import Schema from './schema.js';

export default class Component {

  data = [];
  ecs;
  Instance;
  map = {};
  pool = [];
  static properties = {};
  static $$schema;

  constructor(ecs) {
    this.ecs = ecs;
    this.Instance = this.instanceFromSchema();
  }

  allocateMany(count) {
    const results = [];
    while (count > 0) {
      results.push(
        this.pool.length > 0
          ? this.pool.pop()
          : this.data.push(new this.Instance()) - 1,
      )
      count -= 1;
    }
    return results;
  }

  async create(entityId, values) {
    const [created] = await this.createMany([[entityId, values]]);
    return created;
  }

  async createMany(entries) {
    if (0 === entries.length) {
      return [];
    }
    const allocated = this.allocateMany(entries.length);
    const {properties} = this.constructor.schema.specification;
    const keys = Object.keys(properties);
    const promises = [];
    for (let i = 0; i < entries.length; ++i) {
      const [entityId, values = {}] = entries[i];
      this.map[entityId] = allocated[i];
      this.data[allocated[i]].entity = entityId;
      for (let k = 0; k < keys.length; ++k) {
        const j = keys[k];
        const {defaultValue} = properties[j];
        const instance = this.data[allocated[i]];
        if (j in values) {
          instance[j] = values[j];
        }
        else if ('undefined' !== typeof defaultValue) {
          instance[j] = defaultValue;
        }
      }
      promises.push(this.load(this.data[allocated[i]]));
    }
    await Promise.all(promises);
    const created = [];
    for (let i = 0; i < allocated.length; ++i) {
      created.push(this.data[allocated[i]]);
    }
    return created;
  }

  deserialize(entityId, view, offset) {
    const {properties} = this.constructor.schema.specification;
    const instance = this.get(entityId);
    const deserialized = this.constructor.schema.deserialize(view, offset);
    for (const key in properties) {
      instance[key] = deserialized[key];
    }
  }

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

  destroyMany(entities) {
    this.freeMany(
      entities
        .map((entityId) => {
          if ('undefined' !== typeof this.map[entityId]) {
            return this.map[entityId];
          }
          throw new Error(`can't free for non-existent id ${entityId}`);
        }),
    );
    for (let i = 0; i < entities.length; i++) {
      this.data[this.map[entities[i]]].destroy();
      this.map[entities[i]] = undefined;
    }
  }

  static filterDefaults(instance) {
    const {properties} = this.schema.specification;
    const json = {};
    for (const key in properties) {
      const {defaultValue} = properties[key];
      if (key in instance && instance[key] !== defaultValue) {
        json[key] = instance[key];
      }
    }
    return json;
  }

  freeMany(indices) {
    for (let i = 0; i < indices.length; ++i) {
      this.pool.push(indices[i]);
    }
  }

  get(entityId) {
    return this.data[this.map[entityId]];
  }

  async insertMany(entities) {
    const creating = [];
    for (let i = 0; i < entities.length; i++) {
      const [entityId, values] = entities[i];
      if (!this.get(entityId)) {
        creating.push([entityId, values]);
      }
      else {
        const instance = this.get(entityId);
        for (const i in values) {
          instance[i] = values[i];
        }
      }
    }
    await this.createMany(creating);
  }

  instanceFromSchema() {
    const Component = this;
    const {specification} = Component.constructor.schema;
    const Instance = class {
      $$entity = 0;
      constructor() {
        this.$$reset();
      }
      $$reset() {
        for (const key in specification.properties) {
          const {defaultValue} = specification.properties[key];
          this[`$$${key}`] = defaultValue;
        }
      }
      destroy() {}
      toJSON() {
        return Component.constructor.filterDefaults(this);
      }
    };
    const properties = {};
    properties.entity = {
      get: function get() {
        return this.$$entity;
      },
      set: function set(v) {
        this.$$entity = v;
        this.$$reset();
      },
    };
    for (const key in specification.properties) {
      properties[key] = {
        get: function get() {
          return this[`$$${key}`];
        },
        set: function set(value) {
          if (this[`$$${key}`] !== value) {
            this[`$$${key}`] = value;
            Component.markChange(this.entity, key, value);
          }
        },
      };
    }
    Object.defineProperties(Instance.prototype, properties);
    return Instance;
  }

  async load(instance) {
    return instance;
  }

  markChange(entityId, key, value) {
    this.ecs.markChange(entityId, {[this.constructor.componentName]: {[key]: value}})
  }

  mergeDiff(original, update) {
    return {...original, ...update};
  }

  static get schema() {
    if (!this.$$schema) {
      this.$$schema = new Schema({
        type: 'object',
        properties: this.properties,
      });
    }
    return this.$$schema;
  }

  serialize(entityId, view, offset) {
    this.constructor.schema.serialize(this.get(entityId), view, offset);
  }

  sizeOf(entityId) {
    return this.constructor.schema.sizeOf(this.get(entityId));
  }

}