/* ISLE SLINGERS — core.js
 * Pure, deterministic game core: physics, rules, scoring, events.
 * No DOM, no audio, no Math.random — the renderer consumes state.events
 * for visual-only effects. Loadable in browser (window.ISLE_CORE) or node.
 */
(function (root, factory) {
  var api = factory();
  if (typeof module !== 'undefined' && module.exports) module.exports = api;
  else root.ISLE_CORE = api;
})(typeof globalThis !== 'undefined' ? globalThis : this, function () {
  'use strict';

  var WORLD = { w: 2400, ground: 900 };
  var VIEW = { w: 1280, h: 720 }; // base viewport (renderer renders at this size,
                                  // then CSS-scales; camera math lives in the core)

  var MATERIALS = {
    wood:  { hp: 1300, density: 1.0,  restitution: 0.18, dmgFactor: 0.9,  score: 500,  maxVel: 520 },
    ice:   { hp: 480,  density: 0.7,  restitution: 0.05, dmgFactor: 1.6,  score: 800,  maxVel: 560 },
    // stone: retuned 2026-09-28 (RC-0D193E, Commander bug #3 "blocks and pig
    // bad guys too hard to kill"): at hp 3400 with dmgFactor 0.35 a 70x70
    // cube took ~11 full-power direct hits — stone walls were functionally
    // unbreakable, so every enemy behind one was unkillable. Now ~2-3 hits.
    stone: { hp: 1400, density: 2.2,  restitution: 0.04, dmgFactor: 0.8, score: 300,  maxVel: 480 }
  };

  var BIRD_TYPES = {
    wren:    { r: 20, mass: 3.0, label: 'Wren',    ability: 'fury'   }, // tap: horizontal burst
    zippy:   { r: 17, mass: 2.2, label: 'Zippy',   ability: 'dive'   }, // tap: steep dive
    boulder: { r: 26, mass: 6.5, label: 'Boulder', ability: 'quake'  }  // tap: radial shock
  };

  var ENEMY_TYPES = {
    mogg: { hp: 1, r: 24, score: 5000,  crushVel: 330, crushDmg: 1.2 },
    grum: { hp: 2, r: 32, score: 8000,  crushVel: 380, crushDmg: 1.0 },
    king: { hp: 3, r: 38, score: 15000, crushVel: 430, crushDmg: 0.85 }
  };

  var GRAVITY = 1500;
  var LAUNCH_POWER = 11.5;     // velocity per px of pull
  var MAX_PULL = 150;
  var MIN_PULL = 14;
  var AIR_DRAG = 0.999;
  var BIRD_BOUNCE = 0.34;
  var BIRD_GROUND_FRICTION = 0.86;
  var REST_SPEED = 14;         // below this a bird counts as settling
  var SETTLE_TIME = 0.9;       // seconds under REST_SPEED before bird is spent
  var BIRD_MAX_AGE = 12;
  var ABILITY_CD = 0.35;       // min seconds after launch before ability usable
  var BIRD_BONUS = 10000;

  // ------------------------------------------------------------------ state

  function createGame(levelDef) {
    var g = {
      level: levelDef,
      world: { w: WORLD.w, ground: WORLD.ground },
      time: 0,
      score: 0,
      birds: [],
      blocks: [],
      enemies: [],
      events: [],          // visual/audio events for the renderer
      scorePopups: [],     // {x,y,text,age}
      hadEnemies: levelDef.enemies.length > 0,
      camera: { x: levelDef.sling.x + 260, y: 560, zoom: 1, shake: 0, snap: true },
      status: 'ready',     // ready | flying | won | lost
      activeBird: -1,
      launched: 0,
      wonAt: null,
      lostAt: null,
      stats: { impacts: 0, destroyedBlocks: 0, destroyedEnemies: 0, abilityUses: 0, distance: 0 }
    };
    g.blocks = levelDef.blocks.map(function (b, i) {
      var m = MATERIALS[b.mat];
      return {
        id: i, x: b.x, y: b.y, w: b.w, h: b.h, mat: b.mat,
        hp: m.hp, maxHp: m.hp,
        vx: 0, vy: 0, rest: 1,
        mass: m.density * b.w * b.h / 1400
      };
    });
    g.enemies = levelDef.enemies.map(function (e, i) {
      var t = ENEMY_TYPES[e.kind];
      // level data y is the CENTER (the level-integrity test treats it the
      // same way); spawning at e.y - r made every enemy drop 24-38px on
      // load — a visible "objects moving on their own" wobble at start
      return {
        id: i, kind: e.kind, x: e.x, y: e.y, r: t.r,
        hp: t.hp, maxHp: t.hp, vx: 0, vy: 0, rest: 1, dead: false, deathAge: 0
      };
    });
    var i;
    for (i = 0; i < levelDef.birds.length; i++) {
      g.birds.push(makeBird(levelDef.birds[i], i));
    }
    g.activeBird = g.birds.length ? 0 : -1;
    if (g.activeBird >= 0) {
      var fb = g.birds[0];
      fb.state = 'aiming';
      fb.x = levelDef.sling.x;
      fb.y = levelDef.sling.y;
    }
    return g;
  }

  function makeBird(kind, idx) {
    var t = BIRD_TYPES[kind];
    return {
      id: idx, kind: kind, r: t.r, mass: t.mass,
      x: 0, y: 0, vx: 0, vy: 0,
      state: 'queued',      // queued | aiming | flying | spent
      abilityUsed: false,
      settleTimer: 0, age: 0,
      launchT: 0
    };
  }

  function activeBird(g) { return g.activeBird >= 0 ? g.birds[g.activeBird] : null; }

  // ---------------------------------------------------------------- aiming

  // Returns {vx,vy,pull} if a valid launch for the given drag, else null.
  function aimVector(g, sling, drag) {
    var dx = sling.x - drag.x, dy = sling.y - drag.y;
    var len = Math.sqrt(dx * dx + dy * dy);
    if (len < MIN_PULL) return null;
    var cl = Math.min(len, MAX_PULL);
    var v = cl * LAUNCH_POWER;
    return { vx: (dx / len) * v, vy: (dy / len) * v, pull: cl };
  }

  // Pure trajectory preview: identical integrator + substepping as the live
   // sim (2x 1/120 per output point), so the dotted preview matches the real
   // flight exactly. Gravity + drag only; stops at the ground.
   function trajectory(g, sx, sy, vx, vy, steps) {
     var pts = [];
     var x = sx, y = sy, i, sub;
     for (i = 0; i < steps; i++) {
       for (sub = 0; sub < 2; sub++) {
         var dt = 1 / 120;
         var nvy = vy + GRAVITY * dt;
         x += vx * dt;
         y += (vy + nvy) * 0.5 * dt;
         vx *= AIR_DRAG;
         vy = nvy;
       }
       if (y > WORLD.ground - 18) { pts.push({ x: x, y: WORLD.ground - 18, last: true }); break; }
       pts.push({ x: x, y: y, last: false });
     }
     return pts;
   }

  function launch(g, dragPos) {
    var b = activeBird(g);
    if (!b || b.state !== 'aiming' || g.status !== 'ready') return false;
    var v = aimVector(g, { x: g.level.sling.x, y: g.level.sling.y }, dragPos);
    if (!v) return false;
    b.x = g.level.sling.x; b.y = g.level.sling.y;
    b.vx = v.vx; b.vy = v.vy;
    b.state = 'flying';
    b.launchT = g.time;
    g.status = 'flying';
    g.launched++;
    g.events.push({ type: 'launch', x: b.x, y: b.y });
    return true;
  }

  function triggerAbility(g) {
    var b = activeBird(g);
    if (!b || b.state !== 'flying' || b.abilityUsed) return false;
    if (g.time - b.launchT < ABILITY_CD) return false;
    var kind = b.kind;
    if (kind === 'wren') {
      b.vx = b.vx * 0.4 + 980;
      g.events.push({ type: 'ability_fury', x: b.x, y: b.y });
    } else if (kind === 'zippy') {
      b.vy = Math.max(b.vy, 0) + 1050;
      b.vx *= 0.55;
      g.events.push({ type: 'ability_dive', x: b.x, y: b.y });
    } else if (kind === 'boulder') {
      var R = 150;
      var i, d, f, ent;
      for (i = 0; i < g.blocks.length; i++) {
        var bl = g.blocks[i];
        if (bl.hp <= 0) continue;
        d = Math.hypot(bl.x - b.x, bl.y - b.y) - (bl.w + bl.h) / 4;
        if (d < R) { f = 1 - Math.max(0, d) / R; damageBlock(g, bl, 120 + 300 * f, 'quake'); }
      }
      for (i = 0; i < g.enemies.length; i++) {
        ent = g.enemies[i];
        if (ent.dead) continue;
        d = Math.hypot(ent.x - b.x, ent.y - b.y) - ent.r;
        if (d < R) { f = 1 - Math.max(0, d) / R; damageEnemy(g, ent, 0.7 + 1.6 * f); }
      }
      g.camera.shake = Math.max(g.camera.shake, 14);
      g.events.push({ type: 'ability_quake', x: b.x, y: b.y, r: R });
    }
    b.abilityUsed = true;
    g.stats.abilityUses++;
    return true;
  }

  // ---------------------------------------------------------------- damage

  function damageBlock(g, bl, dmg, src) {
    if (bl.hp <= 0) return;
    bl.hp -= dmg;
    if (bl.hp <= 0) {
      bl.hp = 0;
      g.score += MATERIALS[bl.mat].score;
      g.stats.destroyedBlocks++;
      g.scorePopups.push({ x: bl.x, y: bl.y, text: '+' + MATERIALS[bl.mat].score, age: 0 });
      g.events.push({ type: 'break', x: bl.x, y: bl.y, mat: bl.mat, big: bl.w * bl.h > 12000 });
      g.camera.shake = Math.max(g.camera.shake, 4 + bl.w * bl.h / 4000);
    } else if (dmg > 40) {
      g.events.push({ type: 'crack', x: bl.x, y: bl.y, mat: bl.mat });
    }
  }

  function damageEnemy(g, e, dmg) {
    if (e.dead) return;
    e.hp -= dmg;
    if (e.hp <= 0) {
      e.dead = true;
      e.deathAge = 0;
      g.score += ENEMY_TYPES[e.kind].score;
      g.stats.destroyedEnemies++;
      g.scorePopups.push({ x: e.x, y: e.y - 30, text: '+' + ENEMY_TYPES[e.kind].score, age: 0 });
      g.events.push({ type: 'pop', x: e.x, y: e.y, kind: e.kind });
      g.camera.shake = Math.max(g.camera.shake, 7);
    }
  }

  // ----------------------------------------------------------------- step

  function step(g, dt) {
    g.time += dt;
    if (g.status === 'won' || g.status === 'lost') {
      // let physics settle for a beat so the win/lose screen lands naturally
      stepPhysics(g, dt);
      updatePopups(g, dt);
      decayCamera(g, dt);
      return;
    }
    stepPhysics(g, dt);
    updatePopups(g, dt);
    decayCamera(g, dt);
    updateCameraTarget(g);
    checkEndStates(g);
  }

  function stepPhysics(g, dt) {
    var i, b;

    // active bird flight
    b = activeBird(g);
    if (b && b.state === 'flying') {
      b.age += dt;
      var nvy = b.vy + GRAVITY * dt;
      b.x += b.vx * dt;
      b.y += (b.vy + nvy) * 0.5 * dt;
      b.vx *= AIR_DRAG;
      b.vy = nvy;
      g.stats.distance = Math.max(g.stats.distance, b.x);
      collideBirdWorld(g, b);
      collideBirdBlocks(g, b);
      collideBirdEnemies(g, b);
      // settle / spend detection (low speed anywhere = spent, whether on
      // the ground or perched on a beam; jitter-tolerant accumulation)
      var sp = Math.hypot(b.vx, b.vy);
      if (sp < REST_SPEED) b.settleTimer += dt;
      else b.settleTimer = Math.max(0, b.settleTimer - dt * 4);
      if (b.settleTimer > SETTLE_TIME || b.age > BIRD_MAX_AGE || b.x > WORLD.w + 200 || b.x < -200) {
        spendBird(g, b);
      }
    }

    // blocks: gravity + integration + collisions
    for (i = 0; i < g.blocks.length; i++) {
      var bl = g.blocks[i];
      if (bl.hp <= 0) continue;
      bl.vy = Math.min(bl.vy + GRAVITY * dt, MATERIALS[bl.mat].maxVel);
      bl.vx *= 0.995;
      bl.x += bl.vx * dt;
      bl.y += bl.vy * dt;
      // ground
      var halfH = bl.h / 2;
      if (bl.y + halfH > WORLD.ground) {
        var impact = bl.vy;
        bl.y = WORLD.ground - halfH;
        if (impact > 90) {
          bl.vy = -impact * MATERIALS[bl.mat].restitution;
          bl.vx *= 0.8;
          if (impact > 240) {
            damageBlock(g, bl, (impact - 240) * 0.45, 'ground');
            g.events.push({ type: 'block_impact', x: bl.x, y: WORLD.ground, mat: bl.mat, strength: impact });
          }
          bl.rest = 0;
        } else {
          bl.vy = 0;
          bl.vx *= 0.82; // rolling friction
          if (Math.abs(bl.vx) < 4) { bl.vx = 0; bl.rest = 1; }
        }
      }
      // walls (keep the mess on the island)
      if (bl.x - bl.w / 2 < 0) { bl.x = bl.w / 2; bl.vx = Math.abs(bl.vx) * 0.2; }
      if (bl.x + bl.w / 2 > WORLD.w) { bl.x = WORLD.w - bl.w / 2; bl.vx = -Math.abs(bl.vx) * 0.2; }
    }
    // block vs block (positional + 1D impulse, 2 relaxation passes)
    var pass, j, a, c;
    for (pass = 0; pass < 2; pass++) {
      for (i = 0; i < g.blocks.length; i++) {
        a = g.blocks[i];
        if (a.hp <= 0) continue;
        for (j = i + 1; j < g.blocks.length; j++) {
          c = g.blocks[j];
          if (c.hp <= 0) continue;
          resolveBoxPair(g, a, c);
        }
      }
    }
    // block vs bird (crush)
    if (b && b.state === 'flying') {
      for (i = 0; i < g.blocks.length; i++) {
        var blk = g.blocks[i];
        if (blk.hp <= 0) continue;
        crushCircleVsBox(g, blk, b, false);
      }
    }

    // enemies: settle on ground/blocks, take crush damage
    for (i = 0; i < g.enemies.length; i++) {
      var e = g.enemies[i];
      if (e.dead) { e.deathAge += dt; continue; }
      e.vy = Math.min(e.vy + GRAVITY * dt, 700);
      e.x += e.vx * dt;
      e.y += e.vy * dt;
      e.vx *= 0.9;
      if (e.y + e.r > WORLD.ground) {
        if (e.vy > 420) { e.vy = -e.vy * 0.25; e.vx *= 0.6; }
        else { e.vy = 0; e.y = WORLD.ground - e.r; e.vx *= 0.8; }
      }
      for (j = 0; j < g.blocks.length; j++) {
        var bb = g.blocks[j];
        if (bb.hp <= 0) continue;
        crushCircleVsBox(g, bb, e, true);
      }
    }
  }

  function crushCircleVsBox(g, box, ent, isEnemy) {
    var cx = Math.max(box.x - box.w / 2, Math.min(ent.x, box.x + box.w / 2));
    var cy = Math.max(box.y - box.h / 2, Math.min(ent.y, box.y + box.h / 2));
    var dx = ent.x - cx, dy = ent.y - cy;
    var d2 = dx * dx + dy * dy;
    if (d2 >= ent.r * ent.r) return;
    var d = Math.sqrt(d2) || 0.001;
    var nx = dx / d, ny = dy / d;
    var overlap = ent.r - d;
    ent.x += nx * overlap * 0.9;
    ent.y += ny * overlap * 0.9;
    // impulse: relative velocity along normal
    var rvx = (ent.vx || 0) - (box.vx || 0), rvy = (ent.vy || 0) - (box.vy || 0);
    var rel = rvx * nx + rvy * ny;
    if (rel < -30) {
      var relSpeed = -rel;
      ent.vx -= nx * rel * 1.4;
      ent.vy -= ny * rel * 1.4;
      if (isEnemy) {
        // crush damage: fast falling boxes hurt what they land on
        var spec = ENEMY_TYPES[ent.kind];
        var boxSpeed = Math.hypot(box.vx || 0, box.vy || 0);
        if (boxSpeed > spec.crushVel && ny < -0.3) {
          damageEnemy(g, ent, (boxSpeed - spec.crushVel) * 0.004 * spec.crushDmg + 0.35);
          g.events.push({ type: 'crush', x: ent.x, y: ent.y });
        }
      } else {
        // bird: transfer momentum into the box
        var dmg = relSpeed * 0.32 * (ent.mass || 3) * 0.25;
        if (dmg > 25) damageBlock(g, box, dmg, 'bird');
        box.vx += nx * rel * 0.05 * (ent.mass || 3);
        box.vy += ny * rel * 0.05 * (ent.mass || 3);
      }
    } else if (rel < 0) {
      // slow resting contact: remove the normal approach velocity so a
      // perched enemy/box pair stops oscillating under gravity
      ent.vx -= nx * rel;
      ent.vy -= ny * rel;
    }
  }

  function collideBirdWorld(g, b) {
    if (b.y + b.r > WORLD.ground) {
      var impact = -b.vy;
      b.y = WORLD.ground - b.r;
      if (b.vy > 0) b.vy = -b.vy * BIRD_BOUNCE;
      b.vx *= BIRD_GROUND_FRICTION;
      if (impact > 250) {
        g.events.push({ type: 'bird_ground', x: b.x, y: WORLD.ground, strength: impact });
        g.camera.shake = Math.max(g.camera.shake, 5);
      }
      if (Math.abs(b.vy) < 30) b.vy = 0;
    }
    if (b.x - b.r < 0) { b.x = b.r; b.vx = Math.abs(b.vx) * 0.3; }
  }

  function collideBirdBlocks(g, b) {
    var i;
    for (i = 0; i < g.blocks.length; i++) {
      var bl = g.blocks[i];
      if (bl.hp <= 0) continue;
      var cx = Math.max(bl.x - bl.w / 2, Math.min(b.x, bl.x + bl.w / 2));
      var cy = Math.max(bl.y - bl.h / 2, Math.min(b.y, bl.y + bl.h / 2));
      var dx = b.x - cx, dy = b.y - cy;
      var d2 = dx * dx + dy * dy;
      if (d2 >= b.r * b.r) continue;
      var d = Math.sqrt(d2) || 0.001;
      var nx = dx / d, ny = dy / d;
      var overlap = b.r - d;
      b.x += nx * overlap;
      b.y += ny * overlap;
      var rvx = b.vx - bl.vx, rvy = b.vy - bl.vy;
      var rel = rvx * nx + rvy * ny;
      if (rel < 0) {
        var relSpeed = -rel;
        // impulse: j = -(1+e)*rel / (1/m1 + 1/m2)
        var invM = 1 / b.mass + 1 / bl.mass;
        var j = -(1 + BIRD_BOUNCE) * rel / invM;
        b.vx += (j / b.mass) * nx;
        b.vy += (j / b.mass) * ny;
        bl.vx -= (j / bl.mass) * nx;
        bl.vy -= (j / bl.mass) * ny;
        g.stats.impacts++;
        var dmg = relSpeed * 0.55 * (b.mass / 3) * MATERIALS[bl.mat].dmgFactor;
        if (dmg > 30) {
          damageBlock(g, bl, dmg, 'bird');
          g.events.push({ type: 'hit', x: cx, y: cy, mat: bl.mat, strength: relSpeed });
          g.camera.shake = Math.max(g.camera.shake, Math.min(12, relSpeed / 90));
        }
        b.vx *= 0.985; b.vy *= 0.985;
      }
    }
  }

  function collideBirdEnemies(g, b) {
    var i;
    for (i = 0; i < g.enemies.length; i++) {
      var e = g.enemies[i];
      if (e.dead) continue;
      var dx = e.x - b.x, dy = e.y - b.y;
      var rr = e.r + b.r;
      var d2 = dx * dx + dy * dy;
      if (d2 >= rr * rr) continue;
      var d = Math.sqrt(d2) || 0.001;
      var nx = dx / d, ny = dy / d;
      var rel = (b.vx - e.vx) * nx + (b.vy - e.vy) * ny;
      if (rel > 0) {
        e.vx += nx * rel * 0.8;
        e.vy += ny * rel * 0.8 - 120;
        // per-target hit cooldown so one pass-through = one damage instance
        if (g.time - (e.lastHit || -9) > 0.12) {
          var speed = Math.hypot(b.vx, b.vy);
          // retuned 2026-09-28 (RC-0D193E, Commander bug #3): the old curve
          // gave ~0.9 dmg to a soft wren lob — a mogg (hp1) could not be
          // killed without a perfect full-power hit. Bumped so a decent
          // medium shot connects; the king (hp3) still survives one
          // full-power wren hit (pinned in test/sim.test.mjs).
          var dmg = 0.35 + speed / 800 * (b.mass / 3);
          damageEnemy(g, e, dmg);
          e.lastHit = g.time;
          g.events.push({ type: 'bird_hit_enemy', x: e.x, y: e.y, strength: speed });
        }
        b.vx *= 0.92; b.vy *= 0.92;
      }
    }
  }

  // Resting-contact clamp: inelastic contacts + zeroing below this speed,
  // so stacked blocks settle to exactly still instead of oscillating under
  // gravity re-injection.
  var REST_VEL_CLAMP = 30; // |v| below this on a resting contact is zeroed

  function resolveBoxPair(g, a, c) {
    var ox = (a.w / 2 + c.w / 2) - Math.abs(a.x - c.x);
    var oy = (a.h / 2 + c.h / 2) - Math.abs(a.y - c.y);
    if (ox <= 0 || oy <= 0) return;
    if (ox < oy) {
      // side contact: push apart along x
      var n = c.x >= a.x ? 1 : -1; // direction from a toward c
      a.x -= n * ox * 0.5; c.x += n * ox * 0.5;
      var relv = (c.vx - a.vx) * n;
      if (relv < 0) { // approaching
        var avg = (a.vx + c.vx) / 2;
        a.vx = avg; c.vx = avg;
      }
      a.vx *= 0.9; c.vx *= 0.9;
    } else {
      // stacked contact: push apart along y, then kill resting velocity
      var n2 = c.y >= a.y ? 1 : -1;
      a.y -= n2 * oy * 0.5; c.y += n2 * oy * 0.5;
      var relv2 = (c.vy - a.vy) * n2;
      if (relv2 < -REST_VEL_CLAMP) {
        // real impact: inelastic average (blocks do not bounce off each other)
        var avgY = (a.vy + c.vy) / 2;
        a.vy = avgY; c.vy = avgY;
      } else if (relv2 < 0) {
        // resting: top takes the bottom's velocity (kills the relative
        // velocity), then zero both below the clamp so stacks stop
        // oscillating under gravity re-injection
        var top = n2 === 1 ? a : c;
        var bot = n2 === 1 ? c : a;
        top.vy = bot.vy;
        if (Math.abs(top.vy) < REST_VEL_CLAMP) { top.vy = 0; bot.vy = 0; }
      } else {
        // separating / at rest: clamp near-zero velocities
        if (Math.abs(a.vy) < 2) a.vy = 0;
        if (Math.abs(c.vy) < 2) c.vy = 0;
      }
    }
  }

  function spendBird(g, b) {
    b.state = 'spent';
    b.vx = 0; b.vy = 0;
    g.events.push({ type: 'bird_gone', x: b.x, y: b.y });
    // next bird onto the sling
    var next = -1;
    for (var i = g.activeBird + 1; i < g.birds.length; i++) {
      if (g.birds[i].state === 'queued') { next = i; break; }
    }
    g.activeBird = next;
    if (next >= 0) {
      var nb = g.birds[next];
      nb.state = 'aiming';
      nb.x = g.level.sling.x; nb.y = g.level.sling.y;
      g.status = 'ready';
      g.events.push({ type: 'bird_load', x: nb.x, y: nb.y, kind: nb.kind });
    }
  }

  function checkEndStates(g) {
    if (g.status === 'won' || g.status === 'lost') return;
    var alive = 0;
    for (var i = 0; i < g.enemies.length; i++) if (!g.enemies[i].dead) alive++;
    if (g.hadEnemies && alive === 0 && g.launched > 0) {
      g.status = 'won';
      g.wonAt = g.time;
      g.score += BIRD_BONUS * birdsRemaining(g);
      g.events.push({ type: 'level_won', x: g.camera.x, y: 400 });
      return;
    }
    var b = activeBird(g);
    var inFlight = false;
    for (var k = 0; k < g.birds.length; k++) if (g.birds[k].state === 'flying') inFlight = true;
    if (!inFlight && !b && g.status === 'flying') {
      // last bird spent, enemies remain
      g.status = 'lost';
      g.lostAt = g.time;
      g.events.push({ type: 'level_lost', x: g.camera.x, y: 400 });
    }
  }

  function birdsRemaining(g) {
    var n = 0;
    for (var i = 0; i < g.birds.length; i++) if (g.birds[i].state === 'queued') n++;
    return n;
  }

  function starsFor(g) {
    var th = g.level.stars;
    if (!th) return 0;
    if (g.score >= th[2]) return 3;
    if (g.score >= th[1]) return 2;
    if (g.score >= th[0] || g.status === 'won') return 1;
    return 0;
  }

  function updatePopups(g, dt) {
    for (var i = g.scorePopups.length - 1; i >= 0; i--) {
      g.scorePopups[i].age += dt;
      g.scorePopups[i].y -= 40 * dt;
      if (g.scorePopups[i].age > 1.4) g.scorePopups.splice(i, 1);
    }
  }

  function updateCameraTarget(g) {
    var b = activeBird(g);
    var cam = g.camera;
    var tx, ty, tz;
    if (b && b.state === 'flying') {
      // in flight: follow the slinger 1:1 (the bird IS the point of interest)
      tx = Math.max(420, Math.min(WORLD.w - 420, b.x + 220));
      ty = Math.max(380, Math.min(WORLD.ground - 160, b.y + 60));
      tz = 1;
    } else {
      // aiming / waiting: frame the slingshot AND the whole action zone
      // (live blocks + enemies) so launch point and target are always
      // visible at once — zooming out when the level needs it. Without
      // this the sling was visible but the fort was off-screen (or
      // vice-versa mid-flight), making aiming pure guesswork.
      var left = g.level.sling.x - 190;
      var right = left + 300;
      for (var i = 0; i < g.blocks.length; i++) {
        var bl = g.blocks[i];
        if (bl.hp > 0) right = Math.max(right, bl.x + bl.w / 2 + 90);
      }
      for (var k = 0; k < g.enemies.length; k++) {
        var en = g.enemies[k];
        if (!en.dead) right = Math.max(right, en.x + en.r + 90);
      }
      var span = right - left;
      tz = Math.min(1, VIEW.w / span);
      tx = left + span / 2;
      // ground at ~78% down the view, whatever the zoom
      ty = Math.max(300, Math.min(WORLD.ground, WORLD.ground - (0.28 * VIEW.h) / tz));
    }
    if (cam.snap) { // first frame of a level: land on target, no pan
      cam.x = tx; cam.y = ty; cam.zoom = tz; cam.snap = false;
      return;
    }
    cam.x += (tx - cam.x) * 0.06;
    cam.y += (ty - cam.y) * 0.06;
    cam.zoom = (cam.zoom || 1) + (tz - (cam.zoom || 1)) * 0.08;
  }

  function decayCamera(g, dt) {
    if (g.camera.shake > 0) {
      g.camera.shake *= Math.pow(0.03, dt); // fast decay
      if (g.camera.shake < 0.3) g.camera.shake = 0;
    }
  }

  // ------------------------------------------------------------------ API

  return {
    WORLD: WORLD,
    VIEW: VIEW,
    MATERIALS: MATERIALS,
    BIRD_TYPES: BIRD_TYPES,
    ENEMY_TYPES: ENEMY_TYPES,
    GRAVITY: GRAVITY,
    MAX_PULL: MAX_PULL,
    MIN_PULL: MIN_PULL,
    LAUNCH_POWER: LAUNCH_POWER,
    BIRD_BONUS: BIRD_BONUS,
    createGame: createGame,
    activeBird: activeBird,
    aimVector: aimVector,
    trajectory: trajectory,
    launch: launch,
    triggerAbility: triggerAbility,
    step: step,
    starsFor: starsFor,
    birdsRemaining: birdsRemaining,
    AIR_DRAG: AIR_DRAG
  };
});