feat: add page image caching to improve PDF navigation performance

src/commands/handlers/PdfHandler.js

@@ -15,7 +15,7 @@ class PdfHandler {
   constructor() {
     this.storageDir = process.env.PDF_STORAGE_DIR || path.join(process.cwd(), 'data', 'pdfs');
     this.sessionFile = path.join(this.storageDir, 'sessions.json');
-    this.sessions = new Map(); // messageId -> { pdfPath, totalPages, ownerId, createdAt, downloadUrl, isPublic }
+    this.sessions = new Map(); // messageId -> { pdfPath, totalPages, ownerId, createdAt, downloadUrl, isPublic, imagePaths }
     pdfjsLib.GlobalWorkerOptions.workerSrc = require('pdfjs-dist/build/pdf.worker.min.js');
     this.ensureStorageDir();
     this.loadSessions();
@@ -60,7 +60,9 @@ class PdfHandler {
         return;
       }
 
-      const pageBuffer = await this.renderPage(pdf, 1);
+      const imagePaths = await this.renderAllPages(pdf, totalPages);
+
+      const pageBuffer = fs.readFileSync(imagePaths[0]);
       const title = this.getPdfTitle(sourceUrl);
       const messageOptions = this.buildMessageOptions(pageBuffer, 1, totalPages, interaction.user.id, sourceUrl, title);
 
@@ -78,7 +80,8 @@ class PdfHandler {
         ownerId: interaction.user.id,
         createdAt: Date.now(),
         downloadUrl: sourceUrl,
-        isPublic
+        isPublic,
+        imagePaths
       });
       this.saveSessions();
 
@@ -123,8 +126,18 @@ class PdfHandler {
     }
 
     try {
-      const { pdf } = await this.loadPdf(session.pdfPath);
-      const pageBuffer = await this.renderPage(pdf, clampedPage);
+      let pageBuffer;
+      if (session.imagePaths?.[clampedPage - 1] && fs.existsSync(session.imagePaths[clampedPage - 1])) {
+        pageBuffer = fs.readFileSync(session.imagePaths[clampedPage - 1]);
+      } else {
+        const { pdf } = await this.loadPdf(session.pdfPath);
+        const buffer = await this.renderPage(pdf, clampedPage);
+        const filePath = this.writeImageFile(buffer, clampedPage);
+        session.imagePaths = session.imagePaths || [];
+        session.imagePaths[clampedPage - 1] = filePath;
+        this.saveSessions();
+        pageBuffer = buffer;
+      }
       const title = this.getPdfTitle(session.downloadUrl);
       const messageOptions = this.buildMessageOptions(pageBuffer, clampedPage, totalPages, ownerId, session.downloadUrl, title);
 
@@ -175,6 +188,29 @@ class PdfHandler {
     return sharp(buffer).png({ quality: 90 }).toBuffer();
   }
 
+  /**
+   * Rend toutes les pages et retourne la liste des chemins de fichiers
+   */
+  async renderAllPages(pdf, totalPages) {
+    const paths = [];
+    for (let i = 1; i <= totalPages; i++) {
+      const buffer = await this.renderPage(pdf, i);
+      const filePath = this.writeImageFile(buffer, i);
+      paths.push(filePath);
+    }
+    return paths;
+  }
+
+  /**
+   * Écrit une image en cache et retourne le chemin
+   */
+  writeImageFile(buffer, pageIndex) {
+    const fileName = `page-${pageIndex}-${Date.now()}-${Math.random().toString(36).slice(2)}.png`;
+    const targetPath = path.join(this.storageDir, fileName);
+    fs.writeFileSync(targetPath, buffer);
+    return targetPath;
+  }
+
   /**
    * Construit le message Discord avec image + boutons
    */