async showInputBox()

in quickinput-sample/src/multiStepInput.ts [248:305]
58 lines of code
10 McCabe index (conditional complexity)

	async showInputBox<P extends InputBoxParameters>({ title, step, totalSteps, value, prompt, validate, buttons, shouldResume }: P) {
		const disposables: Disposable[] = [];
		try {
			return await new Promise<string | (P extends { buttons: (infer I)[] } ? I : never)>((resolve, reject) => {
				const input = window.createInputBox();
				input.title = title;
				input.step = step;
				input.totalSteps = totalSteps;
				input.value = value || '';
				input.prompt = prompt;
				input.buttons = [
					...(this.steps.length > 1 ? [QuickInputButtons.Back] : []),
					...(buttons || [])
				];
				let validating = validate('');
				disposables.push(
					input.onDidTriggerButton(item => {
						if (item === QuickInputButtons.Back) {
							reject(InputFlowAction.back);
						} else {
							resolve(<any>item);
						}
					}),
					input.onDidAccept(async () => {
						const value = input.value;
						input.enabled = false;
						input.busy = true;
						if (!(await validate(value))) {
							resolve(value);
						}
						input.enabled = true;
						input.busy = false;
					}),
					input.onDidChangeValue(async text => {
						const current = validate(text);
						validating = current;
						const validationMessage = await current;
						if (current === validating) {
							input.validationMessage = validationMessage;
						}
					}),
					input.onDidHide(() => {
						(async () => {
							reject(shouldResume && await shouldResume() ? InputFlowAction.resume : InputFlowAction.cancel);
						})()
							.catch(reject);
					})
				);
				if (this.current) {
					this.current.dispose();
				}
				this.current = input;
				this.current.show();
			});
		} finally {
			disposables.forEach(d => d.dispose());
		}
	}