# Task 3.1 Implementation: DynamoDB Storage Service Wrapper

## Overview
Enhanced the existing DynamoDB client from Task 2.1 with retry logic, connection pooling, transaction support, and batch operations.

## Implementation Details

### 1. Enhanced Client Configuration
- **Retry Strategy**: Configured with exponential backoff and jitter
  - Max attempts: 5
  - Max backoff: 20 seconds
  - Prevents thundering herd with jitter
- **Connection Pooling**: Uses AWS SDK's default HTTP client with built-in connection pooling

### 2. Transaction Support
Implemented `TransactWriteItems` method for ACID transactions:
- Supports multiple write operations in a single atomic transaction
- Automatic retry on transient failures
- Proper error handling and wrapping

### 3. Batch Operations
Implemented two batch operation methods:

#### BatchGetItems
- Retrieves multiple items in a single request
- Automatically retries unprocessed keys with exponential backoff
- Merges results from retry attempts
- Max 5 retry attempts with increasing backoff (100ms → 20s)

#### BatchWriteItems
- Writes multiple items in a single request
- Automatically retries unprocessed items with exponential backoff
- Max 5 retry attempts with increasing backoff (100ms → 20s)

### 4. Standard Operations
Wrapped standard DynamoDB operations with automatic retry:
- `PutItem` - Put a single item
- `GetItem` - Get a single item
- `UpdateItem` - Update a single item
- `DeleteItem` - Delete a single item
- `Query` - Query items

All operations include proper error handling and wrapping.

### 5. Comprehensive Testing
Created `dynamodb_test.go` with tests for:
- Client initialization
- Transaction operations
- Batch get operations
- Batch write operations
- Put and get operations
- Update operations
- Delete operations
- Query operations

Tests include:
- Automatic skip when DynamoDB is not available
- Helper function for test setup with dummy AWS credentials
- Table creation and cleanup helpers
- Verification of all operations

## Files Modified/Created

### Modified
- `internal/storage/dynamodb.go` - Enhanced with retry logic, transactions, and batch operations

### Created
- `internal/storage/dynamodb_test.go` - Comprehensive test suite
- `internal/storage/README.md` - Documentation for the storage service
- `docs/task-3.1-implementation.md` - This implementation document

## Requirements Addressed

✅ **Requirement 8.1**: Immediate persistence with reliable operations
✅ **Requirement 8.8**: Efficient scaling through batch operations and connection pooling
✅ **Design**: Retry logic with exponential backoff
✅ **Design**: Transaction support (TransactWrite)
✅ **Design**: Batch operations (BatchGet, BatchWrite)
✅ **Design**: Connection pooling

## Testing

### Running Tests
```bash
# Start DynamoDB Local
docker-compose up -d

# Run all storage tests
go test -v ./internal/storage

# Run specific tests
go test -v ./internal/storage -run TestTransactWriteItems
```

### Test Coverage
- ✅ Client initialization with retry configuration
- ✅ Transaction writes with multiple items
- ✅ Batch get with multiple items
- ✅ Batch write with multiple items
- ✅ Single item operations (Put, Get, Update, Delete)
- ✅ Query operations
- ✅ Graceful skip when DynamoDB unavailable

## Usage Example

```go
// Create client
ctx := context.Background()
client, err := storage.NewDynamoDBClient(ctx, "http://localhost:8000")
if err != nil {
    log.Fatal(err)
}

// Transaction example
err = client.TransactWriteItems(ctx, &dynamodb.TransactWriteItemsInput{
    TransactItems: []types.TransactWriteItem{
        {
            Put: &types.Put{
                TableName: aws.String("MyTable"),
                Item: map[string]types.AttributeValue{
                    "id": &types.AttributeValueMemberS{Value: "item1"},
                },
            },
        },
    },
})

// Batch write example
err = client.BatchWriteItems(ctx, &dynamodb.BatchWriteItemInput{
    RequestItems: map[string][]types.WriteRequest{
        "MyTable": {
            {
                PutRequest: &types.PutRequest{
                    Item: map[string]types.AttributeValue{
                        "id": &types.AttributeValueMemberS{Value: "item1"},
                    },
                },
            },
        },
    },
})

// Batch get example
output, err := client.BatchGetItems(ctx, &dynamodb.BatchGetItemInput{
    RequestItems: map[string]types.KeysAndAttributes{
        "MyTable": {
            Keys: []map[string]types.AttributeValue{
                {"id": &types.AttributeValueMemberS{Value: "item1"}},
            },
        },
    },
})
```

## Next Steps

This enhanced storage service is now ready to be used by:
- Task 3.2: Data model implementations
- Task 3.3: Table schema creation
- All future tasks requiring DynamoDB operations

The retry logic, transaction support, and batch operations provide a solid foundation for building scalable, reliable data access patterns.