/* ============================================================
   VYNDR 2.0 — THE COLOR CONTRACT (DS3, DESIGN-SPEC Part 1).
   Plain CommonJS so .tsx components import it AND the Jest suite
   requires it directly (same pattern as vyndrTokens.js / archetypes.js).

   ONE law, enforced in one place, tested in colorContract.test.js:
   - Signal-green (#00D4A0 / var(--g-a)) means exactly ONE thing:
     edge / active / A-tier / primary CTA. Never decorative, never an
     archetype hue, never a green rendered on a NEGATIVE number.
   - Edge / CLV / delta is colored by SIGN: positive = signal-green,
     negative = muted red (var(--miss)), zero = neutral (no edge).
   - Grades are colored by TIER (A/A+ green, B blue, C amber, D/F red).
   - GLOW is the scarcest cue in the system: A / A+ ONLY.
   ============================================================ */

const SIGNAL_GREEN = '#00D4A0';

/* Archetype hues must clear this CIE76 ΔE from SIGNAL_GREEN so that
   #00D4A0 stays uniquely "edge" and is never diluted by an archetype
   chip. 20 sits above the ~10 "clearly a different color" boundary. */
const MIN_ARCHETYPE_DELTA_E = 20;

/* Sign → token. Positive edge is the ONE green meaning; negative is
   muted red; a zero (or non-numeric) edge is no edge → neutral. */
const EDGE_POSITIVE = 'var(--g-a)';
const EDGE_NEGATIVE = 'var(--miss)';
const EDGE_NEUTRAL = 'var(--text-2)';

/**
 * edgeColor(value) — the single source of truth for coloring any
 * edge / CLV / delta figure by SIGN. A -33.3% edge can NEVER render
 * green (audit #3). Accepts number or numeric string; null/NaN/0 → neutral.
 */
function edgeColor(value) {
  const n = typeof value === 'number' ? value : parseFloat(value);
  if (!Number.isFinite(n) || n === 0) return EDGE_NEUTRAL;
  return n > 0 ? EDGE_POSITIVE : EDGE_NEGATIVE;
}

/* Grade → tier color. Mirrors vyndrTokens.gradeColor for the shared
   keys (a test locks the two in sync) and extends F → red. */
const TIER_COLORS = {
  'A+': 'var(--g-ap)', A: 'var(--g-a)', 'A-': 'var(--g-a)',
  'B+': 'var(--g-b)', B: 'var(--g-b)', 'B-': 'var(--g-b)',
  C: 'var(--g-c)', D: 'var(--g-d)', F: 'var(--g-d)',
};

function normalizeGrade(grade) {
  return (grade == null ? '' : String(grade)).trim().toUpperCase();
}

/** gradeTierColor(grade) — A/A+ green, B blue, C amber, D/F red. */
function gradeTierColor(grade) {
  return TIER_COLORS[normalizeGrade(grade)] || 'var(--text-0)';
}

/**
 * gradeGlows(grade) — GLOW = A / A+ ONLY (audit #3: a glowing C
 * devalues the cue). A- is NOT a glow tier. Every phosphor/textShadow/
 * boxShadow glow on a grade element must gate through this.
 */
function gradeGlows(grade) {
  const g = normalizeGrade(grade);
  return g === 'A+' || g === 'A';
}

/* ---- perceptual color distance (CIE76 in CIE-Lab) ---------------- */
function hexToRgb(hex) {
  const h = String(hex).replace('#', '');
  return [parseInt(h.slice(0, 2), 16), parseInt(h.slice(2, 4), 16), parseInt(h.slice(4, 6), 16)];
}
function srgbToLinear(c) {
  c /= 255;
  return c <= 0.04045 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4);
}
function hexToLab(hex) {
  const [r, g, b] = hexToRgb(hex).map(srgbToLinear);
  let x = (r * 0.4124 + g * 0.3576 + b * 0.1805) / 0.95047;
  let y = r * 0.2126 + g * 0.7152 + b * 0.0722;
  let z = (r * 0.0193 + g * 0.1192 + b * 0.9505) / 1.08883;
  const f = (t) => (t > 0.008856 ? Math.cbrt(t) : 7.787 * t + 16 / 116);
  const fx = f(x), fy = f(y), fz = f(z);
  return [116 * fy - 16, 500 * (fx - fy), 200 * (fy - fz)];
}
/** deltaE(a, b) — CIE76 perceptual distance between two hex colors. */
function deltaE(a, b) {
  const A = hexToLab(a), B = hexToLab(b);
  return Math.sqrt((A[0] - B[0]) ** 2 + (A[1] - B[1]) ** 2 + (A[2] - B[2]) ** 2);
}

/** isSignalGreen(hex) — true when a hue is close enough to the signal
 *  green that it would dilute the "edge" meaning (archetype dedup gate). */
function isSignalGreen(hex) {
  return deltaE(hex, SIGNAL_GREEN) < MIN_ARCHETYPE_DELTA_E;
}

module.exports = {
  SIGNAL_GREEN,
  MIN_ARCHETYPE_DELTA_E,
  EDGE_POSITIVE,
  EDGE_NEGATIVE,
  EDGE_NEUTRAL,
  TIER_COLORS,
  edgeColor,
  gradeTierColor,
  gradeGlows,
  deltaE,
  isSignalGreen,
};