'use strict';
/* ====================================================================
   IonExSim — Реакции ионного обмена
   ==================================================================== */

class IonExSim {

  /* ── Данные реакций ──────────────────────────────────────────────── */

  static RXN = {
    ba_so4: {
      name: 'BaCl₂ + Na₂SO₄',
      left:  [{ f: 'Ba²⁺', color: '#4FC3F7', count: 7 }, { f: 'Cl⁻',   color: '#AED581', count: 14 }],
      right: [{ f: 'Na⁺',  color: '#FFD54F', count: 14 }, { f: 'SO₄²⁻', color: '#F48FB1', count: 7 }],
      reacts: ['Ba²⁺', 'SO₄²⁻'],
      spectators: ['Cl⁻', 'Na⁺'],
      product: { f: 'BaSO₄', color: '#E0E0E0' },
      mol:      'BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl',
      full_ion: 'Ba²⁺ + 2Cl⁻ + 2Na⁺ + SO₄²⁻ → BaSO₄↓ + 2Na⁺ + 2Cl⁻',
      net_ion:  'Ba²⁺ + SO₄²⁻ → BaSO₄↓',
      type: 'precip', pcolor: '#E0E0E0', pname: 'BaSO₄ — белый осадок',
      sign: '↓', signColor: '#E0E0E0',
    },
    ag_cl: {
      name: 'AgNO₃ + NaCl',
      left:  [{ f: 'Ag⁺',  color: '#E0E0E0', count: 10 }, { f: 'NO₃⁻', color: '#FFCC02', count: 10 }],
      right: [{ f: 'Na⁺',  color: '#FFD54F', count: 10 }, { f: 'Cl⁻',  color: '#AED581', count: 10 }],
      reacts: ['Ag⁺', 'Cl⁻'],
      spectators: ['NO₃⁻', 'Na⁺'],
      product: { f: 'AgCl', color: '#F5F5F5' },
      mol:      'AgNO₃ + NaCl → AgCl↓ + NaNO₃',
      full_ion: 'Ag⁺ + NO₃⁻ + Na⁺ + Cl⁻ → AgCl↓ + Na⁺ + NO₃⁻',
      net_ion:  'Ag⁺ + Cl⁻ → AgCl↓',
      type: 'precip', pcolor: '#F5F5F5', pname: 'AgCl — белый творожистый осадок',
      sign: '↓', signColor: '#F5F5F5',
    },
    co3_hcl: {
      name: 'Na₂CO₃ + HCl',
      left:  [{ f: 'Na⁺',   color: '#FFD54F', count: 10 }, { f: 'CO₃²⁻', color: '#CE93D8', count: 5 }],
      right: [{ f: 'H⁺',    color: '#EF5350', count: 10 }, { f: 'Cl⁻',   color: '#AED581', count: 10 }],
      reacts: ['CO₃²⁻', 'H⁺'],
      spectators: ['Na⁺', 'Cl⁻'],
      product: { f: 'CO₂↑', color: '#B0BEC5' },
      mol:      'Na₂CO₃ + 2HCl → 2NaCl + CO₂↑ + H₂O',
      full_ion: '2Na⁺ + CO₃²⁻ + 2H⁺ + 2Cl⁻ → 2Na⁺ + 2Cl⁻ + CO₂↑ + H₂O',
      net_ion:  'CO₃²⁻ + 2H⁺ → CO₂↑ + H₂O',
      type: 'gas', gcolor: '#B0BEC5', gname: 'CO₂ — углекислый газ',
      sign: '↑', signColor: '#B0BEC5',
    },
    pb_i: {
      name: 'Pb(NO₃)₂ + KI',
      left:  [{ f: 'Pb²⁺', color: '#F48FB1', count: 6 }, { f: 'NO₃⁻', color: '#FFCC02', count: 12 }],
      right: [{ f: 'K⁺',   color: '#80CBC4', count: 12 }, { f: 'I⁻',  color: '#CE93D8', count: 12 }],
      reacts: ['Pb²⁺', 'I⁻'],
      spectators: ['NO₃⁻', 'K⁺'],
      product: { f: 'PbI₂', color: '#F9A825' },
      mol:      'Pb(NO₃)₂ + 2KI → PbI₂↓ + 2KNO₃',
      full_ion: 'Pb²⁺ + 2NO₃⁻ + 2K⁺ + 2I⁻ → PbI₂↓ + 2K⁺ + 2NO₃⁻',
      net_ion:  'Pb²⁺ + 2I⁻ → PbI₂↓',
      type: 'precip', pcolor: '#F9A825', pname: 'PbI₂ — ярко-жёлтый осадок',
      sign: '↓', signColor: '#F9A825',
    },
    ca_co3: {
      name: 'CaCl₂ + Na₂CO₃',
      left:  [{ f: 'Ca²⁺', color: '#FF8A65', count: 8 }, { f: 'Cl⁻',   color: '#AED581', count: 16 }],
      right: [{ f: 'Na⁺',  color: '#FFD54F', count: 16 }, { f: 'CO₃²⁻', color: '#CE93D8', count: 8 }],
      reacts: ['Ca²⁺', 'CO₃²⁻'],
      spectators: ['Cl⁻', 'Na⁺'],
      product: { f: 'CaCO₃', color: '#F5F5F5' },
      mol:      'CaCl₂ + Na₂CO₃ → CaCO₃↓ + 2NaCl',
      full_ion: 'Ca²⁺ + 2Cl⁻ + 2Na⁺ + CO₃²⁻ → CaCO₃↓ + 2Na⁺ + 2Cl⁻',
      net_ion:  'Ca²⁺ + CO₃²⁻ → CaCO₃↓',
      type: 'precip', pcolor: '#F5F5F5', pname: 'CaCO₃ — белый осадок (мел)',
      sign: '↓', signColor: '#F5F5F5',
    },
  };

  constructor(canvas) {
    this.canvas = canvas;
    this.ctx    = canvas.getContext('2d');
    this.rxnId  = 'ba_so4';
    this._raf   = null;
    this._last  = 0;
    this._t     = 0;
    this._phase = 'idle';   // idle | mixing | pairing | done
    this._prog  = 0;
    this._stepIdx   = 0;
    this._stepTimer = 0;
    this._ions   = [];
    this._pairs  = [];
    this._precip = [];
    this._gas    = [];
    /* edu-tooltip */
    this._eduTooltipAge   = -1;
    this._eduTooltipLines = [];
    /* product label */
    this._prodLabelAge  = -1;
    this._prodLabelText = '';
    this._prodLabelType = 'precip';
    this.W = 0; this.H = 0;
    this.onUpdate = null;
    this.fit();
    this._initIons();
  }

  fit() {
    const dpr = window.devicePixelRatio || 1;
    const W = this.canvas.offsetWidth  || 600;
    const H = this.canvas.offsetHeight || 400;
    this.canvas.width  = Math.round(W * dpr);
    this.canvas.height = Math.round(H * dpr);
    this.ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
    this.W = W; this.H = H;
    this._initIons();
  }

  setReaction(id) {
    if (!IonExSim.RXN[id]) return;
    this.rxnId = id;
    this.reset();
  }

  reset() {
    this._phase = 'idle'; this._prog = 0;
    this._stepIdx = 0; this._stepTimer = 0;
    this._pairs = []; this._precip = []; this._gas = [];
    this._initIons();
    this.draw();
  }

  _initIons() {
    const { W, H } = this;
    const rxn = IonExSim.RXN[this.rxnId];
    const bTop = H * 0.10, bBot = H * 0.78;
    this._ions = [];
    /* Left beaker ions */
    rxn.left.forEach(spec => {
      for (let i = 0; i < spec.count; i++) {
        this._ions.push({
          x: W * 0.10 + Math.random() * W * 0.36,
          y: bTop + 20 + Math.random() * (bBot - bTop - 40),
          vx: (Math.random() - 0.5) * 0.8, vy: (Math.random() - 0.5) * 0.8,
          spec: spec.f, color: spec.color,
          r: 8 + Math.random() * 3,
          phase: Math.random() * Math.PI * 2,
          active: true, side: 'L',
          reacts: rxn.reacts.includes(spec.f),
          paired: false,
        });
      }
    });
    /* Right beaker ions */
    rxn.right.forEach(spec => {
      for (let i = 0; i < spec.count; i++) {
        this._ions.push({
          x: W * 0.54 + Math.random() * W * 0.36,
          y: bTop + 20 + Math.random() * (bBot - bTop - 40),
          vx: (Math.random() - 0.5) * 0.8, vy: (Math.random() - 0.5) * 0.8,
          spec: spec.f, color: spec.color,
          r: 8 + Math.random() * 3,
          phase: Math.random() * Math.PI * 2,
          active: true, side: 'R',
          reacts: rxn.reacts.includes(spec.f),
          paired: false,
        });
      }
    });
  }

  start() {
    if (this._phase !== 'idle') this.reset();
    this._phase = 'mixing'; this._prog = 0;
    if (window.LabFX) {
      LabFX.sound.play('pour');
      const { W, H } = this;
      LabFX.particles.emit({ ctx: this.ctx, x: W * 0.3, y: H * 0.4, count: 10,
        color: '#4CC9F0', speed: 40, spread: 2.0, angle: 0,
        gravity: 120, life: 700, shape: 'splash' });
      LabFX.particles.emit({ ctx: this.ctx, x: W * 0.7, y: H * 0.4, count: 10,
        color: '#EF476F', speed: 40, spread: 2.0, angle: 0,
        gravity: 120, life: 700, shape: 'splash' });
    }
    if (this._raf) return;
    this._last = performance.now();
    const loop = t => { this._raf = requestAnimationFrame(loop); this._tick(t); };
    this._raf = requestAnimationFrame(loop);
  }

  stop() { cancelAnimationFrame(this._raf); this._raf = null; }

  /* ── Физика ─────────────────────────────────────────────────────── */

  _tick(t) {
    const dt = Math.min((t - this._last) / 1000, 0.05);
    this._last = t; this._t += dt;
    if (window.LabFX) LabFX.particles.update(dt);
    const { W, H } = this;
    const rxn = IonExSim.RXN[this.rxnId];

    if (this._phase === 'mixing') {
      this._prog = Math.min(1, this._prog + dt * 0.32);
      this._ions.forEach(ion => {
        if (!ion.active) return;
        const tx = W * 0.5 + (Math.random() - 0.5) * W * 0.72;
        const ty = H * 0.44 + (Math.random() - 0.5) * H * 0.38;
        ion.vx += (tx - ion.x) * 0.003 * this._prog;
        ion.vy += (ty - ion.y) * 0.003 * this._prog;
        ion.vx += (Math.random() - 0.5) * 0.7;
        ion.vy += (Math.random() - 0.5) * 0.7;
        ion.vx *= 0.88; ion.vy *= 0.88;
        ion.x += ion.vx; ion.y += ion.vy;
        ion.phase += dt * 2;
        this._clampIon(ion);
      });
      if (this._prog >= 1) { this._phase = 'pairing'; this._prog = 0; }
    }

    if (this._phase === 'pairing') {
      this._prog = Math.min(1, this._prog + dt * 0.16);
      this._stepTimer += dt;
      if (this._stepTimer > 1.5 && this._stepIdx < 2) { this._stepIdx++; this._stepTimer = 0; }

      this._ions.forEach(ion => {
        if (!ion.active || ion.paired) return;
        ion.vx += (Math.random() - 0.5) * 0.8;
        ion.vy += (Math.random() - 0.5) * 0.8;
        ion.vx *= 0.88; ion.vy *= 0.88;
        ion.x += ion.vx; ion.y += ion.vy;
        ion.phase += dt * 2;
        this._clampIon(ion);
      });

      /* Pair up reactive ions */
      if (Math.random() < 0.10 * (0.5 + this._prog)) this._doPair(rxn);

      /* Animate pairs */
      this._pairs.forEach(p => {
        p.flashT = Math.max(0, p.flashT - dt * 2.5);
        if (rxn.type === 'precip') {
          p.vy = Math.min(p.vy + 0.15, 5);
          p.y += p.vy;
          if (p.y >= H * 0.78 && !p.settled) {
            p.y = H * 0.78; p.vy = 0; p.settled = true;
            this._precip.push({ x: p.x, y: p.y, r: p.r, id: p.id });
            if (window.LabFX) {
              const now2 = performance.now();
              if (!this._fxFizzLast || now2 - this._fxFizzLast > 800) {
                this._fxFizzLast = now2;
                LabFX.sound.play('fizz');
              }
              LabFX.particles.emit({ ctx: this.ctx, x: p.x, y: H * 0.78, count: 5,
                color: '#888888', speed: 15, spread: 1.8, angle: -Math.PI / 2,
                gravity: 30, life: 1200, shape: 'dust' });
            }
          }
        } else if (rxn.type === 'gas') {
          p.vy = Math.max(p.vy - 0.08, -4);
          p.y += p.vy;
          p.alpha = Math.max(0, p.alpha - 0.004);
        }
      });
      this._pairs = this._pairs.filter(p => !p.settled && (p.alpha === undefined || p.alpha > 0));

      if (this._prog >= 1) { this._phase = 'done'; this._stepIdx = 2; }
    }

    if (this._phase === 'done') {
      this._ions.forEach(ion => {
        if (!ion.active || ion.paired) return;
        ion.vx += (Math.random() - 0.5) * 0.45;
        ion.vy += (Math.random() - 0.5) * 0.45;
        ion.vx *= 0.92; ion.vy *= 0.92;
        ion.x += ion.vx; ion.y += ion.vy;
        ion.phase += dt;
        this._clampIon(ion);
      });
      /* trigger product label + edu-tooltip once on transition to done */
      if (window.ChemVisuals && this._prodLabelAge < 0) {
        const rxn = IonExSim.RXN[this.rxnId];
        if (rxn.type === 'precip') {
          this._prodLabelText = (rxn.pname || '') + ' ';
          this._prodLabelType = 'precip';
          this._prodLabelAge  = 0;
        } else if (rxn.type === 'gas') {
          this._prodLabelText = (rxn.gname || '') + ' ';
          this._prodLabelType = 'gas';
          this._prodLabelAge  = 0;
        }
        /* edu tooltip from reaction net_ion */
        if (this._eduTooltipAge < 0) {
          const netIon = (rxn.net_ion || '').replace(/→/g, '->');
          this._eduTooltipLines = [
            'Краткое ионное уравнение:',
            netIon.length > 32 ? netIon.slice(0, 32) + '...' : netIon,
            (rxn.pname || rxn.gname || '').slice(0, 34),
          ].filter(Boolean).slice(0, 4);
          this._eduTooltipAge = 0;
        }
      }
    }

    /* advance ages */
    if (this._eduTooltipAge >= 0) {
      this._eduTooltipAge += dt / 4.0;
      if (this._eduTooltipAge >= 1.0) this._eduTooltipAge = -1;
    }
    if (this._prodLabelAge >= 0) {
      this._prodLabelAge += dt / 3.0;
      if (this._prodLabelAge >= 1.0) this._prodLabelAge = -1;
    }

    this.draw();
    if (this.onUpdate) this.onUpdate(this.info());
  }

  _clampIon(ion) {
    const { W, H } = this;
    const bTop = H * 0.10, bBot = H * 0.78;
    if (ion.x < ion.r + 6)     { ion.x = ion.r + 6;     ion.vx *= -0.5; }
    if (ion.x > W - ion.r - 6) { ion.x = W - ion.r - 6; ion.vx *= -0.5; }
    if (ion.y < bTop + ion.r)  { ion.y = bTop + ion.r;   ion.vy *= -0.5; }
    if (ion.y > bBot - ion.r)  { ion.y = bBot - ion.r;   ion.vy *= -0.5; }
  }

  _doPair(rxn) {
    const r1 = rxn.reacts[0], r2 = rxn.reacts[1];
    const pool1 = this._ions.filter(i => i.active && !i.paired && i.spec === r1);
    const pool2 = this._ions.filter(i => i.active && !i.paired && i.spec === r2);
    if (!pool1.length || !pool2.length) return;
    const a = pool1[Math.floor(Math.random() * pool1.length)];
    const b = pool2[Math.floor(Math.random() * pool2.length)];
    a.paired = true; b.paired = true;
    a.active = false; b.active = false;
    this._pairs.push({
      id: this._t + Math.random(),
      x: (a.x + b.x) / 2, y: (a.y + b.y) / 2,
      vy: rxn.type === 'gas' ? -2 : 0,
      r: 7, flashT: 1, settled: false, alpha: 1,
    });
  }

  /* ── Рендеринг ──────────────────────────────────────────────────── */

  draw() {
    const { ctx, W, H } = this;
    const rxn = IonExSim.RXN[this.rxnId];

    ctx.fillStyle = '#07071A';
    ctx.fillRect(0, 0, W, H);

    /* Dot grid */
    ctx.fillStyle = 'rgba(255,255,255,0.07)';
    for (let x = 0; x < W; x += 28) {
      for (let y = 0; y < H; y += 28) {
        ctx.beginPath(); ctx.arc(x, y, 0.8, 0, Math.PI * 2); ctx.fill();
      }
    }

    /* desk */
    if (window.ChemVisuals) {
      ChemVisuals.drawDeskBackground(ctx, W, H, H * 0.80);
    }

    if (this._phase === 'idle') {
      this._drawTwoBeakers(ctx, W, H, rxn);
    } else {
      this._drawSingleBeaker(ctx, W, H);
    }

    this._drawIons(ctx, rxn);
    this._drawPairs(ctx, rxn);
    this._drawPrecipitate(ctx, rxn);
    this._drawPanel(ctx, W, H, rxn);
    if (window.LabFX) LabFX.particles.draw(ctx);

    /* animated product label */
    if (window.ChemVisuals && this._prodLabelAge >= 0) {
      const labelY = this._prodLabelType === 'gas' ? H * 0.12 : H * 0.74;
      ChemVisuals.drawProductLabel(ctx, W / 2, labelY, this._prodLabelText, this._prodLabelType, this._prodLabelAge);
      if (this._prodLabelType === 'gas') {
        ChemVisuals.animateGasBubbles(ctx, W / 2, H * 0.15, 'rgba(200,235,255,0.8)', this._t);
      } else {
        ChemVisuals.animatePrecipitateFall(ctx, W / 2, H * 0.72, rxn.pcolor || '#CCC', this._t);
      }
    }

    /* edu tooltip */
    if (window.ChemVisuals && this._eduTooltipAge >= 0 && this._eduTooltipLines.length > 0) {
      ChemVisuals.drawEduTooltip(ctx, W / 2, H * 0.10, 210, this._eduTooltipLines, this._eduTooltipAge);
    }
  }

  _drawTwoBeakers(ctx, W, H, rxn) {
    const drawB = (x, y, w, h, ions) => {
      ctx.save();
      ctx.strokeStyle = 'rgba(120,185,255,0.55)'; ctx.lineWidth = 2;
      ctx.beginPath();
      ctx.moveTo(x, y); ctx.lineTo(x, y + h);
      ctx.lineTo(x + w, y + h); ctx.lineTo(x + w, y);
      ctx.stroke();
      ctx.beginPath(); ctx.moveTo(x - 4, y); ctx.lineTo(x + w + 4, y); ctx.stroke();
      /* Rim highlight */
      const hlg = ctx.createLinearGradient(x, y, x + 14, y + h);
      hlg.addColorStop(0, 'rgba(200,230,255,0.15)');
      hlg.addColorStop(1, 'rgba(200,230,255,0.02)');
      ctx.strokeStyle = hlg; ctx.lineWidth = 5;
      ctx.beginPath(); ctx.moveTo(x + 7, y + 6); ctx.lineTo(x + 7, y + h - 6); ctx.stroke();
      /* Formula label */
      ctx.fillStyle = 'rgba(255,255,255,0.22)'; ctx.font = 'bold 11px monospace';
      ctx.textAlign = 'center'; ctx.textBaseline = 'bottom';
      const label = ions.map(s => s.f).join(', ');
      ctx.fillText(label, x + w / 2, y - 4);
      ctx.restore();
    };
    const bTop = H * 0.10, bH = H * 0.70;
    drawB(W * 0.04, bTop, W * 0.40, bH, rxn.left);
    drawB(W * 0.56, bTop, W * 0.40, bH, rxn.right);

    /* Mix arrow */
    ctx.save();
    const mx = W * 0.50, my = H * 0.44;
    ctx.strokeStyle = 'rgba(255,255,255,0.22)'; ctx.lineWidth = 2;
    ctx.fillStyle   = 'rgba(255,255,255,0.22)';
    ctx.beginPath(); ctx.moveTo(mx - 16, my); ctx.lineTo(mx + 16, my); ctx.stroke();
    ctx.beginPath(); ctx.moveTo(mx + 10, my - 5); ctx.lineTo(mx + 16, my); ctx.lineTo(mx + 10, my + 5); ctx.fill();
    ctx.restore();
  }

  _drawSingleBeaker(ctx, W, H) {
    const bx = W * 0.04, by = H * 0.08, bw = W * 0.92, bh = H * 0.72;
    ctx.save();
    ctx.strokeStyle = 'rgba(120,185,255,0.60)'; ctx.lineWidth = 2.5;
    ctx.beginPath();
    ctx.moveTo(bx, by); ctx.lineTo(bx, by + bh);
    ctx.lineTo(bx + bw, by + bh); ctx.lineTo(bx + bw, by);
    ctx.stroke();
    ctx.beginPath(); ctx.moveTo(bx - 5, by); ctx.lineTo(bx + bw + 5, by); ctx.stroke();
    const hlg = ctx.createLinearGradient(bx, by, bx + 18, by + bh);
    hlg.addColorStop(0, 'rgba(200,230,255,0.18)');
    hlg.addColorStop(1, 'rgba(200,230,255,0.02)');
    ctx.strokeStyle = hlg; ctx.lineWidth = 6;
    ctx.beginPath(); ctx.moveTo(bx + 8, by + 8); ctx.lineTo(bx + 8, by + bh - 8); ctx.stroke();
    ctx.restore();
  }

  _drawIons(ctx, rxn) {
    this._ions.forEach(ion => {
      if (!ion.active) return;
      const isSpec = rxn.spectators.includes(ion.spec);
      ctx.save();
      ctx.globalAlpha = (isSpec && this._phase !== 'idle') ? 0.40 : 0.88;
      ctx.shadowColor = ion.color;
      ctx.shadowBlur  = 7 + Math.sin(ion.phase) * 3;
      ctx.beginPath(); ctx.arc(ion.x, ion.y, ion.r, 0, Math.PI * 2);
      ctx.fillStyle = ion.color; ctx.fill();
      ctx.strokeStyle = 'rgba(255,255,255,0.18)'; ctx.lineWidth = 1; ctx.stroke();
      ctx.shadowBlur = 0; ctx.globalAlpha = 1;
      /* Formula label */
      const fs = Math.min(Math.round(ion.r * 0.60), 9);
      ctx.fillStyle = 'rgba(0,0,0,0.80)';
      ctx.font = `bold ${fs}px monospace`;
      ctx.textAlign = 'center'; ctx.textBaseline = 'middle';
      ctx.fillText(ion.spec, ion.x, ion.y);
      ctx.restore();
    });
  }

  _drawPairs(ctx, rxn) {
    const pcolor = rxn.pcolor || rxn.gcolor || '#FFF';
    this._pairs.forEach(p => {
      ctx.save();
      const alpha = p.alpha !== undefined ? p.alpha : 1;
      ctx.globalAlpha = alpha * 0.92;
      ctx.shadowColor = p.flashT > 0 ? '#FFFFFF' : pcolor;
      ctx.shadowBlur  = p.flashT > 0 ? 28 * p.flashT : 8;
      ctx.beginPath(); ctx.arc(p.x, p.y, p.r, 0, Math.PI * 2);
      ctx.fillStyle = p.flashT > 0 ? `rgba(255,255,255,${p.flashT * 0.9})` : pcolor;
      ctx.fill();
      ctx.shadowBlur = 0; ctx.globalAlpha = 1;
      /* Product label */
      ctx.fillStyle = 'rgba(0,0,0,0.80)';
      ctx.font = 'bold 7px monospace';
      ctx.textAlign = 'center'; ctx.textBaseline = 'middle';
      ctx.fillText(rxn.product.f, p.x, p.y);
      ctx.restore();
    });
  }

  _drawPrecipitate(ctx, rxn) {
    if (rxn.type !== 'precip' || !this._precip.length) return;
    ctx.save();
    this._precip.forEach(p => {
      ctx.shadowColor = rxn.pcolor; ctx.shadowBlur = 3;
      ctx.beginPath(); ctx.arc(p.x, p.y, p.r, 0, Math.PI * 2);
      ctx.fillStyle = rxn.pcolor; ctx.fill();
    });
    ctx.restore();
    if (this._precip.length > 4) {
      ctx.save();
      ctx.fillStyle = rxn.pcolor; ctx.font = 'bold 10px monospace';
      ctx.textAlign = 'center'; ctx.textBaseline = 'bottom';
      ctx.shadowColor = rxn.pcolor; ctx.shadowBlur = 6;
      ctx.fillText(`↓ ${rxn.pname}`, this.W / 2, this.H * 0.80 - 4);
      ctx.restore();
    }
  }

  _drawPanel(ctx, W, H, rxn) {
    const py = H * 0.82;
    ctx.fillStyle = 'rgba(7,7,26,0.95)';
    ctx.fillRect(0, py, W, H - py);
    ctx.strokeStyle = 'rgba(100,165,255,0.22)'; ctx.lineWidth = 1;
    ctx.beginPath(); ctx.moveTo(0, py); ctx.lineTo(W, py); ctx.stroke();

    if (this._phase === 'idle') {
      ctx.fillStyle = '#37474F'; ctx.font = '11px monospace';
      ctx.textAlign = 'center'; ctx.textBaseline = 'middle';
      ctx.fillText('← Нажми «Смешать» для начала реакции →', W / 2, py + (H - py) / 2);
      return;
    }

    const steps = [
      { lbl: 'Молекулярное:', txt: rxn.mol,      col: '#B0BEC5' },
      { lbl: 'Полное ионное:',  txt: rxn.full_ion, col: '#CE93D8' },
      { lbl: 'Краткое ионное:', txt: rxn.net_ion,  col: '#FFD166' },
    ];

    const panH = H - py;
    const n = Math.min(this._stepIdx + 1, steps.length);
    for (let i = 0; i < n; i++) {
      const s = steps[i];
      const y = py + 11 + i * (panH * 0.29);
      ctx.save();
      if (i === this._stepIdx && this._phase !== 'done') {
        ctx.fillStyle = 'rgba(255,255,255,0.04)';
        ctx.fillRect(8, y - 9, W - 16, 20);
      }
      ctx.fillStyle = s.col; ctx.font = 'bold 9.5px monospace';
      ctx.textAlign = 'left'; ctx.textBaseline = 'middle';
      ctx.fillText(s.lbl, 14, y);
      ctx.fillStyle = (i === this._stepIdx && this._phase !== 'done') ? '#FFF' : 'rgba(255,255,255,0.62)';
      ctx.font = '9.5px monospace';
      ctx.fillText(s.txt, 14 + ctx.measureText(s.lbl).width + 8, y);
      ctx.restore();
    }

    if (this._phase === 'done') {
      ctx.save();
      ctx.fillStyle = rxn.signColor; ctx.font = 'bold 10px monospace';
      ctx.textAlign = 'right'; ctx.textBaseline = 'top';
      ctx.shadowColor = rxn.signColor; ctx.shadowBlur = 8;
      const label = rxn.type === 'precip' ? `✓ ${rxn.sign} осадок` : `✓ ${rxn.sign} газ`;
      ctx.fillText(label, W - 14, py + 3);
      ctx.restore();
    }
  }

  info() {
    const rxn = IonExSim.RXN[this.rxnId];
    return {
      rxn:    rxn.name,
      phase:  this._phase,
      prog:   Math.round(this._prog * 100),
      precip: this._precip.length,
    };
  }
}
