import Digraph from '@/util/digraph.js';

import Query from './query.js';

export default class System {

  active = false;

  destroying = [];

  ecs;

  elapsed = 0;

  frequency;

  queries = {};

  constructor(ecs) {
    this.ecs = ecs;
    const queries = this.constructor.queries();
    for (const i in queries) {
      this.queries[i] = new Query(queries[i], ecs);
    }
    this.reindex(ecs.entities);
  }

  createEntity(components) {
    return this.ecs.create(components);
  }

  createManyEntities(componentsList) {
    return this.ecs.createMany(componentsList);
  }

  deindex(entityIds) {
    for (const i in this.queries) {
      this.queries[i].deindex(entityIds);
    }
  }

  destroyEntity(entityId) {
    this.destroyManyEntities([entityId]);
  }

  destroyManyEntities(entityIds) {
    for (let i = 0; i < entityIds.length; i++) {
      this.destroying.push(entityIds[i]);
    }
  }

  async insertComponents(entityId, components) {
    return this.ecs.insert(entityId, components);
  }

  async insertManyComponents(components) {
    return this.ecs.insertMany(components);
  }

  static get priority() {
    return {
      phase: 'normal',
    }
  }

  static queries() {
    return {};
  }

  reindex(entityIds) {
    for (const i in this.queries) {
      this.queries[i].reindex(entityIds);
    }
  }

  removeComponents(entityId, components) {
    this.ecs.remove(entityId, components);
  }

  removeManyComponents(entityIds) {
    this.ecs.removeMany(entityIds);
  }

  select(query) {
    return this.queries[query].select();
  }

  static sort(Systems) {
    const phases = {
      'pre': new Digraph(),
      'normal': new Digraph(),
      'post': new Digraph(),
    };
    for (const systemName in Systems) {
      const {priority} = Systems[systemName];
      const phase = phases[priority.phase || 'normal'];
      phase.ensureTail(systemName);
      if (priority.before) {
        for (const before of Array.isArray(priority.before) ? priority.before : [priority.before]) {
          phase.addDependency(before, systemName);
        }
      }
      if (priority.after) {
        for (const after of Array.isArray(priority.after) ? priority.after : [priority.after]) {
          phase.addDependency(systemName, after);
        }
      }
    }
    const sorted = [
      ...phases['pre'].sort(),
      ...phases['normal'].sort(),
      ...phases['post'].sort(),
    ];
    return Object.fromEntries(
      Object.entries(Systems)
        .toSorted(([l], [r]) => sorted.indexOf(l) - sorted.indexOf(r)),
    );
  }

  tickDestruction() {
    if (this.destroying.length > 0) {
      this.deindex(this.destroying);
    }
    this.destroying = [];
  }

  tick() {}

}