Split-flap board

pnpm add cn

/*
 * Bevel foundation. Every component builds on these tokens and utilities;
 * component stylesheets only add their own palettes and shapes.
 *
 * Layers:
 *   1. Light     one source, above and slightly in front of the screen.
 *   2. Depth     named elevations built from the light: recessed, flush,
 *                raised, pressed, object.
 *   3. Material  a surface recipe (leather, plastic, metal) that reads
 *                --bevel-material and --bevel-material-edge.
 *   4. Motion    two curves, a spring, and durations named by purpose.
 *   5. Shape     radii, stitching, and the type scale for amounts.
 */

:root {
  /* 1. Light */
  --bevel-highlight: oklch(1 0 0 / 0.22);
  --bevel-highlight-strong: oklch(1 0 0 / 0.35);
  --bevel-shade: oklch(0 0 0 / 0.32);
  --bevel-shade-strong: oklch(0 0 0 / 0.5);
  --bevel-cast: oklch(0.25 0.03 50 / 0.22);
  /* Stamped into a surface: shaded on the upper inner edge, lit below. */
  --bevel-deboss: 0 -1px 0 oklch(0 0 0 / 0.45), 0 1px 0 oklch(1 0 0 / 0.12);

  /* 3. Material defaults; components and variants override these. */
  --bevel-material: oklch(0.47 0.085 52);
  --bevel-material-edge: oklch(0.3 0.06 44);
  --bevel-material-recess: oklch(0.2 0.008 260); /* neutral dark; materials set their own */
  --bevel-grain: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='180' height='180'%3E%3Cfilter id='g'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.7' numOctaves='3' stitchTiles='stitch'/%3E%3CfeColorMatrix values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .7 0 0 0 0'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23g)'/%3E%3C/svg%3E");
  --bevel-grain-size: 180px;

  /* 2. Depth */
  --bevel-depth-recessed:
    inset 0 1px 2px var(--bevel-shade-strong),
    0 1px 0 var(--bevel-highlight);
  --bevel-depth-flush:
    inset 0 1px 0 var(--bevel-highlight),
    inset 0 -1px 0 var(--bevel-shade);
  --bevel-depth-raised:
    inset 0 1px 0 var(--bevel-highlight),
    0 1px 0 var(--bevel-material-edge),
    0 2px 0 var(--bevel-material-edge),
    0 3px 5px var(--bevel-shade);
  --bevel-depth-pressed:
    inset 0 1px 2px var(--bevel-shade),
    0 1px 0 var(--bevel-highlight);
  /* A whole object resting on the page. */
  --bevel-depth-object:
    inset 0 1px 0 var(--bevel-highlight),
    inset 0 -1px 0 var(--bevel-shade),
    0 0 0 1px var(--bevel-material-edge),
    0 1px 1px var(--bevel-cast),
    0 6px 12px -2px var(--bevel-cast),
    0 18px 32px -8px var(--bevel-cast);
  /* The shadow under a loose object, for filter: drop-shadow(). */
  --bevel-depth-cast-sm: 0 4px 6px var(--bevel-cast);
  /* A thin object (a card) lying on another surface. */
  --bevel-depth-sheet:
    inset 0 1px 0 var(--bevel-highlight-strong),
    inset 0 0 0 1px oklch(0 0 0 / 0.12),
    0 -1px 2px oklch(0 0 0 / 0.18);

  /* 4. Motion */
  --bevel-ease-out: cubic-bezier(0.23, 1, 0.32, 1);
  --bevel-ease-in-out: cubic-bezier(0.77, 0, 0.175, 1);
  /* Underdamped spring, ~8% overshoot. Pure CSS; pair with --bevel-duration-move or longer. */
  --bevel-ease-spring: linear(0, 0.06, 0.202, 0.38, 0.561, 0.723, 0.856, 0.955, 1.023, 1.062, 1.081, 1.083, 1.075, 1.062, 1.047, 1.032, 1.019, 1.009, 1.002, 0.997, 0.994, 0.993, 0.993, 0.994, 1);
  --bevel-duration-press: 100ms; /* a control giving under a finger */
  --bevel-duration-small: 200ms; /* hover lifts, tabs, small state changes */
  --bevel-duration-move: 300ms; /* objects moving: cards, drawers */
  --bevel-duration-ambient: 520ms; /* whole-scene changes: lighting */
  --bevel-stagger: 30ms;
  --bevel-lift: 3px; /* how far an object rises on hover */
  --bevel-perspective: 30rem; /* viewing distance for parts that turn in 3D (covers, flaps) */
  /* Unchosen items in a group sit back in shadow. */
  --bevel-dim: 0.82;

  /* 5. Shape */
  --bevel-radius-xs: 0.25rem;
  --bevel-radius-sm: 0.5rem;
  --bevel-radius-md: 0.625rem;
  --bevel-radius-lg: 1rem;
  --bevel-radius-xl: 1.5rem;
  --bevel-stitch-width: 1.5px;
  --bevel-stitch-inset: 0.375rem;
  /* Amounts: the figure, its secondary parts (currency, cents), labels, fine print. */
  --bevel-amount: 2.25rem;
  --bevel-amount-minor: 1.25rem;
  --bevel-label: 0.75rem;
  --bevel-fine: 0.6875rem;
  --bevel-tracking-label: 0.08em; /* stamped labels */
  --bevel-tracking-print: 0.06em; /* printed marks on cards */

  /* Paper and ink */
  --bevel-paper: oklch(0.975 0.008 85);
  --bevel-paper-foreground: oklch(0.28 0.02 260);
  --bevel-paper-muted: oklch(0.48 0.015 260);
  --bevel-paper-rule: oklch(0.78 0.04 240 / 0.45);
  --bevel-paper-margin: oklch(0.68 0.14 25 / 0.45);
  --bevel-fibre: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='240' height='240'%3E%3Cfilter id='f'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.9 .35' numOctaves='2' stitchTiles='stitch'/%3E%3CfeColorMatrix values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 .18 0 0 0 0'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23f)'/%3E%3C/svg%3E");
  /* Ink soaks unevenly: mostly solid with pale specks. Used as a mask. */
  --bevel-ink-texture: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='160' height='160'%3E%3Cfilter id='i'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.85' numOctaves='2' stitchTiles='stitch'/%3E%3CfeColorMatrix values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -2.4 0 0 0 2.1'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23i)'/%3E%3C/svg%3E");
  --bevel-ink-red: oklch(0.52 0.19 27);
  --bevel-ink-blue: oklch(0.44 0.14 262);
  --bevel-ink-green: oklch(0.5 0.12 155);
  --bevel-ink-black: oklch(0.3 0.01 260);
  --bevel-ink-amber: oklch(0.55 0.13 65);

  /* Brass and ivory: instrument hardware and dial faces */
  --bevel-brass: oklch(0.76 0.11 82);
  --bevel-brass-edge: oklch(0.52 0.08 70);
  --bevel-ivory: oklch(0.95 0.025 90);
  --bevel-ivory-foreground: oklch(0.25 0.015 60);
  --bevel-needle: oklch(0.55 0.2 27);

  /* Desk stationery: legal pads, pens, pencils, exhibit stickers */
  --bevel-pad: oklch(0.95 0.075 98); /* yellow legal pad */
  --bevel-pad-foreground: oklch(0.27 0.03 255);
  --bevel-pad-rule: oklch(0.72 0.06 235 / 0.45);
  --bevel-pad-margin: oklch(0.62 0.16 25 / 0.55);
  --bevel-pen-red: oklch(0.52 0.2 27); /* correcting pen */
  --bevel-pen-blue: oklch(0.42 0.15 262); /* writing pen */
  --bevel-pencil: oklch(0.55 0.01 260); /* not written in ink yet */
  --bevel-sticker: oklch(0.9 0.12 95); /* exhibit sticker */
  --bevel-sticker-foreground: oklch(0.26 0.03 70);
  /* Handwriting. Bring a marker font (e.g. Permanent Marker) for the full effect; these are fallbacks. */
  --bevel-font-marker: "Permanent Marker", "Marker Felt", "Chalkboard SE", ui-rounded, "Arial Rounded MT Bold", system-ui, sans-serif;
}

.dark {
  --bevel-highlight: oklch(1 0 0 / 0.14);
  /* Paper under dim light, not inverted: it's still paper. */
  --bevel-paper: oklch(0.88 0.008 85);
  --bevel-ivory: oklch(0.86 0.022 90);
  --bevel-pad: oklch(0.86 0.07 98);
  --bevel-cast: oklch(0 0 0 / 0.55);
}

/* Depth */
@utility bevel-recessed {
  background-color: var(--bevel-material-recess);
  box-shadow: var(--bevel-depth-recessed);
}
@utility bevel-flush {
  box-shadow: var(--bevel-depth-flush);
}
@utility bevel-raised {
  background-color: color-mix(in oklch, var(--bevel-material), white 7%);
  background-image: linear-gradient(to bottom, var(--bevel-highlight), transparent 60%);
  box-shadow: var(--bevel-depth-raised);
}
@utility bevel-pressed {
  background-color: color-mix(in oklch, var(--bevel-material), black 4%);
  background-image: none;
  box-shadow: var(--bevel-depth-pressed);
}
@utility bevel-object {
  box-shadow: var(--bevel-depth-object);
}

/* Materials */
@utility bevel-leather {
  background-color: var(--bevel-material);
  background-image:
    var(--bevel-grain),
    linear-gradient(to bottom, var(--bevel-highlight), transparent 28%, transparent 72%, var(--bevel-shade));
  background-size: var(--bevel-grain-size) var(--bevel-grain-size), 100% 100%;
  background-blend-mode: soft-light, normal;
}
@utility bevel-plastic {
  background-color: var(--bevel-material);
  background-image:
    linear-gradient(115deg, var(--bevel-highlight-strong), transparent 40%),
    linear-gradient(to bottom, transparent 25%, oklch(0 0 0 / 0.45));
  box-shadow: var(--bevel-depth-sheet);
}
@utility bevel-metal {
  background-color: var(--bevel-material);
  background-image:
    linear-gradient(to bottom, var(--bevel-highlight-strong), transparent 45%, var(--bevel-shade) 100%),
    repeating-linear-gradient(90deg, oklch(1 0 0 / 0.06) 0 1px, transparent 1px 3px);
  box-shadow:
    inset 0 0 0 1px oklch(0 0 0 / 0.25),
    inset 0 1px 0 var(--bevel-highlight-strong);
}

/* Details */
@utility bevel-deboss {
  text-shadow: var(--bevel-deboss);
}
@utility bevel-stitch {
  border-color: var(--bevel-stitch, oklch(0.88 0.05 82 / 0.8));
  border-style: dashed;
  border-width: var(--bevel-stitch-width);
  filter: drop-shadow(0 1px 0 var(--bevel-shade));
}
/* A lit fill sitting in a recess (meters, progress). Colour from --bevel-fill. */
@utility bevel-fill {
  background-color: var(--bevel-fill);
  background-image: linear-gradient(to bottom, oklch(1 0 0 / 0.55), transparent 55%, oklch(0 0 0 / 0.18));
  box-shadow: 0 0 6px -1px var(--bevel-fill);
}
/* A small indicator light. Colour from --bevel-led. */
@utility bevel-led {
  background-color: var(--bevel-led);
  background-image: radial-gradient(circle at 35% 30%, oklch(1 0 0 / 0.85), transparent 45%);
  box-shadow:
    0 0 6px var(--bevel-led),
    inset 0 -1px 1px oklch(0 0 0 / 0.35),
    0 1px 0 var(--bevel-highlight);
}

/* Paper: a sheet resting on the surface, with fibre in it. */
@utility bevel-paper {
  background-color: var(--bevel-paper);
  background-image: var(--bevel-fibre);
  background-size: 240px 240px;
  color: var(--bevel-paper-foreground);
  box-shadow:
    0 1px 1px var(--bevel-cast),
    0 6px 14px -4px var(--bevel-cast);
}
/* Ink on paper: multiplies into the surface and soaks unevenly. Colour from --bevel-ink. */
@utility bevel-ink {
  color: var(--bevel-ink, var(--bevel-ink-red));
  border-color: currentColor;
  mix-blend-mode: multiply;
  mask-image: var(--bevel-ink-texture);
  mask-size: 160px 160px;
}
/* Glass over an instrument window: one reflection from the light above. Put on an overlay element. */
@utility bevel-glass {
  pointer-events: none;
  background-image: linear-gradient(165deg, var(--bevel-highlight-strong) 0%, transparent 38%, transparent 70%, var(--bevel-shade) 100%);
}

/* Material families: one per screen. Set on the screen's container. */
[data-bevel-family="leather"] {
  --bevel-cast: oklch(0.25 0.03 50 / 0.22);
}
[data-bevel-family="paper"] {
  --bevel-cast: oklch(0.3 0.01 250 / 0.16);
}
.dark :is([data-bevel-family="leather"], [data-bevel-family="paper"]) {
  --bevel-cast: oklch(0 0 0 / 0.55);
}

/*
 * Ruled paper: rules every --bevel-rule-height and a margin line at
 * --bevel-rule-margin. Set --bevel-sheet for the paper colour. The ruling
 * scrolls with the content.
 */
@utility bevel-ruled {
  background-color: var(--bevel-sheet, var(--bevel-paper));
  background-image:
    linear-gradient(
      to right,
      transparent calc(var(--bevel-rule-margin) - 1px),
      var(--bevel-sheet-margin, var(--bevel-paper-margin)) calc(var(--bevel-rule-margin) - 1px) calc(var(--bevel-rule-margin) + 1px),
      transparent calc(var(--bevel-rule-margin) + 1px)
    ),
    repeating-linear-gradient(
      to bottom,
      transparent 0 calc(var(--bevel-rule-height) - 1px),
      var(--bevel-sheet-rule, var(--bevel-paper-rule)) calc(var(--bevel-rule-height) - 1px) var(--bevel-rule-height)
    ),
    var(--bevel-fibre);
  background-size: 100% 100%, 100% 100%, 240px 240px;
  background-attachment: local;
  color: var(--bevel-paper-foreground);
  box-shadow:
    0 1px 1px var(--bevel-cast),
    0 6px 14px -4px var(--bevel-cast);
}

"use client"

import * as React from "react"
import { cn } from "cn"

type SplitFlapContextValue = { changed: (row: string) => void }

const SplitFlapContext = React.createContext<SplitFlapContextValue | null>(null)
const SplitFlapRowContext = React.createContext<string>("")

function toMilliseconds(value: string, fallback: number) {
  const n = parseFloat(value)
  if (Number.isNaN(n)) return fallback
  return value.trim().endsWith("ms") ? n : n * 1000
}

/**
 * A split-flap status board. The text is the truth; the flaps only show
 * it. Changes are gathered and announced once, by row, not letter by
 * letter. Give it an aria-label.
 */
function SplitFlap({ className, children, ...props }: React.ComponentProps<"div">) {
  const [message, setMessage] = React.useState("")
  const pending = React.useRef(new Set<string>())
  const timer = React.useRef<number>(undefined)
  const root = React.useRef<HTMLDivElement>(null)

  const changed = React.useCallback((row: string) => {
    pending.current.add(row)
    if (timer.current !== undefined) return
    const wait = root.current
      ? toMilliseconds(getComputedStyle(root.current).getPropertyValue("--split-flap-announce-after"), 1200)
      : 1200
    timer.current = window.setTimeout(() => {
      setMessage(`Updated: ${[...pending.current].join(", ")}.`)
      pending.current.clear()
      timer.current = undefined
    }, wait)
  }, [])
  React.useEffect(() => () => window.clearTimeout(timer.current), [])

  return (
    <SplitFlapContext value={{ changed }}>
      <div
        ref={root}
        role="group"
        data-slot="split-flap"
        className={cn("bevel-metal bevel-object max-w-full overflow-x-auto rounded-(--bevel-radius-md) p-3", className)}
        {...props}
      >
        <ul className="flex w-max flex-col gap-1.5">{children}</ul>
        <p role="status" className="sr-only">
          {message}
        </p>
      </div>
    </SplitFlapContext>
  )
}

type SplitFlapRowProps = React.ComponentProps<"li"> & {
  /** How this row is announced when it changes: “BA 117”. */
  name: string
}

/** One line of the board. */
function SplitFlapRow({ className, name, ...props }: SplitFlapRowProps) {
  return (
    <SplitFlapRowContext value={name}>
      <li data-slot="split-flap-row" className={cn("flex items-center gap-3", className)} {...props} />
    </SplitFlapRowContext>
  )
}

type SplitFlapTextProps = Omit<React.ComponentProps<"span">, "children"> & {
  value: string
  /** Number of flaps. Shorter text is padded; longer is cut. */
  length: number
  tone?: "white" | "amber"
}

/** A run of flaps showing one value. Each character flips when it changes, left to right. */
function SplitFlapText({ className, value, length, tone = "white", ...props }: SplitFlapTextProps) {
  const context = React.useContext(SplitFlapContext)
  const row = React.useContext(SplitFlapRowContext)
  const text = value.toUpperCase().slice(0, length).padEnd(length, " ")
  const [shown, setShown] = React.useState({ text, previous: text, flips: 0 })
  if (shown.text !== text) setShown({ text, previous: shown.text, flips: shown.flips + 1 })

  const announced = React.useRef(text)
  React.useEffect(() => {
    if (announced.current === text) return
    announced.current = text
    context?.changed(row)
  }, [text, row, context])

  return (
    <span
      data-slot="split-flap-text"
      data-tone={tone}
      className={cn(
        "flex gap-px font-mono font-bold text-(--split-flap-foreground) data-[tone=amber]:text-(--split-flap-amber)",
        className
      )}
      {...props}
    >
      <span className="sr-only">{value}</span>
      {text.split("").map((char, i) => (
        <SplitFlapCell
          key={i}
          char={char}
          previous={shown.previous[i] ?? " "}
          flip={shown.previous[i] !== char ? shown.flips : 0}
          index={i}
        />
      ))}
    </span>
  )
}

function Half({ char, half, className, style }: { char: string; half: "top" | "bottom"; className?: string; style?: React.CSSProperties }) {
  return (
    <span
      className={cn(
        "absolute inset-x-0 h-1/2 overflow-hidden backface-hidden",
        half === "top" ? "top-0 rounded-t-(--bevel-radius-xs) bg-(--split-flap-flap)" : "bottom-0 rounded-b-(--bevel-radius-xs) bg-(--split-flap-flap-lower)",
        className
      )}
      style={style}
    >
      <span
        className={cn(
          "absolute inset-x-0 flex h-(--split-flap-cell-height) items-center justify-center",
          half === "top" ? "top-0" : "bottom-0"
        )}
      >
        {char}
      </span>
    </span>
  )
}

/** One character: static halves, plus a pair of flaps that fall when it changes. */
function SplitFlapCell({ char, previous, flip, index }: { char: string; previous: string; flip: number; index: number }) {
  const delay = { "--split-flap-delay": `calc(var(--bevel-stagger) * ${index})` } as React.CSSProperties
  const flipping = flip > 0
  return (
    <span
      aria-hidden
      data-slot="split-flap-cell"
      className="relative block h-(--split-flap-cell-height) w-(--split-flap-cell-width) shrink-0 perspective-(--bevel-perspective)"
    >
      <Half char={char} half="top" />
      {/* Underneath the falling flap, the old lower half shows until the new one lands. */}
      <Half char={flipping ? previous : char} half="bottom" className="motion-reduce:hidden" />
      <Half char={char} half="bottom" className="hidden motion-reduce:block" />
      {flipping && (
        <React.Fragment key={flip}>
          <Half char={previous} half="top" className="split-flap-top z-10 motion-reduce:hidden" style={delay} />
          <Half char={char} half="bottom" className="split-flap-bottom z-10 motion-reduce:hidden" style={delay} />
          {/* Reduced motion: no flaps, the new character fades in. */}
          <span className="split-flap-fade absolute inset-0 hidden motion-reduce:block">
            <Half char={char} half="top" />
            <Half char={char} half="bottom" />
          </span>
        </React.Fragment>
      )}
      <span className="absolute inset-x-0 top-1/2 z-20 h-px -translate-y-1/2 bg-(--split-flap-hinge)" />
    </span>
  )
}

export { SplitFlap, SplitFlapRow, SplitFlapText }
export type { SplitFlapRowProps, SplitFlapTextProps }

/*
 * Split-flap board: each character is a pair of flaps on a hinge. When it
 * changes, the top flap falls to show the new character, column by
 * column. Builds on bevel.css (metal, motion).
 */

:root {
  --split-flap-housing: oklch(0.22 0.01 260);
  --split-flap-housing-edge: oklch(0.14 0.01 260);
  --split-flap-flap: oklch(0.2 0.005 260);
  --split-flap-flap-lower: oklch(0.17 0.005 260);
  --split-flap-hinge: oklch(0.08 0 0);
  --split-flap-foreground: oklch(0.95 0.02 90);
  --split-flap-amber: oklch(0.84 0.16 80);
  --split-flap-cell-width: 1.15em;
  --split-flap-cell-height: 1.6em;
  --split-flap-delay: 0s; /* set per column, for the left-to-right cascade */
  --split-flap-announce-after: 1200ms; /* gather changes, then announce once */
}

[data-slot="split-flap"] {
  --bevel-material: var(--split-flap-housing);
  --bevel-material-edge: var(--split-flap-housing-edge);
}

@keyframes split-flap-top {
  to {
    transform: rotateX(-90deg);
  }
}
@keyframes split-flap-bottom {
  from {
    transform: rotateX(90deg);
  }
}
@keyframes split-flap-fade {
  from {
    opacity: 0;
  }
}
/* The upper flap falls away, then the lower one lands. */
@utility split-flap-top {
  transform-origin: bottom;
  animation: split-flap-top calc(var(--bevel-duration-small) / 2) var(--bevel-ease-in-out) both;
  animation-delay: var(--split-flap-delay);
}
@utility split-flap-bottom {
  transform-origin: top;
  animation: split-flap-bottom calc(var(--bevel-duration-small) / 2) var(--bevel-ease-out) both;
  animation-delay: calc(var(--split-flap-delay) + var(--bevel-duration-small) / 2);
}
@utility split-flap-fade {
  animation: split-flap-fade var(--bevel-duration-small) var(--bevel-ease-out) both;
}

@import "./bevel.css";
@import "./split-flap.css";