add loader on uploading installation report

installations/templates/installations/installation_report_step.html

@@ -31,6 +31,60 @@
   .removal-checkbox:checked:focus {
     box-shadow: 0 0 0 0.25rem rgba(220, 53, 69, 0.25) !important;
   }
+
+  /* Upload Loader Overlay */
+  #uploadLoader {
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    background-color: rgba(0, 0, 0, 0.7);
+    z-index: 9999;
+    display: none;
+    justify-content: center;
+    align-items: center;
+  }
+
+  #uploadLoader.active {
+    display: flex;
+  }
+
+  .loader-content {
+    background: white;
+    padding: 2rem;
+    border-radius: 12px;
+    text-align: center;
+    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.3);
+    max-width: 300px;
+  }
+
+  .loader-spinner {
+    width: 50px;
+    height: 50px;
+    border: 5px solid #f3f3f3;
+    border-top: 5px solid #696cff;
+    border-radius: 50%;
+    animation: spin 1s linear infinite;
+    margin: 0 auto 1rem;
+  }
+
+  @keyframes spin {
+    0% { transform: rotate(0deg); }
+    100% { transform: rotate(360deg); }
+  }
+
+  .loader-text {
+    font-size: 1.1rem;
+    font-weight: 500;
+    color: #333;
+    margin-bottom: 0.5rem;
+  }
+
+  .loader-subtext {
+    font-size: 0.9rem;
+    color: #666;
+  }
 </style>
 {% endblock %}
 
@@ -38,6 +92,15 @@
 
 {% include '_toasts.html' %}
 
+<!-- Upload Loader Overlay -->
+<div id="uploadLoader">
+  <div class="loader-content">
+    <div class="loader-spinner"></div>
+    <div class="loader-text">در حال آپلود...</div>
+    <div class="loader-subtext">لطفا تا بارگذاری کامل گزارش منتظر بمانید.</div>
+  </div>
+</div>
+
 <!-- Instance Info Modal -->
 {% instance_info_modal instance %}
 
@@ -516,7 +579,7 @@
               {% if user_is_installer %}
                 <button type="submit" class="btn btn-success" form="installation-report-form">ثبت گزارش</button>
               {% endif %}
-              {% if next_step and not edit_mode %}
+              {% if next_step and not edit_mode and report %}
                 <a href="{% url 'processes:step_detail' instance.id next_step.id %}" class="btn btn-primary">
                   بعدی
                   <i class="bx bx-chevron-left bx-sm me-sm-n2"></i>
@@ -638,6 +701,9 @@
   // Require date and show success toast on submit (persist across redirect)
   (function(){
     const form = document.querySelector('form[enctype]') || document.querySelector('form');
+    const loader = document.getElementById('uploadLoader');
+    const submitButton = document.querySelector('button[type="submit"][form="installation-report-form"]');
+    
     if (!form) return;
     form.addEventListener('submit', function(ev){
       const display = document.getElementById('id_visited_date_display');
@@ -663,8 +729,32 @@
           return false;
         }
       } catch(_) {}
+      
+      // Show loader overlay when form is valid and submitting
+      if (loader) {
+        loader.classList.add('active');
+      }
+      
+      // Disable submit button to prevent double submission
+      if (submitButton) {
+        submitButton.disabled = true;
+        submitButton.innerHTML = '<span class="spinner-border spinner-border-sm me-2"></span>در حال ارسال...';
+      }
+      
       try { sessionStorage.setItem('install_report_saved', '1'); } catch(_) {}
     }, false);
+    
+    // Hide loader on back navigation or page show (in case of errors)
+    window.addEventListener('pageshow', function(event) {
+      if (loader) {
+        loader.classList.remove('active');
+      }
+      if (submitButton) {
+        submitButton.disabled = false;
+        submitButton.innerHTML = 'ثبت گزارش';
+      }
+    });
+    
     // on load, if saved flag exists, show toast
     try {
       if (sessionStorage.getItem('install_report_saved') === '1') {