core/scripts/check-contrast.sh

#!/usr/bin/env bash
# check-contrast.sh — WCAG AA contrast ratio checker for theme tokens.
# Parses variables.css for dark/light token pairs, checks text-on-background contrast.
# Usage: bash scripts/check-contrast.sh [variables.css]

set -euo pipefail
CSS_FILE="${1:-src/css/variables.css}"

# Verify python3 is available
if ! command -v python3 &>/dev/null; then
  echo "ERROR: python3 required for luminance computation" >&2
  exit 1
fi

# ── Extract tokens from a CSS block ─────────────────────
# Usage: extract_tokens <label> <start-pattern>
# Populates an associative array via eval
extract_block() {
  local label="$1" start_pat="$2"
  local in_block=0 depth=0
  declare -gA "$label"
  while IFS= read -r line; do
    if [[ "$line" =~ $start_pat ]]; then
      in_block=1; depth=0
    fi
    if (( in_block )); then
      # Count braces
      opens="${line//[^\{]/}"; depth=$((depth + ${#opens}))
      closes="${line//[^\}]/}"; depth=$((depth - ${#closes}))
      # Extract token definitions
      if [[ "$line" =~ --([a-zA-Z0-9_-]+):[[:space:]]*([^;]+)\; ]]; then
        local key="${BASH_REMATCH[1]}" val="${BASH_REMATCH[2]}"
        val="${val%"${val##*[![:space:]]}"}"  # trim trailing ws
        eval "${label}[${key}]=\"${val}\""
      fi
      (( depth <= 0 && in_block )) && in_block=0
    fi
  done < "$CSS_FILE"
}

extract_block "DARK" "^:root"
extract_block "LIGHT" '^\[data-theme="light"\]'

# ── Semantic pairings to check ──────────────────────────
# Format: "foreground_token:background_token:context:threshold"
# threshold: 4.5 = AA normal text, 3.0 = AA large text (>=18px bold or >=24px)
PAIRINGS=(
  "text:bg:body text:4.5"
  "text:bg-surface:surface text:4.5"
  "text:bg-raised:raised text:4.5"
  "text:bg-hover:hover text:4.5"
  "text:bg-active:active text:4.5"
  "text-2:bg:secondary text on body:4.5"
  "text-2:bg-surface:secondary text on surface:4.5"
  "text-2:bg-raised:secondary text on raised:4.5"
  "text-3:bg:muted text on body:3.0"
  "text-3:bg-surface:muted text on surface:3.0"
  "text-3:bg-raised:muted text on raised:3.0"
  "accent:bg:accent on body:3.0"
  "accent:bg-surface:accent on surface:3.0"
  "accent:bg-raised:accent on raised:3.0"
  "accent-light:accent-dim:badge accent:3.0"
  "danger-light:danger-dim:badge danger:3.0"
  "success-light:success-dim:badge success:3.0"
  "warning-light:warning-dim:badge warning:3.0"
  "text-on-color:accent:text on accent btn:3.0"
  "text-on-color:danger:text on danger btn:3.0"
  "text-on-color:success:text on success btn:3.0"
  "text-on-warning:warning:text on warning:4.5"
  "text:input-bg:input text:4.5"
  "text-3:input-bg:placeholder on input:3.0"
)

# ── Python script for contrast computation ──────────────
CONTRAST_PY=$(cat <<'PYEOF'
import sys, re, json

def parse_color(val, base_bg=None):
    """Parse hex or rgba() color to (r,g,b) tuple, 0-255."""
    val = val.strip()
    m = re.match(r'^#([0-9a-fA-F]{6})$', val)
    if m:
        h = m.group(1)
        return (int(h[0:2],16), int(h[2:4],16), int(h[4:6],16))
    m = re.match(r'^#([0-9a-fA-F]{3})$', val)
    if m:
        h = m.group(1)
        return (int(h[0]*2,16), int(h[1]*2,16), int(h[2]*2,16))
    m = re.match(r'^rgba?\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*(?:,\s*([\d.]+))?\s*\)$', val)
    if m:
        r,g,b = int(m.group(1)), int(m.group(2)), int(m.group(3))
        a = float(m.group(4)) if m.group(4) else 1.0
        if a < 1.0 and base_bg:
            br, bg_, bb = base_bg
            r = int(r * a + br * (1 - a))
            g = int(g * a + bg_ * (1 - a))
            b = int(b * a + bb * (1 - a))
        return (r, g, b)
    return None

def relative_luminance(rgb):
    """WCAG 2.1 relative luminance."""
    def linearize(c):
        s = c / 255.0
        return s / 12.92 if s <= 0.04045 else ((s + 0.055) / 1.055) ** 2.4
    r, g, b = rgb
    return 0.2126 * linearize(r) + 0.7152 * linearize(g) + 0.0722 * linearize(b)

def contrast_ratio(c1, c2):
    l1, l2 = relative_luminance(c1), relative_luminance(c2)
    if l1 < l2: l1, l2 = l2, l1
    return (l1 + 0.05) / (l2 + 0.05)

# Read input: JSON with dark/light tokens + pairings
data = json.loads(sys.stdin.read())
results = []
for theme_name, tokens in [("dark", data["dark"]), ("light", data["light"])]:
    base_bg = parse_color(tokens.get("bg", "#000000"))
    for p in data["pairings"]:
        fg_key, bg_key, ctx = p[0], p[1], p[2]
        fg_val = tokens.get(fg_key)
        bg_val = tokens.get(bg_key)
        if not fg_val or not bg_val:
            results.append({"theme": theme_name, "fg": fg_key, "bg": bg_key, "context": ctx,
                           "ratio": "N/A", "result": "SKIP", "note": "token missing"})
            continue
        fg_rgb = parse_color(fg_val, base_bg)
        bg_rgb = parse_color(bg_val, base_bg)
        if not fg_rgb or not bg_rgb:
            results.append({"theme": theme_name, "fg": fg_key, "bg": bg_key, "context": ctx,
                           "ratio": "N/A", "result": "SKIP", "note": "unparseable color"})
            continue
        ratio = contrast_ratio(fg_rgb, bg_rgb)
        threshold = p[3] if len(p) > 3 else 4.5
        passed = ratio >= threshold
        level = "AA" if threshold >= 4.5 else "AA-lg"
        results.append({"theme": theme_name, "fg": fg_key, "bg": bg_key, "context": ctx,
                        "fg_val": fg_val, "bg_val": bg_val,
                        "ratio": f"{ratio:.2f}:1", "result": "PASS" if passed else "FAIL",
                        "level": level})

json.dump(results, sys.stdout)
PYEOF
)

# ── Build JSON input for Python ─────────────────────────
build_tokens_json() {
  local -n arr=$1
  echo "{"
  local first=true
  for key in "${!arr[@]}"; do
    $first && first=false || echo ","
    # Escape any quotes in value
    local val="${arr[$key]}"
    printf '  "%s": "%s"' "$key" "$val"
  done
  echo ""
  echo "}"
}

build_pairings_json() {
  echo "["
  local first=true
  for p in "${PAIRINGS[@]}"; do
    IFS=':' read -r fg bg ctx threshold <<< "$p"
    threshold="${threshold:-4.5}"
    $first && first=false || echo ","
    printf '  ["%s", "%s", "%s", %s]' "$fg" "$bg" "$ctx" "$threshold"
  done
  echo ""
  echo "]"
}

INPUT_JSON=$(cat <<JSONEOF
{
  "dark": $(build_tokens_json DARK),
  "light": $(build_tokens_json LIGHT),
  "pairings": $(build_pairings_json)
}
JSONEOF
)

RESULTS=$(echo "$INPUT_JSON" | python3 -c "$CONTRAST_PY")

# ── Format output ───────────────────────────────────────
echo "╔══════════════════════════════════════════════════════════════════════════════════╗"
echo "║                      WCAG AA Contrast Ratio Report                             ║"
echo "╠══════════════════════════════════════════════════════════════════════════════════╣"
printf "║ %-6s │ %-20s │ %-16s │ %-10s │ %-6s │ %-5s │ %-6s ║\n" "Theme" "Context" "FG Token" "BG Token" "Ratio" "Level" "Result"
echo "╠══════════════════════════════════════════════════════════════════════════════════╣"

pass=0 fail=0 skip=0
while IFS= read -r row; do
  theme=$(echo "$row" | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['theme'])")
  ctx=$(echo "$row" | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['context'])")
  fg=$(echo "$row" | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['fg'])")
  bg=$(echo "$row" | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['bg'])")
  ratio=$(echo "$row" | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['ratio'])")
  result=$(echo "$row" | python3 -c "import sys,json; d=json.load(sys.stdin); print(d['result'])")
  level=$(echo "$row" | python3 -c "import sys,json; d=json.load(sys.stdin); print(d.get('level','AA'))")

  case "$result" in
    PASS) pass=$((pass + 1));;
    FAIL) fail=$((fail + 1));;
    SKIP) skip=$((skip + 1));;
  esac
  printf "║ %-6s │ %-20s │ %-16s │ %-10s │ %-6s │ %-5s │ %-6s ║\n" "$theme" "$ctx" "$fg" "$bg" "$ratio" "$level" "$result"
done < <(echo "$RESULTS" | python3 -c "
import sys, json
for item in json.loads(sys.stdin.read()):
    print(json.dumps(item))
")

echo "╚══════════════════════════════════════════════════════════════════════════════════╝"
echo ""
echo "Summary: $pass PASS, $fail FAIL, $skip SKIP"
echo ""

if (( fail > 0 )); then
  echo "RESULT: FAIL — $fail contrast violation(s) found"
  exit 1
else
  echo "RESULT: PASS — all checked pairings meet WCAG AA (4.5:1)"
  exit 0
fi