Snap Slider

'use client'

import { useRef, useState } from 'react'
import './snap-slider.css'

export interface SnapStop { value: string; label: string }
export interface SnapSliderProps {
  stops: SnapStop[]
  value?: string
  defaultValue?: string
  onValueChange?: (v: string) => void
  label?: string
  fill?: 'dark' | 'light'
  className?: string
}

/** A slider that springs into labelled stops. */
export function SnapSlider({ stops, value, defaultValue, onValueChange, label = 'Value', fill = 'dark', className }: SnapSliderProps) {
  const [inner, setInner] = useState(defaultValue ?? stops[0]?.value)
  const v = value ?? inner
  const idx = Math.max(0, stops.findIndex((s) => s.value === v))
  const [drag, setDrag] = useState<number | null>(null)
  const track = useRef<HTMLDivElement>(null)
  const n = stops.length - 1
  const pct = (drag ?? idx / n) * 100
  const at = (cx: number) => { const r = track.current!.getBoundingClientRect(); return Math.min(1, Math.max(0, (cx - r.left) / r.width)) }
  const set = (i: number) => { const j = Math.min(n, Math.max(0, i)); setInner(stops[j].value); onValueChange?.(stops[j].value) }
  const near = drag !== null ? Math.round(drag * n) : idx
  return (
    <div className={['sd-sns', className].filter(Boolean).join(' ')} data-fill={fill}>
      <div className="sd-sns__top"><span className="sd-sns__cap">{label}</span><span key={near} className="sd-sns__val">{stops[near].label}</span></div>
      <div
        ref={track}
        className="sd-sns__track"
        data-drag={drag !== null || undefined}
        onPointerDown={(e) => { e.currentTarget.setPointerCapture(e.pointerId); setDrag(at(e.clientX)) }}
        onPointerMove={(e) => drag !== null && setDrag(at(e.clientX))}
        onPointerUp={() => { if (drag !== null) set(Math.round(drag * n)); setDrag(null) }}
      >
        <span className="sd-sns__rail" />
        <span className="sd-sns__fill" style={{ width: `${pct}%` }} />
        {stops.map((s, i) => <span key={s.value} className="sd-sns__tick" style={{ left: `${(i / n) * 100}%` }} />)}
        <span
          className="sd-sns__thumb"
          role="slider"
          tabIndex={0}
          aria-label={label}
          aria-valuemin={0}
          aria-valuemax={n}
          aria-valuenow={idx}
          aria-valuetext={stops[idx].label}
          style={{ left: `${pct}%` }}
          onKeyDown={(e) => {
            const m: Record<string, number> = { ArrowRight: idx + 1, ArrowUp: idx + 1, ArrowLeft: idx - 1, ArrowDown: idx - 1, Home: 0, End: n }
            if (e.key in m) { e.preventDefault(); set(m[e.key]) }
          }}
        />
      </div>
      <div className="sd-sns__labs" aria-hidden>
        {stops.map((s, i) => <span key={s.value} className="sd-sns__lab" data-on={i === near || undefined} style={{ left: `${(i / n) * 100}%` }}>{i === 0 || i === n || stops.length <= 4 ? s.label : '·'}</span>)}
      </div>
    </div>
  )
}

.sd-sns { --bg: #1c1c1c; --fg: #f6f6f6; --mute: #8e8e8e; --line: rgb(255 255 255 / 0.1); --soft: rgb(255 255 255 / 0.07); --strong: #fafafa; --on: #111; 
  color: var(--fg); font-size: 14px; line-height: 1.4; -webkit-tap-highlight-color: transparent; }
.sd-sns[data-fill='light'] { --bg: #fff; --fg: #121212; --mute: #6f6f6f; --line: rgb(0 0 0 / 0.09); --soft: rgb(0 0 0 / 0.05); --strong: #111; --on: #fff; }
.sd-sns button { font: inherit; color: inherit; background: none; border: 0; padding: 0; cursor: pointer; }
.sd-sns :focus-visible { outline: 2px solid var(--fg); outline-offset: 2px; }
.sd-sns .sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip-path: inset(50%); white-space: nowrap; }
.sd-sns { width: min(100%, 320px); padding: 18px 18px 14px; border-radius: 18px; background: var(--bg); box-shadow: inset 0 0 0 1px var(--line); }
.sd-sns__top { display: flex; justify-content: space-between; align-items: baseline; margin-bottom: 18px; }
.sd-sns__cap { font-size: 12.5px; color: var(--mute); }
.sd-sns__val { font-size: 18px; font-weight: 650; animation: sd-sns-in 220ms ease; }
@keyframes sd-sns-in { from { opacity: 0; transform: translateY(4px); } }
.sd-sns__track { position: relative; height: 28px; margin: 0 10px; touch-action: none; cursor: pointer; }
.sd-sns__rail { position: absolute; left: 0; right: 0; top: 12px; height: 4px; border-radius: 4px; background: var(--soft); }
.sd-sns__fill { position: absolute; left: 0; top: 12px; height: 4px; border-radius: 4px; background: var(--fg); }
.sd-sns__tick { position: absolute; top: 10px; width: 2px; height: 8px; margin-left: -1px; border-radius: 2px; background: var(--mute); opacity: 0.5; }
.sd-sns__thumb { position: absolute; top: 2px; width: 24px; height: 24px; margin-left: -12px; border-radius: 99px; background: var(--strong); box-shadow: 0 0 0 4px var(--bg), 0 2px 6px rgb(0 0 0 / 0.3); outline: 0; transition: transform 150ms; }
.sd-sns__thumb:focus-visible { box-shadow: 0 0 0 4px var(--bg), 0 0 0 6px var(--fg); }
.sd-sns__track[data-drag] .sd-sns__thumb { transform: scale(1.12); }
.sd-sns__track:not([data-drag]) .sd-sns__thumb, .sd-sns__track:not([data-drag]) .sd-sns__fill { transition: left 340ms cubic-bezier(0.3, 1.5, 0.4, 1), width 340ms cubic-bezier(0.3, 1.5, 0.4, 1), transform 150ms; }
.sd-sns__labs { position: relative; height: 18px; margin: 8px 10px 0; }
.sd-sns__lab { position: absolute; transform: translateX(-50%); font-size: 11.5px; color: var(--mute); white-space: nowrap; transition: color 200ms; }
.sd-sns__lab:first-child { transform: none; margin-left: -6px; }
.sd-sns__lab:last-child { transform: translateX(-100%); margin-left: 6px; }
.sd-sns__lab[data-on] { color: var(--fg); font-weight: 600; }
@media (prefers-reduced-motion: reduce) { .sd-sns *, .sd-sns *::before, .sd-sns *::after { animation: none !important; transition: none !important; } }