#!/usr/bin/env python3
"""Guard against invisible-text palettes (BACKLOG items 25 + 27).

Asserts, for every themes/*.json, the WCAG contrast ratio of each
hex-on-hex fg/bg pairing the generated swaync/waybar/rofi CSS uses.
Pairings built from alpha(@text) / #RRGGBBAA text tints are
contrast-by-construction and need no assert. Status glyph accents
(good/warn/bad on base) are deliberately NOT held to a text ratio —
several palettes sit at 2.0–2.7 there by design.

Wired as `checks.theme-contrast` in flake.nix; also runnable directly:
    python3 tools/check-theme-contrast.py themes/
"""
import json
import sys
from pathlib import Path

# (fg role, bg role, minimum ratio, consumer). Text pairings only —
# borders (@accent/@bad on @base in swaync) are decorative and not held
# to a text ratio (miasma's bad-on-base is 2.3, fine for a border).
PAIRINGS = [
    ("text", "base",   4.5, "swaync body / waybar modules / rofi rows"),
    # symmetric ratio also covers accent-on-base (waybar updates, rofi prompt)
    ("base", "accent", 3.0, "swaync button:hover / waybar active ws / rofi selected row"),
    # Adopted from the item-28 design audit: summer-day/flexoki-light
    # shipped subtext == base (ratio 1.0 — invisible secondary text; the
    # palette-level cause of items 25/27). Never again.
    ("subtext", "base", 3.0, "secondary text (tooltips, hints, fastfetch labels)"),
]


def channel(c: int) -> float:
    c /= 255
    return c / 12.92 if c <= 0.03928 else ((c + 0.055) / 1.055) ** 2.4


def luminance(hexstr: str) -> float:
    hexstr = hexstr.lstrip("#")
    r, g, b = (int(hexstr[i:i + 2], 16) for i in (0, 2, 4))
    return 0.2126 * channel(r) + 0.7152 * channel(g) + 0.0722 * channel(b)


def ratio(fg: str, bg: str) -> float:
    hi, lo = sorted((luminance(fg), luminance(bg)), reverse=True)
    return (hi + 0.05) / (lo + 0.05)


def main() -> int:
    themes_dir = Path(sys.argv[1] if len(sys.argv) > 1 else "themes")
    failures = []
    themes = sorted(themes_dir.glob("*.json"))
    if not themes:
        print(f"no theme JSONs found under {themes_dir}", file=sys.stderr)
        return 1
    for path in themes:
        colors = json.loads(path.read_text())["colors"]
        for fg, bg, minimum, consumer in PAIRINGS:
            r = ratio(colors[fg], colors[bg])
            if r < minimum:
                failures.append(
                    f"{path.stem}: {fg} on {bg} = {r:.2f} < {minimum}"
                    f" ({consumer}; {colors[fg]} on {colors[bg]})"
                )
    if failures:
        print("theme contrast failures:", file=sys.stderr)
        for f in failures:
            print(f"  {f}", file=sys.stderr)
        return 1
    print(f"{len(themes)} themes x {len(PAIRINGS)} pairings: all pass")
    return 0


if __name__ == "__main__":
    sys.exit(main())