Tear Button

"use client";

/**
 * @author: @dorianbaffier
 * @description: Tear Button
 * @version: 1.0.0
 * @date: 2026-10-14
 * @license: MIT
 * @website: https://kokonutui.com
 * @github: https://github.com/kokonut-labs/kokonutui
 */

import {
  type KeyboardEvent,
  type PointerEvent,
  type ReactNode,
  useCallback,
  useEffect,
  useRef,
  useState,
} from "react";
import { cn } from "@/lib/utils";

const HEIGHT = 68;
const BODY_WIDTH = 236;
const STUB_WIDTH = 76;
// How far (deg) the stub swings, about the foot of the perforation, before
// the last fibre gives.
const TEAR_ANGLE = 34;
// The perforation tears hole by hole: each one holds for a moment, then
// gives. That stick-slip is what makes it feel like paper.
const HOLES = 7;
const HOLD = 0.55;
const HOLD_SHARE = 0.3;
// The stub's swing chases the hand on a stiff spring, so the slips snap.
const SWING_STIFFNESS = 900;
const SWING_DAMPING = 42;
const RETURN_STIFFNESS = 520;
const RETURN_DAMPING = 22;
// Once free: px and seconds.
const GRAVITY = 2600;
const FALL_DISTANCE = 220;
const STEP = 1 / 120;
// Ragged edge of the tear, as offsets in px along the perforation.
const FIBRES = [
  1.6, 0.4, 2.2, 0.9, 1.8, 0.2, 2.4, 1.1, 0.5, 2, 1.4, 0.3, 2.3, 0.8, 1.7, 0.1,
  2.1, 1.2, 0.6, 1.9,
];
const EASE_OUT = "cubic-bezier(0.23, 1, 0.32, 1)";

type Phase = "idle" | "tearing" | "flying" | "torn";

function clamp(value: number, min: number, max: number) {
  return Math.min(Math.max(value, min), max);
}

function haptic(ms: number) {
  if (typeof navigator !== "undefined" && "vibrate" in navigator) {
    navigator.vibrate(ms);
  }
}

/** Raw pull (0..1+) to how far the tear has run, holding at each hole. */
function stickSlip(pull: number) {
  const scaled = clamp(pull, 0, 1) * HOLES;
  const hole = Math.min(Math.floor(scaled), HOLES - 1);
  const f = scaled - hole;
  const given =
    f < HOLD
      ? (f / HOLD) * HOLD_SHARE
      : HOLD_SHARE + ((f - HOLD) / (1 - HOLD)) * (1 - HOLD_SHARE);
  return (hole + given) / HOLES;
}

/**
 * One side of the tear as a clip-path: ragged down to `tip` (px from the
 * top), straight below. `side` is 1 for the body's right edge, -1 for the
 * stub's left edge.
 */
function tornEdge(tip: number, width: number, side: 1 | -1) {
  const points: string[] = [];
  const edge = side === 1 ? width : 0;
  const far = side === 1 ? 0 : width;
  points.push(`${far}px 0px`);
  const rows = Math.ceil((tip / HEIGHT) * FIBRES.length);
  for (let k = 0; k <= rows; k++) {
    const y = Math.min((k / FIBRES.length) * HEIGHT, tip);
    const x = edge - side * FIBRES[k % FIBRES.length];
    points.push(`${x.toFixed(1)}px ${y.toFixed(1)}px`);
  }
  points.push(`${edge}px ${tip.toFixed(1)}px`, `${edge}px ${HEIGHT}px`);
  points.push(`${far}px ${HEIGHT}px`);
  return `polygon(${points.join(",")})`;
}

// Ticket notches, cut where the perforation meets the top and bottom edges.
const NOTCH = 7;
const bodyMask = `radial-gradient(circle at 100% 0, #0000 ${NOTCH}px, #000 ${NOTCH + 0.5}px) top / 100% 51% no-repeat, radial-gradient(circle at 100% 100%, #0000 ${NOTCH}px, #000 ${NOTCH + 0.5}px) bottom / 100% 51% no-repeat`;
const stubMask = `radial-gradient(circle at 0 0, #0000 ${NOTCH}px, #000 ${NOTCH + 0.5}px) top / 100% 51% no-repeat, radial-gradient(circle at 0 100%, #0000 ${NOTCH}px, #000 ${NOTCH + 0.5}px) bottom / 100% 51% no-repeat`;

const TONES = {
  default: {
    paper: "bg-zinc-900 text-white dark:bg-zinc-100 dark:text-zinc-900",
    chip: "bg-white/10 dark:bg-zinc-900/10",
    chipDone: "bg-white text-zinc-900 dark:bg-zinc-900 dark:text-white",
    sub: "text-white/55 dark:text-zinc-900/55",
    stub: "text-white/60 dark:text-zinc-900/60",
    perforation: "border-white/30 dark:border-zinc-900/30",
  },
  muted: {
    paper: "bg-zinc-100 text-zinc-900 dark:bg-zinc-800 dark:text-zinc-100",
    chip: "bg-zinc-900/5 dark:bg-white/10",
    chipDone: "bg-zinc-900 text-white dark:bg-white dark:text-zinc-900",
    sub: "text-zinc-500 dark:text-zinc-400",
    stub: "text-zinc-500 dark:text-zinc-400",
    perforation: "border-zinc-900/20 dark:border-white/25",
  },
  danger: {
    paper: "bg-red-600 text-white",
    chip: "bg-white/15",
    chipDone: "bg-white text-red-600",
    sub: "text-white/70",
    stub: "text-white/75",
    perforation: "border-white/40",
  },
} as const;

const TRASH = (
  <svg
    aria-hidden="true"
    className="size-4"
    fill="none"
    stroke="currentColor"
    strokeLinecap="round"
    strokeLinejoin="round"
    strokeWidth={2}
    viewBox="0 0 24 24"
  >
    <path d="M4 7h16M10 11v6M14 11v6M6 7l1 12a2 2 0 0 0 2 2h6a2 2 0 0 0 2-2l1-12M9 7V4h6v3" />
  </svg>
);

export interface TearButtonProps {
  /** Paper colour. */
  tone?: keyof typeof TONES;
  /** Shown in the round chip until the stub is torn; a trash can by default. */
  icon?: ReactNode;
  label?: string;
  description?: string;
  stubLabel?: string;
  confirmedLabel?: string;
  confirmedDescription?: string;
  /** Called once the stub comes away. */
  onConfirm?: () => void;
  /** Print a fresh stub this many ms after confirming. Off when 0. */
  resetAfter?: number;
  className?: string;
}

export default function TearButton({
  tone = "default",
  icon = TRASH,
  label = "Delete workspace",
  description = "Tear off the stub to confirm",
  stubLabel = "Tear",
  confirmedLabel = "Workspace deleted",
  confirmedDescription = "Kept in trash for 30 days",
  onConfirm,
  resetAfter = 2400,
  className,
}: TearButtonProps) {
  const [phase, setPhase] = useState<Phase>("idle");
  const [generation, setGeneration] = useState(0);
  const rootRef = useRef<HTMLDivElement>(null);
  const bodyRef = useRef<HTMLDivElement>(null);
  const stubRef = useRef<HTMLButtonElement>(null);
  // Set when the stub tears away with focus on it, so focus can follow.
  const hadFocusRef = useRef(false);

  const sim = useRef({
    angle: 0,
    speed: 0,
    target: 0,
    held: false,
    grabAngle: 0,
    hole: 0,
    raf: 0,
    last: 0,
    carry: 0,
    // Free flight, once torn.
    x: 0,
    y: 0,
    vx: 0,
    vy: 0,
    spin: 0,
    // The hand's recent movement, for the throw.
    px: 0,
    py: 0,
    pt: 0,
    pvx: 0,
    pvy: 0,
    auto: 0,
    flying: false,
    reduceMotion: false,
  });

  const latest = useRef({ onConfirm });
  latest.current = { onConfirm };

  const hinge = useCallback(() => {
    const rect = rootRef.current?.getBoundingClientRect();
    return rect
      ? { x: rect.left + BODY_WIDTH, y: rect.top + HEIGHT }
      : { x: 0, y: 0 };
  }, []);

  const drawTear = useCallback(() => {
    const s = sim.current;
    const tip = clamp(s.angle / TEAR_ANGLE, 0, 1) * HEIGHT;
    const stub = stubRef.current;
    const body = bodyRef.current;
    if (body) {
      body.style.clipPath = tip > 0.5 ? tornEdge(tip, BODY_WIDTH, 1) : "";
    }
    if (stub) {
      stub.style.clipPath = tip > 0.5 ? tornEdge(tip, STUB_WIDTH, -1) : "";
      stub.style.transform = `rotate(${s.angle.toFixed(2)}deg)`;
    }
  }, []);

  const drawFlight = useCallback(() => {
    const s = sim.current;
    const stub = stubRef.current;
    if (!stub) {
      return;
    }
    const fade = clamp(
      1 - (s.y - FALL_DISTANCE * 0.5) / (FALL_DISTANCE * 0.5),
      0,
      1
    );
    stub.style.transform = `translate(${s.x.toFixed(1)}px, ${s.y.toFixed(1)}px) rotate(${s.angle.toFixed(1)}deg)`;
    stub.style.opacity = fade.toFixed(3);
  }, []);

  const detach = useCallback(() => {
    const s = sim.current;
    s.held = false;
    haptic(14);
    // The stub leaves with the swing it had, plus the hand's throw.
    const rad = (s.angle * Math.PI) / 180;
    const tangential = ((s.speed * Math.PI) / 180) * HEIGHT;
    s.x = 0;
    s.y = 0;
    s.vx = Math.cos(rad) * tangential + clamp(s.pvx, -900, 900) * 0.6 + 90;
    s.vy = Math.sin(rad) * tangential + clamp(s.pvy, -900, 900) * 0.6 - 120;
    s.spin = s.speed * 0.6 + 140;
    s.flying = true;
    if (stubRef.current) {
      stubRef.current.style.transition = "none";
      hadFocusRef.current = document.activeElement === stubRef.current;
    }
    setPhase("flying");
    latest.current.onConfirm?.();
  }, []);

  // While attached: the swing chases its target, held or springing home.
  const stepSwing = useCallback(() => {
    const s = sim.current;
    const stiffness = s.held || s.auto ? SWING_STIFFNESS : RETURN_STIFFNESS;
    const damping = s.held || s.auto ? SWING_DAMPING : RETURN_DAMPING;
    const force = (s.target - s.angle) * stiffness - s.speed * damping;
    s.speed += force * STEP;
    s.angle += s.speed * STEP;
    // A tick for each hole that gives.
    const hole = Math.floor(clamp(s.angle / TEAR_ANGLE, 0, 1) * HOLES);
    if (hole > s.hole) {
      haptic(3);
    }
    s.hole = hole;
    return s.angle >= TEAR_ANGLE * 0.995;
  }, []);

  const stepFlight = useCallback(() => {
    const s = sim.current;
    s.vy += GRAVITY * STEP;
    s.x += s.vx * STEP;
    s.y += s.vy * STEP;
    s.angle += s.spin * STEP;
    return s.y > FALL_DISTANCE;
  }, []);

  // Runs the fixed steps owed since the last frame; true once this phase is
  // over (the stub tore through, or it has fallen out of sight).
  const advance = useCallback(
    (elapsed: number) => {
      const s = sim.current;
      s.carry += elapsed;
      let finished = false;
      while (s.carry >= STEP && !finished) {
        s.carry -= STEP;
        if (s.flying) {
          finished = stepFlight();
        } else if (s.auto) {
          s.target = Math.min(s.target + STEP * 60, TEAR_ANGLE * 1.05);
          finished = stepSwing();
        } else {
          finished = stepSwing() && s.held;
        }
      }
      return finished;
    },
    [stepFlight, stepSwing]
  );

  const tick = useCallback(
    (now: number) => {
      const s = sim.current;
      s.raf = 0;
      const elapsed = s.last ? Math.min((now - s.last) / 1000, 0.05) : STEP;
      s.last = now;
      const { flying } = s;
      const finished = advance(elapsed);
      if (flying) {
        drawFlight();
        if (finished) {
          s.last = 0;
          setPhase("torn");
          return;
        }
        s.raf = requestAnimationFrame(tick);
        return;
      }
      drawTear();
      if (finished) {
        s.auto = 0;
        detach();
        s.raf = requestAnimationFrame(tick);
        return;
      }
      const resting =
        !(s.held || s.auto) &&
        Math.abs(s.angle) < 0.02 &&
        Math.abs(s.speed) < 0.05;
      if (!resting) {
        s.raf = requestAnimationFrame(tick);
        return;
      }
      s.angle = 0;
      s.speed = 0;
      s.last = 0;
      drawTear();
      setPhase("idle");
    },
    [advance, detach, drawFlight, drawTear]
  );

  const wake = useCallback(() => {
    const s = sim.current;
    if (!s.raf) {
      s.raf = requestAnimationFrame(tick);
    }
  }, [tick]);

  useEffect(() => {
    const s = sim.current;
    const query = window.matchMedia("(prefers-reduced-motion: reduce)");
    s.reduceMotion = query.matches;
    const onChange = () => {
      s.reduceMotion = query.matches;
    };
    query.addEventListener("change", onChange);
    return () => {
      query.removeEventListener("change", onChange);
      cancelAnimationFrame(s.raf);
      s.raf = 0;
    };
  }, []);

  // A fresh stub, a little while after the last one came away.
  useEffect(() => {
    if (phase !== "torn" || !resetAfter) {
      return;
    }
    const id = window.setTimeout(() => {
      const s = sim.current;
      s.angle = 0;
      s.speed = 0;
      s.target = 0;
      s.hole = 0;
      s.flying = false;
      setGeneration((g) => g + 1);
      setPhase("idle");
    }, resetAfter);
    return () => window.clearTimeout(id);
  }, [phase, resetAfter]);

  // The torn stub unmounts, which would drop focus on <body>. Hold it on the
  // ticket meanwhile and hand it to the fresh stub when one is printed.
  useEffect(() => {
    if (!hadFocusRef.current) {
      return;
    }
    if (phase === "torn") {
      rootRef.current?.focus({ preventScroll: true });
    } else if (phase === "idle") {
      hadFocusRef.current = false;
      stubRef.current?.focus({ preventScroll: true });
    }
  }, [phase]);

  // In reduced motion the stub doesn't fall: it fades where it tore.
  useEffect(() => {
    if (phase !== "flying" || !sim.current.reduceMotion) {
      return;
    }
    const s = sim.current;
    cancelAnimationFrame(s.raf);
    s.raf = 0;
    s.last = 0;
    const stub = stubRef.current;
    if (stub) {
      stub.style.transition = `opacity 180ms ${EASE_OUT}`;
      stub.style.opacity = "0";
    }
    const id = window.setTimeout(() => setPhase("torn"), 180);
    return () => window.clearTimeout(id);
  }, [phase]);

  const handlePointerDown = (event: PointerEvent<HTMLButtonElement>) => {
    const s = sim.current;
    if (phase === "flying" || phase === "torn") {
      return;
    }
    if (event.pointerType === "mouse" && event.button !== 0) {
      return;
    }
    event.preventDefault();
    event.currentTarget.setPointerCapture(event.pointerId);
    const h = hinge();
    s.grabAngle =
      (Math.atan2(event.clientY - h.y, event.clientX - h.x) * 180) / Math.PI -
      s.angle;
    s.held = true;
    s.px = event.clientX;
    s.py = event.clientY;
    s.pt = event.timeStamp;
    s.pvx = 0;
    s.pvy = 0;
    setPhase("tearing");
    wake();
  };

  const handlePointerMove = (event: PointerEvent<HTMLButtonElement>) => {
    const s = sim.current;
    if (!s.held) {
      return;
    }
    const dt = event.timeStamp - s.pt;
    if (dt > 0) {
      s.pvx = s.pvx * 0.5 + ((event.clientX - s.px) / dt) * 500;
      s.pvy = s.pvy * 0.5 + ((event.clientY - s.py) / dt) * 500;
    }
    s.px = event.clientX;
    s.py = event.clientY;
    s.pt = event.timeStamp;
    const h = hinge();
    const raw =
      (Math.atan2(event.clientY - h.y, event.clientX - h.x) * 180) / Math.PI -
      s.grabAngle;
    // Pushing the stub back into the body only gives a little.
    const pull = raw < 0 ? raw * 0.15 : raw;
    s.target =
      pull >= TEAR_ANGLE
        ? TEAR_ANGLE * 1.05
        : stickSlip(Math.max(pull, 0) / TEAR_ANGLE) * TEAR_ANGLE +
          Math.min(pull, 0);
    wake();
  };

  const handlePointerUp = () => {
    const s = sim.current;
    if (!s.held) {
      return;
    }
    s.held = false;
    // Not torn through: the stub swings back and the perforation holds.
    s.target = 0;
    wake();
  };

  const handleKeyDown = (event: KeyboardEvent<HTMLButtonElement>) => {
    if (event.key !== "Enter" && event.key !== " ") {
      return;
    }
    event.preventDefault();
    const s = sim.current;
    if (phase !== "idle" || event.repeat) {
      return;
    }
    // From the keyboard the stub tears itself, hole by hole.
    s.auto = 1;
    s.target = 0;
    setPhase("tearing");
    wake();
  };

  const done = phase === "flying" || phase === "torn";
  const colors = TONES[tone];

  return (
    <div
      className={cn("relative select-none outline-none", className)}
      ref={rootRef}
      style={{ width: BODY_WIDTH + STUB_WIDTH, height: HEIGHT }}
      tabIndex={-1}
    >
      <div
        className={cn(
          "absolute inset-y-0 left-0 flex items-center gap-3 rounded-l-2xl px-4",
          colors.paper
        )}
        ref={bodyRef}
        style={{ width: BODY_WIDTH, mask: bodyMask, WebkitMask: bodyMask }}
      >
        <span
          aria-hidden="true"
          className={cn(
            "flex size-9 shrink-0 items-center justify-center rounded-full transition-colors duration-300 ease-out",
            done ? colors.chipDone : colors.chip
          )}
        >
          {done ? (
            <svg
              aria-hidden="true"
              className="size-4"
              fill="none"
              stroke="currentColor"
              strokeLinecap="round"
              strokeLinejoin="round"
              strokeWidth={2}
              viewBox="0 0 24 24"
            >
              <path d="M5 12.5l4.5 4.5L19 7.5" />
            </svg>
          ) : (
            icon
          )}
        </span>
        <span className="relative grid min-w-0 flex-1">
          {[
            { key: "ask", on: !done, title: label, sub: description },
            {
              key: "done",
              on: done,
              title: confirmedLabel,
              sub: confirmedDescription,
            },
          ].map((line) => (
            <span
              aria-hidden={!line.on}
              className={cn(
                "col-start-1 row-start-1 min-w-0 transition-[opacity,filter,translate] duration-300 ease-[cubic-bezier(0.23,1,0.32,1)] motion-reduce:transition-opacity",
                line.on
                  ? "translate-y-0 opacity-100 blur-0"
                  : "pointer-events-none translate-y-1 opacity-0 blur-[3px]"
              )}
              key={line.key}
            >
              <span className="block truncate font-medium text-sm">
                {line.title}
              </span>
              <span className={cn("block truncate text-xs", colors.sub)}>
                {line.sub}
              </span>
            </span>
          ))}
        </span>
      </div>

      {phase === "torn" ? null : (
        <button
          aria-label={`${label}: ${description}`}
          className={cn(
            "absolute inset-y-0 flex touch-none flex-col items-center justify-center gap-1 rounded-r-2xl outline-none",
            // The notch mask clips anything drawn outside the stub, so the
            // focus ring sits inside it.
            "focus-visible:ring-2 focus-visible:ring-current focus-visible:ring-inset",
            colors.paper,
            colors.stub,
            "starting:-translate-x-3 starting:opacity-0 transition-[opacity,translate] duration-300 ease-[cubic-bezier(0.23,1,0.32,1)]",
            phase === "tearing" ? "cursor-grabbing" : "cursor-grab"
          )}
          // A new stub per tear, so no inline style from the last one lingers.
          key={generation}
          onKeyDown={handleKeyDown}
          onLostPointerCapture={handlePointerUp}
          onPointerCancel={handlePointerUp}
          onPointerDown={handlePointerDown}
          onPointerMove={handlePointerMove}
          onPointerUp={handlePointerUp}
          ref={stubRef}
          style={{
            left: BODY_WIDTH,
            width: STUB_WIDTH,
            mask: stubMask,
            WebkitMask: stubMask,
            transformOrigin: "0 100%",
          }}
          type="button"
        >
          {/* The perforation. */}
          <span
            aria-hidden="true"
            className={cn(
              "absolute inset-y-2.5 left-0 border-l-2 border-dotted",
              colors.perforation
            )}
          />
          <svg
            aria-hidden="true"
            className="size-4"
            fill="none"
            stroke="currentColor"
            strokeLinecap="round"
            strokeLinejoin="round"
            strokeWidth={2}
            viewBox="0 0 24 24"
          >
            <path d="M6 6c6 0 12 3 12 11M14 14l4 4 4-4" />
          </svg>
          <span className="font-medium text-xs">{stubLabel}</span>
        </button>
      )}
      <span aria-live="polite" className="sr-only">
        {done ? confirmedLabel : ""}
      </span>
    </div>
  );
}