# Comparison Offers Feature Documentation

## Overview

The comparison offers feature requires users to provide at least 3 comparison offers for each cost position in their application. This ensures transparency and cost-effectiveness in funding requests. Users can alternatively provide a justification if comparison offers are not applicable for specific cost positions.

## Features

- **3 Offers Requirement**: Each cost position must have at least 3 comparison offers
- **Justification Alternative**: Users can mark that no offers are required and provide a detailed justification
- **Attachment Support**: Each offer can be linked to an uploaded attachment (e.g., quotes, invoices)
- **Visual Indicators**: Cost positions without sufficient offers are highlighted with warning icons
- **Status Tracking**: Real-time status display showing offer count and completion status

## Database Schema

### `comparison_offers` Table
Stores comparison offers for cost positions:
- `id` (INT, PRIMARY KEY) - Unique identifier
- `application_id` (INT) - References the application
- `cost_position_index` (INT) - Index of the cost position in the costs array
- `supplier_name` (VARCHAR 255) - Name of the supplier/vendor
- `amount` (INT) - Offer amount in cents
- `description` (TEXT) - Optional description of the offer
- `url` (VARCHAR 500) - Optional URL to offer document or webpage
- `attachment_id` (INT) - Optional reference to an attachment
- `created_at` (DATETIME) - Creation timestamp
- `updated_at` (DATETIME) - Last update timestamp

### `cost_position_justifications` Table
Stores justifications for positions without offers:
- `id` (INT, PRIMARY KEY) - Unique identifier
- `application_id` (INT) - References the application
- `cost_position_index` (INT) - Index of the cost position
- `no_offers_required` (INT) - Boolean flag (0/1)
- `justification` (TEXT) - Required explanation when no_offers_required is 1
- `created_at` (DATETIME) - Creation timestamp
- `updated_at` (DATETIME) - Last update timestamp

## API Endpoints

### Create Comparison Offer
`POST /api/applications/{pa_id}/costs/{cost_position_index}/offers`
- Request body:
  ```json
  {
    "supplier_name": "Supplier GmbH",
    "amount": 1500.50,
    "description": "Optional description",
    "url": "https://beispiel.de/angebot.pdf",
    "attachment_id": 123
  }
  ```
- Returns: ComparisonOfferResponse with offer details

### Get Cost Position Offers
`GET /api/applications/{pa_id}/costs/{cost_position_index}/offers`
- Returns: CostPositionOffersResponse with all offers and justification info

### Delete Comparison Offer
`DELETE /api/applications/{pa_id}/costs/{cost_position_index}/offers/{offer_id}`
- Removes a specific offer

### Update Cost Position Justification
`PUT /api/applications/{pa_id}/costs/{cost_position_index}/justification`
- Request body:
  ```json
  {
    "no_offers_required": true,
    "justification": "Detailed explanation why no offers are needed..."
  }
  ```

## Frontend Components

### ComparisonOffersDialog
Main dialog for managing offers for a cost position:
- Add/remove comparison offers
- Add URL links to online offers
- Link attachments to offers (either URL or attachment required)
- Mark position as not requiring offers
- Provide justification when needed

### CostPositionsList
Enhanced cost positions list with offer status:
- Visual indicators for offer status
- Warning icons for incomplete positions
- Quick access to manage offers
- Real-time status updates

## User Interface

### Status Indicators
- ✅ **Green checkmark**: Position has 3+ offers
- ℹ️ **Blue info icon**: Position marked as not requiring offers (with justification)
- ⚠️ **Yellow warning**: Position needs more offers or justification
- 🔄 **Loading spinner**: Status being loaded

### Validation Rules
1. Each cost position must have either:
   - At least 3 comparison offers, OR
   - Be marked as "no offers required" with a justification (min. 10 characters)
2. Cost positions without sufficient offers are highlighted in the list
3. Offers must include:
   - Supplier name (required, must be unique per cost position)
   - Amount (required, must be greater than 0)
   - Either URL or attachment (at least one required)
   - Description (optional)
4. Duplicate suppliers: Each supplier can only have one offer per cost position
5. URL format: Must be a valid HTTP/HTTPS URL (protocol is auto-added if missing)
6. Amount format: Accepts both comma and period as decimal separator

## Migration

To add the comparison offers tables to your database:

```sql
mysql -u your_user -p your_database < src/migrations/add_comparison_offers_tables.sql
mysql -u your_user -p your_database < src/migrations/add_url_to_comparison_offers.sql
```

## Usage Example

### In Cost Positions List
```tsx
<CostPositionsList
  costs={formData.costs}
  paId={applicationId}
  paKey={applicationKey}
  isAdmin={false}
  readOnly={false}
  attachments={availableAttachments}
/>
```

### Managing Offers
1. Click "Angebote" button next to any cost position
2. In the dialog:
   - Add up to 5 comparison offers
   - Link existing attachments to offers
   - OR check "no offers required" and provide justification
3. Save changes

## Best Practices

1. **Encourage Early Collection**: Remind users to collect offers before starting the application
2. **Clear Instructions**: Provide examples of valid justifications for positions without offers
3. **Attachment Organization**: Name attachment files clearly to easily link them to offers
4. **Regular Validation**: Check offer status before submission

## Error Handling

- **Duplicate Suppliers**: Shows user-friendly error message when trying to add the same supplier twice
- **Invalid URLs**: Automatically prepends https:// if missing, validates format
- **Invalid Amounts**: Real-time validation with support for German number format (comma as decimal)
- **Missing Data**: Clear error messages when required fields are missing

## Future Enhancements

1. **Bulk Import**: Import multiple offers from CSV/Excel
2. **Templates**: Save common suppliers for quick reuse
3. **Price Comparison**: Automatic highlighting of best offer
4. **History Tracking**: Track changes to offers over time
5. **Export Function**: Export all offers as PDF/Excel report
6. **Smart Validation**: Detect duplicate suppliers or suspicious patterns
7. **URL Validation**: Automatic checking of URL availability and validity
8. **Screenshot Capture**: Automatic capture of web-based offers for archival