Adding webui_set_context and webui_get_context

* webui_set_context
* webui_get_context

Inf: https://github.com/webui-dev/webui/issues/551

include/webui.h

@@ -245,6 +245,43 @@ WEBUI_EXPORT size_t webui_get_new_window_id(void);
  */
 WEBUI_EXPORT size_t webui_bind(size_t window, const char* element, void (*func)(webui_event_t* e));
 
+/**
+ * @brief Use this API after using `webui_bind()` to add any user data to it that can be
+ * read later using `webui_get_context()`.
+ *
+ * @param window The window number
+ * @param element The HTML element / JavaScript object
+ * @param context Any user data
+ *
+ * @example
+ * webui_bind(myWindow, "myFunction", myFunction);
+ * 
+ * webui_set_context(myWindow, "myFunction", myData);
+ * 
+ * void myFunction(webui_event_t* e) {
+ *   void* myData = webui_get_context(e);
+ * }
+ */
+WEBUI_EXPORT void webui_set_context(size_t window, const char* element, void* context);
+
+/**
+ * @brief Get user data that is set using `webui_set_context()`.
+ *
+ * @param e The event struct
+ * 
+ * @return Returns user data pointer.
+ *
+ * @example
+ * webui_bind(myWindow, "myFunction", myFunction);
+ * 
+ * webui_set_context(myWindow, "myFunction", myData);
+ * 
+ * void myFunction(webui_event_t* e) {
+ *   void* myData = webui_get_context(e);
+ * }
+ */
+WEBUI_EXPORT void* webui_get_context(webui_event_t* e);
+
 /**
  * @brief Get the recommended web browser ID to use. If you 
  * are already using one, this function will return the same ID.

src/webui.c

@@ -308,6 +308,7 @@ typedef struct _webui_window_t {
     size_t num; // Window number
     const char* html_elements[WEBUI_MAX_IDS];
     bool has_all_events;
+    void* cb_context[WEBUI_MAX_IDS];
     void(*cb[WEBUI_MAX_IDS])(webui_event_t* e);
     void(*cb_interface[WEBUI_MAX_IDS])(size_t, size_t, char* , size_t, size_t);
     bool ws_block;
@@ -1730,6 +1731,59 @@ bool webui_show_browser(size_t window, const char* content, size_t browser) {
     return _webui_show(win, NULL, content, browser);
 }
 
+void* webui_get_context(webui_event_t* e) {
+
+    #ifdef WEBUI_LOG
+    printf("[User] webui_get_context()\n");
+    #endif
+
+    // Dereference
+    if (_webui_mutex_is_exit_now(WEBUI_MUTEX_NONE) || _webui.wins[e->window] == NULL)
+        return 0;
+    _webui_window_t* win = _webui.wins[e->window];
+
+    // Search
+    size_t cb_index = 0;
+    if (_webui_get_cb_index(win, e->element, &cb_index)) {
+        // Get context
+        #ifdef WEBUI_LOG
+        printf("[User] webui_get_context() -> Found context at %p\n", win->cb_context[cb_index]);
+        #endif
+        return win->cb_context[cb_index];
+    }
+
+    return NULL;
+}
+
+void webui_set_context(size_t window, const char* element, void* context) {
+
+    #ifdef WEBUI_LOG
+    printf("[User] webui_set_context([%zu])\n", window);
+    printf("[User] webui_set_context() -> Element: [%s]\n", element);
+    printf("[User] webui_set_context() -> Context: [%p]\n", context);
+    #endif
+
+    // Initialization
+    _webui_init();
+
+    // Dereference
+    if (_webui_mutex_is_exit_now(WEBUI_MUTEX_NONE) || _webui.wins[window] == NULL)
+        return;
+    _webui_window_t* win = _webui.wins[window];
+    
+    // Get bind Index
+    // We should use `webui_bind()` with NULL to make `webui_set_context()`
+    // works fine if user call it before or after `webui_bind()`.
+    size_t cb_index = webui_bind(window, element, NULL);
+
+    // Set context
+    win->cb_context[cb_index] = context;
+
+    #ifdef WEBUI_LOG
+    printf("[User] webui_set_context() -> Context saved at %zu\n", cb_index);
+    #endif
+}
+
 size_t webui_bind(size_t window, const char* element, void(*func)(webui_event_t* e)) {
 
     #ifdef WEBUI_LOG
@@ -1748,22 +1802,27 @@ size_t webui_bind(size_t window, const char* element, void(*func)(webui_event_t*
     size_t cb_index = 0;
     bool exist = _webui_get_cb_index(win, element, &cb_index);
 
-    // All events
-    if (_webui_is_empty(element)) {
-        win->has_all_events = true;
+    // Free old ID
     size_t index = (exist ? cb_index : _webui.cb_count++);
+    _webui_free_mem((void*)win->html_elements[index]);
+
+    // All events binding
+    if (_webui_is_empty(element)) {
+        // Empty Element ID Binding (New / Update)
         win->html_elements[index] = "";
+        if (func != NULL) {
+            win->has_all_events = true;
             win->cb[index] = func;
             #ifdef WEBUI_LOG
             printf("[User] webui_bind() -> Save bind (all events) at %zu\n", index);
             #endif
-        return index;
         }
-
-    // New bind
+        return index;
+    } else {
+        // Non-empty Element ID Binding (New / Update)
         const char* element_cpy = (const char*)_webui_str_dup(element);
-    size_t index = (exist ? cb_index : _webui.cb_count++);
         win->html_elements[index] = element_cpy;
+        if (func != NULL) {
             win->cb[index] = func;
             #ifdef WEBUI_LOG
             printf("[User] webui_bind() -> Save bind at %zu\n", index);
@@ -1781,6 +1840,8 @@ size_t webui_bind(size_t window, const char* element, void(*func)(webui_event_t*
                 win, 0, WEBUI_CMD_ADD_ID,
                 element, _webui_strlen(element_cpy)
             );        
+        }
+    }
 
     return index;
 }