mykhailoshes/scale-angine

Purpose and runtime

Scale Engine is an Electron desktop gateway between Mettler Toledo scale folders and a remote SFTP middleware. Electron hosts a NestJS application in its main process; no HTTP server or separate service process is started. The renderer is a plain HTML/CSS/JS control UI.

Entry points: src/main/main.ts, src/main/preload.ts, and src/renderer/renderer.js.

Electron shell and UI boundary

The Electron main process creates the application window, exposes constrained preload APIs, and translates renderer actions into IPC requests. The renderer manages configuration input, Start/Stop controls, connection status, and streamed activity logs.

Key paths:

• src/main/main.ts

• src/main/preload.ts

• src/main/ipc.ts

• src/main/ipc-channels.ts

• src/renderer/renderer.js

The renderer does not directly access filesystem, SFTP, or Nest services; those capabilities remain in the main-process IPC boundary.

Nest application composition

NestJS supplies the dependency-injected service layer embedded in Electron. Bootstrap initializes the Nest context, while the root module assembles configuration, SFTP transport, watchers, and the agent orchestrator.

Key paths:

• src/main/nest/bootstrap.ts

• src/main/nest/app.module.ts

• src/main/nest/agent/agent.module.ts

Configuration and credential persistence

Configuration stores the SFTP URL, assigned folder name, and local Import/Export directories in Electron userData as scale-engine-config.json. The configuration service encrypts SFTP passwords through Electron safeStorage, supports legacy plaintext migration, and is used by IPC and agent startup.

Key paths:

• src/main/nest/config/config.service.ts

• src/main/nest/config/config.types.ts

• src/main/nest/config/config.module.ts

This is the main persistence and OS-security boundary; encrypted storage relies on platform facilities such as Windows DPAPI and macOS Keychain.

Agent lifecycle orchestration

The agent service is the operational state machine behind Start and Stop. Start persists configuration, establishes SFTP connectivity, and activates both directional watchers. Stop halts watchers and closes the SFTP session. It also governs whether reconnect behavior should continue after transport loss.

Key paths:

• src/main/nest/agent/agent.service.ts

• src/main/nest/sftp/sftp.service.ts

• src/main/nest/watcher/watcher.module.ts

Shared SFTP transport

A single ssh2-sftp-client wrapper owns the remote session for both watchers. It targets the middleware’s /upload hierarchy, observes end, close, and error failures, and reconnects with exponential backoff while the agent remains running.

Key paths:

• src/main/nest/sftp/sftp.service.ts

• src/main/nest/sftp/sftp.module.ts

External dependency: an SFTP server hosting shared import/export and processed folders.

Bidirectional file-transfer stages

The export watcher polls the local scale Export directory, ignores recently modified files to avoid mid-write reads, uploads receipt XML to /upload/import, then archives the local file under <Export>/processed with a timestamped name.

The import watcher polls /upload/<FolderName>/export/, downloads product XML into the local scale Import directory, then moves the remote source into its processed folder.

Key paths:

• src/main/nest/watcher/export-watcher.service.ts

• src/main/nest/watcher/import-watcher.service.ts

Logging and operational feedback

Services publish activity and error events through an in-process logger bus. IPC mirrors these events to the renderer, where failures and connection state drive the activity log and status indicator.

Key paths:

• src/main/nest/logger.service.ts

• src/main/ipc.ts

• src/renderer/index.html