(() => {
  // Utility short-hands
  const $ = (sel) => document.querySelector(sel);
  const $$ = (sel) => document.querySelectorAll(sel);

  // DOM refs
  const svg = $('#graphSvg');
  const branchListEl = $('#branchList');
  const stashListEl = $('#stashList');
  const currentHeadEl = $('#currentHead');
  const detachedStateEl = $('#detachedState');
  const commitMsgEl = $('#commitMsg');
  const btnCommit = $('#btnCommit');
  const btnCommitAmend = $('#btnCommitAmend');
  const btnUndoCommit = $('#btnUndoCommit');
  const branchNameEl = $('#branchName');
  const btnCreateBranch = $('#btnCreateBranch');
  const switchBranchEl = $('#switchBranch');
  const checkoutCommitEl = $('#checkoutCommit');
  const btnCheckout = $('#btnCheckout');
  const btnDetach = $('#btnDetach');
  const btnMerge = $('#btnMerge');
  const btnRebase = $('#btnRebase');
  const mergeTargetEl = $('#mergeTarget');
  const rebaseTargetEl = $('#rebaseTarget');
  const btnStash = $('#btnStash');
  const btnStashPop = $('#btnStashPop');
  const btnResetHard = $('#btnResetHard');
  const resetTargetEl = $('#resetTarget');
  const btnNewIssue = $('#btnNewIssue');
  const btnNewPR = $('#btnNewPR');
  const issuesListEl = $('#issuesList');
  const prsListEl = $('#prsList');
  const btnFit = $('#btnFit');
  const btnCenterMain = $('#btnCenterMain');
  const btnCenterHead = $('#btnCenterHead');
  const btnDemoBasic = $('#btnDemoBasic');
  const btnDemoPR = $('#btnDemoPR');
  const blameCommitEl = $('#blameCommit');
  const btnBlame = $('#btnBlame');
  const blamePanel = $('#blamePanel');

  // Graph rendering config
  const Lane = {
    width: 140,
    marginX: 90,
    marginY: 36,
    commitRadius: 6
  };

  // Colors
  const cssVar = (name, fallback) => getComputedStyle(document.documentElement).getPropertyValue(name).trim() || fallback;

  // State
  const state = {
    repo: null,
    layout: null,
    nextCommitIndex: 0,
    selectedNodeId: null,
    cardEl: null,
  };

  // Init state
  const initRepo = () => {
    const main = newBranch('main', null);
    const root = newCommit('Initial commit', 'System', { isRoot: true });
    main.head = root.id;

    return {
      commits: new Map([[root.id, root]]),
      branches: new Map([['main', main]]),
      head: { type: 'branch', name: 'main' },
      detachedHeadCommit: null,
      stash: [],
      issues: [],
      prs: [],
      nextId: 1
    };
  };

  // Helpers
  function newId(prefix = 'c') {
    return `${prefix}${String(state.repo.nextId++).padStart(3, '0')}`;
  }
  function newBranch(name, fromCommitId) {
    return {
      name,
      head: fromCommitId || null,
      color: pickBranchColor()
    };
  }
  function pickBranchColor() {
    // Generates an HSL color based on repo state
    const n = state.repo.branches.size + 1;
    const hue = (n * 67) % 360;
    return `hsl(${hue} 72% 60%)`;
  }
  function newCommit(message, author, extra = {}) {
    const id = newId('c');
    const idx = state.nextCommitIndex++;
    return {
      id,
      idx,
      message,
      author,
      parents: extra.parents || [],
      branch: extra.branch || null,
      isRoot: !!extra.isRoot,
      timestamp: Date.now()
    };
  }

  function getCommit(id) { return state.repo.commits.get(id); }
  function getHeadCommit() {
    const head = state.repo.head;
    if (head.type === 'branch') {
      const br = state.repo.branches.get(head.name);
      return br && br.head ? getCommit(br.head) : null;
    } else if (head.type === 'detached') {
      return getCommit(head.commitId);
    }
    return null;
  }
  function getBranchByName(name) { return state.repo.branches.get(name); }

  function isMergedInto(commitId, targetBranchName) {
    // Check if commitId is ancestor of targetBranch head
    const target = getBranchByName(targetBranchName)?.head;
    if (!target) return false;
    let cur = target;
    const visited = new Set();
    while (cur) {
      if (cur === commitId) return true;
      const node = getCommit(cur);
      if (!node) break;
      if (visited.has(cur)) break;
      visited.add(cur);
      cur = node.parents[0] || null;
    }
    return false;
  }

  // History navigation
  function walk(commitId, fn) {
    const visited = new Set();
    let cur = commitId;
    while (cur) {
      if (visited.has(cur)) break;
      visited.add(cur);
      const node = getCommit(cur);
      if (!node) break;
      if (fn(node) === false) break;
      cur = node.parents[0] || null;
    }
  }

  // Index commit for linear layout per first-parent chain
  function buildLayout() {
    let idx = -1;
    const visited = new Set();
    let cur = null;
    // find a head
    const heads = [];
    for (const br of state.repo.branches.values()) {
      if (br.head) heads.push(br.head);
    }
    if (state.repo.head.type === 'detached') heads.push(state.repo.head.commitId);
    // sort heads by existing idx
    heads.sort((a, b) => (getCommit(a)?.idx ?? 0) - (getCommit(b)?.idx ?? 0));
    // Walk each chain to assign indices topologically
    for (const h of heads) {
      cur = h;
      const chain = [];
      while (cur && !visited.has(cur)) {
        visited.add(cur);
        chain.push(cur);
        const c = getCommit(cur);
        cur = c?.parents?.[0] || null;
      }
      // Assign idx descending from 0 upwards
      for (let i = chain.length - 1; i >= 0; i--) {
        const id = chain[i];
        const node = getCommit(id);
        if (node && node.idx === -1) {
          idx += 1;
          node.idx = idx;
        }
      }
    }
    // Keep nextCommitIndex aligned with max idx
    state.nextCommitIndex = idx + 1;

    // Assign lanes (first-come-first-serve)
    const lanes = new Map(); // branchName -> laneIndex
    let laneCursor = 0;
    for (const [name, br] of state.repo.branches) {
      if (!br.head) continue;
      if (!lanes.has(name)) {
        lanes.set(name, laneCursor++);
      }
    }

    // Compute x,y positions
    const nodes = Array.from(state.repo.commits.values());
    nodes.sort((a,b) => a.idx - b.idx);

    const coords = new Map(); // id -> {x,y}
    const xForLane = (i) => Lane.marginX + i * Lane.width;
    const yForIdx = (i) => Lane.marginY + i * 36;

    // First pass: assign rough positions
    for (const c of nodes) {
      const lane = lanes.get(c.branch || '') ?? 0;
      coords.set(c.id, { x: xForLane(lane), y: yForIdx(c.idx) });
    }

    // Second pass: route merges with intermediate waypoints to avoid crossings
    const edges = []; // {from,to,type}
    for (const c of nodes) {
      const a = coords.get(c.id);
      for (const p of (c.parents || [])) {
        const b = coords.get(p);
        const type = c.parents.length > 1 ? 'merge' : 'link';
        edges.push({ from: a, to: b, type });
      }
    }

    // Compute bounding box
    let maxY = 0;
    nodes.forEach(n => {
      const { y } = coords.get(n.id);
      if (y > maxY) maxY = y;
    });

    state.layout = { coords, edges, maxY, lanes: lanes.size, nodes };
  }

  // SVG utilities
  function clearSvg() {
    while (svg.firstChild) svg.removeChild(svg.firstChild);
  }
  function make(tag, attrs = {}, children = []) {
    const el = document.createElementNS('http://www.w3.org/2000/svg', tag);
    for (const [k, v] of Object.entries(attrs)) {
      if (v !== null && v !== undefined) el.setAttribute(k, v);
    }
    if (!Array.isArray(children)) children = [children];
    children.forEach(ch => el.appendChild(ch));
    return el;
  }

  // Draw graph
  function renderGraph() {
    clearSvg();
    buildLayout();

    // Size SVG
    const width = Math.max(900, 2 * Lane.marginX + (state.layout.lanes * Lane.width));
    const height = Math.max(420, state.layout.maxY + Lane.marginY + 40);
    svg.setAttribute('viewBox', `0 0 ${width} ${height}`);
    svg.setAttribute('width', '100%');
    svg.setAttribute('height', '100%');

    // Draw links
    for (const [id, c] of state.repo.commits) {
      for (const p of (c.parents || [])) {
        const a = state.layout.coords.get(id);
        const b = state.layout.coords.get(p);
        if (!a || !b) continue;
        const d = curvePath(a, b);
        const cl = make('path', { d, class: `link ${c.parents.length > 1 ? 'merge' : ''}` });
        svg.appendChild(cl);
      }
    }

    // Draw nodes
    const nodes = state.layout.nodes;
    for (const c of nodes) {
      const { x, y } = state.layout.coords.get(c.id);
      const g = make('g', { class: 'node', transform: `translate(${x},${y})`, 'data-id': c.id });
      const isHeadOfBranch = [...state.repo.branches.values()].some(b => b.head === c.id);
      const isHead = (state.repo.head.type === 'branch' && getBranchByName(state.repo.head.name)?.head === c.id)
        || (state.repo.head.type === 'detached' && state.repo.head.commitId === c.id);

      // circle
      const circle = make('circle', { r: Lane.commitRadius });
      g.appendChild(circle);

      // label (commit short id and idx)
      const short = c.id.slice(-6);
      const label = make('text', { class: 'id', x: 12, y: -10 }, document.createTextNode(`${short} · idx:${c.idx}`));
      g.appendChild(label);

      // branch head marker
      const branchNames = [];
      for (const [name, br] of state.repo.branches) {
        if (br.head === c.id) branchNames.push(name);
      }
      const branchLabel = make('text', { class: 'branch', x: 12, y: -22 }, document.createTextNode(branchNames.join(' · ')));
      g.appendChild(branchLabel);

      // HEAD marker
      if (isHead) {
        g.appendChild(make('circle', { r: Lane.commitRadius + 4, class: 'head' }));
      }

      // Merge node indicator: diamond
      if (c.parents.length > 1) {
        g.appendChild(make('rect', { x: -4, y: -4, width: 8, height: 8, class: 'diamond', transform: 'rotate(45)' }));
      }

      // events
      g.addEventListener('click', () => showCommitCard(c.id, x, y));

      svg.appendChild(g);
    }
  }

  function curvePath(a, b) {
    // Cubic Bezier curve between points
    const dx = Math.max(30, Math.abs(a.x - b.x) * 0.35);
    return `M ${a.x} ${a.y} C ${a.x + dx} ${a.y}, ${b.x - dx} ${b.y}, ${b.x} ${b.y}`;
  }

  // Commit card UI
  function showCommitCard(commitId, x, y) {
    if (state.cardEl && state.cardEl.parentNode) state.cardEl.parentNode.removeChild(state.cardEl);
    const c = getCommit(commitId);
    const card = document.createElement('div');
    card.className = 'commit-card';
    card.style.left = Math.min(Math.max(10, x + 14), svg.clientWidth - 280) + 'px';
    card.style.top = Math.min(Math.max(10, y - 20), svg.clientHeight - 160) + 'px';

    const parents = c.parents.length ? c.parents.map(id => getCommit(id)?.id.slice(-6)).join(', ') : 'none';
    const branches = [...state.repo.branches.entries()]
      .filter(([_, br]) => br.head === c.id)
      .map(([name, _]) => name)
      .join(', ') || '-';

    card.innerHTML = `
      <h3>${escapeHtml(c.message)}</h3>
      <div class="meta">
        <span class="tag">${escapeHtml(c.author)}</span>
        <span class="tag">${c.id.slice(-6)}</span>
        <span class="tag">parents: ${parents}</span>
        <span class="tag">branches: ${escapeHtml(branches)}</span>
      </div>
      <div class="actions">
        <button class="btn" data-action="checkout">Checkout</button>
        <button class="btn" data-action="branch">New branch here</button>
        <button class="btn warn" data-action="reset">Reset --hard here</button>
        <button class="btn ghost" data-action="blame">Blame</button>
      </div>
    `;
    card.addEventListener('click', (e) => {
      const action = e.target?.dataset?.action;
      if (!action) return;
      if (action === 'checkout') checkoutCommit(c.id);
      if (action === 'branch') {
        branchNameEl.value = suggestBranchName();
        branchNameEl.dataset.from = c.id;
      }
      if (action === 'reset') resetHardTo(c.id);
      if (action === 'blame') {
        blameCommitEl.value = c.id;
        showBlame(c.id);
        card.remove();
      }
    });

    svg.parentElement.appendChild(card);
    state.cardEl = card;
  }

  function escapeHtml(s) {
    return String(s).replace(/[&<>"']/g, m => ({'&':'&amp;','<':'&lt;','>':'&gt;','"':'&quot;',"'":'&#039;'}[m]));
  }

  // Actions
  function commit(message, { amend = false } = {}) {
    const head = getHeadCommit();
    const parent = head ? head.id : null;
    const branchName = state.repo.head.type === 'branch' ? state.repo.head.name : null;

    if (amend && parent) {
      // Modify last commit (keep same id)
      const last = getCommit(parent);
      if (last) {
        last.message = message || last.message;
        last.author = 'You';
        last.timestamp = Date.now();
        touchRefresh();
        return;
      }
    }

    const c = newCommit(message || defaultCommitMsg(), 'You');
    c.parents = parent ? [parent] : [];
    if (branchName) c.branch = branchName;
    if (state.repo.head.type === 'branch') {
      const br = getBranchByName(branchName);
      br.head = c.id;
    } else if (state.repo.head.type === 'detached') {
      state.repo.head.commitId = c.id;
    }

    state.repo.commits.set(c.id, c);
    touchRefresh();
  }

  function defaultCommitMsg() {
    const n = (state.nextCommitIndex % 8);
    const msgs = [
      'Make it work',
      'Improve naming',
      'Add tests',
      'Refactor utils',
      'Optimize performance',
      'Fix edge cases',
      'Polish UI',
      'Document code'
    ];
    return msgs[n];
  }

  function createBranch(name, fromCommitId) {
    if (!name) return alert('Enter a branch name.');
    if (state.repo.branches.has(name)) return alert('Branch already exists.');
    const from = fromCommitId || getHeadCommit()?.id || null;
    const br = newBranch(name, from);
    state.repo.branches.set(name, br);
    touchRefresh();
  }

  function checkout(branchName) {
    if (!state.repo.branches.has(branchName)) return alert('Branch not found.');
    state.repo.head = { type: 'branch', name: branchName };
    touchRefresh();
  }

  function checkoutCommit(commitId) {
    if (!getCommit(commitId)) return alert('Commit not found.');
    state.repo.head = { type: 'detached', commitId };
    touchRefresh();
  }

  function mergeIntoCurrent(targetBranchName) {
    const curName = state.repo.head.type === 'branch' ? state.repo.head.name : null;
    if (!curName) return alert('You can only merge while on a branch.');
    const target = getBranchByName(targetBranchName);
    if (!target || !target.head) return alert('Target branch has no commits.');

    const curHead = getBranchByName(curName).head;
    const targetHead = target.head;

    if (curHead