Track viewed PDF pages and persist state in sessionStorage

Added logic to monitor which PDF pages have been viewed by the user. The list of unviewed pages and a flag for all pages viewed are stored in sessionStorage and updated as the user navigates. Changes applied to both ui.js and ui.min.js.

EnvelopeGenerator.Web/wwwroot/js/ui.js

@@ -17,8 +17,37 @@
       return !(annotation.isSignature || annotation.description === 'FRAME')
     },
   }).then((instance) => {
+    const totalPages = instance.totalPageCount || 0
+    const storageKeyAll = 'pspdf_all_pages_rendered'
+    const storageKeyUnviewed = 'pspdf_unviewed_pages'
+
+    let unviewed = totalPages > 0 ? Array.from({ length: totalPages }, (_, i) => i + 1) : []
+
+    const saveState = () => {
+      sessionStorage.setItem(storageKeyUnviewed, JSON.stringify(unviewed))
+      sessionStorage.setItem(storageKeyAll, JSON.stringify(unviewed.length === 0 && totalPages > 0))
+    }
+
+    const markPageViewed = (pageIndex) => {
+      const pageNumber = pageIndex + 1
+      if (pageNumber < 1 || pageNumber > totalPages) return
+      const idx = unviewed.indexOf(pageNumber)
+      if (idx >= 0) {
+        unviewed.splice(idx, 1)
+        saveState()
+      }
+    }
+
+    // initial state in session storage
+    saveState()
+
+    // mark the initially visible page
+    const initialPage = instance.viewState?.currentPageIndex ?? 0
+    markPageViewed(initialPage)
+
     instance.addEventListener('viewState.currentPageIndex.change', (pageIndex) => {
       console.log('Active page:', pageIndex + 1)
+      markPageViewed(pageIndex)
     })
 
     return instance