# --------------------------------------------------------
# Adapted from JiT: https://github.com/LTH14/JiT/blob/main/model_jit.py
# References: SiT, Lightning-DiT (see upstream repo)
#
# Unconditional variant: no class labels; conditioning is time t only.
# In-context tokens use learnable positional embeddings only (no label embedding).
# --------------------------------------------------------
from __future__ import annotations

import math

import torch
import torch.nn as nn
import torch.nn.functional as F

try:
    from .jit_model_util import RMSNorm, VisionRotaryEmbeddingFast, get_2d_sincos_pos_embed
except ImportError:
    from jit_model_util import RMSNorm, VisionRotaryEmbeddingFast, get_2d_sincos_pos_embed


def modulate(x, shift, scale):
    return x * (1 + scale.unsqueeze(1)) + shift.unsqueeze(1)


class BottleneckPatchEmbed(nn.Module):
    """Image to patch embedding."""

    def __init__(
        self,
        img_size=224,
        patch_size=16,
        in_chans=3,
        pca_dim=768,
        embed_dim=768,
        bias=True,
    ):
        super().__init__()
        img_size = (img_size, img_size)
        patch_size = (patch_size, patch_size)
        num_patches = (img_size[1] // patch_size[1]) * (img_size[0] // patch_size[0])
        self.img_size = img_size
        self.patch_size = patch_size
        self.num_patches = num_patches

        self.proj1 = nn.Conv2d(in_chans, pca_dim, kernel_size=patch_size, stride=patch_size, bias=False)
        self.proj2 = nn.Conv2d(pca_dim, embed_dim, kernel_size=1, stride=1, bias=bias)

    def forward(self, x):
        b, c, h, w = x.shape
        assert h == self.img_size[0] and w == self.img_size[1], (
            f"Input image size ({h}*{w}) doesn't match model ({self.img_size[0]}*{self.img_size[1]})."
        )

        x = self.proj2(self.proj1(x)).flatten(2).transpose(1, 2)
        return x


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):
        half = dim // 2
        freqs = torch.exp(
            -math.log(max_period) * torch.arange(start=0, end=half, dtype=torch.float32, device=t.device) / half
        )
        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):
        t_freq = self.timestep_embedding(t, self.frequency_embedding_size)
        return self.mlp(t_freq)


def scaled_dot_product_attention(
    query: torch.Tensor,
    key: torch.Tensor,
    value: torch.Tensor,
    dropout_p: float = 0.0,
    training: bool = True,
) -> torch.Tensor:
    scale_factor = 1 / math.sqrt(query.size(-1))
    with torch.cuda.amp.autocast(enabled=False):
        attn_weight = query.float() @ key.float().transpose(-2, -1) * scale_factor
    attn_weight = torch.softmax(attn_weight, dim=-1)
    attn_weight = torch.dropout(attn_weight, dropout_p, train=training)
    return attn_weight @ value


class Attention(nn.Module):
    def __init__(self, dim, num_heads=8, qkv_bias=True, qk_norm=True, attn_drop=0.0, proj_drop=0.0):
        super().__init__()
        self.num_heads = num_heads
        head_dim = dim // num_heads

        self.q_norm = RMSNorm(head_dim) if qk_norm else nn.Identity()
        self.k_norm = RMSNorm(head_dim) if qk_norm else nn.Identity()

        self.qkv = nn.Linear(dim, dim * 3, bias=qkv_bias)
        self.attn_drop = nn.Dropout(attn_drop)
        self.proj = nn.Linear(dim, dim)
        self.proj_drop = nn.Dropout(proj_drop)

    def forward(self, x, rope):
        b, n, c = x.shape
        qkv = self.qkv(x).reshape(b, n, 3, self.num_heads, c // self.num_heads).permute(2, 0, 3, 1, 4)
        q, k, v = qkv[0], qkv[1], qkv[2]

        q = self.q_norm(q)
        k = self.k_norm(k)

        q = rope(q)
        k = rope(k)

        x = scaled_dot_product_attention(
            q,
            k,
            v,
            dropout_p=self.attn_drop.p if self.training else 0.0,
            training=self.training,
        )

        x = x.transpose(1, 2).reshape(b, n, c)

        x = self.proj(x)
        x = self.proj_drop(x)
        return x


class SwiGLUFFN(nn.Module):
    def __init__(self, dim: int, hidden_dim: int, drop=0.0, bias=True) -> None:
        super().__init__()
        hidden_dim = int(hidden_dim * 2 / 3)
        self.w12 = nn.Linear(dim, 2 * hidden_dim, bias=bias)
        self.w3 = nn.Linear(hidden_dim, dim, bias=bias)
        self.ffn_dropout = nn.Dropout(drop)

    def forward(self, x):
        x12 = self.w12(x)
        x1, x2 = x12.chunk(2, dim=-1)
        hidden = F.silu(x1) * x2
        return self.w3(self.ffn_dropout(hidden))


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

    def __init__(self, hidden_size, patch_size, out_channels):
        super().__init__()
        self.norm_final = RMSNorm(hidden_size)
        self.linear = nn.Linear(hidden_size, patch_size * patch_size * 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)
        return self.linear(x)


class JiTBlock(nn.Module):
    def __init__(self, hidden_size, num_heads, mlp_ratio=4.0, attn_drop=0.0, proj_drop=0.0):
        super().__init__()
        self.norm1 = RMSNorm(hidden_size, eps=1e-6)
        self.attn = Attention(
            hidden_size,
            num_heads=num_heads,
            qkv_bias=True,
            qk_norm=True,
            attn_drop=attn_drop,
            proj_drop=proj_drop,
        )
        self.norm2 = RMSNorm(hidden_size, eps=1e-6)
        mlp_hidden_dim = int(hidden_size * mlp_ratio)
        self.mlp = SwiGLUFFN(hidden_size, mlp_hidden_dim, drop=proj_drop)
        self.adaLN_modulation = nn.Sequential(nn.SiLU(), nn.Linear(hidden_size, 6 * hidden_size, bias=True))

    def forward(self, x, c, feat_rope=None):
        shift_msa, scale_msa, gate_msa, shift_mlp, scale_mlp, gate_mlp = self.adaLN_modulation(c).chunk(6, dim=-1)
        x = x + gate_msa.unsqueeze(1) * self.attn(
            modulate(self.norm1(x), shift_msa, scale_msa), rope=feat_rope
        )
        x = x + gate_mlp.unsqueeze(1) * self.mlp(modulate(self.norm2(x), shift_mlp, scale_mlp))
        return x


class JiT(nn.Module):
    """
    Just image Transformer — unconditional (time embedding only).
    """

    def __init__(
        self,
        input_size=256,
        patch_size=16,
        in_channels=3,
        hidden_size=1024,
        depth=24,
        num_heads=16,
        mlp_ratio=4.0,
        attn_drop=0.0,
        proj_drop=0.0,
        bottleneck_dim=128,
        in_context_len=32,
        in_context_start=8,
    ):
        super().__init__()
        self.in_channels = in_channels
        self.out_channels = in_channels
        self.patch_size = patch_size
        self.num_heads = num_heads
        self.hidden_size = hidden_size
        self.input_size = input_size
        self.in_context_len = in_context_len
        self.in_context_start = in_context_start

        self.t_embedder = TimestepEmbedder(hidden_size)

        self.x_embedder = BottleneckPatchEmbed(
            input_size, patch_size, in_channels, bottleneck_dim, hidden_size, bias=True
        )

        num_patches = self.x_embedder.num_patches
        self.pos_embed = nn.Parameter(torch.zeros(1, num_patches, hidden_size), requires_grad=False)

        if self.in_context_len > 0:
            self.in_context_posemb = nn.Parameter(torch.zeros(1, self.in_context_len, hidden_size))
            torch.nn.init.normal_(self.in_context_posemb, std=0.02)

        half_head_dim = hidden_size // num_heads // 2
        hw_seq_len = input_size // patch_size
        self.feat_rope = VisionRotaryEmbeddingFast(
            dim=half_head_dim, pt_seq_len=hw_seq_len, num_cls_token=0
        )
        self.feat_rope_incontext = VisionRotaryEmbeddingFast(
            dim=half_head_dim, pt_seq_len=hw_seq_len, num_cls_token=self.in_context_len
        )

        self.blocks = nn.ModuleList(
            [
                JiTBlock(
                    hidden_size,
                    num_heads,
                    mlp_ratio=mlp_ratio,
                    attn_drop=attn_drop if (depth // 4 * 3 > i >= depth // 4) else 0.0,
                    proj_drop=proj_drop if (depth // 4 * 3 > i >= depth // 4) else 0.0,
                )
                for i in range(depth)
            ]
        )

        self.final_layer = FinalLayer(hidden_size, patch_size, self.out_channels)

        self.initialize_weights()

    def initialize_weights(self):
        def _basic_init(module):
            if isinstance(module, nn.Linear):
                torch.nn.init.xavier_uniform_(module.weight)
                if module.bias is not None:
                    nn.init.constant_(module.bias, 0)

        self.apply(_basic_init)

        pos_embed = get_2d_sincos_pos_embed(self.pos_embed.shape[-1], int(self.x_embedder.num_patches**0.5))
        self.pos_embed.data.copy_(torch.from_numpy(pos_embed).float().unsqueeze(0))

        w1 = self.x_embedder.proj1.weight.data
        nn.init.xavier_uniform_(w1.view([w1.shape[0], -1]))
        w2 = self.x_embedder.proj2.weight.data
        nn.init.xavier_uniform_(w2.view([w2.shape[0], -1]))
        nn.init.constant_(self.x_embedder.proj2.bias, 0)

        nn.init.normal_(self.t_embedder.mlp[0].weight, std=0.02)
        nn.init.normal_(self.t_embedder.mlp[2].weight, std=0.02)

        for block in self.blocks:
            nn.init.constant_(block.adaLN_modulation[-1].weight, 0)
            nn.init.constant_(block.adaLN_modulation[-1].bias, 0)

        nn.init.constant_(self.final_layer.adaLN_modulation[-1].weight, 0)
        nn.init.constant_(self.final_layer.adaLN_modulation[-1].bias, 0)

        nn.init.constant_(self.final_layer.linear.weight, 0)
        nn.init.constant_(self.final_layer.linear.bias, 0)

    def unpatchify(self, x, p):
        c = self.out_channels
        h = w = int(x.shape[1] ** 0.5)
        assert h * w == x.shape[1]

        x = x.reshape(shape=(x.shape[0], h, w, p, p, c))
        x = torch.einsum("nhwpqc->nchpwq", x)
        imgs = x.reshape(shape=(x.shape[0], c, h * p, h * p))
        return imgs

    def forward(self, x: torch.Tensor, t: torch.Tensor) -> torch.Tensor:
        """
        Args:
            x: (N, C, H, W)
            t: (N,) timesteps in [0, 1] (or arbitrary floats, as in upstream)
        Returns:
            (N, C, H, W) predicted velocity / noise depending on training objective
        """
        c_emb = self.t_embedder(t)

        x = self.x_embedder(x)
        x = x + self.pos_embed

        for i, block in enumerate(self.blocks):
            if self.in_context_len > 0 and i == self.in_context_start:
                b = x.shape[0]
                in_context_tokens = self.in_context_posemb.expand(b, self.in_context_len, -1)
                x = torch.cat([in_context_tokens, x], dim=1)
            x = block(x, c_emb, self.feat_rope if i < self.in_context_start else self.feat_rope_incontext)

        x = x[:, self.in_context_len :]

        x = self.final_layer(x, c_emb)
        return self.unpatchify(x, self.patch_size)


def JiT_B_16(**kwargs):
    return JiT(
        depth=12,
        hidden_size=768,
        num_heads=12,
        bottleneck_dim=128,
        in_context_len=32,
        in_context_start=4,
        patch_size=16,
        **kwargs,
    )


def JiT_B_32(**kwargs):
    return JiT(
        depth=12,
        hidden_size=768,
        num_heads=12,
        bottleneck_dim=128,
        in_context_len=32,
        in_context_start=4,
        patch_size=32,
        **kwargs,
    )


def JiT_L_16(**kwargs):
    return JiT(
        depth=24,
        hidden_size=1024,
        num_heads=16,
        bottleneck_dim=128,
        in_context_len=32,
        in_context_start=8,
        patch_size=16,
        **kwargs,
    )


def JiT_L_32(**kwargs):
    return JiT(
        depth=24,
        hidden_size=1024,
        num_heads=16,
        bottleneck_dim=128,
        in_context_len=32,
        in_context_start=8,
        patch_size=32,
        **kwargs,
    )


def JiT_H_16(**kwargs):
    return JiT(
        depth=32,
        hidden_size=1280,
        num_heads=16,
        bottleneck_dim=256,
        in_context_len=32,
        in_context_start=10,
        patch_size=16,
        **kwargs,
    )


def JiT_H_32(**kwargs):
    return JiT(
        depth=32,
        hidden_size=1280,
        num_heads=16,
        bottleneck_dim=256,
        in_context_len=32,
        in_context_start=10,
        patch_size=32,
        **kwargs,
    )


JiT_models = {
    "JiT-B/16": JiT_B_16,
    "JiT-B/32": JiT_B_32,
    "JiT-L/16": JiT_L_16,
    "JiT-L/32": JiT_L_32,
    "JiT-H/16": JiT_H_16,
    "JiT-H/32": JiT_H_32,
}