#!/usr/bin/env python3
"""theme-contrast.py — check every theme's foreground colours against its panels.

    python3 tools/theme-contrast.py

Themes are easy to get subtly wrong: Solarized Light shipped with accent colours that
scored 2.6:1 on its own panels, which read as broken rather than stylish. This walks
every theme block in build/template.html, resolves the variables the page actually
uses, and reports WCAG contrast against --panel.

Fails (exit 1) if anything drops below MIN_CONTRAST.
"""
import re
import sys
from pathlib import Path

MIN_CONTRAST = 3.0
ROOT = Path(__file__).resolve().parent.parent
SRC = ROOT / "build" / "template.html"

# every variable used as a foreground somewhere in the page
FOREGROUNDS = [
    "--txt", "--dim", "--dim2", "--bright", "--acc", "--acc-d", "--acc2",
    "--warn", "--miss", "--ok", "--steam",
    "--k-tag", "--k-item", "--k-ach", "--k-miss", "--k-boss", "--k-area",
    "--k-mode", "--k-extra",
]


def block(css, selector):
    m = re.search(re.escape(selector) + r"\{(.*?)\}", css, re.S)
    return m.group(1) if m else ""


def variables(text):
    return dict(re.findall(r"(--[a-z0-9-]+)\s*:\s*([^;]+);", text))


def to_rgb(value):
    v = value.strip()
    m = re.fullmatch(r"#([0-9a-fA-F]{6})", v)
    if m:
        n = int(m.group(1), 16)
        return ((n >> 16) & 255, (n >> 8) & 255, n & 255)
    m = re.fullmatch(r"#([0-9a-fA-F]{3})", v)
    if m:
        return tuple(int(c * 2, 16) for c in m.group(1))
    return None


def luminance(rgb):
    def channel(x):
        x /= 255
        return x / 12.92 if x <= 0.03928 else ((x + 0.055) / 1.055) ** 2.4
    r, g, b = rgb
    return 0.2126 * channel(r) + 0.7152 * channel(g) + 0.0722 * channel(b)


def contrast(a, b):
    la, lb = luminance(a), luminance(b)
    hi, lo = max(la, lb), min(la, lb)
    return (hi + 0.05) / (lo + 0.05)


def main():
    css = SRC.read_text(encoding="utf-8")
    root = variables(block(css, ":root"))
    themes = {m.group(1): variables(m.group(2))
              for m in re.finditer(r'html\[data-theme="([^"]+)"\]\{(.*?)\}', css, re.S)}

    if not themes:
        print("no theme blocks found in", SRC)
        return 1

    panel = to_rgb(root["--panel"])
    failures = []
    print(f"{'theme':<18}{'worst':>7}  {'':<3}colours below {MIN_CONTRAST}:1")
    print("-" * 72)
    for name, overrides in themes.items():
        merged = dict(root)
        merged.update(overrides)
        rows = []
        for fg in FOREGROUNDS:
            value = merged.get(fg, "")
            if not value.startswith("#"):
                continue
            rgb = to_rgb(value)
            if rgb:
                rows.append((contrast(rgb, panel), fg))
        rows.sort()
        bad = [f"{fg}={r:.1f}" for r, fg in rows if r < MIN_CONTRAST]
        if bad:
            failures.append((name, bad))
        worst, worst_name = rows[0]
        print(f"{name:<18}{worst:>6.1f}   {'' if not bad else '<- ' + ', '.join(bad)}")

    # text drawn on top of an accent fill (buttons, chips, tick boxes)
    print()
    print(f"{'theme':<18}{'on-acc/acc':>11}   status")
    print("-" * 72)
    for name, overrides in themes.items():
        merged = dict(root)
        merged.update(overrides)
        a, b = to_rgb(merged.get("--on-acc", "")), to_rgb(merged.get("--acc", ""))
        if not a or not b:
            continue
        ratio = contrast(a, b)
        bad = ratio < MIN_CONTRAST
        if bad:
            failures.append((name, [f"--on-acc on --acc={ratio:.1f}"]))
        print(f"{name:<18}{ratio:>10.1f}   {'' if not bad else '<- LOW'}")

    print()
    if failures:
        print("FAILED — these themes have unreadable foreground/background pairs:")
        for name, bad in failures:
            print(f"  {name}: {', '.join(bad)}")
        print("\nDarken the offending colour for that theme, then re-run ./deploy.sh")
        return 1
    print(f"all {len(themes)} themes are at or above {MIN_CONTRAST}:1 against --panel")
    return 0


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