"""Sega Master System VDP (315-5124) palette.

The SMS palette is 64 colours: each CRAM byte is %00BBGGRR -- 2 bits per channel
(x85 -> 0,85,170,255).  The colour index IS the byte written to CRAM, so PALETTE
is indexed by hardware value 0-63.  Two 16-colour palettes (background + sprite)
are loaded; an image uses up to 32 colours on screen.
"""
from __future__ import annotations

import numpy as np

from ..palette import srgb_to_lab


def _rgb(c):
    r = (c & 3) * 85
    g = ((c >> 2) & 3) * 85
    b = ((c >> 4) & 3) * 85
    return (r, g, b)


PALETTE = np.array([_rgb(c) for c in range(64)], dtype=np.float64)

# greys: R==G==B -> byte where the three 2-bit fields are equal (0,21,42,63).
GREYS = [c for c in range(64) if PALETTE[c, 0] == PALETTE[c, 1] == PALETTE[c, 2]]


def get_palette() -> np.ndarray:
    return PALETTE


def palette_lab() -> np.ndarray:
    return srgb_to_lab(PALETTE)