[IMP] model: add canDispatch method

Add the method `canDispatch` in the model, that will run the given commands
against the `allowDispatch` of the handlers, and return the result.

This will be useful to dynamically display errors in side panels, without
waiting for user confirmation.

Part of task 3271348

Part-of: #2331

src/model.ts

@@ -448,6 +448,14 @@ export class Model extends EventBus<any> implements CommandDispatcher {
     this.status = Status.Ready;
   }
 
+  /**
+   * Check if a command can be dispatched, and returns a DispatchResult object with the possible
+   * reasons the dispatch failed.
+   */
+  canDispatch: CommandDispatcher["canDispatch"] = (type: string, payload?: any) => {
+    return this.checkDispatchAllowed({ ...payload, type });
+  };
+
   /**
    * The dispatch method is the only entry point to manipulate data in the model.
    * This is through this method that commands are dispatched most of the time

src/types/commands.ts

@@ -1160,6 +1160,10 @@ export interface CommandDispatcher {
     type: T,
     r: Omit<C, "type">
   ): DispatchResult;
+  canDispatch<T extends CommandTypes, C extends Extract<Command, { type: T }>>(
+    type: T,
+    r: Omit<C, "type">
+  ): DispatchResult;
 }
 
 export interface CoreCommandDispatcher {
@@ -1170,6 +1174,10 @@ export interface CoreCommandDispatcher {
     type: T,
     r: Omit<C, "type">
   ): DispatchResult;
+  canDispatch<T extends CoreCommandTypes, C extends Extract<CoreCommand, { type: T }>>(
+    type: T,
+    r: Omit<C, "type">
+  ): DispatchResult;
 }
 
 export type CommandTypes = Command["type"];

tests/model.test.ts

@@ -111,6 +111,31 @@ describe("Model", () => {
     featurePluginRegistry.remove("myUIPlugin");
   });
 
+  test("canDispatch method is exposed and works", () => {
+    class MyCorePlugin extends CorePlugin {
+      allowDispatch(cmd: CoreCommand) {
+        if (cmd.type === "CREATE_SHEET") {
+          return CommandResult.CancelledForUnknownReason;
+        }
+        return CommandResult.Success;
+      }
+    }
+    corePluginRegistry.add("myCorePlugin", MyCorePlugin);
+    const model = new Model();
+    expect(model.canDispatch("CREATE_SHEET", { sheetId: "42", position: 1 })).toBeCancelledBecause(
+      CommandResult.CancelledForUnknownReason
+    );
+    expect(model.dispatch("CREATE_SHEET", { sheetId: "42", position: 1 })).toBeCancelledBecause(
+      CommandResult.CancelledForUnknownReason
+    );
+
+    expect(model.canDispatch("UPDATE_CELL", { sheetId: "42", col: 0, row: 0, content: "hey" }))
+      .toBeSuccessfullyDispatched;
+    expect(model.dispatch("UPDATE_CELL", { sheetId: "42", col: 0, row: 0, content: "hey" }))
+      .toBeSuccessfullyDispatched;
+    corePluginRegistry.remove("myCorePlugin");
+  });
+
   test("Can open a model in readonly mode", () => {
     const model = new Model({}, { mode: "readonly" });
     expect(model.getters.isReadonly()).toBe(true);