TURNCRAFT/src/machines/tonearm.ts

// LANE D — tonearm machine ×2 (D3).
// A rigid arm pivoting about a rear pedestal. While the deck plays AND the
// stylus is fitted, it cues to the outer groove then tracks slowly inward
// (~TRACK_SECONDS for a full pass) before auto-returning to rest. The headshell
// is the "needle plow": a slow kinematic aabb that pushes the player along.

import * as THREE from 'three';
import { PLATTER, Y_RECORD_TOP } from '../core/constants';
import { bus } from '../core/events';
import type { ColliderShape, KinematicCollider, Vec3 } from '../core/types';
import { MachineBase } from './machine';
import { blockMaterial } from './util';

const HEAD_Y = Y_RECORD_TOP + 2.6;   // hovers above the vinyl, clearing the mid terrace
const R_INNER = 16;                   // inner groove — stays outside the label
                                      // plateau (r 14, top +2) and the tower
const R_OUTER = PLATTER.recordRadius - 3; // outer groove
const R_REST = PLATTER.radius + 1;    // parked just off the platter rim
const TRACK_SECONDS = 240;            // ~4 min for a full inward pass
const CUE_SECONDS = 1.6;              // drop-to-outer-groove cue time
const RETURN_RATE = 0.6;              // rad/s auto-return sweep

type State = 'rest' | 'cueing' | 'tracking' | 'returning';

export class Tonearm extends MachineBase {
  readonly deck: 'A' | 'B';
  /** Wired by createMachines to the deck's platter. */
  deckPlaying: () => boolean = () => false;

  private readonly px: number;
  private readonly pz: number;
  private readonly L: number;         // rigid arm length (pivot → headshell)
  private readonly baseX: number;     // unit baseline dir (pivot → spindle), xz
  private readonly baseZ: number;
  private readonly sign: 1 | -1;      // which side of the baseline the arm swings
  private readonly phiRest: number;
  private readonly phiOuter: number;

  private state: State = 'rest';
  private phi: number;                // current sweep angle from baseline
  private trackT = 0;                 // 0..1 inward progress while tracking
  private stylus: boolean;

  private readonly head: Vec3 = [0, 0, 0];
  private readonly prevHead: Vec3 = [0, 0, 0];
  private readonly headVel: Vec3 = [0, 0, 0];
  private headInit = false;

  private readonly tube: THREE.Mesh;
  private readonly headGroup = new THREE.Group();
  private readonly stylusMesh: THREE.Mesh;
  private readonly counterweight: THREE.Mesh;
  private readonly headShape: { kind: 'aabb'; min: Vec3; max: Vec3 };
  // The arm is a chain of small AABBs tiling the pivot→head line (the brief's
  // "2–3 segment aabb chain"). A single endpoint-bounding box would balloon into
  // a huge phantom collider over the rideable record when the arm is diagonal.
  private readonly armSegs: { kind: 'aabb'; min: Vec3; max: Vec3 }[] = [];
  private static readonly ARM_SEGMENTS = 3;

  constructor(deck: 'A' | 'B', spindleX: number, spindleZ: number, pivot: Vec3, initialStylus: boolean) {
    super(`tonearm${deck}`);
    this.deck = deck;
    this.px = pivot[0];
    this.pz = pivot[2];
    this.stylus = initialStylus;

    const dx = spindleX - this.px;
    const dz = spindleZ - this.pz;
    const D = Math.hypot(dx, dz);
    this.baseX = dx / D;
    this.baseZ = dz / D;
    this.L = D - R_INNER;               // φ=0 lands the headshell at the inner groove
    this.phiRest = this.solvePhi(D, R_REST);
    this.phiOuter = this.solvePhi(D, R_OUTER);

    // Pick the swing side that carries the headshell toward the front (−z).
    const testZ = (s: 1 | -1) => this.rotZ(this.baseX, this.baseZ, s * this.phiOuter);
    this.sign = testZ(1) < testZ(-1) ? 1 : -1;

    this.phi = this.phiRest;

    // ---- Colliders (positions filled by first update) ----
    this.headShape = { kind: 'aabb', min: [0, 0, 0], max: [0, 0, 0] };
    const headCollider: KinematicCollider = {
      id: `${this.id}_head`,
      shape: this.headShape as ColliderShape,
      velocityAt: () => [this.headVel[0], this.headVel[1], this.headVel[2]],
    };
    this.colliders = [headCollider];
    for (let i = 0; i < Tonearm.ARM_SEGMENTS; i++) {
      const seg = { kind: 'aabb' as const, min: [0, 0, 0] as Vec3, max: [0, 0, 0] as Vec3 };
      this.armSegs.push(seg);
      this.colliders.push({
        id: `${this.id}_arm${i}`,
        shape: seg as ColliderShape,
        velocityAt: () => [this.headVel[0] * 0.4, 0, this.headVel[2] * 0.4],
      });
    }

    // ---- Visuals ----
    const chrome = blockMaterial(11);            // chrome
    const dark = blockMaterial(5);               // matte_black counterweight

    const pedestal = new THREE.Mesh(new THREE.CylinderGeometry(2.2, 2.6, 8, 16), chrome);
    pedestal.position.set(this.px, HEAD_Y - 3, this.pz);
    this.group.add(pedestal);

    this.tube = new THREE.Mesh(new THREE.CylinderGeometry(0.7, 0.7, 1, 12), chrome);
    this.group.add(this.tube);

    const cw = new THREE.Mesh(new THREE.CylinderGeometry(2.6, 2.6, 4, 16), dark);
    cw.rotation.z = Math.PI / 2; // counterweight, positioned each frame with the arm

    const headBody = new THREE.Mesh(new THREE.BoxGeometry(3, 2.4, 2.4), dark);
    this.headGroup.add(headBody);
    this.stylusMesh = new THREE.Mesh(new THREE.ConeGeometry(0.5, 2.2, 10), chrome);
    this.stylusMesh.position.y = -1.8;
    this.stylusMesh.visible = this.stylus;
    this.headGroup.add(this.stylusMesh);
    this.group.add(this.headGroup);

    this.counterweight = cw;
    this.group.add(cw);

    this.tickGeometry(0); // place everything for frame 0
  }

  /** Angle from the baseline so the headshell sits at radius r from the spindle. */
  private solvePhi(D: number, r: number): number {
    const c = (D * D + this.L * this.L - r * r) / (2 * D * this.L);
    return Math.acos(Math.max(-1, Math.min(1, c)));
  }

  /** z-component of baseline rotated by angle a about +Y (for side selection). */
  private rotZ(vx: number, vz: number, a: number): number {
    return -vx * Math.sin(a) + vz * Math.cos(a);
  }

  setStylus(on: boolean): void {
    this.stylus = on;
    this.stylusMesh.visible = on;
    if (on) bus.emit('machine:interact', { machineId: this.id, action: 'stylus_fitted' });
  }

  hasStylus(): boolean { return this.stylus; }

  private enabled(): boolean { return this.stylus && this.deckPlaying(); }

  update(dt: number): void {
    // ---- State machine over the sweep angle φ ----
    switch (this.state) {
      case 'rest':
        if (this.enabled()) { this.state = 'cueing'; }
        break;
      case 'cueing': {
        // Lerp rest → outer over CUE_SECONDS.
        const step = (this.phiRest - this.phiOuter) * (dt / CUE_SECONDS);
        this.phi -= step;
        if (this.phi <= this.phiOuter) { this.phi = this.phiOuter; this.state = 'tracking'; this.trackT = 0; }
        if (!this.enabled()) this.state = 'returning';
        break;
      }
      case 'tracking':
        this.trackT = Math.min(1, this.trackT + dt / TRACK_SECONDS);
        this.phi = this.phiOuter * (1 - this.trackT); // → 0 (inner) as trackT → 1
        if (!this.enabled() || this.trackT >= 1) this.state = 'returning';
        break;
      case 'returning':
        this.phi += RETURN_RATE * dt;
        if (this.phi >= this.phiRest) { this.phi = this.phiRest; this.state = 'rest'; }
        break;
    }
    this.tickGeometry(dt);
  }

  /** Recompute headshell world pos, arm transform, colliders, and velocity. */
  private tickGeometry(dt: number): void {
    const a = this.sign * this.phi;
    // Direction pivot→headshell = baseline rotated by a.
    const dirX = this.baseX * Math.cos(a) + this.baseZ * Math.sin(a);
    const dirZ = -this.baseX * Math.sin(a) + this.baseZ * Math.cos(a);
    const hx = this.px + dirX * this.L;
    const hz = this.pz + dirZ * this.L;
    this.head[0] = hx; this.head[1] = HEAD_Y; this.head[2] = hz;

    // Headshell velocity (finite difference; zero on first frame).
    if (this.headInit && dt > 0) {
      this.headVel[0] = (hx - this.prevHead[0]) / dt;
      this.headVel[1] = 0;
      this.headVel[2] = (hz - this.prevHead[2]) / dt;
    } else {
      this.headVel[0] = this.headVel[1] = this.headVel[2] = 0;
    }
    this.prevHead[0] = hx; this.prevHead[1] = HEAD_Y; this.prevHead[2] = hz;
    this.headInit = true;

    // Headshell group + stylus.
    this.headGroup.position.set(hx, HEAD_Y, hz);

    // Tube: unit cylinder scaled to length L, midpoint pivot↔head.
    const mx = (this.px + hx) / 2, mz = (this.pz + hz) / 2;
    this.tube.position.set(mx, HEAD_Y, mz);
    this.tube.scale.set(1, this.L, 1);
    const dir = _dir.set(hx - this.px, 0, hz - this.pz).normalize();
    this.tube.quaternion.setFromUnitVectors(UP, dir);

    // Counterweight behind the pivot.
    this.counterweight.position.set(this.px - dir.x * 6, HEAD_Y, this.pz - dir.z * 6);

    // Headshell aabb (the plow).
    setAabb(this.headShape, hx, HEAD_Y, hz, 2, 2.6, 2);

    // Arm collider chain: tile the pivot→head line in N small AABBs so the box
    // hugs the diagonal tube instead of enclosing the whole bounding rectangle.
    const n = Tonearm.ARM_SEGMENTS;
    for (let i = 0; i < n; i++) {
      const t0 = i / n, t1 = (i + 1) / n;
      const x0 = this.px + (hx - this.px) * t0, z0 = this.pz + (hz - this.pz) * t0;
      const x1 = this.px + (hx - this.px) * t1, z1 = this.pz + (hz - this.pz) * t1;
      const s = this.armSegs[i];
      s.min[0] = Math.min(x0, x1) - 1; s.max[0] = Math.max(x0, x1) + 1;
      s.min[1] = HEAD_Y - 1.5;         s.max[1] = HEAD_Y + 1.5;
      s.min[2] = Math.min(z0, z1) - 1; s.max[2] = Math.max(z0, z1) + 1;
    }
  }
}

const _dir = new THREE.Vector3(); // scratch, reused each tick (fix #5)

const UP = new THREE.Vector3(0, 1, 0);

function setAabb(s: { min: Vec3; max: Vec3 }, cx: number, cy: number, cz: number, hx: number, hy: number, hz: number): void {
  s.min[0] = cx - hx; s.min[1] = cy - hy; s.min[2] = cz - hz;
  s.max[0] = cx + hx; s.max[1] = cy + hy; s.max[2] = cz + hz;
}