/*****************************************************************************
 * Open MCT, Copyright (c) 2014-2023, United States Government
 * as represented by the Administrator of the National Aeronautics and Space
 * Administration. All rights reserved.
 *
 * Open MCT is 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
 * http://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.
 *
 * Open MCT includes source code licensed under additional open source
 * licenses. See the Open Source Licenses file (LICENSES.md) included with
 * this source code distribution or the Licensing information page available
 * at runtime from the About dialog for additional information.
 *****************************************************************************/

import EventEmitter from 'EventEmitter';

export default class SinewaveLimitProvider extends EventEmitter {
  #openmct;
  #observingStaleness;
  #watchingTheClock;
  #isRealTime;

  constructor(openmct) {
    super();

    this.#openmct = openmct;
    this.#observingStaleness = {};
    this.#watchingTheClock = false;
    this.#isRealTime = undefined;
  }

  supportsStaleness(domainObject) {
    return domainObject.type === 'generator';
  }

  isStale(domainObject, options) {
    if (!this.#providingStaleness(domainObject)) {
      return;
    }

    const id = this.#getObjectKeyString(domainObject);

    if (!this.#observerExists(id)) {
      this.#createObserver(id);
    }

    return Promise.resolve({
      isStale: this.#observingStaleness[id].isStale,
      utc: Date.now()
    });
  }

  subscribeToStaleness(domainObject, callback) {
    const id = this.#getObjectKeyString(domainObject);

    if (this.#isRealTime === undefined) {
      this.#updateRealTime(this.#openmct.time.clock());
    }

    this.#handleClockUpdate();

    if (this.#observerExists(id)) {
      this.#addCallbackToObserver(id, callback);
    } else {
      this.#createObserver(id, callback);
    }

    const intervalId = setInterval(() => {
      if (this.#providingStaleness(domainObject)) {
        this.#updateStaleness(id, !this.#observingStaleness[id].isStale);
      }
    }, 10000);

    return () => {
      clearInterval(intervalId);
      this.#updateStaleness(id, false);
      this.#handleClockUpdate();
      this.#destroyObserver(id);
    };
  }

  #handleClockUpdate() {
    let observers = Object.values(this.#observingStaleness).length > 0;

    if (observers && !this.#watchingTheClock) {
      this.#watchingTheClock = true;
      this.#openmct.time.on('clock', this.#updateRealTime, this);
    } else if (!observers && this.#watchingTheClock) {
      this.#watchingTheClock = false;
      this.#openmct.time.off('clock', this.#updateRealTime, this);
    }
  }

  #updateRealTime(clock) {
    this.#isRealTime = clock !== undefined;

    if (!this.#isRealTime) {
      Object.keys(this.#observingStaleness).forEach((id) => {
        this.#updateStaleness(id, false);
      });
    }
  }

  #updateStaleness(id, isStale) {
    this.#observingStaleness[id].isStale = isStale;
    this.#observingStaleness[id].utc = Date.now();
    this.#observingStaleness[id].callback({
      isStale: this.#observingStaleness[id].isStale,
      utc: this.#observingStaleness[id].utc
    });
    this.emit('stalenessEvent', {
      id,
      isStale: this.#observingStaleness[id].isStale
    });
  }

  #createObserver(id, callback) {
    this.#observingStaleness[id] = {
      isStale: false,
      utc: Date.now()
    };

    if (typeof callback === 'function') {
      this.#addCallbackToObserver(id, callback);
    }
  }

  #destroyObserver(id) {
    if (this.#observingStaleness[id]) {
      delete this.#observingStaleness[id];
    }
  }

  #providingStaleness(domainObject) {
    return domainObject.telemetry?.staleness === true && this.#isRealTime;
  }

  #getObjectKeyString(object) {
    return this.#openmct.objects.makeKeyString(object.identifier);
  }

  #addCallbackToObserver(id, callback) {
    this.#observingStaleness[id].callback = callback;
  }

  #observerExists(id) {
    return this.#observingStaleness?.[id];
  }
}