/**
 * LANE-RENDER — build ghost. Shows the selected machine at the hovered tile:
 * cyan when it fits, red when its footprint collides with something already placed.
 *
 * Occupancy is read straight off the snapshot's entity footprints — the sim still gets
 * the final say when the place command lands; this is only the player's preview.
 */
import * as THREE from 'three';
import type { Dir, MachineDef, SimSnapshot, Vec2 } from '../contracts';
import { AssetRegistry } from './registry';
import { centerOf, tileKey, tilesOf, yawFor } from './coords';
import { idleOf, type IdleFn } from './registry';
import { WORLD_HALF } from './camera';

const VALID = 0x3fd4ff;
const INVALID = 0xff3b30;

function ghostMaterial(color: number): THREE.MeshStandardMaterial {
  return new THREE.MeshStandardMaterial({
    color,
    emissive: color,
    emissiveIntensity: 0.85,
    transparent: true,
    opacity: 0.42,
    depthWrite: false,
    roughness: 0.4,
  });
}

export class GhostLayer {
  readonly group = new THREE.Group();
  private obj: THREE.Object3D | null = null;
  private objDef: string | null = null;
  private objVersion = -1;
  /** GLB clones share the template's geometry — only dispose what we built ourselves. */
  private owns = false;
  private idle: IdleFn | null = null;
  private def: MachineDef | null = null;
  private pos: Vec2 | null = null;
  private dir: Dir = 0;
  private occupied = new Set<number>();
  private matValid = ghostMaterial(VALID);
  private matInvalid = ghostMaterial(INVALID);

  constructor(private registry: AssetRegistry, private defs: Map<string, MachineDef>) {
    this.group.name = 'ghost';
    this.group.renderOrder = 10;
  }

  set(defId: string | null, pos: Vec2 | null, dir: Dir): void {
    const def = defId ? this.defs.get(defId) ?? null : null;
    this.def = def;
    this.pos = def && pos ? pos : null;
    this.dir = dir;

    if (!def || !this.pos) {
      this.group.visible = false;
      return;
    }
    const entry = this.registry.get(def.asset);
    if (!entry) {
      this.group.visible = false;
      return;
    }
    if (!this.obj || this.objDef !== def.id || this.objVersion !== entry.version) {
      this.rebuild(def);
      this.objDef = def.id;
      this.objVersion = entry.version;
    }
    this.group.visible = true;
  }

  private rebuild(def: MachineDef): void {
    this.drop();
    const entry = this.registry.get(def.asset)!;
    const obj = entry.create();
    this.owns = !entry.isGLB;
    this.idle = idleOf(obj);
    // Replace (never mutate) materials: a hot-swapped GLB's materials are shared
    // with every placed copy of that machine.
    obj.traverse((o) => {
      const m = o as THREE.Mesh;
      if (!m.isMesh) return;
      m.material = this.matValid;
      m.castShadow = m.receiveShadow = false;
    });
    this.group.add(obj);
    this.obj = obj;
  }

  private drop(): void {
    if (!this.obj) return;
    this.group.remove(this.obj);
    if (this.owns) {
      this.obj.traverse((o) => {
        const m = o as THREE.Mesh;
        if (m.isMesh) m.geometry?.dispose(); // materials here are the shared ghost mats
      });
    }
    this.obj = null;
  }

  update(snap: SimSnapshot, timeSec: number): void {
    if (!this.group.visible || !this.def || !this.pos || !this.obj) return;

    this.occupied.clear();
    for (const e of snap.entities) {
      const d = this.defs.get(e.def);
      if (!d) continue;
      for (const t of tilesOf(e.pos, d, e.dir)) this.occupied.add(tileKey(t.x, t.y));
    }

    const want = tilesOf(this.pos, this.def, this.dir);
    const ok = want.every(
      (t) =>
        !this.occupied.has(tileKey(t.x, t.y)) &&
        t.x >= -WORLD_HALF && t.x < WORLD_HALF &&
        t.y >= -WORLD_HALF && t.y < WORLD_HALF,
    );
    const mat = ok ? this.matValid : this.matInvalid;
    this.obj.traverse((o) => {
      const m = o as THREE.Mesh;
      if (m.isMesh) m.material = mat;
    });

    centerOf(this.pos, this.def, this.dir, this.obj.position);
    this.obj.position.y += 0.02;
    this.obj.rotation.y = yawFor(this.dir);
    this.idle?.(timeSec);
  }
}