Download terms on demand for export

Instead of simply disabling terms that have not yet been downloaded from
export, allow the user to select those terms and have their data
automatically downloaded and included in the export.

public/home.html

@@ -189,6 +189,7 @@ <h3 id="export_modal_title">Export Data</h3>
           </label>
         </li>
       </ul>
+      <p>Status: <span id="export_status"></span></p>
       <button id="export_button">Export</button>
     </div>        
   </div>

public/js/buttonFunctions.js

@@ -293,18 +293,64 @@ let exportTableData = async function(prefs) {
   if (prefs.recent) obj.recent = currentTableData.recent;
   if (prefs.schedule) obj.schedule = currentTableData.schedule;
   if (prefs.terms) {
-    obj.terms = {};
-    termConverter.forEach(term => {
-      if (prefs.terms[term]) obj.terms[term] = currentTableData.terms[term];
-    });
+    const origCurrentTerm = currentTerm;
+    try {
+      terms = await Promise.all(termConverter.map(async term => {
+        // Term is selected by user and its data are already downloaded
+        if (prefs.terms[term] && currentTableData.terms[term].classes) {
+          return currentTableData.terms[term];
+        } 
+        // Term is selected by user and its data have not been downloaded
+        else if (prefs.terms[term] && !currentTableData.imported) {
+          try {
+            $("#export_status").html(
+              `Downloading quarter "${term}" from Aspen…`
+            );
+            const response = await $.ajax({
+              url: "/data",
+              method: "POST",
+              data: { quarter: parseInt(term.match(/\d+/)[0]) },
+              dataType: "json json"
+            });
+            currentTerm = term;
+            responseCallbackPartial(response);
+            $("#export_status").html("");
+            return currentTableData.terms[term];
+          }
+          catch (err) {
+            throw `Error while downloading quarter "${term}".`;
+          }
+        }
+      }));
+      obj.terms = {};
+      // Add the term data to obj.terms
+      termConverter.forEach((term, i) => {
+        if (terms[i]) {
+          obj.terms[term] = terms[i];
+        }
+      });
+    }
+    catch (err) {
+      $("#export_status").html(err);
+    }
+    finally {
+      currentTerm = origCurrentTerm;
+      currentTableData.currentTermData = currentTableData.terms[currentTerm];
+      classesTable.setData(currentTableData.currentTermData.classes);
+      classesTable.redraw();
+    }
   }
   if (prefs.cumGPA) obj.cumGPA = currentTableData.cumGPA;
 
   let jsonString = JSON.stringify(obj);
 
+  const filename = `aspine-export-${new Date().toISOString()}.json`;
+
+  $("#export_status").html(`Generated file "${filename}".`);
+
   saveAs(new Blob([jsonString], {
     type: "application/json;charset=utf-8"
-  }), `aspine-export-${new Date().toISOString()}.json`);
+  }), filename);
   return jsonString;
 };
 

public/js/home.js

@@ -566,9 +566,25 @@ let classesTable = new Tabulator("#classesTable", {
             title: "Export Table Data",
             titleFormatter: () => '<i class="fa fa-file-download header-icon" aria-hidden="true"></i>',
             headerClick: async () => {
-                // Disable checkboxes for terms whose data have not yet been downloaded
+                // Disable checkboxes for inaccessible terms
                 termConverter.forEach(term => {
-                    if (currentTableData.terms[term].classes) {
+                    // Boolean storing whether or not this term is 'accessible'
+                    let accessible = true;
+                    // If no GPA is available for the term, it is inaccessible
+                    // (the term was not included in Aspen's overview)
+                    if (!currentTableData.terms[term].GPA.percent) {
+                        accessible = false;
+                    }
+                    // If currentTableData is imported, we cannot scrape Aspen
+                    // for more data, so any terms not included in the import
+                    // are inaccessible
+                    if (
+                        currentTableData.imported &&
+                        !currentTableData.terms[term].classes
+                    ) accessible = false;
+
+                    // Disable the checkboxes
+                    if (accessible) {
                         $(`#export_checkbox_terms_${term}`).removeAttr("disabled");
                     }
                     else {