequence length
        qkv = self.qkv(x)
        qkv_shape = (B, N, 3, self.num_heads, self.head_dim)

        qkv = qkv.view(qkv_shape)

        sp_group = get_sequence_parallel_group()

        # apply all_to_all to gather sequence and split attention heads
        # [B, SUB_N, 3, NUM_HEAD, HEAD_DIM] -> [B, N, 3, NUM_HEAD_PER_DEVICE, HEAD_DIM]
        qkv = all_to_all(qkv, sp_group, scatter_dim=3, gather_dim=1)

        if self.enable_flashattn:
            qkv_permute_shape = (2, 0, 1, 3, 4)  # [3, B, N, NUM_HEAD_PER_DEVICE, HEAD_DIM]
        else:
            qkv_permute_shape = (2, 0, 3, 1, 4)  # [3, B, NUM_HEAD_PER_DEVICE, N, HEAD_DIM]
        qkv = qkv.permute(qkv_permute_shape)

        q, k, v = qkv.unbind(0)
        q, k = self.q_norm(q), self.k_norm(k)
        if self.enable_flashattn:
            from flash_attn import flash_attn_func

            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

        if not self.enable_flashattn:
            x = x.transpose(1, 2)

        # apply all to all to gather back attention heads and split sequence
        # [B, N, NUM_HEAD_PER_DEVICE, HEAD_DIM]  -> [B, SUB_N, NUM_HEAD, HEAD_DIM]
        x = all_to_all(x, sp_group, scatter_dim=1, gather_dim=2)

        # reshape outputs back to [B, N, C]
        x_output_shape = (B, N, C)
        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
        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, op=xformers.ops.fmha.MemoryEfficientAttentionFlashAttentionOp)

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


class SeqParallelMultiHeadCrossAttention(MultiHeadCrossAttention):
    def __init__(
        self,
        d_model,
        num_heads,
        attn_drop=0.0,
        proj_drop=0.0,
    ):
        super().__init__(d_model=d_model, num_heads=num_heads, attn_drop=attn_drop, proj_drop=proj_drop)

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

        # shape:
        # q, k, v: [B, SUB_N, NUM_HEADS, HEAD_DIM]
        q = self.q_linear(x).view(B, -1, self.num_heads, self.head_dim)
        kv = self.kv_linear(cond).view(B, -1, 2, self.num_heads, self.head_dim)
        k, v = kv.unbind(2)

        # apply all_to_all to gather sequence and split attention heads
        q = all_to_all(q, sp_group, scatter_dim=2, gather_dim=1)

        k = split_forward_gather_backward(k, get_sequence_parallel_group(), dim=2, grad_scale="down")
        v = split_forward_gather_backward(v, get_sequence_parallel_group(), dim=2, grad_scale="down")

        q = q.view(1, -1, self.num_heads // sp_size, self.head_dim)
        k = k.view(1, -1, self.num_heads // sp_size, self.head_dim)
        v = v.view(1, -1, self.num_heads // sp_size, self.head_dim)

        # compute attention
        attn_bias = None
        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)
        
        # apply all to all to gather back attention heads and scatter sequence
        x = x.view(B, -1, self.num_heads // sp_size, self.head_dim)
        x = all_to_all(x, sp_group, scatter_dim=1, gather_dim=2)

        # apply output projection
        x = x.view(B, -1, C)
        x = self.proj(x)
        x = self.proj_drop(x)
        return x


class FinalLayer(nn.Module):
    """
    The final layer of DiT.
    """

    def __init__(self, hidden_size, num_patch, out_channels):
        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.adaLN_modulation = nn.Sequential(nn.SiLU(), nn.Linear(hidden_size, 2 * hidden_size, bias=True))

    def forward(self, x, c):
        shift, scale = self.adaLN_modulation(c).chunk(2, dim=1)
        x = modulate(self.norm_final, x, shift, scale)
        x = self.linear(x)
        return x


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

    def __init__(self, hidden_size, num_patch, out_channels):
        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

    def forward(self, x, t):
        shift, scale = (self.scale_shift_table[None] + t[:, None]).chunk(2, dim=1)
        x = t2i_modulate(self.norm_final(x), shift, scale)
        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 LabelEmbedder(nn.Module):
    """
    Embeds class labels into vector representations. Also handles label dropout for classifier-free guidance.
    """

    def __init__(self, num_classes, hidden_size, dropout_prob):
        super().__init__()
        use_cfg_embedding = dropout_prob > 0
        self.embedding_table = nn.Embedding(num_classes + use_cfg_embedding, hidden_size)
        self.num_classes = num_classes
        self.dropout_prob = dropout_prob

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

    def forward(self, labels, train, force_drop_ids=None):
        use_dropout = self.dropout_prob > 0
        if (train and use_dropout) or (force_drop_ids is not None):
            labels = self.token_drop(labels, force_drop_ids)
        return self.embedding_table(labels)


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", nn.Parameter(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


# ===============================================
# Sine/Cosine Positional Embedding Functions
# ===============================================
# https://github.com/facebookresearch/mae/blob/main/util/pos_embed.py


def get_2d_sincos_pos_embed(embed_dim, grid_size, cls_token=False, extra_tokens=0, scale=1.0, base_size=None):
    """
    grid_size: int of the grid height and width
    return:
    pos_embed: [grid_size*grid_size, embed_dim] or [1+grid_size*grid_size, embed_dim] (w/ or w/o cls_token)
    """
    if not isinstance(grid_size, tuple):
        grid_size = (grid_size, grid_size)

    grid_h = np.arange(grid_size[0], dtype=np.float32) / scale
    grid_w = np.arange(grid_size[1], dtype=np.float32) / scale
    if base_size is not None:
        grid_h *= base_size / grid_size[0]
        grid_w *= base_size / grid_size[1]
    grid = np.meshgrid(grid_w, grid_h)  # here w goes first
    grid = np.stack(grid, axis=0)

    grid = grid.reshape([2, 1, grid_size[1], grid_size[0]])
    pos_embed = get_2d_sincos_pos_embed_from_grid(embed_dim, grid)
    if cls_token and extra_tokens > 0:
        pos_embed = np.concatenate([np.zeros([extra_tokens, embed_dim]), pos_embed], axis=0)
    return pos_embed


def get_2d_sincos_pos_embed_from_grid(embed_dim, grid):
    assert embed_dim % 2 == 0

    # use half of dimensions to encode grid_h
    emb_h = get_1d_sincos_pos_embed_from_grid(embed_dim // 2, grid[0])  # (H*W, D/2)
    emb_w = get_1d_sincos_pos_embed_from_grid(embed_dim // 2, grid[1])  # (H*W, D/2)

    emb = np.concatenate([emb_h, emb_w], axis=1)  # (H*W, D)
    return emb


def get_1d_sincos_pos_embed(embed_dim, length, scale=1.0):
    pos = np.arange(0, length)[..., None] / scale
    return get_1d_sincos_pos_embed_from_grid(embed_dim, pos)


def get_1d_sincos_pos_embed_from_grid(embed_dim, pos):
    """
    embed_dim: output dimension for each position
    pos: a list of positions to be encoded: size (M,)
    out: (M, D)
    """
    assert embed_dim % 2 == 0
    omega = np.arange(embed_dim // 2, dtype=np.float64)
    omega /= embed_dim / 2.0
    omega = 1.0 / 10000**omega  # (D/2,)

    pos = pos.reshape(-1)  # (M,)
    out = np.einsum("m,d->md", pos, omega)  # (M, D/2), outer product

    emb_sin = np.sin(out)  # (M, D/2)
    emb_cos = np.cos(out)  # (M, D/2)

    emb = np.concatenate([emb_sin, emb_cos], axis=1)  # (M, D)
    return emb
