test-simple-calculator-docs/architecture/working-spec.md

Working Spec

Overview

SDLC SIMPCALC3 — Simple Calculator 3 is a browser-based web application that provides the four fundamental arithmetic operations: addition, subtraction, multiplication, and division. The application is delivered as a single-page web app through the AI-SDLC pipeline. It is intended to be lightweight, accessible, and easy to use without any installation or account creation.

Actors

Actor	Description
End User	Any person who opens the web app in a browser to perform arithmetic calculations. No authentication or account is required.

Functional Requirements

1. Addition — The user can enter two numeric operands and compute their sum.
2. Subtraction — The user can enter two numeric operands and compute their difference.
3. Multiplication — The user can enter two numeric operands and compute their product.
4. Division — The user can enter two numeric operands and compute their quotient.
5. Division by zero handling — When the divisor is zero, the application displays a clear error message rather than crashing or displaying Infinity/NaN.
6. Result display — The computed result is displayed prominently on screen immediately after the user triggers the calculation.
7. Clear / reset — The user can clear the current inputs and result to start a new calculation.
8. Keyboard input — The user can enter operands and trigger calculations using a standard keyboard.
9. Decimal number support — The application accepts and correctly computes floating-point (decimal) operands.
10. Operator selection — The user can select the desired arithmetic operator via the UI (e.g., buttons or a dropdown).

Non-Functional Requirements

ID	Category	Requirement
NFR-1	Performance	The result must appear within 100 ms of user action on any modern browser.
NFR-2	Usability	The UI must be usable on desktop and mobile screen sizes (responsive design).
NFR-3	Accessibility	The app must meet WCAG 2.1 Level AA contrast and keyboard-navigation requirements.
NFR-4	Compatibility	The app must function correctly in the latest stable versions of Chrome, Firefox, Safari, and Edge.
NFR-5	Maintainability	Code must be modular and covered by unit tests for all arithmetic logic.
NFR-6	Deployability	The app must be deployable as a static site (no server-side runtime required).

Assumptions

1. The target user base requires no server-side persistence; all computation is performed client-side in the browser.
2. No user authentication, account management, or history/logging feature is in scope for this version.
3. The calculator operates on two operands per operation (binary operations only); chained multi-step expression input (e.g., a full expression parser) is out of scope.
4. Numeric precision follows standard IEEE 754 double-precision floating-point; no arbitrary-precision arithmetic is required.
5. The application will be delivered as a static web app (HTML/CSS/JavaScript); a specific front-end framework will be determined during technical architecture.
6. Internationalisation (i18n) and localisation (l10n) are out of scope for this version.
7. Offline (PWA/service-worker) support is not required for this version.