feat: implement 3-layer Nextcloud URL configuration strategy

- Add window.__LIBRESIGN_CONFIG__ support for pre-configured URL (Layer 1)
- Add ?nc_url= query parameter support for manual override (Layer 2)
- Keep window.location.origin fallback for auto-detection (Layer 3)
- Refactor button handlers with proper error handling
- Extract document context from query params and ONLYOFFICE context
- Add message listeners for future modal/sidebar mode support
- Improve logging for debugging configuration issues
- Document URL resolution strategy in code comments

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

index.html

@@ -138,41 +138,152 @@
   w.Asc = w.Asc || {};
   w.Asc.plugin = w.Asc.plugin || {};
 
-  function getBaseUrl() {
-    /* The plugin iframe and Nextcloud share the same nginx origin */
+  /**
+   * Get Nextcloud base URL with 3-layer fallback strategy
+   * Layer 1: Window config object (most reliable, pre-configured)
+   * Layer 2: Query parameter from URL (allows manual override)
+   * Layer 3: Auto-detect from origin (fallback when in same iframe context)
+   */
+  function getNextcloudUrl() {
+    // Layer 1: Pre-configured by Nextcloud app
+    if (w.__LIBRESIGN_CONFIG__ && w.__LIBRESIGN_CONFIG__.nextcloudUrl) {
+      return w.__LIBRESIGN_CONFIG__.nextcloudUrl;
+    }
+
+    // Layer 2: Query parameter for manual override
+    var params = new URLSearchParams(w.location.search);
+    if (params.has('nc_url')) {
+      return params.get('nc_url');
+    }
+
+    // Layer 3: Auto-detect from current origin (same-origin context)
     return w.location.origin;
   }
 
+  /**
+   * Get current document ID and filename from Document Server context
+   */
+  function getDocumentContext() {
+    var title = document.title || '';
+    var context = {
+      fileName: title,
+      fileId: null,
+      fileUrl: null
+    };
+
+    // Try to extract from ONLYOFFICE context if available
+    if (w.Asc && w.Asc.documentId) {
+      context.fileId = w.Asc.documentId;
+    }
+
+    // Try to extract from query params if available
+    var params = new URLSearchParams(w.location.search);
+    if (params.has('filePath')) {
+      context.fileUrl = decodeURIComponent(params.get('filePath'));
+      context.fileName = context.fileUrl.split('/').pop();
+    }
+
+    return context;
+  }
+
+  /**
+   * Open LibreSign in new tab (default behavior)
+   * Allows communication back via window.opener after signing
+   */
+  function openLibreSignNewTab(nextcloudUrl, documentContext) {
+    var url = nextcloudUrl + '/apps/libresign/#/f/filelist/sign';
+    var target = '_blank';
+    
+    var child = w.open(url, target);
+    
+    if (child) {
+      // Allow new window to communicate back when signing complete
+      child.postMessage({
+        type: 'libresign:documentContext',
+        context: documentContext
+      }, nextcloudUrl);
+    }
+  }
+
+  /**
+   * Handle sign button click
+   * Future: Will support modal/sidebar modes via postMessage to Nextcloud
+   */
+  function handleSignClick() {
+    var nextcloudUrl = getNextcloudUrl();
+    var context = getDocumentContext();
+
+    // Log for debugging configuration
+    console.log('[LibreSign Plugin]', {
+      nextcloudUrl: nextcloudUrl,
+      context: context,
+      strategy: 'new-tab'
+    });
+
+    openLibreSignNewTab(nextcloudUrl, context);
+  }
+
+  /**
+   * Handle request signatures button click
+   * Opens request signature view in new tab
+   */
+  function handleRequestClick() {
+    var nextcloudUrl = getNextcloudUrl();
+    var url = nextcloudUrl + '/apps/libresign/#/f/request';
+
+    w.open(url, '_blank');
+  }
+
   function applyTheme(isDark) {
     document.body.classList.toggle('dark', isDark);
     document.getElementById('logo').src = isDark
       ? 'resources/dark/icon.png'
       : 'resources/light/icon.png';
   }
 
+  /**
+   * Plugin initialization
+   * Called by ONLYOFFICE plugin system
+   */
   w.Asc.plugin.init = function () {
-    var base = getBaseUrl();
-
-    document.getElementById('btn-sign').addEventListener('click', function () {
-      w.open(base + '/apps/libresign/#/f/filelist/sign', '_blank');
-    });
-
-    document.getElementById('btn-request').addEventListener('click', function () {
-      w.open(base + '/apps/libresign/#/f/request', '_blank');
-    });
+    document.getElementById('btn-sign').addEventListener('click', handleSignClick);
+    document.getElementById('btn-request').addEventListener('click', handleRequestClick);
 
     /* Apply initial theme */
     if (w.Asc.plugin.theme) {
       applyTheme(w.Asc.plugin.theme.type === 'dark');
     }
   };
 
+  /**
+   * Theme change handler
+   * Called by ONLYOFFICE when user changes theme
+   */
   w.Asc.plugin.onThemeChanged = function (theme) {
     applyTheme(theme.type === 'dark');
   };
 
+  /**
+   * Button placeholder (ONLYOFFICE API requirement)
+   */
   w.Asc.plugin.button = function () {};
 
+  /**
+   * Listen for messages from LibreSign (for future modal/sidebar modes)
+   */
+  w.addEventListener('message', function (e) {
+    // Verify origin matches Nextcloud
+    var nextcloudUrl = getNextcloudUrl();
+    if (!e.origin.startsWith(nextcloudUrl)) {
+      return;
+    }
+
+    if (e.data && e.data.type === 'libresign:signatureComplete') {
+      console.log('[LibreSign Plugin] Signature complete:', e.data.result);
+      // Future: Annotate document with signature if in sidebar mode
+    }
+  });
+
 }(window));
 </script>
 </body>