aggregate.js

"use strict";

import {
  BASE_URL,
  QUERY_PARAMS_COMBINED,
  getMetadataPlusObservationsFromSingleOrMultipleDatastreams,
} from "./appChart.js";

/**
 * Create 24-hour time strings for a time interval delimited by a start time and an end time. It is assumed that the start time is at "00:00:00" and the end time is at "23:45:00" (when the sampling rate of observations is 15 min) or "23:00:00" (when the sampling rate of observations is 60 min)
 * @param {String} phenomenonSamplingRate The sampling rate of the phenomenon of interest represented as a string, e.g. "15 min", "60 min"
 * @returns {Array} An array of two 24-hour strings representing the start time and end time
 */
const createTimeStringsForInterval = function (phenomenonSamplingRate) {
  const fifteenMinutes = "15 min";
  const sixtyMinutes = "60 min";

  const startTime = "00:00:00";
  const endTimeFifteenMinutes = "23:45:00";
  const endTimeSixtyMinutes = "23:00:00";

  if (
    phenomenonSamplingRate !== fifteenMinutes &&
    phenomenonSamplingRate !== sixtyMinutes
  )
    return;

  // 15 min sampling rate
  if (phenomenonSamplingRate === fifteenMinutes) {
    return [startTime, endTimeFifteenMinutes];
  }

  // 60 min sampling rate
  if (phenomenonSamplingRate === sixtyMinutes) {
    return [startTime, endTimeSixtyMinutes];
  }
};

/**
 * Create an ISO 8601 date and time string
 * @param {String} inputCalendarDate Calendar date string in "YYYY-MM-DD" format
 * @param {String} inputTwentyFourHourTime 24-hour time string in "hh:mm:ss" format
 * @returns {String} An ISO 8601 date and time string
 */
const createIso8601DateTimeString = function (
  inputCalendarDate,
  inputTwentyFourHourTime
) {
  return `${inputCalendarDate}T${inputTwentyFourHourTime}.000Z`;
};

/**
 * Calculate the index of a timestamp in an array of timestamps
 * @param {Array} inputTimestampArr An array of timestamps, extracted from an array of observations
 * @param {String} timestampOfInterest A string representing the timestamp of interest in ISO 8601 format
 * @returns {Number} An integer representing the index of the timestamp of interest in the array of timestamps
 */
const getIndexOfTimestamp = function (inputTimestampArr, timestampOfInterest) {
  const timestampIndex = inputTimestampArr.findIndex(
    (timestamp) => timestamp === timestampOfInterest
  );

  // If the timestamp does not exist in the timestamp array
  if (timestampIndex === -1)
    throw new Error(
      "A start or end timestamp could not be found in the timestamp array"
    );

  // If the timestamp exists in the timestamp array
  return timestampIndex;
};

/**
 * Aggregate observations within a time interval delimited by a start date and end date. The start date may be the same as the end date.
 * @param {Array} obsArray An array of observations (timestamp + value) that is response from SensorThings API
 * @param {String} samplingRate The sampling rate of observations as a string, e.g. "15 min", "60 min"
 * @param {String} startDate A 24-hour date string representing the start date
 * @param {String} endDate A 24-hour date string representing the end date
 * @returns {Number} A floating-point number representing the aggregated observation value
 */
const aggregateObservationsWithinTimeInterval = function (
  obsArray,
  samplingRate,
  startDate,
  endDate
) {
  // Extract the timestamps and values from the observations
  const obsTimestampArr = obsArray.map((obs) => obs[0]);
  const obsValuesArr = obsArray.map((obs) => obs[1]);

  // Create array of 24-hour strings for the start and end of interval
  const startPlusEndTimeStrings = createTimeStringsForInterval(samplingRate);

  // Extract 24-hour strings for the start and end of interval
  const [startTimeString, endTimeString] = startPlusEndTimeStrings;

  // Create ISO 8601 strings for the start and end of interval
  const startIso8601DateTimeString = createIso8601DateTimeString(
    startDate,
    startTimeString
  );
  const endIso8601DateTimeString = createIso8601DateTimeString(
    endDate,
    endTimeString
  );

  // Calculate the indexes of the timestamps for the start and end of interval
  const indexStartTimestamp = getIndexOfTimestamp(
    obsTimestampArr,
    startIso8601DateTimeString
  );
  const indexEndTimestamp = getIndexOfTimestamp(
    obsTimestampArr,
    endIso8601DateTimeString
  );

  // Extract the observations that fall within our time interval
  const obsValuesForTimeIntervalArr = obsValuesArr.slice(
    indexStartTimestamp,
    indexEndTimestamp + 1
  );

  // Calculate the aggregated observation value
  const aggregatedObsValue = obsValuesForTimeIntervalArr.reduce(
    (accumulator, currentValue) => accumulator + currentValue
  );

  return aggregatedObsValue;
};

/**
 * Test aggregation of observations from a single datastream
 */
const testAggregation = async function () {
  const sensorOfInterestNestedArr = [["225", "vl", "60min"]];

  const observationsPlusMetadata =
    await getMetadataPlusObservationsFromSingleOrMultipleDatastreams(
      BASE_URL,
      QUERY_PARAMS_COMBINED,
      sensorOfInterestNestedArr
    );

  // Extract the observations and metadata for each sensor
  // Array elements in same order as input array
  const [[obsSensorOneArr], [metadataSensorOne]] = observationsPlusMetadata;

  // Aggregated observations
  const observationsBau225VLAggregated =
    aggregateObservationsWithinTimeInterval(
      obsSensorOneArr,
      "60 min",
      "2020-02-01",
      "2020-03-31"
    );

  // console.log(observationsBau225VLAggregated);
};

// testAggregation();