refactor: simplify Observable creation using of() operator in HistoricalQueryHandler

src/datasources/tag/CurrentQueryHandler.ts

@@ -2,10 +2,11 @@ import { DataFrameDTO, FieldType, TimeRange } from "@grafana/data";
 import { QueryHandler, TagWithValue } from "./types";
 import { convertTagValue } from "./utils";
 import { Workspace } from "core/types";
+import { Observable, of } from "rxjs";
 
 export class CurrentQueryHandler extends QueryHandler {
-    handleQuery(tagsWithValues: TagWithValue[], result: DataFrameDTO, _workspaces: Workspace[], _range: TimeRange, _maxDataPoints: number | undefined, queryProperties: boolean): Promise<DataFrameDTO> {
-        return Promise.resolve(this.handleCurrentQuery(queryProperties, tagsWithValues, result));
+    handleQuery(tagsWithValues: TagWithValue[], result: DataFrameDTO, _workspaces: Workspace[], _range: TimeRange, _maxDataPoints: number | undefined, queryProperties: boolean): Observable<DataFrameDTO> {
+        return of(this.handleCurrentQuery(queryProperties, tagsWithValues, result));
     }
 
     private handleCurrentQuery(queryProperties: boolean, tagsWithValues: TagWithValue[], result: DataFrameDTO): DataFrameDTO {

src/datasources/tag/HistoricalQueryHandler.ts

@@ -3,44 +3,47 @@ import { PostFn, QueryHandler, TagHistoryResponse, TagWithValue, TimeAndTagTypeV
 import { convertTagValue } from "./utils";
 import { getWorkspaceName } from "core/utils";
 import { Workspace } from "core/types";
+import { map, merge, Observable, of, switchMap } from "rxjs";
 
 export class HistoricalQueryHandler extends QueryHandler {
     constructor(
-        private readonly post: PostFn,
+        private readonly post$: PostFn,
         private readonly baseUrl?: string
     ) {
         super();
     }
 
-    handleQuery(tagsWithValues: TagWithValue[], result: DataFrameDTO, workspaces: Workspace[], range: TimeRange, maxDataPoints: number | undefined, _queryProperties: boolean): Promise<DataFrameDTO> {
-        return this.handleHistoricalQuery(tagsWithValues, workspaces, range, maxDataPoints, result);
+    handleQuery(tagsWithValues: TagWithValue[], result: DataFrameDTO, workspaces: Workspace[], range: TimeRange, maxDataPoints: number | undefined, _queryProperties: boolean): Observable<DataFrameDTO> {
+        return this.handleHistoricalQuery$(tagsWithValues, workspaces, range, maxDataPoints, result);
     }
 
-    private async handleHistoricalQuery(
+    private handleHistoricalQuery$(
         tagsWithValues: TagWithValue[],
         workspaces: Workspace[],
         range: TimeRange,
         maxDataPoints: number | undefined,
         result: DataFrameDTO,
-    ): Promise<DataFrameDTO> {
+    ): Observable<DataFrameDTO> {
         const tagPathCount = this.countTagPaths(tagsWithValues);
         const workspaceTagMap = this.groupTagsByWorkspace(tagsWithValues);
         const tagPropertiesMap = this.buildTagPropertiesMap(tagsWithValues, tagPathCount, workspaces);
 
-        const tagsDecimatedHistory = await this.fetchTagsHistory(
+        return this.fetchTagsHistory$(
             workspaceTagMap,
             workspaces,
             range,
             maxDataPoints,
             tagPathCount
-        );
+        ).pipe(
+            map((tagsDecimatedHistory) => {
+                const mergedTagValuesWithType = this.mergeTagsHistoryValues(tagsDecimatedHistory);
 
-        const mergedTagValuesWithType = this.mergeTagsHistoryValues(tagsDecimatedHistory);
+                this.addTimeFieldToResult(result, mergedTagValuesWithType.timestamps);
+                this.addTagFieldsToResult(result, mergedTagValuesWithType.values, tagPropertiesMap);
 
-        this.addTimeFieldToResult(result, mergedTagValuesWithType.timestamps);
-        this.addTagFieldsToResult(result, mergedTagValuesWithType.values, tagPropertiesMap);
-
-        return result;
+                return result;
+            }
+        ));
     }
 
     private countTagPaths(tagsWithValues: TagWithValue[]): Record<string, number> {
@@ -78,35 +81,35 @@ export class HistoricalQueryHandler extends QueryHandler {
         return tagPropertiesMap;
     }
 
-    private async fetchTagsHistory(
+    private fetchTagsHistory$(
         workspaceTagMap: Record<string, TagWithValue[]>,
         workspaces: Workspace[],
         range: TimeRange,
         maxDataPoints: number | undefined,
         tagPathCount: Record<string, number>
-    ): Promise<Record<string, TypeAndValues>> {
+    ): Observable<Record<string, TypeAndValues>> {
         const tagsDecimatedHistory: Record<string, TypeAndValues> = {};
 
-        for (const workspace in workspaceTagMap) {
-            const tagHistoryResponse = await this.getTagHistoryWithChunks(
-                workspaceTagMap[workspace],
-                workspace,
-                range,
-                maxDataPoints || 0,
+        const observables$ = Object.entries(workspaceTagMap).map(([workspace, tags]) => {
+            return this.getTagHistoryWithChunks$(tags, workspace, range, maxDataPoints || 0).pipe(
+                map(tagHistoryResponse => {
+                    for (const path in tagHistoryResponse.results) {
+                        const prefixedPath =
+                            tagPathCount[path] > 1
+                                ? `${getWorkspaceName(workspaces, workspace)}.${path}`
+                                : path;
+
+                        tagsDecimatedHistory[prefixedPath] = tagHistoryResponse.results[path];
+                    }
+                })
             );
+        });
 
-            for (const path in tagHistoryResponse.results) {
-                const prefixedPath = tagPathCount[path] > 1
-                    ? `${getWorkspaceName(workspaces, workspace)}.${path}`
-                    : path;
-                tagsDecimatedHistory[prefixedPath] = tagHistoryResponse.results[path];
-            }
-        }
-
-        return tagsDecimatedHistory;
+        return merge(...observables$)
+            .pipe(map(() => tagsDecimatedHistory));
     }
 
-    private async getTagHistoryWithChunks(paths: TagWithValue[], workspace: string, range: TimeRange, intervals: number): Promise<TagHistoryResponse> {
+    private getTagHistoryWithChunks$(paths: TagWithValue[], workspace: string, range: TimeRange, intervals: number): Observable<TagHistoryResponse> {
         const chunkSize = 10;
         const pathChunks: TagWithValue[][] = [];
         for (let i = 0; i < paths.length; i += chunkSize) {
@@ -115,26 +118,32 @@ export class HistoricalQueryHandler extends QueryHandler {
 
         const aggregatedResults: TagHistoryResponse = { results: {} };
 
-        const chunkResults = await Promise.all(
-            pathChunks.map((chunk) => this.getTagHistoryValues(chunk.map(({ tag }) => tag.path), workspace, range, intervals))
-        );
-
-        for (const chunkResult of chunkResults) {
-            for (const [path, data] of Object.entries(chunkResult.results)) {
-                if (!aggregatedResults.results[path]) {
-                    aggregatedResults.results[path] = data;
-                } else {
-                    aggregatedResults.results[path].values.push(...data.values);
-                }
-            }
-        }
 
-        return aggregatedResults;
+        const chunkResults$ = pathChunks.map((chunk) => this.getTagHistoryValues(chunk.map(({ tag }) => tag.path), workspace, range, intervals))
+
+        return chunkResults$.reduce((acc$, chunk$) =>
+            acc$.pipe(
+                switchMap(aggregated =>
+                    chunk$.pipe(
+                        map(chunkResult => {
+                            for (const [path, data] of Object.entries(chunkResult.results)) {
+                                if (!aggregated.results[path]) {
+                                    aggregated.results[path] = data;
+                                } else {
+                                    aggregated.results[path].values.push(...data.values);
+                                }
+                            }
+                            return aggregated;
+                        })
+                    )
+                )
+            ),
+            of(aggregatedResults));
     }
 
-    private async getTagHistoryValues(paths: string[], workspace: string, range: TimeRange, intervals: number): Promise<TagHistoryResponse> {
+    private getTagHistoryValues(paths: string[], workspace: string, range: TimeRange, intervals: number): Observable<TagHistoryResponse> {
         const tagHistoryUrl = this.baseUrl + '/nitaghistorian/v2/tags';
-        return await this.post<TagHistoryResponse>(`${tagHistoryUrl}/query-decimated-history`, {
+        return this.post$<TagHistoryResponse>(`${tagHistoryUrl}/query-decimated-history`, {
             paths,
             workspace,
             startTime: range.from.toISOString(),

src/datasources/tag/QueryHandlerFactory.ts

@@ -3,7 +3,7 @@ import { HistoricalQueryHandler } from "./HistoricalQueryHandler";
 import { PostFn, QueryHandler, TagQueryType } from "./types";
 
 export class QueryHandlerFactory {
-    constructor(private post: PostFn, private baseUrl?: string) {}
+    constructor(private post: PostFn, private baseUrl?: string) { }
 
     public createQueryHandler(queryType: TagQueryType): QueryHandler {
         switch (queryType) {

src/datasources/tag/TagDataSource.ts

@@ -11,10 +11,12 @@ import {
   TagQuery,
   TagQueryType,
   TagsWithValues,
+  TagWithValue,
 } from './types';
 import { Throw } from 'core/utils';
 import { expandMultipleValueVariable } from "./utils";
 import { QueryHandlerFactory } from './QueryHandlerFactory';
+import { forkJoin, map, Observable, switchMap } from 'rxjs';
 
 export class TagDataSource extends DataSourceBase<TagQuery, TagDataSourceOptions> {
   public defaultQuery: Omit<TagQuery, 'refId'> = {
@@ -25,7 +27,7 @@ export class TagDataSource extends DataSourceBase<TagQuery, TagDataSourceOptions
   };
 
   private readonly tagUrl = this.instanceSettings.url + '/nitag/v2';
-  private readonly queryHandlerFactory = new QueryHandlerFactory(this.post.bind(this), this.instanceSettings.url);
+  private readonly queryHandlerFactory = new QueryHandlerFactory(this.post$.bind(this), this.instanceSettings.url);
 
   constructor(
     readonly instanceSettings: DataSourceInstanceSettings<TagDataSourceOptions>,
@@ -35,16 +37,23 @@ export class TagDataSource extends DataSourceBase<TagQuery, TagDataSourceOptions
     super(instanceSettings, backendSrv, templateSrv);
   }
 
-  async runQuery(query: TagQuery, { range, maxDataPoints, scopedVars }: DataQueryRequest): Promise<DataFrameDTO> {
-    const tagsWithValues = await this.getMostRecentTagsByMultiplePaths(
+  runQuery(query: TagQuery, { range, maxDataPoints, scopedVars }: DataQueryRequest): Observable<DataFrameDTO> {
+    const tagsWithValues$ = this.getMostRecentTagsByMultiplePaths$(
       this.generatePathsFromTemplate(query, scopedVars),
       this.templateSrv.replace(query.workspace, scopedVars)
     );
+    const workspacesPromise = this.getWorkspaces();
 
-    const workspaces = await this.getWorkspaces();
-    const result: DataFrameDTO = { refId: query.refId, fields: [] };
+    return forkJoin([
+      tagsWithValues$,
+      workspacesPromise
+    ]).pipe(
+      switchMap(([tagsWithValues, workspaces]) => {
+        const result: DataFrameDTO = { refId: query.refId, fields: [] };
 
-    return this.queryHandlerFactory.createQueryHandler(query.type).handleQuery(tagsWithValues, result, workspaces, range, maxDataPoints, query.properties);
+        return this.queryHandlerFactory.createQueryHandler(query.type).handleQuery(tagsWithValues, result, workspaces, range, maxDataPoints, query.properties);
+      })
+    );
   }
 
   /**
@@ -54,27 +63,31 @@ export class TagDataSource extends DataSourceBase<TagQuery, TagDataSourceOptions
    **/
   private generatePathsFromTemplate(query: TagQuery, scopedVars: Record<string, any>): string[] {
     let paths: string[] = [query.path];
-    
+
     const replacedPath = this.templateSrv.replace(
       query.path,
       scopedVars,
       (v: string | string[]): string => `{${v}}`
     );
-    
+
     paths = expandMultipleValueVariable(replacedPath);
-    
+
     return paths;
   }
 
-  private async getMostRecentTagsByMultiplePaths(paths: string[], workspace: string) {
+  private getMostRecentTagsByMultiplePaths$(paths: string[], workspace: string): Observable<TagWithValue[]> {
     const workspaceQuery = [workspace || "*"];
-    const response = await this.post<TagsWithValues>(`${this.tagUrl}/fetch-tags-with-values`, {
+    const response = this.post$<TagsWithValues>(`${this.tagUrl}/fetch-tags-with-values`, {
       paths: paths,
       workspaces: workspaceQuery,
       take: 100,
-    });
+    }).pipe(
+      map((res: TagsWithValues) => {
+        return res.tagsWithValues.length ? res.tagsWithValues : Throw(`No tags matched the path '${paths}'`);
+      })
+    );
 
-    return response.tagsWithValues.length ? response.tagsWithValues : Throw(`No tags matched the path '${paths}'`)
+    return response;
   }
 
   shouldRunQuery(query: TagQuery): boolean {