"""Render every Mode x Palette x Dither variation of an image, for the GUI's
"Explore variations" contact sheet.  Kept import-light (no Qt) so it can run in
ProcessPoolExecutor worker processes.
"""

from __future__ import annotations

from . import imageprep
from .convert import MODES, render_preview, convert_image

PALETTES = ["colodore", "pepto"]
DITHERS = ["bayer", "floyd", "atkinson", "none"]

# (mode, palette, dither) for every concrete mode (auto is excluded on purpose).
COMBOS = [(m, p, d) for m in MODES for p in PALETTES for d in DITHERS]


def render_variation(args):
    """Worker entry point. ``args`` = (path, mode, palette, dither, prep_kwargs).

    Returns (mode, palette, dither, error, rgb) where rgb is the displayed-
    resolution (320x200) preview as a uint8 HxWx3 array.
    """
    path, mode, palette, dither, prep_kwargs = args
    prep = imageprep.PrepOptions(**prep_kwargs)
    conv = convert_image(path, mode=mode, palette_name=palette,
                         dither_mode=dither, intensive=False, prep_opt=prep)
    rgb = render_preview(conv, palette, scale=1)
    return (mode, palette, dither, conv.error, rgb)