---
status: Accepted
date: 2026-07-15
applyTo:
  - "Fuchs_DataService/**"
  - "Fuchs/Services/PeriodicHostedService.cs"
  - "Fuchs/Program.cs"
supersededBy: ""
---

# 0010 — MFR ERP sync runs in-process in the web app; Fuchs_DataService is a library

## Context
`Fuchs_DataService` was a standalone console/Windows Service hosted by **Topshelf**.
It carried its own `appsettings.json`, its own file-based configuration bootstrap
(`FdsConfig.Initialize()` reading the file), its own logging provider
(`FdsLoggerProvider`/`AddFdsLogging`), and a machine-name guard in `Main()` that
disabled the service on developer PCs. In practice the web app (`Fuchs`) already
referenced the project, already called `fds.FdsConfig.Initialize(builder.Configuration)`,
already registered `IFdsMfr`, and already created `FdsMfrClient` via
`IMfrClientFactory` — so the sync logic and the web app were sharing the same code
and the same connection strings while the service kept a second, parallel copy of
configuration/logging/hosting.

Maintaining a separate process, a second `appsettings.json` (duplicating connection
strings + MFR credentials), Topshelf, and a machine-name guard added drift risk and
operational overhead for no benefit the web host couldn't provide.

## Decision
- **`Fuchs_DataService` is now a class library** (no `OutputType Exe`, no Topshelf,
  no own `appsettings.json`, no `install.bat`/`un-install.bat`, no
  `System.Configuration.ConfigurationManager`). It contains only the MFR sync
  logic (`FdsMfr`/`IFdsMfr`, `FdsMfrClient`), the DATEV/zip helpers, `FdsShared`,
  `FdsDebug`, and `FdsConfig`.
- **The host owns configuration.** `FdsConfig` keeps only
  `Initialize(IConfiguration)` (the file-based overload is gone). The Fuchs web app
  injects its `IConfiguration`; connection strings (`fuchs_fds_ConnectionString`)
  and MFR credentials (`Fds:MFR_*`, Key Vault-managed) come from Fuchs.
- **The host owns logging.** `FdsLoggerProvider`/`AddFdsLogging` were removed; the
  library uses only `ILogger`/`ILoggerFactory` injected from Fuchs's logging
  (`AddFuchsLogging`). The library depends only on
  `Microsoft.Extensions.Logging.Abstractions` + `Microsoft.Extensions.Configuration.Binder`.
- **The sync runs in-process.** `PeriodicHostedService` (the generic
  multi-job `BackgroundService`) moved to `Fuchs/Services/` and is registered in
  `Program.cs` as a hosted service. The single `MfrSync` job calls
  `UpdateIfNecessary_async` → `UpdateRequested_async` → `GetInvoiceFiles_async`.
- **A config flag replaces the machine-name guard.** Registration is gated by
  `Fds:SyncEnabled` (default `false` when unset): `true` in production
  `appsettings.json`, `false` in `appsettings.Development.json`, so developer
  machines never poll the ERP. Interval (`Fds:ExecutionFrequency_Minutes`, default
  15) and debug verbosity (`Fds:DebugDetails`) also come from the `Fds` section.

## Consequences
- One process, one configuration surface, one logging pipeline. The sync inherits
  the web app's OpenTelemetry, DI, and lifetime automatically.
- **Instance fan-out is a consideration:** the sync now runs in *every* web instance
  where `Fds:SyncEnabled` is true. The intranet is deployed single-instance, so this
  is acceptable; if Fuchs is ever scaled out, gate the sync to a single instance
  (leader election / dedicated instance flag) to avoid concurrent MFR polling.
- Enabling/disabling the sync per environment is now a config change, not a
  redeploy of a separate service.
- `Fuchs_DataService` is intentionally kept as a separate project (not folded into
  `Fuchs`) so the sync logic stays isolated and unit-testable; `Fuchs.Tests` covers
  it via `InternalsVisibleTo`.
- **The `Squid-Box.SevenZipSharp` native dependency (and the bundled `7z.dll`) was
  removed** from both `Fuchs_DataService` and `Fuchs`. The only live archive use — the
  DATEV export — is a plain, unencrypted zip, now produced via the native
  `OCORE.zip.filesToZipArchive` (`System.IO.Compression`). The 7-Zip-only paths
  (`.7z`/LZMA2, AES-encrypted archives, extraction, `FastAppend`) had no callers.
  Trade-off accepted: `System.IO.Compression` cannot produce `.7z` or password/AES
  archives; if that is ever required, a compression library must be reintroduced.

## Alternatives considered
- **Native `dotnet` Worker Service (separate process).** Would modernize off
  Topshelf but keep the duplicate-config/duplicate-logging/second-process problem.
  Rejected because the web app already hosts everything the sync needs.
- **Fold the code directly into `Fuchs`.** Rejected to preserve a clean, separately
  testable sync library and avoid enlarging the web project.