[Expressions] Refactor expression functions to use observables underneath

docs/development/plugins/expressions/public/kibana-plugin-plugins-expressions-public.expressionfunctiondefinition.md

@@ -23,7 +23,7 @@ export interface ExpressionFunctionDefinition<Name extends string, Input, Argume
 |  [help](./kibana-plugin-plugins-expressions-public.expressionfunctiondefinition.help.md) | <code>string</code> | Help text displayed in the Expression editor. This text should be internationalized. |
 |  [inputTypes](./kibana-plugin-plugins-expressions-public.expressionfunctiondefinition.inputtypes.md) | <code>Array&lt;TypeToString&lt;Input&gt;&gt;</code> | List of allowed type names for input value of this function. If this property is set the input of function will be cast to the first possible type in this list. If this property is missing the input will be provided to the function as-is. |
 |  [name](./kibana-plugin-plugins-expressions-public.expressionfunctiondefinition.name.md) | <code>Name</code> | The name of the function, as will be used in expression. |
-|  [type](./kibana-plugin-plugins-expressions-public.expressionfunctiondefinition.type.md) | <code>TypeToString&lt;UnwrapPromiseOrReturn&lt;Output&gt;&gt;</code> | Name of type of value this function outputs. |
+|  [type](./kibana-plugin-plugins-expressions-public.expressionfunctiondefinition.type.md) | <code>TypeString&lt;Output&gt; &#124; UnmappedTypeStrings</code> | Name of type of value this function outputs. |
 
 ## Methods
 

docs/development/plugins/expressions/public/kibana-plugin-plugins-expressions-public.expressionfunctiondefinition.type.md

@@ -9,5 +9,5 @@ Name of type of value this function outputs.
 <b>Signature:</b>
 
 ```typescript
-type?: TypeToString<UnwrapPromiseOrReturn<Output>>;
+type?: TypeString<Output> | UnmappedTypeStrings;
 ```

docs/development/plugins/expressions/server/kibana-plugin-plugins-expressions-server.expressionfunctiondefinition.md

@@ -23,7 +23,7 @@ export interface ExpressionFunctionDefinition<Name extends string, Input, Argume
 |  [help](./kibana-plugin-plugins-expressions-server.expressionfunctiondefinition.help.md) | <code>string</code> | Help text displayed in the Expression editor. This text should be internationalized. |
 |  [inputTypes](./kibana-plugin-plugins-expressions-server.expressionfunctiondefinition.inputtypes.md) | <code>Array&lt;TypeToString&lt;Input&gt;&gt;</code> | List of allowed type names for input value of this function. If this property is set the input of function will be cast to the first possible type in this list. If this property is missing the input will be provided to the function as-is. |
 |  [name](./kibana-plugin-plugins-expressions-server.expressionfunctiondefinition.name.md) | <code>Name</code> | The name of the function, as will be used in expression. |
-|  [type](./kibana-plugin-plugins-expressions-server.expressionfunctiondefinition.type.md) | <code>TypeToString&lt;UnwrapPromiseOrReturn&lt;Output&gt;&gt;</code> | Name of type of value this function outputs. |
+|  [type](./kibana-plugin-plugins-expressions-server.expressionfunctiondefinition.type.md) | <code>TypeString&lt;Output&gt; &#124; UnmappedTypeStrings</code> | Name of type of value this function outputs. |
 
 ## Methods
 

docs/development/plugins/expressions/server/kibana-plugin-plugins-expressions-server.expressionfunctiondefinition.type.md

@@ -9,5 +9,5 @@ Name of type of value this function outputs.
 <b>Signature:</b>
 
 ```typescript
-type?: TypeToString<UnwrapPromiseOrReturn<Output>>;
+type?: TypeString<Output> | UnmappedTypeStrings;
 ```

src/plugins/expressions/common/expression_functions/specs/map_column.ts

@@ -6,24 +6,24 @@
  * Side Public License, v 1.
  */
 
-import { Observable } from 'rxjs';
-import { take } from 'rxjs/operators';
+import { Observable, defer, of, zip } from 'rxjs';
+import { map } from 'rxjs/operators';
 import { i18n } from '@kbn/i18n';
 import { ExpressionFunctionDefinition } from '../types';
 import { Datatable, DatatableColumn, getType } from '../../expression_types';
 
 export interface MapColumnArguments {
   id?: string | null;
   name: string;
-  expression?(datatable: Datatable): Observable<boolean | number | string | null>;
+  expression(datatable: Datatable): Observable<boolean | number | string | null>;
   copyMetaFrom?: string | null;
 }
 
 export const mapColumn: ExpressionFunctionDefinition<
   'mapColumn',
   Datatable,
   MapColumnArguments,
-  Promise<Datatable>
+  Observable<Datatable>
 > = {
   name: 'mapColumn',
   aliases: ['mc'], // midnight commander. So many times I've launched midnight commander instead of moving a file.
@@ -80,57 +80,56 @@ export const mapColumn: ExpressionFunctionDefinition<
       default: null,
     },
   },
-  fn: (input, args) => {
-    const expression = (...params: Parameters<Required<MapColumnArguments>['expression']>) =>
-      args
-        .expression?.(...params)
-        .pipe(take(1))
-        .toPromise() ?? Promise.resolve(null);
+  fn(input, args) {
+    const existingColumnIndex = input.columns.findIndex(({ id, name }) =>
+      args.id ? id === args.id : name === args.name
+    );
+    const id = input.columns[existingColumnIndex]?.id ?? args.id ?? args.name;
 
-    const columns = [...input.columns];
-    const existingColumnIndex = columns.findIndex(({ id, name }) => {
-      if (args.id) {
-        return id === args.id;
-      }
-      return name === args.name;
-    });
-    const columnId =
-      existingColumnIndex === -1 ? args.id ?? args.name : columns[existingColumnIndex].id;
-
-    const rowPromises = input.rows.map((row) => {
-      return expression({
-        type: 'datatable',
-        columns,
-        rows: [row],
-      }).then((val) => ({
-        ...row,
-        [columnId]: val,
-      }));
-    });
+    return defer(() => {
+      const rows$ = input.rows.length
+        ? zip(
+            ...input.rows.map((row) =>
+              args
+                .expression({
+                  type: 'datatable',
+                  columns: [...input.columns],
+                  rows: [row],
+                })
+                .pipe(map((value) => ({ ...row, [id]: value })))
+            )
+          )
+        : of([]);
 
-    return Promise.all(rowPromises).then((rows) => {
-      const type = rows.length ? getType(rows[0][columnId]) : 'null';
-      const newColumn: DatatableColumn = {
-        id: columnId,
-        name: args.name,
-        meta: { type, params: { id: type } },
-      };
-      if (args.copyMetaFrom) {
-        const metaSourceFrom = columns.find(({ id }) => id === args.copyMetaFrom);
-        newColumn.meta = { ...newColumn.meta, ...(metaSourceFrom?.meta || {}) };
-      }
+      return rows$.pipe<Datatable>(
+        map((rows) => {
+          const type = getType(rows[0]?.[id]);
+          const newColumn: DatatableColumn = {
+            id,
+            name: args.name,
+            meta: { type, params: { id: type } },
+          };
+          if (args.copyMetaFrom) {
+            const metaSourceFrom = input.columns.find(
+              ({ id: columnId }) => columnId === args.copyMetaFrom
+            );
+            newColumn.meta = { ...newColumn.meta, ...(metaSourceFrom?.meta ?? {}) };
+          }
 
-      if (existingColumnIndex === -1) {
-        columns.push(newColumn);
-      } else {
-        columns[existingColumnIndex] = newColumn;
-      }
+          const columns = [...input.columns];
+          if (existingColumnIndex === -1) {
+            columns.push(newColumn);
+          } else {
+            columns[existingColumnIndex] = newColumn;
+          }
 
-      return {
-        type: 'datatable',
-        columns,
-        rows,
-      } as Datatable;
+          return {
+            columns,
+            rows,
+            type: 'datatable',
+          };
+        })
+      );
     });
   },
 };