from __future__ import annotations

from PIL import Image

from .config import MotionPreset
from .motion import apply_camera_motion


def interpolate_frames(keyframes: list[Image.Image], *, total_frames: int, motion: MotionPreset) -> list[Image.Image]:
    if not keyframes:
        raise ValueError("At least one keyframe is required.")
    total_frames = max(2, int(total_frames))
    if len(keyframes) == 1:
        return [apply_camera_motion(keyframes[0], t=i / max(1, total_frames - 1), motion=motion) for i in range(total_frames)]
    frames: list[Image.Image] = []
    spans = len(keyframes) - 1
    for frame_idx in range(total_frames):
        global_t = frame_idx / max(1, total_frames - 1)
        pos = global_t * spans
        left = min(spans - 1, int(pos))
        local_t = pos - left
        eased_t = _smoothstep(local_t)
        blended = Image.blend(keyframes[left].convert("RGB"), keyframes[left + 1].convert("RGB"), eased_t)
        frames.append(apply_camera_motion(blended, t=global_t, motion=motion))
    return frames


def _smoothstep(t: float) -> float:
    t = max(0.0, min(1.0, float(t)))
    return t * t * (3.0 - 2.0 * t)