03Entropy-bit value display — the strength value comes from a calculation multiplying the character-set size value by the length value

<main class="stage">
<div class="eb is-demo" id="eb">
  <label class="eb__field">
    <input class="eb__input" id="ebInput" type="text" autocomplete="off" spellcheck="false" value="">
  </label>
  <div class="eb__bits"><b id="ebBits">0</b><span>bit</span></div>
  <div class="eb__track" id="ebTrack">
    <span class="eb__tick" style="--tick-at:20%"></span>
    <span class="eb__tick" style="--tick-at:40%"></span>
    <span class="eb__tick" style="--tick-at:60%"></span>
    <span class="eb__tick" style="--tick-at:80%"></span>
    <div class="eb__fill" id="ebFill"></div>
  </div>
  <div class="eb__meta">Char set <b id="ebSet">0</b> · Length <b id="ebLen">0</b></div>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;

// 계산 겹: 문자 집합 크기 값 × 글자 수 값에 log2 를 취해 비트 값을 만든다 —
// 채움 막대(scaleX)는 그 비트 값을 상한(100비트) 대비 비율로 보여줄 뿐이다.
@include stage($stage-orange);

.eb {
  width: 100%;
  max-width: 320px;
  display: grid;
  gap: $sp-3;
}

.eb__field { display: block; }

.eb__input {
  width: 100%;
  box-sizing: border-box;
  padding: $sp-3 $sp-4;
  border-radius: $r-control;
  border: 0;
  background: $subject-cream;
  color: $subject-ink;
  font: 500 16px/1.3 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  letter-spacing: .04em;
  -webkit-text-security: disc;

  &:focus { outline: 2px solid $subject-ink; outline-offset: 2px; }
}

.eb__bits {
  display: flex;
  align-items: baseline;
  gap: $sp-1;
  color: $subject-ink;

  b { font: 800 34px/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif; font-variant-numeric: tabular-nums; }
  span { font: 600 13px/1 -apple-system, sans-serif; opacity: .75; }
}

.eb__track {
  position: relative;
  height: $sp-3;
  border-radius: $r-sm;
  background: rgba($subject-ink, .14);
  overflow: hidden;
}

.eb__fill {
  position: absolute;
  inset: 0;
  border-radius: $r-sm;
  background: $subject-blue;
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform $dur-base $ease-out;
}

.eb__tick {
  position: absolute;
  top: 0;
  left: var(--tick-at);
  width: 2px;
  height: 100%;
  background: rgba($subject-ink, .3);
  z-index: 1;
}

.eb__meta {
  font: 600 13px/1.2 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: $subject-ink;

  b { font-variant-numeric: tabular-nums; }
}

@media (max-width: 340px) {
  .eb { max-width: 260px; }
  .eb__input { padding: $sp-2 $sp-3; font-size: 14px; }
  .eb__bits b { font-size: 26px; }
  .eb__meta { font-size: 11px; }
}

@media (prefers-reduced-motion: reduce) {
  .eb__fill { transition: none; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.eb {
  width: 100%;
  max-width: 320px;
  display: grid;
  gap: 12px;
}

.eb__field {
  display: block;
}

.eb__input {
  width: 100%;
  box-sizing: border-box;
  padding: 12px 16px;
  border-radius: 12px;
  border: 0;
  background: #fff7e6;
  color: #17141a;
  font: 500 16px/1.3 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  letter-spacing: 0.04em;
  -webkit-text-security: disc;
}
.eb__input:focus {
  outline: 2px solid #17141a;
  outline-offset: 2px;
}

.eb__bits {
  display: flex;
  align-items: baseline;
  gap: 4px;
  color: #17141a;
}
.eb__bits b {
  font: 800 34px/1 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-variant-numeric: tabular-nums;
}
.eb__bits span {
  font: 600 13px/1 -apple-system, sans-serif;
  opacity: 0.75;
}

.eb__track {
  position: relative;
  height: 12px;
  border-radius: 8px;
  background: rgba(23, 20, 26, 0.14);
  overflow: hidden;
}

.eb__fill {
  position: absolute;
  inset: 0;
  border-radius: 8px;
  background: #2f6df6;
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 300ms ease-out;
}

.eb__tick {
  position: absolute;
  top: 0;
  left: var(--tick-at);
  width: 2px;
  height: 100%;
  background: rgba(23, 20, 26, 0.3);
  z-index: 1;
}

.eb__meta {
  font: 600 13px/1.2 -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: #17141a;
}
.eb__meta b {
  font-variant-numeric: tabular-nums;
}

@media (max-width: 340px) {
  .eb {
    max-width: 260px;
  }
  .eb__input {
    padding: 8px 12px;
    font-size: 14px;
  }
  .eb__bits b {
    font-size: 26px;
  }
  .eb__meta {
    font-size: 11px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .eb__fill {
    transition: none;
  }
}

(function () {
  var root = document.getElementById('eb');
  var input = document.getElementById('ebInput');
  var bitsEl = document.getElementById('ebBits');
  var fill = document.getElementById('ebFill');
  var setEl = document.getElementById('ebSet');
  var lenEl = document.getElementById('ebLen');
  var MAX_BITS = 100; // 막대 눈금의 오른쪽 끝 — 이 Value 이상은 꽉 찬 막대로 표시

  // 계산 겹: 섞인 문자 종류로 Char set 크기 값을 구하고, Length 값을 곱한 뒤
  // 밑이 2인 로그를 취해 비트 값을 만든다 (엔트로피 = Length × log2(Char set 크기)).
  function charsetSize(value) {
    var size = 0;
    if (/[a-z]/.test(value)) size += 26;
    if (/[A-Z]/.test(value)) size += 26;
    if (/[0-9]/.test(value)) size += 10;
    if (/[^A-Za-z0-9]/.test(value)) size += 32;
    return size;
  }

  function bitsOf(value) {
    var size = charsetSize(value);
    if (!value.length || size === 0) return { bits: 0, size: size };
    return { bits: value.length * (Math.log(size) / Math.log(2)), size: size };
  }

  function paint(value) {
    var r = bitsOf(value);
    var bits = Math.round(r.bits);
    bitsEl.textContent = String(bits);
    fill.style.transform = 'scaleX(' + Math.min(1, r.bits / MAX_BITS) + ')';
    setEl.textContent = String(r.size);
    lenEl.textContent = String(value.length);
  }

  input.addEventListener('input', function () {
    root.classList.remove('is-demo');
    stopAutoplay();
    paint(input.value);
  });

  paint(input.value);

  // 자동 루프: 시드 고정 문자열 배열로 길이·문자 집합을 함께 늘렸다 줄인다.
  var SEQ = ['', 'abc', 'abcdef', 'abcdefgh12', 'abcdefgh12AB', 'abcdefgh12AB!@',
             'abcdefgh12AB!@#$%^', 'abcdefgh12AB!@', 'abcdefgh12AB', 'abcdefgh12', 'abcdef', 'abc', ''];
  var si = 0;
  var autoTimer = null;
  function autoTick() { input.value = SEQ[si]; paint(SEQ[si]); si = (si + 1) % SEQ.length; }
  function stopAutoplay() { if (autoTimer) { clearInterval(autoTimer); autoTimer = null; } }
  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  if (!reduce) { autoTimer = setInterval(autoTick, 320); autoTick(); }
})();

import { useEffect, useRef } from "react";
import styles from "./EntropyGauge.module.scss";

type Box<T> = { current: T };

const MAX_BITS = 100;

export default function EntropyGauge() {
  const rootRef = useRef(null) as unknown as Box<HTMLDivElement | null>;

  useEffect(() => {
    const root = rootRef.current;
    if (!root) return;
    const input = root.querySelector(`.${styles.input}`) as HTMLInputElement | null;
    const bitsEl = root.querySelector(`.${styles.bitsNum}`) as HTMLElement | null;
    const fill = root.querySelector(`.${styles.fill}`) as HTMLElement | null;
    const setEl = root.querySelector(`.${styles.setSize}`) as HTMLElement | null;
    const lenEl = root.querySelector(`.${styles.len}`) as HTMLElement | null;
    if (!input || !bitsEl || !fill || !setEl || !lenEl) return;

    // 계산 겹: 섞인 문자 종류로 문자 집합 크기 값을 구하고, 글자 수 값을 곱한 뒤
    // 밑이 2인 로그를 취해 비트 값을 만든다.
    function charsetSize(value: string) {
      let size = 0;
      if (/[a-z]/.test(value)) size += 26;
      if (/[A-Z]/.test(value)) size += 26;
      if (/[0-9]/.test(value)) size += 10;
      if (/[^A-Za-z0-9]/.test(value)) size += 32;
      return size;
    }

    function bitsOf(value: string) {
      const size = charsetSize(value);
      if (!value.length || size === 0) return { bits: 0, size };
      return { bits: value.length * (Math.log(size) / Math.log(2)), size };
    }

    function paint(value: string) {
      const r = bitsOf(value);
      bitsEl!.textContent = String(Math.round(r.bits));
      fill!.style.transform = "scaleX(" + Math.min(1, r.bits / MAX_BITS) + ")";
      setEl!.textContent = String(r.size);
      lenEl!.textContent = String(value.length);
    }

    function onInput() {
      root!.classList.remove(styles["is-demo"]);
      stopAutoplay();
      paint(input!.value);
    }
    input.addEventListener("input", onInput);
    paint(input.value);

    // 자동 루프: 시드 고정 문자열 배열로 길이·문자 집합을 함께 늘렸다 줄인다.
    const SEQ = ["", "abc", "abcdef", "abcdefgh12", "abcdefgh12AB", "abcdefgh12AB!@",
      "abcdefgh12AB!@#$%^", "abcdefgh12AB!@", "abcdefgh12AB", "abcdefgh12", "abcdef", "abc", ""];
    let si = 0;
    let autoTimer: number | null = null;
    function autoTick() { input!.value = SEQ[si]; paint(SEQ[si]); si = (si + 1) % SEQ.length; }
    function stopAutoplay() { if (autoTimer !== null) { window.clearInterval(autoTimer); autoTimer = null; } }
    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    if (!reduce) { autoTimer = window.setInterval(autoTick, 320); autoTick(); }

    return () => {
      stopAutoplay();
      input.removeEventListener("input", onInput);
    };
  }, []);

  return (
    <div ref={rootRef} className={`${styles.stage} ${styles.eb} ${styles["is-demo"]}`}>
      <label className={styles.field}>
        <input className={styles.input} type="text" autoComplete="off" spellCheck={false} defaultValue="" />
      </label>
      <div className={styles.bits}><b className={styles.bitsNum}>0</b><span>bit</span></div>
      <div className={styles.track}>
        <span className={styles.tick} style={{ left: "20%" }} />
        <span className={styles.tick} style={{ left: "40%" }} />
        <span className={styles.tick} style={{ left: "60%" }} />
        <span className={styles.tick} style={{ left: "80%" }} />
        <div className={styles.fill} />
      </div>
      <div className={styles.meta}>문자 집합 <b className={styles.setSize}>0</b> · 글자 수 <b className={styles.len}>0</b></div>
    </div>
  );
}