"""Shared temporal sampling for coaf_dataset_24_25.

RGB (I2V target): 24 frames via uniform indices over raw episode steps.
Reason modalities + state + action: 25 frames via a separate uniform index
array so each reason frame k uses state[k] and action[k] from the same
raw timestep.
"""

from __future__ import annotations

import numpy as np

RGB_FRAMES = 24
REASON_FRAMES = 25


def sampled_indices(length: int, target: int) -> np.ndarray:
    """Uniformly sample `target` indices in [0, length - 1]."""
    if length < 1:
        raise ValueError(f"length must be >= 1, got {length}")
    if target < 1:
        raise ValueError(f"target must be >= 1, got {target}")
    if length < target:
        raise ValueError(f"length {length} < target {target}")
    return np.linspace(0, length - 1, target).astype(np.int64)


def rgb_indices(num_steps: int) -> np.ndarray:
    return sampled_indices(num_steps, RGB_FRAMES)


def reason_indices(num_steps: int) -> np.ndarray:
    return sampled_indices(num_steps, REASON_FRAMES)