[tab] jasmine/genie.py (python)
from typing import Dict, Optional

import einops
import jax
import jax.numpy as jnp
import flax.nnx as nnx
import orbax.checkpoint as ocp

from models.dynamics import DynamicsMaskGIT, DynamicsCausal, DynamicsDiffusion
from models.lam import LatentActionModel
from models.tokenizer import TokenizerVQVAE, TokenizerMAE


class Genie(nnx.Module):
    """Genie model"""

    def __init__(
        self,
        in_dim: int,
        tokenizer_dim: int,
        tokenizer_ffn_dim: int,
        latent_patch_dim: int,
        num_patch_latents: int,
        patch_size: int,
        tokenizer_type: str,
        tokenizer_num_blocks: int,
        tokenizer_num_heads: int,
        lam_dim: int,
        lam_ffn_dim: int,
        latent_action_dim: int,
        num_actions: int,
        lam_patch_size: int,
        lam_num_blocks: int,
        lam_num_heads: int,
        lam_co_train: bool,
        use_gt_actions: bool,
        dyna_type: str,
        dyna_dim: int,
        dyna_ffn_dim: int,
        dyna_num_blocks: int,
        dyna_num_heads: int,
        param_dtype: jnp.dtype,
        dtype: jnp.dtype,
        use_flash_attention: bool,
        decode: bool,
        rngs: nnx.Rngs,
        dropout: float = 0.0,
        mask_limit: float = 0.0,
        diffusion_denoise_steps: int = 0,
    ):
        # --- Tokenizer ---
        self.in_dim = in_dim
        self.tokenizer_dim = tokenizer_dim
        self.tokenizer_ffn_dim = tokenizer_ffn_dim
        self.latent_patch_dim = latent_patch_dim
        self.num_patch_latents = num_patch_latents
        self.patch_size = patch_size
        self.tokenizer_num_blocks = tokenizer_num_blocks
        self.tokenizer_num_heads = tokenizer_num_heads
        # --- LAM ---
        self.lam_dim = lam_dim
        self.lam_ffn_dim = lam_ffn_dim
        self.latent_action_dim = latent_action_dim
        self.num_actions = num_actions
        self.lam_patch_size = lam_patch_size
        self.lam_num_blocks = lam_num_blocks
        self.lam_num_heads = lam_num_heads
        self.lam_co_train = lam_co_train
        self.use_gt_actions = use_gt_actions
        # --- Dynamics ---
        self.dyna_type = dyna_type
        self.dyna_dim = dyna_dim
        self.dyna_ffn_dim = dyna_ffn_dim
        self.dyna_num_blocks = dyna_num_blocks
        self.dyna_num_heads = dyna_num_heads
        self.param_dtype = param_dtype
        self.dtype = dtype
        self.use_flash_attention = use_flash_attention
        self.dropout = dropout
        self.mask_limit = mask_limit
        self.diffusion_denoise_steps = diffusion_denoise_steps
        self.decode = decode
        self.tokenizer_type = tokenizer_type
        if self.tokenizer_type == "vqvae":
            self.tokenizer = TokenizerVQVAE(
                in_dim=self.in_dim,
                model_dim=self.tokenizer_dim,
                ffn_dim=self.tokenizer_ffn_dim,
                latent_dim=self.latent_patch_dim,
                num_latents=self.num_patch_latents,
                patch_size=self.patch_size,
                num_blocks=self.tokenizer_num_blocks,
                num_heads=self.tokenizer_num_heads,
                dropout=0.0,
                codebook_dropout=0.0,
                param_dtype=self.param_dtype,
                dtype=self.dtype,
                use_flash_attention=self.use_flash_attention,
                rngs=rngs,
            )
        elif self.tokenizer_type == "mae":
            self.tokenizer = TokenizerMAE(
                in_dim=self.in_dim,
                model_dim=self.tokenizer_dim,
                ffn_dim=self.tokenizer_ffn_dim,
                latent_dim=self.latent_patch_dim,
                num_latents=self.num_patch_latents,
                patch_size=self.patch_size,
                num_blocks=self.tokenizer_num_blocks,
                num_heads=self.tokenizer_num_heads,
                dropout=0.0,
                max_mask_ratio=0.0,
                param_dtype=self.param_dtype,
                dtype=self.dtype,
                use_flash_attention=self.use_flash_attention,
                rngs=rngs,
            )
        else:
            raise ValueError(f"Invalid tokenizer type: {self.tokenizer_type}")
        if self.use_gt_actions:
            self.action_embed = nnx.Embed(
                self.num_actions, self.latent_action_dim, rngs=rngs
            )
            self.lam = None
        else:
            self.lam = LatentActionModel(
                in_dim=self.in_dim,
                model_dim=self.lam_dim,
                ffn_dim=self.lam_ffn_dim,
                latent_dim=self.latent_patch_dim,
                num_latents=self.num_actions,
                patch_size=self.lam_patch_size,
                num_blocks=self.lam_num_blocks,
                num_heads=self.lam_num_heads,
                dropout=0.0,
                codebook_dropout=0.0,
                param_dtype=self.param_dtype,
                dtype=self.dtype,
                use_flash_attention=self.use_flash_attention,
                rngs=rngs,
            )
            self.action_embed = None
        if self.dyna_type == "maskgit":
            self.dynamics = DynamicsMaskGIT(
                model_dim=self.dyna_dim,
                ffn_dim=self.dyna_ffn_dim,
                num_latents=self.num_patch_latents,
                latent_action_dim=self.latent_action_dim,
                num_blocks=self.dyna_num_blocks,
                num_heads=self.dyna_num_heads,
                dropout=self.dropout,
                mask_limit=self.mask_limit,
                param_dtype=self.param_dtype,
                dtype=self.dtype,
                use_flash_attention=self.use_flash_attention,
                rngs=rngs,
            )
        elif self.dyna_type == "causal":
            self.dynamics = DynamicsCausal(
                model_dim=self.dyna_dim,
                ffn_dim=self.dyna_ffn_dim,
                num_latents=self.num_patch_latents,
                latent_action_dim=self.latent_action_dim,
                num_blocks=self.dyna_num_blocks,
                num_heads=self.dyna_num_heads,
                dropout=self.dropout,
                param_dtype=self.param_dtype,
                dtype=self.dtype,
                use_flash_attention=self.use_flash_attention,
                decode=decode,
                rngs=rngs,
            )
        elif self.dyna_type == "diffusion":
            assert (
                self.diffusion_denoise_steps > 0
            ), "diffusion_denoise_steps must be greater than 0 when using the diffusion backend"
            self.dynamics = DynamicsDiffusion(
                input_dim=self.latent_patch_dim,
                model_dim=self.dyna_dim,
                ffn_dim=self.dyna_ffn_dim,
                out_dim=self.latent_patch_dim,
                num_latents=self.num_patch_latents,
                latent_action_dim=self.latent_action_dim,
                num_blocks=self.dyna_num_blocks,
                num_heads=self.dyna_num_heads,
                denoise_steps=self.diffusion_denoise_steps,
                dropout=self.dropout,
                param_dtype=self.param_dtype,
                dtype=self.dtype,
                use_flash_attention=self.use_flash_attention,
                decode=decode,
                rngs=rngs,
            )
        else:
            raise ValueError(f"Invalid dynamics type: {self.dyna_type}")

    def __call__(
        self,
        batch: Dict[str, jax.Array],
    ) -> Dict[str, jax.Array]:
        videos_BTHWC = batch["videos"]
        H, W = videos_BTHWC.shape[2:4]
        latent_actions_BTm11L = None
        action_embeddings_BTm11L = None
        if self.use_gt_actions:
            assert self.action_embed is not None
            action_indices_E = None
            action_embeddings_BT1L = self.action_embed(batch["actions"]).reshape(
                *batch["actions"].shape[:2], 1, self.latent_action_dim
            )
            action_embeddings_BTm11L = action_embeddings_BT1L[:, :-1]
        else:
            assert self.lam is not None
            lam_outputs = self.lam.vq_encode(videos_BTHWC, training=False)
            z_q_BTm11L = lam_outputs["z_q"]
            action_indices_E = lam_outputs["indices"]
            latent_actions_BTm11L = jax.lax.cond(
                self.lam_co_train,
                lambda: z_q_BTm11L,
                lambda: jax.lax.stop_gradient(z_q_BTm11L),
            )

        if self.dyna_type == "diffusion":
            rng, _rng = jax.random.split(batch["rng"])
            tokenizer_outputs = self.tokenizer.mask_and_encode(videos_BTHWC, rng)
            token_latents_BTNL = tokenizer_outputs["z"]
            outputs = dict(
                token_latents=token_latents_BTNL,
                latent_actions=(
                    action_embeddings_BTm11L
                    if self.use_gt_actions
                    else latent_actions_BTm11L
                ),
                rng=rng,
            )
            x_pred, t = self.dynamics(outputs)
            outputs["x_pred"] = x_pred
            outputs["x_gt"] = token_latents_BTNL
            outputs["signal_level"] = t
            outputs["recon"] = self.tokenizer.decode(x_pred, video_hw=(H, W))
            return outputs

        tokenizer_outputs = self.tokenizer.vq_encode(videos_BTHWC, training=False)
        token_indices_BTN = tokenizer_outputs["indices"]
        outputs = dict(
            video_tokens=jax.lax.stop_gradient(token_indices_BTN),
            latent_actions=(
                action_embeddings_BTm11L
                if self.use_gt_actions
                else latent_actions_BTm11L
            ),
        )
        outputs["mask_rng"] = batch["rng"]
        dyna_logits_BTNV, dyna_mask = self.dynamics(outputs)
        outputs["token_logits"] = dyna_logits_BTNV
        outputs["mask"] = dyna_mask
        mle_indices_BTN = jnp.argmax(outputs["token_logits"], axis=-1)
        outputs["recon"] = self.tokenizer.decode(mle_indices_BTN, (H, W))
        if action_indices_E is not None:
            outputs["lam_indices"] = action_indices_E
        return outputs

    def sample(
        self,
        batch: Dict[str, jax.Array],
        seq_len: int,
        temperature: float = 1,
        sample_argmax: bool = False,
        maskgit_steps: int = 25,
        diffusion_steps: int = 64,
        window_size: Optional[int] = None,
    ) -> tuple[jax.Array, jax.Array]:
        if self.dyna_type == "maskgit":
            return self.sample_maskgit(
                batch, seq_len, maskgit_steps, temperature, sample_argmax
            )
        elif self.dyna_type == "causal":
            return self.sample_causal(batch, seq_len, temperature, sample_argmax)
        elif self.dyna_type == "diffusion":
            return self.sample_diffusion(batch, seq_len, diffusion_steps, window_size)
        else:
            raise ValueError(f"Dynamics model type unknown: {self.dyna_type}")

    def sample_maskgit(
        self,
        batch: Dict[str, jax.Array],
        seq_len: int,
        steps: int = 25,
        temperature: float = 1,
        sample_argmax: bool = False,
    ) -> tuple[jax.Array, jax.Array]:
        """
        Autoregressively samples up to `seq_len` future frames, following Figure 8 of the paper.

        - Input frames are tokenized once.
        - Future frames are generated autoregressively in token space.
        - All frames are detokenized in a single pass.

        Note:
        - For interactive or step-wise sampling, detokenization should occur after each action.
        - To maintain consistent tensor shapes across timesteps, all current and future frames are decoded at every step.
        - Temporal causal structure is preserved by
            a) reapplying the mask before each decoding step.
            b) a temporal causal mask is applied within each ST-transformer block.

        Dimension keys:
            B: batch size
            T: number of input (conditioning) frames
            N: number of patches per frame
            M: model dimension
            S: sequence length
            H: height
            W: width
            E: B * (S - 1)
            P: S * N
        """
        assert isinstance(self.dynamics, DynamicsMaskGIT)
        # --- Encode videos and actions ---
        videos_BTHWC = batch["videos"]
        tokenizer_out = self.tokenizer.vq_encode(videos_BTHWC, training=False)
        token_idxs_BTN = tokenizer_out["indices"]
        B, T, N = token_idxs_BTN.shape
        pad_shape = (B, seq_len - T, N)
        pad = jnp.zeros(pad_shape, dtype=token_idxs_BTN.dtype)
        token_idxs_BSN = jnp.concatenate([token_idxs_BTN, pad], axis=1)
        init_logits_BSNV = jnp.zeros(
            shape=(*token_idxs_BSN.shape, self.num_patch_latents)
        )
        if self.use_gt_actions:
            assert self.action_embed is not None
            latent_actions_BT1L = self.action_embed(batch["actions"]).reshape(
                *batch["actions"].shape[:2], 1, self.latent_action_dim
            )
            latent_actions_BTm11L = latent_actions_BT1L[:, :-1]
            action_tokens_EL = latent_actions_BTm11L.reshape(-1, self.latent_action_dim)
        else:
            assert self.lam is not None
            latent_actions_E = batch["latent_actions"]
            action_tokens_EL = self.lam.vq.get_codes(latent_actions_E)

        # --- Extract submodule state ---
        dynamics_state = nnx.state(self.dynamics)

        @nnx.scan(in_axes=(nnx.Carry, 0), out_axes=nnx.Carry)
        def maskgit_step_fn(
            carry: tuple[jax.Array, jax.Array, jax.Array, jax.Array, jax.Array],
            step: jax.Array,
        ) -> tuple[jax.Array, jax.Array, jax.Array, jax.Array, jax.Array]:
            rng, token_idxs_BSN, logits_BSNV, mask_BSN, action_tokens_EL = carry
            S, N = token_idxs_BSN.shape[1:]
            L = action_tokens_EL.shape[-1]

            # We need to reconstruct the submodule inside scan body to prevent trace context mismatches
            dynamics_maskgit = DynamicsMaskGIT(
                model_dim=self.dyna_dim,
                ffn_dim=self.dyna_ffn_dim,
                num_latents=self.num_patch_latents,
                latent_action_dim=self.latent_action_dim,
                num_blocks=self.dyna_num_blocks,
                num_heads=self.dyna_num_heads,
                dropout=self.dropout,
                mask_limit=self.mask_limit,
                param_dtype=self.param_dtype,
                dtype=self.dtype,
                use_flash_attention=self.use_flash_attention,
                rngs=nnx.Rngs(0),
            )
            nnx.update(dynamics_maskgit, dynamics_state)

            # --- Construct + encode video ---
            vid_embed_BSNM = dynamics_maskgit.patch_embed(token_idxs_BSN)
            mask_token_111M = dynamics_maskgit.mask_token.value
            mask_expanded_BSN1 = mask_BSN[..., None]
            vid_embed_BSNM = jnp.where(
                mask_expanded_BSN1, mask_token_111M, vid_embed_BSNM
            )

            # --- Predict transition ---
            action_tokens_BSm1L = jnp.reshape(action_tokens_EL, (B, S - 1, L))
            act_embed_BSm1M = dynamics_maskgit.action_up(action_tokens_BSm1L)
            act_embed_BSM = jnp.pad(act_embed_BSm1M, ((0, 0), (1, 0), (0, 0)))
            act_embed_BS1M = jnp.reshape(
                act_embed_BSM, (B, S, 1, act_embed_BSM.shape[-1])
            )
            vid_embed_BSNp1M = jnp.concatenate([act_embed_BS1M, vid_embed_BSNM], axis=2)
            unmasked_ratio = jnp.cos(jnp.pi * (step + 1) / (steps * 2))
            step_temp = temperature * (1.0 - unmasked_ratio)
            final_logits_BSNp1V = (
                dynamics_maskgit.transformer(vid_embed_BSNp1M) / step_temp
            )
            final_logits_BSNV = final_logits_BSNp1V[:, :, 1:]

            # --- Sample new tokens for final frame ---
            if sample_argmax:
                sampled_token_idxs_BSN = jnp.argmax(final_logits_BSNV, axis=-1)
            else:
                rng, _rng = jax.random.split(rng)
                sampled_token_idxs_BSN = jax.random.categorical(_rng, final_logits_BSNV)
            gather_fn = jax.vmap(jax.vmap(jax.vmap(lambda x, y: x[y])))
            final_token_probs_BSN = gather_fn(
                jax.nn.softmax(final_logits_BSNV), sampled_token_idxs_BSN
            )
            final_token_probs_BSN += ~mask_BSN
            # Update masked tokens and logits only
            token_idxs_BSN = jnp.where(mask_BSN, sampled_token_idxs_BSN, token_idxs_BSN)
            logits_BSNV = jnp.where(
                jnp.expand_dims(mask_BSN, -1), final_logits_BSNV, logits_BSNV
            )

            # --- Update mask ---
            num_unmasked_tokens = jnp.round(N * (1.0 - unmasked_ratio)).astype(int)
            final_token_probs_flat_BP = einops.rearrange(
                final_token_probs_BSN, "b s n -> b (s n)"
            )
            idx_mask_P = (
                jnp.arange(final_token_probs_flat_BP.shape[-1])
                <= N - num_unmasked_tokens
            )
            sorted_idxs_BP = jnp.argsort(final_token_probs_flat_BP, axis=-1)
            mask_update_fn = jax.vmap(lambda msk, ids: msk.at[ids].set(idx_mask_P))
            mask_flat_BP = einops.rearrange(mask_BSN, "b s n -> b (s n)")
            new_mask_flat_BP = mask_update_fn(mask_flat_BP, sorted_idxs_BP)
            new_mask_BSN = einops.rearrange(new_mask_flat_BP, "b (s n) -> b s n", n=N)

            new_carry = (
                rng,
                token_idxs_BSN,
                logits_BSNV,
                new_mask_BSN,
                action_tokens_EL,
            )
            return new_carry

        @nnx.scan(in_axes=(nnx.Carry, 0), out_axes=nnx.Carry)
        def generation_step_fn(
            carry: tuple[jax.Array, jax.Array, jax.Array], step_t: jax.Array
        ) -> tuple[jax.Array, jax.Array, jax.Array]:
            rng, current_token_idxs_BSN, current_logits_BSNV = carry
            rng, step_rng = jax.random.split(rng)

            # Mask current frame (i.e., t == step_t)
            mask_S = jnp.arange(seq_len) == step_t
            mask_BSN = jnp.broadcast_to(mask_S[None, :, None], (B, seq_len, N)).astype(
                bool
            )
            masked_token_idxs_BSN = current_token_idxs_BSN * ~mask_BSN
            masked_logits_BSNV = current_logits_BSNV * jnp.expand_dims(~mask_BSN, -1)

            # --- Initialize and run MaskGIT loop ---
            init_carry_maskgit = (
                step_rng,
                masked_token_idxs_BSN,
                masked_logits_BSNV,
                mask_BSN,
                action_tokens_EL,
            )
            final_carry_maskgit = maskgit_step_fn(init_carry_maskgit, jnp.arange(steps))
            updated_token_idxs_BSN = final_carry_maskgit[1]
            updated_logits_BSNV = final_carry_maskgit[2]
            new_carry = (rng, updated_token_idxs_BSN, updated_logits_BSNV)
            return new_carry

        # --- Run the autoregressive generation using jax.lax.scan ---
        initial_carry = (batch["rng"], token_idxs_BSN, init_logits_BSNV)
        timesteps_to_scan = jnp.arange(T, seq_len)
        final_carry = generation_step_fn(initial_carry, timesteps_to_scan)
        final_token_idxs_BSN = final_carry[1]
        final_logits_BSNV = final_carry[2]

        # --- Decode all tokens at once at the end ---
        H, W = batch["videos"].shape[2:4]
        final_frames_BSHWC = self.tokenizer.decode(
            final_token_idxs_BSN,
            video_hw=(H, W),
        )
        return final_frames_BSHWC, final_logits_BSNV

    def sample_causal(
        self,
        batch: Dict[str, jax.Array],
        seq_len: int,
        temperature: float = 1,
        sample_argmax: bool = False,
    ) -> tuple[jax.Array, jax.Array]:
        """
        Autoregressively samples up to `seq_len` future frames, following Figure 8 of the paper.

        - Input frames are tokenized once.
        - Future frames are generated autoregressively in token space.
        - All frames are detokenized in a single pass.

        Note:
        - For interactive or step-wise sampling, detokenization should occur after each action.
        - To maintain consistent tensor shapes across timesteps, all current and future frames are decoded at every step.
        - Temporal causal structure is preserved by
            a) reapplying the mask before each decoding step.
            b) a temporal causal mask is applied within each ST-transformer block.

        Dimension keys:
            B: batch size
            T: number of input (conditioning) frames
            N: number of patches per frame
            M: model dimension
            S: sequence length
            H: height
            W: width
            E: B * (S - 1)
        """
        assert isinstance(self.dynamics, DynamicsCausal)
        # --- Encode videos and actions ---
        videos_BTHWC = batch["videos"]
        tokenizer_out = self.tokenizer.vq_encode(videos_BTHWC, training=False)
        token_idxs_BTN = tokenizer_out["indices"]
        B, T, N = token_idxs_BTN.shape
        pad_shape = (B, seq_len - T, N)
        pad = jnp.zeros(pad_shape, dtype=token_idxs_BTN.dtype)
        token_idxs_BSN = jnp.concatenate([token_idxs_BTN, pad], axis=1)
        logits_BSNV = jnp.zeros((*token_idxs_BSN.shape, self.num_patch_latents))
        dynamics_state = nnx.state(self.dynamics)

        if self.use_gt_actions:
            assert self.action_embed is not None
            latent_actions_BT1L = self.action_embed(batch["actions"]).reshape(
                *batch["actions"].shape[:2], 1, self.latent_action_dim
            )
            latent_actions_BTm11L = latent_actions_BT1L[:, :-1]
            action_tokens_EL = latent_actions_BTm11L.reshape(-1, self.latent_action_dim)
        else:
            assert self.lam is not None
            latent_actions_E = batch["latent_actions"]
            action_tokens_EL = self.lam.vq.get_codes(latent_actions_E)

        @nnx.scan(in_axes=(nnx.Carry, 0), out_axes=nnx.Carry)
        def causal_step_fn(
            carry: tuple[jax.Array, jax.Array, jax.Array, jax.Array, jax.Array],
            step_n: jax.Array,
        ) -> tuple[jax.Array, jax.Array, jax.Array, jax.Array, jax.Array]:
            rng, token_idxs_BSN, logits_BSNV, action_tokens_EL, step_t = carry
            S, N = token_idxs_BSN.shape[1:]
            L = action_tokens_EL.shape[-1]

            # We need to reconstruct the submodule inside scan body to prevent trace context mismatches
            dynamics_causal = DynamicsCausal(
                model_dim=self.dyna_dim,
                ffn_dim=self.dyna_ffn_dim,
                num_latents=self.num_patch_latents,
                latent_action_dim=self.latent_action_dim,
                num_blocks=self.dyna_num_blocks,
                num_heads=self.dyna_num_heads,
                dropout=self.dropout,
                param_dtype=self.param_dtype,
                dtype=self.dtype,
                use_flash_attention=self.use_flash_attention,
                decode=self.decode,
                rngs=nnx.Rngs(0),
            )
            nnx.update(dynamics_causal, dynamics_state)

            # --- Construct + encode video ---
            vid_embed_BSNM = dynamics_causal.patch_embed(token_idxs_BSN)

            # --- Predict transition ---
            action_tokens_BSm1L = jnp.reshape(action_tokens_EL, (B, S - 1, L))
            act_embed_BSm1M = dynamics_causal.action_up(action_tokens_BSm1L)
            act_embed_BSM = jnp.pad(act_embed_BSm1M, ((0, 0), (1, 0), (0, 0)))
            act_embed_BS1M = jnp.reshape(
                act_embed_BSM, (B, S, 1, act_embed_BSM.shape[-1])
            )
            vid_embed_BSNp1M = jnp.concatenate([act_embed_BS1M, vid_embed_BSNM], axis=2)
            final_logits_BTNp1V = (
                dynamics_causal.transformer(vid_embed_BSNp1M, (step_t, step_n))
                / temperature
            )
            final_logits_BV = final_logits_BTNp1V[:, step_t, step_n, :]

            # --- Sample new tokens for final frame ---
            if sample_argmax:
                sampled_token_idxs_B = jnp.argmax(final_logits_BV, axis=-1)
            else:
                rng, _rng = jax.random.split(rng)
                sampled_token_idxs_B = jax.random.categorical(_rng, final_logits_BV)
            # Update next tokens only
            token_idxs_BSN = token_idxs_BSN.at[:, step_t, step_n].set(
                sampled_token_idxs_B
            )
            logits_BSNV = logits_BSNV.at[:, step_t, step_n].set(final_logits_BV)

            new_carry = (rng, token_idxs_BSN, logits_BSNV, action_tokens_EL, step_t)
            return new_carry

        @nnx.scan(in_axes=(nnx.Carry, 0), out_axes=nnx.Carry)
        def generation_step_fn(
            carry: tuple[jax.Array, jax.Array, jax.Array], step_t: jax.Array
        ) -> tuple[jax.Array, jax.Array, jax.Array]:
            rng, current_token_idxs_BSN, current_logits_BSNV = carry
            rng, step_rng = jax.random.split(rng)

            # --- Initialize and run causal loop ---
            init_carry_causal = (
                step_rng,
                current_token_idxs_BSN,
                current_logits_BSNV,
                action_tokens_EL,
                step_t,
            )
            final_carry_causal = causal_step_fn(init_carry_causal, jnp.arange(N))
            updated_token_idxs_BSN = final_carry_causal[1]
            updated_logits_BSNV = final_carry_causal[2]
            new_carry = (rng, updated_token_idxs_BSN, updated_logits_BSNV)
            return new_carry

        # --- Run the autoregressive generation using jax.lax.scan ---
        initial_carry = (batch["rng"], token_idxs_BSN, logits_BSNV)
        timesteps_to_scan = jnp.arange(T, seq_len)
        final_carry = generation_step_fn(initial_carry, timesteps_to_scan)
        final_token_idxs_BSN = final_carry[1]
        final_logits_BSNV = final_carry[2]

        # --- Decode all tokens at once at the end ---
        H, W = batch["videos"].shape[2:4]
        final_frames_BSHWC = self.tokenizer.decode(
            final_token_idxs_BSN,
            video_hw=(H, W),
        )
        return final_frames_BSHWC, final_logits_BSNV

    def sample_diffusion(
        self,
        batch: Dict[str, jax.Array],
        seq_len: int,
        diffusion_steps: int,
        window_size: Optional[int] = None,
    ) -> tuple[jax.Array, jax.Array]:
        assert isinstance(self.dynamics, DynamicsDiffusion)
        # --- Encode videos and actions ---
        videos_BTHWC = batch["videos"]
        H, W = videos_BTHWC.shape[2:4]
        window_size = window_size or seq_len
        rng, _rng_mask, _rng_noise_window, _rng_noise_full = jax.random.split(
            batch["rng"], 4
        )
        tokenizer_outputs = self.tokenizer.mask_and_encode(videos_BTHWC, _rng_mask)
        token_latents_BTNL = tokenizer_outputs["z"]
        B, T, N, L = token_latents_BTNL.shape
        pad_shape_window = (B, min(window_size, seq_len) - T, N, L)
        pad_window = jax.random.normal(_rng_noise_window, pad_shape_window)
        token_latents_BSNL = jnp.concatenate([token_latents_BTNL, pad_window], axis=1)
        pad_shape_full = (B, seq_len - T, N, L)
        pad_full = jax.random.normal(_rng_noise_full, pad_shape_full)
        token_latents_BFNL = jnp.concatenate([token_latents_BTNL, pad_full], axis=1)

        if self.use_gt_actions:
            assert self.action_embed is not None
            latent_actions_BT1L = self.action_embed(batch["actions"]).reshape(
                *batch["actions"].shape[:2], 1, self.latent_action_dim
            )
            latent_actions_BTm11L = latent_actions_BT1L[:, :-1]
            action_tokens_EL = latent_actions_BTm11L.reshape(-1, self.latent_action_dim)
        else:
            assert self.lam is not None
            latent_actions_E = batch["latent_actions"]
            action_tokens_EL = self.lam.vq.get_codes(latent_actions_E)

        action_tokens_BSm1L = jnp.reshape(action_tokens_EL, (B, seq_len - 1, -1))
        act_embed_BSL = jnp.pad(action_tokens_BSm1L, ((0, 0), (1, 0), (0, 0)))
        act_embed_BSM = self.dynamics.action_up(act_embed_BSL)

        delta_t = 1.0 / diffusion_steps

        @nnx.scan(in_axes=(nnx.Carry, 0), out_axes=nnx.Carry)
        def denoise_step_fn(carry, denoise_step: jax.Array) -> jax.Array:
            tok_latents_BSNL, frame_i = carry

            # align actions with sliding window of frames
            act_embed_window_BSM, frame_i_window = nnx.cond(
                frame_i < window_size,
                lambda: (act_embed_BSM[:, :window_size], frame_i),
                lambda: (
                    jax.lax.dynamic_slice(
                        act_embed_BSM,
                        (0, frame_i - window_size + 1, 0),
                        (B, window_size, act_embed_BSM.shape[-1]),
                    ),
                    window_size - 1,
                ),
            )

            act_embed_window_BSM = act_embed_window_BSM.at[:, 0].set(0)

            t = denoise_step / diffusion_steps

            # TODO mihir: corrupt the context frames like in Dreamer 4 section 3.2
            t_vector = jnp.ones((B, min(window_size, seq_len)))
            t_vector = t_vector.at[:, frame_i_window].set(t)

            dt_flow = jnp.log2(diffusion_steps).astype(jnp.int32)
            dt_base = (
                jnp.ones((B, min(window_size, seq_len)), dtype=jnp.int32) * dt_flow
            )  # Smallest dt.

            v_pred_BSNL = self.dynamics.diffusion_transformer(
                tok_latents_BSNL, t_vector, dt_base, act_embed_window_BSM
            )
            tok_latents_BNL = (
                tok_latents_BSNL[:, frame_i_window]
                + v_pred_BSNL[:, frame_i_window] * delta_t
            )
            tok_latents_BSNL = tok_latents_BSNL.at[:, frame_i_window].set(
                tok_latents_BNL
            )
            new_carry = (tok_latents_BSNL, frame_i_window)
            return new_carry

        @nnx.scan(in_axes=(nnx.Carry, 0), out_axes=nnx.Carry)
        def autoregressive_step_fn(carry, frame_t: jax.Array) -> jax.Array:
            tok_latents_BSNL, tok_latents_BFNL, rng = carry
            rng, _rng_noise = jax.random.split(rng)

            # slide the window forward by 1 frame if necessary
            tok_latents_BSNL, frame_id_window = nnx.cond(
                frame_t < window_size,
                lambda: (tok_latents_BSNL, frame_t),
                lambda: (
                    jnp.roll(tok_latents_BSNL, -1, axis=1)
                    .at[:, -1]
                    .set(jax.random.normal(_rng_noise, (B, N, L))),
                    window_size - 1,
                ),
            )

            carry_denoise = (tok_latents_BSNL, frame_id_window)
            final_carry_denoise = denoise_step_fn(
                carry_denoise, jnp.arange(diffusion_steps)
            )
            tok_latents_BSNL = final_carry_denoise[0]
            tok_latents_BFNL = tok_latents_BFNL.at[:, frame_t].set(
                tok_latents_BSNL[:, frame_id_window]
            )
            new_carry = (tok_latents_BSNL, tok_latents_BFNL, rng)
            return new_carry

        rng, _rng_sample = jax.random.split(rng)
        initial_carry = (token_latents_BSNL, token_latents_BFNL, _rng_sample)
        final_carry = autoregressive_step_fn(initial_carry, jnp.arange(T, seq_len))
        final_token_latents_BFNL = final_carry[1]

        final_videos_BFHWC = self.tokenizer.decode(
            final_token_latents_BFNL, video_hw=(H, W)
        )

        return final_videos_BFHWC, None  # TODO return something meaningful?

    def vq_encode(self, batch: Dict[str, jax.Array], training: bool) -> jax.Array:
        # --- Preprocess videos ---
        assert self.lam is not None
        video_BTHWC = batch["videos"]
        lam_output: Dict[str, jax.Array] = self.lam.vq_encode(
            video_BTHWC, training=training
        )
        lam_indices_E = lam_output["indices"]
        return lam_indices_E


# FIXME (f.srambical): add conversion script for old checkpoints
def restore_genie_components(
    optimizer: nnx.ModelAndOptimizer,
    sharding: jax.sharding.NamedSharding,
    rng: jax.Array,
    args,
) -> nnx.ModelAndOptimizer:
    """Restore pre-trained Genie components"""
    rng_tokenizer, rng_lam = jax.random.split(rng)
    rngs_tokenizer = nnx.Rngs(rng_tokenizer)
    rngs_lam = nnx.Rngs(rng_lam)

    tx = optimizer.tx
    model = optimizer.model
    handler_registry = ocp.handlers.DefaultCheckpointHandlerRegistry()
    handler_registry.add(
        "model_state", ocp.args.PyTreeRestore, ocp.handlers.PyTreeCheckpointHandler
    )

    checkpoint_options = ocp.CheckpointManagerOptions(
        step_format_fixed_length=6,
    )
    tokenizer_checkpoint_manager = ocp.CheckpointManager(
        directory=args.tokenizer_checkpoint,
        options=checkpoint_options,
        handler_registry=handler_registry,
    )
    if args.tokenizer_type == "vqvae":
        dummy_tokenizer = TokenizerVQVAE(
            in_dim=args.image_channels,
            model_dim=args.tokenizer_dim,
            ffn_dim=args.tokenizer_ffn_dim,
            latent_dim=args.latent_patch_dim,
            num_latents=args.num_patch_latents,
            patch_size=args.patch_size,
            num_blocks=args.tokenizer_num_blocks,
            num_heads=args.tokenizer_num_heads,
            dropout=args.dropout,
            codebook_dropout=args.dropout,
            param_dtype=args.param_dtype,
            dtype=args.dtype,
            use_flash_attention=args.use_flash_attention,
            rngs=rngs_tokenizer,
        )
    elif args.tokenizer_type == "mae":
        dummy_tokenizer = TokenizerMAE(
            in_dim=args.image_channels,
            model_dim=args.tokenizer_dim,
            ffn_dim=args.tokenizer_ffn_dim,
            latent_dim=args.latent_patch_dim,
            num_latents=args.num_patch_latents,
            patch_size=args.patch_size,
            num_blocks=args.tokenizer_num_blocks,
            num_heads=args.tokenizer_num_heads,
            dropout=args.dropout,
            max_mask_ratio=0.0,
            param_dtype=args.param_dtype,
            dtype=args.dtype,
            use_flash_attention=args.use_flash_attention,
            rngs=rngs_tokenizer,
        )
    else:
        raise ValueError(f"Invalid tokenizer type: {args.tokenizer_type}")
    dummy_tokenizer_optimizer = nnx.ModelAndOptimizer(dummy_tokenizer, tx)
    dummy_tokenizer_optimizer_state = nnx.state(dummy_tokenizer_optimizer)
    abstract_sharded_tokenizer_optimizer_state = _create_abstract_sharded_pytree(
        dummy_tokenizer_optimizer_state, sharding
    )
    restored_tokenizer = tokenizer_checkpoint_manager.restore(
        step=tokenizer_checkpoint_manager.latest_step(),
        args=ocp.args.Composite(
            model_state=ocp.args.PyTreeRestore(  # type: ignore
                abstract_sharded_tokenizer_optimizer_state  # type: ignore
            ),
        ),
    )["model_state"]
    nnx.update(dummy_tokenizer_optimizer.model, restored_tokenizer.model)
    model.tokenizer = dummy_tokenizer_optimizer.model
    tokenizer_checkpoint_manager.close()

    if args.lam_checkpoint:
        lam_checkpoint_manager = ocp.CheckpointManager(
            directory=args.lam_checkpoint,
            options=checkpoint_options,
            handler_registry=handler_registry,
        )
        dummy_lam = LatentActionModel(
            in_dim=args.image_channels,
            model_dim=args.lam_dim,
            ffn_dim=args.lam_ffn_dim,
            latent_dim=args.latent_patch_dim,
            num_latents=args.num_actions,
            patch_size=args.lam_patch_size,
            num_blocks=args.lam_num_blocks,
            num_heads=args.lam_num_heads,
            dropout=args.dropout,
            codebook_dropout=args.dropout,
            param_dtype=args.param_dtype,
            dtype=args.dtype,
            use_flash_attention=args.use_flash_attention,
            rngs=rngs_lam,
        )
        dummy_lam_optimizer = nnx.ModelAndOptimizer(dummy_lam, tx)
        dummy_lam_optimizer_state = nnx.state(dummy_lam_optimizer)
        abstract_sharded_lam_optimizer_state = _create_abstract_sharded_pytree(
            dummy_lam_optimizer_state, sharding
        )
        restored_lam_optimizer = lam_checkpoint_manager.restore(
            step=lam_checkpoint_manager.latest_step(),
            args=ocp.args.Composite(
                model_state=ocp.args.PyTreeRestore(  # type: ignore
                    abstract_sharded_lam_optimizer_state  # type: ignore
                ),
            ),
        )["model_state"]
        nnx.update(dummy_lam_optimizer.model, restored_lam_optimizer.model)
        model.lam = dummy_lam_optimizer.model
        # Remove the LAM decoder to save memory and avoid unnecessary computation.
        del model.lam.decoder
        lam_checkpoint_manager.close()

    # Reinitialize the optimizer states
    optimizer = nnx.ModelAndOptimizer(model, tx)
    return optimizer


def _create_abstract_sharded_pytree(
    pytree_template: nnx.GraphState, sharding_spec: jax.sharding.NamedSharding
) -> jax.Array:
    """Replaces arrays in a pytree with ShapeDtypeStructs having the given sharding."""

    def map_fn(leaf_template):
        if hasattr(leaf_template, "shape") and hasattr(leaf_template, "dtype"):
            return jax.ShapeDtypeStruct(
                leaf_template.shape, leaf_template.dtype, sharding=sharding_spec
            )
        return leaf_template

    return jax.tree_util.tree_map(map_fn, pytree_template)