'use strict';
/* ═══════════════════════════════════════════════════════════════════
   HydroSim v2 — Гидростатика
   Модули: давление · поверхностное натяжение · сообщающиеся сосуды · Архимед
   Canvas 2D, pure-JS physics (no external libraries)
   ═══════════════════════════════════════════════════════════════════ */

class HydroSim {
  static G = 9.81;

  static LIQUIDS = {
    water:     { name: 'Вода',         rho: 1000,  color: '#2979FF', sigma: 0.073 },
    saltwater: { name: 'Солёная вода', rho: 1030,  color: '#1565C0', sigma: 0.074 },
    oil:       { name: 'Масло',        rho: 900,   color: '#FFA000', sigma: 0.033 },
    alcohol:   { name: 'Спирт',        rho: 790,   color: '#CE93D8', sigma: 0.022 },
    glycerin:  { name: 'Глицерин',     rho: 1260,  color: '#FFCC02', sigma: 0.063 },
    mercury:   { name: 'Ртуть',        rho: 13600, color: '#B0BEC5', sigma: 0.500 },
  };

  static MATERIALS = {
    styrofoam: { name: 'Пенопласт', rho: 30,    color: '#F5F5F5' },
    cork:      { name: 'Пробка',    rho: 120,   color: '#8D6E63' },
    wood:      { name: 'Дерево',    rho: 500,   color: '#A1887F' },
    ice:       { name: 'Лёд',       rho: 900,   color: '#B3E5FC' },
    plastic:   { name: 'Пластик',   rho: 1100,  color: '#EF5350' },
    glass:     { name: 'Стекло',    rho: 2500,  color: '#90CAF9' },
    aluminum:  { name: 'Алюминий',  rho: 2700,  color: '#CFD8DC' },
    iron:      { name: 'Железо',    rho: 7800,  color: '#78909C' },
    gold:      { name: 'Золото',    rho: 19300, color: '#FFD700' },
  };

  constructor(canvas, mode = 'pressure') {
    this.canvas = canvas;
    this.ctx    = canvas.getContext('2d');
    this.mode   = mode;
    this._raf   = null;
    this._running    = false;
    this.onUpdate    = null;
    this._lastNotify = 0;
    this._t          = 0;

    this.liquidKey   = 'water';
    this.materialKey = 'wood';
    this.g           = HydroSim.G;

    /* pressure */
    this._probe = { vy: 0.5, dragging: false };

    /* surface */
    this._stMode       = 'capillary';
    this._contactAngle = 20;

    /* communicating */
    this._numVessels   = 2;
    this._liquidFrac   = 0.45;
    this._valveOpen    = true;
    this._vesselShapes = ['rect', 'wide'];
    this._animLevel    = null;
    this._targetLevel  = null;
    this._recalcVessels();

    /* archimedes */
    this._archReady  = false;
    this._bodies     = [];
    this._waterLevel = 0.60;
    this._bodyShape  = 'rect';

    /* -- GraphPanel widget -- */
    this._graphsOn = false;
    this._graphUI  = null;

    this._bindEvents();
    this._ro = new ResizeObserver(() => this.fit());
    this._ro.observe(canvas.parentElement || canvas);
    requestAnimationFrame(() => { this.fit(); this.play(); });
  }

  /* ── Public API ── */
  setMode(m) {
    this.mode = m;
    if (m === 'archimedes') this._initArch();
    else this._destroyArch();
    this._notify();
  }
  setLiquid(key)   { this.liquidKey = key; this._notify(); }
  setMaterial(key) { this.materialKey = key; if (this.mode === 'archimedes') this._archReset(); this._notify(); }
  setContactAngle(deg) { this._contactAngle = deg; }
  setNumVessels(n) {
    this._numVessels   = n;
    this._vesselShapes = Array.from({ length: n }, (_, i) => ['rect','wide','narrow','trapezoid'][i % 4]);
    this._recalcVessels(); this._notify();
  }
  setValve(open) {
    this._valveOpen = open;
    this._recalcVessels();
    if (window.LabFX) LabFX.sound.play('click', { pitch: 0.7 });
    this._notify();
  }
  addLiquid() {
    this._liquidFrac = Math.min(0.85, this._liquidFrac + 0.05);
    this._recalcVessels();
    if (window.LabFX) {
      LabFX.sound.play('pour');
      /* splash at approximate pour point (top-center of tank) */
      const W = this.W || 600, H = this.H || 400;
      const pourX = W * 0.27, pourY = H * 0.10;
      LabFX.particles.emit({
        ctx: this.ctx, x: pourX, y: pourY,
        count: 12, color: HydroSim.LIQUIDS[this.liquidKey].color,
        speed: 60, spread: Math.PI / 1.5, angle: Math.PI / 2,
        gravity: 150, life: 500, shape: 'splash', size: 3,
      });
    }
  }
  removeLiquid() { this._liquidFrac = Math.max(0.05, this._liquidFrac - 0.05); this._recalcVessels(); }
  setBodyShape(s){ this._bodyShape = s; if (this.mode === 'archimedes') this._archReset(); }
  addBody()      { this._archAddBody(); }
  clearBodies()  { this._archClear(); this._notify(); }

  getInfo() {
    const liq = HydroSim.LIQUIDS[this.liquidKey];
    const mat = HydroSim.MATERIALS[this.materialKey];
    switch (this.mode) {
      case 'pressure': {
        const h = this._probe.vy * this._tankH_m();
        const P = liq.rho * this.g * h;
        return { h: h.toFixed(3), rho: liq.rho, P: Math.round(P), liqName: liq.name,
          formula: `P = ρ·g·h = ${liq.rho}·${this.g.toFixed(1)}·${h.toFixed(3)} = ${Math.round(P)} Па` };
      }
      case 'surface': {
        const r = 0.001, theta = this._contactAngle * Math.PI / 180;
        const h = 2 * liq.sigma * Math.cos(theta) / (liq.rho * this.g * r);
        return { sigma: liq.sigma, theta: this._contactAngle, h: (h * 1000).toFixed(1), liqName: liq.name,
          formula: `h = 2σ·cos(θ)/(ρgr) = ${(h*1000).toFixed(1)} мм  (r=1мм)` };
      }
      case 'communicating': {
        const lvl = this._animLevel ?? this._targetLevel ?? this._liquidFrac * 0.8;
        const h = lvl * this._tankH_m(), P = liq.rho * this.g * h;
        return { h: h.toFixed(3), rho: liq.rho, P: Math.round(P), liqName: liq.name,
          vessels: this._numVessels, valve: this._valveOpen,
          formula: `h₁ = h₂ = ${h.toFixed(3)} м;  P = ${Math.round(P)} Па` };
      }
      case 'archimedes': {
        if (!this._bodies.length) return { liqName: liq.name, matName: mat.name };
        const b = this._bodies[0];
        const Vs = b.submergedFrac * b.volume;
        const FA = liq.rho * this.g * Vs, mg = mat.rho * b.volume * this.g;
        const state = mat.rho < liq.rho * 0.99 ? 'ВСПЛЫВАЕТ'
                    : mat.rho > liq.rho * 1.01 ? 'ТОНЕТ' : 'ВЗВЕШЕНО';
        return { FA: FA.toFixed(4), mg: mg.toFixed(4), state, liqName: liq.name, matName: mat.name,
          rhoMat: mat.rho, rhoLiq: liq.rho,
          formula: `Fₐ = ρж·g·Vпог = ${liq.rho}·${this.g.toFixed(1)}·${Vs.toFixed(5)} = ${FA.toFixed(4)} Н` };
      }
    }
    return {};
  }

  fit() {
    const el = this.canvas.parentElement || this.canvas;
    const w  = el.clientWidth || 600, h = el.clientHeight || 400;
    if (w < 50 || h < 50) return;
    this.canvas.width = w; this.canvas.height = h;
    this.W = w; this.H = h;
    /* archimedes: no walls to rebuild — pure JS physics */
  }

  play()  { if (!this._running) { this._running = true; requestAnimationFrame(t => this._loop(t)); } }
  stop()  { this._running = false; if (this._raf) cancelAnimationFrame(this._raf); }
  destroy() {
    this.stop(); this._destroyArch(); this._ro?.disconnect();
    this.canvas.removeEventListener('pointerdown', this._onPD);
    this.canvas.removeEventListener('pointermove', this._onPM);
    window.removeEventListener('pointerup', this._onPU);
  }

  /* ── Loop ── */
  _loop(t) {
    if (!this._running) return;
    this._raf = requestAnimationFrame(ts => this._loop(ts));
    const dt = this._loopLast ? Math.min((t - this._loopLast) / 1000, 0.05) : 0.016;
    this._loopLast = t;
    this._t   = t;
    if (window.LabFX) LabFX.particles.update(dt);
    this._update(t);
    this._draw(t);
    if (window.LSGraphPanel && this._graphsOn && this._graphUI && this.mode === 'archimedes' && this._archReady) {
      const bodies = this._bodies;
      if (bodies && bodies.length > 0) {
        const b = bodies[0];
        const submersion = b ? Math.max(0, Math.min(1, b.submergedFrac || 0)) : 0;
        const depth = b ? (b.y || 0) : 0;
        const vel   = b ? (b.vy || 0) : 0;
        this._graphUI.push(this._t / 1000, [depth, vel, submersion]);
      }
    }
    if (t - this._lastNotify > 120) { this._lastNotify = t; this._notify(); }
  }

  _update(t) {
    if (this.mode === 'communicating' && this._targetLevel !== null) {
      if (this._animLevel === null) this._animLevel = this._targetLevel;
      const d = this._targetLevel - this._animLevel;
      this._animLevel += d * 0.07;
      if (Math.abs(d) < 0.001) this._animLevel = this._targetLevel;
    }
    this._waveT = ((this._waveT || 0) + 0.025);
    if (this.mode === 'archimedes' && this._archReady) this._archPhysStep();
  }

  _draw(t) {
    if (!this.W || !this.H) return;
    this.ctx.clearRect(0, 0, this.W, this.H);
    /* opaque background — prevents page bg colour bleeding through transparent canvas */
    this.ctx.fillStyle = '#0d0920';
    this.ctx.fillRect(0, 0, this.W, this.H);
    switch (this.mode) {
      case 'pressure':      this._drawPressure(t);      break;
      case 'surface':       this._drawSurface(t);       break;
      case 'communicating': this._drawCommunicating(t); break;
      case 'archimedes':    this._drawArchimedes(t);    break;
    }
    if (window.LabFX) LabFX.particles.draw(this.ctx);
  }

  /* ═══════════════════════════════════════════════════
     МОДУЛЬ 1 — ДАВЛЕНИЕ
  ═══════════════════════════════════════════════════ */
  _drawPressure(t) {
    const ctx = this.ctx, W = this.W, H = this.H;
    const liq = HydroSim.LIQUIDS[this.liquidKey];

    /* tank */
    const tw = Math.min(W * 0.30, 200), th = H * 0.72;
    const tx = W * 0.12, ty = H * 0.10;

    /* pressure at probe */
    const h    = this._probe.vy * this._tankH_m();
    const P    = liq.rho * this.g * h;
    const maxP = liq.rho * this.g * this._tankH_m();

    /* draw pressure-gradient zones inside tank */
    this._drawPressureZones(ctx, tx, ty, tw, th, maxP, liq.color);

    /* vessel over zones */
    this._drawGlassVessel(ctx, tx, ty, tw, th);

    /* wave surface */
    const liqY = ty;
    this._drawWaveSurface(ctx, tx + 3, liqY, tw - 6, liq.color, this._waveT);

    /* depth ruler */
    this._drawRuler(ctx, tx - 36, ty, th, '0 м', '1 м');

    /* probe */
    const pX = tx + tw * 0.5, pY = ty + this._probe.vy * th;

    /* depth dashed line */
    ctx.save();
    ctx.setLineDash([5, 4]); ctx.strokeStyle = 'rgba(255,255,255,0.18)'; ctx.lineWidth = 1;
    ctx.beginPath(); ctx.moveTo(tx - 36, pY); ctx.lineTo(tx + tw + 80, pY); ctx.stroke();
    ctx.setLineDash([]); ctx.restore();

    /* depth label */
    ctx.save();
    ctx.fillStyle = 'rgba(255,255,255,0.55)'; ctx.font = '12px Manrope,sans-serif';
    ctx.textAlign = 'right';
    ctx.fillText('h = ' + h.toFixed(2) + ' м', tx - 40, pY + 4);
    ctx.restore();

    /* pressure arrows */
    const maxLen = Math.min(60, tw * 0.42);
    const arLen  = maxP > 0 ? (P / maxP) * maxLen : 0;
    const arCol  = this._lerpColor('#FFD166', '#F15BB5', P / Math.max(maxP, 1));
    const dirs   = [{ dx: 1, dy: 0 }, { dx: -1, dy: 0 }, { dx: 0, dy: 1 }, { dx: 0, dy: -1 }];
    for (const d of dirs) this._drawArrow(ctx, pX, pY, d.dx * arLen, d.dy * arLen, arCol, 4);

    /* pressure value label */
    if (P > 5) {
      ctx.save();
      ctx.fillStyle = arCol; ctx.font = 'bold 14px "JetBrains Mono",monospace';
      ctx.textAlign = 'center'; ctx.shadowColor = arCol; ctx.shadowBlur = 8;
      ctx.fillText(Math.round(P) + ' Па', pX, pY - 22);
      ctx.shadowBlur = 0; ctx.restore();
    }

    /* probe dot */
    ctx.save();
    ctx.shadowColor = '#06D6E0'; ctx.shadowBlur = this._probe.dragging ? 24 : 14;
    ctx.fillStyle = '#06D6E0';
    ctx.beginPath(); ctx.arc(pX, pY, 12, 0, Math.PI * 2); ctx.fill();
    ctx.strokeStyle = '#fff'; ctx.lineWidth = 2.5; ctx.stroke();
    ctx.shadowBlur = 0;
    ctx.fillStyle = 'rgba(255,255,255,0.9)'; ctx.font = 'bold 10px monospace';
    ctx.textAlign = 'center'; ctx.textBaseline = 'middle';
    ctx.fillText('P', pX, pY);
    ctx.textBaseline = 'alphabetic'; ctx.restore();

    /* drag hint */
    ctx.fillStyle = 'rgba(6,214,224,0.4)'; ctx.font = '10px Manrope,sans-serif';
    ctx.textAlign = 'center'; ctx.fillText('↕ тяни', pX, pY + 28);

    /* gauge */
    const gR  = Math.min(48, H * 0.11);
    const gCx = tx + tw + 22 + gR, gCy = ty + th * 0.50;
    this._drawGauge(ctx, gCx, gCy, P, maxP, 'Па', gR);

    /* right-side info panel */
    this._drawInfoPanel(ctx, tx + tw + 22 + gR * 2 + 12, ty + 4, W - (tx + tw + 22 + gR * 2 + 16), th - 8, [
      { label: 'Жидкость', value: liq.name },
      { label: 'ρ', value: liq.rho + ' кг/м³' },
      { label: 'h', value: h.toFixed(3) + ' м' },
      { label: 'P', value: Math.round(P) + ' Па', color: arCol },
    ]);

    /* formula strip */
    this._drawFormula(ctx, W / 2, H - 12,
      `P = ρ·g·h = ${liq.rho}·${this.g.toFixed(1)}·${h.toFixed(2)} = ${Math.round(P)} Па`,
      '#FFD166');
  }

  _drawPressureZones(ctx, x, y, w, h, maxP, color) {
    ctx.save();
    ctx.beginPath(); ctx.rect(x + 3, y, w - 6, h); ctx.clip();
    /* deep-color gradient */
    const g = ctx.createLinearGradient(0, y, 0, y + h);
    g.addColorStop(0,   color + '22');
    g.addColorStop(0.4, color + '55');
    g.addColorStop(1,   color + 'CC');
    ctx.fillStyle = g; ctx.fillRect(x + 3, y, w - 6, h);
    /* isobar lines */
    ctx.strokeStyle = 'rgba(255,255,255,0.10)'; ctx.lineWidth = 1;
    ctx.setLineDash([4, 6]);
    for (let i = 1; i < 10; i++) {
      const iy = y + (i / 10) * h;
      ctx.beginPath(); ctx.moveTo(x + 3, iy); ctx.lineTo(x + w - 3, iy); ctx.stroke();
    }
    ctx.setLineDash([]);
    /* caustic shimmer */
    ctx.globalAlpha = 0.06;
    for (let i = 0; i < 6; i++) {
      const cx2 = x + 10 + ((i * 47 + (this._waveT || 0) * 15) % (w - 20));
      const cy2 = y + h * 0.3 + Math.sin(i + (this._waveT || 0) * 0.5) * h * 0.15;
      ctx.fillStyle = '#fff';
      ctx.beginPath(); ctx.ellipse(cx2, cy2, 12, 5, 0.4, 0, Math.PI * 2); ctx.fill();
    }
    ctx.globalAlpha = 1; ctx.restore();
  }

  /* ═══════════════════════════════════════════════════
     МОДУЛЬ 2 — ПОВЕРХНОСТНОЕ НАТЯЖЕНИЕ
  ═══════════════════════════════════════════════════ */
  _drawSurface(t) {
    if (this._stMode === 'capillary')
      this._drawCapillaries(t);
    else
      this._drawDrop(t);
  }

  _drawCapillaries(t) {
    const ctx = this.ctx, W = this.W, H = this.H;
    const liq = HydroSim.LIQUIDS[this.liquidKey];

    const diameters = [0.5, 1.0, 2.0, 4.0];
    const n    = diameters.length;
    const tW   = W * 0.76, tX = W * 0.12;
    const tY   = H * 0.55, tH = H * 0.28;

    /* wide container */
    this._fillLiquidRect(ctx, tX + 3, tY, tW - 6, tH, liq.color);
    this._drawGlassVessel(ctx, tX, tY, tW, tH);
    this._drawWaveSurface(ctx, tX + 3, tY, tW - 6, liq.color, this._waveT);

    const capTubeW = Math.max(26, Math.min(W * 0.055, 40));
    const step  = tW / (n + 1);
    const theta = this._contactAngle * Math.PI / 180;
    const cosT  = Math.cos(theta);
    const capH  = H * 0.52;

    for (let i = 0; i < n; i++) {
      const r_m    = diameters[i] * 0.5 * 0.001;
      const h_m    = 2 * liq.sigma * cosT / (liq.rho * this.g * r_m);
      const cx     = tX + step * (i + 1);
      const capBot = tY;
      const capTop = tY - capH;
      const inner  = capTubeW - 10;

      /* tube walls — rendered as filled rects with gradient */
      const wallG = ctx.createLinearGradient(cx - capTubeW / 2, 0, cx + capTubeW / 2, 0);
      wallG.addColorStop(0,    'rgba(140,180,255,0.55)');
      wallG.addColorStop(0.18, 'rgba(200,225,255,0.25)');
      wallG.addColorStop(0.82, 'rgba(200,225,255,0.12)');
      wallG.addColorStop(1,    'rgba(140,180,255,0.45)');
      ctx.save();
      ctx.fillStyle = wallG;
      ctx.fillRect(cx - capTubeW / 2, capTop, capTubeW, capH);
      /* hollow out centre */
      ctx.clearRect(cx - inner / 2, capTop, inner, capH);
      ctx.restore();

      /* glass highlight on left wall interior */
      ctx.save();
      ctx.fillStyle = 'rgba(255,255,255,0.18)';
      ctx.fillRect(cx - inner / 2, capTop, 2, capH);
      ctx.restore();

      /* liquid rise height (visual scale: 5cm = full tube) */
      const scaledH = (h_m / 0.05) * capH * 0.9;
      const liqH    = Math.min(Math.max(scaledH, 0), capH);
      const liqTop  = capBot - liqH;

      if (liqH > 1) {
        /* cylindrical-look radial gradient */
        const rg = ctx.createRadialGradient(cx, liqTop + liqH / 2, 0, cx, liqTop + liqH / 2, inner / 2);
        rg.addColorStop(0,   liq.color + 'EE');
        rg.addColorStop(0.6, liq.color + 'BB');
        rg.addColorStop(1,   liq.color + '55');
        ctx.save();
        ctx.beginPath(); ctx.rect(cx - inner / 2, liqTop, inner, liqH); ctx.clip();
        ctx.fillStyle = rg; ctx.fillRect(cx - inner / 2, liqTop, inner, liqH);
        ctx.restore();
      }

      /* meniscus */
      this._drawMeniscus(ctx, cx, liqTop, inner, this._contactAngle, liq.color);

      /* meniscus specular highlight */
      if (this._contactAngle < 90 && liqH > 3) {
        const dip = (inner / 2) * Math.cos(theta) * 1.1;
        ctx.save();
        ctx.globalAlpha = 0.28;
        ctx.fillStyle = '#fff';
        ctx.beginPath();
        ctx.ellipse(cx - inner * 0.15, liqTop - dip * 0.3, inner * 0.22, Math.max(2, dip * 0.35), 0, 0, Math.PI * 2);
        ctx.fill();
        ctx.restore();
      }

      /* tube top cap */
      ctx.save();
      ctx.strokeStyle = 'rgba(140,180,255,0.5)'; ctx.lineWidth = 1;
      ctx.beginPath();
      ctx.moveTo(cx - capTubeW / 2, capTop);
      ctx.lineTo(cx + capTubeW / 2, capTop);
      ctx.stroke(); ctx.restore();

      /* diameter label */
      ctx.fillStyle = 'rgba(255,255,255,0.60)'; ctx.font = '12px Manrope,sans-serif';
      ctx.textAlign = 'center'; ctx.fillText('d=' + diameters[i] + ' мм', cx, capTop - 22);

      /* rise height label */
      if (liqH > 14) {
        ctx.fillStyle = liq.color; ctx.font = 'bold 13px monospace';
        ctx.textAlign = 'center'; ctx.fillText((h_m * 1000).toFixed(1) + ' мм', cx, liqTop - 10);
      }

      /* vertical bracket showing rise */
      if (liqH > 28) {
        ctx.save();
        ctx.strokeStyle = liq.color + '88'; ctx.lineWidth = 1; ctx.setLineDash([2, 3]);
        ctx.beginPath();
        ctx.moveTo(cx + capTubeW / 2 + 6, capBot);
        ctx.lineTo(cx + capTubeW / 2 + 6, liqTop);
        ctx.stroke(); ctx.setLineDash([]); ctx.restore();
      }
    }

    /* contact angle status */
    const isH = this._contactAngle < 90;
    ctx.fillStyle = isH ? '#06D6E0' : '#F15BB5';
    ctx.font = '13px Manrope,sans-serif'; ctx.textAlign = 'left';
    ctx.fillText('θ = ' + this._contactAngle + '°  — ' + (isH ? 'смачивание ↑' : 'несмачивание ↓'), tX, H - 34);

    this._drawFormula(ctx, W / 2, H - 12,
      'h = 2σ·cos(θ) / (ρgr)   σ=' + liq.sigma + ' Н/м   θ=' + this._contactAngle + '°', '#06D6E0');
  }

  _drawMeniscus(ctx, cx, topY, innerW, angleDeg, color) {
    const r = innerW / 2;
    ctx.save();
    if (angleDeg < 90) {
      const dip = r * Math.cos(angleDeg * Math.PI / 180) * 1.1;
      ctx.beginPath(); ctx.moveTo(cx - r, topY); ctx.quadraticCurveTo(cx, topY - dip, cx + r, topY);
    } else {
      const bulge = r * 0.5;
      ctx.beginPath(); ctx.moveTo(cx - r, topY); ctx.quadraticCurveTo(cx, topY + bulge, cx + r, topY);
    }
    ctx.strokeStyle = color; ctx.lineWidth = 2.5; ctx.stroke();
    ctx.restore();
  }

  _drawDrop(t) {
    const ctx = this.ctx, W = this.W, H = this.H;
    const liq = HydroSim.LIQUIDS[this.liquidKey];
    const theta        = this._contactAngle * Math.PI / 180;
    const isHydrophobic = this._contactAngle >= 90;
    const surfY        = H * 0.60;

    /* surface plane */
    ctx.save();
    const sg = ctx.createLinearGradient(0, surfY - 4, 0, surfY + H * 0.18);
    sg.addColorStop(0, isHydrophobic ? 'rgba(155,93,229,0.55)' : 'rgba(6,214,224,0.55)');
    sg.addColorStop(1, 'rgba(0,0,0,0)');
    ctx.fillStyle = sg; ctx.fillRect(W * 0.05, surfY, W * 0.90, H * 0.18);
    ctx.strokeStyle = isHydrophobic ? '#9B5DE5' : '#06D6E0'; ctx.lineWidth = 2.5;
    ctx.beginPath(); ctx.moveTo(W * 0.05, surfY); ctx.lineTo(W * 0.95, surfY); ctx.stroke();
    ctx.restore();

    /* surface label */
    ctx.fillStyle = 'rgba(255,255,255,0.38)'; ctx.font = '12px Manrope,sans-serif';
    ctx.textAlign = 'center';
    ctx.fillText(isHydrophobic ? 'Гидрофобная поверхность' : 'Гидрофильная поверхность', W / 2, surfY + 20);

    /* drop shape */
    const dropVol  = 0.0002;
    const cos3     = Math.cos(theta);
    const Rpow     = 2 - 3 * cos3 + cos3 * cos3 * cos3;
    const R        = Math.pow((3 * dropVol) / (Math.PI * Math.max(Rpow, 0.01)), 1 / 3);
    const Rpx      = Math.min(R * 2200, W * 0.24);
    const contactR = Rpx * Math.sin(theta);
    const centerY  = surfY - Rpx * Math.cos(theta);
    const wobble   = 1 + Math.sin(t * 0.002) * 0.012; /* slight oscillation */

    ctx.save();
    ctx.shadowColor = liq.color; ctx.shadowBlur = 22;
    ctx.beginPath(); ctx.rect(0, 0, W, surfY + 1); ctx.clip();
    const dg = ctx.createRadialGradient(
      W / 2 - Rpx * 0.28, centerY - Rpx * 0.28, Rpx * 0.04,
      W / 2, centerY, Rpx * wobble
    );
    dg.addColorStop(0,   liq.color + 'EE');
    dg.addColorStop(0.5, liq.color + 'BB');
    dg.addColorStop(1,   liq.color + '44');
    ctx.fillStyle = dg;
    ctx.beginPath();
    ctx.ellipse(W / 2, centerY, Rpx * wobble, Rpx / wobble, 0, 0, Math.PI * 2);
    ctx.fill();
    /* specular highlight */
    ctx.globalAlpha = 0.50; ctx.fillStyle = '#fff';
    ctx.beginPath();
    ctx.ellipse(W / 2 - Rpx * 0.28, centerY - Rpx * 0.28, Rpx * 0.20, Rpx * 0.10, -0.5, 0, Math.PI * 2);
    ctx.fill();
    ctx.restore();

    /* contact angle arc */
    ctx.save();
    ctx.strokeStyle = '#FFD166'; ctx.lineWidth = 2.5;
    const arcR = 34, tangAngle = Math.PI - theta;
    ctx.beginPath();
    ctx.arc(W / 2 - contactR, surfY, arcR, -Math.PI * 0.5, tangAngle - Math.PI * 0.5);
    ctx.stroke();
    ctx.fillStyle = '#FFD166'; ctx.font = 'bold 13px monospace'; ctx.textAlign = 'left';
    ctx.fillText('θ = ' + this._contactAngle + '°', W / 2 - contactR + arcR + 6, surfY - 8);
    ctx.restore();

    this._drawFormula(ctx, W / 2, H - 12,
      'σ = ' + liq.sigma + ' Н/м   ΔP = 2σ/R ≈ ' + (2 * liq.sigma / (R || 0.001)).toFixed(1) + ' Па',
      '#F15BB5');
  }

  /* ═══════════════════════════════════════════════════
     МОДУЛЬ 3 — СООБЩАЮЩИЕСЯ СОСУДЫ
  ═══════════════════════════════════════════════════ */
  _drawCommunicating(t) {
    const ctx = this.ctx, W = this.W, H = this.H;
    const liq = HydroSim.LIQUIDS[this.liquidKey];
    const n   = this._numVessels;

    /* ── Geometry ────────────────────────────────────────
       One unified container, internal partitions stop
       PIPE_H above the floor → shared bottom pipe zone.
       Vessels = sections between outer walls + partitions. */
    const CX   = W * 0.09, CW = W * 0.82;   // container left + width
    const CY   = H * 0.09, CH = H * 0.73;   // container top + height
    const PIPE_H = Math.max(22, CH * 0.07);  // connecting pipe zone height
    const PIPE_Y = CY + CH - PIPE_H;         // pipe zone top Y
    const FLOOR  = CY + CH;                  // container floor Y
    const PART_W = 5;                        // partition thickness (px)
    const SEC_W  = (CW - (n - 1) * PART_W) / n; // each section width

    const isOpen = this._valveOpen;
    const liqFrac = isOpen
      ? (this._animLevel ?? this._targetLevel ?? this._liquidFrac * 0.8)
      : this._liquidFrac * 0.8;

    /* usable height for liquid level display (above pipe zone) */
    const USABLE  = CH - PIPE_H;
    const liqTopY = PIPE_Y - liqFrac * USABLE;  // liquid surface Y
    const liqH    = FLOOR - liqTopY;             // total liquid column height

    /* ── 1. Liquid fill in each section ─────────────────── */
    for (let i = 0; i < n; i++) {
      const sx = CX + i * (SEC_W + PART_W);
      const lg = ctx.createLinearGradient(0, liqTopY, 0, FLOOR);
      lg.addColorStop(0,   liq.color + '42');
      lg.addColorStop(0.4, liq.color + '88');
      lg.addColorStop(1,   liq.color + 'CC');
      ctx.fillStyle = lg;
      ctx.fillRect(sx, liqTopY, SEC_W, liqH);
    }

    /* ── 2. Pipe zone fill (open = liquid, closed = dark) ── */
    for (let i = 0; i < n - 1; i++) {
      const px = CX + i * (SEC_W + PART_W) + SEC_W;
      if (isOpen) {
        const pg = ctx.createLinearGradient(0, PIPE_Y, 0, FLOOR);
        pg.addColorStop(0, liq.color + '88');
        pg.addColorStop(1, liq.color + 'CC');
        ctx.fillStyle = pg;
      } else {
        ctx.fillStyle = 'rgba(8,4,18,0.95)';
      }
      ctx.fillRect(px, PIPE_Y, PART_W, PIPE_H);
    }

    /* ── 3. Wave on each liquid surface ─────────────────── */
    for (let i = 0; i < n; i++) {
      const sx = CX + i * (SEC_W + PART_W);
      this._drawWaveSurface(ctx, sx + 2, liqTopY, SEC_W - 4, liq.color, this._waveT + i * 1.3);
    }

    /* ── 4. Outer container walls (U-shape, open at top) ── */
    ctx.save();
    ctx.strokeStyle = 'rgba(200,225,255,0.55)';
    ctx.lineWidth = 2.5; ctx.lineCap = 'round';
    ctx.shadowColor = 'rgba(180,210,255,0.22)'; ctx.shadowBlur = 8;
    ctx.beginPath();
    ctx.moveTo(CX, CY);          // left wall top
    ctx.lineTo(CX, FLOOR);       // left wall
    ctx.lineTo(CX + CW, FLOOR);  // bottom floor
    ctx.lineTo(CX + CW, CY);     // right wall
    ctx.stroke();
    /* glass reflection strip */
    ctx.shadowBlur = 0;
    ctx.strokeStyle = 'rgba(255,255,255,0.12)'; ctx.lineWidth = 1;
    ctx.beginPath(); ctx.moveTo(CX + 5, CY); ctx.lineTo(CX + 5, FLOOR); ctx.stroke();
    ctx.restore();

    /* ── 5. Internal partitions (stop at pipe zone top) ─── */
    ctx.save();
    ctx.strokeStyle = 'rgba(200,225,255,0.42)';
    ctx.lineWidth = PART_W; ctx.lineCap = 'butt';
    ctx.shadowColor = 'rgba(180,210,255,0.15)'; ctx.shadowBlur = 4;
    for (let i = 0; i < n - 1; i++) {
      const px = CX + i * (SEC_W + PART_W) + SEC_W + PART_W / 2;
      ctx.beginPath();
      ctx.moveTo(px, CY);
      ctx.lineTo(px, PIPE_Y);   // stop above pipe zone
      ctx.stroke();
    }
    ctx.restore();

    /* ── 6. Valve icon in each pipe gap ─────────────────── */
    for (let i = 0; i < n - 1; i++) {
      const px = CX + i * (SEC_W + PART_W) + SEC_W;
      const vm = px + PART_W / 2;
      const vc = PIPE_Y + PIPE_H / 2;
      if (isOpen) {
        /* flow arrows ← → */
        this._drawArrow(ctx, vm - 16, vc,  12, 0, '#06D6A0', 1.8);
        this._drawArrow(ctx, vm + 16, vc, -12, 0, '#06D6A0', 1.8);
      } else {
        ctx.save();
        ctx.translate(vm, vc); ctx.rotate(Math.PI / 4);
        ctx.strokeStyle = '#F15BB5'; ctx.lineWidth = 2.5;
        ctx.shadowColor = '#F15BB5'; ctx.shadowBlur = 10;
        ctx.strokeRect(-6, -6, 12, 12);
        ctx.restore();
      }
    }

    /* ── 7. Height labels + dashed brackets ─────────────── */
    for (let i = 0; i < n; i++) {
      const sx = CX + i * (SEC_W + PART_W);
      if (liqFrac > 0.02) {
        const h_m = liqFrac * this._tankH_m();
        ctx.fillStyle = liq.color;
        ctx.font = 'bold 11px monospace'; ctx.textAlign = 'center';
        ctx.fillText('h = ' + h_m.toFixed(2) + ' м', sx + SEC_W / 2, liqTopY - 10);
        /* dashed bracket */
        ctx.save();
        ctx.strokeStyle = liq.color + '55'; ctx.lineWidth = 1; ctx.setLineDash([2, 4]);
        ctx.beginPath();
        ctx.moveTo(sx + SEC_W - 6, PIPE_Y);
        ctx.lineTo(sx + SEC_W - 6, liqTopY);
        ctx.stroke(); ctx.setLineDash([]);
        ctx.restore();
      }
    }

    /* ── 8. Equal-level dashed line ─────────────────────── */
    if (isOpen && liqFrac > 0.02) {
      ctx.save();
      ctx.setLineDash([12, 6]);
      ctx.strokeStyle = '#06D6E0'; ctx.lineWidth = 1.5;
      ctx.globalAlpha = 0.55; ctx.shadowColor = '#06D6E0'; ctx.shadowBlur = 4;
      ctx.beginPath();
      ctx.moveTo(CX - 14, liqTopY);
      ctx.lineTo(CX + CW + 14, liqTopY);
      ctx.stroke();
      ctx.setLineDash([]); ctx.globalAlpha = 1; ctx.shadowBlur = 0;
      this._labelPill(ctx, CX + CW + 18, liqTopY, 'h₁ = h₂', '#06D6E0');
      ctx.restore();
    }

    /* ── 9. Status + formula ─────────────────────────────── */
    ctx.fillStyle = isOpen ? '#06D6A0' : '#F15BB5';
    ctx.font = '12px Manrope,sans-serif'; ctx.textAlign = 'right';
    ctx.fillText('Кран: ' + (isOpen ? 'открыт' : 'закрыт'), W - 12, H - 34);

    const h_m = liqFrac * this._tankH_m();
    this._drawFormula(ctx, W / 2, H - 12,
      'h₁ = h₂ = ' + h_m.toFixed(2) + ' м   P = ρgh = ' + Math.round(liq.rho * this.g * h_m) + ' Па',
      '#9B5DE5');
  }

  /* ═══════════════════════════════════════════════════
     МОДУЛЬ 4 — АРХИМЕД
  ═══════════════════════════════════════════════════ */
  _archTank() {
    const W = this.W || 600, H = this.H || 400;
    const tx = W * 0.03, ty = H * 0.06;
    const tw = W * 0.60, th = H * 0.80;
    const waterlineY = ty + th * (1 - this._waterLevel);
    return { tx, ty, tw, th, waterlineY };
  }

  _initArch() {
    if (this._archReady) return;
    this._bodies = [];
    this._archReady = true;
    this._archAddBody();
  }

  _destroyArch() {
    this._archReady = false;
    this._bodies = [];
  }

  /* pure-JS physics helpers ─────────────────────────── */
  _archAddBody() {
    if (!this._archReady && this.mode === 'archimedes') { this._initArch(); return; }
    if (!this._archReady) return;
    const mat = HydroSim.MATERIALS[this.materialKey];
    const liq = HydroSim.LIQUIDS[this.liquidKey];
    const { tx, ty, tw, th, waterlineY } = this._archTank();
    const size    = Math.max(46, Math.min(tw * 0.20, 76));
    const eqFrac  = Math.min(1.0, mat.rho / liq.rho);
    const sinks   = eqFrac >= 1.0;

    /* spawn at equilibrium → zero entry velocity, no overshooting */
    let y = sinks
      ? waterlineY + (ty + th - waterlineY) * 0.32
      : waterlineY + size * (eqFrac - 0.5);
    y = Math.max(ty + size * 0.55, Math.min(ty + th - size * 0.55, y));

    const spread = Math.min(tw * 0.26, size + 20);
    const x      = tx + tw * 0.25 + this._bodies.length * spread;
    const s_m    = size * 0.0018;
    const volume = this._bodyShape === 'circle'
      ? Math.PI * (s_m / 2) ** 2 * 0.08
      : s_m * s_m * 0.08;

    this._bodies.push({
      x, y, vy: 0, size, shape: this._bodyShape,
      mat: this.materialKey, submergedFrac: sinks ? 1 : eqFrac,
      wobble: 0, volume,
    });

    if (window.LabFX) {
      const liq2 = HydroSim.LIQUIDS[this.liquidKey];
      LabFX.sound.play('bounce', { pitch: 0.5 });
      LabFX.particles.emit({
        ctx: this.ctx, x, y: waterlineY,
        count: 20, color: liq2.color, speed: 80,
        spread: Math.PI / 1.5, angle: -Math.PI / 2,
        gravity: 200, life: 600, shape: 'splash', size: 3,
      });
    }
  }

  _archClear()  { this._bodies = []; }
  _archReset()  { this._bodies = []; this._archAddBody(); }

  _archPhysStep() {
    const liq  = HydroSim.LIQUIDS[this.liquidKey];
    const { ty, th, waterlineY } = this._archTank();
    const botY = ty + th - 3, topY = ty + 3;
    const G    = 0.38;   /* px/frame²  — gravitational accel in canvas units */
    const DAMP = 0.22;   /* viscous damping fraction/frame at full submersion  */
    const VMAX = 8;      /* speed cap px/frame                                */

    for (const b of this._bodies) {
      const mat  = HydroSim.MATERIALS[b.mat];
      const half = b.size / 2;
      const bot  = b.y + half, top = b.y - half;

      /* submerged fraction */
      let frac = 0;
      if (bot > waterlineY) {
        frac = top >= waterlineY ? 1.0 : (bot - waterlineY) / b.size;
        frac = Math.max(0, Math.min(1, frac));
      }
      b.submergedFrac = frac;

      /* net downward acceleration: G·(1 − ρж/ρт·frac)
         positive = downward (canvas Y), negative = floats up              */
      const rhoRatio = Math.min(liq.rho / mat.rho, 10.0);
      b.vy += G * (1.0 - rhoRatio * frac);

      /* viscous drag — heavier when deeper */
      if (frac > 0) b.vy *= (1.0 - DAMP * frac);

      b.vy = Math.max(-VMAX, Math.min(VMAX, b.vy));
      b.y += b.vy;

      /* soft collisions */
      if (b.y + half >= botY) { b.y = botY - half; b.vy *= -0.12; }
      if (b.y - half <= topY) { b.y = topY + half; b.vy = Math.abs(b.vy) * 0.08; }

      /* visual wobble driven by vertical speed */
      b.wobble = (b.wobble || 0) * 0.86 + b.vy * 0.004;
    }
  }

  /* ── Draw ─────────────────────────────────────────── */
  _drawArchimedes(t) {
    const ctx = this.ctx, W = this.W, H = this.H;
    const liq = HydroSim.LIQUIDS[this.liquidKey];
    const { tx, ty, tw, th, waterlineY } = this._archTank();

    /* ── air zone (above waterline) */
    const airH = Math.max(0, waterlineY - ty);
    if (airH > 1) {
      ctx.save();
      const ag = ctx.createLinearGradient(0, ty, 0, waterlineY);
      ag.addColorStop(0, 'rgba(18,12,38,0.0)');
      ag.addColorStop(1, 'rgba(18,12,38,0.28)');
      ctx.fillStyle = ag; ctx.fillRect(tx + 4, ty, tw - 8, airH);
      ctx.restore();
    }

    /* ── liquid zone (below waterline) */
    const liqH = ty + th - waterlineY;
    if (liqH > 1) {
      this._fillLiquidRect(ctx, tx + 4, waterlineY, tw - 8, liqH, liq.color);
    }

    /* ── glass vessel + wave */
    this._drawGlassVessel(ctx, tx, ty, tw, th);
    this._drawWaveSurface(ctx, tx + 4, waterlineY, tw - 8, liq.color, this._waveT);

    /* ── waterline dashed rule */
    ctx.save();
    ctx.setLineDash([10, 7]); ctx.strokeStyle = liq.color + 'BB'; ctx.lineWidth = 1.5;
    ctx.beginPath(); ctx.moveTo(tx + 4, waterlineY); ctx.lineTo(tx + tw - 4, waterlineY); ctx.stroke();
    ctx.setLineDash([]);
    ctx.fillStyle = liq.color + 'CC'; ctx.font = '11px Manrope,sans-serif'; ctx.textAlign = 'right';
    ctx.fillText('← ' + liq.name, tx + tw - 6, waterlineY - 7);
    ctx.restore();

    /* ── bodies (clip to tank interior) */
    ctx.save();
    ctx.beginPath(); ctx.rect(tx + 4, ty + 1, tw - 8, th - 2); ctx.clip();
    for (const b of this._bodies) this._archDrawBody(ctx, b, waterlineY, liq);
    ctx.restore();

    /* ── force arrows — clipped to tank band so mg↓ never bleeds below the glass floor */
    ctx.save();
    ctx.beginPath(); ctx.rect(0, 0, W, ty + th); ctx.clip();
    for (const b of this._bodies) this._archDrawForces(ctx, b, liq);
    ctx.restore();

    /* ── info panel (right side) */
    const panX = tx + tw + 16, panW = W - panX - 8;
    if (panW > 80) this._archDrawPanel(ctx, panX, ty, panW, th, liq);

    /* ── bottom formula */
    if (this._bodies.length > 0) {
      const b  = this._bodies[0];
      const FA = liq.rho * this.g * b.volume * b.submergedFrac;
      const mg = HydroSim.MATERIALS[b.mat].rho * b.volume * this.g;
      this._drawFormula(ctx, tx + tw * 0.5, H - 12,
        `Fₐ = ${FA.toFixed(4)} Н   mg = ${mg.toFixed(4)} Н   ρж/ρт = ${(liq.rho / HydroSim.MATERIALS[b.mat].rho).toFixed(2)}`,
        '#06D6E0');
    } else {
      this._drawFormula(ctx, tx + tw * 0.5, H - 12, 'Fₐ = ρж · g · Vпогружённый  —  закон Архимеда', '#06D6E0');
    }
  }

  _archDrawBody(ctx, b, waterlineY, liq) {
    const mat  = HydroSim.MATERIALS[b.mat];
    const half = b.size / 2;

    /* submerged liquid tint on body */
    if (b.submergedFrac > 0.01) {
      ctx.save();
      const subTop = b.y - half;
      ctx.beginPath(); ctx.rect(b.x - half - 1, waterlineY, b.size + 2, b.y + half - waterlineY + 1); ctx.clip();
      ctx.globalAlpha = 0.22; ctx.fillStyle = liq.color;
      if (b.shape === 'circle') { ctx.beginPath(); ctx.arc(b.x, b.y, half, 0, Math.PI * 2); ctx.fill(); }
      else { ctx.fillRect(b.x - half, b.y - half, b.size, b.size); }
      ctx.restore();
    }

    /* main body */
    ctx.save();
    ctx.translate(b.x, b.y); ctx.rotate(b.wobble || 0);
    ctx.shadowColor = mat.color + 'BB'; ctx.shadowBlur = 18;
    ctx.fillStyle   = mat.color;
    if (b.shape === 'circle') {
      ctx.beginPath(); ctx.arc(0, 0, half, 0, Math.PI * 2); ctx.fill();
    } else {
      const r = Math.min(10, half * 0.25);
      if (ctx.roundRect) ctx.roundRect(-half, -half, b.size, b.size, r);
      else ctx.rect(-half, -half, b.size, b.size);
      ctx.fill();
    }
    ctx.shadowBlur = 0;

    /* material texture */
    this._archMatTex(ctx, b.mat, half, b.shape);

    /* outline */
    ctx.strokeStyle = 'rgba(255,255,255,0.38)'; ctx.lineWidth = 2;
    if (b.shape === 'circle') { ctx.beginPath(); ctx.arc(0, 0, half, 0, Math.PI * 2); ctx.stroke(); }
    else {
      const r = Math.min(10, half * 0.25);
      if (ctx.roundRect) ctx.roundRect(-half, -half, b.size, b.size, r);
      else ctx.rect(-half, -half, b.size, b.size);
      ctx.stroke();
    }
    ctx.restore();

    /* name tag below body */
    ctx.save();
    ctx.fillStyle = 'rgba(255,255,255,0.72)'; ctx.font = 'bold 11px Manrope,sans-serif'; ctx.textAlign = 'center';
    ctx.fillText(mat.name, b.x, b.y + half + 16);
    ctx.restore();
  }

  _archMatTex(ctx, matKey, half, shape) {
    ctx.save(); ctx.globalAlpha = 0.60;
    if (matKey === 'wood' || matKey === 'cork') {
      ctx.strokeStyle = 'rgba(0,0,0,0.18)'; ctx.lineWidth = 1.5;
      if (shape === 'circle') {
        for (let r = half * 0.35; r < half; r += half * 0.30) {
          ctx.beginPath(); ctx.arc(0, 0, r, 0, Math.PI * 2); ctx.stroke();
        }
      } else {
        for (let y2 = -half + 10; y2 < half; y2 += 10) {
          ctx.beginPath(); ctx.moveTo(-half + 3, y2); ctx.lineTo(half - 3, y2); ctx.stroke();
        }
      }
    } else if (['iron','gold','aluminum','glass','plastic'].includes(matKey)) {
      const g = ctx.createRadialGradient(-half * 0.3, -half * 0.3, 0, 0, 0, half * 1.1);
      g.addColorStop(0, 'rgba(255,255,255,0.55)'); g.addColorStop(0.45, 'rgba(255,255,255,0.12)'); g.addColorStop(1, 'rgba(0,0,0,0.28)');
      ctx.fillStyle = g;
      if (shape === 'circle') { ctx.beginPath(); ctx.arc(0, 0, half, 0, Math.PI * 2); ctx.fill(); }
      else ctx.fillRect(-half, -half, half * 2, half * 2);
    } else if (matKey === 'ice') {
      ctx.strokeStyle = 'rgba(180,240,255,0.65)'; ctx.lineWidth = 1.5;
      ctx.beginPath(); ctx.moveTo(-half * 0.5, -half * 0.5); ctx.lineTo(half * 0.5, half * 0.5); ctx.stroke();
      ctx.beginPath(); ctx.moveTo(half * 0.5, -half * 0.5); ctx.lineTo(-half * 0.5, half * 0.5); ctx.stroke();
    } else if (matKey === 'styrofoam') {
      ctx.fillStyle = 'rgba(255,255,255,0.40)';
      for (let i = 0; i < 6; i++) {
        const ax = Math.cos(i * 1.047) * half * 0.52, ay = Math.sin(i * 1.047) * half * 0.52;
        ctx.beginPath(); ctx.arc(ax, ay, half * 0.09, 0, Math.PI * 2); ctx.fill();
      }
    }
    ctx.restore();
  }

  _archDrawForces(ctx, b, liq) {
    const mat  = HydroSim.MATERIALS[b.mat];
    const half = b.size / 2;

    /* buoyancy arrows only when partly submerged */
    const FA_rel = (liq.rho / mat.rho) * b.submergedFrac; /* relative to mg */
    const showFA = b.submergedFrac > 0.01;
    const BASE   = 54;
    const maxRel = Math.max(FA_rel, 1.0, 0.001);
    const Fa_px  = showFA ? Math.max(22, Math.min(90, (FA_rel / maxRel) * BASE)) : 0;
    const mg_px  = Math.max(22, Math.min(90, (1.0 / maxRel) * BASE));

    const lx = b.x - half - 20, rx = b.x + half + 20;
    if (showFA) this._drawArrow(ctx, lx, b.y, 0, -Fa_px, '#06D6E0', 3.5, 'Fₐ');
    this._drawArrow(ctx, rx, b.y, 0, mg_px, '#F15BB5', 3.5, 'mg');
  }

  _archDrawPanel(ctx, x, y, w, h, liq) {
    /* background */
    ctx.save();
    ctx.fillStyle = 'rgba(6,4,20,0.78)'; ctx.strokeStyle = 'rgba(255,255,255,0.07)'; ctx.lineWidth = 1;
    if (ctx.roundRect) ctx.roundRect(x, y, w, h, 10); else ctx.rect(x, y, w, h);
    ctx.fill(); ctx.stroke(); ctx.restore();

    if (!this._bodies.length) {
      ctx.fillStyle = 'rgba(255,255,255,0.20)'; ctx.font = '12px Manrope,sans-serif'; ctx.textAlign = 'center';
      ctx.fillText('+ Добавьте тело', x + w / 2, y + h / 2);
      return;
    }

    const b   = this._bodies[0];
    const mat = HydroSim.MATERIALS[b.mat];
    const FA  = liq.rho * this.g * b.volume * b.submergedFrac;
    const mg  = mat.rho * b.volume * this.g;
    const state = mat.rho < liq.rho * 0.99 ? 'ВСПЛЫВАЕТ'
                : mat.rho > liq.rho * 1.01 ? 'ТОНЕТ' : 'ВЗВЕШЕНО';
    const stC   = state === 'ВСПЛЫВАЕТ' ? '#06D6A0' : state === 'ТОНЕТ' ? '#F15BB5' : '#FFD166';
    const pulse = state !== 'ВЗВЕШЕНО' ? 0.7 + Math.sin(this._t * 0.004) * 0.3 : 1.0;

    const pad = 11, lh = 20;
    let cy = y + 20;

    /* ── state badge ── */
    ctx.save();
    ctx.fillStyle = stC + '1E'; ctx.strokeStyle = stC + '66'; ctx.lineWidth = 1.5;
    if (ctx.roundRect) ctx.roundRect(x + pad, cy - 15, w - pad * 2, 30, 7);
    else ctx.rect(x + pad, cy - 15, w - pad * 2, 30);
    ctx.fill(); ctx.stroke();
    ctx.globalAlpha = pulse; ctx.fillStyle = stC;
    ctx.font = 'bold 14px Manrope,sans-serif'; ctx.textAlign = 'center';
    ctx.shadowColor = stC; ctx.shadowBlur = 10;
    ctx.fillText(state, x + w / 2, cy + 4);
    ctx.globalAlpha = 1; ctx.shadowBlur = 0; ctx.restore();
    cy += 38;

    /* ── separator ── */
    ctx.save(); ctx.strokeStyle = 'rgba(255,255,255,0.07)'; ctx.lineWidth = 1;
    ctx.beginPath(); ctx.moveTo(x + pad, cy); ctx.lineTo(x + w - pad, cy); ctx.stroke(); ctx.restore();
    cy += 13;

    /* ── material + liquid ── */
    ctx.save(); ctx.font = '10px Manrope,sans-serif'; ctx.textAlign = 'left';
    ctx.fillStyle = 'rgba(255,255,255,0.32)'; ctx.fillText('МАТЕРИАЛ', x + pad, cy); cy += lh * 0.8;
    ctx.fillStyle = mat.color; ctx.fillRect(x + pad, cy - 11, 12, 12);
    ctx.strokeStyle = 'rgba(255,255,255,0.18)'; ctx.lineWidth = 0.5; ctx.strokeRect(x + pad, cy - 11, 12, 12);
    ctx.fillStyle = '#fff'; ctx.font = '12px Manrope,sans-serif'; ctx.fillText(mat.name, x + pad + 16, cy);
    cy += lh * 0.7;
    ctx.fillStyle = 'rgba(255,255,255,0.48)'; ctx.font = '11px "JetBrains Mono",monospace';
    ctx.fillText('ρт = ' + mat.rho + ' кг/м³', x + pad, cy); cy += lh * 0.9;
    ctx.fillText('ρж = ' + liq.rho + ' кг/м³', x + pad, cy); cy += lh * 1.2; ctx.restore();

    /* ── force bars ── */
    ctx.save(); ctx.font = '10px Manrope,sans-serif'; ctx.textAlign = 'left';
    ctx.fillStyle = 'rgba(255,255,255,0.32)'; ctx.fillText('СИЛЫ', x + pad, cy); cy += lh * 0.85;
    const barW  = w - pad * 2;
    const maxF  = Math.max(FA, mg, 1e-14);
    const faW   = Math.max(3, (FA / maxF) * barW);
    const mgW   = Math.max(3, (mg / maxF) * barW);

    /* Fа row */
    ctx.fillStyle = 'rgba(6,214,224,0.12)'; ctx.fillRect(x + pad, cy - 12, barW, 17);
    ctx.fillStyle = '#06D6E0'; ctx.fillRect(x + pad, cy - 12, faW, 17);
    ctx.fillStyle = '#fff'; ctx.font = '10px "JetBrains Mono",monospace';
    ctx.fillText('Fа ↑', x + pad + 3, cy); ctx.textAlign = 'right';
    ctx.fillText(FA.toFixed(5), x + pad + barW - 2, cy); ctx.textAlign = 'left';
    cy += lh * 1.05;

    /* mg row */
    ctx.fillStyle = 'rgba(241,91,181,0.12)'; ctx.fillRect(x + pad, cy - 12, barW, 17);
    ctx.fillStyle = '#F15BB5'; ctx.fillRect(x + pad, cy - 12, mgW, 17);
    ctx.fillStyle = '#fff';
    ctx.fillText('mg ↓', x + pad + 3, cy); ctx.textAlign = 'right';
    ctx.fillText(mg.toFixed(5), x + pad + barW - 2, cy); ctx.textAlign = 'left';
    cy += lh * 1.35; ctx.restore();

    /* ── density ratio bar ── */
    ctx.save(); ctx.font = '10px Manrope,sans-serif'; ctx.fillStyle = 'rgba(255,255,255,0.32)';
    const ratio = (liq.rho / mat.rho);
    ctx.fillText('ρж / ρт = ' + (ratio).toFixed(2), x + pad, cy); cy += lh * 0.85;
    const rbW = w - pad * 2;
    /* bar covers ratio 0..4; mark at ratio=1 */
    const normR  = Math.min(ratio / 4, 1.0);
    const mark1  = x + pad + rbW * 0.25;          /* ratio = 1 position */
    ctx.fillStyle = 'rgba(255,255,255,0.07)'; ctx.fillRect(x + pad, cy - 10, rbW, 13);
    const rg = ctx.createLinearGradient(x + pad, 0, x + pad + rbW, 0);
    rg.addColorStop(0, '#F15BB5'); rg.addColorStop(0.25, '#FFD166'); rg.addColorStop(1, '#06D6A0');
    ctx.fillStyle = rg; ctx.fillRect(x + pad, cy - 10, normR * rbW, 13);
    /* cursor on bar */
    const curX = x + pad + normR * rbW;
    ctx.fillStyle = '#fff'; ctx.fillRect(curX - 2, cy - 13, 4, 19);
    /* neutral marker */
    ctx.fillStyle = 'rgba(255,255,255,0.45)'; ctx.fillRect(mark1 - 1, cy - 13, 2, 19);
    ctx.fillStyle = 'rgba(255,255,255,0.30)'; ctx.font = '8px monospace'; ctx.textAlign = 'center';
    ctx.fillText('=1', mark1, cy + 14);
    ctx.restore();
  }

  /* ═══════════════════════════════════════════════════
     HELPERS — RENDERING
  ═══════════════════════════════════════════════════ */

  _drawGlassVessel(ctx, x, y, w, h) {
    ctx.save();
    /* thick wall gradient — left */
    const lG = ctx.createLinearGradient(x, 0, x + 14, 0);
    lG.addColorStop(0,   'rgba(160,200,255,0.65)');
    lG.addColorStop(0.5, 'rgba(160,200,255,0.30)');
    lG.addColorStop(1,   'rgba(160,200,255,0.05)');
    ctx.fillStyle = lG; ctx.fillRect(x, y, 14, h + 14);
    /* right */
    const rG = ctx.createLinearGradient(x + w - 14, 0, x + w, 0);
    rG.addColorStop(0,   'rgba(160,200,255,0.05)');
    rG.addColorStop(0.5, 'rgba(160,200,255,0.25)');
    rG.addColorStop(1,   'rgba(160,200,255,0.60)');
    ctx.fillStyle = rG; ctx.fillRect(x + w - 14, y, 14, h + 14);
    /* bottom */
    const bG = ctx.createLinearGradient(0, y + h, 0, y + h + 14);
    bG.addColorStop(0, 'rgba(160,200,255,0.35)');
    bG.addColorStop(1, 'rgba(0,0,0,0)');
    ctx.fillStyle = bG; ctx.fillRect(x, y + h, w, 14);
    /* outline */
    ctx.strokeStyle = 'rgba(200,225,255,0.55)'; ctx.lineWidth = 2.5;
    ctx.beginPath();
    ctx.moveTo(x + 2, y); ctx.lineTo(x + 2, y + h + 12); ctx.lineTo(x + w - 2, y + h + 12); ctx.lineTo(x + w - 2, y);
    ctx.stroke();
    /* inner reflection */
    ctx.strokeStyle = 'rgba(255,255,255,0.18)'; ctx.lineWidth = 1;
    ctx.beginPath(); ctx.moveTo(x + 6, y); ctx.lineTo(x + 6, y + h); ctx.stroke();
    ctx.restore();
  }

  _fillLiquidRect(ctx, x, y, w, h, color) {
    ctx.save();
    const g = ctx.createLinearGradient(0, y, 0, y + h);
    g.addColorStop(0,    color + '33');
    g.addColorStop(0.25, color + '66');
    g.addColorStop(0.75, color + 'AA');
    g.addColorStop(1,    color + 'CC');
    ctx.fillStyle = g;
    ctx.fillRect(x, y, w, h);
    /* deep shadow at bottom */
    const dG = ctx.createLinearGradient(0, y + h * 0.75, 0, y + h);
    dG.addColorStop(0, 'rgba(0,0,30,0)');
    dG.addColorStop(1, 'rgba(0,0,30,0.22)');
    ctx.fillStyle = dG; ctx.fillRect(x, y + h * 0.75, w, h * 0.25);
    ctx.restore();
  }

  _drawWaveSurface(ctx, x, y, w, color, wt) {
    ctx.save();
    ctx.strokeStyle = color + 'CC'; ctx.lineWidth = 1.8;
    ctx.beginPath();
    for (let px = x; px <= x + w; px += 2) {
      const wy = y + Math.sin(px * 0.055 + wt) * 2.5 + Math.sin(px * 0.13 + wt * 1.3) * 1.0;
      px === x ? ctx.moveTo(px, wy) : ctx.lineTo(px, wy);
    }
    ctx.stroke();
    /* surface sheen */
    ctx.strokeStyle = 'rgba(255,255,255,0.14)'; ctx.lineWidth = 1;
    ctx.beginPath();
    for (let px = x; px <= x + w; px += 2) {
      const wy = y + Math.sin(px * 0.055 + wt + 0.4) * 2.5;
      px === x ? ctx.moveTo(px, wy - 2) : ctx.lineTo(px, wy - 2);
    }
    ctx.stroke();
    ctx.restore();
  }

  _drawLiquidShaped(ctx, x, y, w, h, frac, color, shape, wt) {
    const liqH = h * Math.max(0, Math.min(frac, 1));
    const liqY = y + h - liqH;
    if (liqH < 2) return;
    ctx.save();
    /* shape clip */
    ctx.beginPath();
    switch (shape) {
      case 'wide':      ctx.rect(x - w*0.15, y, w*1.3, h); break;
      case 'narrow':    ctx.rect(x + w*0.2, y, w*0.6, h); break;
      case 'trapezoid': {
        const bl = x - w*0.12, br = x+w+w*0.12, tl = x, tr = x+w;
        ctx.moveTo(tl, y); ctx.lineTo(bl, y+h); ctx.lineTo(br, y+h); ctx.lineTo(tr, y); ctx.closePath();
        break;
      }
      default: ctx.rect(x, y, w, h);
    }
    ctx.clip();
    const g = ctx.createLinearGradient(0, liqY, 0, y + h);
    g.addColorStop(0,   color + '44'); g.addColorStop(0.4, color + '88'); g.addColorStop(1, color + 'BB');
    ctx.fillStyle = g; ctx.fillRect(x - w*0.2, liqY, w*1.4, liqH);
    ctx.restore();
  }

  _drawVesselShaped(ctx, x, y, w, h, shape) {
    ctx.save();
    ctx.strokeStyle = 'rgba(200,225,255,0.55)'; ctx.lineWidth = 2.5;
    ctx.shadowColor = 'rgba(180,210,255,0.20)'; ctx.shadowBlur = 6;
    ctx.beginPath();
    switch (shape) {
      case 'wide':
        ctx.moveTo(x - w*0.15, y); ctx.lineTo(x - w*0.15, y+h); ctx.lineTo(x+w+w*0.15, y+h); ctx.lineTo(x+w+w*0.15, y);
        break;
      case 'narrow':
        ctx.moveTo(x + w*0.2, y); ctx.lineTo(x+w*0.2, y+h); ctx.lineTo(x+w*0.8, y+h); ctx.lineTo(x+w*0.8, y);
        break;
      case 'trapezoid':
        ctx.moveTo(x, y); ctx.lineTo(x-w*0.12, y+h); ctx.lineTo(x+w+w*0.12, y+h); ctx.lineTo(x+w, y);
        break;
      default:
        ctx.moveTo(x, y); ctx.lineTo(x, y+h); ctx.lineTo(x+w, y+h); ctx.lineTo(x+w, y);
    }
    ctx.stroke();
    /* inner reflection strip */
    ctx.shadowBlur = 0; ctx.strokeStyle = 'rgba(255,255,255,0.14)'; ctx.lineWidth = 1;
    const lx = shape === 'wide' ? x - w*0.15 + 5 : shape === 'narrow' ? x+w*0.2+5 : x+5;
    ctx.beginPath(); ctx.moveTo(lx, y); ctx.lineTo(lx, y+h); ctx.stroke();
    ctx.restore();
  }

  _shapeRect(x, w, shape) {
    if (shape === 'wide')   return [x - w*0.15, w*1.3];
    if (shape === 'narrow') return [x + w*0.2,  w*0.6];
    return [x, w];
  }

  _drawArrow(ctx, x, y, dx, dy, color, lw = 3, label) {
    const len = Math.hypot(dx, dy);
    if (len < 2) return;
    ctx.save();
    ctx.strokeStyle = color; ctx.fillStyle = color;
    ctx.lineWidth = lw; ctx.shadowColor = color; ctx.shadowBlur = 7;
    ctx.beginPath(); ctx.moveTo(x, y); ctx.lineTo(x+dx, y+dy); ctx.stroke();
    const a = Math.atan2(dy, dx), ar = 11;
    ctx.beginPath();
    ctx.moveTo(x+dx, y+dy);
    ctx.lineTo(x+dx - ar*Math.cos(a-0.35), y+dy - ar*Math.sin(a-0.35));
    ctx.lineTo(x+dx - ar*Math.cos(a+0.35), y+dy - ar*Math.sin(a+0.35));
    ctx.closePath(); ctx.fill();
    if (label) {
      ctx.shadowBlur = 0;
      const lx = x + dx * 0.5 + (dy === 0 ? 0 : 16);
      const ly = y + dy * 0.5 + (dx === 0 ? -10 : -6);
      /* pill background */
      ctx.font = 'bold 12px monospace';
      const tw2 = ctx.measureText(label).width + 8;
      ctx.fillStyle = 'rgba(0,0,0,0.55)';
      ctx.beginPath();
      if (ctx.roundRect) ctx.roundRect(lx - tw2/2, ly - 9, tw2, 16, 4); else ctx.rect(lx - tw2/2, ly - 9, tw2, 16);
      ctx.fill();
      ctx.fillStyle = color; ctx.textAlign = 'center'; ctx.textBaseline = 'middle';
      ctx.fillText(label, lx, ly - 1); ctx.textBaseline = 'alphabetic';
    }
    ctx.restore();
  }

  _drawRuler(ctx, x, y, h, labelTop, labelBot) {
    ctx.save();
    ctx.strokeStyle = 'rgba(255,255,255,0.25)'; ctx.lineWidth = 1;
    ctx.beginPath(); ctx.moveTo(x+8, y); ctx.lineTo(x+8, y+h); ctx.stroke();
    for (let i = 0; i <= 10; i++) {
      const ty2 = y + (i/10)*h, tw2 = i%5===0 ? 10 : 5;
      ctx.beginPath(); ctx.moveTo(x+8-tw2, ty2); ctx.lineTo(x+8, ty2); ctx.stroke();
      if (i % 5 === 0) {
        ctx.fillStyle = 'rgba(255,255,255,0.4)'; ctx.font = '10px monospace'; ctx.textAlign = 'right';
        ctx.fillText(i === 0 ? labelTop : (i === 10 ? labelBot : ''), x+5, ty2+4);
      }
    }
    ctx.restore();
  }

  _drawGauge(ctx, cx, cy, val, maxVal, unit, r = 44) {
    const frac   = Math.min(val / Math.max(maxVal, 1), 1);
    const startA = Math.PI * 0.75, endA = Math.PI * 2.25;
    const valA   = startA + (endA - startA) * frac;
    const color  = this._lerpColor('#06D6E0', '#F15BB5', frac);
    ctx.save();
    /* outer ring */
    ctx.strokeStyle = 'rgba(255,255,255,0.06)'; ctx.lineWidth = r * 0.22 + 4;
    ctx.beginPath(); ctx.arc(cx, cy, r, startA, endA); ctx.stroke();
    /* track */
    ctx.strokeStyle = 'rgba(255,255,255,0.08)'; ctx.lineWidth = r * 0.22;
    ctx.beginPath(); ctx.arc(cx, cy, r, startA, endA); ctx.stroke();
    /* value arc */
    ctx.strokeStyle = color; ctx.shadowColor = color; ctx.shadowBlur = 12;
    ctx.beginPath(); ctx.arc(cx, cy, r, startA, valA); ctx.stroke();
    ctx.shadowBlur = 0;
    /* tick marks */
    ctx.strokeStyle = 'rgba(255,255,255,0.25)'; ctx.lineWidth = 1;
    for (let i = 0; i <= 4; i++) {
      const a = startA + (endA - startA) * (i / 4);
      ctx.beginPath();
      ctx.moveTo(cx + (r - 8)*Math.cos(a), cy + (r - 8)*Math.sin(a));
      ctx.lineTo(cx + (r + 3)*Math.cos(a), cy + (r + 3)*Math.sin(a));
      ctx.stroke();
    }
    /* needle */
    ctx.strokeStyle = '#fff'; ctx.lineWidth = 2;
    ctx.beginPath(); ctx.moveTo(cx, cy);
    ctx.lineTo(cx + (r - 12)*Math.cos(valA), cy + (r - 12)*Math.sin(valA)); ctx.stroke();
    ctx.fillStyle = '#fff'; ctx.beginPath(); ctx.arc(cx, cy, 4, 0, Math.PI*2); ctx.fill();
    /* value */
    ctx.fillStyle = color; ctx.font = 'bold 13px monospace'; ctx.textAlign = 'center';
    ctx.fillText(Math.round(val) + ' ' + unit, cx, cy + r + 20);
    ctx.restore();
  }

  _drawInfoPanel(ctx, x, y, w, h, rows) {
    if (w < 50) return;
    ctx.save();
    ctx.fillStyle = 'rgba(8,6,20,0.55)'; ctx.strokeStyle = 'rgba(255,255,255,0.07)'; ctx.lineWidth = 1;
    ctx.beginPath();
    if (ctx.roundRect) ctx.roundRect(x, y, w, Math.min(h, rows.length * 22 + 20), 8);
    else ctx.rect(x, y, w, rows.length * 22 + 20);
    ctx.fill(); ctx.stroke();
    ctx.font = '12px Manrope,sans-serif'; ctx.textAlign = 'left';
    rows.forEach((r, i) => {
      const ry = y + 16 + i * 22;
      ctx.fillStyle = 'rgba(255,255,255,0.35)'; ctx.fillText(r.label, x + 10, ry);
      ctx.fillStyle = r.color || 'rgba(255,255,255,0.85)';
      ctx.textAlign = 'right'; ctx.fillText(r.value, x + w - 10, ry);
      ctx.textAlign = 'left';
    });
    ctx.restore();
  }

  _labelPill(ctx, x, y, text, color) {
    ctx.save();
    ctx.font = 'bold 12px Manrope,sans-serif';
    const tw2 = ctx.measureText(text).width + 16;
    ctx.fillStyle = 'rgba(0,0,0,0.55)';
    ctx.beginPath();
    if (ctx.roundRect) ctx.roundRect(x, y - 11, tw2, 20, 5); else ctx.rect(x, y - 11, tw2, 20);
    ctx.fill();
    ctx.fillStyle = color; ctx.textAlign = 'left'; ctx.textBaseline = 'middle';
    ctx.fillText(text, x + 8, y - 1); ctx.textBaseline = 'alphabetic';
    ctx.restore();
  }

  _drawFormula(ctx, x, y, text, color) {
    ctx.save();
    ctx.font = '12px "JetBrains Mono",monospace';
    const tw2 = ctx.measureText(text).width;
    const pad = 12, bh = 28;
    let bx = x - (tw2 + pad*2) / 2;
    bx = Math.max(4, Math.min((this.W||600) - tw2 - pad*2 - 4, bx));
    const by = y - bh;
    ctx.fillStyle = 'rgba(6,4,18,0.90)'; ctx.strokeStyle = color; ctx.lineWidth = 1.3;
    ctx.shadowColor = color; ctx.shadowBlur = 6;
    const rr = 7;
    ctx.beginPath();
    ctx.moveTo(bx+rr, by); ctx.lineTo(bx+tw2+pad*2-rr, by);
    ctx.quadraticCurveTo(bx+tw2+pad*2, by, bx+tw2+pad*2, by+rr);
    ctx.lineTo(bx+tw2+pad*2, by+bh-rr);
    ctx.quadraticCurveTo(bx+tw2+pad*2, by+bh, bx+tw2+pad*2-rr, by+bh);
    ctx.lineTo(bx+rr, by+bh); ctx.quadraticCurveTo(bx, by+bh, bx, by+bh-rr);
    ctx.lineTo(bx, by+rr); ctx.quadraticCurveTo(bx, by, bx+rr, by);
    ctx.closePath(); ctx.fill(); ctx.stroke();
    ctx.shadowBlur = 0; ctx.fillStyle = color;
    ctx.textAlign = 'left'; ctx.textBaseline = 'middle';
    ctx.fillText(text, bx+pad, by+bh/2); ctx.textBaseline = 'alphabetic';
    ctx.restore();
  }

  /* ═══ Physics helpers ═══ */
  _tankH_m()     { return 1.0; }
  _recalcVessels() {
    this._targetLevel = this._valveOpen ? this._liquidFrac * 0.82 : null;
    if (!this._valveOpen) this._animLevel = null;
  }

  /* ═══ Events ═══ */
  _bindEvents() {
    this._onPD = e => this._pointerDown(e);
    this._onPM = e => this._pointerMove(e);
    this._onPU = () => { this._probe.dragging = false; };
    this.canvas.addEventListener('pointerdown', this._onPD);
    this.canvas.addEventListener('pointermove', this._onPM);
    window.addEventListener('pointerup', this._onPU);
  }
  _cp(e) {
    const r = this.canvas.getBoundingClientRect();
    return { x: (e.clientX-r.left)*(this.W/r.width), y: (e.clientY-r.top)*(this.H/r.height) };
  }
  _pointerDown(e) {
    if (this.mode !== 'pressure') return;
    const { x, y } = this._cp(e);
    const tw = Math.min(this.W*0.30, 200), tx = this.W*0.12, ty = this.H*0.10, th = this.H*0.72;
    const pX = tx + tw*0.5, pY = ty + this._probe.vy * th;
    if (Math.hypot(x-pX, y-pY) < 22) { this._probe.dragging = true; this.canvas.setPointerCapture(e.pointerId); }
  }
  _pointerMove(e) {
    if (!this._probe.dragging) return;
    const { y } = this._cp(e);
    const ty = this.H*0.10, th = this.H*0.72;
    this._probe.vy = Math.max(0.02, Math.min(0.98, (y-ty)/th));
  }

  /* ═══ Utils ═══ */
  _lerpColor(c1, c2, t) {
    const h  = s => parseInt(s.slice(1), 16);
    const p  = (a, b, t2) => Math.round(Math.max(0, Math.min(255, a + (b-a)*t2)));
    const v1 = h(c1), v2 = h(c2);
    return '#' + [[(v1>>16)&255,(v2>>16)&255],[(v1>>8)&255,(v2>>8)&255],[v1&255,v2&255]]
      .map(([a,b]) => p(a,b,t).toString(16).padStart(2,'0')).join('');
  }
  _notify() { if (this.onUpdate) try { this.onUpdate(this.getInfo()); } catch {} }

  toggleGraphs(canvasWrap) {
    if (!window.LSGraphPanelUI) return false;
    this._graphsOn = !this._graphsOn;
    if (this._graphsOn) {
      this._simT = 0;
      this._graphUI = new GraphPanelUI(canvasWrap, {
        maxPoints: 300,
        traces: ['depth', 'vy', 'sub'],
        labels: ['Глубина', 'v', 'Погружение'],
        units: ['пкс', 'пкс/с', '0..1'],
        colors: ['#06D6E0', '#FFD166', '#7BF5A4'],
        toggleBtnId: 'btn-hydro-graphs',
        title: 'Погружение'
      });
      this._graphUI.isOn = true;
      this._graphUI._build();
    } else {
      if (this._graphUI) { this._graphUI._destroy(); this._graphUI = null; }
    }
    return this._graphsOn;
  }
}

/* ─── lab UI init ─────────────────────────────────── */
  var hydroSim = null;
  let _hydroValveOpen = true;

  function _openHydro(preset) {
    document.getElementById('sim-topbar-title').textContent = 'Гидростатика';
    _simShow('sim-hydro');
    document.getElementById('ctrl-hydro').style.display = '';
    _registerSimState('hydrostatics',
      () => ({ mode: hydroSim?.mode, liq: hydroSim?.liquidKey }),
      st => { if (st?.mode && hydroSim) hydroMode(st.mode); });
    if (_embedMode) _startStateEmit('hydrostatics');
    window.addEventListener('load', () => {}, { once: true });
    requestAnimationFrame(() => requestAnimationFrame(() => {
      const canvas = document.getElementById('hydro-canvas');
      const mode   = preset || 'pressure';
      if (!hydroSim) {
        hydroSim = new HydroSim(canvas, mode);
        hydroSim.onUpdate = _hydroUpdateUI;
      } else {
        hydroSim.fit();
        hydroSim.play();
      }
      hydroMode(mode);
    }));
  }

  function hydroMode(mode) {
    if (!hydroSim) return;
    hydroSim.setMode(mode);
    const sel = document.getElementById('hydro-mode-sel');
    if (sel) sel.value = mode;
    // show/hide sub-controls
    ['arch','comm','surf','mat'].forEach(k => {
      const el = document.getElementById('hydro-panel-' + k);
      const el2 = document.getElementById('hydro-' + k + '-ctrl');
      if (el)  el.style.display  = 'none';
      if (el2) el2.style.display = 'none';
    });
    const gpRow = document.getElementById('hydro-graphs-row');
    if (gpRow) gpRow.style.display = mode === 'archimedes' ? '' : 'none';
    if (mode === 'archimedes') {
      const a = document.getElementById('hydro-panel-mat');
      const b = document.getElementById('hydro-arch-ctrl');
      if (a) a.style.display = '';
      if (b) b.style.display = 'flex';
    }
    if (mode === 'surface') {
      const a = document.getElementById('hydro-panel-theta');
      const b = document.getElementById('hydro-surf-ctrl');
      if (a) a.style.display = '';
      if (b) b.style.display = 'flex';
    }
    if (mode === 'communicating') {
      const a = document.getElementById('hydro-panel-comm');
      const b = document.getElementById('hydro-comm-ctrl');
      if (a) a.style.display = '';
      if (b) b.style.display = 'flex';
    }
  }

  function hydroToggleSurface() {
    if (!hydroSim) return;
    if (window.LabFX) LabFX.sound.play('chime', { pitch: 1.4, volume: 0.3 });
    const next = hydroSim._stMode === 'capillary' ? 'drop' : 'capillary';
    hydroSim._stMode = next;
    const label = next === 'capillary' ? '\u041A\u0430\u043F\u0438\u043B\u043B\u044F\u0440\u044B' : '\u041A\u0430\u043F\u043B\u044F';
    ['hydro-surf-toggle','hydro-surf-toggle-panel'].forEach(id => {
      const el = document.getElementById(id);
      if (el) el.textContent = label;
    });
  }

  function hydroToggleValve() {
    if (!hydroSim) return;
    _hydroValveOpen = !_hydroValveOpen;
    hydroSim.setValve(_hydroValveOpen);
    const label = _hydroValveOpen ? 'Кран: открыт' : 'Кран: закрыт';
    const color = _hydroValveOpen ? '#06D6A0' : '#F15BB5';
    ['hydro-valve-btn','hydro-valve-panel-btn'].forEach(id => {
      const el = document.getElementById(id);
      if (el) { el.textContent = label; el.style.color = color; el.style.borderColor = _hydroValveOpen ? 'rgba(6,214,160,.3)' : 'rgba(241,91,181,.3)'; }
    });
  }

  function hydroToggleGraphs() {
    if (!hydroSim || typeof hydroSim.toggleGraphs !== 'function') return;
    const canvasWrap = document.getElementById('hydro-canvas-wrap');
    if (!canvasWrap) return;
    const on = hydroSim.toggleGraphs(canvasWrap);
    const btn = document.getElementById('btn-hydro-graphs');
    if (btn) btn.classList.toggle('active', on);
  }

  function hydroSetVessels(n, btn) {
    if (hydroSim) hydroSim.setNumVessels(n);
    document.querySelectorAll('.hydro-nv').forEach(b => b.classList.remove('active'));
    if (btn) btn.classList.add('active');
  }

  function _hydroUpdateUI(info) {
    if (!info) return;
    const el = document.getElementById('hydro-formulas');
    if (!el) return;
    const lines = [];
    if (info.formula) lines.push(`<span style="color:#FFD166">${info.formula}</span>`);
    if (info.liqName) lines.push(`Жидкость: ${info.liqName}${info.rho ? ' (ρ=' + info.rho + ')' : ''}`);
    if (info.matName) lines.push(`Материал: ${info.matName}`);
    if (info.FA)      lines.push(`<span style="color:#06D6E0">F_A = ${info.FA} Н</span>`);
    if (info.mg)      lines.push(`<span style="color:#F15BB5">mg  = ${info.mg} Н</span>`);
    if (info.sigma)   lines.push(`σ = ${info.sigma} Н/м,  θ = ${info.theta}°`);
    if (info.h && !info.FA) lines.push(`h_подъём = ${info.h} мм`);
    el.innerHTML = lines.join('<br>');
    // result badge
    const rb = document.getElementById('hydro-result');
    if (rb && info.state) {
      const colors = { 'ВСПЛЫВАЕТ': '#06D6A0', 'ТОНЕТ': '#F15BB5', 'ВЗВЕШЕНО': '#FFD166' };
      rb.style.display = '';
      rb.style.color = colors[info.state] || '#fff';
      rb.style.background = (colors[info.state] || '#9B5DE5') + '18';
      rb.style.border = '1px solid ' + (colors[info.state] || '#9B5DE5') + '44';
      rb.textContent = info.state;
    } else if (rb) {
      rb.style.display = 'none';
    }
  }