(() => {
  'use strict';
  const KEY = 'system-simulation:pipe-submodels-layout-demo:v1';
  const $ = id => document.getElementById(id);
  const safe = value => String(value).replace(/[&<>"']/g, char => ({ '&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;', "'": '&#39;' })[char]);
  // The demo never stores component coordinates or connection endpoints in editable state.
  const endpoints = Object.freeze({
    'A.1': Object.freeze({ label: '储气罐 A · 端口 1', state: 'out' }),
    'N1.1': Object.freeze({ label: '节点 N1 · 端口 1', state: 'out' }),
    'N1.2': Object.freeze({ label: '节点 N1 · 端口 2（参考）', state: 'in' }),
    'N1.3': Object.freeze({ label: '节点 N1 · 端口 3', state: 'out' }),
    'N1.4': Object.freeze({ label: '节点 N1 · 端口 4', state: 'out' }),
    'B.2': Object.freeze({ label: '阀门 B · 端口 2', state: 'in' }),
    'C.1': Object.freeze({ label: '封堵 C · 端口 1', state: 'in' }),
    'D.1': Object.freeze({ label: '封堵 D · 端口 1', state: 'in' }),
  });
  const PIPES = Object.freeze([
    Object.freeze({ id: 'L1', a: 'A.1', b: 'N1.1', path: 'M175 360H460', x: 315, y: 334, anchor: 'middle' }),
    Object.freeze({ id: 'L2', a: 'N1.2', b: 'B.2', path: 'M500 360H790', x: 645, y: 334, anchor: 'middle' }),
    Object.freeze({ id: 'L3', a: 'C.1', b: 'N1.3', path: 'M480 134V340', x: 507, y: 240, anchor: 'start' }),
    Object.freeze({ id: 'L4', a: 'N1.4', b: 'D.1', path: 'M480 380V566', x: 507, y: 485, anchor: 'start' }),
  ]);
  const MODELS = [
    { id: 'PNL00R', name: '阻性管路', sections: ['R'], ends: ['in', 'in'], caption: '压降 · 无储气', description: '计算摩擦压降，不增加管内储气状态。', states: 0, fields: ['length', 'diameter', 'roughness'] },
    { id: 'PNL0001', name: '单端储气管路', sections: ['C', 'R'], ends: ['in', 'out'], caption: '单端储气', description: '考虑摩擦压降与一处储气容积，包含 2 个热力状态。', states: 2, fields: ['length', 'diameter', 'roughness', 'pressure', 'temperature'] },
    { id: 'PNL0002', name: '中间储气管路', sections: ['R', 'C', 'R'], ends: ['in', 'in'], caption: '中间储气', description: '考虑摩擦压降与中间储气容积，包含 2 个热力状态。', states: 2, fields: ['length', 'diameter', 'roughness', 'pressure', 'temperature'] },
    { id: 'PNL0003', name: '双端储气管路', sections: ['C', 'R', 'C'], ends: ['out', 'out'], caption: '双端储气', description: '考虑摩擦压降与两端储气容积，包含 4 个热力状态。', states: 4, fields: ['length', 'diameter', 'roughness', 'pressure', 'temperature', 'pressure2', 'temperature2'] },
  ];
  const FIELDS = {
    length: { name: '管长', unit: 'm', min: 0, positive: true, default: '' },
    diameter: { name: '内径', unit: 'mm', min: 0, positive: true, default: '' },
    roughness: { name: '相对粗糙度', unit: '—', min: 0, max: .1, default: '0.00001' },
    pressure: { name: '初始压力', unit: 'bar(a)', min: 0, positive: true, default: '1' },
    temperature: { name: '初始温度', unit: 'K', min: 0, positive: true, default: '293.15' },
    pressure2: { name: '端口 2 初始压力', unit: 'bar(a)', min: 0, positive: true, default: '1' },
    temperature2: { name: '端口 2 初始温度', unit: 'K', min: 0, positive: true, default: '293.15' },
  };
  const modelById = id => MODELS.find(model => model.id === id);
  const pipeById = id => PIPES.find(pipe => pipe.id === id);
  const initial = () => ({ version: 1, mode: 'submodel', selected: 'L1', configs: Object.fromEntries(PIPES.map(pipe => [pipe.id, { model: null, params: {} }])) });
  let state = initial();
  let preview = null, storageOK = true, consoleOpen = true;
  let pan = null, view = { zoom: 1, x: 0, y: 0 }, baseScale = 1;
  let log = [{ kind: 'INFO', text: '选择中间画布的管路，再从左侧指定子模型。' }, { kind: 'INFO', text: '位置和连接关系固定；支持缩放与空白区平移查看。' }];
  const activePipe = () => pipeById(state.selected);
  const activeConfig = () => state.configs[state.selected];
  function compatible(pipe, model) {
    const a = endpoints[pipe.a].state, b = endpoints[pipe.b].state;
    return (a !== model.ends[0] && b !== model.ends[1]) || (a !== model.ends[1] && b !== model.ends[0]);
  }
  function candidates(pipe) { return MODELS.filter(model => compatible(pipe, model)); }
  function choosePreview() { preview = activeConfig().model || candidates(activePipe())[0]?.id || null; }
  function load() {
    try {
      const data = JSON.parse(localStorage.getItem(KEY) || 'null');
      if (!data || data.version !== 1 || !data.configs || typeof data.configs !== 'object') return;
      const restored = initial();
      if (['modeling', 'submodel', 'parameters', 'check'].includes(data.mode)) restored.mode = data.mode;
      if (pipeById(data.selected)) restored.selected = data.selected;
      PIPES.forEach(pipe => {
        const item = data.configs[pipe.id];
        if (!item || !modelById(item.model) || !compatible(pipe, modelById(item.model))) return;
        restored.configs[pipe.id] = { model: item.model, params: Object.fromEntries(Object.keys(FIELDS)
          .filter(key => ['string', 'number'].includes(typeof item.params?.[key]))
          .map(key => [key, String(item.params[key]).slice(0, 64)])) };
      });
      state = restored;
    } catch { storageOK = false; }
  }
  function save() {
    try { localStorage.setItem(KEY, JSON.stringify(state)); storageOK = true; }
    catch { storageOK = false; }
    $('save-state').textContent = storageOK ? '演示已保存' : '仅当前页面保留';
  }
  function tell(text) { $('notice').textContent = text; }
  function addLog(text, kind = 'INFO') { log = [...log.slice(-15), { kind, text }]; renderLog(); }
  function valid(key, value) {
    const spec = FIELDS[key], number = Number(value);
    return String(value ?? '').trim() !== '' && Number.isFinite(number) && (spec.positive ? number > spec.min : number >= spec.min) && (spec.max === undefined || number <= spec.max);
  }
  function missing(pipe) {
    const config = state.configs[pipe.id];
    return (modelById(config.model)?.fields || []).filter(key => !valid(key, config.params[key]));
  }
  function pipeStatus(pipe) {
    const config = state.configs[pipe.id];
    return !config.model ? '未指定' : missing(pipe).length ? '待填参数' : '配置完成';
  }
  function pipeIcon(model) {
    const width = 58 / model.sections.length;
    return `<svg viewBox="0 0 84 44" aria-hidden="true"><path d="M1 22H13M71 22H83" fill="none" stroke="currentColor" stroke-width="1.5"/><rect x="13" y="10" width="58" height="24" fill="white" stroke="currentColor" stroke-width="1.5"/>${model.sections.map((section, index) => `${index ? `<path d="M${13 + index * width} 10V34" stroke="currentColor" stroke-width="1"/>` : ''}<text x="${13 + width * (index + .5)}" y="26" text-anchor="middle" font-family="Segoe UI,sans-serif" font-size="12" fill="currentColor">${section}</text>`).join('')}</svg>`;
  }
  function renderLibrary() {
    const pipe = activePipe(), editable = state.mode === 'submodel';
    const list = $('compatible-only').checked ? candidates(pipe) : MODELS;
    $('library').innerHTML = list.map(model => {
      const ok = compatible(pipe, model);
      return `<button type="button" class="model-tile" data-model="${model.id}" draggable="false" aria-label="${model.id} ${model.name}${ok ? '' : '，不兼容'}" aria-pressed="${preview === model.id}" ${!ok || !editable ? 'disabled' : ''} title="${ok ? model.description : '与当前管路两端的变量供需不匹配'}">${pipeIcon(model)}<strong>${model.id}</strong><small>${model.caption}</small></button>`;
    }).join('');
    $('library-hint').textContent = editable ? `${pipe.id}：${candidates(pipe).length} 个兼容型号。点击预览，应用后生效。` : '切换到“子模型”模式可更换管路型号。';
    $('pipe-list').innerHTML = PIPES.map(item => `<button type="button" data-pipe="${item.id}" aria-label="${item.id} ${pipeStatus(item)}" aria-pressed="${item.id === state.selected}"><span class="state-dot ${state.configs[item.id].model ? missing(item).length ? 'assigned' : 'ready' : ''}"></span><strong>${item.id}</strong><span class="model-id">${state.configs[item.id].model || '未指定'}</span></button>`).join('');
  }
  function drawFixedComponents() {
    const port = (x, y, label = '') => `<circle cx="${x}" cy="${y}" r="4" fill="white" stroke="#b3809a" stroke-width="1.2"/>${label ? `<text class="port-label" x="${x + 9}" y="${y - 10}">${label}</text>` : ''}`;
    $('component-layer').innerHTML = `
      <g class="fixed-component" data-component="A" transform="translate(140 360)"><rect x="-35" y="-40" width="70" height="80" rx="0" fill="white" stroke="#be8ca5" stroke-width="1.5"/>${port(35, 0)}<text class="component-label" x="0" y="76" text-anchor="middle">储气罐 A</text><text class="component-code" x="0" y="101" text-anchor="middle">PNCH023</text></g>
      <g class="fixed-component" data-component="N1" transform="translate(480 360)"><path d="M-20 0H20M0-20V20" stroke="#ae7391" stroke-width="1.6" fill="none"/>${port(-20, 0, '1')}${port(20, 0, '2')}${port(0, -20, '3')}${port(0, 20, '4')}<text class="component-label" x="36" y="63">节点 N1</text><text class="component-code" x="36" y="88">P4NODE2 · 固定</text></g>
      <g class="fixed-component" data-component="B" transform="translate(825 360)"><path d="M-35 0H35M-20-17Q0 9 20-17M-20 17Q0-9 20 17M-18 31L18-31" stroke="#be8ca5" stroke-width="1.6" fill="none"/><path d="M18-31L9-23L18-20Z" fill="#be8ca5"/>${port(-35, 0)}<text class="component-label" x="0" y="76" text-anchor="middle">阀门 B</text><text class="component-code" x="0" y="101" text-anchor="middle">PNVO001</text></g>
      <g class="fixed-component" data-component="C" transform="translate(480 130)"><path d="M-15-4H15M-12-4L-7-11M-3-4L2-11M6-4L11-11" stroke="#ba829f" stroke-width="1.5" fill="none"/>${port(0, 4)}<text class="component-label" x="30" y="5">封堵 C</text></g>
      <g class="fixed-component" data-component="D" transform="translate(480 570)"><path d="M-15 4H15M-12 4L-7 11M-3 4L2 11M6 4L11 11" stroke="#ba829f" stroke-width="1.5" fill="none"/>${port(0, -4)}<text class="component-label" x="30" y="5">封堵 D</text></g>`;
  }
  function renderWires() {
    $('wire-layer').innerHTML = PIPES.map(pipe => `<g><path class="wire ${state.configs[pipe.id].model ? 'assigned' : ''} ${pipe.id === state.selected ? 'selected' : ''}" d="${pipe.path}"/><path class="wire-hit" data-pipe="${pipe.id}" d="${pipe.path}"/></g>`).join('');
    const compact = $('canvas').clientWidth < 460;
    $('pipe-label-layer').innerHTML = PIPES.map(pipe => `<text class="pipe-name ${pipe.id === state.selected ? 'selected' : ''}" x="${pipe.x}" y="${pipe.y}" text-anchor="${pipe.anchor}">${pipe.id}${!compact && $('show-labels').checked && state.mode !== 'modeling' ? ' · ' + (state.configs[pipe.id].model || '未指定') : ''}</text>`).join('');
    $('diagram').classList.toggle('compact', compact);
    applyView();
  }
  function resizeCanvas() {
    const width = $('canvas').clientWidth, height = $('canvas').clientHeight;
    if (!width || !height) return;
    $('diagram').setAttribute('viewBox', `0 0 ${width} ${height}`);
    baseScale = Math.max(.1, Math.min((width - 30) / 960, (height - 35) / 660));
    renderWires();
  }
  function applyView() {
    const width = $('canvas').clientWidth, height = $('canvas').clientHeight;
    const scale = baseScale * view.zoom;
    const x = (width - 960 * scale) / 2 + view.x, y = (height - 660 * scale) / 2 + view.y;
    $('scene').setAttribute('transform', `translate(${x} ${y}) scale(${scale})`);
    $('zoom-value').textContent = `${Math.round(view.zoom * 100)}%`;
    const textScale = Math.max(baseScale, .42);
    $('scene').querySelectorAll('.component-label,.pipe-name').forEach(label => { label.style.fontSize = `${12 / textScale}px`; });
    $('scene').querySelectorAll('.component-code').forEach(label => { label.style.fontSize = `${10 / textScale}px`; });
    $('grid-pattern').setAttribute('width', 20 * view.zoom);
    $('grid-pattern').setAttribute('height', 20 * view.zoom);
    $('grid-pattern').setAttribute('patternTransform', `translate(${view.x} ${view.y})`);
  }
  function portMapping(pipe, model) {
    if (model.ends[0] === model.ends[1]) return `端口 1：${endpoints[pipe.a].label}；端口 2：${endpoints[pipe.b].label}。两端接口对称。`;
    const forward = endpoints[pipe.a].state !== model.ends[0];
    return `端口 1：${endpoints[forward ? pipe.a : pipe.b].label}；端口 2：${endpoints[forward ? pipe.b : pipe.a].label}。`;
  }
  function renderProperties() {
    const pipe = activePipe(), config = activeConfig();
    const model = modelById(state.mode === 'submodel' ? preview : config.model);
    $('selected-pipe').textContent = pipe.id;
    const editable = state.mode === 'submodel';
    $('model-properties').innerHTML = `<table class="property-table"><tbody>
      <tr><th>对象</th><td>管路 ${pipe.id}</td></tr>
      <tr><th>连接端 A</th><td>${safe(endpoints[pipe.a].label)}</td></tr>
      <tr><th>连接端 B</th><td>${safe(endpoints[pipe.b].label)}</td></tr>
      <tr><th>已用型号</th><td>${config.model || '未指定'}</td></tr>
      </tbody></table>${model ? `<div class="preview"><div class="preview-title">${pipeIcon(model)}<div><strong>${model.id}</strong><small>${model.name}${editable && model.id !== config.model ? ' · 待应用' : ''}</small></div></div><p class="preview-description">${model.description}</p>
      ${editable ? `<div class="apply-buttons"><button type="button" class="primary" data-action="apply" ${model.id === config.model ? 'disabled' : ''}>应用到 ${pipe.id}</button><button type="button" data-action="apply-next">应用并下一条</button></div>` : ''}
      <details class="property-details"><summary>端口方向与选型说明</summary><p>${safe(portMapping(pipe, model))}</p><p>按接口筛选；储气、压降等物理作用由所选型号决定。</p><p>C 表示储气，R 表示阻力。图标沿用建模区表示方式。</p></details></div>` : '<div class="empty-hint">在“子模型”模式从左侧选择管路型号。</div>'}`;
    renderParameters();
  }
  function renderParameters() {
    const config = activeConfig(), model = modelById(config.model), editable = state.mode === 'parameters';
    $('edit-parameters').disabled = !model || editable;
    if (!model) { $('parameter-properties').innerHTML = '<div class="empty-hint">应用管路子模型后显示所需参数。</div>'; return; }
    $('parameter-properties').innerHTML = `<table class="parameter-table"><thead><tr><th>参数</th><th>数值</th><th>单位</th></tr></thead><tbody>${model.fields.map(key => {
      const spec = FIELDS[key];
      const label = model.id === 'PNL0003' && ['pressure', 'temperature'].includes(key) ? '端口 1 ' + spec.name : spec.name;
      return `<tr><td><label for="parameter-${key}">${label}</label></td><td><input id="parameter-${key}" type="number" data-parameter="${key}" value="${safe(config.params[key] ?? '')}" min="${spec.min}" ${spec.max !== undefined ? `max="${spec.max}"` : ''} step="any" ${editable ? '' : 'readonly'} aria-invalid="${editable && !valid(key, config.params[key])}" placeholder="待填"></td><td>${spec.unit}</td></tr>`;
    }).join('')}</tbody></table><div class="parameter-note" id="parameter-note"></div>`;
    updateParameterNote();
  }
  function updateParameterNote() {
    const note = $('parameter-note');
    if (!note) return;
    const count = missing(activePipe()).length;
    note.classList.toggle('ready', !count);
    note.textContent = state.mode !== 'parameters' ? '当前只读；进入参数模式填写实际值。' : count ? `待填写或修正 ${count} 项。` : '参数完整 · 已保存到此演示。';
  }
  function updateProgress() {
    const assigned = PIPES.filter(pipe => state.configs[pipe.id].model).length;
    const ready = PIPES.filter(pipe => state.configs[pipe.id].model && !missing(pipe).length).length;
    $('progress').textContent = `${assigned}/4 已选型 · ${ready}/4 参数完整`;
  }
  function renderLog() {
    const items = state.mode === 'check' ? PIPES.map(pipe => {
      const config = state.configs[pipe.id];
      return { kind: !config.model || missing(pipe).length ? 'WARN' : 'OK', text: `${pipe.id}　${config.model || '未指定子模型'}　${pipeStatus(pipe)}`, pipe: !config.model || missing(pipe).length ? pipe.id : null };
    }) : log;
    $('console-content').innerHTML = items.map(item => `<div class="log-row"><span class="log-kind ${item.kind === 'WARN' ? 'warn' : item.kind === 'OK' ? 'ok' : ''}">${item.kind}</span>${item.pipe ? `<button type="button" data-fix="${item.pipe}">${safe(item.text)} → 处理</button>` : `<span>${safe(item.text)}</span>`}</div>`).join('');
    if (state.mode === 'check') {
      const complete = items.every(item => item.kind === 'OK');
      $('console-summary').textContent = complete ? '局部配置检查通过 · 未执行仿真' : '点击问题项定位';
    } else $('console-summary').textContent = '仅配置演示，不执行仿真';
  }
  function render() {
    document.querySelectorAll('[data-mode]').forEach(button => button.setAttribute('aria-pressed', String(button.dataset.mode === state.mode)));
    $('mode-marker').textContent = ({ modeling: '建模预览', submodel: '子模型模式', parameters: '参数模式', check: '配置检查' })[state.mode];
    renderLibrary(); renderWires(); renderProperties(); renderLog(); updateProgress();
  }
  function setMode(mode) {
    state.mode = mode; choosePreview(); render(); save();
    tell(mode === 'modeling' ? '此 demo 的部件、位置与连接固定；进入子模型模式选择管路型号。' : mode === 'submodel' ? '选中管路，在左侧预览型号，在右侧应用。' : mode === 'parameters' ? '在右侧填写选中管路的实际参数。' : '当前仅检查演示的接口匹配和必填参数。');
    if (mode === 'check') { consoleOpen = true; renderConsoleVisibility(); }
  }
  function selectPipe(id) {
    if (!pipeById(id)) return;
    state.selected = id; choosePreview(); render(); save();
    tell(`${id} 已选中。部件与连线位置保持锁定。`);
  }
  function nextUnassigned() {
    const start = PIPES.findIndex(pipe => pipe.id === state.selected);
    const ordered = [...PIPES.slice(start + 1), ...PIPES.slice(0, start + 1)];
    const next = ordered.find(pipe => !state.configs[pipe.id].model);
    if (next) { setMode('submodel'); selectPipe(next.id); }
    else tell('所有管路均已选型。可进入参数模式继续填写。');
  }
  function applyModel(next = false) {
    if (state.mode !== 'submodel') return;
    const pipe = activePipe(), model = modelById(preview), config = activeConfig();
    if (!model || !compatible(pipe, model)) return;
    config.model = model.id;
    model.fields.forEach(key => { if (config.params[key] === undefined) config.params[key] = FIELDS[key].default; });
    render(); save(); addLog(`${pipe.id} 已应用 ${model.id}。${model.description}`);
    tell(`${pipe.id} 已应用 ${model.id}。`);
    if (next) {
      if (PIPES.some(item => !state.configs[item.id].model)) nextUnassigned();
      else { const target = PIPES.find(item => missing(item).length); if (target) state.selected = target.id; setMode('parameters'); tell('管路选型完成；填写实际管长、内径后检查配置。'); }
    }
  }
  function zoom(factor, anchor = null) {
    const next = Math.max(.5, Math.min(3, view.zoom * factor));
    if (anchor) {
      const width = $('canvas').clientWidth, height = $('canvas').clientHeight;
      const ratio = next / view.zoom;
      view.x = anchor.x - width / 2 - (anchor.x - width / 2 - view.x) * ratio;
      view.y = anchor.y - height / 2 - (anchor.y - height / 2 - view.y) * ratio;
    }
    view.zoom = next; applyView();
  }
  function renderConsoleVisibility() {
    $('console').classList.toggle('collapsed', !consoleOpen);
    $('toggle-console').setAttribute('aria-expanded', String(consoleOpen));
    $('toggle-console').textContent = `${consoleOpen ? '▾' : '▸'} 配置信息`;
  }
  document.querySelectorAll('[data-mode]').forEach(button => button.addEventListener('click', () => setMode(button.dataset.mode)));
  $('pipe-list').addEventListener('click', event => { const id = event.target.closest('[data-pipe]')?.dataset.pipe; if (id) selectPipe(id); });
  $('diagram').addEventListener('click', event => {
    if (pan?.moved) return;
    const pipe = event.target.closest('[data-pipe]');
    if (pipe) selectPipe(pipe.dataset.pipe);
    else if (event.target.closest('[data-component]')) tell('此 demo 只开放管路子模型，部件与 pnode 固定。');
  });
  $('diagram').addEventListener('dblclick', event => { const id = event.target.closest('[data-pipe]')?.dataset.pipe; if (id) { setMode('submodel'); selectPipe(id); $('library').querySelector('button:not(:disabled)')?.focus(); } });
  $('library').addEventListener('click', event => {
    const target = event.target.closest('[data-model]');
    if (!target || target.disabled || state.mode !== 'submodel') return;
    preview = target.dataset.model; renderLibrary(); renderProperties();
    tell(`预览 ${preview}；点击“应用到 ${state.selected}”生效。`);
  });
  $('library').addEventListener('dblclick', event => { const target = event.target.closest('[data-model]'); if (target && !target.disabled) { preview = target.dataset.model; applyModel(); } });
  $('compatible-only').addEventListener('change', renderLibrary);
  $('show-labels').addEventListener('change', renderWires);
  $('next-unassigned').addEventListener('click', nextUnassigned);
  $('model-properties').addEventListener('click', event => { const action = event.target.closest('[data-action]')?.dataset.action; if (action === 'apply' || action === 'apply-next') applyModel(action === 'apply-next'); });
  $('edit-parameters').addEventListener('click', () => setMode('parameters'));
  $('parameter-properties').addEventListener('input', event => {
    if (state.mode !== 'parameters') return;
    const key = event.target.dataset.parameter;
    if (!FIELDS[key]) return;
    activeConfig().params[key] = event.target.value;
    event.target.setAttribute('aria-invalid', String(!valid(key, event.target.value)));
    updateParameterNote(); updateProgress(); renderLibrary(); save();
  });
  $('console-content').addEventListener('click', event => {
    const id = event.target.closest('[data-fix]')?.dataset.fix;
    if (id) { selectPipe(id); setMode(state.configs[id].model ? 'parameters' : 'submodel'); }
  });
  $('toggle-console').addEventListener('click', () => { consoleOpen = !consoleOpen; renderConsoleVisibility(); });
  $('fit-view').addEventListener('click', () => { view = { zoom: 1, x: 0, y: 0 }; applyView(); });
  $('zoom-in').addEventListener('click', () => zoom(1.2));
  $('zoom-out').addEventListener('click', () => zoom(1 / 1.2));
  $('diagram').addEventListener('wheel', event => { event.preventDefault(); const bounds = $('diagram').getBoundingClientRect(); zoom(event.deltaY < 0 ? 1.1 : 1 / 1.1, { x: event.clientX - bounds.left, y: event.clientY - bounds.top }); }, { passive: false });
  // Only viewport movement is supported. No component/port/edge drag handler exists.
  $('diagram').addEventListener('pointerdown', event => {
    if (event.button !== 1 && !(event.button === 0 && event.target.hasAttribute('data-background'))) return;
    event.preventDefault();
    pan = { id: event.pointerId, x: event.clientX, y: event.clientY, initialX: view.x, initialY: view.y, moved: false };
    $('diagram').setPointerCapture(event.pointerId); $('diagram').classList.add('panning');
  });
  $('diagram').addEventListener('pointermove', event => {
    if (!pan || pan.id !== event.pointerId) return;
    const dx = event.clientX - pan.x, dy = event.clientY - pan.y;
    pan.moved ||= Math.abs(dx) + Math.abs(dy) > 3;
    view.x = pan.initialX + dx; view.y = pan.initialY + dy; applyView();
  });
  function endPan(event) {
    if (!pan || pan.id !== event.pointerId) return;
    if ($('diagram').hasPointerCapture(event.pointerId)) $('diagram').releasePointerCapture(event.pointerId);
    $('diagram').classList.remove('panning'); pan = null;
  }
  $('diagram').addEventListener('pointerup', endPan);
  $('diagram').addEventListener('pointercancel', endPan);
  $('diagram').addEventListener('lostpointercapture', endPan);
  document.addEventListener('dragstart', event => { if (event.target.closest('#diagram,#library')) event.preventDefault(); });
  document.addEventListener('keydown', event => {
    if (event.key === 'Delete' && !event.target.closest('input,textarea,[contenteditable=true]')) { event.preventDefault(); tell('子模型演示的部件和连接固定，不能删除或移动。'); }
  });
  $('reset').addEventListener('click', () => {
    state = initial(); view = { zoom: 1, x: 0, y: 0 }; pan = null; choosePreview();
    log = [{ kind: 'INFO', text: '已重置本页的管路选型与参数。固定布局保持原样。' }];
    render(); save(); tell('已重置此 demo；上一版和正式工程不受影响。');
  });
  load(); choosePreview(); drawFixedComponents(); render(); save();
  new ResizeObserver(resizeCanvas).observe($('canvas'));
})();