import { map as _map, cloneDeep, extend, has, isString, omit, pick, reduce } from 'lodash';
import { lastValueFrom, merge, Observable, of, throwError } from 'rxjs';
import { catchError, map } from 'rxjs/operators';

import {
  AdHocVariableFilter,
  AnnotationEvent,
  DataFrame,
  DataQueryError,
  DataQueryRequest,
  DataQueryResponse,
  DataSourceGetTagKeysOptions,
  DataSourceGetTagValuesOptions,
  DataSourceInstanceSettings,
  dateMath,
  DateTime,
  escapeRegex,
  FieldType,
  MetricFindValue,
  QueryResultMeta,
  QueryVariableModel,
  RawTimeRange,
  ScopedVars,
  TIME_SERIES_TIME_FIELD_NAME,
  TIME_SERIES_VALUE_FIELD_NAME,
  TimeSeries,
  toDataFrame,
} from '@grafana/data';
import {
  BackendDataSourceResponse,
  DataSourceWithBackend,
  FetchResponse,
  getBackendSrv,
  getTemplateSrv,
  TemplateSrv,
} from '@grafana/runtime';
import { QueryFormat, SQLQuery } from '@grafana/sql';
import config from 'app/core/config';

import { AnnotationEditor } from './components/editor/annotation/AnnotationEditor';
import { FluxQueryEditor } from './components/editor/query/flux/FluxQueryEditor';
import { BROWSER_MODE_DISABLED_MESSAGE } from './constants';
import { toRawSql } from './fsql/sqlUtil';
import InfluxQueryModel from './influx_query_model';
import InfluxSeries from './influx_series';
import { buildMetadataQuery } from './influxql_query_builder';
import { prepareAnnotation } from './migrations';
import { buildRawQuery, removeRegexWrapper } from './queryUtils';
import ResponseParser from './response_parser';
import { DEFAULT_POLICY, InfluxOptions, InfluxQuery, InfluxVariableQuery, InfluxVersion } from './types';
import { InfluxVariableSupport } from './variables';

export default class InfluxDatasource extends DataSourceWithBackend<InfluxQuery, InfluxOptions> {
  type: string;
  urls: string[];
  username: string;
  password: string;
  name: string;
  database?: string;
  basicAuth?: string;
  withCredentials?: boolean;
  access: 'direct' | 'proxy';
  responseParser: ResponseParser;
  httpMode: string;
  version?: InfluxVersion;
  isProxyAccess: boolean;
  showTagTime: string;

  constructor(
    instanceSettings: DataSourceInstanceSettings<InfluxOptions>,
    readonly templateSrv: TemplateSrv = getTemplateSrv()
  ) {
    super(instanceSettings);

    this.type = 'influxdb';
    this.urls = (instanceSettings.url ?? '').split(',').map((url) => {
      return url.trim();
    });

    this.username = instanceSettings.username ?? '';
    this.password = instanceSettings.password ?? '';
    this.name = instanceSettings.name;
    this.basicAuth = instanceSettings.basicAuth;
    this.withCredentials = instanceSettings.withCredentials;
    this.access = instanceSettings.access;
    const settingsData: InfluxOptions = instanceSettings.jsonData ?? {};
    this.database = settingsData.dbName ?? instanceSettings.database;
    this.interval = settingsData.timeInterval;
    this.showTagTime = settingsData.showTagTime || '';
    this.httpMode = settingsData.httpMode || 'GET';
    this.responseParser = new ResponseParser();
    this.version = settingsData.version ?? InfluxVersion.InfluxQL;
    this.isProxyAccess = instanceSettings.access === 'proxy';
    this.variables = new InfluxVariableSupport(this, this.templateSrv);

    if (this.version === InfluxVersion.Flux) {
      // When flux, use an annotation processor rather than the `annotationQuery` lifecycle
      this.annotations = {
        QueryEditor: FluxQueryEditor,
      };
    } else {
      this.annotations = {
        QueryEditor: AnnotationEditor,
        prepareAnnotation,
      };
    }
  }

  query(request: DataQueryRequest<InfluxQuery>): Observable<DataQueryResponse> {
    if (!this.isProxyAccess) {
      const error = new Error(BROWSER_MODE_DISABLED_MESSAGE);
      return throwError(() => error);
    }

    return this._query(request);
  }

  _query(request: DataQueryRequest<InfluxQuery>): Observable<DataQueryResponse> {
    // for not-flux queries we call `this.classicQuery`, and that
    // handles the is-hidden situation.
    // for the flux-case, we do the filtering here
    const filteredRequest = {
      ...request,
      targets: request.targets.filter((t) => t.hide !== true),
    };

    // migrate annotations
    if (filteredRequest.targets.some((target: InfluxQuery) => target.fromAnnotations)) {
      const streams: Array<Observable<DataQueryResponse>> = [];

      for (const target of filteredRequest.targets) {
        if (target.query) {
          streams.push(
            new Observable((subscriber) => {
              this.annotationEvents(filteredRequest, target)
                .then((events) => subscriber.next({ data: [toDataFrame(events)] }))
                .catch((ex) => subscriber.error(new Error(ex)))
                .finally(() => subscriber.complete());
            })
          );
        }
      }

      return merge(...streams);
    }

    if (this.version === InfluxVersion.InfluxQL && !this.isMigrationToggleOnAndIsAccessProxy()) {
      // Fallback to classic query support
      return this.classicQuery(request);
    }

    return super.query(filteredRequest);
  }

  getQueryDisplayText(query: InfluxQuery) {
    switch (this.version) {
      case InfluxVersion.Flux:
        return query.query;
      case InfluxVersion.SQL:
        return toRawSql(query);
      case InfluxVersion.InfluxQL:
        return new InfluxQueryModel(query).render(false);
      default:
        return '';
    }
  }

  /**
   * Returns false if the query should be skipped
   */
  filterQuery(query: InfluxQuery): boolean {
    if (this.version === InfluxVersion.Flux) {
      return !!query.query;
    }
    return true;
  }

  applyTemplateVariables(
    query: InfluxQuery,
    scopedVars: ScopedVars,
    filters?: AdHocVariableFilter[]
  ): InfluxQuery & SQLQuery {
    const variables = scopedVars || {};

    // We want to interpolate these variables on backend.
    // The pre-calculated values are replaced with the variable strings.
    variables.__interval = {
      value: '$__interval',
    };
    variables.__interval_ms = {
      value: '$__interval_ms',
    };

    if (this.version === InfluxVersion.Flux) {
      return {
        ...query,
        query: this.templateSrv.replace(query.query ?? '', variables), // The raw query text
      };
    }

    if (this.version === InfluxVersion.SQL || this.isMigrationToggleOnAndIsAccessProxy()) {
      query = this.applyVariables(query, variables, filters);
      if (query.adhocFilters?.length) {
        query.adhocFilters = (query.adhocFilters ?? []).map((af) => {
          const { condition, ...asTag } = af;
          asTag.value = this.templateSrv.replace(asTag.value ?? '', variables);
          return asTag;
        });
        query.tags = [...(query.tags ?? []), ...query.adhocFilters];
      }
    }

    return query;
  }

  targetContainsTemplate(target: InfluxQuery) {
    // for flux-mode we just take target.query,
    // for influxql-mode we use InfluxQueryModel to create the text-representation
    const queryText = this.version === InfluxVersion.Flux ? target.query : buildRawQuery(target);

    return this.templateSrv.containsTemplate(queryText);
  }

  interpolateVariablesInQueries(queries: InfluxQuery[], scopedVars: ScopedVars): InfluxQuery[] {
    if (!queries || queries.length === 0) {
      return [];
    }

    return queries.map((query) => {
      if (this.version === InfluxVersion.Flux) {
        return {
          ...query,
          datasource: this.getRef(),
          query: this.templateSrv.replace(
            query.query ?? '',
            scopedVars,
            (value: string | string[] = [], variable: QueryVariableModel) =>
              this.interpolateQueryExpr(value, variable, query.query)
          ), // The raw query text
        };
      }

      return {
        ...query,
        datasource: this.getRef(),
        ...this.applyVariables(query, scopedVars),
      };
    });
  }

  applyVariables(query: InfluxQuery & SQLQuery, scopedVars: ScopedVars, filters?: AdHocVariableFilter[]) {
    const expandedQuery = { ...query };
    if (query.groupBy) {
      expandedQuery.groupBy = query.groupBy.map((groupBy) => {
        return {
          ...groupBy,
          params: groupBy.params?.map((param) => this.templateSrv.replace(param.toString(), undefined)),
        };
      });
    }

    if (query.select) {
      expandedQuery.select = query.select.map((selects) => {
        return selects.map((select) => {
          return {
            ...select,
            params: select.params?.map((param) => this.templateSrv.replace(param.toString(), scopedVars)),
          };
        });
      });
    }

    if (query.tags) {
      expandedQuery.tags = query.tags.map((tag) => {
        // Remove the regex wrapper if the operator is not a regex operator
        if (tag.operator !== '=~' && tag.operator !== '!~') {
          tag.value = removeRegexWrapper(tag.value);
        }

        return {
          ...tag,
          key: this.templateSrv.replace(tag.key, scopedVars),
          value: this.templateSrv.replace(
            tag.value ?? '',
            scopedVars,
            (value: string | string[] = [], variable: QueryVariableModel) =>
              this.interpolateQueryExpr(value, variable, tag.value)
          ),
        };
      });
    }

    return {
      ...expandedQuery,
      adhocFilters: filters ?? [],
      query: this.templateSrv.replace(
        query.query ?? '',
        scopedVars,
        (value: string | string[] = [], variable: QueryVariableModel) =>
          this.interpolateQueryExpr(value, variable, query.query)
      ), // The raw sql query text
      rawSql: this.templateSrv.replace(
        query.rawSql ?? '',
        scopedVars,
        (value: string | string[] = [], variable: QueryVariableModel) =>
          this.interpolateQueryExpr(value, variable, query.rawSql)
      ), // The raw sql query text
      alias: this.templateSrv.replace(query.alias ?? '', scopedVars),
      limit: this.templateSrv.replace(query.limit?.toString() ?? '', scopedVars),
      measurement: this.templateSrv.replace(
        query.measurement ?? '',
        scopedVars,
        (value: string | string[] = [], variable: QueryVariableModel) =>
          this.interpolateQueryExpr(value, variable, query.measurement)
      ),
      policy: this.templateSrv.replace(query.policy ?? '', scopedVars),
      slimit: this.templateSrv.replace(query.slimit?.toString() ?? '', scopedVars),
      tz: this.templateSrv.replace(query.tz ?? '', scopedVars),
    };
  }

  interpolateQueryExpr(value: string | string[] = [], variable: QueryVariableModel, query?: string) {
    if (typeof value === 'string') {
      // Check the value is a number. If not run to escape special characters
      if (!isNaN(parseFloat(value))) {
        return value;
      }
    }

    // If template variable is a multi-value variable
    // we always want to deal with special chars.
    if (variable.multi) {
      if (typeof value === 'string') {
        // Check the value is a number. If not run to escape special characters
        if (isNaN(parseFloat(value))) {
          return escapeRegex(value);
        }
        return value;
      }

      // If the value is a string array first escape them then join them with pipe
      // then put inside parenthesis.
      return `(${value.map((v) => escapeRegex(v)).join('|')})`;
    }

    // If the variable is not a multi-value variable
    // we want to see how it's been used. If it is used in a regex expression
    // we escape it. Otherwise, we return it directly.
    // The regex below searches for regexes within the query string
    const regexMatcher = new RegExp(
      /(\s*(=|!)~\s*)\/((?![*+?])(?:[^\r\n\[/\\]|\\.|\[(?:[^\r\n\]\\]|\\.)*\])+)\/((?:g(?:im?|mi?)?|i(?:gm?|mg?)?|m(?:gi?|ig?)?)?)/,
      'gm'
    );
    // If matches are found this regex is evaluated to check if the variable is contained in the regex /^...$/ (^ and $ is optional)
    // i.e. /^$myVar$/ or /$myVar/ or /^($myVar)$/
    const regex = new RegExp(`\\/(?:\\^)?(.*)(\\$${variable.name})(.*)(?:\\$)?\\/`, 'gm');

    // We need to validate the type of the query as some legacy cases can pass a query value with a different type
    if (!query || typeof query !== 'string') {
      return value;
    }

    const queryMatches = query.match(regexMatcher);
    if (!queryMatches) {
      return value;
    }
    for (const match of queryMatches) {
      if (!match.match(regex)) {
        continue;
      }

      // If the value is a string array first escape them then join them with pipe
      // then put inside parenthesis.
      return typeof value === 'string' ? escapeRegex(value) : `(${value.map((v) => escapeRegex(v)).join('|')})`;
    }

    return value;
  }

  async runMetadataQuery(target: InfluxQuery): Promise<MetricFindValue[]> {
    return lastValueFrom(
      super.query({
        targets: [target],
      } as DataQueryRequest)
    ).then(this.toMetricFindValue);
  }

  async metricFindQuery(query: InfluxVariableQuery, options?: any): Promise<MetricFindValue[]> {
    if (
      this.version === InfluxVersion.Flux ||
      this.version === InfluxVersion.SQL ||
      this.isMigrationToggleOnAndIsAccessProxy()
    ) {
      const target: InfluxQuery & SQLQuery = {
        refId: 'metricFindQuery',
        query: query.query,
        rawQuery: true,
        ...(this.version === InfluxVersion.SQL ? { rawSql: query.query, format: QueryFormat.Table } : {}),
      };
      return lastValueFrom(
        super.query({
          ...(options ?? {}), // includes 'range'
          maxDataPoints: query.maxDataPoints,
          targets: [target],
        })
      ).then(this.toMetricFindValue);
    }

    const interpolated = this.templateSrv.replace(
      query.query,
      options?.scopedVars,
      (value: string | string[] = [], variable: QueryVariableModel) =>
        this.interpolateQueryExpr(value, variable, query.query)
    );

    return lastValueFrom(this._seriesQuery(interpolated, options)).then((resp) => {
      return this.responseParser.parse(query.query, resp);
    });
  }

  toMetricFindValue(rsp: DataQueryResponse): MetricFindValue[] {
    const valueMap = new Map<string, MetricFindValue>();
    // Create MetricFindValue object for all frames
    rsp?.data?.forEach((frame: DataFrame) => {
      if (frame && frame.length > 0) {
        let field = frame.fields.find((f) => f.type === FieldType.string);
        if (!field) {
          field = frame.fields.find((f) => f.type !== FieldType.time);
        }
        if (field) {
          field.values.forEach((v) => {
            valueMap.set(v.toString(), { text: v.toString() });
          });
        }
      }
    });
    return Array.from(valueMap.values());
  }
  // By implementing getTagKeys and getTagValues we add ad-hoc filters functionality
  // Used in public/app/features/variables/adhoc/picker/AdHocFilterKey.tsx::fetchFilterKeys
  getTagKeys(options?: DataSourceGetTagKeysOptions<InfluxQuery>) {
    const query = buildMetadataQuery({
      type: 'TAG_KEYS',
      templateService: this.templateSrv,
      database: this.database,
      withTimeFilter: this.showTagTime,
    });

    return this.metricFindQuery({ refId: 'get-tag-keys', query });
  }

  getTagValues(options: DataSourceGetTagValuesOptions<InfluxQuery>) {
    const query = buildMetadataQuery({
      type: 'TAG_VALUES',
      templateService: this.templateSrv,
      database: this.database,
      withKey: options.key,
      withTimeFilter: this.showTagTime,
    });

    return this.metricFindQuery({ refId: 'get-tag-values', query });
  }

  /**
   * @deprecated
   */
  _seriesQuery(query: string, options?: any) {
    if (!query) {
      return of({ results: [] });
    }

    if (options && options.range) {
      const timeFilter = this.getTimeFilter({ rangeRaw: options.range, timezone: options.timezone });
      query = query.replace('$timeFilter', timeFilter);
    }

    return this._influxRequest(this.httpMode, '/query', { q: query, epoch: 'ms' }, options);
  }

  /**
   * @deprecated
   */
  serializeParams(params: any) {
    if (!params) {
      return '';
    }

    return reduce(
      params,
      (memo: string[], value, key) => {
        if (value === null || value === undefined) {
          return memo;
        }
        memo.push(encodeURIComponent(key) + '=' + encodeURIComponent(value));
        return memo;
      },
      []
    ).join('&');
  }

  /**
   * @deprecated
   */
  _influxRequest(method: string, url: string, data: any, options?: any) {
    const currentUrl = this.urls.shift()!;
    this.urls.push(currentUrl);

    const params: any = {};

    if (this.username) {
      params.u = this.username;
      params.p = this.password;
    }

    if (options && options.database) {
      params.db = options.database;
    } else if (this.database) {
      params.db = this.database;
    }

    if (options?.policy && options.policy !== DEFAULT_POLICY) {
      params.rp = options.policy;
    }

    const { q } = data;

    if (method === 'POST' && has(data, 'q')) {
      // verb is POST and 'q' param is defined
      extend(params, omit(data, ['q']));
      data = this.serializeParams(pick(data, ['q']));
    } else if (method === 'GET' || method === 'POST') {
      // verb is GET, or POST without 'q' param
      extend(params, data);
      data = null;
    }

    const req: any = {
      method: method,
      url: currentUrl + url,
      params: params,
      data: data,
      precision: 'ms',
      inspect: { type: 'influxdb' },
      paramSerializer: this.serializeParams,
    };

    req.headers = req.headers || {};
    if (this.basicAuth || this.withCredentials) {
      req.withCredentials = true;
    }
    if (this.basicAuth) {
      req.headers.Authorization = this.basicAuth;
    }

    if (method === 'POST') {
      req.headers['Content-type'] = 'application/x-www-form-urlencoded';
    }

    return getBackendSrv()
      .fetch(req)
      .pipe(
        map((result: FetchResponse) => {
          const { data } = result;
          if (data) {
            data.executedQueryString = q;
            if (data.results) {
              const errors = result.data.results.filter((elem: any) => elem.error);

              if (errors.length > 0) {
                throw {
                  message: 'InfluxDB Error: ' + errors[0].error,
                  data,
                };
              }
            }
          }
          return data;
        }),
        catchError((err) => {
          if (err.cancelled) {
            return of(err);
          }

          return throwError(this.handleErrors(err));
        })
      );
  }

  /**
   * @deprecated
   */
  handleErrors(err: any) {
    const error: DataQueryError = {
      message:
        (err && err.status) ||
        (err && err.message) ||
        'Unknown error during query transaction. Please check JS console logs.',
    };

    if ((Number.isInteger(err.status) && err.status !== 0) || err.status >= 300) {
      if (err.data && err.data.error) {
        error.message = 'InfluxDB Error: ' + err.data.error;
        error.data = err.data;
        // @ts-ignore
        error.config = err.config;
      } else {
        error.message = 'Network Error: ' + err.statusText + '(' + err.status + ')';
        error.data = err.data;
        // @ts-ignore
        error.config = err.config;
      }
    }

    return error;
  }

  getTimeFilter(options: { rangeRaw: RawTimeRange; timezone: string }) {
    const from = this.getInfluxTime(options.rangeRaw.from, false, options.timezone);
    const until = this.getInfluxTime(options.rangeRaw.to, true, options.timezone);

    return 'time >= ' + from + ' and time <= ' + until;
  }

  getInfluxTime(date: DateTime | string, roundUp: boolean, timezone: string) {
    let outPutDate;
    if (isString(date)) {
      if (date === 'now') {
        return 'now()';
      }

      const parts = /^now-(\d+)([dhms])$/.exec(date);
      if (parts) {
        const amount = parseInt(parts[1], 10);
        const unit = parts[2];
        return 'now() - ' + amount + unit;
      }
      outPutDate = dateMath.parse(date, roundUp, timezone);
      if (!outPutDate) {
        throw new Error('unable to parse date');
      }
      date = outPutDate;
    }

    return date.valueOf() + 'ms';
  }

  // ------------------------ Legacy Code - Before Backend Migration ---------------

  isMigrationToggleOnAndIsAccessProxy() {
    return config.featureToggles.influxdbBackendMigration && this.access === 'proxy';
  }

  /**
   * The unchanged pre 7.1 query implementation
   * @deprecated
   */
  classicQuery(options: any): Observable<DataQueryResponse> {
    let timeFilter = this.getTimeFilter(options);
    const scopedVars = options.scopedVars;
    const targets = cloneDeep(options.targets);
    const queryTargets: any[] = [];

    let i, y;

    let allQueries = _map(targets, (target) => {
      if (target.hide) {
        return '';
      }

      queryTargets.push(target);

      // backward compatibility
      scopedVars.interval = scopedVars.__interval;

      return new InfluxQueryModel(target, this.templateSrv, scopedVars).render(true);
    }).reduce((acc, current) => {
      if (current !== '') {
        acc += ';' + current;
      }
      return acc;
    });

    if (allQueries === '') {
      return of({ data: [] });
    }

    // add global adhoc filters to timeFilter
    const adhocFilters = options.filters;
    const adhocFiltersFromDashboard = options.targets.flatMap((target: InfluxQuery) => target.adhocFilters ?? []);
    if (adhocFilters?.length || adhocFiltersFromDashboard?.length) {
      const ahFilters = adhocFilters?.length ? adhocFilters : adhocFiltersFromDashboard;
      const tmpQuery = new InfluxQueryModel({ refId: 'A' }, this.templateSrv, scopedVars);
      timeFilter += ' AND ' + tmpQuery.renderAdhocFilters(ahFilters);
    }
    // replace grafana variables
    scopedVars.timeFilter = { value: timeFilter };

    // replace templated variables
    allQueries = this.templateSrv.replace(allQueries, scopedVars);

    return this._seriesQuery(allQueries, options).pipe(
      map((data) => {
        if (!data || !data.results) {
          return { data: [] };
        }

        const seriesList = [];
        for (i = 0; i < data.results.length; i++) {
          const result = data.results[i];
          if (!result || !result.series) {
            continue;
          }

          const target = queryTargets[i];
          let alias = target.alias;
          if (alias) {
            alias = this.templateSrv.replace(target.alias, options.scopedVars);
          }

          const meta: QueryResultMeta = {
            executedQueryString: data.executedQueryString,
          };

          const influxSeries = new InfluxSeries({
            refId: target.refId,
            series: data.results[i].series,
            alias: alias,
            meta,
          });

          switch (target.resultFormat) {
            case 'logs':
              meta.preferredVisualisationType = 'logs';
            case 'table': {
              seriesList.push(influxSeries.getTable());
              break;
            }
            default: {
              const timeSeries = influxSeries.getTimeSeries();
              for (y = 0; y < timeSeries.length; y++) {
                seriesList.push(timeSeriesToDataFrame(timeSeries[y]));
              }
              break;
            }
          }
        }

        return { data: seriesList };
      })
    );
  }

  async annotationEvents(options: DataQueryRequest, annotation: InfluxQuery): Promise<AnnotationEvent[]> {
    if (this.version === InfluxVersion.Flux) {
      return Promise.reject({
        message: 'Flux requires the standard annotation query',
      });
    }

    // InfluxQL puts a query string on the annotation
    if (!annotation.query) {
      return Promise.reject({
        message: 'Query missing in annotation definition',
      });
    }

    if (this.isMigrationToggleOnAndIsAccessProxy()) {
      // We want to send our query to the backend as a raw query
      const target: InfluxQuery = {
        refId: 'metricFindQuery',
        datasource: this.getRef(),
        query: this.templateSrv.replace(
          annotation.query,
          undefined,
          (value: string | string[] = [], variable: QueryVariableModel) =>
            this.interpolateQueryExpr(value, variable, annotation.query)
        ),
        rawQuery: true,
      };

      return lastValueFrom(
        getBackendSrv()
          .fetch<BackendDataSourceResponse>({
            url: '/api/ds/query',
            method: 'POST',
            headers: this.getRequestHeaders(),
            data: {
              from: options.range.from.valueOf().toString(),
              to: options.range.to.valueOf().toString(),
              queries: [target],
            },
            requestId: annotation.name,
          })
          .pipe(
            map(
              async (res: FetchResponse<BackendDataSourceResponse>) =>
                await this.responseParser.transformAnnotationResponse(annotation, res, target)
            )
          )
      );
    }

    const timeFilter = this.getTimeFilter({ rangeRaw: options.range.raw, timezone: options.timezone });
    let query = annotation.query.replace('$timeFilter', timeFilter);
    query = this.templateSrv.replace(query, undefined, (value: string | string[] = [], variable: QueryVariableModel) =>
      this.interpolateQueryExpr(value, variable, query)
    );

    return lastValueFrom(this._seriesQuery(query, options)).then((data) => {
      if (!data || !data.results || !data.results[0]) {
        throw { message: 'No results in response from InfluxDB' };
      }
      return new InfluxSeries({
        series: data.results[0].series,
        annotation: annotation,
      }).getAnnotations();
    });
  }
}

// we detect the field type based on the value-array
function getFieldType(values: unknown[]): FieldType {
  // the values-array may contain a lot of nulls.
  // we need the first not-null item
  const firstNotNull = values.find((v) => v !== null);

  if (firstNotNull === undefined) {
    // we could not find any not-null values
    return FieldType.number;
  }

  const valueType = typeof firstNotNull;

  switch (valueType) {
    case 'string':
      return FieldType.string;
    case 'boolean':
      return FieldType.boolean;
    case 'number':
      return FieldType.number;
    default:
      // this should never happen, influxql values
      // can only be numbers, strings and booleans.
      throw new Error(`InfluxQL: invalid value type ${valueType}`);
  }
}

// this conversion function is specialized to work with the timeseries
// data returned by InfluxDatasource.getTimeSeries()
function timeSeriesToDataFrame(timeSeries: TimeSeries): DataFrame {
  const times: number[] = [];
  const values: unknown[] = [];

  // the data we process here is not correctly typed.
  // the typescript types say every data-point is number|null,
  // but in fact it can be string or boolean too.

  const points = timeSeries.datapoints;
  for (const point of points) {
    values.push(point[0]);
    times.push(point[1] as number);
  }

  const timeField = {
    name: TIME_SERIES_TIME_FIELD_NAME,
    type: FieldType.time,
    config: {},
    values: times,
  };

  const valueField = {
    name: TIME_SERIES_VALUE_FIELD_NAME,
    type: getFieldType(values),
    config: {
      displayNameFromDS: timeSeries.title,
    },
    values: values,
    labels: timeSeries.tags,
  };

  const fields = [timeField, valueField];

  return {
    name: timeSeries.target,
    refId: timeSeries.refId,
    meta: timeSeries.meta,
    fields,
    length: values.length,
  };
}