Extract the duplicated positive integer field validation into a shared helper

[ekwe7]

closes #96

Summary

This PR consolidates the repeated numeric validation logic used across multiple forms into a single reusable utility. The new helper provides a consistent, typed interface for validating integer inputs while preserving the existing validation rules and user-facing behavior.

The change reduces duplication, improves maintainability, and increases confidence through dedicated unit tests.

Problem

Numeric validation was implemented independently in multiple locations:

• src/app/services/new/page.tsx
• src/app/services/[serviceId]/edit/page.tsx
• src/app/usage/page.tsx

Although the validation requirements differ slightly between forms, the underlying parse-and-validate logic was largely duplicated.

This duplication increases maintenance overhead and creates the risk of validation behavior drifting over time.

Solution

Introduced a shared validation utility:

src/lib/validateNumber.ts

The helper exposes typed validation functions that return structured results:

{ ok: true, value: number }

or

{ ok: false, message: string }

This approach centralizes validation logic while allowing each form to preserve its existing acceptance criteria.

Changes

New Validation Utility

Created:

• src/lib/validateNumber.ts

Added:

• parseNonNegativeInt()
• parsePositiveInt()

Features:

• Typed validation results
• Consistent error messages
• Reusable validation behavior across forms
• JSDoc documentation

Form Updates

Updated:

• src/app/services/new/page.tsx
• src/app/services/[serviceId]/edit/page.tsx
• src/app/usage/page.tsx

Changes include:

• Replacing inline validation logic with shared helper functions

• Preserving existing accepted ranges:

  • Price (priceStroops): >= 0
  • Requests: >= 1

• Maintaining existing submission behavior and payload structure

• Surfacing validation errors through existing TextField error props

Testing

Added:

• src/lib/__tests__/validateNumber.test.ts

Updated affected page tests to verify:

• Shared validation integration
• Existing validation behavior remains unchanged
• Error states render correctly

Edge Cases Covered

Validation tests include:

• Empty input
• Negative values
• Floating-point values
• Leading-zero values
• Valid non-negative integers
• Valid positive integers
• Boundary values for each accepted range

Validation

Executed:

npm run lint
npm run typecheck
npm test
npm run build

Acceptance Criteria

• Shared validation helper created
• Typed validation result structure implemented
• Service creation form uses shared helper
• Service edit form uses shared helper
• Usage form uses shared helper
• Existing accepted ranges preserved
• Validation messages surfaced through TextField error props
• Wire payloads unchanged
• Unit tests added for helper
• Edge cases covered
• JSDoc documentation added
• README updated with validation rules

Benefits

• Eliminates duplicated validation code
• Ensures consistent validation behavior across forms
• Simplifies future maintenance and enhancements
• Improves testability through isolated validation utilities
• Reduces risk of validation regressions
• Keeps form behavior unchanged for end users

[mikewheeleer]

solid — in it goes 🚀