Prompt Engineering for Code

make a login form

Create a login form component in React with TypeScript.

Requirements:
- Email and password fields
- Client-side validation (email format, password min 8 chars)
- Show validation errors below each field
- Submit button disabled until form is valid
- On submit, call the onLogin(email, password) prop
- Show loading state while submitting

Style: Use Tailwind CSS, match existing form components

I'm building a Next.js 14 app with App Router.
The project uses TypeScript, Tailwind CSS, and Prisma for the database.
The user is already authenticated (session available via useSession hook).

Build a user profile page that:
- Displays user name, email, and avatar
- Allows editing name (inline editing)
- Shows "last active" relative time
- Has a "delete account" button with confirmation

Input: User object from session
{
  id: string
  name: string
  email: string
  avatar: string | null
  lastActive: Date
}

Output: React component that renders the profile

Style guidelines:
- Follow existing component patterns in /components
- Use the Button component from /components/ui/Button
- Use react-hook-form for form handling
- Error messages should use the ErrorMessage component

Example of inline editing behavior:
1. User clicks on name → Input field appears
2. User types new name
3. User clicks away or presses Enter → Save
4. Show loading spinner during save
5. Revert if save fails

Build a file upload feature. Let's do this step by step:

Step 1: Create a FileUpload component that:
- Accepts drag-and-drop
- Shows file preview for images
- Limits to 5MB max size

(wait for response, verify)

Step 2: Add the upload handler that:
- Uploads to S3 via presigned URL
- Shows progress bar
- Handles errors gracefully

(wait for response, verify)

Step 3: Integrate with the post creation form

I need a function that formats currency.

Examples:
formatCurrency(1234.5, 'USD') → '$1,234.50'
formatCurrency(1234.5, 'EUR') → '€1,234.50'
formatCurrency(1000000, 'USD') → '$1,000,000.00'
formatCurrency(0.99, 'USD') → '$0.99'

Handle edge cases:
- Negative numbers: -$1,234.50
- null/undefined: Return empty string
- Unknown currency: Use currency code as symbol

Here's my current component:

[paste component]

Modify it to:
- Add pagination (10 items per page)
- Keep existing filtering
- Add "load more" button instead of page numbers
- Preserve the loading and error states

Create an API route for user registration.

Hard constraints (must follow exactly):
- POST /api/auth/register
- Validate email format and password strength
- Hash password with bcrypt (12 rounds)
- Store in Prisma users table
- Return 201 with user object (no password)
- Return 400 for validation errors
- Return 409 if email already exists

Do NOT:
- Send any emails (handled elsewhere)
- Create sessions (separate endpoint)
- Log passwords or sensitive data

Build a function that satisfies these tests:

describe('calculateDiscount', () => {
  it('returns 0 for orders under $50', () => {
    expect(calculateDiscount(49.99)).toBe(0);
  });
  
  it('returns 10% for orders $50-99', () => {
    expect(calculateDiscount(50)).toBe(5);
    expect(calculateDiscount(99)).toBe(9.9);
  });
  
  it('returns 20% for orders $100+', () => {
    expect(calculateDiscount(100)).toBe(20);
  });
  
  it('handles edge cases', () => {
    expect(calculateDiscount(0)).toBe(0);
    expect(calculateDiscount(-10)).toBe(0);
  });
});

AI generates code → Wrong → Regenerate from scratch
AI generates code → Still wrong → Regenerate again
AI generates code → Different wrong → Give up

AI generates code → Wrong
"The error handling is missing. Add try/catch around the fetch call and show an error message in the UI if it fails."

AI fixes → Partially right
"Good, but the error message should disappear after 5 seconds."

AI fixes → Correct

Here's the current state of the component:

[paste current code]

Now add the sorting feature we discussed.

Quick recap of what we've built:
- UserList component with pagination
- Uses React Query for data fetching
- Filters by status and date range

Now let's add the export to CSV feature.

Update the UserCard component in /components/UserCard.tsx
to match the styling in /components/ProjectCard.tsx

Bug: Form validation message doesn't disappear

Expected: Error message shows on invalid input, disappears when input becomes valid
Actual: Error message appears but never disappears

Relevant code:
[paste the validation logic]

I've tried: Adding onChange handler to clear errors—didn't work

Why might this useEffect be running twice?

useEffect(() => {
  fetchData();
}, [userId]);

Environment: React 18, StrictMode enabled

Help me debug this step by step:

The user clicks "Save" but nothing happens.

1. What should I check first?
2. How can I verify each step?
3. What are common causes of this pattern?