# Task 3.3 Implementation Summary: Create Error DTOs and Exceptions

## Overview
Successfully implemented error DTOs and exceptions for the Expedia Rapid API Integration as specified in task 3.3.

## Implementation Details

### 1. PriceChangedException
**Location:** `src/main/java/com/flightticket/exception/PriceChangedException.java`

**Features:**
- Extends `Exception` (checked exception) to force explicit handling
- Contains three fields:
  - `originalPrice` (BigDecimal): The initial price shown to the user
  - `newPrice` (BigDecimal): The updated price from Expedia
  - `currency` (String): The currency code (e.g., "USD")
- Provides getter methods for all fields
- Generates a descriptive error message: "Price changed from {currency} {originalPrice} to {currency} {newPrice}. User confirmation required."
- Validates Requirements: 11.5, 7.1, 7.2, 7.3

**Usage Example:**
```java
throw new PriceChangedException(
    new BigDecimal("150.00"),
    new BigDecimal("175.00"),
    "USD"
);
```

### 2. LinkExpiredException
**Location:** `src/main/java/com/flightticket/exception/LinkExpiredException.java`

**Features:**
- Extends `RuntimeException` (unchecked exception)
- Thrown when a cached HATEOAS link has expired
- Provides two constructors:
  - `LinkExpiredException(String message)`: Simple message constructor
  - `LinkExpiredException(String message, Throwable cause)`: Constructor with cause for exception chaining
- Validates Requirements: 11.5, 6.4

**Usage Example:**
```java
throw new LinkExpiredException("Price check link has expired. Please search again.");
```

### 3. ExpediaServiceException
**Location:** `src/main/java/com/flightticket/exception/ExpediaServiceException.java`

**Features:**
- Extends `RuntimeException` (unchecked exception)
- Contains an `ErrorType` enum with the following values:
  - `TIMEOUT`: Request exceeded time limit
  - `CIRCUIT_BREAKER_OPEN`: Circuit breaker is open, preventing requests
  - `SERVICE_UNAVAILABLE`: Expedia API is unavailable
  - `LINK_EXPIRED`: HATEOAS link has expired
  - `PRICE_CHANGED`: Room price has changed
  - `PAYMENT_FAILED`: Payment processing failed
  - `UNKNOWN`: Unknown error occurred
- Provides two constructors:
  - `ExpediaServiceException(String message, ErrorType errorType)`: Simple constructor
  - `ExpediaServiceException(String message, Throwable cause, ErrorType errorType)`: Constructor with cause
- Provides `getErrorType()` method to retrieve the error type
- Follows the same pattern as `AmadeusServiceException` for consistency
- Validates Requirements: 11.5, 13.3

**Usage Example:**
```java
throw new ExpediaServiceException(
    "Expedia API request timed out",
    ExpediaServiceException.ErrorType.TIMEOUT
);
```

## Design Decisions

1. **PriceChangedException as Checked Exception:**
   - Made it extend `Exception` (checked) rather than `RuntimeException` because price changes are an expected business scenario that must be explicitly handled
   - Forces developers to handle this case and present the new price to users for confirmation

2. **LinkExpiredException and ExpediaServiceException as Unchecked Exceptions:**
   - Made them extend `RuntimeException` (unchecked) because they represent exceptional conditions that may not always be recoverable
   - Follows the same pattern as existing exceptions in the codebase (e.g., `AmadeusServiceException`)

3. **ErrorType Enum:**
   - Provides type-safe error categorization
   - Enables different handling strategies based on error type
   - Supports monitoring and alerting by error category

4. **Consistency with Existing Code:**
   - Followed the same patterns as `AmadeusServiceException` for consistency
   - Used similar constructor patterns as other exceptions in the codebase
   - Added requirement references in Javadoc comments

## Verification

✅ All three exception classes created successfully
✅ No compilation errors
✅ Maven build successful (mvn clean compile -DskipTests)
✅ Follows existing code patterns and conventions
✅ Includes proper Javadoc with requirement references

## Requirements Validated

- **Requirement 11.5:** Define error response DTOs for price change scenarios
- **Requirement 7.1, 7.2, 7.3:** Price change detection and handling
- **Requirement 6.4:** Link expiration handling
- **Requirement 13.3:** Exception handling patterns consistent with existing architecture

## Next Steps

The error DTOs and exceptions are now ready to be used in:
- Task 5.1: Link caching component (will throw `LinkExpiredException`)
- Task 6.2: Expedia client implementation (will throw `ExpediaServiceException`)
- Task 8.3: Price validation service (will throw `PriceChangedException`)
- Task 11.1: REST controller error handling

## Files Created

1. `src/main/java/com/flightticket/exception/PriceChangedException.java`
2. `src/main/java/com/flightticket/exception/ExpediaServiceException.java`
3. `src/main/java/com/flightticket/exception/LinkExpiredException.java`

## Task Status

✅ **Task 3.3 COMPLETED**