import {RESOLUTION} from '@/constants.js'
import {System} from '@/ecs/index.js';

class SpatialHash {

  constructor({x, y}) {
    this.area = {x, y};
    this.chunkSize = {x: RESOLUTION.x / 2, y: RESOLUTION.y / 2};
    this.chunks = Array(Math.ceil(this.area.x / this.chunkSize.x))
      .fill(0)
      .map(() => (
        Array(Math.ceil(this.area.y / this.chunkSize.y))
        .fill(0)
        .map(() => [])
      ));
    this.data = {};
  }

  clamp(x, y) {
    return [
      Math.max(0, Math.min(x, this.area.x - 1)),
      Math.max(0, Math.min(y, this.area.y - 1))
    ];
  }

  chunkIndex(x, y) {
    const [cx, cy] = this.clamp(x, y);
    return [
      Math.floor(cx / this.chunkSize.x),
      Math.floor(cy / this.chunkSize.y),
    ];
  }

  remove(datum) {
    if (datum in this.data) {
      for (const [cx, cy] of this.data[datum]) {
        const chunk = this.chunks[cx][cy];
        chunk.splice(chunk.indexOf(datum), 1);
      }
    }
    this.data[datum] = [];
  }

  update({x0, x1, y0, y1}, datum) {
    this.remove(datum);
    for (const [x, y] of [[x0, y0], [x0, y1], [x1, y0], [x1, y1]]) {
      const [cx, cy] = this.chunkIndex(x, y);
      this.data[datum].push([cx, cy]);
      this.chunks[cx][cy].push(datum);
    }
  }

}

export default class UpdateSpatialHash extends System {

  deindex(entities) {
    super.deindex(entities);
    for (const id of entities) {
      this.hash.remove(id);
    }
  }

  reindex(entities) {
    for (const id of entities) {
      if (1 === id) {
        this.hash = new SpatialHash(this.ecs.get(1).AreaSize);
      }
    }
    super.reindex(entities);
    for (const id of entities) {
      this.updateHash(this.ecs.get(id));
    }
  }

  updateHash(entity) {
    if (!entity.VisibleAabb) {
      return;
    }
    this.hash.update(entity.VisibleAabb, entity.id);
  }

  tick() {
    for (const entity of this.ecs.changed(['VisibleAabb'])) {
      this.updateHash(entity);
    }
  }

  nearby(entity) {
    const [cx0, cy0] = this.hash.chunkIndex(
      entity.Position.x - RESOLUTION.x * 0.75,
      entity.Position.y - RESOLUTION.x * 0.75,
    );
    const [cx1, cy1] = this.hash.chunkIndex(
      entity.Position.x + RESOLUTION.x * 0.75,
      entity.Position.y + RESOLUTION.x * 0.75,
    );
    const nearby = new Set();
    for (let cy = cy0; cy <= cy1; ++cy) {
      for (let cx = cx0; cx <= cx1; ++cx) {
        this.hash.chunks[cx][cy].forEach((id) => {
          nearby.add(this.ecs.get(id));
        });
      }
    }
    return nearby;
  }

}