nexarch/web/pdf-viewer/lib/viewerState.ts

// Reine Zustandslogik des Viewers — bewusst getrennt von der PDF.js-/
// Canvas-Anbindung (components/PdfViewer.tsx), damit Seiten-/Zoom-
// Navigation und Tastaturbedienung (Akzeptanzkriterium 2) ohne echten
// Browser/Canvas testbar sind.

export const MIN_ZOOM = 0.5;
export const MAX_ZOOM = 3.0;
export const ZOOM_STEP = 0.25;

export interface ViewerState {
  currentPage: number;
  numPages: number;
  zoom: number;
}

export function initialViewerState(numPages: number): ViewerState {
  return { currentPage: 1, numPages, zoom: 1.0 };
}

function clampPage(page: number, numPages: number): number {
  if (page < 1) return 1;
  if (page > numPages) return numPages;
  return page;
}

function clampZoom(zoom: number): number {
  if (zoom < MIN_ZOOM) return MIN_ZOOM;
  if (zoom > MAX_ZOOM) return MAX_ZOOM;
  return Math.round(zoom * 100) / 100;
}

export function goToPage(state: ViewerState, page: number): ViewerState {
  return { ...state, currentPage: clampPage(page, state.numPages) };
}

export function nextPage(state: ViewerState): ViewerState {
  return goToPage(state, state.currentPage + 1);
}

export function previousPage(state: ViewerState): ViewerState {
  return goToPage(state, state.currentPage - 1);
}

export function zoomIn(state: ViewerState): ViewerState {
  return { ...state, zoom: clampZoom(state.zoom + ZOOM_STEP) };
}

export function zoomOut(state: ViewerState): ViewerState {
  return { ...state, zoom: clampZoom(state.zoom - ZOOM_STEP) };
}

export function resetZoom(state: ViewerState): ViewerState {
  return { ...state, zoom: 1.0 };
}

// Action-Typen fuer die Tastaturbedienung (Akzeptanzkriterium 2).
export type ViewerAction =
  | { type: "nextPage" }
  | { type: "previousPage" }
  | { type: "zoomIn" }
  | { type: "zoomOut" }
  | { type: "resetZoom" }
  | { type: "focusSearch" };

// mapKeyToAction übersetzt eine Tastatur-Eingabe in eine Viewer-Aktion —
// reine Funktion, unabhängig von React/DOM-Events, damit die Tastatur-
// bedienung ohne echten Browser getestet werden kann. Gibt null zurück,
// wenn die Taste keine Bedeutung für den Viewer hat (z. B. während der
// Nutzer im Suchfeld tippt, siehe ignoreWhenTyping).
export function mapKeyToAction(key: string, ignoreWhenTyping: boolean): ViewerAction | null {
  if (ignoreWhenTyping) {
    return null;
  }
  switch (key) {
    case "ArrowRight":
    case "PageDown":
      return { type: "nextPage" };
    case "ArrowLeft":
    case "PageUp":
      return { type: "previousPage" };
    case "+":
    case "=":
      return { type: "zoomIn" };
    case "-":
      return { type: "zoomOut" };
    case "0":
      return { type: "resetZoom" };
    case "/":
      return { type: "focusSearch" };
    default:
      return null;
  }
}

export function applyViewerAction(state: ViewerState, action: ViewerAction): ViewerState {
  switch (action.type) {
    case "nextPage":
      return nextPage(state);
    case "previousPage":
      return previousPage(state);
    case "zoomIn":
      return zoomIn(state);
    case "zoomOut":
      return zoomOut(state);
    case "resetZoom":
      return resetZoom(state);
    case "focusSearch":
      return state; // Seiteneffekt (Fokus setzen) lebt in der Komponente.
  }
}