Silk Weft

"use client";

import { useEffect, useRef } from "react";
import { mountShaderSurface } from "@/lib/shader-surface";

/**
 * A variation on `SilkField` that turns the drapery on its side: the exact
 * same fold math (two-scale sine bands riding a low-frequency fbm warp),
 * the exact same pointer contract, and the exact same live amber ramp — the
 * only thing that changes is which axis the bands run along. `silk-drape`'s
 * folds hang top to bottom; these run left to right, "weft" being the
 * crosswise thread in a woven fabric where "warp" (confusingly, in the
 * weaving sense, not the shader sense) runs the other way.
 *
 * The gradient turns with the bands: pale gold anchored on the left,
 * deepening through gold and umber into deep umber on the right, instead of
 * pale-at-base/deep-at-top.
 *
 * The pointer's contract is unchanged from `silk-drape`: it parts the bands
 * nearest it and leaves a soft warm bloom, as if the fabric were touched
 * from behind — just turned ninety degrees with everything else.
 *
 * Drop it into any `position: relative`/`isolate` parent — it fills the box.
 * Same degradation contract as `SilkField`: no WebGL, a blocked or lost
 * context, a hidden tab, or `prefers-reduced-motion` all leave the CSS
 * `.iris-silkweftfield__floor` underneath visible.
 */
const FRAG = `
uniform vec2  u_res;
uniform float u_time;
uniform float u_scale;
uniform vec3  u_pointer;  /* x, y (0 bottom .. 1 top), presence 0..1 */

uniform vec3 u_deep;    /* --color-accent-950, the right edge of the field */
uniform vec3 u_umber;   /* --color-accent-800, right-mid */
uniform vec3 u_gold;    /* --color-accent-600, left-mid */
uniform vec3 u_pale;    /* --color-accent-300, the left edge */

uniform vec4  u_readA;
uniform float u_guard;

/* Bands across the height, at two scales — a slow, wide sway and a finer
   thread count riding on top of it. Identical constants to SilkField;
   only the axis they read along changes. */
const float FOLDS   = 6.0;
const float THREADS = 22.0;

void main() {
  vec2 res = u_res / u_scale;
  vec2 uv  = gl_FragCoord.xy / u_scale / res;          /* 0..1, y up */
  float aspect = res.x / res.y;
  vec2 P = (uv - 0.5) * vec2(aspect, 1.0);

  vec2 ptr = (u_pointer.xy - 0.5) * vec2(aspect, 1.0);
  vec2 toP = P - ptr;
  float dP = length(toP);
  float pull = u_pointer.z * exp(-dP * dP * 50.0);

  /* the touch parts the weft: bands near the cursor bend toward it, as if
     the fabric were being pulled from behind the cursor */
  vec2 wp = P - toP * pull * 1.1;

  /* the same low-amplitude warp as silk-drape, just reading its primary
     coordinate off wp.y instead of wp.x, so it perturbs horizontal bands
     rather than vertical ones */
  float warp = fbm(vec2(wp.y * 1.4, wp.x * 0.8 + u_time * 0.02)) * 0.30;
  float phase = wp.y * FOLDS + warp + u_time * 0.035;

  float coarse = sin(phase * 3.14159265);
  float fine   = sin((wp.y * THREADS + warp * 1.6) * 3.14159265);
  float weft   = clamp(coarse * 0.72 + fine * 0.28, -1.0, 1.0);
  weft = sign(weft) * pow(abs(weft), 0.82);            /* widen the bright peaks a touch */

  /* ---- the horizontal gradient, pale at the left, deep at the right ---- */
  vec3 base = u_pale;
  base = mix(base, u_gold,  smoothstep(0.10, 0.52, uv.x));
  base = mix(base, u_umber, smoothstep(0.42, 0.80, uv.x));
  base = mix(base, u_deep,  smoothstep(0.70, 1.05, uv.x));

  vec3 col = base * (0.58 + 0.62 * (0.5 + 0.5 * weft));

  /* the touch: a soft warm bloom, and the nearest bands catch extra light */
  col += u_pale * pull * 0.42;
  col += base   * pull * (0.5 + 0.5 * weft) * 0.5;

  col = max(col, 0.0);

  /* ---- the reading guard (see TileField for the full rationale) ---- */
  vec2 rd = abs(uv - u_readA.xy) / max(u_readA.zw, vec2(0.02));
  float m = mix(max(rd.x, rd.y), length(rd), 0.4);
  float band = 1.0 - smoothstep(0.72, 2.1, m);
  col = mix(col, holdUnder(col, 0.09), band * u_guard);

  col += (bayer8(gl_FragCoord.xy) - 0.5) * (2.2 / 255.0);

  gl_FragColor = vec4(col, 1.0);
}
`;

export interface SilkWeftFieldProps {
  className?: string;
  /**
   * CSS selector for the block the reading guard should keep readable,
   * resolved against `document`. `null` (the default) turns the guard off.
   */
  guardSelector?: string | null;
}

export function SilkWeftField({ className, guardSelector = null }: SilkWeftFieldProps) {
  const canvasRef = useRef<HTMLCanvasElement>(null);

  useEffect(() => {
    const canvas = canvasRef.current;
    if (!canvas) return;

    const guardOn = guardSelector != null;
    let guardEl: Element | null | undefined;
    const readGuardEl = () => {
      if (guardEl === undefined) {
        guardEl = guardOn ? document.querySelector(guardSelector as string) : null;
      }
      return guardEl;
    };

    return mountShaderSurface(canvas, {
      fragment: FRAG,
      colors: {
        u_deep: "--color-accent-950",
        u_umber: "--color-accent-800",
        u_gold: "--color-accent-600",
        u_pale: "--color-accent-300",
      },
      uniforms: ["u_readA", "u_guard"],
      onInit: (gl, u) => {
        if (u.u_readA) gl.uniform4f(u.u_readA, 0.5, 0.5, 0.44, 0.32);
        if (u.u_guard) gl.uniform1f(u.u_guard, guardOn ? 1 : 0);
      },
      onFrame: (gl, u, s) => {
        if (!guardOn || !u.u_readA) return;
        let cx = 0.5, cy = 0.5, hw = 0.44, hh = 0.32;
        const el = readGuardEl();
        const { rect } = s;
        if (el && rect.width > 0 && rect.height > 0) {
          const r = el.getBoundingClientRect();
          const padX = rect.width * 0.09;
          const padY = rect.height * 0.11;
          cx = (r.left + r.width / 2 - rect.left) / rect.width;
          cy = 1 - (r.top + r.height / 2 - rect.top) / rect.height;
          hw = (r.width / 2 + padX) / rect.width;
          hh = (r.height / 2 + padY) / rect.height;
        }
        gl.uniform4f(u.u_readA, cx, cy, hw, hh);
      },
      onPainted: () => canvas.setAttribute("data-shader", "on"),
      /* No onIdle — same contract as `SilkField`: once the field has painted
         once, its last frame stays on screen while the surface is parked
         off-view, instead of crossfading to the static floor on every
         scroll-away/back. A lost context still clears it below. */
      onLost: () => canvas.removeAttribute("data-shader"),
      maxPixels: 2_200_000,
      dprCap: 1.5,
    });
  }, [guardSelector]);

  return (
    <div className={`absolute inset-0 overflow-hidden${className ? ` ${className}` : ""}`} aria-hidden="true">
      <div className="iris-silkweftfield__floor absolute inset-0 [background:linear-gradient(_90deg,var(--color-accent-300)_0%,var(--color-accent-600)_28%,var(--color-accent-800)_58%,var(--color-accent-950)_100%_)]" />
      <canvas ref={canvasRef} className="absolute inset-0 w-full h-full opacity-0 transition-opacity duration-[--duration-slow] ease-[--ease-standard] data-[shader=on]:opacity-100" />
    </div>
  );
}