feat(history-plugin): allow custom clear function

akita/__tests__/stateHistory.spec.ts

@@ -184,6 +184,34 @@ describe('StateHistory', () => {
       present: { counter: 5 },
       future: [{ counter: 4 }]
     });
+
+    stateHistory.clear((history) => {
+      return {
+        past: history.past,
+        present: history.present,
+        future: []
+      };
+    });
+
+    expect(stateHistory.history).toEqual({
+      past: [{ counter: 0 }, { counter: 2 }, { counter: 4 }],
+      present: { counter: 5 },
+      future: []
+    });
+
+    stateHistory.clear((history) => {
+      return {
+        past: [],
+        present: history.present,
+        future: history.future
+      };
+    });
+
+    expect(stateHistory.history).toEqual({
+      past: [],
+      present: { counter: 5 },
+      future: []
+    });
   });
 });
 

akita/src/plugins/stateHistory/stateHistoryPlugin.ts

@@ -3,12 +3,19 @@ import { toBoolean } from '../../toBoolean';
 import { AkitaPlugin, Queries } from '../plugin';
 import { EntityParam } from '../entityCollectionPlugin';
 import { logAction } from '../../actions';
+import { isFunction } from '../../isFunction';
 
 export interface StateHistoryParams {
   maxAge?: number;
   comparator?: (prevState, currentState) => boolean;
 }
 
+export type History<S> = {
+  past: S[],
+  present: S | null,
+  future: S[]
+}
+
 export class StateHistoryPlugin<E = any, S = any> extends AkitaPlugin<E, S> {
   /** Allow skipping an update from outside */
   private skip = false;
@@ -124,9 +131,24 @@ export class StateHistoryPlugin<E = any, S = any> extends AkitaPlugin<E, S> {
     this.update('Redo');
   }
 
-  clear() {
-    this.history = {
-      past: [],
+  /**
+   * Clear the history
+   * 
+   * @param customUpdateFn Callback function for only clearing part of the history
+   * 
+   * @example
+   * 
+   * stateHistory.clear((history) => {
+   *  return {
+   *    past: history.past,
+   *    present: history.present,
+   *    future: []
+   *  };
+   * });
+   */
+  clear(customUpdateFn?: (history: History<S>) => History<S>) {
+    this.history = isFunction(customUpdateFn) ? customUpdateFn(this.history) : {
+      past:  [],
       present: null,
       future: []
     };