# Task 4.1 Implementation: PageService with CRUD Operations

## Overview
Implemented the PageService with all required CRUD operations for managing user pages in the Custom Start Page application.

## Implementation Details

### File: `internal/services/page_service.go`

#### Methods Implemented

1. **GetPages(ctx, userID) ([]*Page, error)**
   - Queries all pages for a user from DynamoDB
   - Sorts pages by their order field
   - Returns pages in display order

2. **CreatePage(ctx, userID, name) (*Page, error)**
   - Creates a new page with a unique UUID
   - Automatically assigns the next order number
   - Sets timestamps (CreatedAt, UpdatedAt)
   - Persists to DynamoDB Pages table

3. **CreateDefaultPage(ctx, userID) (*Page, error)**
   - Creates the default "Home" page for new users
   - Wrapper around CreatePage with "Home" as the name
   - Satisfies Requirement 2.1

4. **UpdatePage(ctx, userID, pageID, name) (*Page, error)**
   - Updates a page's name
   - Updates the UpdatedAt timestamp
   - Returns the updated page
   - Uses DynamoDB UpdateItem with ReturnValues

5. **DeletePage(ctx, userID, pageID) error**
   - Validates that it's not the last page (prevents deletion)
   - Queries all widgets associated with the page
   - Cascade deletes all widgets in batches of 25 (DynamoDB limit)
   - Deletes the page itself
   - Satisfies Requirements 2.5, 2.6

6. **ReorderPages(ctx, userID, pageOrder) error**
   - Validates all page IDs exist and belong to the user
   - Validates the order list length matches existing pages
   - Updates each page's order field atomically
   - Updates timestamps
   - Satisfies Requirement 2.7

#### Helper Functions

- **sortPagesByOrder(pages)**: In-place bubble sort for pages by order field

## Requirements Satisfied

- ✅ **Requirement 2.1**: Default "Home" page creation for new users
- ✅ **Requirement 2.2**: Page creation with name prompt
- ✅ **Requirement 2.3**: Page name updates
- ✅ **Requirement 2.5**: Page deletion with cascade delete of widgets
- ✅ **Requirement 2.6**: Prevention of last page deletion
- ✅ **Requirement 2.7**: Page reordering with persistence
- ✅ **Requirement 2.8**: Immediate persistence to storage

## Testing

### Unit Tests (`internal/services/page_service_test.go`)

Comprehensive test coverage including:

1. **TestCreateDefaultPage**: Verifies default "Home" page creation
2. **TestGetPages**: Tests retrieving and sorting multiple pages
3. **TestGetPagesEmptyResult**: Tests empty result handling
4. **TestCreatePage**: Tests page creation with auto-incrementing order
5. **TestUpdatePage**: Tests page name updates
6. **TestDeletePage**: Tests page deletion
7. **TestDeleteLastPagePrevention**: Validates last page deletion prevention
8. **TestDeletePageWithWidgets**: Tests cascade deletion of widgets
9. **TestReorderPages**: Tests page reordering
10. **TestReorderPagesInvalidLength**: Tests validation of order list length
11. **TestReorderPagesInvalidPageID**: Tests validation of page IDs
12. **TestReorderPagesPersistence**: Tests persistence of reordered pages

### Unit Tests Without DynamoDB (`internal/services/page_service_unit_test.go`)

Tests that don't require DynamoDB:

1. **TestSortPagesByOrder**: Tests sorting function
2. **TestSortPagesByOrderAlreadySorted**: Tests already sorted pages
3. **TestSortPagesByOrderReversed**: Tests reversed pages
4. **TestSortPagesByOrderEmpty**: Tests empty slice
5. **TestSortPagesByOrderSingle**: Tests single page

**Status**: All unit tests pass ✅

## Key Design Decisions

1. **Cascade Deletion**: When a page is deleted, all associated widgets are automatically deleted to maintain data integrity.

2. **Last Page Protection**: The service prevents deletion of the last page to ensure users always have at least one page.

3. **Batch Operations**: Widget deletion uses DynamoDB BatchWriteItem with batches of 25 items to handle pages with many widgets efficiently.

4. **Order Management**: Pages maintain an order field that determines display sequence. The CreatePage method automatically assigns the next available order number.

5. **Validation**: ReorderPages validates that all page IDs exist and belong to the user before making any changes.

6. **Atomic Updates**: Each page update is atomic, ensuring consistency even with concurrent operations.

## Dependencies

- `github.com/aws/aws-sdk-go-v2`: AWS SDK for DynamoDB operations
- `github.com/google/uuid`: UUID generation for page IDs
- `github.com/stretchr/testify`: Testing assertions

## Integration Points

- **Storage Layer**: Uses `internal/storage/DynamoDBClient` for all database operations
- **Models**: Uses `internal/models.Page` and `internal/models.Widget` data structures
- **Future Integration**: Will be used by HTTP handlers in `internal/handlers` for page management endpoints

## Notes

- Tests require DynamoDB local running on `http://localhost:8000`
- AWS credentials must be configured (can be dummy credentials for local testing)
- The service is stateless and thread-safe
- All operations use context for cancellation and timeout support

## Next Steps

Task 4.2 will implement the HTTP endpoints that use this service:
- GET /dashboard
- GET /pages/:id
- POST /pages
- PUT /pages/:id
- DELETE /pages/:id
- POST /pages/reorder