tilt/shared/ai.js

import { RINK, randomIcePoint, rinkPenetration } from './rink.js';
import { SKATE, speedOf } from './skaterSim.js';
import { clamp } from './scalar.js';

/**
 * Waypoint AI.
 *
 * Deliberately dumb: pick a spot, steer at it, get out of everyone's way.
 * It exists to exercise the locomotion — the interesting question for this
 * spike is whether the *skating* reads, and a bot that just holds a direction
 * answers that better than one making tactical decisions.
 *
 * Everything is produced as a steering *intent*, never as a position fix, so
 * when a real controller or a puck-chasing brain replaces this the movement
 * layer underneath does not change at all.
 */

const AI = {
  /** Considered arrived inside this radius. */
  arriveR: 2.6,
  /** New waypoints are at least this far away, so bots commit to a line. */
  minTravel: 9,
  /** Repath anyway after this long, in case a waypoint became unreachable. */
  patience: 9,
  /** Start avoiding another skater inside this range. */
  personalSpace: 3.4,
  /** Weight of the avoidance push relative to the waypoint pull. */
  avoidGain: 1.5,
  /** Much weaker while racing for a puck — you contest it, you don't yield. */
  avoidChasing: 0.25,
  /** Seconds of velocity looked ahead when checking for boards. */
  boardLookahead: 0.9,
  /** Steer away once the lookahead point is within this of the boards. */
  boardMargin: 2.2,
  boardGain: 2.2,
  /** Slow down for the last stretch so they don't overshoot every waypoint. */
  easeR: 6,
};

export function createBrain(rand, opts = {}) {
  return {
    rand,
    target: null,
    age: 0,
    /** Personality: some bots cruise, some chase every waypoint flat out. */
    eagerness: opts.eagerness ?? (0.35 + rand() * 0.6),
    /** Small heading wobble so three bots on the same errand don't lockstep. */
    wobblePhase: rand() * Math.PI * 2,
    wobbleRate: 0.5 + rand() * 0.7,
  };
}

function pickWaypoint(brain, from) {
  for (let i = 0; i < 12; i++) {
    const p = randomIcePoint(brain.rand, 3.5);
    if (Math.hypot(p.x - from.x, p.z - from.z) >= AI.minTravel) return p;
  }
  return randomIcePoint(brain.rand, 3.5);
}

/**
 * Produce this frame's intent for one skater.
 *
 * @param {object} brain   from createBrain
 * @param {object} s       skater state (mutated: ix, iz, sprint)
 * @param {object[]} others other skater states to keep clear of
 * @param {number} dt
 */
export function steer(brain, s, others, dt, play = null) {
  brain.age += dt;

  // ---- what am I doing --------------------------------------------------
  // With a puck on the ice there is something to want. Without one this falls
  // back to wandering, which is what spike 1 did and is still what happens
  // between whistles.
  if (play?.puck) {
    const mine = play.carrier === s.id;
    const teammateHas = play.carrier != null && play.carrierTeam === s.team && !mine;
    // Only the closest skater on each side actually goes for it. Letting all
    // six chase does produce contact, but it also produces a single moving
    // scrum with nobody anywhere else on the ice, which reads as a bug rather
    // than as hockey.
    const chaser = play.chaser?.[s.team] === s.id;
    if (mine) {
      // Carrying: head for open ice up the attacking end.
      const attackX = s.team === 0 ? RINK.halfX * 0.7 : -RINK.halfX * 0.7;
      brain.target = { x: attackX, z: clamp(play.puck.z * 0.6, -RINK.halfZ * 0.6, RINK.halfZ * 0.6) };
      brain.age = 0;
    } else if (chaser) {
      // Go and get it. This is what makes contact happen on its own.
      brain.target = { x: play.puck.x, z: play.puck.z };
      brain.age = 0;
    } else {
      // Everyone else finds space: ahead of the puck when their side has it,
      // between the puck and their own end when it does not.
      const dir = s.team === 0 ? 1 : -1;
      const depth = teammateHas ? RINK.halfX * 0.42 : -RINK.halfX * 0.18;
      const side = s.id % 2 === 0 ? 1 : -1;
      brain.target = {
        x: clamp(play.puck.x + dir * depth, -RINK.halfX * 0.85, RINK.halfX * 0.85),
        z: clamp(play.puck.z + side * RINK.halfZ * 0.55, -RINK.halfZ * 0.8, RINK.halfZ * 0.8),
      };
      brain.age = 0;
    }
  }

  const reached = brain.target
    && Math.hypot(brain.target.x - s.x, brain.target.z - s.z) < AI.arriveR;
  if (!brain.target || (reached && !play?.puck) || brain.age > AI.patience) {
    brain.target = pickWaypoint(brain, s);
    brain.age = 0;
  }

  // ---- pull toward the waypoint ------------------------------------------
  let dx = brain.target.x - s.x;
  let dz = brain.target.z - s.z;
  const dist = Math.hypot(dx, dz) || 1e-6;
  dx /= dist;
  dz /= dist;

  // ---- push away from other skaters --------------------------------------
  // Box3D resolves the actual bump; this only stops the bots from queueing up
  // to walk through each other, which looks like a bug even when it isn't.
  //
  // Chasing a loose puck is the exception, and an important one: at full
  // avoidance six skaters converging on the same puck politely peel off before
  // they ever touch, and the entire hit system never fires in normal play.
  // Competing for a puck means being willing to skate into somebody.
  const avoid = play?.puck && play.chaser?.[s.team] === s.id ? AI.avoidChasing : AI.avoidGain;
  for (const o of others) {
    if (o === s) continue;
    const ox = s.x - o.x;
    const oz = s.z - o.z;
    const d = Math.hypot(ox, oz);
    if (d >= AI.personalSpace || d < 1e-4) continue;
    const w = (1 - d / AI.personalSpace) * avoid;
    dx += (ox / d) * w;
    dz += (oz / d) * w;
  }

  // ---- push away from the boards -----------------------------------------
  // Checked against where they will be, not where they are: on ice, noticing
  // the boards at arm's length is already too late.
  const ahead = AI.boardLookahead;
  const pen = rinkPenetration(s.x + s.vx * ahead, s.z + s.vz * ahead, SKATE.radius);
  if (pen.dist > -AI.boardMargin) {
    const w = clamp((pen.dist + AI.boardMargin) / AI.boardMargin, 0, 1) * AI.boardGain;
    dx += pen.nx * w;
    dz += pen.nz * w;
  }

  // ---- wobble + normalise -------------------------------------------------
  brain.wobblePhase += brain.wobbleRate * dt;
  const wob = Math.sin(brain.wobblePhase) * 0.12;
  const len = Math.hypot(dx, dz) || 1e-6;
  const yaw = Math.atan2(dx / len, dz / len) + wob;
  s.ix = Math.sin(yaw);
  s.iz = Math.cos(yaw);

  // Ease off approaching the waypoint, and only sprint on the long straights.
  // Chasing a puck is the exception: you do not coast in on a loose puck, you
  // get there first, so the ease and the arrival brake are both dropped.
  const chasing = !!play?.puck && play.chaser?.[s.team] === s.id;
  const ease = chasing ? 1 : clamp(dist / AI.easeR, 0.25, 1);
  s.ix *= ease;
  s.iz *= ease;
  s.sprint = chasing ? dist > 2 : (dist > AI.easeR * 1.5 && brain.eagerness > 0.5);
  // Hard stop rather than a lazy drift when arriving hot.
  s.brake = !chasing && dist < AI.arriveR * 1.4 && speedOf(s) > 4.5;
}

/**
 * Starting lineup: each team in its own half, everyone facing centre ice.
 *
 * Laid out like a faceoff rather than scattered at random, because that is the
 * arrangement every later spike starts from — drop a puck at centre and this is
 * already the right picture. Ordered team by team, so index `i` belongs to
 * team `Math.floor(i / perTeam)` and the returned `team` field agrees.
 *
 * The depth pattern is one skater up, the rest spread behind: with three a side
 * that reads as a forward and two defenders without encoding any positional
 * rules the game does not have yet.
 */
export function spawnLineup(perTeam = 3, teams = 2) {
  const out = [];
  for (let t = 0; t < teams; t++) {
    // Team 0 defends the -X end, team 1 the +X end.
    const sign = t === 0 ? -1 : 1;
    for (let i = 0; i < perTeam; i++) {
      const lead = i === 0;
      const x = sign * (lead ? RINK.halfX * 0.18 : RINK.halfX * 0.42);
      // Fan the back line across the width; a single one sits on the centre.
      const back = perTeam > 1 ? (i - 1) / Math.max(1, perTeam - 2) : 0.5;
      const z = lead ? 0 : (back * 2 - 1) * RINK.halfZ * 0.55;
      out.push({ x, z, yaw: Math.atan2(-x, -z), team: t });
    }
  }
  return out;
}