appChart.js

"use strict";

const BASE_URL = "http://193.196.39.91:8080/frost-icity-tp31/v1.1";

/**
 * Retrieve the datastream ID that corresponds to a particular building
 * @param {Number | String} buildingNumber Integer representing the building ID
 * @param {String} phenomenon String representing the phenomenon of interest
 * @param {String} samplingRate String representing the sampling rate of the observations
 * @returns {Number} Datastream corresponding to the input building
 */
const getDatastreamIdFromBuildingNumber = function (
  buildingNumber,
  phenomenon,
  samplingRate
) {
  const buildingToDatastreamMapping = {
    101: {
      vl: { "15min": "69", "60min": "75" },
      rl: { "15min": "81", "60min": "87" },

      // These Datastreams do not yet have Observations
      // flow: { "15min": "93", "60min": "99" },
      // power: { "15min": "105", "60min": "111" },
      // energy: { "15min": "117", "60min": "123" },
      // energy_verb: { "15min": "129", "60min": "135" },
    },

    102: {
      vl: { "15min": "70", "60min": "76" },
      rl: { "15min": "82", "60min": "88" },

      // These Datastreams do not yet have Observations
      // flow: { "15min": "94", "60min": "100" },
      // power: { "15min": "106", "60min": "112" },
      // energy: { "15min": "118", "60min": "124" },
      // energy_verb: { "15min": "130", "60min": "136" },
    },

    107: {
      vl: { "15min": "71", "60min": "77" },
      rl: { "15min": "83", "60min": "89" },

      // These Datastreams do not yet have Observations
      // flow: { "15min": "95", "60min": "101" },
      // power: { "15min": "107", "60min": "113" },
      // energy: { "15min": "119", "60min": "125" },
      // energy_verb: { "15min": "131", "60min": "137" },
    },

    "112, 118": {
      vl: { "15min": "72", "60min": "78" },
      rl: { "15min": "84", "60min": "90" },

      // These Datastreams do not yet have Observations
      // flow: { "15min": "96", "60min": "102" },
      // power: { "15min": "108", "60min": "114" },
      // energy: { "15min": "120", "60min": "126" },
      // energy_verb: { "15min": "132", "60min": "138" },
    },

    125: {
      vl: { "15min": "73", "60min": "79" },
      rl: { "15min": "85", "60min": "91" },

      // These Datastreams do not yet have Observations
      // flow: { "15min": "97", "60min": "103" },
      // power: { "15min": "109", "60min": "115" },
      // energy: { "15min": "121", "60min": "127" },
      // energy_verb: { "15min": "133", "60min": "139" },
    },

    225: {
      vl: { "15min": "74", "60min": "80" },
      rl: { "15min": "86", "60min": "92" },
      flow: { "15min": "98", "60min": "104" },
      power: { "15min": "110", "60min": "116" },
      energy: { "15min": "122", "60min": "128" },
      energy_verb: { "15min": "134", "60min": "140" },
    },

    weather_station_521: {
      outside_temp: { "15min": "141", "60min": "142" },
    },
  };

  if (
    buildingToDatastreamMapping?.[buildingNumber]?.[phenomenon]?.[
      samplingRate
    ] === undefined
  )
    return;

  const datastreamIdMatched = Number(
    buildingToDatastreamMapping[buildingNumber][phenomenon][samplingRate]
  );

  return datastreamIdMatched;
};

/**
 * Create URL to fetch the details of single Datastream
 * @param {String} baseUrl Base URL of the STA server
 * @param {Number} datastreamID Integer representing the Datastream ID
 * @returns {String} URL string for fetching a single Datastream
 */
const getDatastreamUrl = function (baseUrl, datastreamID) {
  if (!datastreamID) return;
  const fullDatastreamURL = `${baseUrl}/Datastreams(${datastreamID})`;
  return fullDatastreamURL;
};

/**
 * Create URL to fetch Observations
 * @param {String} baseUrl Base URL of the STA server
 * @param {Number} datastreamID Integer representing the Datastream ID
 * @returns {String} URL string for fetching Observations
 */
const getObservationsUrl = function (baseUrl, datastreamID) {
  if (!datastreamID) return;
  const fullObservationsURL = `${baseUrl}/Datastreams(${datastreamID})/Observations`;
  return fullObservationsURL;
};

/**
 * Create a temporal filter string for the fetched Observations
 * @param {String} dateStart Start date in YYYY-MM-DD format
 * @param {String} dateStop Stop date in YYYY-MM-DD format
 * @returns {String} Temporal filter string
 */
const createTemporalFilterString = function (dateStart, dateStop) {
  if (!dateStart || !dateStop) return;
  const filterString = `resultTime ge ${dateStart}T00:00:00.000Z and resultTime le ${dateStop}T00:00:00.000Z`;
  return filterString;
};

// const BASE_URL_OBSERVATIONS = getObservationsUrl(80);
const QUERY_PARAM_RESULT_FORMAT = "dataArray";
const QUERY_PARAM_ORDER_BY = "phenomenonTime asc";
const QUERY_PARAM_FILTER = createTemporalFilterString(
  "2020-01-01",
  "2021-01-01"
);
const QUERY_PARAM_SELECT = "result,phenomenonTime";
const QUERY_PARAMS_COMBINED = {
  "$resultFormat": QUERY_PARAM_RESULT_FORMAT,
  "$orderBy": QUERY_PARAM_ORDER_BY,
  "$filter": QUERY_PARAM_FILTER,
  "$select": QUERY_PARAM_SELECT,
};

/**
 * Perform a GET request using the Axios library
 * @param {String} urlObservations A URL that fetches Observations from an STA instance
 * @param {Object} urlParamObj The URL parameters to be sent together with the GET request
 * @returns {Promise} A promise that contains the first page of results when fulfilled
 */
const axiosGetRequest = function (urlObservations, urlParamObj) {
  return axios.get(urlObservations, {
    params: urlParamObj,
  });
};

/**
 * Retrieve the metadata for a single datastream
 * @async
 * @param {String} urlDatastream A URL that fetches a Datastream from an STA instance
 * @returns {Promise} A promise that contains a metadata object for a Datastream when fulfilled
 */
const getMetadataFromSingleDatastream = async function (urlDatastream) {
  try {
    // Extract properties of interest
    const {
      data: { description, name, unitOfMeasurement },
    } = await axiosGetRequest(urlDatastream);

    return { description, name, unitOfMeasurement };
  } catch (err) {
    console.error(err);
  }
};

/**
 * Retrieve metadata from multiple datastreams
 * @async
 * @param {Array} datastreamsUrlArr An array that contains N Datastream URL strings
 * @returns {Promise} A promise that contains an array of N Datastream metadata objects when fulfilled
 */
const getMetadataFromMultipleDatastreams = async function (datastreamsUrlArr) {
  try {
    // Array to store our final result
    const datastreamMetadataArr = [];

    // Use for/of loop - we need to maintain the order of execution of the async operations
    for (const datastreamUrl of datastreamsUrlArr) {
      // Metadata from a single Datastream
      const datastreamMetadata = await getMetadataFromSingleDatastream(
        datastreamUrl
      );
      datastreamMetadataArr.push(datastreamMetadata);
    }

    return datastreamMetadataArr;
  } catch (err) {
    console.error(err);
  }
};

/**
 * Format the response containing a Datastream's metadata from Sensorthings API
 * @param {Object} datastreamMetadata An object containing a Datastream's metadata
 * @returns {Object} An object containing the formatted metadata that is suitable for use in a line chart or heatmap
 */
const formatDatastreamMetadataForChart = function (datastreamMetadata) {
  const {
    description: datastreamDescription,
    name: datastreamName,
    unitOfMeasurement,
  } = datastreamMetadata;

  // Extract phenomenon name from Datastream name
  const regex = /\/ (.*) DS/;
  const phenomenonName = datastreamName.match(regex)[1]; // use second element in array

  // Match the unitOfMeasurement's string representation of a symbol
  // to an actual symbol, where necessary
  const unitOfMeasurementSymbol = (() => {
    if (unitOfMeasurement.symbol === "degC") {
      return "℃";
    } else if (unitOfMeasurement.symbol === "m3/h") {
      return "m<sup>3</sup>/h";
    } else {
      return unitOfMeasurement.symbol;
    }
  })();

  return {
    datastreamDescription,
    datastreamName,
    phenomenonName,
    unitOfMeasurementSymbol,
  };
};

/**
 * Format the response from SensorThings API to make it suitable for heatmap
 * @param {Array} obsArray Response from SensorThings API as array
 * @returns {Array} Array of formatted observations suitable for use in a heatmap
 */
const formatSTAResponseForHeatMap = function (obsArray) {
  if (!obsArray) return;

  const dataSTAFormatted = obsArray.map((obs) => {
    // Get the date/time string; first element in input array; remove trailing "Z"
    const obsDateTimeInput = obs[0].slice(0, -1);
    // Get the "date" part of an observation
    const obsDateInput = obs[0].slice(0, 10);
    // Create Date objects
    const obsDateTime = new Date(obsDateTimeInput);
    const obsDate = new Date(obsDateInput);
    // x-axis -> timestamp; will be the same for observations from the same date
    const timestamp = Date.parse(obsDate);
    // y-axis -> hourOfDay
    const hourOfDay = obsDateTime.getHours();
    // value -> the observation's value; second element in input array
    const value = obs[1];
    return [timestamp, hourOfDay, value];
  });

  return dataSTAFormatted;
};

/**
 * Draw a heatmap using Highcharts library
 * @param {Array} formattedObsArrayForHeatmap Response from SensorThings API formatted for use in a heatmap
 * @param {Object} formattedDatastreamMetadata Object containing Datastream metadata
 * @returns {undefined} undefined
 */
const drawHeatMapHC = function (
  formattedObsArrayForHeatmap,
  formattedDatastreamMetadata
) {
  const {
    datastreamDescription: DATASTREAM_DESCRIPTION,
    datastreamName: DATASTREAM_NAME,
    phenomenonName: PHENOMENON_NAME,
    unitOfMeasurementSymbol: PHENOMENON_SYMBOL,
  } = formattedDatastreamMetadata;

  // Function returns the min and max observation values
  const {
    minObsValue: MINIMUM_VALUE_COLOR_AXIS,
    maxObsValue: MAXIMUM_VALUE_COLOR_AXIS,
  } = (() => {
    // The observation value is the third element in array
    const obsValueArr = formattedObsArrayForHeatmap.map((obs) => obs[2]);

    // Extract integer part
    const minValue = Math.trunc(Math.min(...obsValueArr));
    const maxValue = Math.trunc(Math.max(...obsValueArr));

    // Calculate the closest multiple of 5
    const minObsValue = minValue - (minValue % 5);
    const maxObsValue = maxValue + (5 - (maxValue % 5));

    return { minObsValue, maxObsValue };
  })();

  Highcharts.chart("chart-heatmap", {
    chart: {
      type: "heatmap",
      zoomType: "x",
    },

    boost: {
      useGPUTranslations: true,
    },

    title: {
      text: DATASTREAM_DESCRIPTION,
      align: "left",
      x: 40,
    },

    subtitle: {
      text: DATASTREAM_NAME,
      align: "left",
      x: 40,
    },

    xAxis: {
      type: "datetime",
      // min: Date.UTC(2017, 0, 1),
      // max: Date.UTC(2017, 11, 31, 23, 59, 59),
      labels: {
        align: "left",
        x: 5,
        y: 14,
        format: "{value:%B}", // long month
      },
      showLastLabel: false,
      tickLength: 16,
    },

    yAxis: {
      title: {
        text: null,
      },
      labels: {
        format: "{value}:00",
      },
      minPadding: 0,
      maxPadding: 0,
      startOnTick: false,
      endOnTick: false,
      tickPositions: [0, 3, 6, 9, 12, 15, 18, 21, 24],
      tickWidth: 1,
      min: 0,
      max: 23,
      reversed: true,
    },

    colorAxis: {
      stops: [
        [0, "#3060cf"],
        [0.5, "#fffbbc"],
        [0.9, "#c4463a"],
        [1, "#c4463a"],
      ],
      min: MINIMUM_VALUE_COLOR_AXIS,
      max: MAXIMUM_VALUE_COLOR_AXIS,
      startOnTick: false,
      endOnTick: false,
      labels: {
        // format: "{value}℃",
        format: `{value}${PHENOMENON_SYMBOL}`,
      },
    },

    series: [
      {
        data: formattedObsArrayForHeatmap,
        boostThreshold: 100,
        borderWidth: 0,
        nullColor: "#525252",
        colsize: 24 * 36e5, // one day
        tooltip: {
          headerFormat: `${PHENOMENON_NAME}<br/>`,
          valueDecimals: 2,
          pointFormat:
            // "{point.x:%e %b, %Y} {point.y}:00: <b>{point.value} ℃</b>",
            `{point.x:%e %b, %Y} {point.y}:00: <b>{point.value} ${PHENOMENON_SYMBOL}</b>`,
          nullFormat: `{point.x:%e %b, %Y} {point.y}:00: <b>null</b>`,
        },
        turboThreshold: Number.MAX_VALUE, // #3404, remove after 4.0.5 release
      },
    ],
  });
};

/**
 * Convert the observations' phenomenonTime from an ISO 8601 string to Unix epoch
 * @param {Array} obsArray Response from SensorThings API as array
 * @returns {Array} Array of formatted observations suitable for use in a line chart or scatter plot
 */
const formatSTAResponseForLineChartOrScatterPlot = function (obsArray) {
  if (!obsArray) return;

  const dataSTAFormatted = obsArray.map((result) => {
    const timestampObs = new Date(result[0].slice(0, -1)).getTime(); // slice() removes trailing "Z" character in timestamp
    const valueObs = result[1];
    return [timestampObs, valueObs];
  });

  return dataSTAFormatted;
};

/**
 * Draw a line chart using Highcharts library
 * @param {Array} formattedObsArrayForLineChart Response from SensorThings API formatted for use in a line chart
 * @param {Object} formattedDatastreamMetadata Object containing Datastream metadata
 * @returns {undefined} undefined
 */
const drawLineChartHC = function (
  formattedObsArrayForLineChart,
  formattedDatastreamMetadata
) {
  const {
    datastreamDescription: DATASTREAM_DESCRIPTION,
    datastreamName: DATASTREAM_NAME,
    phenomenonName: PHENOMENON_NAME,
    unitOfMeasurementSymbol: PHENOMENON_SYMBOL,
  } = formattedDatastreamMetadata;

  Highcharts.stockChart("chart-line", {
    chart: {
      zoomType: "x",
    },

    rangeSelector: {
      selected: 5,
    },

    title: {
      text: DATASTREAM_DESCRIPTION,
      "align": "left",
    },

    subtitle: {
      text: DATASTREAM_NAME,
      align: "left",
    },

    series: [
      {
        name: `${PHENOMENON_NAME} (${PHENOMENON_SYMBOL})`,
        data: formattedObsArrayForLineChart,
        tooltip: {
          valueDecimals: 2,
        },
        turboThreshold: Number.MAX_VALUE, // #3404, remove after 4.0.5 release
      },
    ],
  });
};

/**
 * Determines the timestamps that are missing from a smaller set of observations. Based on the comparison of two observation arrays, where one array is larger than the other
 * @param {Array} obsTimestampArrayOne An array of timestamps for the first set of observations
 * @param {Array} obsTimestampArrayTwo An array of timstamps for the second set of observations
 * @returns {Array} An array of timestamps missing from either set of observations
 */
const getSymmetricDifferenceBetweenArrays = function (
  obsTimestampArrayOne,
  obsTimestampArrayTwo
) {
  const differenceBetweenArrays = obsTimestampArrayOne
    .filter((timestampOne) => !obsTimestampArrayTwo.includes(timestampOne))
    .concat(
      obsTimestampArrayTwo.filter(
        (timestampTwo) => !obsTimestampArrayTwo.includes(timestampTwo)
      )
    );

  return differenceBetweenArrays;
};

/**
 * Determines the indexes of timestamps that are missing from a smaller set of observatiuons. Based on the comparison of two observation arrays, where one array is larger than the other
 * @param {Array} missingTimestampsArr An array of strings representing the missing timestamps
 * @param {Array} largerObsTimestampArr An array of timestamps for the larger array of observations
 * @returns {Array} An array of the indexes of the missing observations
 */
const getIndexOfMissingObservation = function (
  missingTimestampsArr,
  largerObsTimestampArr
) {
  const indexesMissingObs = missingTimestampsArr.map((index) =>
    largerObsTimestampArr.indexOf(index)
  );

  return indexesMissingObs;
};

/**
 * Removes observations (by modifying array in place) from a larger set of observations that are missing from a smaller set of observatiuons. Based on the comparison of two observation arrays, where one array is larger than the other
 * @param {Array} missingIndexesArr An array of the indexes of the observations missing from the smaller set of observations
 * @param {Array} largerObsArr The larger array of observations (timestamp + value) which is modified in place
 * @returns {undefined}
 */
const removeMissingObservationFromLargerArray = function (
  missingIndexesArr,
  largerObsArr
) {
  missingIndexesArr.forEach((index) => {
    if (index > -1) {
      largerObsArr.splice(index, 1);
    }
  });
};

/**
 * Compares the length of two input arrays to determine the larger one
 * @param {Array} firstArr First input array
 * @param {Array} secondArr Second input array
 * @returns {Array} The larger array
 */
const getLargerArrayBetweenTwoInputArrays = function (firstArr, secondArr) {
  if (firstArr.length === secondArr.length) return;

  if (firstArr.length > secondArr.length) return firstArr;

  if (firstArr.length < secondArr.length) return secondArr;
};

/**
 * Extracts and combines observation values from two imput observation arrays of equal length
 * @param {Array} obsArrayOne First set of N observations (timestamp + value)
 * @param {Array} obsArrayTwo Second set of N observations (timestamp + value)
 * @returns {Array} A 2*N array of observation values from both input observation arrays
 */
const createCombinedObservationValues = function (obsArrayOne, obsArrayTwo) {
  // Extract the values from the two observation arrays
  const obsValuesOne = obsArrayOne.map((result) => result[1]);
  const obsValuesTwo = obsArrayTwo.map((result) => result[1]);

  //  Since the arrays are of equal length, we need only use one of the arrays for looping
  const obsValuesOnePlusTwo = obsValuesOne.map((obsValOne, i) => {
    return [obsValOne, obsValuesTwo[i]];
  });

  return obsValuesOnePlusTwo;
};

/**
 * Format the response from SensorThings API to make it suitable for scatter plot
 * @param {Array} obsArrayOne Response from SensorThings API as array
 * @param {Array} obsArrayTwo Response from SensorThings API as array
 * @returns {Array} Array of formatted observations suitable for use in a scatter plot
 */
const formatSTAResponseForScatterPlot = function (obsArrayOne, obsArrayTwo) {
  // When our observation arrays have DIFFERENT lengths
  if (obsArrayOne.length !== obsArrayTwo.length) {
    // Create arrays with timestamps only
    const obsArrayOneTimestamp = obsArrayOne.map(
      (obsTimeValue) => obsTimeValue[0]
    );
    const obsArrayTwoTimestamp = obsArrayTwo.map(
      (obsTimeValue) => obsTimeValue[0]
    );

    const missingTimestamp = getSymmetricDifferenceBetweenArrays(
      obsArrayOneTimestamp,
      obsArrayTwoTimestamp
    );

    // Determine the larger observation timestamp array
    const biggerObsTimestampArr = getLargerArrayBetweenTwoInputArrays(
      obsArrayOneTimestamp,
      obsArrayTwoTimestamp
    );

    // Indexes of the missing observations
    const indexesMissingObsArr = getIndexOfMissingObservation(
      missingTimestamp,
      biggerObsTimestampArr
    );

    // Determine the larger observation array
    const biggerObsArr = getLargerArrayBetweenTwoInputArrays(
      obsArrayOne,
      obsArrayTwo
    );

    // Remove the missing observation from the larger array of observations
    // Modifies the array in place
    removeMissingObservationFromLargerArray(indexesMissingObsArr, biggerObsArr);

    return createCombinedObservationValues(obsArrayOne, obsArrayTwo);
  }

  // When our observation arrays already have SAME lengths
  return createCombinedObservationValues(obsArrayOne, obsArrayTwo);
};

/**
 * Draw a scatter plot using Highcharts library
 * @param {*} formattedObsArrayForSeriesOnePlusSeriesTwo Response from SensorThings API formatted for use in a scatter plot
 * @param {*} formattedDatastreamMetadataSeriesOne Object containing Datastream metadata for the first chart series
 * @param {*} formattedDatastreamMetadataSeriesTwo Object containing Datastream metadata for the second chart series
 * @returns {undefined}
 */
const drawScatterPlotHC = function (
  formattedObsArrayForSeriesOnePlusSeriesTwo,
  formattedDatastreamMetadataSeriesOne,
  formattedDatastreamMetadataSeriesTwo
) {
  const {
    datastreamDescription: DATASTREAM_DESCRIPTION_SERIES_1,
    datastreamName: DATASTREAM_NAME_SERIES_1,
    phenomenonName: PHENOMENON_NAME_SERIES_1,
    unitOfMeasurementSymbol: PHENOMENON_SYMBOL_SERIES_1,
  } = formattedDatastreamMetadataSeriesOne;

  const {
    datastreamDescription: DATASTREAM_DESCRIPTION_SERIES_2,
    datastreamName: DATASTREAM_NAME_SERIES_2,
    phenomenonName: PHENOMENON_NAME_SERIES_2,
    unitOfMeasurementSymbol: PHENOMENON_SYMBOL_SERIES_2,
  } = formattedDatastreamMetadataSeriesTwo;

  // Order of axes
  // Y-Axis -- Series 2
  // X-Axis -- Series 1

  const CHART_TITLE = `${PHENOMENON_NAME_SERIES_2} Versus ${PHENOMENON_NAME_SERIES_1}`;
  const CHART_SUBTITLE = `Source: ${DATASTREAM_NAME_SERIES_2} & ${DATASTREAM_NAME_SERIES_1}`;

  const SERIES_1_NAME = `${PHENOMENON_NAME_SERIES_1}`;
  const SERIES_1_SYMBOL = `${PHENOMENON_SYMBOL_SERIES_1}`;

  const SERIES_2_NAME = `${PHENOMENON_NAME_SERIES_2}`;
  const SERIES_2_SYMBOL = `${PHENOMENON_SYMBOL_SERIES_2}`;

  const SERIES_COMBINED_NAME = "Y, X";
  const SERIES_COMBINED_SYMBOL_COLOR_RGB_ELEMENTS = "223, 83, 83";
  const SERIES_COMBINED_SYMBOL_COLOR_OPACITY = ".3";
  const SERIES_COMBINED_SYMBOL_COLOR = `rgba(${SERIES_COMBINED_SYMBOL_COLOR_RGB_ELEMENTS}, ${SERIES_COMBINED_SYMBOL_COLOR_OPACITY})`;

  const MARKER_RADIUS = 2;

  Highcharts.chart("chart-scatter-plot", {
    chart: {
      type: "scatter",
      zoomType: "xy",
    },

    boost: {
      useGPUTranslations: true,
      usePreAllocated: true,
    },

    title: {
      text: CHART_TITLE,
    },

    subtitle: {
      text: CHART_SUBTITLE,
    },

    xAxis: {
      labels: {
        format: `{value}`,
      },
      title: {
        enabled: true,
        text: `${SERIES_1_NAME} [${SERIES_1_SYMBOL}]`,
      },
      startOnTick: true,
      endOnTick: true,
      showLastLabel: true,
    },

    yAxis: [
      {
        labels: {
          format: `{value}`,
        },
        title: {
          text: `${SERIES_2_NAME} [${SERIES_2_SYMBOL}]`,
        },
      },
    ],

    legend: {
      enabled: false,
    },

    plotOptions: {
      scatter: {
        marker: {
          radius: MARKER_RADIUS,
          states: {
            hover: {
              enabled: true,
              lineColor: "rgb(100,100,100)",
            },
          },
        },
        states: {
          hover: {
            marker: {
              enabled: false,
            },
          },
        },
        tooltip: {
          headerFormat: "{series.name}<br>",
          pointFormat: `<b>{point.y:.2f} ${SERIES_1_SYMBOL}, {point.x:.2f} ${SERIES_2_SYMBOL}</b>`,
        },
      },
    },

    series: [
      {
        name: SERIES_COMBINED_NAME,
        color: SERIES_COMBINED_SYMBOL_COLOR,
        data: formattedObsArrayForSeriesOnePlusSeriesTwo,
      },
    ],
  });
};

/**
 * Follows "@iot.nextLink" links in SensorThingsAPI's response
 * Appends new results to existing results
 * @async
 * @param {Promise} responsePromise Promise object resulting from an Axios GET request
 * @returns {Object} Object containing results from all the "@iot.nextLink" links
 */
const followNextLink = function (responsePromise) {
  if (!responsePromise) return;
  return responsePromise
    .then((lastSuccess) => {
      if (lastSuccess.data["@iot.nextLink"]) {
        return followNextLink(
          axios.get(lastSuccess.data["@iot.nextLink"])
        ).then((nextLinkSuccess) => {
          nextLinkSuccess.data.value = lastSuccess.data.value.concat(
            nextLinkSuccess.data.value
          );
          return nextLinkSuccess;
        });
      } else {
        return lastSuccess;
      }
    })
    .catch((err) => {
      console.error(err);
    });
};

/**
 * Retrieve all the Observations from a Datastream after traversing all the "@iot.nextLink" links
 * @async
 * @param {Promise} httpGetRequestPromise Promise object resulting from an Axios GET request
 * @returns {Promise} A promise that contains an array of Observations from a single Datastream when fulfilled
 */
const getCombinedObservationsFromAllNextLinks = function (
  httpGetRequestPromise
) {
  return followNextLink(httpGetRequestPromise)
    .then((success) => {
      const successValue = success.data.value;
      // Array that will hold the combined observations
      const combinedObservations = [];
      successValue.forEach((dataObj) => {
        // Each page of results will have a dataArray that holds the observations
        const dataArrays = dataObj.dataArray;
        combinedObservations.push(...dataArrays);
      });

      return new Promise((resolve, reject) => {
        resolve(combinedObservations);
      });
    })
    .catch((err) => {
      console.error(err);
    });
};

/**
 * Retrieve the metadata for a Datastream as well as the Observations corresponding to it
 * @async
 * @param {Promise} metadataPlusObsPromiseArray An array that contains two promises, one for datastream metadata, the other for observations
 * @returns {Promise} A promise that contains two arrays when fulfilled, one for datastream metadata and the other for observations
 */
const getMetadataPlusObservationsFromSingleDatastream = async function (
  metadataPlusObsPromiseArray
) {
  try {
    // Array to store our final result
    const combinedResolvedPromises = [];

    // Use for/of loop - we need to maintain the order of execution of the async operations
    for (const promise of metadataPlusObsPromiseArray) {
      // Resolved value of a single promise
      const resolvedPromise = await promise;
      combinedResolvedPromises.push(resolvedPromise);
    }

    return combinedResolvedPromises;
  } catch (err) {
    console.error(err);
  }
};

/**
 * Retrieve all the Observations from an array of Observations promises
 * @async
 * @param {Promise} observationPromiseArray An array that contains N observation promises
 * @returns {Promise} A promise that contains an array of Observations from multiple Datastreams when fulfilled
 */
const getObservationsFromMultipleDatastreams = async function (
  observationPromiseArray
) {
  try {
    // Array to store our final result
    const observationsAllDatastreamsArr = [];

    // Use for/of loop - we need to maintain the order of execution of the async operations
    for (const observationPromise of observationPromiseArray) {
      // Observations from a single Datastream
      const observations = await observationPromise;
      observationsAllDatastreamsArr.push(observations);
    }

    return observationsAllDatastreamsArr;
  } catch (err) {
    console.error(err);
  }
};

/**
 * Retrieve the metadata from multiple Datastreams and the Observations corresponding to these Datastreams
 * @async
 * @param {Array} bldgSensorSamplingRateArr A 3*N array containing buildings, sensors & sampling rates as strings, e.g. ["101", "rl", "60min"]
 * @returns {Promise} A promise that contains a N*2 array (the first element is an array of Observations and the second element is an array of Datastream metadata objects) when fulfilled
 */
const getMetadataPlusObservationsFromMultipleDatastreams = async function (
  bldgSensorSamplingRateArr
) {
  try {
    if (!bldgSensorSamplingRateArr) return;

    // Datastreams IDs
    const datastreamsIdsArr = bldgSensorSamplingRateArr.map(
      (bldgSensorSamplingRate) =>
        getDatastreamIdFromBuildingNumber(...bldgSensorSamplingRate)
    );

    // Observations URLs
    const observationsUrlArr = datastreamsIdsArr.map((datastreamId) =>
      getObservationsUrl(BASE_URL, datastreamId)
    );

    // Datastreams URLs
    const datastreamsUrlArr = datastreamsIdsArr.map((datastreamId) =>
      getDatastreamUrl(BASE_URL, datastreamId)
    );

    // Promise objects - Observations
    const observationsPromisesArr = observationsUrlArr.map((obsUrl) =>
      getCombinedObservationsFromAllNextLinks(
        axiosGetRequest(obsUrl, QUERY_PARAMS_COMBINED)
      )
    );

    // Observations array
    const observationsArr = await getObservationsFromMultipleDatastreams(
      observationsPromisesArr
    );

    // Metadata array
    const metadataArr = await getMetadataFromMultipleDatastreams(
      datastreamsUrlArr
    );

    return [observationsArr, metadataArr];
  } catch (err) {
    console.error(err);
  }
};

/**
 * Test drawing of scatter plot chart
 */
const drawScatterPlotHCTest2 = async function () {
  const sensorsOfInterestArr = [
    ["225", "vl", "60min"],
    // ["125", "rl", "60min"],
    ["weather_station_521", "outside_temp", "60min"],
  ];

  const observationsPlusMetadata =
    await getMetadataPlusObservationsFromMultipleDatastreams(
      sensorsOfInterestArr
    );

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

  drawScatterPlotHC(
    formatSTAResponseForScatterPlot(obsSensorOneArr, obsSensorTwoArr),
    formatDatastreamMetadataForChart(metadataSensorOne),
    formatDatastreamMetadataForChart(metadataSensorTwo)
  );
};

(async () => {
  await drawScatterPlotHCTest2();
})();

export {
  BASE_URL,
  QUERY_PARAMS_COMBINED,
  getDatastreamIdFromBuildingNumber,
  getDatastreamUrl,
  getObservationsUrl,
  createTemporalFilterString,
  axiosGetRequest,
  getMetadataFromSingleDatastream,
  formatDatastreamMetadataForChart,
  formatSTAResponseForHeatMap,
  drawHeatMapHC,
  formatSTAResponseForLineChartOrScatterPlot,
  drawLineChartHC,
  getCombinedObservationsFromAllNextLinks,
  getMetadataPlusObservationsFromSingleDatastream,
};