/**
 * Body style — three appearance sliders inspired by dreamfall simhuman
 * global morphs (mass / muscle / fat).
 *
 * Plain numbers only: Party, C path, and client mesh build all share this.
 * Ranges match vibe-human MODELING_CONTROLS for body.global.*:
 *   mass   −1 lean … +1 heavy
 *   muscle −1 soft … +1 muscular
 *   fat     0 base … +1 fat  (no negative target in the reference)
 */

export const BODY_STYLE_DEFAULTS = Object.freeze({
  mass: 0,
  muscle: 0,
  fat: 0,
});

/** Slider metadata for the kit chest UI. */
export const BODY_STYLE_SLIDERS = Object.freeze([
  {
    id: 'mass',
    label: 'Mass',
    min: -1,
    max: 1,
    step: 0.01,
    left: 'Lean',
    right: 'Heavy',
  },
  {
    id: 'muscle',
    label: 'Muscle',
    min: -1,
    max: 1,
    step: 0.01,
    left: 'Soft',
    right: 'Muscular',
  },
  {
    id: 'fat',
    label: 'Fat',
    min: 0,
    max: 1,
    step: 0.01,
    left: 'Base',
    right: 'Heavy',
  },
]);

function clamp(v, lo, hi) {
  const n = Number(v);
  if (!Number.isFinite(n)) return lo;
  return Math.max(lo, Math.min(hi, n));
}

/**
 * Normalize a partial body bag. Missing keys become 0 (average build).
 * @param {unknown} raw
 * @returns {{ mass: number, muscle: number, fat: number }}
 */
export function normalizeBodyStyle(raw) {
  if (!raw || typeof raw !== 'object') {
    return { ...BODY_STYLE_DEFAULTS };
  }
  return {
    mass: clamp(raw.mass, -1, 1),
    muscle: clamp(raw.muscle, -1, 1),
    fat: clamp(raw.fat, 0, 1),
  };
}

/** True when every channel is at the neutral default. */
export function isDefaultBodyStyle(style) {
  const s = normalizeBodyStyle(style);
  return s.mass === 0 && s.muscle === 0 && s.fat === 0;
}

/**
 * Compact wire form for full-roster snapshots (two decimals).
 * @returns {{ m: number, u: number, f: number }}
 */
export function packBodyStyle(style) {
  const s = normalizeBodyStyle(style);
  return {
    m: Math.round(s.mass * 100) / 100,
    u: Math.round(s.muscle * 100) / 100,
    f: Math.round(s.fat * 100) / 100,
  };
}

/** Inverse of packBodyStyle — also accepts full { mass, muscle, fat }. */
export function unpackBodyStyle(raw) {
  if (!raw || typeof raw !== 'object') return normalizeBodyStyle(null);
  if ('mass' in raw || 'muscle' in raw || 'fat' in raw) {
    return normalizeBodyStyle(raw);
  }
  return normalizeBodyStyle({
    mass: raw.m,
    muscle: raw.u,
    fat: raw.f,
  });
}

/**
 * Ease unit strength so mid-slider stays mild and the last third punches
 * harder into caricature (leaner / bulkier / more cut / fatter).
 * @param {number} t 0..1
 * @returns {number} 0..1
 */
function easeExtreme(t) {
  const a = clamp(t, 0, 1);
  // ~0.35 at half travel, 1.0 at the end — more of the gain sits near the stop.
  return a * 0.35 + a * a * 0.25 + a * a * a * 0.4;
}

/** Signed ease: preserves direction, applies easeExtreme on |v|. */
function shapedSigned(v) {
  if (v === 0) return 0;
  return Math.sign(v) * easeExtreme(Math.abs(v));
}

/**
 * Map mass/muscle/fat onto the loft physique scalars used by buildBodyGeometry.
 *
 * Ends of each slider push hard (ease-in + large peak gains). Mid values stay
 * readable so average builds do not jump. Seeded rng still adds a small natural
 * variation so two fighters with the same sliders are not voxel-identical.
 *
 * @param {{ mass: number, muscle: number, fat: number }} style
 * @param {{ range: (a: number, b: number) => number }} rng
 */
export function physiqueFromBodyStyle(style, rng) {
  const s = normalizeBodyStyle(style);
  // Shaped channels: mild near 0, extreme at ±1 / 1.
  const mass = shapedSigned(s.mass);
  const muscle = shapedSigned(s.muscle);
  const fat = easeExtreme(s.fat);

  // Peak gains (at shaped = ±1 / 1) — roughly 2× the first-pass response so
  // full lean / tank / soft / cut / fat reads clearly under armor.
  // Overall girth: mass + fat dominate; muscle adds a little.
  const bulkBase = 1 + mass * 0.32 + fat * 0.26 + muscle * 0.1;
  // Waist: fat fills hard, muscle nips, mass thickens.
  const waistBase = 1 + fat * 0.48 + mass * 0.2 - muscle * 0.18;
  // Shoulders / chest: muscle primary.
  const shoulderBase = 1 + muscle * 0.42 + mass * 0.16 + fat * 0.1;
  // Arms: muscle, with a little mass/fat.
  const armBase = 1 + muscle * 0.48 + mass * 0.14 + fat * 0.12;
  // Legs: fat + mass, muscle secondary.
  const legBase = 1 + fat * 0.36 + mass * 0.2 + muscle * 0.16;
  // Head: slight only — keeps helm fit.
  const headBase = 1 + mass * 0.06 + fat * 0.05;

  const jitter = (base, lo = 0.97, hi = 1.03) => base * (rng?.range?.(lo, hi) ?? 1);

  return {
    bulk: jitter(bulkBase),
    // Lower floors so full lean/soft can actually go thin.
    waistF: Math.max(0.52, jitter(waistBase, 0.98, 1.02)),
    shoulderF: Math.max(0.62, jitter(shoulderBase, 0.98, 1.02)),
    armF: Math.max(0.58, jitter(armBase, 0.97, 1.03)),
    legF: Math.max(0.6, jitter(legBase, 0.97, 1.03)),
    headF: Math.max(0.85, jitter(headBase, 0.98, 1.02)),
    style: s,
  };
}