/* ISLE SLINGERS -- physics/step/index.js (submodule: step)
 * RC-375D84 S-2 modularization (behavior-neutral split of the original
 * js/core.js monolith). Installs its units into ONE shared physics scope `P`
 * that every physics submodule sees -- the same single-scope semantics the
 * monolith had. Must load before js/physics/index.js (the aggregator that
 * attaches the public ISLE_CORE API). Surface installed: step, stepPhysics, spendBird.
 */
(function (root, factory) {
  var part = factory();
  if (typeof module !== 'undefined' && module.exports) module.exports = part;
  else (root.ISLE_PHYSICS_PARTS = root.ISLE_PHYSICS_PARTS || []).push(part);
})(typeof globalThis !== 'undefined' ? globalThis : this, function () {
  'use strict';
  return function (P) {
  P.step = function(g, dt) {
    g.time += dt;
    if (g.status === 'won' || g.status === 'lost') {
      // S-5: the level is over -- landed bodies no longer exist (their window
      // was "while another bird was active"), so remove them; the rest of the
      // world still settles a beat for the win/lose screen.
      for (var lb = 0; lb < g.birds.length; lb++) {
        if (g.birds[lb].state === 'landed') {
          g.birds[lb].state = 'spent';
          g.events.push({ type: 'bird_gone', x: g.birds[lb].x, y: g.birds[lb].y });
        }
      }
      P.stepPhysics(g, dt);
      P.updatePopups(g, dt);
      P.decayCamera(g, dt);
      return;
    }
    P.stepPhysics(g, dt);
    P.updatePopups(g, dt);
    P.decayCamera(g, dt);
    P.updateCameraTarget(g);
    P.checkEndStates(g);
  }

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

    // active bird flight
    b = P.activeBird(g);
    if (b && b.state === 'flying') {
      b.age += dt;
      var nvy = b.vy + P.GRAVITY * dt;
      b.x += b.vx * dt;
      b.y += (b.vy + nvy) * 0.5 * dt;
      b.vx *= P.AIR_DRAG;
      b.vy = nvy;
      g.stats.distance = Math.max(g.stats.distance, b.x);
      P.collideBirdWorld(g, b);
      P.collideBirdBlocks(g, b);
      P.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 < P.REST_SPEED) b.settleTimer += dt;
      else b.settleTimer = Math.max(0, b.settleTimer - dt * 4);
      if (b.age > P.BIRD_MAX_AGE || b.x > P.WORLD.w + 200 || b.x < -200) {
        // gone for good (off the island or aged out) -> spent, next bird loads
        P.spendBird(g, b);
      } else if (b.settleTimer > P.SETTLE_TIME) {
        // S-5 (RC-375D84, Q2): the "another bird is already active" window.
        // A bird that settles while MORE birds are in play (queued or active)
        // is NOT a corpse: it becomes a LANDED body -- real continuous
        // gravity, no lifetime timer. It falls if its support breaks,
        // chain-damages blocks it lands on, and can kill enemies, for as long
        // as the level runs. The level-end rule (last bird, no window left)
        // keeps the pre-S-5 behaviour exactly: the bird is spent there, so
        // win/lose resolve unchanged.
        // ANOTHER bird must be in play (queued, or flying/aiming): the settled
        // bird lingers only during the "another bird is already active" window.
        // It never counts itself -- for the LAST bird this stays false and the
        // pre-S-5 spend path runs exactly as before (win/lose unchanged).
        var moreBirds = P.birdsRemaining(g) > 0;
        if (!moreBirds) {
          for (var ob = 0; ob < g.birds.length; ob++) {
            if (ob === g.birds.indexOf(b)) continue;
            if (g.birds[ob].state === 'flying' || g.birds[ob].state === 'landed' || g.birds[ob].state === 'aiming') { moreBirds = true; break; }
          }
        }
        if (moreBirds) {
          b.state = 'landed';
          b.vx = 0; b.vy = 0;
          g.events.push({ type: 'bird_landed', x: b.x, y: b.y, kind: b.kind });
          P.advanceToNextBird(g);
        } else {
          P.spendBird(g, b);
        }
      }
    }

    // S-5: landed birds stay physical bodies -- real gravity, fall when their
    // support breaks, hit blocks (chain damage) and enemies (kills). No
    // lifetime timer: they live until the level resolves.
    for (i = 0; i < g.birds.length; i++) {
      var lb = g.birds[i];
      if (lb.state !== 'landed') continue;
      var lvy = lb.vy + P.GRAVITY * dt;
      lb.x += lb.vx * dt;
      lb.y += (lb.vy + lvy) * 0.5 * dt;
      lb.vy = lvy;
      lb.vx *= 0.999; // a landed body keeps (almost) all of its momentum
      P.collideBirdWorld(g, lb);
      P.collideBirdBlocks(g, lb);
      P.collideBirdEnemies(g, lb);
    }

    // blocks: gravity + integration + collisions
    for (i = 0; i < g.blocks.length; i++) {
      var bl = g.blocks[i];
      if (bl.hp <= 0) continue;
      if (bl.pivoting) continue; // rotate about its pivot; integrated by toppleBlocks
      bl.vy = Math.min(bl.vy + P.GRAVITY * dt, P.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 > P.WORLD.ground) {
        var impact = bl.vy;
        bl.y = P.WORLD.ground - halfH;
        if (impact > 90) {
          bl.vy = -impact * P.MATERIALS[bl.mat].restitution;
          bl.vx *= 0.8;
          if (impact > 240) {
            P.damageBlock(g, bl, (impact - 240) * 0.45, 'ground');
            g.events.push({ type: 'block_impact', x: bl.x, y: P.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 > P.WORLD.w) { bl.x = P.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 || a.pivoting) continue;
        for (j = i + 1; j < g.blocks.length; j++) {
          c = g.blocks[j];
          if (c.hp <= 0 || c.pivoting) continue;
          P.resolveBoxPair(g, a, c);
        }
      }
    }
    // block tip/topple (S-3): rotate about a support-edge pivot, land, impact
    P.toppleBlocks(g, dt);
    // block vs bird (crush) -- S-5: the active bird AND any landed bodies
    for (i = 0; i < g.birds.length; i++) {
      var cb = g.birds[i];
      if (cb.state !== 'flying' && cb.state !== 'landed') continue;
      for (var ci = 0; ci < g.blocks.length; ci++) {
        var blk = g.blocks[ci];
        if (blk.hp <= 0 || blk.pivoting) continue;
        P.crushCircleVsBox(g, blk, cb, 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 + P.GRAVITY * dt, 700);
      e.x += e.vx * dt;
      e.y += e.vy * dt;
      e.vx *= 0.9;
      if (e.y + e.r > P.WORLD.ground) {
        if (e.vy > 420) { e.vy = -e.vy * 0.25; e.vx *= 0.6; }
        else { e.vy = 0; e.y = P.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 || bb.pivoting) continue;
        P.crushCircleVsBox(g, bb, e, true);
      }
    }
  }
  // next bird onto the sling (shared by spendBird and the S-5 landed
  // transition -- the same "another bird is already active" moment)
  P.advanceToNextBird = function(g) {
    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 });
    }
  }

  P.spendBird = function(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
    P.advanceToNextBird(g);
  }
  };
});