import Schema from './schema.js';

export default class Component {

  ecs;
  Instance;
  instances = {};
  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()
          : new this.Instance(),
      )
      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 {
      constructor: Schema,
      specification: {concrete: {properties}},
    } = this.constructor.schema;
    const defaults = {};
    for (const key in properties) {
      defaults[key] = ((key) => () => Schema.defaultValue(properties[key]))(key);
      switch (properties[key].type) {
        case 'float32':
        case 'float64':
        case 'int8':
        case 'int16':
        case 'int32':
        case 'int64':
        case 'string':
        case 'uint8':
        case 'uint16':
        case 'uint32':
        case 'uint64': {
          defaults[key] = defaults[key]();
          break;
        }
      }
    }
    const promises = [];
    for (let i = 0; i < entries.length; ++i) {
      const [entityId, values] = entries[i];
      const instance = allocated[i];
      instance.entity = entityId;
      this.instances[entityId] = instance;
      const keys = new Set(Object.keys(defaults));
      for (const key in values) {
        keys.delete(key);
      }
      const defaultValues = {};
      for (const key of keys) {
        defaultValues[key] = 'function' === typeof defaults[key]
          ? defaults[key]()
          : defaults[key];
      }
      instance.initialize(values, defaultValues);
      promises.push(this.load(instance));
    }
    await Promise.all(promises);
    return allocated;
  }

  deserialize(entityId, view, offset) {
    const {properties} = this.constructor.schema.specification.concrete;
    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(new Set([entityId]));
  }

  destroyMany(entityIds) {
    for (const entityId of entityIds) {
      const instance = this.instances[entityId];
      if ('undefined' === typeof instance) {
        throw new Error(`can't free for non-existent id ${entityId}`);
      }
      instance.destroy();
      this.pool.push(instance);
      delete this.instances[entityId];
    }
  }

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

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

  async insertMany(entities) {
    await this.createMany(entities);
  }

  instanceFromSchema() {
    const Component = this;
    const {concrete} = Component.constructor.schema.specification;
    const Instance = class {
      $$entity = 0;
      destroy() {}
      initialize(values, defaults) {
        for (const key in values) {
          this[`$$${key}`] = values[key];
        }
        for (const key in defaults) {
          this[`$$${key}`] = defaults[key];
        }
        Component.ecs.markChange(this.entity, {[Component.constructor.componentName]: values})
      }
      toNet(recipient, data) {
        return data || Component.constructor.filterDefaults(this);
      }
      toJSON() {
        return Component.constructor.filterDefaults(this);
      }
      async update(values) {
        for (const key in values) {
          if (concrete.properties[key]) {
            this[`$$${key}`] = values[key];
          }
          else {
            this[key] = values[key];
          }
        }
      }
    };
    const properties = {};
    properties.entity = {
      get: function get() {
        return this.$$entity;
      },
      set: function set(v) {
        this.$$entity = v;
      },
    };
    for (const key in concrete.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));
  }

  async updateMany(entities) {
    const promises = [];
    for (let i = 0; i < entities.length; i++) {
      const [entityId, values] = entities[i];
      promises.push(this.get(entityId).update(values));
    }
    return Promise.all(promises);
  }

}