/*
 * Copyright The OpenTelemetry Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { SDK_INFO } from '@opentelemetry/core';
import { TELEMETRY_SDK_RESOURCE } from './constants';
import { ResourceAttributes } from './types';

/**
 * A Resource describes the entity for which a signals (metrics or trace) are
 * collected.
 */
export class Resource {
  static readonly EMPTY = new Resource({});

  /**
   * Returns an empty Resource
   */
  static empty(): Resource {
    return Resource.EMPTY;
  }

  /**
   * Returns a Resource that indentifies the SDK in use.
   */
  static createTelemetrySDKResource(): Resource {
    return new Resource({
      [TELEMETRY_SDK_RESOURCE.LANGUAGE]: SDK_INFO.LANGUAGE,
      [TELEMETRY_SDK_RESOURCE.NAME]: SDK_INFO.NAME,
      [TELEMETRY_SDK_RESOURCE.VERSION]: SDK_INFO.VERSION,
    });
  }

  constructor(
    /**
     * A dictionary of attributes with string keys and values that provide
     * information about the entity as numbers, strings or booleans
     * TODO: Consider to add check/validation on attributes.
     */
    readonly attributes: ResourceAttributes
  ) {}

  /**
   * Returns a new, merged {@link Resource} by merging the current Resource
   * with the other Resource. In case of a collision, other Resource takes
   * precedence.
   *
   * @param other the Resource that will be merged with this.
   * @returns the newly merged Resource.
   */
  merge(other: Resource | null): Resource {
    if (!other || !Object.keys(other.attributes).length) return this;

    // SpanAttributes from resource overwrite attributes from other resource.
    const mergedAttributes = Object.assign(
      {},
      this.attributes,
      other.attributes
    );
    return new Resource(mergedAttributes);
  }
}
