Merge value formatter (#197)

* use value formatter for calculating values

* validate $user dialect

* 2.6.75

.eslintrc

@@ -4,7 +4,7 @@
     "plugin:node/recommended"
 ],
   "parserOptions": {
-    "ecmaVersion": 2015,
+    "ecmaVersion": 2018,
     "sourceType": "module"
   },
   "env": {

ValueFormatter.d.ts

@@ -0,0 +1,44 @@
+import { DataModelBase } from "@themost/common";
+import { AsyncSeriesEventEmitter } from '@themost/events';
+import { DataContext } from "./types";
+import { DataModel } from './data-model';
+
+export declare interface ResolvingVariable {
+    name: string;
+    model?: DataModelBase;
+    context?: DataContext;
+    target?: any;
+    value?: any;
+}
+
+
+/**
+ * Class responsible for formatting values within a given data context.
+ */
+export declare class ValueFormatter {
+
+    readonly resolvingVariable: AsyncSeriesEventEmitter<ResolvingVariable>;
+    /**
+     * Creates an instance of ValueFormatter.
+     * @param context - The data context in which the formatter operates.
+     */
+    constructor(context: DataContext, model?: DataModel, target?: any);
+
+    /**
+     * Formats the given value according to the rules defined in the data context.
+     * @param value - The value to be formatted.
+     * @returns The formatted value.
+     */
+    format(value: unknown): any;
+
+    static register(name: string, definition: { [k: string]:  (...value: any[]) => Promise<any> }): void;
+}
+
+export declare class ValueDialect {
+    /**
+     * Creates an instance of ValueDialect.
+     * @param context - The data context in which the dialect operates.
+     */
+    constructor(context: DataContext, model: DataModel, target: any);
+
+}