(() => {
  const {
    Engine,
    Render,
    Runner,
    World,
    Body,
    Bodies,
    Constraint,
    Events,
    Query,
    Vector,
  } = Matter;

  const { scenes = [], defaultSceneId } = window.PhysilinksScenes || {};

  const config = {
    gravity: 1,
    spawnIntervalMs: 520,
    minChain: 3,
    palette: ["#ff595e", "#ffca3a", "#8ac926", "#1982c4", "#6a4c93"],
    ballRadius: 18,
    link: {
      stiffness: 0.85,
      lengthScale: 1.05, // max stretch factor; slack below this
      damping: 0.08,
      lineWidth: 3,
      rope: true,
      renderType: "line",
      maxLengthMultiplier: 3.1,
    },
  };

  const ui = window.PhysilinksUI.create();
  const { sceneEl } = ui;

  let width = sceneEl.clientWidth;
  let height = sceneEl.clientHeight;

  const engine = Engine.create();
  engine.gravity.y = config.gravity;
  const world = engine.world;

  const render = Render.create({
    element: sceneEl,
    engine,
    options: {
      width,
      height,
      wireframes: false,
      background: "transparent",
      showAngleIndicator: false,
      pixelRatio: window.devicePixelRatio || 1,
    },
  });
  Render.run(render);

  const runner = Runner.create();
  Runner.run(runner, engine);
  let runnerActive = true;

  const startRunner = () => {
    if (!runnerActive) {
      Runner.run(runner, engine);
      runnerActive = true;
    }
  };

  const stopRunner = () => {
    if (runnerActive) {
      Runner.stop(runner);
      runnerActive = false;
    }
  };

  // Static boundaries and scene-specific obstacles.
  let boundaries = [];
  let rotators = [];
  let currentScene =
    scenes.find((s) => s.id === defaultSceneId) || scenes[0] || null;

  if (currentScene && currentScene.config) {
    Object.assign(config, currentScene.config);
    config.link = { ...currentScene.config.link };
  }

  const rebuildSceneBodies = () => {
    boundaries.forEach((b) => World.remove(world, b));
    boundaries = currentScene.createBodies(width, height);
    rotators = boundaries.filter((b) => b.plugin && b.plugin.rotSpeed);
    World.add(world, boundaries);
  };

  const balls = [];
  let spawnTimer = null;
  let score = 0;
  let highScore = 0;
  let gameOver = false;
  let isPaused = false;

  const makeStorageKey = (sceneId) => `physilinks-highscore-${sceneId}`;

  const loadHighScore = (sceneId) => {
    try {
      const raw = localStorage.getItem(makeStorageKey(sceneId));
      const parsed = parseInt(raw, 10);
      return Number.isFinite(parsed) ? parsed : 0;
    } catch (err) {
      return 0;
    }
  };

  const saveHighScore = () => {
    try {
      localStorage.setItem(makeStorageKey(currentScene.id), String(highScore));
    } catch (err) {
      // ignore write failures (private mode or blocked storage)
    }
  };

  const applyScene = (sceneId) => {
    const next = scenes.find((s) => s.id === sceneId) || scenes[0];
    currentScene = next;
    ui.setSceneSelection(next.id);
    Object.assign(config, next.config);
    config.link = { ...next.config.link };
    engine.gravity.y = config.gravity;
    highScore = loadHighScore(next.id);
    rebuildSceneBodies();
    buildLegend();
    restartGame();
    updateHud();
  };

  const chain = {
    active: false,
    color: null,
    bodies: [],
    constraints: [],
    pointer: null,
  };

  const getMaxLinkDistance = () => {
    const linkCfg = config.link || {};
    if (Number.isFinite(linkCfg.maxLinkLength)) {
      return linkCfg.maxLinkLength;
    }
    const mult = linkCfg.maxLengthMultiplier ?? 3;
    return mult * config.ballRadius;
  };

  const spawnBall = () => {
    if (gameOver) return;
    const color =
      config.palette[Math.floor(Math.random() * config.palette.length)];
    const x = Math.max(
      config.ballRadius + 10,
      Math.min(width - config.ballRadius - 10, Math.random() * width),
    );
    const y = -config.ballRadius * 2;
    const ball = Bodies.circle(x, y, config.ballRadius, {
      restitution: 0.72,
      friction: 0.01,
      frictionAir: 0.015,
      render: {
        fillStyle: color,
        strokeStyle: "#0b1222",
        lineWidth: 2,
      },
    });
    ball.plugin = { color, hasEntered: false, entryCheckId: null };
    balls.push(ball);
    World.add(world, ball);
    ball.plugin.entryCheckId = setTimeout(() => {
      ball.plugin.entryCheckId = null;
      if (gameOver) return;
      if (!ball.plugin.hasEntered && Math.abs(ball.velocity.y) < 0.2) {
        triggerGameOver();
      }
    }, 1500);
  };

  const startSpawner = () => {
    if (spawnTimer) clearInterval(spawnTimer);
    spawnTimer = setInterval(spawnBall, config.spawnIntervalMs);
  };

  const stopSpawner = () => {
    if (spawnTimer) {
      clearInterval(spawnTimer);
      spawnTimer = null;
    }
  };

  const cleanupBall = (ball) => {
    if (ball.plugin && ball.plugin.entryCheckId) {
      clearTimeout(ball.plugin.entryCheckId);
      ball.plugin.entryCheckId = null;
    }
  };

  const triggerGameOver = () => {
    if (gameOver) return;
    gameOver = true;
    isPaused = false;
    resetChainVisuals();
    stopSpawner();
    stopRunner();
    engine.timing.timeScale = 0;
    ui.setPauseState(false);
    ui.showGameOver(score);
  };

  const restartGame = () => {
    gameOver = false;
    isPaused = false;
    score = 0;
    resetChainVisuals();
    balls.forEach((ball) => {
      cleanupBall(ball);
      World.remove(world, ball);
    });
    balls.length = 0;
    ui.hideGameOver();
    ui.setPauseState(false);
    engine.timing.timeScale = 1;
    startRunner();
    updateHud();
    startSpawner();
  };

  const setHighlight = (body, on) => {
    body.render.lineWidth = on ? 4 : 2;
    body.render.strokeStyle = on ? "#f8fafc" : "#0b1222";
  };

  const setPaused = (state) => {
    if (gameOver) return;
    if (state === isPaused) return;
    isPaused = state;
    ui.setPauseState(isPaused);
    if (isPaused) {
      resetChainVisuals();
      stopSpawner();
      stopRunner();
      engine.timing.timeScale = 0;
    } else {
      startRunner();
      startSpawner();
      engine.timing.timeScale = 1;
    }
  };

  const resetChainVisuals = () => {
    chain.bodies.forEach((b) => setHighlight(b, false));
    chain.constraints.forEach((c) => World.remove(world, c));
    chain.active = false;
    chain.color = null;
    chain.bodies = [];
    chain.constraints = [];
    chain.pointer = null;
    updateHud();
  };

  const removeLastFromChain = () => {
    const removedConstraint = chain.constraints.pop();
    if (removedConstraint) {
      World.remove(world, removedConstraint);
    }
    const removedBody = chain.bodies.pop();
    if (removedBody) setHighlight(removedBody, false);
    updateHud();
  };

  const addToChain = (body) => {
    const last = chain.bodies[chain.bodies.length - 1];
    const dist = Vector.magnitude(Vector.sub(last.position, body.position));
    const linkCfg = config.link || {};
    const constraint = Constraint.create({
      bodyA: last,
      bodyB: body,
      length: dist * (linkCfg.lengthScale ?? 1),
      stiffness: linkCfg.stiffness ?? 0.9,
      damping: linkCfg.damping ?? 0,
      render: {
        strokeStyle: chain.color,
        lineWidth: linkCfg.lineWidth ?? 3,
        type: linkCfg.renderType || "line",
      },
    });
    constraint.plugin = {
      restLength: dist * (linkCfg.lengthScale ?? 1),
      rope: linkCfg.rope ?? false,
      baseStiffness: linkCfg.stiffness ?? 0.9,
      maxLength: dist * (linkCfg.lengthScale ?? 1),
    };
    chain.constraints.push(constraint);
    chain.bodies.push(body);
    setHighlight(body, true);
    World.add(world, constraint);
    updateHud();
  };

  const finishChain = (releasePoint) => {
    if (!chain.active || gameOver || isPaused) return;
    if (chain.bodies.length >= config.minChain) {
      const gain = 10 * Math.pow(chain.bodies.length, 2);
      score += gain;
      if (score > highScore) {
        highScore = score;
        saveHighScore();
      }
      ui.spawnScorePopup(releasePoint || chain.pointer, gain, chain.color);
      chain.constraints.forEach((c) => World.remove(world, c));
      chain.bodies.forEach((body) => {
        cleanupBall(body);
        World.remove(world, body);
      });
      // Remove cleared balls from tracking list.
      for (let i = balls.length - 1; i >= 0; i -= 1) {
        if (chain.bodies.includes(balls[i])) {
          balls.splice(i, 1);
        }
      }
    } else {
      chain.constraints.forEach((c) => World.remove(world, c));
      chain.bodies.forEach((b) => setHighlight(b, false));
    }
    chain.active = false;
    chain.color = null;
    chain.bodies = [];
    chain.constraints = [];
    chain.pointer = null;
    updateHud();
  };

  const pickBody = (point) => {
    const hits = Query.point(balls, point);
    return hits[0];
  };

  const getPointerPosition = (evt) => {
    const rect = render.canvas.getBoundingClientRect();
    const clientX = evt.touches ? evt.touches[0].clientX : evt.clientX;
    const clientY = evt.touches ? evt.touches[0].clientY : evt.clientY;
    return {
      x: clientX - rect.left,
      y: clientY - rect.top,
    };
  };

  const handlePointerDown = (evt) => {
    if (gameOver || isPaused) return;
    const point = getPointerPosition(evt);
    const body = pickBody(point);
    if (!body) return;
    chain.active = true;
    chain.color = body.plugin.color;
    chain.bodies = [body];
    chain.constraints = [];
    chain.pointer = point;
    setHighlight(body, true);
    updateHud();
  };

  const handlePointerMove = (evt) => {
    if (!chain.active) return;
    if (gameOver || isPaused) return;
    const point = getPointerPosition(evt);
    chain.pointer = point;
    const body = pickBody(point);
    if (!body) return;
    const alreadyInChain = chain.bodies.includes(body);
    if (alreadyInChain) {
      const targetIndex = chain.bodies.indexOf(body);
      if (chain.bodies.length > 1 && targetIndex === chain.bodies.length - 2) {
        removeLastFromChain();
      }
      return;
    }
    if (body.plugin.color !== chain.color) return;
    const maxLinkDist = getMaxLinkDistance();
    const dist = Vector.magnitude(
      Vector.sub(chain.bodies[chain.bodies.length - 1].position, body.position),
    );
    if (dist > maxLinkDist) return;
    addToChain(body);
  };

  const handlePointerUp = () => finishChain(chain.pointer);

  render.canvas.addEventListener("mousedown", handlePointerDown);
  render.canvas.addEventListener("mousemove", handlePointerMove);
  window.addEventListener("mouseup", handlePointerUp);
  render.canvas.addEventListener(
    "touchstart",
    (e) => {
      e.preventDefault();
      handlePointerDown(e);
    },
    { passive: false },
  );
  render.canvas.addEventListener(
    "touchmove",
    (e) => {
      e.preventDefault();
      handlePointerMove(e);
    },
    { passive: false },
  );
  render.canvas.addEventListener(
    "touchend",
    (e) => {
      e.preventDefault();
      handlePointerUp(e);
    },
    { passive: false },
  );

  const updateHud = () => {
    ui.updateHud({
      spawnIntervalMs: config.spawnIntervalMs,
      minChain: config.minChain,
      chainLength: chain.bodies.length,
      score,
      highScore,
      activeColor: chain.color,
    });
  };

  const buildLegend = () => {
    ui.buildLegend(config.palette);
  };

  const handleResize = () => {
    width = sceneEl.clientWidth;
    height = sceneEl.clientHeight;
    render.canvas.width = width;
    render.canvas.height = height;
    render.options.width = width;
    render.options.height = height;
    Render.lookAt(render, {
      min: { x: 0, y: 0 },
      max: { x: width, y: height },
    });
    rebuildSceneBodies();
  };

  Events.on(engine, "afterUpdate", () => {
    // Keep stray balls within the play area horizontally.
    balls.forEach((ball) => {
      if (
        !ball.plugin.hasEntered &&
        ball.position.y > config.ballRadius * 1.5
      ) {
        ball.plugin.hasEntered = true;
      }
      if (
        ball.position.x < -100 ||
        ball.position.x > width + 100 ||
        ball.position.y > height + 500
      ) {
        cleanupBall(ball);
        ball.plugin.hasEntered = true;
        Matter.Body.setPosition(ball, { x: Math.random() * width, y: -40 });
        Matter.Body.setVelocity(ball, { x: 0, y: 0 });
      }
    });
  });

  Events.on(engine, "beforeUpdate", () => {
    // Rope-like constraint handling: allow shortening without push-back, tension when stretched.
    chain.constraints.forEach((c) => {
      if (!c.plugin || !c.plugin.rope) return;
      const current = Vector.magnitude(
        Vector.sub(c.bodyA.position, c.bodyB.position),
      );
      const maxLen = c.plugin.maxLength ?? c.length;
      if (current <= maxLen) {
        c.length = current;
        c.stiffness = 0;
      } else {
        c.length = maxLen;
        c.stiffness = c.plugin.baseStiffness ?? c.stiffness;
      }
    });
    // Rotate any scene rotators slowly.
    const dt = (engine.timing && engine.timing.delta) || 16;
    const timeScale = engine.timing?.timeScale ?? 1;
    if (isPaused || gameOver || timeScale === 0) return;
    rotators.forEach((b) => {
      const speed = b.plugin.rotSpeed || 0;
      if (speed !== 0) {
        Body.rotate(b, speed * ((dt * timeScale) / 1000));
      }
    });
  });

  Events.on(render, "afterRender", () => {
    if (!chain.active || !chain.pointer || chain.bodies.length === 0) return;
    const last = chain.bodies[chain.bodies.length - 1];
    const ctx = render.context;
    const maxLinkDist = getMaxLinkDistance();
    const delta = Vector.sub(chain.pointer, last.position);
    const dist = Vector.magnitude(delta);
    // Pull back the preview line slightly so it does not suggest a link will land on a too-distant ball.
    const previewMargin = config.ballRadius;
    const cappedDist = Math.max(
      0,
      Math.min(dist, Math.max(0, maxLinkDist - previewMargin)),
    );
    const safeTarget =
      dist > 0
        ? Vector.add(
            last.position,
            Vector.mult(Vector.normalise(delta), cappedDist),
          )
        : chain.pointer;
    ctx.save();
    ctx.strokeStyle = chain.color || "#fff";
    ctx.lineWidth = 3;
    ctx.setLineDash([6, 6]);
    ctx.beginPath();
    ctx.moveTo(last.position.x, last.position.y);
    ctx.lineTo(safeTarget.x, safeTarget.y);
    ctx.stroke();
    ctx.restore();
  });

  window.addEventListener("resize", handleResize);
  ui.setHandlers({
    onPauseToggle: () => setPaused(!isPaused),
    onRestart: restartGame,
    onSceneChange: (id) => applyScene(id),
  });
  ui.setSceneOptions(
    scenes,
    (currentScene && currentScene.id) || defaultSceneId,
  );
  applyScene((currentScene && currentScene.id) || defaultSceneId);
})();