FAQ Accordion in React Beside an Opal Glass Globe Lamp in WebGL That Glows Brighter as Each Answer Opens

import { useEffect, useId, useRef, useState, type KeyboardEvent } from "react";
import { useReducedMotion } from "framer-motion";

/** The questions. Swap these for your own; the lamp brightens with every answer that is open. */
const faqs = [
  { q: "What bulb does the lamp take?", a: "A single E14 LED of up to 6 watts, warm white. One ships in the box, and the opal glass hides its shape completely, so any shape of bulb works." },
  { q: "Can I dim it?", a: "Yes. The cord switch has a soft dimmer: hold it down and the light slowly falls to a glow, tap it once to go back to full." },
  { q: "Is the glass hand blown?", a: "Every globe is mouth blown into a beechwood mould and then acid etched inside and out, which gives the milky, even finish with no hot spot." },
  { q: "How long does delivery take?", a: "Three to five working days in most of Europe and North America. Each lamp travels in a moulded pulp cradle, so nothing has to be thrown away." },
  { q: "What if the glass breaks?", a: "Send us a photo within two years and we post a new globe free of charge. After that, replacement globes are sold on their own." },
];

const OPEN_AT_START = [0]; // which answers are open when the page loads
const GLOW_STEP = 0.145; // how much each open answer adds to the lamp (0 to 1); one open answer is a low glow
const GLOW_FIRST = 0.42; // brightness with one answer open
const WALL = "#16232e"; // the painted wall and the panel the questions sit on
const INK = "#efe6d8";
const GROTESK = '"Inter Tight", "Inter", ui-sans-serif, system-ui, sans-serif';

/* ---- photoreal kit (pasted, see PHOTOREAL-KIT.md) ---- */
const FULLSCREEN_VS = `#version 300 es
out vec2 vUv;
void main() { vec2 p = vec2(float((gl_VertexID << 1) & 2), float(gl_VertexID & 2)); vUv = p; gl_Position = vec4(p * 2.0 - 1.0, 0.0, 1.0); }`;
const GLSL_HEADER = `#version 300 es
precision highp float;
uniform vec2 uRes;      // drawing buffer size in pixels
uniform float uFrame;   // sample index since the last reset (drives every random number)
uniform float uTime;    // seconds, for things that really move
uniform vec3 uCamPos, uCamRt, uCamUp, uCamFw;
uniform float uTan, uAspect, uAperture, uFocus;
uniform vec2 uShift;    // lens shift (architectural framing): move the subject in frame without tilting verticals
out vec4 o;`;
const GLSL_COMMON = `
#define PI 3.14159265359
float saturate(float x) { return clamp(x, 0.0, 1.0); }
float hash12(vec2 p) { vec3 p3 = fract(vec3(p.xyx) * 0.1031); p3 += dot(p3, p3.yzx + 33.33); return fract((p3.x + p3.y) * p3.z); }
float hash13(vec3 p3) { p3 = fract(p3 * 0.1031); p3 += dot(p3, p3.zyx + 31.32); return fract((p3.x + p3.y) * p3.z); }
float ign(vec2 p) { return fract(52.9829189 * fract(dot(p, vec2(0.06711056, 0.00583715)))); }
float vnoise(vec2 p) {
  vec2 i = floor(p), f = fract(p); f = f * f * (3.0 - 2.0 * f);
  return mix(mix(hash12(i), hash12(i + vec2(1, 0)), f.x), mix(hash12(i + vec2(0, 1)), hash12(i + vec2(1, 1)), f.x), f.y);
}
float vnoise3(vec3 p) {
  vec3 i = floor(p), f = fract(p); f = f * f * (3.0 - 2.0 * f);
  return mix(mix(mix(hash13(i), hash13(i + vec3(1, 0, 0)), f.x), mix(hash13(i + vec3(0, 1, 0)), hash13(i + vec3(1, 1, 0)), f.x), f.y),
             mix(mix(hash13(i + vec3(0, 0, 1)), hash13(i + vec3(1, 0, 1)), f.x), mix(hash13(i + vec3(0, 1, 1)), hash13(i + vec3(1, 1, 1)), f.x), f.y), f.z);
}
float fbm(vec2 p) { float a = 0.5, s = 0.0; for (int i = 0; i < 5; i++) { s += a * vnoise(p); p = mat2(1.6, 1.2, -1.2, 1.6) * p + 3.1; a *= 0.5; } return s; }
float fbm3(vec3 p) { float a = 0.5, s = 0.0; for (int i = 0; i < 4; i++) { s += a * vnoise3(p); p = p * 2.03 + vec3(1.7, 9.2, 3.1); a *= 0.5; } return s; }
// Clamp one sample before it is averaged: a single lucky glossy ray hitting the window would otherwise leave
// a bright speck ("firefly") that takes hundreds of frames to fade. Call on the final colour in main().
vec3 clampSample(vec3 c, float m) { float l = max(c.r, max(c.g, c.b)); return l > m ? c * (m / l) : c; }
// A new well-spread 2D random point per pixel AND per frame: the R2 low-discrepancy sequence over frames,
// rotated by a per-pixel white-noise offset (structured offsets such as ign() show diagonal hatching while moving).
// Use a different salt for every decision (pixel jitter, lens, sun disc, gloss...). Accumulation averages them.
vec2 rand2(float salt) {
  vec2 f = gl_FragCoord.xy + salt * 17.13;
  return fract(vec2(hash12(f), hash12(f + 71.7)) + uFrame * vec2(0.7548776662, 0.5698402910));
}`;
const GLSL_SAMPLING = `
mat3 basisOf(vec3 n) { vec3 t = abs(n.y) < 0.999 ? normalize(cross(vec3(0.0, 1.0, 0.0), n)) : vec3(1.0, 0.0, 0.0); return mat3(t, cross(n, t), n); }
vec2 diskSample(vec2 u) { float r = sqrt(u.x), a = 6.2831853 * u.y; return r * vec2(cos(a), sin(a)); }
vec3 cosineSample(vec3 n, vec2 u) { vec2 d = diskSample(u); return basisOf(n) * vec3(d, sqrt(max(0.0, 1.0 - dot(d, d)))); }
// a microfacet normal from the GGX distribution: reflect about it for a rough reflection, refract through it for frosted glass
vec3 ggxSample(vec3 n, float rough, vec2 u) {
  float a = rough * rough;
  float ct = sqrt((1.0 - u.x) / (1.0 + (a * a - 1.0) * u.x)), st = sqrt(max(0.0, 1.0 - ct * ct)), ph = 6.2831853 * u.y;
  return normalize(basisOf(n) * vec3(st * cos(ph), st * sin(ph), ct));
}`;
const GLSL_CAMERA = `
// Thin-lens camera. Sub-pixel jitter = supersampling; a random point on the lens = true depth of field.
// uAperture is the lens radius in scene units (0 = pinhole). uFocus is the distance along the view axis that is sharp.
void cameraRay(out vec3 ro, out vec3 rd) {
  vec2 px = rand2(1.0) - 0.5;
  vec2 ndc = (gl_FragCoord.xy + px) / uRes * 2.0 - 1.0 - uShift;
  vec3 dir = normalize(uCamFw + uCamRt * (ndc.x * uTan * uAspect) + uCamUp * (ndc.y * uTan));
  vec3 fp = uCamPos + dir * (uFocus / dot(dir, uCamFw));
  vec2 lens = diskSample(rand2(2.0)) * uAperture;
  ro = uCamPos + uCamRt * lens.x + uCamUp * lens.y;
  rd = normalize(fp - ro);
}`;
// the light rig, edited for this scene: late low sun through a window on the left, raking along the wall
const GLSL_RIG_SETTINGS = `
const vec3 KEY_DIR = normalize(vec3(-0.86, 0.42, 0.12));
const vec3 KEY_COL = vec3(1.0, 0.8, 0.6) * 1.15;
const float KEY_SPREAD = 0.006;
const float WIN_DIST = 150.0;
const vec2 WIN_HALF = vec2(10.0, 15.0);
const vec2 WIN_OFF = vec2(-6.0, 2.0);
const float BAR = 0.7;
const float BAR_Y = 4.0;
const vec3 SKY_COL = vec3(0.58, 0.66, 0.78) * 0.14;
const vec3 FILL_DIR = normalize(vec3(0.3, 0.42, 1.0));
const vec3 FILL_COL = vec3(1.0, 0.95, 0.88) * 0.1;
const vec3 CEIL_COL = vec3(0.95, 0.9, 0.84) * 0.34;`;
const GLSL_LIGHT_RIG = `
// the window opening with one vertical bar and one transom, in window-plane units
float paneMask(vec2 q, float pen) {
  vec2 e = WIN_HALF - abs(q);
  float open = smoothstep(-pen, pen, e.x) * smoothstep(-pen, pen, e.y);
  float bars = smoothstep(-pen, pen, abs(q.x) - BAR) * smoothstep(-pen, pen, abs(q.y - BAR_Y) - BAR);
  return open * bars;
}
// The gobo: how much of the window a point sees along KEY_DIR. This is what makes light look like it came
// from a real room instead of a CG directional light: a pool with straight edges and bar shadows.
float keyGobo(vec3 p) {
  mat3 B = basisOf(KEY_DIR);
  vec2 q = vec2(dot(p, B[0]), dot(p, B[1])) - WIN_OFF;
  float d = max(WIN_DIST - dot(p, KEY_DIR), 1.0);
  return paneMask(q, 0.25 + d * KEY_SPREAD);
}
// What a mirror sees. The window appears as a bright shape with bars: that shape in every reflection is the
// single strongest "this is a photograph" cue. Everything else is dark so reflections have contrast.
// envStudioRough: the same room seen in a ROUGH surface. Instead of firing random glossy rays at a small, very
// bright window (the source of sand-like speckle and sparkling metal), the window and card are blurred
// analytically by the roughness. Deterministic: zero noise, converges in one frame.
vec3 envStudioRough(vec3 rd, float rough) {
  float a = rough * rough;                       // GGX alpha: roughly the angular blur in radians
  vec3 c = mix(vec3(0.028, 0.025, 0.022), CEIL_COL, smoothstep(0.1 - a, 0.95 + a, rd.y));
  c = mix(c, vec3(0.09, 0.075, 0.06), smoothstep(0.0, -0.5 - a, rd.y));
  float k = dot(rd, KEY_DIR);
  if (k > 0.0) {
    mat3 B = basisOf(KEY_DIR);
    vec2 q = vec2(dot(rd, B[0]), dot(rd, B[1])) / k * WIN_DIST - WIN_OFF;
    float pen = 1.2 + a * WIN_DIST;
    // a blurred window spreads the same light over a larger area: keep its energy, so the peak drops
    float spread = (WIN_HALF.x * WIN_HALF.y) / ((WIN_HALF.x + pen) * (WIN_HALF.y + pen));
    c += vec3(1.0, 0.96, 0.9) * 26.0 * paneMask(q, pen) * mix(1.0, spread, saturate(a * 4.0));
  }
  float f = dot(rd, FILL_DIR);
  if (f > 0.0) {
    mat3 B = basisOf(FILL_DIR);
    vec2 e = vec2(0.6, 0.36) - abs(vec2(dot(rd, B[0]), dot(rd, B[1])) / f);
    float w = 0.18 + a;
    c += FILL_COL * 7.0 * smoothstep(-w, w, e.x) * smoothstep(-w, w, e.y);
  }
  return c;
}
vec3 envStudio(vec3 rd) { return envStudioRough(rd, 0.0); }`;
const GLSL_MATERIALS = `
// q = position in the object's own frame, in CENTIMETRES (scale noise accordingly if your units differ).
// n = geometric normal. Every material returns a perturbed normal: real surfaces are never perfect.
struct Mat { vec3 albedo; float rough; float metal; float coat; vec3 n; };
Mat mk(vec3 a, float r, float m, float c, vec3 n) { Mat x; x.albedo = a; x.rough = r; x.metal = m; x.coat = c; x.n = n; return x; }

// Metals: these are reflectance (F0) colours in linear light, not paint colours.
const vec3 BRASS = vec3(0.88, 0.69, 0.37);
const vec3 GOLD = vec3(1.0, 0.76, 0.33);
const vec3 STEEL = vec3(0.56, 0.56, 0.54);
const vec3 ALUMINIUM = vec3(0.91, 0.92, 0.92);
const vec3 COPPER = vec3(0.95, 0.62, 0.50);

// Brushed: fine parallel scratches along axis. Tilting the normal ACROSS the brushing stretches highlights
// across it, which is how brushed metal really looks.
Mat matBrushed(vec3 q, vec3 n, vec3 f0, vec3 axis) {
  vec3 b = normalize(cross(n, axis) + 1e-4);
  float a = dot(q, axis), c = dot(q, b);
  float s = 0.6 * vnoise(vec2(a * 0.5, c * 240.0)) + 0.4 * vnoise(vec2(a * 0.1, c * 700.0));
  return mk(f0 * (0.96 + 0.04 * s), 0.24 + 0.04 * s, 1.0, 0.0, normalize(n + b * (s - 0.5) * 0.012));
}
// Polished: near mirror, with faint handling haze in patches (no real polished object is uniform).
Mat matPolished(vec3 q, vec3 n, vec3 f0) {
  float h = fbm(q.xz * 0.9 + q.y);
  return mk(f0, 0.04 + 0.09 * smoothstep(0.45, 0.75, h), 1.0, 0.0, n);
}
// Glazed ceramic: coloured body under a glass coat; glaze pools and thins, a few pinholes, gentle waviness.
Mat matCeramic(vec3 q, vec3 n, vec3 glaze) {
  float pool = fbm(q.xz * 0.6 + q.y * 0.4);
  float pin = step(0.996, hash13(floor(q * 22.0)));
  vec3 w = vec3(fbm(q.xy * 1.3) - 0.5, 0.0, fbm(q.zy * 1.3 + 4.0) - 0.5);
  return mk(glaze * (0.78 + 0.4 * pool) * (1.0 - 0.6 * pin), 0.35, 0.0, 1.0, normalize(n + w * 0.025));
}
// Matte paper or card: fibres, never flat white.
Mat matPaper(vec3 q, vec3 n, vec3 tint) {
  float f = fbm(q.xz * 9.0) * 0.6 + vnoise(q.xz * 60.0) * 0.4;
  return mk(tint * (0.93 + 0.08 * f), 0.88, 0.0, 0.0, normalize(n + vec3(f - 0.5, 0.0, f - 0.5) * 0.02));
}
// Linen: plain weave with slubs (thicker uneven threads), about 18 threads per cm.
Mat matLinen(vec3 q, vec3 n, vec3 tint) {
  vec2 u = q.xz * 18.0;
  float wx = 0.5 + 0.5 * sin(u.x * PI), wy = 0.5 + 0.5 * sin(u.y * PI);
  float over = mod(floor(u.x) + floor(u.y), 2.0);
  float th = mix(wx, wy, over);
  float slub = vnoise(vec2(floor(u.x) * 3.1, u.y * 0.08)) * vnoise(vec2(u.x * 0.08, floor(u.y) * 2.7));
  vec3 a = tint * (0.8 + 0.2 * th) * (0.92 + 0.16 * slub);
  return mk(a, 0.9, 0.0, 0.0, normalize(n + vec3(cos(u.x * PI) * (1.0 - over), 0.0, cos(u.y * PI) * over) * 0.08));
}
// Plaster / limewash: broad trowel clouds and fine pores.
Mat matPlaster(vec3 q, vec3 n, vec3 tint) {
  float c = fbm(q.xy * 0.18 + q.z * 0.1), p = vnoise(q.xy * 35.0 + q.z);
  return mk(tint * (0.86 + 0.22 * c) * (0.97 + 0.04 * p), 0.92, 0.0, 0.0, normalize(n + vec3(p - 0.5, c - 0.5, 0.0) * 0.03));
}
// Honed travertine: cream with soft bands along one direction and long shallow pits.
Mat matTravertine(vec3 q, vec3 n) {
  float band = fbm(vec2(q.z * 0.35 + fbm(q.xz * 0.08) * 2.0, q.x * 0.03));
  vec3 a = mix(vec3(0.66, 0.58, 0.47), vec3(0.78, 0.71, 0.6), band);
  float pitN = vnoise(vec2(q.x * 1.6, q.z * 9.0) + 7.0) * vnoise(vec2(q.x * 0.5, q.z * 3.0));
  float pit = smoothstep(0.5, 0.58, pitN);
  a = mix(a, vec3(0.52, 0.44, 0.34), pit * 0.3);
  a *= 0.96 + 0.08 * vnoise(q.xz * 30.0);
  return mk(a, mix(0.42, 0.9, pit), 0.0, 0.0, normalize(n + vec3(0.0, 0.0, pit * 0.08)));
}
// Marble: soft warped veins, polished.
Mat matMarble(vec3 q, vec3 n, vec3 base, vec3 vein) {
  // thin veins that wander but do not curl: low warp, a main vein family and a fainter hairline family
  float w = fbm3(q * 0.15) * 3.2;
  float v = 1.0 - smoothstep(0.0, 0.05, abs(sin(q.x * 0.35 + q.z * 0.18 + w)));
  float hair = 1.0 - smoothstep(0.0, 0.03, abs(sin(q.x * 0.9 - q.z * 0.6 + w * 1.7)));
  vec3 a = mix(base, vein, v * 0.6 + hair * 0.2) * (0.96 + 0.08 * fbm(q.xz * 1.5));
  return mk(a, 0.12, 0.0, 0.6, n);
}
// Wood, grain running along x. Photographic wood is LOW contrast: rings within 25% brightness, not stripes.
const vec3 OAK_LIGHT = vec3(0.52, 0.36, 0.20), OAK_DARK = vec3(0.36, 0.23, 0.12);
const vec3 WALNUT_LIGHT = vec3(0.20, 0.11, 0.06), WALNUT_DARK = vec3(0.11, 0.055, 0.03);
Mat matWood(vec3 q, vec3 n, vec3 light, vec3 dark, float pores) {
  float r = length(q.yz + vec2(9.0, 4.0)) * 3.2 + fbm3(q * vec3(0.05, 0.7, 0.7)) * 3.0;
  float ring = smoothstep(0.4, 0.95, fract(r));
  float streak = vnoise(vec2(q.x * 0.05, q.z * 11.0 + q.y * 11.0)) * 0.6 + vnoise(vec2(q.x * 0.2, q.z * 40.0)) * 0.4;
  vec3 a = mix(light, dark, ring * 0.3 + streak * 0.35);
  float pore = smoothstep(0.78, 0.86, vnoise(vec2(q.x * 1.4, (q.z + q.y) * 55.0))) * pores;
  a *= 1.0 - pore * 0.35;
  return mk(a, 0.45 + 0.2 * pore, 0.0, 0.35, normalize(n + vec3(0.0, 0.0, (streak - 0.5) * 0.03)));
}

// Dielectrics (glass, acrylic, resin). You trace the refracted ray yourself; these do the physics around it.
float fresnelD(float c, float ior) { float r = (1.0 - ior) / (1.0 + ior); r *= r; return r + (1.0 - r) * pow(1.0 - saturate(c), 5.0); }
// Light lost to the colour of the body over a path of length len. absorb is per unit length per channel:
// clear soda glass vec3(0.05, 0.012, 0.03) per cm (green edges); resin uses strong values for deep colour.
vec3 beer(vec3 absorb, float len) { return exp(-absorb * len); }`;
const GLSL_SDF = `
float sdRoundBox(vec3 p, vec3 b, float r) { vec3 q = abs(p) - b + r; return length(max(q, 0.0)) + min(max(q.x, max(q.y, q.z)), 0.0) - r; }
float smax(float a, float b, float k) { float h = max(k - abs(a - b), 0.0); return max(a, b) + h * h * 0.25 / k; }
float smin(float a, float b, float k) { float h = max(k - abs(a - b), 0.0); return min(a, b) - h * h * 0.25 / k; }
// ray vs box centred at the origin: (t near, t far)
vec2 boxI(vec3 ro, vec3 rd, vec3 b) {
  rd = mix(rd, vec3(1e-5), lessThan(abs(rd), vec3(1e-5)));
  vec3 m = 1.0 / rd, n = m * ro, k = abs(m) * b;
  vec3 t1 = -n - k, t2 = -n + k;
  return vec2(max(max(t1.x, t1.y), t1.z), min(min(t2.x, t2.y), t2.z));
}
vec3 boxFaceNormal(vec3 p, vec3 b) { vec3 d = abs(p) / b; return d.x > d.y && d.x > d.z ? vec3(sign(p.x), 0, 0) : d.y > d.z ? vec3(0, sign(p.y), 0) : vec3(0, 0, sign(p.z)); }`;
const GLSL_SHADOW_AO = `
// needs: const float SCENE_TOP, AO_RADIUS; float map(vec3); float mapShadow(vec3); vec3 lightFilter(vec3 p, vec3 l)
// Deterministic penumbra (no random sun points: random shadow rays are the main source of floor speckle).
// SHADOW_SOFT is the penumbra angle in radians: sun-sharp is ~0.01, overcast-soft ~0.08.
const float SHADOW_SOFT = 0.03;
float softShadow(vec3 ro, vec3 rd, float tmin, float tmax) {
  float res = 1.0, t = tmin, ph = 1e10;
  for (int i = 0; i < 48; i++) {
    vec3 p = ro + rd * t;
    if (p.y > SCENE_TOP && rd.y > 0.0) break;
    float h = mapShadow(p);
    if (h < 0.0004) return 0.0;
    float y = h * h / (2.0 * ph), d = sqrt(max(h * h - y * y, 0.0));
    res = min(res, d / (SHADOW_SOFT * max(1e-3, t - y)));
    ph = h;
    t += clamp(h, 0.01, 3.0);
    if (t > tmax) break;
  }
  res = saturate(res);
  return res * res * (3.0 - 2.0 * res);
}
vec3 shadowCol(vec3 ro, vec3 rd) { return softShadow(ro, rd, 0.01, 200.0) * lightFilter(ro, rd); }
float calcAO(vec3 p, vec3 n) {
  float occ = 0.0, s = 1.0;
  for (int i = 0; i < 5; i++) { float h = AO_RADIUS * (0.06 + 0.94 * float(i) / 4.0); occ += (h - map(p + n * h)) * s; s *= 0.72; }
  return saturate(1.0 - 1.4 * occ / AO_RADIUS);
}
vec3 calcNormal(vec3 p, float e) {
  vec2 k = vec2(1.0, -1.0);
  return normalize(k.xyy * map(p + k.xyy * e) + k.yyx * map(p + k.yyx * e) + k.yxy * map(p + k.yxy * e) + k.xxx * map(p + k.xxx * e));
}`;
const GLSL_LIGHTING = `
// One opaque surface under the rig. Diffuse from the key (through the window gobo, with smooth analytic
// shadows), cool sky and the card; specular reflects the room along the mirror direction with the window
// pre-blurred by roughness (envStudioRough). Everything here is deterministic, so it adds NO per-frame noise:
// accumulation only has to clean up edges, depth of field and any glass you trace yourself.
// coat adds a sharp glaze/lacquer layer.
vec3 litOpaque(vec3 p, vec3 v, Mat m, float ao) {
  vec3 n = m.n;
  float NoV = max(dot(n, v), 1e-3);
  vec3 L = KEY_DIR;
  float NoL = max(dot(n, L), 0.0);
  vec3 sun = NoL > 0.0 ? KEY_COL * NoL * keyGobo(p) * shadowCol(p + n * 0.015, L) : vec3(0.0);
  vec3 f0 = mix(vec3(0.04), m.albedo, m.metal);
  vec3 F = f0 + (1.0 - f0) * pow(1.0 - NoV, 5.0);
  vec3 amb = SKY_COL * (0.55 + 0.45 * n.y) + FILL_COL * 1.6 * max(dot(n, FILL_DIR) + 0.25, 0.0);
  vec3 col = (1.0 - F) * (1.0 - m.metal) * m.albedo * (sun + amb * ao);
  vec3 r = reflect(-v, n);
  // rough surfaces lose some of the grazing Fresnel boost
  vec3 Fr = f0 + (max(vec3(1.0 - m.rough), f0) - f0) * pow(1.0 - NoV, 5.0);
  col += Fr * envStudioRough(r, m.rough) * mix(vec3(1.0), shadowCol(p + n * 0.015, r), 1.0 - m.rough * 0.6) * mix(1.0, ao, 0.6);
  if (m.coat > 0.0) {
    vec3 rc = reflect(-v, n);
    float Fc = (0.04 + 0.96 * pow(1.0 - NoV, 5.0)) * m.coat;
    col = col * (1.0 - Fc) + Fc * envStudio(rc) * shadowCol(p + n * 0.015, rc);
  }
  return col;
}
// Light that a lit translucent body gives off from inside (resin, wax, jade, frosted acrylic).
vec3 subsurface(vec3 p, vec3 n, vec3 scatterCol, float strength) {
  return scatterCol * strength * (KEY_COL * keyGobo(p) * (0.35 + 0.65 * max(dot(n, KEY_DIR), 0.0)) + SKY_COL);
}`;
const OUTPUT_FS = `#version 300 es
precision highp float;
uniform sampler2D uAccum;
uniform vec2 uPx;
uniform float uExposure, uGrain, uVignette, uSeed, uHalation;
in vec2 vUv;
out vec4 o;
float ign(vec2 p) { return fract(52.9829189 * fract(dot(p, vec2(0.06711056, 0.00583715)))); }
float hash(vec2 p) { vec3 p3 = fract(vec3(p.xyx) * 0.1031); p3 += dot(p3, p3.yzx + 33.33); return fract((p3.x + p3.y) * p3.z); }
// ACES filmic fit: highlights roll off instead of clipping, which is most of the "camera" look
vec3 aces(vec3 x) { return clamp((x * (2.51 * x + 0.03)) / (x * (2.43 * x + 0.59) + 0.14), 0.0, 1.0); }
void main() {
  vec3 c = texture(uAccum, vUv).rgb;
  // halation: the brightest highlights bleed a warm glow, like light scattering in film
  vec3 g = vec3(0.0);
  float rot = 6.2831853 * ign(gl_FragCoord.xy);
  for (int k = 0; k < 12; k++) {
    float a = float(k) * 2.39996 + rot, r = 2.0 + 24.0 * sqrt(float(k) / 12.0);
    g += max(texture(uAccum, vUv + vec2(cos(a), sin(a)) * r * uPx).rgb - 2.0, 0.0);
  }
  c += g / 12.0 * vec3(0.42, 0.3, 0.22) * uHalation;
  c = aces(c * uExposure);
  vec2 q = vUv - 0.5;
  c *= 1.0 - uVignette * dot(q, q) * 2.0;
  c = pow(c, vec3(1.0 / 2.2));
  // grain lives in the midtones, never in pure black or white
  float l = dot(c, vec3(0.299, 0.587, 0.114));
  // static grain (it does not crawl), meant to be barely visible: default amplitude 0.012
  c += (hash(gl_FragCoord.xy + uSeed) - 0.5) * uGrain * (0.25 + 3.0 * l * (1.0 - l));
  o = vec4(c, 1.0);
}`;
type Vec3 = [number, number, number];
type Camera = { pos: Vec3; rt: Vec3; up: Vec3; fw: Vec3; tan: number; aspect: number; shift: [number, number]; aperture: number; focus: number };
const sub = (a: Vec3, b: Vec3): Vec3 => [a[0] - b[0], a[1] - b[1], a[2] - b[2]];
const dot = (a: Vec3, b: Vec3) => a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
const norm = (a: Vec3): Vec3 => { const l = Math.hypot(a[0], a[1], a[2]) || 1; return [a[0] / l, a[1] / l, a[2] / l]; };
const cross = (a: Vec3, b: Vec3): Vec3 => [a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0]];
function lookAt(pos: Vec3, target: Vec3, fovYdeg: number, aspect: number, aperture = 0, shift: [number, number] = [0, 0]): Camera {
  const fw = norm(sub(target, pos));
  const rt = norm(cross(fw, [0, 1, 0]));
  const up = cross(rt, fw);
  return { pos, rt, up, fw, tan: Math.tan((fovYdeg * Math.PI) / 360), aspect, shift, aperture, focus: Math.hypot(...sub(target, pos)) };
}
function compileProgram(gl: WebGL2RenderingContext, vs: string, fs: string) {
  const p = gl.createProgram()!;
  for (const [type, src] of [[gl.VERTEX_SHADER, vs], [gl.FRAGMENT_SHADER, fs]] as const) {
    const s = gl.createShader(type)!;
    gl.shaderSource(s, src);
    gl.compileShader(s);
    if (!gl.getShaderParameter(s, gl.COMPILE_STATUS)) throw new Error(gl.getShaderInfoLog(s) || "shader");
    gl.attachShader(p, s);
  }
  gl.linkProgram(p);
  if (!gl.getProgramParameter(p, gl.LINK_STATUS)) throw new Error(gl.getProgramInfoLog(p) || "link");
  return p;
}
type StageOptions = {
  canvas: HTMLCanvasElement;
  wrap: HTMLElement;
  /** full fragment shader: GLSL_HEADER + chunks + your scene. Writes linear HDR to `o`. */
  sceneFS: string;
  /** called once per CSS resize, before drawing: build your camera here and return it */
  camera: (cssW: number, cssH: number) => Camera;
  /** your uniforms, every rendered frame (program is in use) */
  uniforms?: (gl: WebGL2RenderingContext, loc: (name: string) => WebGLUniformLocation | null, t: number) => void;
  /** advance your simulation; return true while anything visible is still moving */
  step?: (dt: number, t: number) => boolean;
  /** samples per pixel when at rest (then drawing stops). Default 128; never below 96 */
  samples?: number;
  /** blend weight of each new frame while moving: 0.25 (default) keeps ~4 frames of history; raise for fast motion */
  motionBlend?: number;
  maxPixels?: number; // cap on drawing buffer pixels, default 2.2e6
  maxDpr?: number; // default 2
  exposure?: number; grain?: number; vignette?: number; halation?: number;
  onFail?: () => void; // WebGL 2 missing, shader error or context lost: show your CSS still
};
function createPhotoStage(o: StageOptions) {
  const { canvas, wrap } = o;
  const fail = () => { o.onFail?.(); return null; };
  const gl = canvas.getContext("webgl2", { antialias: false, alpha: false, depth: false, powerPreference: "high-performance" });
  if (!gl) return fail();
  const float = !!gl.getExtension("EXT_color_buffer_float");
  let scene: WebGLProgram, out: WebGLProgram;
  try {
    scene = compileProgram(gl, FULLSCREEN_VS, o.sceneFS);
    out = compileProgram(gl, FULLSCREEN_VS, OUTPUT_FS);
  } catch (e) {
    console.error(e);
    return fail();
  }
  const SAMPLES = o.samples ?? 128;
  const MOTION = o.motionBlend ?? 0.25;
  let frameNo = 0;
  const maxPixels = o.maxPixels ?? 2.2e6;
  let scale = Math.min(window.devicePixelRatio || 1, o.maxDpr ?? 2);
  const vao = gl.createVertexArray();
  const fbo = gl.createFramebuffer();
  const tex = gl.createTexture();
  const locS = new Map<string, WebGLUniformLocation | null>();
  const loc = (n: string) => { if (!locS.has(n)) locS.set(n, gl.getUniformLocation(scene, n)); return locS.get(n)!; };
  const locO = (n: string) => gl.getUniformLocation(out, n);
  let W = 0, H = 0, cssW = 1, cssH = 1, n = 0, cam: Camera | null = null;

  const resize = () => {
    cssW = Math.max(1, wrap.clientWidth); cssH = Math.max(1, wrap.clientHeight);
    let k = scale;
    if (cssW * cssH * k * k > maxPixels) k = Math.sqrt(maxPixels / (cssW * cssH));
    cam = o.camera(cssW, cssH);
    n = 0;
    const w = Math.max(2, Math.round(cssW * k)), h = Math.max(2, Math.round(cssH * k));
    if (w === W && h === H) return;
    W = w; H = h; canvas.width = W; canvas.height = H;
    gl.bindTexture(gl.TEXTURE_2D, tex);
    gl.texImage2D(gl.TEXTURE_2D, 0, float ? gl.RGBA16F : gl.RGBA8, W, H, 0, gl.RGBA, float ? gl.HALF_FLOAT : gl.UNSIGNED_BYTE, null);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
    gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);
    gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, tex, 0);
  };

  const draw = (t: number, moving: boolean) => {
    const c = cam!;
    gl.bindVertexArray(vao);
    gl.viewport(0, 0, W, H);
    gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);
    gl.useProgram(scene);
    gl.uniform2f(loc("uRes"), W, H);
    gl.uniform1f(loc("uFrame"), frameNo++); // never repeats, so moving frames keep exploring new samples
    gl.uniform1f(loc("uTime"), t);
    gl.uniform3fv(loc("uCamPos"), c.pos); gl.uniform3fv(loc("uCamRt"), c.rt); gl.uniform3fv(loc("uCamUp"), c.up); gl.uniform3fv(loc("uCamFw"), c.fw);
    gl.uniform1f(loc("uTan"), c.tan); gl.uniform1f(loc("uAspect"), c.aspect); gl.uniform1f(loc("uAperture"), c.aperture); gl.uniform1f(loc("uFocus"), c.focus);
    gl.uniform2fv(loc("uShift"), c.shift);
    o.uniforms?.(gl, loc, t);
    // blend the new jittered frame into the running average: alpha 1/(n+1) is an exact mean;
    // while moving keep a SHORT history instead of restarting: alpha 0.25 is about 4 frames (a touch of motion
    // blur, no speckle). When it stops, carry on averaging from there: n continues at 1/MOTION samples.
    const alpha = moving ? MOTION : 1 / (n + 1);
    gl.enable(gl.BLEND);
    gl.blendFunc(gl.CONSTANT_ALPHA, gl.ONE_MINUS_CONSTANT_ALPHA);
    gl.blendColor(0, 0, 0, n === 0 ? 1 : alpha);
    gl.drawArrays(gl.TRIANGLES, 0, 3);
    gl.disable(gl.BLEND);
    gl.bindFramebuffer(gl.FRAMEBUFFER, null);
    gl.useProgram(out);
    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, tex);
    gl.uniform1i(locO("uAccum"), 0);
    gl.uniform2f(locO("uPx"), 1 / W, 1 / H);
    gl.uniform1f(locO("uExposure"), o.exposure ?? 1);
    gl.uniform1f(locO("uGrain"), o.grain ?? 0.012);
    gl.uniform1f(locO("uVignette"), o.vignette ?? 0.35);
    gl.uniform1f(locO("uHalation"), o.halation ?? 0.6);
    gl.uniform1f(locO("uSeed"), 0);
    gl.drawArrays(gl.TRIANGLES, 0, 3);
    n = moving ? Math.round(1 / MOTION) : n + 1;
  };

  resize();
  const ro = new ResizeObserver(resize);
  ro.observe(wrap);

  let raf = 0, last = performance.now(), slow = 0, onScreen = true, dead = false;
  const t0 = last;
  const tick = (now: number) => {
    raf = 0;
    const real = now - last;
    last = now;
    const dt = Math.min(real / 1000, 0.05);
    const t = (now - t0) / 1000;
    const moving = o.step ? o.step(dt, t) : false;
    if (moving || n < SAMPLES) {
      if (moving) {
        // measure, do not guess: if moving frames run long, draw fewer pixels
        slow = slow * 0.9 + (real > 28 ? 0.1 : 0);
        if (slow > 0.55 && scale > 0.45) { scale *= 0.85; slow = 0; W = 0; resize(); }
      }
      draw(t, moving);
    }
    if (onScreen && !document.hidden) raf = requestAnimationFrame(tick);
  };
  const wake = () => { if (!raf && !dead && onScreen && !document.hidden) { last = performance.now(); raf = requestAnimationFrame(tick); } };
  const io = new IntersectionObserver(([e]) => { onScreen = e.isIntersecting; wake(); });
  io.observe(wrap);
  document.addEventListener("visibilitychange", wake);
  const lost = (e: Event) => { e.preventDefault(); dead = true; o.onFail?.(); };
  canvas.addEventListener("webglcontextlost", lost);
  wake();

  return {
    /** something changed that is not animated (theme, text, reduced-motion snap): restart accumulation */
    invalidate() { n = 0; wake(); },
    /** call after step() starts moving from rest (input), so the loop is running */
    wake,
    camera: () => cam!,
    size: () => [cssW, cssH] as const,
    dispose() {
      dead = true;
      cancelAnimationFrame(raf);
      ro.disconnect(); io.disconnect();
      document.removeEventListener("visibilitychange", wake);
      canvas.removeEventListener("webglcontextlost", lost);
      gl.getExtension("WEBGL_lose_context")?.loseContext();
    },
  };
}
function springStep(s: { x: number; v: number }, target: number, dt: number, k = 900, damping = 38) {
  const sub = Math.max(1, Math.ceil(dt / 0.004));
  for (let i = 0; i < sub; i++) {
    const h = dt / sub;
    s.v += (k * (target - s.x) - damping * s.v) * h;
    s.x += s.v * h;
  }
  if (Math.abs(s.v) < 0.02 && Math.abs(target - s.x) < 0.002) { s.x = target; s.v = 0; return false; }
  return true;
}
const STILL_GRAIN =
  "url(\"data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='160' height='160'><filter id='n'><feTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2' stitchTiles='stitch'/><feColorMatrix values='0 0 0 0 0.5 0 0 0 0 0.5 0 0 0 0 0.5 0 0 0 0.9 0'/></filter><rect width='100%' height='100%' filter='url(%23n)'/></svg>\")";
/* ---- end of kit ---- */

// The scene, in centimetres: an opal glass globe lamp on a brass collar, on a walnut table, against a painted
// plaster wall. The bulb sits at the centre of the globe; uGlow (0 to 1) is how bright it burns.
const SCENE = `
const float SCENE_TOP = 40.0;
const float AO_RADIUS = 2.4;
uniform float uGlow;
const vec3 GC = vec3(0.0, 11.2, 0.0);
const float GR = 8.0;
const float WALL_Z = -26.0;
const vec3 LAMP = vec3(1.0, 0.6, 0.3);
float sdCyl(vec3 p, float r, float h, float e) { vec2 d = vec2(length(p.xz) - r + e, abs(p.y) - h + e); return min(max(d.x, d.y), 0.0) + length(max(d, 0.0)) - e; }
float brass(vec3 p) {
  float foot = sdCyl(p - vec3(0.0, 0.32, 0.0), 5.4, 0.32, 0.14);
  float neck = sdCyl(p - vec3(0.0, 2.0, 0.0), 2.3, 1.6, 0.2);
  float cup = sdCyl(p - vec3(0.0, 3.85, 0.0), 3.6, 0.5, 0.2);
  return smin(smin(foot, neck, 0.6), cup, 0.5);
}
vec2 scene(vec3 p, int skip) {
  vec2 r = vec2(p.y, 0.0);
  float w = p.z - WALL_Z; if (w < r.x) r = vec2(w, 1.0);
  float b = brass(p); if (b < r.x) r = vec2(b, 2.0);
  if (skip != 3) { float g = length(p - GC) - GR; if (g < r.x) r = vec2(g, 3.0); }
  return r;
}
float map(vec3 p) { return scene(p, -1).x; }
// the window is imagined in the left wall, so the back wall does not block the sun
float mapShadow(vec3 p) { return min(brass(p), length(p - GC) - GR); }
vec3 lightFilter(vec3 p, vec3 l) { return vec3(1.0); }
`;
const SCENE_MAIN = `
// Light from the globe onto the table, the wall and the brass: a large warm source, so a broad wrap and a
// soft shadow from the collar. Deterministic, no sampling.
vec3 lampLight(vec3 p, vec3 n, vec3 v, Mat m) {
  if (uGlow <= 0.0) return vec3(0.0);
  vec3 d = GC - p;
  float dist = length(d);
  vec3 l = d / dist;
  float wrap = saturate((dot(n, l) + 0.35) / 1.35);
  float fall = 1.0 / (dist * dist * 0.012 + 0.35);
  // only the collar can hide the globe; stop the shadow ray before it reaches the glass
  float sh = 1.0, t = 0.05;
  for (int i = 0; i < 28; i++) {
    float h = brass(p + l * t);
    sh = min(sh, 6.0 * h / t);
    t += clamp(h, 0.05, 2.0);
    if (t > dist - GR * 0.7 || sh < 0.0) break;
  }
  sh = saturate(sh);
  vec3 E = LAMP * uGlow * 14.0 * fall * smoothstep(0.0, 1.0, sh);
  vec3 f0 = mix(vec3(0.04), m.albedo, m.metal);
  vec3 h = normalize(l + v);
  float spec = pow(max(dot(m.n, h), 0.0), mix(400.0, 8.0, m.rough)) * mix(1.0, 0.25, m.rough);
  return E * ((1.0 - m.metal) * m.albedo * wrap + f0 * spec * max(dot(m.n, l), 0.0) * 6.0);
}
vec3 shadeGlobe(vec3 p, vec3 v, vec3 n) {
  vec3 q = p - GC;
  // acid-etched opal glass: a milky body with a soft gloss, a slow cloud in the etch
  float etch = fbm(q.xy * 0.9 + q.z * 0.4);
  Mat m = mk(vec3(0.82, 0.81, 0.78) * (0.95 + 0.1 * etch), 0.55, 0.0, 0.55, normalize(n + vec3(etch - 0.5) * 0.02));
  vec3 col = litOpaque(p, v, m, 1.0) * 0.7 + subsurface(p, n, vec3(0.92, 0.9, 0.86), 0.22);
  // the burning bulb: light scattered through the opal, a touch brighter where we look through the most glass
  float NoV = saturate(dot(n, v));
  float lower = smoothstep(-GR, -GR * 0.35, q.y);                // the brass cup hides the bottom of the globe
  float core = exp(-pow(length(q - dot(q, v) * v) / GR, 2.0) * 2.2); // the bulb seen through the frost
  float g = uGlow * uGlow * 0.6 + uGlow * 0.4;
  vec3 glow = LAMP * g * (1.1 * (0.18 + 0.82 * pow(NoV, 1.3)) + 1.5 * core * core) * (0.94 + 0.12 * etch) * mix(0.35, 1.0, lower);
  return col * (1.0 - 0.5 * uGlow) + glow;
}
vec3 shadeOpaque(int id, vec3 p, vec3 v) {
  vec3 n = calcNormal(p, 0.003);
  float ao = calcAO(p, n);
  Mat m;
  if (id == 0) m = matWood(p.zyx, n, vec3(0.24, 0.135, 0.075), WALNUT_DARK * 1.3, 1.0);
  else if (id == 1) m = matPlaster(p, n, vec3(0.055, 0.095, 0.13));
  else { m = matBrushed(p, n, BRASS * 0.92, vec3(1.0, 0.0, 0.0)); m.rough = 0.34; }
  return litOpaque(p, v, m, ao) + lampLight(p, n, v, m) * mix(1.0, ao, 0.5);
}
void main() {
  vec3 ro, rd;
  cameraRay(ro, rd);
  float t = 0.0;
  vec2 h = vec2(1e9, 0.0);
  bool hit = false;
  for (int s = 0; s < 200; s++) {
    h = scene(ro + rd * t, -1);
    if (h.x < 0.0003 * t) { hit = true; break; }
    t += h.x;
    if (t > 1200.0) break;
  }
  vec3 p = ro + rd * t, col;
  int id = int(h.y + 0.5);
  if (!hit) col = envStudio(rd);
  else if (id == 3) col = shadeGlobe(p, -rd, normalize(p - GC));
  else col = shadeOpaque(id, p, -rd);
  o = vec4(clampSample(col, 5.0), 1.0);
}
`;

const SCENE_FS = [GLSL_HEADER, GLSL_COMMON, GLSL_SAMPLING, GLSL_CAMERA, GLSL_RIG_SETTINGS, GLSL_LIGHT_RIG, GLSL_MATERIALS, GLSL_SDF, SCENE, GLSL_SHADOW_AO, GLSL_LIGHTING, SCENE_MAIN].join("\n");

const glowFor = (count: number) => (count === 0 ? 0 : Math.min(1, GLOW_FIRST + GLOW_STEP * (count - 1)));

/** The lamp. Purely decorative: the accordion beside it is the real control. */
function Lamp({ glow }: { glow: number }) {
  const reduce = useReducedMotion();
  const wrapRef = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);
  const [still, setStill] = useState(false);
  const sim = useRef({ glow: { x: glow, v: 0 }, target: glow, wake: () => {} });

  useEffect(() => {
    sim.current.target = glow;
    sim.current.wake();
  }, [glow]);

  useEffect(() => {
    const wrap = wrapRef.current, canvas = canvasRef.current;
    if (!wrap || !canvas) return;
    const s = sim.current;
    const stage = createPhotoStage({
      canvas,
      wrap,
      sceneFS: SCENE_FS,
      samples: 128,
      exposure: 1.05,
      vignette: 0.4,
      motionBlend: 0.3,
      onFail: () => setStill(true),
      camera: (w, h) => {
        const aspect = w / h;
        const fov = 17;
        const el = 0.44;
        const target: Vec3 = [0, 8.6, 0];
        const fitH = 21.0 / Math.tan((fov * Math.PI) / 360); // the lamp and some table, top to bottom
        const fitW = 15 / (Math.tan((fov * Math.PI) / 360) * aspect); // and across, on wide short frames
        const dist = Math.max(fitH, fitW);
        return lookAt([dist * 0.18, target[1] + Math.sin(el) * dist, Math.cos(el) * dist], target, fov, aspect, dist * 0.012, [0, -0.04]);
      },
      uniforms: (gl, loc) => gl.uniform1f(loc("uGlow"), Math.max(0, s.glow.x)),
      // a filament warms up and cools down; it never snaps (unless motion is reduced)
      step: (dt) => {
        if (reduce) {
          if (s.glow.x === s.target) return false;
          s.glow.x = s.target; s.glow.v = 0;
          return true;
        }
        return springStep(s.glow, s.target, dt, 26, 10);
      },
    });
    if (!stage) return;
    s.wake = () => stage.wake();
    return () => { s.wake = () => {}; stage.dispose(); };
  }, [reduce]);

  return (
    <div ref={wrapRef} className="relative h-[380px] w-full sm:h-[460px] lg:h-[760px]">
      <canvas ref={canvasRef} aria-hidden="true" className={`absolute inset-0 h-full w-full ${still ? "hidden" : ""}`} />
      {still && (
        <div aria-hidden="true" className="absolute inset-0" style={{ background: WALL }}>
          <div className="absolute inset-x-0 bottom-0 h-[34%]" style={{ background: "#2b1a10" }} />
          <div
            className="absolute left-1/2 top-[30%] aspect-square w-[34%] max-w-[220px] -translate-x-1/2 rounded-full transition-[box-shadow,background-color] duration-700"
            style={{ backgroundColor: glow > 0 ? "#f6dcb4" : "#cfccc4", boxShadow: glow > 0 ? `0 0 ${60 + 120 * glow}px ${10 + 30 * glow}px rgba(255,170,90,${0.25 + 0.35 * glow})` : "none" }}
          />
          <div className="absolute left-1/2 top-[calc(30%+min(34cqw,220px))] h-3 w-[16%] max-w-[110px] -translate-x-1/2 rounded-full" style={{ background: "#7a6136" }} />
          <div className="absolute inset-0 opacity-30 mix-blend-overlay" style={{ backgroundImage: STILL_GRAIN }} />
        </div>
      )}
    </div>
  );
}

export default function FaqAccordionOpalLamp() {
  const reduce = useReducedMotion();
  const uid = useId();
  const [many, setMany] = useState(true);
  const [open, setOpen] = useState<number[]>(OPEN_AT_START);
  const btns = useRef<(HTMLButtonElement | null)[]>([]);

  const toggle = (i: number) =>
    setOpen((cur) => (cur.includes(i) ? cur.filter((x) => x !== i) : many ? [...cur, i].sort((a, b) => a - b) : [i]));
  const setMode = (m: boolean) => {
    setMany(m);
    if (!m) setOpen((cur) => cur.slice(0, 1));
  };
  // the WAI-ARIA accordion keys: up and down move between questions, Home and End jump to the ends
  const onKey = (e: KeyboardEvent<HTMLButtonElement>, i: number) => {
    const n = faqs.length;
    const to = e.key === "ArrowDown" ? (i + 1) % n : e.key === "ArrowUp" ? (i - 1 + n) % n : e.key === "Home" ? 0 : e.key === "End" ? n - 1 : -1;
    if (to < 0) return;
    e.preventDefault();
    btns.current[to]?.focus();
  };

  const glow = glowFor(open.length);
  const lit = open.length === 0 ? "Lamp off" : `${open.length} of ${faqs.length} open`;

  return (
    <section className="relative overflow-hidden" style={{ background: WALL, color: INK, fontFamily: GROTESK }}>
      <div className="grid lg:items-start lg:grid-cols-[minmax(0,1fr)_minmax(0,1.08fr)]">
        <div className="order-2 px-5 pb-10 pt-8 sm:px-10 lg:order-1 lg:min-h-[760px] lg:py-16 lg:pl-14 lg:pr-8">
          <p className="text-[11px] font-semibold uppercase tracking-[0.24em] text-[#efe6d8]/60">Opal globe lamp</p>
          <h2 className="mt-3 text-[34px] font-semibold leading-[1.02] tracking-[-0.025em] sm:text-[46px]">Questions, answered.</h2>

          <div role="group" aria-label="How many answers can be open" className="mt-7 inline-flex rounded-full bg-black/25 p-1 text-[13px] font-medium">
            {[["One at a time", false], ["Several at once", true]].map(([label, m]) => (
              <button
                key={String(label)}
                type="button"
                aria-pressed={many === m}
                onClick={() => setMode(m as boolean)}
                className={`rounded-full px-4 py-1.5 outline-none transition-colors focus-visible:ring-2 focus-visible:ring-[#efe6d8]/80 ${many === m ? "bg-[#efe6d8] text-[#16232e]" : "text-[#efe6d8]/70 hover:text-[#efe6d8]"}`}
              >
                {label as string}
              </button>
            ))}
          </div>

          <div className="mt-6 border-t border-[#efe6d8]/15">
            {faqs.map((f, i) => {
              const isOpen = open.includes(i);
              const bid = `${uid}-q${i}`, pid = `${uid}-a${i}`;
              return (
                <div key={f.q} className="border-b border-[#efe6d8]/15">
                  <h3 className="m-0">
                    <button
                      ref={(el) => { btns.current[i] = el; }}
                      id={bid}
                      type="button"
                      aria-expanded={isOpen}
                      aria-controls={pid}
                      onClick={() => toggle(i)}
                      onKeyDown={(e) => onKey(e, i)}
                      className="group flex w-full items-center justify-between gap-6 rounded-md py-5 text-left text-[17px] font-medium leading-snug outline-none focus-visible:ring-2 focus-visible:ring-[#efe6d8]/80 focus-visible:ring-offset-4 focus-visible:ring-offset-[#16232e] sm:text-[19px]"
                    >
                      <span className={`transition-colors ${isOpen ? "text-[#efe6d8]" : "text-[#efe6d8]/85 group-hover:text-[#efe6d8]"}`}>{f.q}</span>
                      <span aria-hidden="true" className="relative h-3.5 w-3.5 shrink-0">
                        <span className="absolute left-0 top-1/2 h-[1.5px] w-full -translate-y-1/2 rounded bg-current" />
                        <span className={`absolute left-1/2 top-0 h-full w-[1.5px] -translate-x-1/2 rounded bg-current ${reduce ? "" : "transition-transform duration-300 ease-out"} ${isOpen ? "scale-y-0" : "scale-y-100"}`} />
                      </span>
                    </button>
                  </h3>
                  <div
                    id={pid}
                    role="region"
                    aria-labelledby={bid}
                    className={`grid ${reduce ? "" : "transition-[grid-template-rows,opacity] duration-300 ease-[cubic-bezier(0.2,0.8,0.2,1)]"} ${isOpen ? "opacity-100" : "opacity-0"}`}
                    style={{ gridTemplateRows: isOpen ? "1fr" : "0fr" }}
                    {...(isOpen ? {} : ({ inert: "" } as Record<string, string>))}
                  >
                    <div className="overflow-hidden">
                      <p className="max-w-[46ch] pb-6 pr-8 text-[15px] leading-relaxed text-[#efe6d8]/70">{f.a}</p>
                    </div>
                  </div>
                </div>
              );
            })}
          </div>
          <p aria-live="polite" className="mt-5 text-[12px] tabular-nums text-[#efe6d8]/50">{lit}</p>
        </div>

        <div className="order-1 lg:sticky lg:top-0 lg:order-2">
          <Lamp glow={glow} />
        </div>
      </div>
    </section>
  );
}