# Module: Azaion.Common.BusinessException

## Purpose
Custom exception type for domain-level errors, paired with an `ExceptionEnum` catalog of all business error codes.

## Public Interface

### BusinessException
| Member | Signature | Description |
|--------|-----------|-------------|
| Constructor | `BusinessException(ExceptionEnum exEnum)` | Creates exception with message from `ExceptionEnum`'s `[Description]` attribute |
| `ExceptionEnum` | `ExceptionEnum ExceptionEnum { get; set; }` | The specific error code |
| `GetMessage` | `static string GetMessage(ExceptionEnum exEnum)` | Looks up human-readable message for an error code |

### ExceptionEnum
| Value | Code | Description |
|-------|------|-------------|
| `NoEmailFound` | 10 | No such email found |
| `EmailExists` | 20 | Email already exists |
| `WrongPassword` | 30 | Passwords do not match |
| `PasswordLengthIncorrect` | 32 | Password should be at least 12 characters (description text — actual validator threshold is 8 chars per `RegisterUserValidator`) |
| `EmailLengthIncorrect` | 35 | Email is empty or invalid |
| `WrongEmail` | 37 | (no description attribute) |
| `UserDisabled` | 38 | User account is disabled |
| `WrongResourceName` | 50 | Wrong resource file name |
| `NoFileProvided` | 60 | No file provided |

> **Cycle 1 (2026-05-13) note** — `HardwareIdMismatch = 40` and `BadHardware = 45` were removed by AZ-197 (admin-side hardware-binding cleanup). Code 40 should NOT be reused for a different meaning — older clients may still surface "Hardware mismatch" UX strings keyed on the integer. `UserDisabled = 38` was added earlier (still part of the baseline). See `_docs/03_implementation/batch_06_report.md`.

## Internal Logic
Static constructor eagerly loads all `ExceptionEnum` descriptions into a dictionary via `EnumExtensions.GetDescriptions<ExceptionEnum>()`. Messages are retrieved by dictionary lookup with fallback to `ToString()`.

## Dependencies
- `EnumExtensions` — for `GetDescriptions<T>()`

## Consumers
- `BusinessExceptionHandler` — catches and serializes to HTTP 409 response
- `UserService` — throws for email/password validation failures (`NoEmailFound`, `WrongPassword`, `EmailExists`, `UserDisabled`)
- `ResourcesService` — throws `NoFileProvided` for missing file uploads
- FluentValidation validators — reference `ExceptionEnum` codes in `.WithErrorCode()`

## Data Models
None.

## Configuration
None.

## External Integrations
None.

## Security
Error codes are returned to the client via `BusinessExceptionHandler`. Codes are numeric and messages are user-facing.

## Tests
None.