Coupon Field

'use client'

import { useEffect, useRef, useState } from 'react'
import './coupon-field.css'

type Result = { ok: true; percent: number } | { ok: false; error: string }
export interface CouponFieldProps {
  subtotal: number
  validate: (code: string) => Promise<Result>
  currency?: string
  defaultOpen?: boolean
  fill?: 'dark' | 'light'
  className?: string
}

function useTween(target: number) {
  const [v, setV] = useState(target)
  const from = useRef(target)
  useEffect(() => {
    const start = performance.now(), a = from.current
    let raf = 0
    const step = (t: number) => {
      const k = Math.min(1, (t - start) / 500), e = 1 - (1 - k) ** 3
      const cur = a + (target - a) * e
      setV(cur); from.current = cur
      if (k < 1) raf = requestAnimationFrame(step)
    }
    raf = requestAnimationFrame(step)
    return () => cancelAnimationFrame(raf)
  }, [target])
  return v
}

/** Promo code entry with an animated total. */
export function CouponField({ subtotal, validate, currency = 'USD', defaultOpen = false, fill = 'dark', className }: CouponFieldProps) {
  const [open, setOpen] = useState(defaultOpen)
  const [code, setCode] = useState('')
  const [busy, setBusy] = useState(false)
  const [err, setErr] = useState('')
  const [shake, setShake] = useState(0)
  const [applied, setApplied] = useState<{ code: string; percent: number } | null>(null)
  const money = (c: number) => (c / 100).toLocaleString('en-US', { style: 'currency', currency })
  const disc = applied ? Math.round((subtotal * applied.percent) / 100) : 0
  const total = useTween(subtotal - disc)
  const apply = async () => {
    setBusy(true); setErr('')
    const r = await validate(code.trim().toUpperCase())
    setBusy(false)
    if (r.ok) { setApplied({ code: code.trim().toUpperCase(), percent: r.percent }); setCode('') }
    else { setErr(r.error); setShake((s) => s + 1) }
  }
  return (
    <div className={['sd-cpn', className].filter(Boolean).join(' ')} data-fill={fill}>
      <div className="sd-cpn__line"><span>Subtotal</span><b>{money(subtotal)}</b></div>
      {applied && <div className="sd-cpn__line sd-cpn__line--disc"><span>Discount ({applied.percent}%)</span><b>−{money(disc)}</b></div>}
      <div className="sd-cpn__tot"><span>Total</span><span aria-live="polite">{money(Math.round(total))}</span></div>
      {applied ? (
        <span className="sd-cpn__chip">{applied.code}<button type="button" aria-label={`Remove code ${applied.code}`} onClick={() => setApplied(null)}><svg viewBox="0 0 10 10" aria-hidden><path d="m2.5 2.5 5 5m0-5-5 5" /></svg></button></span>
      ) : open ? (
        <>
          <form key={shake} className="sd-cpn__row" data-shake={shake ? '' : undefined} onSubmit={(e) => { e.preventDefault(); if (code.trim() && !busy) apply() }}>
            <input className="sd-cpn__in" aria-label="Promo code" placeholder="Promo code" value={code} autoFocus onChange={(e) => { setCode(e.target.value); setErr('') }} />
            <button type="submit" className="sd-cpn__ap" disabled={!code.trim() || busy} aria-label={busy ? 'Checking code' : 'Apply code'}>{busy ? <span className="sd-cpn__spin" aria-hidden /> : 'Apply'}</button>
          </form>
          {err && <p className="sd-cpn__err" role="alert">{err}</p>}
        </>
      ) : (
        <button type="button" className="sd-cpn__link" onClick={() => setOpen(true)}>Have a promo code?</button>
      )}
    </div>
  )
}

.sd-cpn { --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-cpn[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-cpn button { font: inherit; color: inherit; background: none; border: 0; padding: 0; cursor: pointer; }
.sd-cpn :focus-visible { outline: 2px solid var(--fg); outline-offset: 2px; }
.sd-cpn .sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip-path: inset(50%); white-space: nowrap; }
.sd-cpn { width: min(100%, 320px); padding: 16px; border-radius: 18px; background: var(--bg); box-shadow: inset 0 0 0 1px var(--line); font-variant-numeric: tabular-nums; }
.sd-cpn__line { display: flex; justify-content: space-between; font-size: 13.5px; padding: 5px 0; color: var(--mute); }
.sd-cpn__line b { color: var(--fg); font-weight: 500; }
.sd-cpn__line--disc b { animation: sd-cpn-in 300ms ease; }
.sd-cpn__tot { display: flex; justify-content: space-between; align-items: baseline; padding-top: 12px; margin-top: 8px; border-top: 1px solid var(--line); font-weight: 650; font-size: 18px; }
.sd-cpn__link { margin: 12px 0 2px; font-size: 13px; color: var(--mute); text-decoration: underline; text-underline-offset: 3px; }
.sd-cpn__link:hover { color: var(--fg); }
.sd-cpn__row { display: flex; gap: 6px; margin-top: 12px; animation: sd-cpn-in 220ms ease; }
.sd-cpn__row[data-shake] { animation: sd-cpn-shake 320ms; }
.sd-cpn__in { flex: 1; min-width: 0; height: 40px; padding: 0 12px; border: 0; border-radius: 10px; outline: 0; background: var(--soft); color: var(--fg); font: 600 13px/1 ui-monospace, monospace; letter-spacing: 0.08em; text-transform: uppercase; box-shadow: inset 0 0 0 1px transparent; }
.sd-cpn__in:focus { box-shadow: inset 0 0 0 1.5px var(--fg); }
.sd-cpn__in::placeholder { letter-spacing: 0; font-weight: 400; color: var(--mute); text-transform: none; }
.sd-cpn__ap { position: relative; width: 74px; height: 40px; border-radius: 10px; background: var(--strong) !important; color: var(--on) !important; font-weight: 600; font-size: 13px; }
.sd-cpn__ap:disabled { opacity: 0.4; cursor: default; }
.sd-cpn__spin { display: inline-block; width: 14px; height: 14px; border-radius: 99px; border: 2px solid currentColor; border-right-color: transparent; animation: sd-cpn-rot 700ms linear infinite; vertical-align: -2px; }
@keyframes sd-cpn-rot { to { transform: rotate(360deg); } }
.sd-cpn__err { margin: 6px 2px 0; font-size: 12px; color: var(--fg); }
.sd-cpn__chip { display: inline-flex; align-items: center; gap: 8px; margin-top: 12px; height: 32px; padding: 0 6px 0 11px; border-radius: 999px; box-shadow: inset 0 0 0 1px var(--fg); font: 600 12px/1 ui-monospace, monospace; letter-spacing: 0.06em; animation: sd-cpn-pop 320ms cubic-bezier(0.3, 1.6, 0.4, 1); }
.sd-cpn__chip button { display: grid; place-items: center; width: 22px; height: 22px; border-radius: 99px; background: var(--soft) !important; }
.sd-cpn__chip svg { width: 10px; height: 10px; stroke: currentColor; stroke-width: 1.8; stroke-linecap: round; }
@keyframes sd-cpn-in { from { opacity: 0; transform: translateY(-4px); } }
@keyframes sd-cpn-pop { from { transform: scale(0.7); opacity: 0; } }
@keyframes sd-cpn-shake { 25% { transform: translateX(-5px); } 75% { transform: translateX(5px); } }
@media (prefers-reduced-motion: reduce) { .sd-cpn *, .sd-cpn *::before, .sd-cpn *::after { animation: none !important; transition: none !important; } }