import Component from './component.js';
import EntityFactory from './entity-factory.js';
import System from './system.js';

export default class Ecs {

  $$caret = 1;

  diff = {};

  static Types = {};

  Types = {};

  $$entities = {};

  $$entityFactory = new EntityFactory();

  $$systems = [];

  constructor() {
    const {Types} = this.constructor;
    for (const i in Types) {
      this.Types[i] = Component(Types[i]).wrap(i, this);
    }
  }

  addSystem(source) {
    const system = System.wrap(source, this);
    this.$$systems.push(system);
    system.reindex(this.entities);
  }

  apply(patch) {
    const creating = [];
    const destroying = [];
    const removing = [];
    const updating = [];
    for (const entityId in patch) {
      const components = patch[entityId];
      if (false === components) {
        destroying.push(entityId);
        continue;
      }
      const componentsToRemove = [];
      const componentsToUpdate = {};
      for (const i in components) {
        if (false === components[i]) {
          componentsToRemove.push(i);
        }
        else {
          componentsToUpdate[i] = components[i];
        }
      }
      if (componentsToRemove.length > 0) {
        removing.push([entityId, componentsToRemove]);
      }
      if (this.$$entities[entityId]) {
        updating.push([entityId, componentsToUpdate]);
      }
      else {
        creating.push([entityId, componentsToUpdate]);
      }
    }
    this.destroyMany(destroying);
    this.insertMany(updating);
    this.removeMany(removing);
    this.createManySpecific(creating);
  }

  create(components = {}) {
    const [entityId] = this.createMany([components]);
    return entityId;
  }

  createMany(componentsList) {
    const specificsList = [];
    for (const components of componentsList) {
      specificsList.push([this.$$caret++, components]);
    }
    return this.createManySpecific(specificsList);
  }

  createManySpecific(specificsList) {
    const entityIds = [];
    const creating = {};
    for (let i = 0; i < specificsList.length; i++) {
      const [entityId, components] = specificsList[i];
      const componentKeys = [];
      for (const key of Object.keys(components)) {
        if (this.Types[key]) {
          componentKeys.push(key);
        }
      }
      entityIds.push(entityId);
      this.rebuild(entityId, () => componentKeys);
      for (const component of componentKeys) {
        if (!creating[component]) {
          creating[component] = [];
        }
        creating[component].push([entityId, components[component]]);
      }
      this.markChange(entityId, components);
    }
    for (const i in creating) {
      this.Types[i].createMany(creating[i]);
    }
    this.reindex(entityIds);
    return entityIds;
  }

  createSpecific(entityId, components) {
    return this.createManySpecific([[entityId, components]]);
  }

  deindex(entityIds) {
    for (let i = 0; i < this.$$systems.length; i++) {
      this.$$systems[i].deindex(entityIds);
    }
  }

  static deserialize(view) {
    const ecs = new this();
    let cursor = 0;
    const count = view.getUint32(cursor, true);
    const keys = Object.keys(ecs.Types);
    cursor += 4;
    const creating = new Map();
    const updating = new Map();
    const cursors = new Map();
    for (let i = 0; i < count; ++i) {
      const entityId = view.getUint32(cursor, true);
      if (!ecs.$$entities[entityId]) {
        creating.set(entityId, {});
      }
      cursor += 4;
      const componentCount = view.getUint16(cursor, true);
      cursor += 2;
      cursors.set(entityId, {});
      const addedComponents = [];
      for (let j = 0; j < componentCount; ++j) {
        const componentId = view.getUint16(cursor, true);
        cursor += 2;
        const component = keys[componentId];
        if (!component) {
          throw new Error(`can't decode component ${componentId}`);
        }
        if (!ecs.$$entities[entityId]) {
          creating.get(entityId)[component] = false;
        }
        else if (!ecs.$$entities[entityId].constructor.types.includes(component)) {
          addedComponents.push(component);
          if (!updating.has(component)) {
            updating.set(component, []);
          }
          updating.get(component).push([entityId, false]);
        }
        cursors.get(entityId)[component] = cursor;
        cursor += ecs.Types[component].constructor.schema.readSize(view, cursor);
      }
      if (addedComponents.length > 0 && ecs.$$entities[entityId]) {
        ecs.rebuild(entityId, (types) => types.concat(addedComponents));
      }
    }
    ecs.createManySpecific(Array.from(creating.entries()));
    for (const [component, entityIds] of updating) {
      ecs.Types[component].createMany(entityIds);
    }
    for (const [entityId, components] of cursors) {
      for (const component in components) {
        ecs.Types[component].deserialize(entityId, view, components[component]);
      }
    }
    return ecs;
  }

  destroy(entityId) {
    this.destroyMany([entityId]);
  }

  destroyAll() {
    this.destroyMany(this.entities);
  }

  destroyMany(entityIds) {
    const destroying = {};
    this.deindex(entityIds);
    for (const entityId of entityIds) {
      if (!this.$$entities[entityId]) {
        throw new Error(`can't destroy non-existent entity ${entityId}`);
      }
      for (const component of this.$$entities[entityId].constructor.types) {
        if (!destroying[component]) {
          destroying[component] = [];
        }
        destroying[component].push(entityId);
      }
      this.$$entities[entityId] = undefined;
      this.diff[entityId] = false;
    }
    for (const i in destroying) {
      this.Types[i].destroyMany(destroying[i]);
    }
  }

  get entities() {
    const it = Object.values(this.$$entities).values();
    return {
      [Symbol.iterator]() {
        return this;
      },
      next: () => {
        let result = it.next();
        while (!result.done && !result.value) {
          result = it.next();
        }
        if (result.done) {
          return {done: true, value: undefined};
        }
        return {done: false, value: result.value.id};
      },
    };
  }

  get(entityId) {
    return this.$$entities[entityId];
  }

  insert(entityId, components) {
    this.insertMany([[entityId, components]]);
  }

  insertMany(entities) {
    const inserting = {};
    const unique = new Set();
    for (const [entityId, components] of entities) {
      this.rebuild(entityId, (types) => [...new Set(types.concat(Object.keys(components)))]);
      const diff = {};
      for (const component in components) {
        if (!inserting[component]) {
          inserting[component] = [];
        }
        diff[component] = {};
        inserting[component].push([entityId, components[component]]);
      }
      unique.add(entityId);
      this.markChange(entityId, diff);
    }
    for (const component in inserting) {
      this.Types[component].insertMany(inserting[component]);
    }
    this.reindex(unique.values());
  }

  markChange(entityId, components) {
    // Deleted?
    if (false === components) {
      this.diff[entityId] = false;
    }
    // Created?
    else if (!this.diff[entityId]) {
      const filtered = {};
      for (const type in components) {
        filtered[type] = false === components[type]
          ? false
          : this.Types[type].constructor.filterDefaults(components[type]);
      }
      this.diff[entityId] = filtered;
    }
    // Otherwise, merge.
    else {
      for (const type in components) {
        this.diff[entityId][type] = false === components[type]
          ? false
          : this.Types[type].mergeDiff(
            this.diff[entityId][type] || {},
            components[type],
          );
      }
    }
  }

  rebuild(entityId, types) {
    let existing = [];
    if (this.$$entities[entityId]) {
      existing.push(...this.$$entities[entityId].constructor.types);
    }
    const Class = this.$$entityFactory.makeClass(types(existing), this.Types);
    this.$$entities[entityId] = new Class(entityId);
  }

  reindex(entityIds) {
    for (let i = 0; i < this.$$systems.length; i++) {
      this.$$systems[i].reindex(entityIds);
    }
  }

  remove(entityId, components) {
    this.removeMany([[entityId, components]]);
  }

  removeMany(entities) {
    const removing = {};
    const unique = new Set();
    for (const [entityId, components] of entities) {
      unique.add(entityId);
      const diff = {};
      for (const component of components) {
        diff[component] = false;
        if (!removing[component]) {
          removing[component] = [];
        }
        removing[component].push(entityId);
      }
      this.markChange(entityId, diff);
      this.rebuild(entityId, (types) => types.filter((type) => !components.includes(type)));
    }
    for (const component in removing) {
      this.Types[component].destroyMany(removing[component]);
    }
    this.reindex(unique.values());
  }

  removeSystem(SystemLike) {
    const index = this.$$systems.findIndex((system) => SystemLike === system.source);
    if (-1 !== index) {
      this.$$systems.splice(index, 1);
    }
  }

  static serialize(ecs, view) {
    if (!view) {
      view = new DataView(new ArrayBuffer(ecs.size()));
    }
    let cursor = 0;
    let entitiesWritten = 0;
    cursor += 4;
    const keys = Object.keys(ecs.Types);
    for (const entityId of ecs.entities) {
      const entity = ecs.get(entityId);
      entitiesWritten += 1;
      view.setUint32(cursor, entityId, true);
      cursor += 4;
      const entityComponents = entity.constructor.types;
      view.setUint16(cursor, entityComponents.length, true);
      const componentsWrittenIndex = cursor;
      cursor += 2;
      for (const component of entityComponents) {
        const instance = ecs.Types[component];
        view.setUint16(cursor, keys.indexOf(component), true);
        cursor += 2;
        instance.serialize(entityId, view, cursor);
        cursor += instance.sizeOf(entityId);
      }
      view.setUint16(componentsWrittenIndex, entityComponents.length, true);
    }
    view.setUint32(0, entitiesWritten, true);
    return view;
  }

  setClean() {
    this.diff = {};
  }

  size() {
    // # of entities.
    let size = 4;
    for (const entityId of this.entities) {
      size += this.get(entityId).size();
    }
    return size;
  }

  system(SystemLike) {
    return this.$$systems.find((system) => SystemLike === system.source)
  }

  tick(elapsed) {
    for (let i = 0; i < this.$$systems.length; i++) {
      this.$$systems[i].tick(elapsed);
    }
    for (let i = 0; i < this.$$systems.length; i++) {
      this.$$systems[i].finalize(elapsed);
    }
    this.tickDestruction();
  }

  tickDestruction() {
    const unique = new Set();
    for (let i = 0; i < this.$$systems.length; i++) {
      for (let j = 0; j < this.$$systems[i].destroying.length; j++) {
        unique.add(this.$$systems[i].destroying[j]);
      }
      this.$$systems[i].tickDestruction();
    }
    if (unique.size > 0) {
      this.destroyMany(unique.values());
    }
  }

}