add a hook to support extending external .html files

qt/aqt/gui_hooks.py

@@ -2844,6 +2844,54 @@ class _UndoStateDidChangeHook:
 undo_state_did_change = _UndoStateDidChangeHook()
 
 
+class _WebviewDidInjectStyleIntoPageHook:
+    '''Called after standard styling is injected into an external
+html file, such as when loading the new graphs. You can use this hook to
+mutate the DOM before the page is revealed.
+
+For example:
+
+def mytest(web: AnkiWebView):
+    page = os.path.basename(web.page().url().path())
+    if page != "graphs.html":
+    	return
+    web.eval(
+        """
+    div = document.createElement("div");
+    div.innerHTML = 'hello';
+    document.body.appendChild(div);
+"""
+    )
+
+gui_hooks.webview_did_inject_style_into_page.append(mytest)
+'''
+
+    _hooks: List[Callable[[AnkiWebView], None]] = []
+
+    def append(self, cb: Callable[[AnkiWebView], None]) -> None:
+        """(webview: AnkiWebView)"""
+        self._hooks.append(cb)
+
+    def remove(self, cb: Callable[[AnkiWebView], None]) -> None:
+        if cb in self._hooks:
+            self._hooks.remove(cb)
+
+    def count(self) -> int:
+        return len(self._hooks)
+
+    def __call__(self, webview: AnkiWebView) -> None:
+        for hook in self._hooks:
+            try:
+                hook(webview)
+            except:
+                # if the hook fails, remove it
+                self._hooks.remove(hook)
+                raise
+
+
+webview_did_inject_style_into_page = _WebviewDidInjectStyleIntoPageHook()
+
+
 class _WebviewDidReceiveJsMessageFilter:
     """Used to handle pycmd() messages sent from Javascript.
 

qt/aqt/webview.py

@@ -598,14 +598,15 @@ body {{ zoom: {zoom}; background: {background}; direction: {lang_dir}; {font} }}
     def inject_dynamic_style_and_show(self):
         "Add dynamic styling, and reveal."
         css = self.standard_css()
+        def after_style(arg):
+            gui_hooks.webview_did_inject_style_into_page(self)
+            self.show()
         self.evalWithCallback(
             f"""
 const style = document.createElement('style');
 style.innerHTML = `{css}`;
 document.head.appendChild(style);
-""",
-            lambda arg: self.show(),
-        )
+""", after_style)
 
     def load_ts_page(self, name: str) -> None:
         from aqt import mw

qt/tools/genhooks_gui.py

@@ -452,6 +452,29 @@ hooks = [
         args=["webview: aqt.webview.AnkiWebView", "menu: QMenu"],
         legacy_hook="AnkiWebView.contextMenuEvent",
     ),
+    Hook(
+        name="webview_did_inject_style_into_page",
+        args=["webview: AnkiWebView"],
+        doc='''Called after standard styling is injected into an external
+html file, such as when loading the new graphs. You can use this hook to
+mutate the DOM before the page is revealed.
+
+For example:
+
+def mytest(web: AnkiWebView):
+    page = os.path.basename(web.page().url().path())
+    if page != "graphs.html":
+    	return
+    web.eval(
+        """
+    div = document.createElement("div");
+    div.innerHTML = 'hello';
+    document.body.appendChild(div);
+"""
+    )
+
+gui_hooks.webview_did_inject_style_into_page.append(mytest)
+'''),
     # Main
     ###################
     Hook(