08四つ角でぶつからない方向ごとにまとめて点く矢印

<main class="stage">
<div class="sc is-demo" id="scRoot">
  <canvas class="sc__canvas" id="scCanvas" width="480" height="300" tabindex="0" aria-label="四つ角でぶつからない方向ごとにまとめて点く矢印"></canvas>
  <p class="sc__status" id="scStatus" aria-live="polite">青信号 — 進行</p>
  <button class="sc__btn" id="scBtn" type="button">一時停止</button>
  <p class="sc__caption">四つ角でぶつからない方向ごとにまとめて点く矢印</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-ink);

.sc {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $subject-ink;
}

.sc__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
}

.sc__canvas:focus-visible {
  outline: 2px solid rgba(255, 255, 255, .85);
  outline-offset: -6px;
}

.sc__status {
  position: absolute;
  left: $sp-3;
  top: $sp-3;
  max-width: 62%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.sc__btn {
  position: absolute;
  right: $sp-3;
  bottom: $sp-3;
  margin: 0;
  padding: $sp-1 $sp-3;
  border: 0;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font: inherit;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  cursor: pointer;
}

.sc__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.sc__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 68%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .sc__caption, .sc__btn { font-size: 10px; padding: $sp-1 $sp-2; }
  .sc__status { font-size: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  .sc { cursor: default; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.sc {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #17141a;
}

.sc__canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
}

.sc__canvas:focus-visible {
  outline: 2px solid rgba(255, 255, 255, 0.85);
  outline-offset: -6px;
}

.sc__status {
  position: absolute;
  left: 12px;
  top: 12px;
  max-width: 62%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 11px;
  line-height: 1.4;
  pointer-events: none;
}

.sc__btn {
  position: absolute;
  right: 12px;
  bottom: 12px;
  margin: 0;
  padding: 4px 12px;
  border: 0;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font: inherit;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  cursor: pointer;
}

.sc__btn:focus-visible {
  outline: 2px solid #ffffff;
  outline-offset: 2px;
}

.sc__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 68%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .sc__caption, .sc__btn {
    font-size: 10px;
    padding: 4px 8px;
  }
  .sc__status {
    font-size: 10px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .sc {
    cursor: default;
  }
}

(function () {
    const W = 480;
    const H = 300;
    const PI2 = Math.PI * 2;
    const FIXED_DT = 16;
    const REDUCE_STEP_MS = 900;
    const REDUCE_START_MS = 1200;
    const KEY_STEP = 12;
    const FONT = '-apple-system, "Segoe UI", "Noto Sans KR", sans-serif';
    const SIG_GREEN = 0;
    const SIG_YELLOW = 1;
    const SIG_RED = 2;
    const GREEN_RGB = [61, 214, 140];
    const YELLOW_RGB = [255, 200, 64];
    const RED_RGB = [255, 92, 102];
    const SIGNAL_RGBS = [GREEN_RGB, YELLOW_RGB, RED_RGB];
    const SKY_RGB = [226, 238, 252];
    const GRASS_RGB = [206, 236, 214];
    const ROAD_RGB = [188, 192, 212];
    const ROAD_EDGE_RGB = [162, 166, 192];
    const MARK_RGB = [250, 250, 255];
    const INK_RGB = [58, 52, 84];
    const CAR_RGBS = [[255, 184, 196], [170, 208, 255], [196, 176, 255], [158, 232, 200], [255, 222, 150], [255, 196, 224]];
    const TXT_GO = '青信号 — 進行';
    const TXT_READY = '黄信号 — 停止の準備';
    const TXT_STOP = '赤信号 — 停止';
    function clamp(v, lo, hi) { return v < lo ? lo : (v > hi ? hi : v); }
    function lerp(a, b, k) { return a + (b - a) * k; }
    function smooth(x) { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
    function rgba(c, a) {
        return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + a.toFixed(3) + ')';
    }
    // 시드 고정 난수 — 같은 시드면 언제나 같은 수열
    function mulberry32(seed) {
        let s = seed >>> 0;
        return function () {
            s = (s + 0x6D2B79F5) >>> 0;
            let t = s;
            t = Math.imul(t ^ (t >>> 15), t | 1);
            t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
            return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
        };
    }
    // 격자 점의 값 — 정수 두 개를 섞어 0..1 로 (같은 입력은 언제나 같은 값)
    function hash2(ix, iy) {
        let h = Math.imul(ix | 0, 374761393) + Math.imul(iy | 0, 668265263);
        h = Math.imul(h ^ (h >>> 13), 1274126177);
        return ((h ^ (h >>> 16)) >>> 0) / 4294967296;
    }
    // 2차원 값 잡음 — 네 격자 점을 부드럽게 보간
    function vnoise(x, y) {
        const ix = Math.floor(x);
        const iy = Math.floor(y);
        const fx = smooth(x - ix);
        const fy = smooth(y - iy);
        return lerp(lerp(hash2(ix, iy), hash2(ix + 1, iy), fx), lerp(hash2(ix, iy + 1), hash2(ix + 1, iy + 1), fx), fy);
    }
    function glow(ctx, x, y, r, c, a) {
        const g = ctx.createRadialGradient(x, y, 0, x, y, r);
        g.addColorStop(0, rgba(c, a));
        g.addColorStop(1, rgba(c, 0));
        ctx.fillStyle = g;
        ctx.fillRect(x - r, y - r, r * 2, r * 2);
    }
    function rrect(ctx, x, y, w, h, r) {
        const rr = Math.min(r, w / 2, h / 2);
        ctx.beginPath();
        ctx.moveTo(x + rr, y);
        ctx.arcTo(x + w, y, x + w, y + h, rr);
        ctx.arcTo(x + w, y + h, x, y + h, rr);
        ctx.arcTo(x, y + h, x, y, rr);
        ctx.arcTo(x, y, x + w, y, rr);
        ctx.closePath();
    }
    // 주기 [초록, 노랑, 빨강] 프레임 수에서 프레임 f 의 신호 상태
    function phaseAt(f, g, y, r) {
        const total = g + y + r;
        const m = ((f % total) + total) % total;
        return m < g ? SIG_GREEN : (m < g + y ? SIG_YELLOW : SIG_RED);
    }
    function stateText(state) {
        return state === SIG_GREEN ? TXT_GO : (state === SIG_YELLOW ? TXT_READY : TXT_STOP);
    }
    // 신호 상태 -> 빨강·노랑·초록 렌즈 밝기 (위에서 아래)
    function litOf(state) {
        return [state === SIG_RED ? 1 : 0, state === SIG_YELLOW ? 1 : 0, state === SIG_GREEN ? 1 : 0];
    }
    const LENS_RGBS = [RED_RGB, YELLOW_RGB, GREEN_RGB];
    // 세로 신호등 머리 — 렌즈 세 개와 켜진 렌즈의 빛 번짐
    function drawHead(ctx, cx, cy, r, lit) {
        const step = r * 2.5;
        rrect(ctx, cx - r * 1.45, cy - step - r * 1.45, r * 2.9, step * 2 + r * 2.9, r * 0.9);
        ctx.fillStyle = rgba(INK_RGB, 1);
        ctx.fill();
        for (let i = 0; i < 3; i += 1) {
            const ly = cy + (i - 1) * step;
            ctx.beginPath();
            ctx.arc(cx, ly, r, 0, PI2);
            ctx.fillStyle = rgba(LENS_RGBS[i], 0.2 + 0.8 * lit[i]);
            ctx.fill();
            if (lit[i] > 0.02) {
                glow(ctx, cx, ly, r * 3.2, LENS_RGBS[i], 0.55 * lit[i]);
            }
        }
    }
    // 위에서 본 차 — 앞 범퍼가 x, 가운데가 y. 제동 중이면 뒷등이 켜진다
    function drawCar(ctx, x, y, len, wid, rgb, braking) {
        const x0 = x - len;
        rrect(ctx, x0, y - wid / 2, len, wid, 6);
        ctx.fillStyle = rgba(rgb, 1);
        ctx.fill();
        rrect(ctx, x - len * 0.62, y - wid / 2 + 3, len * 0.34, wid - 6, 3);
        ctx.fillStyle = 'rgba(255,255,255,0.62)';
        ctx.fill();
        ctx.fillStyle = 'rgba(255,248,214,1)';
        ctx.fillRect(x - 3, y - wid / 2 + 2, 3, 4);
        ctx.fillRect(x - 3, y + wid / 2 - 6, 3, 4);
        ctx.fillStyle = braking ? rgba(RED_RGB, 1) : 'rgba(150,120,150,0.8)';
        ctx.fillRect(x0, y - wid / 2 + 2, 3, 4);
        ctx.fillRect(x0, y + wid / 2 - 6, 3, 4);
        if (braking) {
            glow(ctx, x0, y, 12, RED_RGB, 0.45);
        }
    }
    // 한 줄 도로 장면의 바탕 — 잔디 위에 도로띠 하나, 정지선과 횡단보도
    function drawLaneBackdrop(ctx, roadY, roadH, stopX, seedTrees) {
        ctx.fillStyle = rgba(GRASS_RGB, 1);
        ctx.fillRect(0, 0, W, H);
        const rnd = mulberry32(seedTrees);
        for (let i = 0; i < 14; i += 1) {
            const tx = 16 + rnd() * (W - 32);
            const up = rnd() < 0.5;
            const ty = up ? roadY - roadH / 2 - 22 - rnd() * 26 : roadY + roadH / 2 + 22 + rnd() * 26;
            ctx.beginPath();
            ctx.arc(tx, ty, 9 + rnd() * 6, 0, PI2);
            ctx.fillStyle = 'rgba(160,214,184,0.9)';
            ctx.fill();
        }
        ctx.fillStyle = rgba(ROAD_RGB, 1);
        ctx.fillRect(0, roadY - roadH / 2, W, roadH);
        ctx.fillStyle = rgba(ROAD_EDGE_RGB, 1);
        ctx.fillRect(0, roadY - roadH / 2, W, 2);
        ctx.fillRect(0, roadY + roadH / 2 - 2, W, 2);
        ctx.fillStyle = rgba(MARK_RGB, 0.8);
        for (let x = 6; x < W; x += 36) {
            ctx.fillRect(x, roadY - 1, 18, 2);
        }
        for (let k = 0; k < 5; k += 1) {
            ctx.fillRect(stopX + 5, roadY - roadH / 2 + 3 + k * (roadH - 6) / 5, 12, (roadH - 6) / 5 - 3);
        }
        ctx.fillRect(stopX - 2, roadY - roadH / 2, 3, roadH);
    }
    // 한 줄 차량 흐름 — 앞차 간격(IDM)과 정지선을 같은 식으로 다룬다. 차는 앞쪽부터 0번이다
    class Lane {
        constructor(seed, p) {
            this.cars = [];
            this.nextAt = 0;
            this.made = 0;
            this.p = p;
            this.rnd = mulberry32(seed);
        }
        accelFor(v, s, vL, g0) {
            const p = this.p;
            const sStar = g0 + Math.max(0, v * p.headway + v * (v - vL) / (2 * Math.sqrt(p.accel * p.brake)));
            return p.accel * (1 - Math.pow(v / p.vmax, p.delta) - Math.pow(sStar / Math.max(s, 0.5), 2));
        }
        // f 프레임에, 뒤쪽이 비어 있고 때가 됐으면 한 대 들여보낸다
        maybeSpawn(f, minGap, maxGap, v0) {
            if (f < this.nextAt) {
                return false;
            }
            const last = this.cars.length > 0 ? this.cars[this.cars.length - 1] : null;
            if (last && last.x - last.len < this.p.gap + 10) {
                return false;
            }
            const rgb = CAR_RGBS[this.made % CAR_RGBS.length];
            this.cars.push({ x: -2, v: v0, len: this.p.len, rgb: rgb, go: false, decided: false, sigK: -1, brake: false, id: this.made });
            this.made += 1;
            this.nextAt = f + minGap + Math.floor(this.rnd() * (maxGap - minGap + 1));
            return true;
        }
        // 신호 목록은 x 오름차순. 한 번 호출 = 한 프레임. 정지선을 넘은 차(detect 용) id 를 돌려준다
        step(sigs, onCross, watchX) {
            const p = this.p;
            for (let i = 0; i < this.cars.length; i += 1) {
                const c = this.cars[i];
                let acc = this.accelFor(c.v, 1e6, c.v, p.gap);
                if (i > 0) {
                    const L = this.cars[i - 1];
                    acc = Math.min(acc, this.accelFor(c.v, (L.x - L.len) - c.x, L.v, p.gap));
                }
                let k = -1;
                for (let j = 0; j < sigs.length; j += 1) {
                    if (sigs[j].x >= c.x) {
                        k = j;
                        break;
                    }
                }
                let clampX = 1e9;
                if (k >= 0) {
                    const sg = sigs[k];
                    if (c.sigK !== k) {
                        c.sigK = k;
                        c.decided = false;
                        c.go = false;
                    }
                    if (sg.state === SIG_GREEN) {
                        c.decided = false;
                        c.go = false;
                    }
                    else {
                        if (!c.decided) {
                            c.decided = true;
                            c.go = c.v * c.v / (2 * p.brake) > sg.x - c.x;
                        }
                        if (!c.go) {
                            acc = Math.min(acc, this.accelFor(c.v, sg.x - c.x - 2, 0, p.lineGap));
                            clampX = sg.x - 1.5;
                        }
                    }
                }
                acc = Math.max(acc, -p.brake * 3);
                const prevX = c.x;
                c.v = Math.max(0, c.v + acc);
                c.x += c.v;
                if (c.x > clampX && prevX <= clampX) {
                    c.x = clampX;
                    c.v = 0;
                }
                c.brake = acc < -0.012 || c.v < 0.05;
                if (prevX < watchX && c.x >= watchX) {
                    onCross(c, watchX);
                }
            }
            while (this.cars.length > 0 && this.cars[0].x - this.cars[0].len > W + 20) {
                this.cars.shift();
            }
        }
        // 정지선 뒤에서 서 있는 차 수
        waiting(stopX) {
            let n = 0;
            for (let i = 0; i < this.cars.length; i += 1) {
                const c = this.cars[i];
                if (c.v < 0.25 && c.x < stopX + 2 && c.x > stopX - 260) {
                    n += 1;
                }
            }
            return n;
        }
    }
    function main(rootEl, canvas, statusEl, btnEl) {
        const ctx0 = canvas.getContext('2d');
        if (!ctx0) {
            return function () { return; };
        }
        canvas.width = W;
        canvas.height = H;
        const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
        const scene = makeScene(ctx0, reduce);
        if (reduce) {
            rootEl.classList.remove('is-demo');
        }
        let paused = false;
        let rafId = 0;
        let lastTs = null;
        let accMs = 0;
        let lastLabel = '';
        let px = W / 2;
        let py = H / 2;
        const cleaners = [];
        function listen(target, type, fn) {
            target.addEventListener(type, fn);
            cleaners.push(function () { target.removeEventListener(type, fn); });
        }
        function show() {
            scene.draw();
            const t = scene.label();
            if (t !== lastLabel) {
                lastLabel = t;
                statusEl.textContent = t;
            }
        }
        function advance(ms) {
            const n = Math.round(ms / FIXED_DT);
            for (let i = 0; i < n; i += 1) {
                scene.step();
            }
        }
        function setButton() {
            btnEl.textContent = reduce ? '次の場面' : (paused ? '再生' : '一時停止');
        }
        function toLocal(e) {
            const r = canvas.getBoundingClientRect();
            return [clamp((e.clientX - r.left) * W / r.width, 0, W), clamp((e.clientY - r.top) * H / r.height, 0, H)];
        }
        function moved() {
            if (scene.point) {
                scene.point(px, py);
            }
            if (reduce) {
                show();
            }
        }
        function onButton() {
            if (reduce) {
                advance(REDUCE_STEP_MS);
                show();
                return;
            }
            paused = !paused;
            if (paused) {
                rootEl.classList.remove('is-demo');
            }
            else {
                rootEl.classList.add('is-demo');
            }
            setButton();
        }
        function onAction() {
            if (scene.tap) {
                scene.tap();
                if (reduce) {
                    show();
                }
                return;
            }
            onButton();
        }
        function tick(ts) {
            if (lastTs === null) {
                lastTs = ts;
            }
            const frameDt = Math.min(ts - lastTs, 160);
            lastTs = ts;
            if (!paused) {
                accMs += frameDt;
                while (accMs >= FIXED_DT) {
                    scene.step();
                    accMs -= FIXED_DT;
                }
                show();
            }
            rafId = requestAnimationFrame(tick);
        }
        listen(btnEl, 'click', function () { onButton(); });
        listen(canvas, 'pointerdown', function (e) {
            const p = toLocal(e);
            px = p[0];
            py = p[1];
            moved();
            if (scene.tap) {
                scene.tap();
                if (reduce) {
                    show();
                }
            }
        });
        listen(canvas, 'pointermove', function (e) {
            const p = toLocal(e);
            px = p[0];
            py = p[1];
            moved();
        });
        listen(canvas, 'keydown', function (e) {
            const k = e.key;
            if (k === 'Enter' || k === ' ') {
                e.preventDefault();
                onAction();
                return;
            }
            let dx = 0;
            let dy = 0;
            if (k === 'ArrowLeft') {
                dx = -KEY_STEP;
            }
            else if (k === 'ArrowRight') {
                dx = KEY_STEP;
            }
            else if (k === 'ArrowUp') {
                dy = -KEY_STEP;
            }
            else if (k === 'ArrowDown') {
                dy = KEY_STEP;
            }
            else {
                return;
            }
            e.preventDefault();
            px = clamp(px + dx, 0, W);
            py = clamp(py + dy, 0, H);
            moved();
        });
        advance(REDUCE_START_MS);
        setButton();
        show();
        if (!reduce) {
            rafId = requestAnimationFrame(tick);
        }
        function destroy() {
            cancelAnimationFrame(rafId);
            for (let i = 0; i < cleaners.length; i += 1) {
                cleaners[i]();
            }
        }
        return destroy;
    }
    const ARROW_LEN = 13;
    const ALL_RED_GAP = 16;
    const PHASE_GREEN = 72;
    const LANE_OFFSET = 11;
    const PATH_REACH = 112;
    const SAMPLES = 48;
    const APPROACH_N = 14;
    const TURN_N = 20;
    const EXIT_N = 14;
    const TURN_HALF = 22;
    const CENTER_X = 240;
    const CENTER_Y = 146;
    const DOTS_PER_MOVE = 3;
    const DOT_SPEED = 0.011;
    function makeScene(ctx, reduce) {
        const dirs = [[0, 1], [-1, 0], [0, -1], [1, 0]];
        // 진행 방향 d 의 오른쪽 · 왼쪽 벡터 (화면 y 는 아래로 자란다)
        function rightOf(d) { return [-d[1], d[0]]; }
        function leftOf(d) { return [d[1], -d[0]]; }
        function makeMove(approach, left) {
            const d = dirs[approach];
            const r = rightOf(d);
            const p0 = [CENTER_X + r[0] * LANE_OFFSET - d[0] * PATH_REACH, CENTER_Y + r[1] * LANE_OFFSET - d[1] * PATH_REACH];
            const pts = [];
            if (!left) {
                const p1 = [CENTER_X + r[0] * LANE_OFFSET + d[0] * PATH_REACH, CENTER_Y + r[1] * LANE_OFFSET + d[1] * PATH_REACH];
                for (let i = 0; i <= SAMPLES; i += 1) {
                    const u = i / SAMPLES;
                    pts.push([lerp(p0[0], p1[0], u), lerp(p0[1], p1[1], u)]);
                }
            }
            else {
                // 좌회전 — 먼 곳에서 교차로 가장자리까지는 직선, 교차로 안에서만 2차 곡선으로 꺾는다
                const l = leftOf(d);
                const e = [CENTER_X + r[0] * LANE_OFFSET - d[0] * TURN_HALF, CENTER_Y + r[1] * LANE_OFFSET - d[1] * TURN_HALF];
                const c = [CENTER_X - l[0] * LANE_OFFSET + d[0] * LANE_OFFSET, CENTER_Y - l[1] * LANE_OFFSET + d[1] * LANE_OFFSET];
                const x = [CENTER_X + d[0] * LANE_OFFSET + l[0] * TURN_HALF, CENTER_Y + d[1] * LANE_OFFSET + l[1] * TURN_HALF];
                const p2 = [CENTER_X + d[0] * LANE_OFFSET + l[0] * PATH_REACH, CENTER_Y + d[1] * LANE_OFFSET + l[1] * PATH_REACH];
                for (let i = 0; i < APPROACH_N; i += 1) {
                    const u = i / APPROACH_N;
                    pts.push([lerp(p0[0], e[0], u), lerp(p0[1], e[1], u)]);
                }
                for (let i = 0; i < TURN_N; i += 1) {
                    const u = i / TURN_N;
                    const a = (1 - u) * (1 - u);
                    const b = 2 * u * (1 - u);
                    const q = u * u;
                    pts.push([a * e[0] + b * c[0] + q * x[0], a * e[1] + b * c[1] + q * x[1]]);
                }
                for (let i = 0; i <= EXIT_N; i += 1) {
                    const u = i / EXIT_N;
                    pts.push([lerp(x[0], p2[0], u), lerp(x[1], p2[1], u)]);
                }
            }
            return { approach: approach, left: left, pts: pts };
        }
        const moves = [makeMove(0, false), makeMove(2, false), makeMove(0, true), makeMove(2, true), makeMove(1, false), makeMove(3, false), makeMove(1, true), makeMove(3, true)];
        // 충돌표 — 같은 쪽에서 나오는 둘, 마주 보는 직진과 좌회전, 직각으로 만나는 모든 짝이 서로 부딪힌다.
        // 마주 보는 직진끼리, 마주 보는 좌회전끼리만 부딪히지 않는다
        function collides(a, b) {
            if (a.approach === b.approach) {
                return true;
            }
            if ((a.approach + 2) % 4 === b.approach) {
                return a.left !== b.left;
            }
            return true;
        }
        const CONFLICT_MASK = [];
        for (let i = 0; i < moves.length; i += 1) {
            let mask = 0;
            for (let j = 0; j < moves.length; j += 1) {
                if (i !== j && collides(moves[i], moves[j])) {
                    mask |= 1 << j;
                }
            }
            CONFLICT_MASK.push(mask);
        }
        // 위상 묶기 — 먼저 나온 묶음에 충돌하는 방향이 없으면 거기에 넣는다
        const PHASE_ORDER = [];
        for (let i = 0; i < moves.length; i += 1) {
            let placed = false;
            for (let g = 0; g < PHASE_ORDER.length && !placed; g += 1) {
                let ok = true;
                for (let k = 0; k < PHASE_ORDER[g].length; k += 1) {
                    if ((CONFLICT_MASK[i] >> PHASE_ORDER[g][k]) & 1) {
                        ok = false;
                    }
                }
                if (ok) {
                    PHASE_ORDER[g].push(i);
                    placed = true;
                }
            }
            if (!placed) {
                PHASE_ORDER.push([i]);
            }
        }
        const slot = PHASE_GREEN + ALL_RED_GAP;
        const cycle = slot * PHASE_ORDER.length;
        let f = 30;
        function phaseIndex() { return Math.floor((((f % cycle) + cycle) % cycle) / slot); }
        function inGap() { return ((((f % cycle) + cycle) % cycle) % slot) >= PHASE_GREEN; }
        function activeSet() { return inGap() ? [] : PHASE_ORDER[phaseIndex()]; }
        function posOn(m, u) {
            const t = clamp(u, 0, 1) * SAMPLES;
            const i = Math.min(Math.floor(t), SAMPLES - 1);
            const k = t - i;
            return [lerp(m.pts[i][0], m.pts[i + 1][0], k), lerp(m.pts[i][1], m.pts[i + 1][1], k)];
        }
        const scene = {
            step: function () { f += 1; },
            label: function () {
                if (inGap()) {
                    return '全方向停止 — すき間';
                }
                const g = PHASE_ORDER[phaseIndex()];
                const m0 = moves[g[0]];
                const ns = m0.approach === 0 || m0.approach === 2;
                if (ns) {
                    return m0.left ? '南北左折 — 向かい合う左折だけ' : '南北直進 — 向かい合う直進だけ';
                }
                return m0.left ? '東西左折 — 向かい合う左折だけ' : '東西直進 — 向かい合う直進だけ';
            },
            draw: function () {
                ctx.fillStyle = rgba(GRASS_RGB, 1);
                ctx.fillRect(0, 0, W, H);
                const half = LANE_OFFSET + 14;
                ctx.fillStyle = rgba(ROAD_RGB, 1);
                ctx.fillRect(CENTER_X - half, 0, half * 2, H);
                ctx.fillRect(0, CENTER_Y - half, W, half * 2);
                ctx.fillStyle = rgba(MARK_RGB, 0.8);
                for (let y = 4; y < H; y += 20) {
                    if (Math.abs(y - CENTER_Y) > half + 6) {
                        ctx.fillRect(CENTER_X - 1, y, 2, 10);
                    }
                }
                for (let x = 4; x < W; x += 20) {
                    if (Math.abs(x - CENTER_X) > half + 6) {
                        ctx.fillRect(x, CENTER_Y - 1, 10, 2);
                    }
                }
                const act = activeSet();
                const lit = [false, false, false, false];
                for (let a = 0; a < act.length; a += 1) {
                    lit[moves[act[a]].approach] = true;
                }
                // 팔마다 차로 색칠 — 켜진 쪽은 초록, 꺼진 쪽은 옅은 빨강
                for (let a = 0; a < 4; a += 1) {
                    ctx.fillStyle = rgba(lit[a] ? GREEN_RGB : RED_RGB, lit[a] ? 0.2 : 0.08);
                    if (a === 0) {
                        ctx.fillRect(CENTER_X - half, 0, half * 2, CENTER_Y - half);
                    }
                    else if (a === 2) {
                        ctx.fillRect(CENTER_X - half, CENTER_Y + half, half * 2, H - CENTER_Y - half);
                    }
                    else if (a === 1) {
                        ctx.fillRect(CENTER_X + half, CENTER_Y - half, W - CENTER_X - half, half * 2);
                    }
                    else {
                        ctx.fillRect(0, CENTER_Y - half, CENTER_X - half, half * 2);
                    }
                }
                // 정지선 신호 띠
                for (let a = 0; a < 4; a += 1) {
                    const d = dirs[a];
                    const r = rightOf(d);
                    const bx = CENTER_X - d[0] * (half + 3) + r[0] * LANE_OFFSET;
                    const by = CENTER_Y - d[1] * (half + 3) + r[1] * LANE_OFFSET;
                    ctx.fillStyle = rgba(lit[a] ? GREEN_RGB : RED_RGB, 1);
                    if (d[0] === 0) {
                        ctx.fillRect(bx - LANE_OFFSET - 2, by - 2, LANE_OFFSET * 2 + 4, 4);
                    }
                    else {
                        ctx.fillRect(bx - 2, by - LANE_OFFSET - 2, 4, LANE_OFFSET * 2 + 4);
                    }
                }
                for (let i = 0; i < moves.length; i += 1) {
                    const m = moves[i];
                    const on = act.indexOf(i) >= 0;
                    ctx.beginPath();
                    ctx.moveTo(m.pts[0][0], m.pts[0][1]);
                    for (let k = 1; k < m.pts.length; k += 1) {
                        ctx.lineTo(m.pts[k][0], m.pts[k][1]);
                    }
                    ctx.lineWidth = on ? 4 : 2;
                    ctx.lineCap = 'round';
                    ctx.strokeStyle = on ? rgba(GREEN_RGB, 0.9) : rgba(RED_RGB, 0.28);
                    ctx.stroke();
                    const e = m.pts[m.pts.length - 1];
                    const q = m.pts[m.pts.length - 3];
                    const ang = Math.atan2(e[1] - q[1], e[0] - q[0]);
                    ctx.beginPath();
                    ctx.moveTo(e[0] + Math.cos(ang) * 6, e[1] + Math.sin(ang) * 6);
                    ctx.lineTo(e[0] + Math.cos(ang + 2.5) * ARROW_LEN * 0.7, e[1] + Math.sin(ang + 2.5) * ARROW_LEN * 0.7);
                    ctx.lineTo(e[0] + Math.cos(ang - 2.5) * ARROW_LEN * 0.7, e[1] + Math.sin(ang - 2.5) * ARROW_LEN * 0.7);
                    ctx.closePath();
                    ctx.fillStyle = on ? rgba(GREEN_RGB, 1) : rgba(RED_RGB, 0.4);
                    ctx.fill();
                    if (on) {
                        for (let k = 0; k < DOTS_PER_MOVE; k += 1) {
                            const u = (((f * DOT_SPEED * 3 + k / DOTS_PER_MOVE + i * 0.13) % 1) + 1) % 1;
                            const p = posOn(m, u);
                            ctx.beginPath();
                            ctx.arc(p[0], p[1], 5.5, 0, PI2);
                            ctx.fillStyle = rgba(CAR_RGBS[(i + k) % CAR_RGBS.length], 1);
                            ctx.fill();
                            ctx.lineWidth = 1.5;
                            ctx.strokeStyle = rgba(INK_RGB, 0.6);
                            ctx.stroke();
                        }
                    }
                }
                ctx.lineCap = 'butt';
                // 모두 빨강인 틈 — 교차로 가운데가 붉게 번진다
                if (inGap()) {
                    glow(ctx, CENTER_X, CENTER_Y, 70, RED_RGB, 0.32);
                }
            }
        };
        if (reduce) {
            f = 30;
        }
        return scene;
    }
    main(document.getElementById('scRoot'), document.getElementById('scCanvas'), document.getElementById('scStatus'), document.getElementById('scBtn'));
})();

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

const W = 480;
const H = 300;
const PI2 = Math.PI * 2;
const FIXED_DT = 16;
const REDUCE_STEP_MS = 900;
const REDUCE_START_MS = 1200;
const KEY_STEP = 12;
const FONT = '-apple-system, "Segoe UI", "Noto Sans KR", sans-serif';

const SIG_GREEN = 0;
const SIG_YELLOW = 1;
const SIG_RED = 2;
const GREEN_RGB = [61, 214, 140];
const YELLOW_RGB = [255, 200, 64];
const RED_RGB = [255, 92, 102];
const SIGNAL_RGBS = [GREEN_RGB, YELLOW_RGB, RED_RGB];
const SKY_RGB = [226, 238, 252];
const GRASS_RGB = [206, 236, 214];
const ROAD_RGB = [188, 192, 212];
const ROAD_EDGE_RGB = [162, 166, 192];
const MARK_RGB = [250, 250, 255];
const INK_RGB = [58, 52, 84];
const CAR_RGBS = [[255, 184, 196], [170, 208, 255], [196, 176, 255], [158, 232, 200], [255, 222, 150], [255, 196, 224]];

const TXT_GO = '초록불 — 진행';
const TXT_READY = '노란불 — 정지 준비';
const TXT_STOP = '빨간불 — 정지';

type Pt = [number, number];
interface Scene {
  step(): void;
  draw(): void;
  label(): string;
  point?(x: number, y: number): void;
  tap?(): void;
}

function clamp(v: number, lo: number, hi: number): number { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a: number, b: number, k: number): number { return a + (b - a) * k; }
function smooth(x: number): number { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function rgba(c: number[], a: number): string {
  return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + a.toFixed(3) + ')';
}
// 시드 고정 난수 — 같은 시드면 언제나 같은 수열
function mulberry32(seed: number): () => number {
  let s = seed >>> 0;
  return function (): number {
    s = (s + 0x6D2B79F5) >>> 0;
    let t = s;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}
// 격자 점의 값 — 정수 두 개를 섞어 0..1 로 (같은 입력은 언제나 같은 값)
function hash2(ix: number, iy: number): number {
  let h = Math.imul(ix | 0, 374761393) + Math.imul(iy | 0, 668265263);
  h = Math.imul(h ^ (h >>> 13), 1274126177);
  return ((h ^ (h >>> 16)) >>> 0) / 4294967296;
}
// 2차원 값 잡음 — 네 격자 점을 부드럽게 보간
function vnoise(x: number, y: number): number {
  const ix = Math.floor(x);
  const iy = Math.floor(y);
  const fx = smooth(x - ix);
  const fy = smooth(y - iy);
  return lerp(lerp(hash2(ix, iy), hash2(ix + 1, iy), fx), lerp(hash2(ix, iy + 1), hash2(ix + 1, iy + 1), fx), fy);
}
function glow(ctx: CanvasRenderingContext2D, x: number, y: number, r: number, c: number[], a: number): void {
  const g = ctx.createRadialGradient(x, y, 0, x, y, r);
  g.addColorStop(0, rgba(c, a));
  g.addColorStop(1, rgba(c, 0));
  ctx.fillStyle = g;
  ctx.fillRect(x - r, y - r, r * 2, r * 2);
}
function rrect(ctx: CanvasRenderingContext2D, x: number, y: number, w: number, h: number, r: number): void {
  const rr = Math.min(r, w / 2, h / 2);
  ctx.beginPath();
  ctx.moveTo(x + rr, y);
  ctx.arcTo(x + w, y, x + w, y + h, rr);
  ctx.arcTo(x + w, y + h, x, y + h, rr);
  ctx.arcTo(x, y + h, x, y, rr);
  ctx.arcTo(x, y, x + w, y, rr);
  ctx.closePath();
}
// 주기 [초록, 노랑, 빨강] 프레임 수에서 프레임 f 의 신호 상태
function phaseAt(f: number, g: number, y: number, r: number): number {
  const total = g + y + r;
  const m = ((f % total) + total) % total;
  return m < g ? SIG_GREEN : (m < g + y ? SIG_YELLOW : SIG_RED);
}
function stateText(state: number): string {
  return state === SIG_GREEN ? TXT_GO : (state === SIG_YELLOW ? TXT_READY : TXT_STOP);
}
// 신호 상태 -> 빨강·노랑·초록 렌즈 밝기 (위에서 아래)
function litOf(state: number): number[] {
  return [state === SIG_RED ? 1 : 0, state === SIG_YELLOW ? 1 : 0, state === SIG_GREEN ? 1 : 0];
}
const LENS_RGBS = [RED_RGB, YELLOW_RGB, GREEN_RGB];
// 세로 신호등 머리 — 렌즈 세 개와 켜진 렌즈의 빛 번짐
function drawHead(ctx: CanvasRenderingContext2D, cx: number, cy: number, r: number, lit: number[]): void {
  const step = r * 2.5;
  rrect(ctx, cx - r * 1.45, cy - step - r * 1.45, r * 2.9, step * 2 + r * 2.9, r * 0.9);
  ctx.fillStyle = rgba(INK_RGB, 1);
  ctx.fill();
  for (let i = 0; i < 3; i += 1) {
    const ly = cy + (i - 1) * step;
    ctx.beginPath();
    ctx.arc(cx, ly, r, 0, PI2);
    ctx.fillStyle = rgba(LENS_RGBS[i], 0.2 + 0.8 * lit[i]);
    ctx.fill();
    if (lit[i] > 0.02) {
      glow(ctx, cx, ly, r * 3.2, LENS_RGBS[i], 0.55 * lit[i]);
    }
  }
}
// 위에서 본 차 — 앞 범퍼가 x, 가운데가 y. 제동 중이면 뒷등이 켜진다
function drawCar(ctx: CanvasRenderingContext2D, x: number, y: number, len: number, wid: number, rgb: number[], braking: boolean): void {
  const x0 = x - len;
  rrect(ctx, x0, y - wid / 2, len, wid, 6);
  ctx.fillStyle = rgba(rgb, 1);
  ctx.fill();
  rrect(ctx, x - len * 0.62, y - wid / 2 + 3, len * 0.34, wid - 6, 3);
  ctx.fillStyle = 'rgba(255,255,255,0.62)';
  ctx.fill();
  ctx.fillStyle = 'rgba(255,248,214,1)';
  ctx.fillRect(x - 3, y - wid / 2 + 2, 3, 4);
  ctx.fillRect(x - 3, y + wid / 2 - 6, 3, 4);
  ctx.fillStyle = braking ? rgba(RED_RGB, 1) : 'rgba(150,120,150,0.8)';
  ctx.fillRect(x0, y - wid / 2 + 2, 3, 4);
  ctx.fillRect(x0, y + wid / 2 - 6, 3, 4);
  if (braking) {
    glow(ctx, x0, y, 12, RED_RGB, 0.45);
  }
}
// 한 줄 도로 장면의 바탕 — 잔디 위에 도로띠 하나, 정지선과 횡단보도
function drawLaneBackdrop(ctx: CanvasRenderingContext2D, roadY: number, roadH: number, stopX: number, seedTrees: number): void {
  ctx.fillStyle = rgba(GRASS_RGB, 1);
  ctx.fillRect(0, 0, W, H);
  const rnd = mulberry32(seedTrees);
  for (let i = 0; i < 14; i += 1) {
    const tx = 16 + rnd() * (W - 32);
    const up = rnd() < 0.5;
    const ty = up ? roadY - roadH / 2 - 22 - rnd() * 26 : roadY + roadH / 2 + 22 + rnd() * 26;
    ctx.beginPath();
    ctx.arc(tx, ty, 9 + rnd() * 6, 0, PI2);
    ctx.fillStyle = 'rgba(160,214,184,0.9)';
    ctx.fill();
  }
  ctx.fillStyle = rgba(ROAD_RGB, 1);
  ctx.fillRect(0, roadY - roadH / 2, W, roadH);
  ctx.fillStyle = rgba(ROAD_EDGE_RGB, 1);
  ctx.fillRect(0, roadY - roadH / 2, W, 2);
  ctx.fillRect(0, roadY + roadH / 2 - 2, W, 2);
  ctx.fillStyle = rgba(MARK_RGB, 0.8);
  for (let x = 6; x < W; x += 36) {
    ctx.fillRect(x, roadY - 1, 18, 2);
  }
  for (let k = 0; k < 5; k += 1) {
    ctx.fillRect(stopX + 5, roadY - roadH / 2 + 3 + k * (roadH - 6) / 5, 12, (roadH - 6) / 5 - 3);
  }
  ctx.fillRect(stopX - 2, roadY - roadH / 2, 3, roadH);
}

interface Car { x: number; v: number; len: number; rgb: number[]; go: boolean; decided: boolean; sigK: number; brake: boolean; id: number; }
interface Sig { x: number; state: number; }
interface LaneParams { accel: number; brake: number; gap: number; lineGap: number; vmax: number; headway: number; delta: number; len: number; }

// 한 줄 차량 흐름 — 앞차 간격(IDM)과 정지선을 같은 식으로 다룬다. 차는 앞쪽부터 0번이다
class Lane {
  cars: Car[] = [];
  p: LaneParams;
  rnd: () => number;
  nextAt = 0;
  made = 0;
  constructor(seed: number, p: LaneParams) {
    this.p = p;
    this.rnd = mulberry32(seed);
  }
  accelFor(v: number, s: number, vL: number, g0: number): number {
    const p = this.p;
    const sStar = g0 + Math.max(0, v * p.headway + v * (v - vL) / (2 * Math.sqrt(p.accel * p.brake)));
    return p.accel * (1 - Math.pow(v / p.vmax, p.delta) - Math.pow(sStar / Math.max(s, 0.5), 2));
  }
  // f 프레임에, 뒤쪽이 비어 있고 때가 됐으면 한 대 들여보낸다
  maybeSpawn(f: number, minGap: number, maxGap: number, v0: number): boolean {
    if (f < this.nextAt) { return false; }
    const last = this.cars.length > 0 ? this.cars[this.cars.length - 1] : null;
    if (last && last.x - last.len < this.p.gap + 10) { return false; }
    const rgb = CAR_RGBS[this.made % CAR_RGBS.length];
    this.cars.push({ x: -2, v: v0, len: this.p.len, rgb: rgb, go: false, decided: false, sigK: -1, brake: false, id: this.made });
    this.made += 1;
    this.nextAt = f + minGap + Math.floor(this.rnd() * (maxGap - minGap + 1));
    return true;
  }
  // 신호 목록은 x 오름차순. 한 번 호출 = 한 프레임. 정지선을 넘은 차(detect 용) id 를 돌려준다
  step(sigs: Sig[], onCross: (c: Car, x: number) => void, watchX: number): void {
    const p = this.p;
    for (let i = 0; i < this.cars.length; i += 1) {
      const c = this.cars[i];
      let acc = this.accelFor(c.v, 1e6, c.v, p.gap);
      if (i > 0) {
        const L = this.cars[i - 1];
        acc = Math.min(acc, this.accelFor(c.v, (L.x - L.len) - c.x, L.v, p.gap));
      }
      let k = -1;
      for (let j = 0; j < sigs.length; j += 1) {
        if (sigs[j].x >= c.x) { k = j; break; }
      }
      let clampX = 1e9;
      if (k >= 0) {
        const sg = sigs[k];
        if (c.sigK !== k) { c.sigK = k; c.decided = false; c.go = false; }
        if (sg.state === SIG_GREEN) {
          c.decided = false;
          c.go = false;
        } else {
          if (!c.decided) {
            c.decided = true;
            c.go = c.v * c.v / (2 * p.brake) > sg.x - c.x;
          }
          if (!c.go) {
            acc = Math.min(acc, this.accelFor(c.v, sg.x - c.x - 2, 0, p.lineGap));
            clampX = sg.x - 1.5;
          }
        }
      }
      acc = Math.max(acc, -p.brake * 3);
      const prevX = c.x;
      c.v = Math.max(0, c.v + acc);
      c.x += c.v;
      if (c.x > clampX && prevX <= clampX) {
        c.x = clampX;
        c.v = 0;
      }
      c.brake = acc < -0.012 || c.v < 0.05;
      if (prevX < watchX && c.x >= watchX) { onCross(c, watchX); }
    }
    while (this.cars.length > 0 && this.cars[0].x - this.cars[0].len > W + 20) {
      this.cars.shift();
    }
  }
  // 정지선 뒤에서 서 있는 차 수
  waiting(stopX: number): number {
    let n = 0;
    for (let i = 0; i < this.cars.length; i += 1) {
      const c = this.cars[i];
      if (c.v < 0.25 && c.x < stopX + 2 && c.x > stopX - 260) { n += 1; }
    }
    return n;
  }
}

function main(rootEl: HTMLElement, canvas: HTMLCanvasElement, statusEl: HTMLElement, btnEl: HTMLButtonElement): () => void {
  const ctx0 = canvas.getContext('2d');
  if (!ctx0) { return function (): void { return; }; }
  canvas.width = W;
  canvas.height = H;
  const reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  const scene = makeScene(ctx0, reduce);
  if (reduce) { rootEl.classList.remove('is-demo'); }
  let paused = false;
  let rafId = 0;
  let lastTs: number | null = null;
  let accMs = 0;
  let lastLabel = '';
  let px = W / 2;
  let py = H / 2;
  const cleaners: Array<() => void> = [];

  function listen(target: EventTarget, type: string, fn: (e: Event) => void): void {
    target.addEventListener(type, fn);
    cleaners.push(function (): void { target.removeEventListener(type, fn); });
  }
  function show(): void {
    scene.draw();
    const t = scene.label();
    if (t !== lastLabel) {
      lastLabel = t;
      statusEl.textContent = t;
    }
  }
  function advance(ms: number): void {
    const n = Math.round(ms / FIXED_DT);
    for (let i = 0; i < n; i += 1) { scene.step(); }
  }
  function setButton(): void {
    btnEl.textContent = reduce ? '다음 장면' : (paused ? '재생' : '멈춤');
  }
  function toLocal(e: PointerEvent): Pt {
    const r = canvas.getBoundingClientRect();
    return [clamp((e.clientX - r.left) * W / r.width, 0, W), clamp((e.clientY - r.top) * H / r.height, 0, H)];
  }
  function moved(): void {
    if (scene.point) { scene.point(px, py); }
    if (reduce) { show(); }
  }
  function onButton(): void {
    if (reduce) {
      advance(REDUCE_STEP_MS);
      show();
      return;
    }
    paused = !paused;
    if (paused) { rootEl.classList.remove('is-demo'); } else { rootEl.classList.add('is-demo'); }
    setButton();
  }
  function onAction(): void {
    if (scene.tap) {
      scene.tap();
      if (reduce) { show(); }
      return;
    }
    onButton();
  }
  function tick(ts: number): void {
    if (lastTs === null) { lastTs = ts; }
    const frameDt = Math.min(ts - lastTs, 160);
    lastTs = ts;
    if (!paused) {
      accMs += frameDt;
      while (accMs >= FIXED_DT) {
        scene.step();
        accMs -= FIXED_DT;
      }
      show();
    }
    rafId = requestAnimationFrame(tick);
  }
  listen(btnEl, 'click', function (): void { onButton(); });
  listen(canvas, 'pointerdown', function (e: Event): void {
    const p = toLocal(e as PointerEvent);
    px = p[0];
    py = p[1];
    moved();
    if (scene.tap) {
      scene.tap();
      if (reduce) { show(); }
    }
  });
  listen(canvas, 'pointermove', function (e: Event): void {
    const p = toLocal(e as PointerEvent);
    px = p[0];
    py = p[1];
    moved();
  });
  listen(canvas, 'keydown', function (e: Event): void {
    const k = (e as KeyboardEvent).key;
    if (k === 'Enter' || k === ' ') {
      e.preventDefault();
      onAction();
      return;
    }
    let dx = 0;
    let dy = 0;
    if (k === 'ArrowLeft') { dx = -KEY_STEP; } else if (k === 'ArrowRight') { dx = KEY_STEP; }
    else if (k === 'ArrowUp') { dy = -KEY_STEP; } else if (k === 'ArrowDown') { dy = KEY_STEP; }
    else { return; }
    e.preventDefault();
    px = clamp(px + dx, 0, W);
    py = clamp(py + dy, 0, H);
    moved();
  });
  advance(REDUCE_START_MS);
  setButton();
  show();
  if (!reduce) {
    rafId = requestAnimationFrame(tick);
  }
  function destroy(): void {
    cancelAnimationFrame(rafId);
    for (let i = 0; i < cleaners.length; i += 1) { cleaners[i](); }
  }
  return destroy;
}

const ARROW_LEN = 13;
const ALL_RED_GAP = 16;
const PHASE_GREEN = 72;
const LANE_OFFSET = 11;
const PATH_REACH = 112;
const SAMPLES = 48;
const APPROACH_N = 14;
const TURN_N = 20;
const EXIT_N = 14;
const TURN_HALF = 22;
const CENTER_X = 240;
const CENTER_Y = 146;
const DOTS_PER_MOVE = 3;
const DOT_SPEED = 0.011;

interface Move { approach: number; left: boolean; pts: Pt[]; }

function makeScene(ctx: CanvasRenderingContext2D, reduce: boolean): Scene {
  const dirs: Pt[] = [[0, 1], [-1, 0], [0, -1], [1, 0]];
  // 진행 방향 d 의 오른쪽 · 왼쪽 벡터 (화면 y 는 아래로 자란다)
  function rightOf(d: Pt): Pt { return [-d[1], d[0]]; }
  function leftOf(d: Pt): Pt { return [d[1], -d[0]]; }
  function makeMove(approach: number, left: boolean): Move {
    const d = dirs[approach];
    const r = rightOf(d);
    const p0: Pt = [CENTER_X + r[0] * LANE_OFFSET - d[0] * PATH_REACH, CENTER_Y + r[1] * LANE_OFFSET - d[1] * PATH_REACH];
    const pts: Pt[] = [];
    if (!left) {
      const p1: Pt = [CENTER_X + r[0] * LANE_OFFSET + d[0] * PATH_REACH, CENTER_Y + r[1] * LANE_OFFSET + d[1] * PATH_REACH];
      for (let i = 0; i <= SAMPLES; i += 1) {
        const u = i / SAMPLES;
        pts.push([lerp(p0[0], p1[0], u), lerp(p0[1], p1[1], u)]);
      }
    } else {
      // 좌회전 — 먼 곳에서 교차로 가장자리까지는 직선, 교차로 안에서만 2차 곡선으로 꺾는다
      const l = leftOf(d);
      const e: Pt = [CENTER_X + r[0] * LANE_OFFSET - d[0] * TURN_HALF, CENTER_Y + r[1] * LANE_OFFSET - d[1] * TURN_HALF];
      const c: Pt = [CENTER_X - l[0] * LANE_OFFSET + d[0] * LANE_OFFSET, CENTER_Y - l[1] * LANE_OFFSET + d[1] * LANE_OFFSET];
      const x: Pt = [CENTER_X + d[0] * LANE_OFFSET + l[0] * TURN_HALF, CENTER_Y + d[1] * LANE_OFFSET + l[1] * TURN_HALF];
      const p2: Pt = [CENTER_X + d[0] * LANE_OFFSET + l[0] * PATH_REACH, CENTER_Y + d[1] * LANE_OFFSET + l[1] * PATH_REACH];
      for (let i = 0; i < APPROACH_N; i += 1) {
        const u = i / APPROACH_N;
        pts.push([lerp(p0[0], e[0], u), lerp(p0[1], e[1], u)]);
      }
      for (let i = 0; i < TURN_N; i += 1) {
        const u = i / TURN_N;
        const a = (1 - u) * (1 - u);
        const b = 2 * u * (1 - u);
        const q = u * u;
        pts.push([a * e[0] + b * c[0] + q * x[0], a * e[1] + b * c[1] + q * x[1]]);
      }
      for (let i = 0; i <= EXIT_N; i += 1) {
        const u = i / EXIT_N;
        pts.push([lerp(x[0], p2[0], u), lerp(x[1], p2[1], u)]);
      }
    }
    return { approach: approach, left: left, pts: pts };
  }
  const moves: Move[] = [makeMove(0, false), makeMove(2, false), makeMove(0, true), makeMove(2, true), makeMove(1, false), makeMove(3, false), makeMove(1, true), makeMove(3, true)];
  // 충돌표 — 같은 쪽에서 나오는 둘, 마주 보는 직진과 좌회전, 직각으로 만나는 모든 짝이 서로 부딪힌다.
  // 마주 보는 직진끼리, 마주 보는 좌회전끼리만 부딪히지 않는다
  function collides(a: Move, b: Move): boolean {
    if (a.approach === b.approach) { return true; }
    if ((a.approach + 2) % 4 === b.approach) { return a.left !== b.left; }
    return true;
  }
  const CONFLICT_MASK: number[] = [];
  for (let i = 0; i < moves.length; i += 1) {
    let mask = 0;
    for (let j = 0; j < moves.length; j += 1) {
      if (i !== j && collides(moves[i], moves[j])) { mask |= 1 << j; }
    }
    CONFLICT_MASK.push(mask);
  }
  // 위상 묶기 — 먼저 나온 묶음에 충돌하는 방향이 없으면 거기에 넣는다
  const PHASE_ORDER: number[][] = [];
  for (let i = 0; i < moves.length; i += 1) {
    let placed = false;
    for (let g = 0; g < PHASE_ORDER.length && !placed; g += 1) {
      let ok = true;
      for (let k = 0; k < PHASE_ORDER[g].length; k += 1) {
        if ((CONFLICT_MASK[i] >> PHASE_ORDER[g][k]) & 1) { ok = false; }
      }
      if (ok) {
        PHASE_ORDER[g].push(i);
        placed = true;
      }
    }
    if (!placed) { PHASE_ORDER.push([i]); }
  }
  const slot = PHASE_GREEN + ALL_RED_GAP;
  const cycle = slot * PHASE_ORDER.length;
  let f = 30;
  function phaseIndex(): number { return Math.floor((((f % cycle) + cycle) % cycle) / slot); }
  function inGap(): boolean { return ((((f % cycle) + cycle) % cycle) % slot) >= PHASE_GREEN; }
  function activeSet(): number[] { return inGap() ? [] : PHASE_ORDER[phaseIndex()]; }
  function posOn(m: Move, u: number): Pt {
    const t = clamp(u, 0, 1) * SAMPLES;
    const i = Math.min(Math.floor(t), SAMPLES - 1);
    const k = t - i;
    return [lerp(m.pts[i][0], m.pts[i + 1][0], k), lerp(m.pts[i][1], m.pts[i + 1][1], k)];
  }
  const scene: Scene = {
    step: function (): void { f += 1; },
    label: function (): string {
      if (inGap()) { return '전 방향 정지 — 빈 틈'; }
      const g = PHASE_ORDER[phaseIndex()];
      const m0 = moves[g[0]];
      const ns = m0.approach === 0 || m0.approach === 2;
      if (ns) { return m0.left ? '남북 좌회전 — 마주 보는 좌회전만' : '남북 직진 — 마주 보는 직진만'; }
      return m0.left ? '동서 좌회전 — 마주 보는 좌회전만' : '동서 직진 — 마주 보는 직진만';
    },
    draw: function (): void {
      ctx.fillStyle = rgba(GRASS_RGB, 1);
      ctx.fillRect(0, 0, W, H);
      const half = LANE_OFFSET + 14;
      ctx.fillStyle = rgba(ROAD_RGB, 1);
      ctx.fillRect(CENTER_X - half, 0, half * 2, H);
      ctx.fillRect(0, CENTER_Y - half, W, half * 2);
      ctx.fillStyle = rgba(MARK_RGB, 0.8);
      for (let y = 4; y < H; y += 20) {
        if (Math.abs(y - CENTER_Y) > half + 6) { ctx.fillRect(CENTER_X - 1, y, 2, 10); }
      }
      for (let x = 4; x < W; x += 20) {
        if (Math.abs(x - CENTER_X) > half + 6) { ctx.fillRect(x, CENTER_Y - 1, 10, 2); }
      }
      const act = activeSet();
      const lit: boolean[] = [false, false, false, false];
      for (let a = 0; a < act.length; a += 1) { lit[moves[act[a]].approach] = true; }
      // 팔마다 차로 색칠 — 켜진 쪽은 초록, 꺼진 쪽은 옅은 빨강
      for (let a = 0; a < 4; a += 1) {
        ctx.fillStyle = rgba(lit[a] ? GREEN_RGB : RED_RGB, lit[a] ? 0.2 : 0.08);
        if (a === 0) { ctx.fillRect(CENTER_X - half, 0, half * 2, CENTER_Y - half); }
        else if (a === 2) { ctx.fillRect(CENTER_X - half, CENTER_Y + half, half * 2, H - CENTER_Y - half); }
        else if (a === 1) { ctx.fillRect(CENTER_X + half, CENTER_Y - half, W - CENTER_X - half, half * 2); }
        else { ctx.fillRect(0, CENTER_Y - half, CENTER_X - half, half * 2); }
      }
      // 정지선 신호 띠
      for (let a = 0; a < 4; a += 1) {
        const d = dirs[a];
        const r = rightOf(d);
        const bx = CENTER_X - d[0] * (half + 3) + r[0] * LANE_OFFSET;
        const by = CENTER_Y - d[1] * (half + 3) + r[1] * LANE_OFFSET;
        ctx.fillStyle = rgba(lit[a] ? GREEN_RGB : RED_RGB, 1);
        if (d[0] === 0) { ctx.fillRect(bx - LANE_OFFSET - 2, by - 2, LANE_OFFSET * 2 + 4, 4); }
        else { ctx.fillRect(bx - 2, by - LANE_OFFSET - 2, 4, LANE_OFFSET * 2 + 4); }
      }
      for (let i = 0; i < moves.length; i += 1) {
        const m = moves[i];
        const on = act.indexOf(i) >= 0;
        ctx.beginPath();
        ctx.moveTo(m.pts[0][0], m.pts[0][1]);
        for (let k = 1; k < m.pts.length; k += 1) { ctx.lineTo(m.pts[k][0], m.pts[k][1]); }
        ctx.lineWidth = on ? 4 : 2;
        ctx.lineCap = 'round';
        ctx.strokeStyle = on ? rgba(GREEN_RGB, 0.9) : rgba(RED_RGB, 0.28);
        ctx.stroke();
        const e = m.pts[m.pts.length - 1];
        const q = m.pts[m.pts.length - 3];
        const ang = Math.atan2(e[1] - q[1], e[0] - q[0]);
        ctx.beginPath();
        ctx.moveTo(e[0] + Math.cos(ang) * 6, e[1] + Math.sin(ang) * 6);
        ctx.lineTo(e[0] + Math.cos(ang + 2.5) * ARROW_LEN * 0.7, e[1] + Math.sin(ang + 2.5) * ARROW_LEN * 0.7);
        ctx.lineTo(e[0] + Math.cos(ang - 2.5) * ARROW_LEN * 0.7, e[1] + Math.sin(ang - 2.5) * ARROW_LEN * 0.7);
        ctx.closePath();
        ctx.fillStyle = on ? rgba(GREEN_RGB, 1) : rgba(RED_RGB, 0.4);
        ctx.fill();
        if (on) {
          for (let k = 0; k < DOTS_PER_MOVE; k += 1) {
            const u = (((f * DOT_SPEED * 3 + k / DOTS_PER_MOVE + i * 0.13) % 1) + 1) % 1;
            const p = posOn(m, u);
            ctx.beginPath();
            ctx.arc(p[0], p[1], 5.5, 0, PI2);
            ctx.fillStyle = rgba(CAR_RGBS[(i + k) % CAR_RGBS.length], 1);
            ctx.fill();
            ctx.lineWidth = 1.5;
            ctx.strokeStyle = rgba(INK_RGB, 0.6);
            ctx.stroke();
          }
        }
      }
      ctx.lineCap = 'butt';
      // 모두 빨강인 틈 — 교차로 가운데가 붉게 번진다
      if (inGap()) {
        glow(ctx, CENTER_X, CENTER_Y, 70, RED_RGB, 0.32);
      }
    }
  };
  if (reduce) { f = 30; }
  return scene;
}

export default function TlFourWayPhaseRingArrows() {
  const rootRef = useRef<HTMLDivElement | null>(null);
  const canvasRef = useRef<HTMLCanvasElement | null>(null);
  const statusRef = useRef<HTMLParagraphElement | null>(null);
  const btnRef = useRef<HTMLButtonElement | null>(null);

  useEffect(() => {
    const root = rootRef.current;
    const canvas = canvasRef.current;
    const statusEl = statusRef.current;
    const btnEl = btnRef.current;
    if (!root || !canvas || !statusEl || !btnEl) return;
    return main(root, canvas, statusEl, btnEl);
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.sc} is-demo`} ref={rootRef}>
        <canvas className={styles.sc__canvas} ref={canvasRef} width={480} height={300} tabIndex={0} aria-label="사거리에서 부딪히지 않는 방향끼리 묶어 켜는 화살표" />
        <p className={styles.sc__status} ref={statusRef} aria-live="polite">초록불 — 진행</p>
        <button className={styles.sc__btn} ref={btnRef} type="button">멈춤</button>
        <p className={styles.sc__caption}>사거리에서 부딪히지 않는 방향끼리 묶어 켜는 화살표</p>
      </div>
    </main>
  );
}