"use client";

import * as React from "react";

/**
 * BitHeadline: a headline whose letters are made of running binary digits.
 *
 * - "solid" lines condense from bits into massive dark type, with digits still moving inside.
 * - "bits" lines stay built from digits only, so they read lighter.
 *
 * The real text stays in the DOM (transparent once the canvas is drawn), so it remains
 * selectable, accessible and visible without JavaScript.
 */

export type BitLine = {
  readonly text: string;
  readonly tone: "solid" | "bits";
};

type Measured = {
  readonly text: string;
  readonly tone: BitLine["tone"];
  readonly x: number;
  readonly baseline: number;
  /** Vertical extent of the glyphs, which can exceed a tight line box. */
  readonly top: number;
  readonly height: number;
  readonly width: number;
  readonly font: string;
  readonly letterSpacing: string;
};

const DARK = "15, 23, 42"; // slate-900
const LIGHT = "255, 255, 255";
const INTRO_MS = 1600;
const FRAME_MS = 1000 / 30;
const POINTER_RADIUS = 170;
const MIN_CELL = 6;

const easeOut = (t: number): number => 1 - Math.pow(1 - t, 3);
const clamp01 = (n: number): number => Math.min(1, Math.max(0, n));

const makeSprite = (
  digit: string,
  color: string,
  cell: number,
  dpr: number,
): HTMLCanvasElement => {
  const sprite = document.createElement("canvas");
  sprite.width = Math.ceil(cell * dpr);
  sprite.height = Math.ceil(cell * dpr);
  const sctx = sprite.getContext("2d");
  if (sctx) {
    sctx.scale(dpr, dpr);
    const mono =
      getComputedStyle(document.documentElement)
        .getPropertyValue("--font-jetbrains-mono")
        .trim() || "ui-monospace";
    sctx.font = `700 ${Math.round(cell * 1.15)}px ${mono}, ui-monospace, Menlo, monospace`;
    sctx.textAlign = "center";
    sctx.textBaseline = "middle";
    sctx.fillStyle = color;
    sctx.fillText(digit, cell / 2, cell / 2 + 0.5);
  }
  return sprite;
};

export const BitHeadline: React.FC<{
  lines: readonly BitLine[];
  className?: string;
  /** Render as this heading level. */
  as?: "h1" | "h2";
  /** Light type on a dark surface. */
  invert?: boolean;
}> = ({ lines, className = "", as: Tag = "h1", invert = false }) => {
  const wrapRef = React.useRef<HTMLHeadingElement>(null);
  const INK = invert ? LIGHT : DARK;
  const PAPER = invert ? DARK : LIGHT;
  const canvasRef = React.useRef<HTMLCanvasElement>(null);
  const [painted, setPainted] = React.useState(false);

  React.useEffect(() => {
    const wrap = wrapRef.current;
    const canvas = canvasRef.current;
    const ctx = canvas?.getContext("2d");
    if (!wrap || !canvas || !ctx) return;

    const off = document.createElement("canvas");
    const offCtx = off.getContext("2d");
    if (!offCtx) return;

    const reducedMotion = window.matchMedia(
      "(prefers-reduced-motion: reduce)",
    ).matches;
    // Touch screens have no pointer to light the digits up, so a spot wanders on its own.
    const noHover = window.matchMedia("(hover: none)").matches;

    let measured: Measured[] = [];
    let width = 0;
    let height = 0;
    let dpr = 1;
    let cell = 12;
    let wash = 0.07;
    let cols = 0;
    let rows = 0;
    let bits = new Uint8Array(0);
    let phase = new Float32Array(0);
    let speed = new Float32Array(0);
    let sprites: {
      light: HTMLCanvasElement[];
      dark: HTMLCanvasElement[];
    } | null = null;
    let raf = 0;
    let startedAt = 0;
    let lastFrame = 0;
    let pointer: { x: number; y: number } | null = null;
    let disposed = false;

    const measure = () => {
      const box = wrap.getBoundingClientRect();
      dpr = Math.min(window.devicePixelRatio || 1, 2);
      width = box.width;
      height = box.height;
      for (const target of [canvas, off]) {
        target.width = Math.ceil(width * dpr);
        target.height = Math.ceil(height * dpr);
      }
      ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
      offCtx.setTransform(dpr, 0, 0, dpr, 0, 0);

      const spans = Array.from(
        wrap.querySelectorAll<HTMLSpanElement>("[data-bit-line]"),
      );
      measured = spans.map((span, index) => {
        const rect = span.getBoundingClientRect();
        const style = getComputedStyle(span);
        const font = `${style.fontStyle} ${style.fontWeight} ${style.fontSize} ${style.fontFamily}`;
        ctx.font = font;
        const metrics = ctx.measureText("Hg");
        const ascent = metrics.fontBoundingBoxAscent;
        const descent = metrics.fontBoundingBoxDescent;
        const lineTop = rect.top - box.top;
        const baseline =
          lineTop + (rect.height - (ascent + descent)) / 2 + ascent;
        return {
          text: span.textContent ?? "",
          tone: lines[index]?.tone ?? "solid",
          x: rect.left - box.left,
          top: baseline - ascent,
          height: ascent + descent,
          width: rect.width,
          baseline,
          font,
          letterSpacing: style.letterSpacing,
        };
      });

      const fontSize = parseFloat(getComputedStyle(wrap).fontSize) || 100;
      // Digits below about 6px are specks, not digits: on phones the cells stay
      // readable and the letters are built from fewer of them.
      cell = Math.round(Math.min(9, Math.max(MIN_CELL, fontSize / 19)));
      // Small type needs a stronger wash under the digits to keep its shape.
      wash = fontSize < 100 ? 0.24 : 0.07;
      cols = Math.ceil(width / cell);
      rows = Math.ceil(height / cell);
      bits = new Uint8Array(cols * rows);
      phase = new Float32Array(cols * rows);
      speed = new Float32Array(cols * rows);
      for (let i = 0; i < bits.length; i++) {
        bits[i] = Math.random() < 0.5 ? 0 : 1;
        phase[i] = Math.random() * Math.PI * 2;
        speed[i] = 0.6 + Math.random() * 1.8;
      }
      sprites = {
        light: [
          makeSprite("0", `rgb(${PAPER})`, cell, dpr),
          makeSprite("1", `rgb(${PAPER})`, cell, dpr),
        ],
        dark: [
          makeSprite("0", `rgb(${INK})`, cell, dpr),
          makeSprite("1", `rgb(${INK})`, cell, dpr),
        ],
      };
    };

    const setFont = (context: CanvasRenderingContext2D, line: Measured) => {
      context.font = line.font;
      context.textBaseline = "alphabetic";
      context.textAlign = "left";
      if ("letterSpacing" in context) {
        (
          context as CanvasRenderingContext2D & { letterSpacing: string }
        ).letterSpacing =
          line.letterSpacing === "normal" ? "0px" : line.letterSpacing;
      }
    };

    /** Digits over one line's box. `strength` scales the alpha, `set` picks the sprite color. */
    const drawDigits = (
      context: CanvasRenderingContext2D,
      line: Measured,
      set: HTMLCanvasElement[],
      seconds: number,
      base: number,
      swing: number,
    ) => {
      const firstRow = Math.max(0, Math.floor(line.top / cell));
      const lastRow = Math.min(
        rows,
        Math.ceil((line.top + line.height) / cell),
      );
      const firstCol = Math.max(0, Math.floor(line.x / cell));
      const lastCol = Math.min(cols, Math.ceil((line.x + line.width) / cell));
      // A soft diagonal scan band that travels across the headline.
      const scan = ((seconds * 0.16) % 1.6) * (width + height) - height * 0.3;

      for (let row = firstRow; row < lastRow; row++) {
        for (let col = firstCol; col < lastCol; col++) {
          const i = row * cols + col;
          const x = col * cell;
          const y = row * cell;
          let alpha =
            base +
            swing *
              (0.5 +
                0.5 * Math.sin(seconds * (speed[i] ?? 1) + (phase[i] ?? 0)));
          const scanDistance = Math.abs(x + y - scan);
          if (scanDistance < 90) alpha += (1 - scanDistance / 90) * 0.45;
          if (pointer) {
            const d = Math.hypot(x - pointer.x, y - pointer.y);
            if (d < POINTER_RADIUS) alpha += (1 - d / POINTER_RADIUS) * 0.7;
          }
          if (alpha <= 0.02) continue;
          // Occasionally flip a bit so the field stays alive.
          if (Math.random() < 0.004) bits[i] = bits[i] === 1 ? 0 : 1;
          const sprite = set[bits[i] ?? 0];
          if (!sprite) continue;
          context.globalAlpha = clamp01(alpha);
          context.drawImage(sprite, x, y, cell, cell);
        }
      }
      context.globalAlpha = 1;
    };

    const paint = (now: number) => {
      if (!sprites) return;
      const seconds = now / 1000;
      const intro = reducedMotion
        ? 1
        : easeOut(clamp01((now - startedAt) / INTRO_MS));

      ctx.clearRect(0, 0, width, height);

      for (const line of measured) {
        offCtx.globalCompositeOperation = "source-over";
        offCtx.clearRect(0, 0, width, height);

        if (line.tone === "solid") {
          // Letters start as pure bits and condense into solid ink.
          drawDigits(
            offCtx,
            line,
            sprites.dark,
            seconds,
            0.75 * (1 - intro),
            0.25 * (1 - intro),
          );
          offCtx.globalCompositeOperation = "destination-in";
          setFont(offCtx, line);
          offCtx.fillStyle = "#000";
          offCtx.fillText(line.text, line.x, line.baseline);
          ctx.drawImage(off, 0, 0, width, height);

          setFont(ctx, line);
          ctx.fillStyle = `rgba(${INK}, ${intro})`;
          ctx.fillText(line.text, line.x, line.baseline);

          // Bright digits keep moving inside the solid letters.
          offCtx.globalCompositeOperation = "source-over";
          offCtx.clearRect(0, 0, width, height);
          drawDigits(
            offCtx,
            line,
            sprites.light,
            seconds,
            0.02 * intro,
            0.16 * intro,
          );
          offCtx.globalCompositeOperation = "destination-in";
          setFont(offCtx, line);
          offCtx.fillText(line.text, line.x, line.baseline);
          ctx.drawImage(off, 0, 0, width, height);
        } else {
          // Stays built from digits only, on a faint wash so the letters keep their shape.
          setFont(ctx, line);
          ctx.fillStyle = `rgba(${INK}, ${wash * intro})`;
          ctx.fillText(line.text, line.x, line.baseline);
          drawDigits(offCtx, line, sprites.dark, seconds, 0.3, 0.5);
          offCtx.globalCompositeOperation = "destination-in";
          setFont(offCtx, line);
          offCtx.fillStyle = "#000";
          offCtx.fillText(line.text, line.x, line.baseline);
          ctx.globalAlpha = 0.25 + 0.75 * intro;
          ctx.drawImage(off, 0, 0, width, height);
          ctx.globalAlpha = 1;
        }
      }
    };

    const loop = (now: number) => {
      if (disposed) return;
      if (now - lastFrame >= FRAME_MS) {
        lastFrame = now;
        if (noHover) {
          const seconds = now / 1000;
          pointer = {
            x: width * (0.5 + 0.46 * Math.sin(seconds * 0.55)),
            y: height * (0.5 + 0.4 * Math.sin(seconds * 0.9 + 1)),
          };
        }
        paint(now);
      }
      raf = requestAnimationFrame(loop);
    };

    const restart = () => {
      cancelAnimationFrame(raf);
      measure();
      // Hidden at this breakpoint (display: none): nothing to draw.
      if (width === 0 || height === 0) return;
      if (reducedMotion) {
        paint(performance.now());
        return;
      }
      raf = requestAnimationFrame(loop);
    };

    const onPointerMove = (event: PointerEvent) => {
      const box = wrap.getBoundingClientRect();
      pointer = { x: event.clientX - box.left, y: event.clientY - box.top };
    };
    const onPointerLeave = () => {
      pointer = null;
    };

    const resizeObserver = new ResizeObserver(() => restart());

    document.fonts.ready.then(() => {
      if (disposed) return;
      startedAt = performance.now();
      restart();
      setPainted(true);
      resizeObserver.observe(wrap);
      if (!reducedMotion && !noHover) {
        window.addEventListener("pointermove", onPointerMove);
        document.addEventListener("pointerleave", onPointerLeave);
      }
    });

    return () => {
      disposed = true;
      cancelAnimationFrame(raf);
      resizeObserver.disconnect();
      window.removeEventListener("pointermove", onPointerMove);
      document.removeEventListener("pointerleave", onPointerLeave);
    };
  }, [lines, INK, PAPER, invert]);

  return (
    <Tag ref={wrapRef} className={`relative m-0 ${className}`}>
      {lines.map((line) => (
        <span
          key={line.text}
          data-bit-line
          className={`block w-fit whitespace-nowrap transition-colors duration-300 ${
            painted
              ? "text-transparent"
              : line.tone === "solid"
                ? invert
                  ? "text-white"
                  : "text-slate-900"
                : invert
                  ? "text-slate-600"
                  : "text-slate-300"
          }`}
        >
          {line.text}
        </span>
      ))}
      <canvas
        ref={canvasRef}
        aria-hidden="true"
        className="pointer-events-none absolute inset-0 h-full w-full"
      />
    </Tag>
  );
};