"""Theme the Run tab: a preset or one brand hex -> the THEME block of run_tab.html.

    python palette.py sky|teal|"#7a3cff"                  print the block and a contrast table
    python palette.py "#7a3cff" --write run_tab/run_tab.html   also write it into the page

Only the sky gradient and the accent change. ok/warn/bad and the log colours stay fixed (R9).
A brand hex that is too light for white button text is darkened until it passes.
Exits 1 if a contrast check still fails.
"""
import re
import sys

WHITE, BLACK = "#ffffff", "#000000"
INK = {"light": "#1c2b33", "dark": "#e6eef4"}
PRESETS = {
    "sky": {"light": {"--sky-top": "#8fc9e8", "--sky-mid": "#bfe3f2", "--sky-bottom": "#eaf6fb",
                      "--accent": "#3d9bd0", "--accent-lite": "#5cb2e2", "--accent-dark": "#16202a"},
            "dark": {"--sky-top": "#0f1b26", "--sky-mid": "#13212e", "--sky-bottom": "#182a38",
                     "--accent": "#3d9bd0", "--accent-lite": "#5cb2e2", "--accent-dark": "#2e5d80"}},
    "teal": {"light": {"--sky-top": "#8fe8ad", "--sky-mid": "#bff2d0", "--sky-bottom": "#eafbf0",
                       "--accent": "#0d9488", "--accent-lite": "#2dd4bf", "--accent-dark": "#16202a"},
             "dark": {"--sky-top": "#0f2617", "--sky-mid": "#132e1c", "--sky-bottom": "#183823",
                      "--accent": "#0d9488", "--accent-lite": "#2dd4bf", "--accent-dark": "#2e5d80"}},
}


def rgb(h):
    return [int(h[i:i + 2], 16) for i in (1, 3, 5)]


def mix(a, b, t):
    """Blend hex colour a toward b by t (0..1)."""
    return "#" + "".join(f"{round(x + (y - x) * t):02x}" for x, y in zip(rgb(a), rgb(b)))


def contrast(a, b):
    """WCAG 2 contrast ratio between two hex colours."""
    def lum(h):
        c = [v / 255 for v in rgb(h)]
        c = [x / 12.92 if x <= 0.03928 else ((x + 0.055) / 1.055) ** 2.4 for x in c]
        return 0.2126 * c[0] + 0.7152 * c[1] + 0.0722 * c[2]
    hi, lo = sorted((lum(a), lum(b)), reverse=True)
    return (hi + 0.05) / (lo + 0.05)


def derive(brand):
    brand = brand.strip().lower()
    if len(brand) == 4:  # #abc -> #aabbcc
        brand = "#" + "".join(ch * 2 for ch in brand[1:])
    accent = brand
    for _ in range(60):  # white text on the Trigger button must stay readable
        if contrast(WHITE, accent) >= 3:
            break
        accent = mix(accent, BLACK, 0.06)
    base = {"--accent": accent, "--accent-lite": mix(accent, WHITE, 0.2)}
    return {
        "light": {"--sky-top": mix(accent, WHITE, 0.55), "--sky-mid": mix(accent, WHITE, 0.72),
                  "--sky-bottom": mix(accent, WHITE, 0.9), **base, "--accent-dark": mix(accent, "#0b1218", 0.85)},
        "dark": {"--sky-top": mix(accent, BLACK, 0.85), "--sky-mid": mix(accent, BLACK, 0.82),
                 "--sky-bottom": mix(accent, BLACK, 0.78), **base, "--accent-dark": mix(accent, BLACK, 0.4)},
    }


def checks(t):
    rows = []
    for mode, m in t.items():
        rows += [(mode, "white text on the Trigger button", contrast(WHITE, m["--accent"]), 3),
                 (mode, "ink on the top of the sky", contrast(INK[mode], m["--sky-top"]), 4.5),
                 (mode, "ink on the bottom of the sky", contrast(INK[mode], m["--sky-bottom"]), 4.5)]
    rows.append(("light", "progress % on the sky", contrast(t["light"]["--accent-dark"], t["light"]["--sky-bottom"]), 4.5))
    return rows


def block(t):
    def line(m):
        r = ",".join(str(v) for v in rgb(m["--accent"]))
        return "; ".join(f"{k}:{v}" for k, v in m.items()) + f"; --accent-rgb:{r};"
    return ("/* THEME:START  (palette.py --write replaces everything down to THEME:END) */\n"
            f":root{{\n  {line(t['light'])}\n}}\nbody.dark{{\n  {line(t['dark'])}\n}}\n/* THEME:END */")


if __name__ == "__main__":
    if len(sys.argv) < 2 or not (sys.argv[1] in PRESETS or sys.argv[1].startswith("#")):
        sys.exit(__doc__)
    t = PRESETS.get(sys.argv[1]) or derive(sys.argv[1])
    css = block(t)
    print(css + "\n")
    rows = checks(t)
    for mode, what, ratio, need in rows:
        print(f"{mode:<6} {what:<34} {ratio:5.2f}:1  needs {need}:1  {'PASS' if ratio >= need else 'FAIL'}")
    if "--write" in sys.argv:
        page = sys.argv[sys.argv.index("--write") + 1]
        html = open(page, encoding="utf-8").read()
        new, n = re.subn(r"/\* THEME:START.*?THEME:END \*/", lambda _: css, html, flags=re.S)
        if n != 1:
            sys.exit(f"THEME:START/END markers not found in {page}")
        open(page, "w", encoding="utf-8").write(new)
        print(f"\nwrote the theme into {page}")
    sys.exit(0 if all(r >= n for *_, r, n in rows) else 1)