#!/usr/bin/env python3 """Palette preview + WCAG contrast + CIEDE2000 perceptual audit. A dev tool for working on the colour palette (`src/theme.rs`). It reads the live `dark()` / `light()` constructors so it never drifts from the code, renders a true-colour swatch + sample for every palette entry on the theme background, prints the WCAG-AA contrast ratio, and reports the pairwise CIEDE2000 (ΔE2000) distance between the syntax-token colours so near-duplicates (distinct hex, indistinguishable on screen) are obvious. Usage: scripts/palette-preview.py scripts/palette-preview.py dark:tok_type=F58AAE light:tok_flag=7A5C00 Each `theme:key=HEX` argument previews a change without editing the source — handy for trying candidate colours. The gates mirrored here are enforced for real by the tests in `src/theme.rs` (NFR-5/NFR-7, ADR-0057): text foregrounds must clear 4.5:1; token pairs must clear ΔE2000 15. """ import math import os import re import sys THEME_RS = os.path.join(os.path.dirname(__file__), "..", "src", "theme.rs") # --- WCAG contrast ----------------------------------------------------- def _lin(c): c = c / 255.0 return c / 12.92 if c <= 0.03928 else ((c + 0.055) / 1.055) ** 2.4 def _luminance(rgb): r, g, b = rgb return 0.2126 * _lin(r) + 0.7152 * _lin(g) + 0.0722 * _lin(b) def contrast(fg, bg): a, b = _luminance(fg), _luminance(bg) hi, lo = max(a, b), min(a, b) return (hi + 0.05) / (lo + 0.05) # --- sRGB -> CIELAB (D65) + CIEDE2000 ---------------------------------- def _f(t): return t ** (1 / 3) if t > 0.008856 else 7.787 * t + 16 / 116 def rgb_to_lab(rgb): r, g, b = (_lin(c) for c in rgb) x = (r * 0.4124 + g * 0.3576 + b * 0.1805) / 0.95047 y = r * 0.2126 + g * 0.7152 + b * 0.0722 z = (r * 0.0193 + g * 0.1192 + b * 0.9505) / 1.08883 fx, fy, fz = _f(x), _f(y), _f(z) return (116 * fy - 16, 500 * (fx - fy), 200 * (fy - fz)) def de2000(lab1, lab2): L1, a1, b1 = lab1 L2, a2, b2 = lab2 avg_Lp = (L1 + L2) / 2 C1, C2 = math.hypot(a1, b1), math.hypot(a2, b2) avg_C = (C1 + C2) / 2 G = 0.5 * (1 - math.sqrt(avg_C ** 7 / (avg_C ** 7 + 25 ** 7))) if avg_C > 0 else 0 a1p, a2p = (1 + G) * a1, (1 + G) * a2 C1p, C2p = math.hypot(a1p, b1), math.hypot(a2p, b2) avg_Cp = (C1p + C2p) / 2 def hp(ap, b): if ap == 0 and b == 0: return 0 ang = math.degrees(math.atan2(b, ap)) return ang + 360 if ang < 0 else ang h1p, h2p = hp(a1p, b1), hp(a2p, b2) dLp, dCp = L2 - L1, C2p - C1p if C1p * C2p == 0: dhp = 0 elif abs(h2p - h1p) <= 180: dhp = h2p - h1p elif h2p - h1p > 180: dhp = h2p - h1p - 360 else: dhp = h2p - h1p + 360 dHp = 2 * math.sqrt(C1p * C2p) * math.sin(math.radians(dhp) / 2) if C1p * C2p == 0: avg_hp = h1p + h2p elif abs(h1p - h2p) <= 180: avg_hp = (h1p + h2p) / 2 elif h1p + h2p < 360: avg_hp = (h1p + h2p + 360) / 2 else: avg_hp = (h1p + h2p - 360) / 2 T = (1 - 0.17 * math.cos(math.radians(avg_hp - 30)) + 0.24 * math.cos(math.radians(2 * avg_hp)) + 0.32 * math.cos(math.radians(3 * avg_hp + 6)) - 0.20 * math.cos(math.radians(4 * avg_hp - 63))) d_ro = 30 * math.exp(-((avg_hp - 275) / 25) ** 2) Rc = 2 * math.sqrt(avg_Cp ** 7 / (avg_Cp ** 7 + 25 ** 7)) if avg_Cp > 0 else 0 Sl = 1 + (0.015 * (avg_Lp - 50) ** 2) / math.sqrt(20 + (avg_Lp - 50) ** 2) Sc, Sh = 1 + 0.045 * avg_Cp, 1 + 0.015 * avg_Cp * T Rt = -math.sin(math.radians(2 * d_ro)) * Rc return math.sqrt((dLp / Sl) ** 2 + (dCp / Sc) ** 2 + (dHp / Sh) ** 2 + Rt * (dCp / Sc) * (dHp / Sh)) # --- parse the live palette from src/theme.rs -------------------------- def parse_palette(path): text = open(path, encoding="utf-8").read() field = re.compile( r"(\w+):\s*Color::Rgb\(0x([0-9A-Fa-f]{2}),\s*0x([0-9A-Fa-f]{2}),\s*0x([0-9A-Fa-f]{2})\)" ) def block(start, end): s = text.index(start) e = text.index(end, s) return {m.group(1): (m.group(2) + m.group(3) + m.group(4)).upper() for m in field.finditer(text[s:e])} return {"dark": block("fn dark()", "fn light()"), "light": block("fn light()", "fn highlight_class_color")} def h(s): return tuple(int(s[i:i + 2], 16) for i in (0, 2, 4)) def fg(rgb): r, g, b = rgb return f"\x1b[38;2;{r};{g};{b}m" def bg(rgb): r, g, b = rgb return f"\x1b[48;2;{r};{g};{b}m" R = "\x1b[0m" TOKENS = ["tok_keyword", "tok_identifier", "tok_type", "tok_number", "tok_string", "tok_flag", "tok_function"] NONTEXT = {"border", "border_advanced"} SAMPLE = { "tok_keyword": "create table", "tok_identifier": "Customers", "tok_type": "serial", "tok_number": "42", "tok_string": "'hello'", "tok_flag": "--all-rows", "tok_function": "count(", "tok_punct": ", ;", "tok_error": "bad", "fg": "body text", "muted": "(none yet)", "system": "done.", "error": "error: nope", "warning": "[WRN] slow", "plan_efficient": "SEARCH idx", "mode_simple": "SIMPLE", "mode_advanced": "ADVANCED", "border": "──────", "border_advanced": "──────", } def main(): themes = parse_palette(THEME_RS) for arg in sys.argv[1:]: th, rest = arg.split(":") k, v = rest.split("=") themes[th][k] = v.upper() for tn, t in themes.items(): B = h(t["bg"]) print(f"\n{'=' * 64}\n {tn.upper()} THEME (bg #{t['bg']})\n{'=' * 64}") for k, hexv in t.items(): if k == "bg": continue c = h(hexv) cr = contrast(c, B) swatch = f"{bg(c)} {R}" text = f"{bg(B)}{fg(c)} {SAMPLE.get(k, k):14}{R}" floor = 3.0 if k in NONTEXT else 4.5 warn = "" if cr >= floor else f" !! < {floor}" print(f" {swatch} {text} #{hexv} {cr:5.2f}:1{warn} {k}") print("\n -- token ΔE2000 (<12 hard to distinguish; gate is >=15) --") labs = {k: rgb_to_lab(h(t[k])) for k in TOKENS if k in t} pairs = sorted( (de2000(labs[a], labs[b]), a, b) for i, a in enumerate(labs) for b in list(labs)[i + 1:] ) for d, a, b in pairs[:6]: flag = " !! TOO CLOSE" if d < 15 else (" ~ close" if d < 18 else "") print(f" {d:5.1f} {a:14} vs {b:14}{flag}") if __name__ == "__main__": main()