---
applyTo: "Fuchs/**,Fuchs_DataService/**,MFR_RESTClient/**,MT940Parser/**"
---

# Logging Instructions

## Overview
All logging in this solution uses `Microsoft.Extensions.Logging.ILogger<T>`.
**Never use** `System.Diagnostics.Debug.Print`, `Debug.WriteLine`, `Console.WriteLine`, or `OCMS.ocms_debug.debug_log` in business or library code.

## Providers

### Fuchs_DataService — `FdsLoggerProvider`
- Location: `Fuchs_DataService/Logging/FdsLoggerProvider.cs`
- Always active: **Debug output** (`System.Diagnostics.Debug.WriteLine`) + **file** (`tmp/DebugLog.txt`, `tmp/ErrorLog.txt`)
- Database logging: prepared via `WriteToDatabase()` but **disabled by default**. Activate with `FdsLoggerProvider.DatabaseLoggingEnabled = true`.
- Registered in `FdsMain.cs` via `LoggerFactory.Create(b => b.SetMinimumLevel(LogLevel.Debug).AddFdsLogging())`.

### Fuchs — `FuchsLoggerProvider`
- Location: `Fuchs/Logging/FuchsLoggerProvider.cs`
- Always active: **Debug output** + **file** (`logs/AppLog.txt`, `logs/ErrorLog.txt`)
- Database logging: prepared but **disabled by default**. Activate with `FuchsLoggerProvider.DatabaseLoggingEnabled = true`.
- Registered in `Program.cs` via `builder.Logging.SetMinimumLevel(LogLevel.Debug).AddFuchsLogging()`.

### MFR_RESTClient — Library (no provider)
- No logging provider — purely a library.
- `MFRClient` accepts `ILogger<MFRClient>?` as an optional constructor parameter.
- Defaults to `NullLogger<MFRClient>.Instance` when no logger is provided.
- Callers supply a logger from the host's `ILoggerFactory`.

### MT940Parser — Library (no provider)
- Location: `../../WebProjectComponents/MT940Parser/` (shared external component)
- No logging provider — purely a library.
- **Public entry point only**: `Parser` accepts `ILogger<Parser>?` as an optional constructor parameter and defaults to `NullLogger<Parser>.Instance`.
- **Internal sub-parsers** (`StatementParser`, `BalanceParser`, `StatementLineParser`, `AdditionalInfoParser`) are pure algorithmic classes. They **do not hold logger fields**. Parse errors are thrown as exceptions (`InvalidDataException`, `FormatException`) and caught by `Parser.Parse()`, which logs them at `LogWarning`.
- Callers supply a logger when constructing `Parser`; the sub-parsers never need one directly.

## Rules
- **DI classes** (singletons, scoped): receive `ILogger<T>` via constructor injection.
- **Library classes** (`MFRClient`, `Parser`): accept `ILogger<T>?` as an optional constructor parameter, default to `NullLogger<T>.Instance`.
- **Internal library helpers** (`StatementParser`, `BalanceParser`, `StatementLineParser`, `AdditionalInfoParser`): pure algorithmic, no logger field. Throw exceptions; the public entry-point catches and logs.
- **Static helpers** (`FdsShared`, `Banking`): accept `ILogger?` as an optional method parameter, or delegate to `FdsDebug.DebugLog` for infrastructure-level errors.
- `FdsDebug` remains the **fallback for static infrastructure code only** (stream helpers, etc.). Do not use it in new class-level code.
- Use structured logging parameters: `_logger.LogError(ex, "Message {Param}", value)` — never string interpolation in the message template.

## Log Levels
| Level | Use for |
|-------|---------|
| `LogDebug` | Timing, row counts, progress traces |
| `LogInformation` | Service start/stop, significant state changes |
| `LogWarning` | Recoverable issues, skipped items |
| `LogError` | Caught exceptions, data sync failures |
| `LogCritical` | Unrecoverable failures that stop a job |

## Enabling Database Logging
```csharp
// Fuchs_DataService
FdsLoggerProvider.DatabaseLoggingEnabled = true;

// Fuchs web
FuchsLoggerProvider.DatabaseLoggingEnabled = true;
```
Uncomment the body of `WriteToDatabase()` in the respective provider and adjust the stored procedure name.