// Headless verification for Angry Birds.
//   node tools/verifyAngryBirds.js
// Exits non-zero on any failure.
//
// 1. Physics invariants — mass properties, resting contacts, stack stability,
//    friction, restitution, anti-tunnel bound, explosion falloff.
// 2. Determinism — seeded replay, frame-rate independence, clone independence.
// 3. Robustness — random-impulse monkey test for NaN / overspeed / sinking.
//
// Rendering, slingshot feel, camera and the editor's Blob export are
// browser-only and must be smoke-tested manually.

import {
  PHYS, createWorld, addBox, addPoly, addCircle, removeBody,
  step, substep, settle, isSettled, applyImpulse, applyExplosion,
  cloneWorld, hashWorld, contactImpulses,
} from '../src/games/angrybirds/AngryBirdsPhysics.js';

let failures = 0;
let passes = 0;
function check(name, cond, detail = '') {
  if (cond) { passes += 1; console.log(`  ok  ${name}`); }
  else { failures += 1; console.error(`FAIL  ${name}${detail ? ` — ${detail}` : ''}`); }
}
const near = (a, b, tol) => Math.abs(a - b) <= tol;

function section(title) { console.log(`\n── ${title} ${'─'.repeat(Math.max(0, 60 - title.length))}`); }

// Deterministic RNG for the monkey test (never Math.random — see the header
// contract in AngryBirdsPhysics.js).
function mulberry32(seed) {
  let a = seed >>> 0;
  return () => {
    a = (a + 0x6d2b79f5) >>> 0;
    let t = Math.imul(a ^ (a >>> 15), 1 | a);
    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

/** Ground plane spanning the test area. */
function withGround(world, y = 800) {
  addBox(world, { x: 600, y: y + 50, w: 4000, h: 100, isStatic: true, friction: 0.7 });
  return world;
}

// ── 1. Mass properties ──────────────────────────────────────────────────────

section('1. Mass properties');
{
  const w = createWorld();
  const b = addBox(w, { x: 0, y: 0, w: 40, h: 20, density: 2 });
  const expectMass = 2 * 40 * 20;
  check('box mass = density x w x h', near(b.mass, expectMass, 1e-6), `${b.mass} vs ${expectMass}`);

  const expectI = (expectMass * (40 * 40 + 20 * 20)) / 12;
  check('box inertia = m(w^2+h^2)/12', near(1 / b.invI, expectI, expectI * 1e-6),
    `${1 / b.invI} vs ${expectI}`);

  const c = addCircle(w, { x: 0, y: 0, r: 10, density: 3 });
  const cMass = 3 * Math.PI * 100;
  check('circle mass = density x pi r^2', near(c.mass, cMass, 1e-6), `${c.mass} vs ${cMass}`);

  const s = addBox(w, { x: 0, y: 0, w: 10, h: 10, isStatic: true });
  check('static body has zero inverse mass', s.invMass === 0 && s.invI === 0);
}
{
  // Winding must be normalized: a CW polygon must produce the same body as CCW.
  const w = createWorld();
  const ccw = addPoly(w, { x: 0, y: 0, verts: [[-10, -10], [10, -10], [10, 10], [-10, 10]], density: 1 });
  const cw = addPoly(w, { x: 0, y: 0, verts: [[-10, 10], [10, 10], [10, -10], [-10, -10]], density: 1 });
  check('polygon winding normalized', near(ccw.mass, cw.mass, 1e-9) && near(ccw.invI, cw.invI, 1e-12),
    `${ccw.mass}/${cw.mass}`);

  // Outward normals must point away from the centroid.
  const outward = ccw.normals.every(([nx, ny], i) => {
    const [vx, vy] = ccw.verts[i];
    return vx * nx + vy * ny > 0;
  });
  check('polygon normals point outward', outward);
}
{
  // Verts are recentred on the centroid, so an off-centre polygon still
  // rotates about its true centre of mass.
  const w = createWorld();
  const b = addPoly(w, { x: 0, y: 0, verts: [[0, 0], [40, 0], [40, 20], [0, 20]], density: 1 });
  const cx = b.verts.reduce((s, v) => s + v[0], 0) / b.verts.length;
  const cy = b.verts.reduce((s, v) => s + v[1], 0) / b.verts.length;
  check('polygon recentred on centroid', near(cx, 0, 1e-9) && near(cy, 0, 1e-9), `${cx},${cy}`);
}

// ── 2. Anti-tunnelling bound ────────────────────────────────────────────────

section('2. Anti-tunnelling');
{
  const travel = PHYS.MAX_SPEED * PHYS.SUBSTEP_DT;
  check('MAX_SPEED x SUBSTEP_DT < MIN_HALF_EXTENT',
    travel < PHYS.MIN_HALF_EXTENT, `${travel.toFixed(2)} !< ${PHYS.MIN_HALF_EXTENT}`);
}
{
  // A fast circle fired at a thin static wall must not pass through it.
  const w = createWorld();
  addBox(w, { x: 400, y: 300, w: 20, h: 400, isStatic: true });
  const ball = addCircle(w, { x: 100, y: 300, r: 12, density: 1 });
  ball.vx = PHYS.MAX_SPEED;
  w.gravity = 0;
  for (let i = 0; i < 240; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('fast body does not tunnel through a wall', ball.x < 400, `x=${ball.x.toFixed(1)}`);
}

// ── 3. Resting contacts and stack stability (THE WAVE 0 GATE) ───────────────

section('3. Resting contacts and stacks');
{
  const w = withGround(createWorld());
  const b = addBox(w, { x: 600, y: 700, w: 60, h: 60, density: 1 });
  for (let i = 0; i < 600; i += 1) substep(w, PHYS.SUBSTEP_DT);
  // Ground top is y=800; a 60-tall box rests with its centre at 770.
  check('single box rests on ground', near(b.y, 770, PHYS.SLOP + 0.5), `y=${b.y.toFixed(3)}`);
  check('resting box does not sink', b.y < 772, `y=${b.y.toFixed(3)}`);
  check('resting box falls asleep', b.sleeping, `timer=${b.sleepTimer.toFixed(2)}`);
}
{
  // THE GATE: a 10-box tower must settle, sleep, and not drift.
  const w = withGround(createWorld());
  const boxes = [];
  // Ground top is y=800, boxes are 40 tall, so box i rests centred at 780-40i.
  // Spawning them exactly at rest isolates solver sag from free-fall settling.
  for (let i = 0; i < 10; i += 1) {
    boxes.push(addBox(w, { x: 600, y: 780 - i * 40, w: 60, h: 40, density: 1, friction: 0.6 }));
  }
  const startX = boxes.map((b) => b.x);

  let sleptAt = -1;
  for (let i = 0; i < 720; i += 1) {          // 3 simulated seconds at 1/240
    substep(w, PHYS.SUBSTEP_DT);
    if (sleptAt < 0 && isSettled(w)) sleptAt = i;
  }
  check('10-box tower settles within 3s', sleptAt >= 0, `never settled`);
  check('10-box tower is fully asleep', boxes.every((b) => b.sleeping),
    `${boxes.filter((b) => !b.sleeping).length} awake`);

  const drift = Math.max(...boxes.map((b, i) => Math.abs(b.x - startX[i])));
  check('tower horizontal drift < 1px', drift < 1, `max drift ${drift.toFixed(3)}px`);

  // Total sag is bounded by SLOP per contact — the solver deliberately stops
  // correcting once penetration is inside the slop band, so 10 stacked
  // contacts can each give up to SLOP. Anything beyond that is real sag.
  const sag = boxes[9].y - (780 - 9 * 40);
  const sagBudget = PHYS.SLOP * 10;
  check('tower sag within the slop budget', Math.abs(sag) < sagBudget,
    `sag ${sag.toFixed(3)}px vs budget ${sagBudget}px`);

  const tilt = Math.max(...boxes.map((b) => Math.abs(b.angle)));
  check('tower stays upright', tilt < 0.02, `max |angle| ${tilt.toFixed(4)} rad`);
}
{
  // A pyramid is the harder stacking case: contacts are shared sideways.
  const w = withGround(createWorld());
  const bodies = [];
  for (let row = 0; row < 5; row += 1) {
    const n = 5 - row;
    for (let i = 0; i < n; i += 1) {
      bodies.push(addBox(w, {
        x: 600 - (n - 1) * 35 + i * 70,
        y: 770 - row * 40,
        w: 64, h: 40, density: 1, friction: 0.6,
      }));
    }
  }
  for (let i = 0; i < 600; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('pyramid settles and sleeps', bodies.every((b) => b.sleeping),
    `${bodies.filter((b) => !b.sleeping).length} awake`);
  const maxTilt = Math.max(...bodies.map((b) => Math.abs(b.angle)));
  check('pyramid stays upright', maxTilt < 0.05, `max |angle| ${maxTilt.toFixed(4)}`);
}

// ── 4. Friction ─────────────────────────────────────────────────────────────

section('4. Friction');
{
  // 15 degrees, mu = 0.8 -> tan(15) = 0.27 < 0.8, so the box must not creep.
  const w = createWorld();
  const slope = 15 * Math.PI / 180;
  addBox(w, { x: 600, y: 800, w: 2000, h: 60, angle: slope, isStatic: true, friction: 0.9 });
  const b = addBox(w, { x: 600, y: 745, w: 60, h: 40, angle: slope, density: 1, friction: 0.9 });
  const x0 = b.x;
  for (let i = 0; i < 900; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('box on 15deg slope does not creep', Math.abs(b.x - x0) < 2,
    `moved ${(b.x - x0).toFixed(2)}px`);
  check('box on slope sleeps', b.sleeping);
}
{
  // 40 degrees, mu = 0.2 -> tan(40) = 0.84 > 0.2, so it must slide.
  const w = createWorld();
  const slope = 40 * Math.PI / 180;
  addBox(w, { x: 600, y: 800, w: 3000, h: 60, angle: slope, isStatic: true, friction: 0.2 });
  const b = addBox(w, { x: 400, y: 800 - 200 * Math.tan(slope) - 52, w: 60, h: 40, angle: slope, density: 1, friction: 0.2 });
  const x0 = b.x;
  for (let i = 0; i < 600; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('low-friction box slides down a steep slope', b.x - x0 > 20,
    `moved ${(b.x - x0).toFixed(2)}px`);
}

// ── 5. Restitution ──────────────────────────────────────────────────────────

section('5. Restitution');
{
  const w = withGround(createWorld());
  const ball = addCircle(w, { x: 600, y: 400, r: 20, density: 1, restitution: 0.8 });
  let peakUp = 0;
  for (let i = 0; i < 400; i += 1) {
    substep(w, PHYS.SUBSTEP_DT);
    if (ball.vy < peakUp) peakUp = ball.vy;
  }
  check('bouncy ball rebounds upward', peakUp < -100, `peak vy ${peakUp.toFixed(1)}`);
}
{
  const w = withGround(createWorld());
  const dead = addCircle(w, { x: 600, y: 400, r: 20, density: 1, restitution: 0 });
  for (let i = 0; i < 900; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('zero-restitution ball comes to rest', dead.sleeping && near(dead.y, 780, 1.5),
    `y=${dead.y.toFixed(2)} sleeping=${dead.sleeping}`);
}

// ── 6. Shape-pair coverage ──────────────────────────────────────────────────

section('6. Shape pairs');
{
  const w = createWorld();
  w.gravity = 0;
  const a = addCircle(w, { x: 100, y: 300, r: 20, density: 1 });
  const b = addCircle(w, { x: 200, y: 300, r: 20, density: 1 });
  a.vx = 200;
  for (let i = 0; i < 200; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('circle-circle transfers momentum', b.vx > 50 && a.vx < 200, `a=${a.vx.toFixed(1)} b=${b.vx.toFixed(1)}`);
}
{
  const w = createWorld();
  w.gravity = 0;
  const c = addCircle(w, { x: 100, y: 300, r: 20, density: 1 });
  const p = addBox(w, { x: 300, y: 300, w: 60, h: 60, density: 1 });
  c.vx = 300;
  for (let i = 0; i < 240; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('circle-poly transfers momentum', p.vx > 20, `box vx=${p.vx.toFixed(1)}`);
  check('circle-poly does not overlap after impact',
    Math.hypot(c.x - p.x, c.y - p.y) > 40, `dist ${Math.hypot(c.x - p.x, c.y - p.y).toFixed(1)}`);
}
{
  // A circle dropped into a closed V must wedge, not squeeze through the seam.
  // Two slabs tilted toward each other, overlapping at the bottom so there is
  // no gap for the ball to slip through.
  const w = createWorld();
  addBox(w, { x: 480, y: 780, w: 400, h: 40, angle: -0.6, isStatic: true, friction: 0.6 });
  addBox(w, { x: 720, y: 780, w: 400, h: 40, angle: 0.6, isStatic: true, friction: 0.6 });
  const ball = addCircle(w, { x: 600, y: 300, r: 25, density: 1 });
  for (let i = 0; i < 1800; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('circle wedges in a V without escaping', ball.y < 820 && ball.sleeping,
    `y=${ball.y.toFixed(1)} sleeping=${ball.sleeping}`);
}

// ── 7. Sleeping and waking ──────────────────────────────────────────────────

section('7. Sleeping');
{
  const w = withGround(createWorld());
  const stack = [];
  for (let i = 0; i < 4; i += 1) stack.push(addBox(w, { x: 600, y: 770 - i * 40, w: 60, h: 40, density: 1 }));
  for (let i = 0; i < 600; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('stack asleep before impact', stack.every((b) => b.sleeping));

  // A projectile must wake the whole island, not just the box it touches.
  const shot = addCircle(w, { x: 200, y: 700, r: 16, density: 4 });
  shot.vx = 1200;
  let allAwake = false;
  for (let i = 0; i < 240; i += 1) {
    substep(w, PHYS.SUBSTEP_DT);
    if (stack.every((b) => !b.sleeping)) { allAwake = true; break; }
  }
  check('impact wakes the whole island', allAwake,
    `${stack.filter((b) => b.sleeping).length} still asleep`);
}
{
  const w = withGround(createWorld());
  const b = addBox(w, { x: 600, y: 700, w: 60, h: 60, density: 1 });
  settle(w, 10);
  check('settle() reaches rest', isSettled(w) && b.sleeping);
  const yRest = b.y;
  for (let i = 0; i < 600; i += 1) substep(w, PHYS.SUBSTEP_DT);
  check('sleeping body does not drift', near(b.y, yRest, 1e-9), `${b.y} vs ${yRest}`);
}

// ── 8. Explosions ───────────────────────────────────────────────────────────

section('8. Explosions');
{
  const w = withGround(createWorld());
  const near1 = addBox(w, { x: 620, y: 700, w: 40, h: 40, density: 1 });
  const far1 = addBox(w, { x: 900, y: 700, w: 40, h: 40, density: 1 });
  const outside = addBox(w, { x: 1400, y: 700, w: 40, h: 40, density: 1 });
  const hit = applyExplosion(w, 600, 700, 400, 600);
  check('explosion hits bodies inside the radius', hit.length === 2, `hit ${hit.length}`);
  check('explosion falls off with distance',
    Math.hypot(near1.vx, near1.vy) > Math.hypot(far1.vx, far1.vy),
    `${Math.hypot(near1.vx, near1.vy).toFixed(1)} vs ${Math.hypot(far1.vx, far1.vy).toFixed(1)}`);
  check('explosion spares bodies outside the radius',
    outside.vx === 0 && outside.vy === 0);
  check('explosion pushes away from the centre', near1.vx > 0 && far1.vx > 0);
  check('explosion wakes sleeping bodies', !near1.sleeping);
}

// ── 9. Determinism ──────────────────────────────────────────────────────────

section('9. Determinism');
function scene() {
  const w = withGround(createWorld());
  for (let i = 0; i < 6; i += 1) addBox(w, { x: 600, y: 770 - i * 40, w: 60, h: 40, density: 1 });
  addBox(w, { x: 660, y: 730, w: 30, h: 120, density: 0.8 });
  const ball = addCircle(w, { x: 200, y: 600, r: 16, density: 4 });
  ball.vx = 900; ball.vy = -120;
  return w;
}
{
  const a = scene();
  const b = scene();
  for (let i = 0; i < 300; i += 1) { substep(a, PHYS.SUBSTEP_DT); substep(b, PHYS.SUBSTEP_DT); }
  check('identical scenes replay bit-identically', hashWorld(a) === hashWorld(b),
    `${hashWorld(a)} vs ${hashWorld(b)}`);
}
{
  // Frame-rate independence: one 1/60 frame must equal exactly N substeps.
  const perFrame = Math.round((1 / 60) / PHYS.SUBSTEP_DT);
  const c = scene();
  const d = scene();
  for (let i = 0; i < 300; i += 1) {
    step(c, 1 / 60);
    for (let k = 0; k < perFrame; k += 1) substep(d, PHYS.SUBSTEP_DT);
  }
  check(`1/60 step == ${perFrame}x substep`, hashWorld(c) === hashWorld(d),
    `${hashWorld(c)} vs ${hashWorld(d)}`);
}
{
  // Ragged frame pacing: the accumulator only ever runs WHOLE substeps, so N
  // substeps reached through jittery frame times must be bit-identical to N
  // substeps reached evenly. (Total elapsed time can differ by up to one
  // substep's worth of carry — that leftover is the accumulator's whole job —
  // so the comparison is on substeps run, not on wall time.)
  const e = scene();
  const f = scene();
  const rng = mulberry32(99);
  let ran = 0;
  for (let i = 0; i < 400; i += 1) ran += step(e, 0.004 + rng() * 0.02);
  for (let i = 0; i < ran; i += 1) substep(f, PHYS.SUBSTEP_DT);
  check('ragged frame pacing matches even pacing', hashWorld(e) === hashWorld(f),
    `${ran} substeps: ${hashWorld(e)} vs ${hashWorld(f)}`);
}
{
  const src = scene();
  for (let i = 0; i < 60; i += 1) substep(src, PHYS.SUBSTEP_DT);
  const before = hashWorld(src);
  const copy = cloneWorld(src);
  check('clone starts hash-identical', before === hashWorld(copy));

  // Stepping the clone must not disturb the original by any route — including
  // through the body references cached on contacts. simulatePreview and the
  // winnability bot both depend on this being airtight.
  for (let i = 0; i < 120; i += 1) substep(copy, PHYS.SUBSTEP_DT);
  check('stepping a clone leaves the original untouched', hashWorld(src) === before,
    `${hashWorld(src)} vs ${before}`);
  check('clone diverges from a stationary original', hashWorld(copy) !== before);

  for (let i = 0; i < 120; i += 1) substep(src, PHYS.SUBSTEP_DT);
  check('clone and original converge when stepped equally', hashWorld(src) === hashWorld(copy),
    `${hashWorld(src)} vs ${hashWorld(copy)}`);
}
{
  // Sequential impulses are Gauss-Seidel, so solve order genuinely affects the
  // answer — bit-identical results across creation orders are NOT achievable
  // and not required. What matters is that the dependence stays sub-pixel, so
  // an author reordering blocks in the editor can't change whether a level
  // works. Exact reproducibility of a GIVEN scene is covered above.
  const build = (reverse) => {
    const w = withGround(createWorld());
    const spec = [];
    for (let i = 0; i < 5; i += 1) spec.push({ x: 600, y: 770 - i * 40 });
    const order = reverse ? [...spec].reverse() : spec;
    for (const s of order) addBox(w, { ...s, w: 60, h: 40, density: 1 });
    return w;
  };
  const fwd = build(false);
  const rev = build(true);
  for (let i = 0; i < 480; i += 1) { substep(fwd, PHYS.SUBSTEP_DT); substep(rev, PHYS.SUBSTEP_DT); }
  const fy = [...fwd.bodies].filter((b) => !b.isStatic).map((b) => b.y).sort((a, b) => a - b);
  const ry = [...rev.bodies].filter((b) => !b.isStatic).map((b) => b.y).sort((a, b) => a - b);
  const worst = Math.max(...fy.map((v, i) => Math.abs(v - ry[i])));
  check('creation order shifts results by under 1px', worst < 1, `worst ${worst.toFixed(3)}px`);
}

// ── 10. Robustness monkey test ──────────────────────────────────────────────

section('10. Robustness');
{
  const seeds = Number((process.argv.find((a) => a.startsWith('--seeds=')) ?? '--seeds=12').split('=')[1]);
  let bad = 0;
  let sank = 0;
  let overspeed = 0;
  for (let s = 0; s < seeds; s += 1) {
    const rng = mulberry32(1000 + s);
    const w = withGround(createWorld());
    const bodies = [];
    for (let i = 0; i < 14; i += 1) {
      const b = rng() < 0.3
        ? addCircle(w, { x: 400 + rng() * 400, y: 300 + rng() * 400, r: 10 + rng() * 18, density: 0.5 + rng() })
        : addBox(w, { x: 400 + rng() * 400, y: 300 + rng() * 400, w: 24 + rng() * 60, h: 24 + rng() * 60, angle: rng() * Math.PI, density: 0.5 + rng() });
      bodies.push(b);
    }
    for (let i = 0; i < 900; i += 1) {
      if (i % 60 === 0) {
        const b = bodies[Math.floor(rng() * bodies.length)];
        applyImpulse(b, (rng() - 0.5) * 4e5, (rng() - 0.5) * 4e5, b.x, b.y);
      }
      substep(w, PHYS.SUBSTEP_DT);
      for (const b of bodies) {
        if (!Number.isFinite(b.x) || !Number.isFinite(b.y) || !Number.isFinite(b.angle)
          || !Number.isFinite(b.vx) || !Number.isFinite(b.vy) || !Number.isFinite(b.omega)) bad += 1;
        if (Math.hypot(b.vx, b.vy) > PHYS.MAX_SPEED + 1e-6) overspeed += 1;
        if (b.y > 1000) sank += 1;
      }
    }
  }
  check(`no NaN across ${seeds} monkey seeds`, bad === 0, `${bad} non-finite samples`);
  check('nothing exceeds MAX_SPEED', overspeed === 0, `${overspeed} samples`);
  check('nothing sinks through the ground', sank === 0, `${sank} samples`);
}
{
  // Bodies must be removable mid-sim without leaving dangling contacts.
  const w = withGround(createWorld());
  const boxes = [];
  for (let i = 0; i < 5; i += 1) boxes.push(addBox(w, { x: 600, y: 770 - i * 40, w: 60, h: 40, density: 1 }));
  for (let i = 0; i < 120; i += 1) substep(w, PHYS.SUBSTEP_DT);
  removeBody(w, boxes[2]);
  let threw = false;
  try { for (let i = 0; i < 480; i += 1) substep(w, PHYS.SUBSTEP_DT); } catch (e) { threw = true; }
  check('removing a mid-stack body is safe', !threw);
  check('stack recovers after a removal', boxes.filter((b, i) => i !== 2).every((b) => b.sleeping),
    `${boxes.filter((b, i) => i !== 2 && !b.sleeping).length} awake`);
}
{
  // contactImpulses is the damage signal the rules layer reads — a hard hit
  // must report a much larger impulse than a resting contact.
  const w = withGround(createWorld());
  const target = addBox(w, { x: 600, y: 770, w: 60, h: 60, density: 1 });
  settle(w, 5);
  substep(w, PHYS.SUBSTEP_DT);
  const resting = contactImpulses(w).get(target.id) ?? 0;

  const shot = addCircle(w, { x: 200, y: 740, r: 16, density: 6 });
  shot.vx = 1800;
  let peak = 0;
  for (let i = 0; i < 240; i += 1) {
    substep(w, PHYS.SUBSTEP_DT);
    peak = Math.max(peak, contactImpulses(w).get(target.id) ?? 0);
  }
  check('impact impulse exceeds resting impulse', peak > resting * 3,
    `peak ${peak.toFixed(0)} vs resting ${resting.toFixed(0)}`);
}

// ── Summary ─────────────────────────────────────────────────────────────────

console.log(`\n${passes} passed, ${failures} failed`);
process.exit(failures ? 1 : 0);