====== Extension Architecture ======

Detailed description of the internal architecture of a WvdS VSCode Extension.

===== Lifecycle =====

<code>
┌─────────────────────────────────────────────────────────────┐
│                    EXTENSION LIFECYCLE                       │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│  1. VS Code Start                                            │
│     ↓                                                        │
│  2. Activation Event triggers                                │
│     (onCommand, onLanguage, onStartupFinished, ...)          │
│     ↓                                                        │
│  3. extension_main.js is loaded                              │
│     ↓                                                        │
│  4. Activate() is called                                     │
│     → Initialize services                                    │
│     → Register commands                                      │
│     → Set up event handlers                                  │
│     ↓                                                        │
│  5. Extension is active                                      │
│     → User interaction                                       │
│     → Command execution                                      │
│     ↓                                                        │
│  6. VS Code Shutdown / Extension deactivated                 │
│     ↓                                                        │
│  7. Deactivate() is called                                   │
│     → Cleanup                                                │
│     → Release resources                                      │
│                                                              │
└─────────────────────────────────────────────────────────────┘
</code>

===== Entry Point =====

Every extension has exactly one entry point: ''extension_main.pas''

<code pascal>
unit extension_main;

{$mode objfpc}{$H+}

interface

uses
  JS, VSCode.API, VSCode.ExtensionExports;

procedure Activate(AContext: TExtensionContext);
procedure Deactivate;

implementation

procedure Activate(AContext: TExtensionContext);
begin
  // Initialization here
end;

procedure Deactivate;
begin
  // Cleanup here
end;

initialization
  ExportActivateDeactivate(@Activate, @Deactivate);

end.
</code>

===== Activation Events =====

^ Event ^ Description ^ Example ^
| onStartupFinished | After VS Code start | Core Extension |
| onCommand:* | On command invocation | wvds.build.run |
| onLanguage:* | On file open | pascal, pxaml |
| onView:* | On view open | wvds.toolbox |
| workspaceContains:** | When file exists | *.lpr, *.pas |
| onCustomEditor:* | On custom editor | wvds.designer |

===== Command Registration =====

<code pascal>
procedure RegisterCommands(AContext: TExtensionContext);
begin
  // Simple command
  RegisterCommand('wvds.feature.action', @HandleAction);

  // Command with arguments
  RegisterCommand('wvds.feature.open', @HandleOpen);

  // Asynchronous command
  RegisterAsyncCommand('wvds.feature.process', @HandleProcessAsync);
end;

procedure HandleAction(Args: TJSValueDynArray);
begin
  ShowInfoMessage('Action executed');
end;

function HandleProcessAsync(Args: TJSValueDynArray): TJSPromise;
begin
  Result := TJSPromise.New(
    procedure(Resolve, Reject: TJSPromiseResolver)
    begin
      // Async work...
      Resolve(nil);
    end
  );
end;
</code>

===== Service Pattern =====

<code pascal>
// Feature.Service.pas
unit Feature.Service;

interface

type
  TWvdSFeatureService = class
  private
    FInitialized: Boolean;
  public
    procedure Initialize;
    procedure Shutdown;
    function DoWork(const AInput: string): string;
  end;

var
  FeatureService: TWvdSFeatureService;

implementation

procedure TWvdSFeatureService.Initialize;
begin
  if FInitialized then Exit;
  // Initialize service
  FInitialized := True;
end;

procedure TWvdSFeatureService.Shutdown;
begin
  if not FInitialized then Exit;
  // Clean up
  FInitialized := False;
end;

initialization
  FeatureService := TWvdSFeatureService.Create;

finalization
  FeatureService.Free;

end.
</code>

===== Disposables =====

VS Code uses Disposables for resource management:

<code pascal>
procedure Activate(AContext: TExtensionContext);
var
  Disposable: TDisposable;
begin
  // Register command and get Disposable
  Disposable := RegisterCommand('wvds.test', @Handler);

  // Add to context for automatic cleanup
  AContext.Subscriptions.Push(Disposable);
end;
</code>

===== WebView Integration =====

<code pascal>
procedure ShowWebViewPanel;
var
  Panel: TWebviewPanel;
begin
  Panel := CreateWebviewPanel(
    'wvds.feature.panel',     // viewType
    'Feature Panel',           // title
    ViewColumn.One,           // showOptions
    WebviewOptions            // options
  );

  // Set HTML
  Panel.Webview.Html := GetPanelHtml;

  // Set up messaging
  Panel.Webview.OnDidReceiveMessage(@HandleWebviewMessage);

  // Send messages
  Panel.Webview.PostMessage(TJSObject.New);
end;
</code>

===== Event Handling =====

<code pascal>
procedure SetupEventHandlers;
begin
  // Configuration change
  OnDidChangeConfiguration(@HandleConfigChange);

  // Document events
  OnDidOpenTextDocument(@HandleDocumentOpen);
  OnDidSaveTextDocument(@HandleDocumentSave);
  OnDidCloseTextDocument(@HandleDocumentClose);

  // Workspace events
  OnDidChangeWorkspaceFolders(@HandleWorkspaceChange);
end;
</code>

===== See Also =====

  * [[.:architektur|Architecture Overview]]
  * [[.:extension-entwicklung|Extension Development]]
  * [[.:vscode-wrapper|VSCode Wrapper API]]