E-book viewer: Allow clicking links in popup footnotes. Fixes #1931646 [Footnotes/Endnotes don't return to text](https://bugs.launchpad.net/calibre/+bug/1931646)

src/pyj/read_book/content_popup.pyj

@@ -58,6 +58,8 @@ class ContentPopupOverlay:
             'ready': self.on_iframe_ready,
             'error': self.view.on_iframe_error,
             'content_loaded': self.on_content_loaded,
+            'print': self.on_print,
+            'link_activated': self.on_link_activated,
         }
         iframe_kw = {
             'seamless': True, 'sandbox': 'allow-scripts', 'style': 'width: 100%; max-height: 70vh'
@@ -72,6 +74,12 @@ class ContentPopupOverlay:
         c = self.container
         c.firstChild.appendChild(iframe)
 
+    def on_print(self, data):
+        print(data.string)
+
+    def on_link_activated(self, data):
+        self.view.link_in_content_popup_activated(data.name, data.frag, data.is_popup, data.title)
+
     @property
     def container(self):
         return document.getElementById('book-content-popup-overlay')

src/pyj/read_book/footnotes.pyj

@@ -4,6 +4,7 @@ from __python__ import bound_methods, hash_literals
 
 from dom import clear
 from iframe_comm import IframeClient
+from read_book.globals import runtime, current_spine_item, set_current_spine_item
 from read_book.resources import finalize_resources, unserialize_html
 from read_book.settings import (
     apply_settings, set_color_scheme_class, update_settings
@@ -194,11 +195,12 @@ class PopupIframeBoss:
         self.blob_url_map = {}
         self.name = None
         self.frag = None
+        self.link_attr = None
 
     def initialize(self, data):
-        window.addEventListener('error', self.onerror)
+        window.addEventListener('error', self.on_error)
 
-    def onerror(self, evt):
+    def on_error(self, evt):
         msg = evt.message
         script_url = evt.filename
         line_number = evt.lineno
@@ -217,6 +219,16 @@ class PopupIframeBoss:
         self.book = data.book
         self.name = data.name
         self.frag = data.frag
+        self.link_attr = 'data-' + self.book.manifest.link_uid
+        spine = self.book.manifest.spine
+        index = spine.indexOf(data.name)
+        set_current_spine_item({
+            'name':data.name,
+            'is_first':index is 0,
+            'is_last':index is spine.length - 1,
+            'index': index,
+            'initial_position':data.initial_position
+        })
         update_settings(data.settings)
         for name in self.blob_url_map:
             window.URL.revokeObjectURL(self.blob_url_map[name])
@@ -224,6 +236,35 @@ class PopupIframeBoss:
         root_data, self.mathjax, self.blob_url_map = finalize_resources(self.book, data.name, data.resource_data)
         self.resource_urls = unserialize_html(root_data, self.content_loaded, self.show_only_footnote, data.name)
 
+    def connect_links(self):
+        for a in document.body.querySelectorAll(f'a[{self.link_attr}]'):
+            a.addEventListener('click', self.link_activated)
+        if runtime.is_standalone_viewer:
+            # links with a target get turned into requests to open a new window by Qt
+            for a in document.body.querySelectorAll('a[target]'):
+                a.removeAttribute('target')
+
+    def link_activated(self, evt):
+        try:
+            data = JSON.parse(evt.currentTarget.getAttribute(self.link_attr))
+        except:
+            print('WARNING: Failed to parse link data {}, ignoring'.format(evt.currentTarget?.getAttribute?(self.link_attr)))
+            return
+        self.activate_link(data.name, data.frag, evt.currentTarget)
+
+    def activate_link(self, name, frag, target_elem):
+        if not name:
+            name = current_spine_item().name
+        try:
+            is_popup = is_footnote_link(target_elem, name, frag, current_spine_item().name, self.book.manifest.link_to_map or {})
+            title = target_elem.textContent
+        except:
+            import traceback
+            traceback.print_exc()
+            is_popup = False
+            title = ''
+        self.comm.send_message('link_activated', is_popup=is_popup, name=name, frag=frag, title=title)
+
     def on_clear(self, data):
         clear(document.head)
         clear(document.body)
@@ -242,6 +283,7 @@ class PopupIframeBoss:
         if not self.comm.encrypted_communications:
             window.setTimeout(self.content_loaded, 2)
             return
+        self.connect_links()
         # this is the loading styles used to suppress scrollbars during load
         # added in unserialize_html
         document.head.removeChild(document.head.firstChild)

src/pyj/read_book/iframe.pyj

@@ -154,6 +154,7 @@ class IframeBoss:
             'scroll_to_anchor': self.on_scroll_to_anchor,
             'scroll_to_frac': self.on_scroll_to_frac,
             'scroll_to_ref': self.on_scroll_to_ref,
+            'fake_popup_activation': self.on_fake_popup_activation,
             'set_reference_mode': self.set_reference_mode,
             'toggle_autoscroll': self.toggle_autoscroll,
             'fake_wheel_event': self.fake_wheel_event,
@@ -718,7 +719,7 @@ class IframeBoss:
             traceback.print_exc()
             is_popup = False
         if is_popup:
-            self.send_message('show_footnote', name=name, frag=frag, title=target_elem.textContent, cols_per_screen=calc_columns_per_screen())
+            self.on_fake_popup_activation({'name': name, 'frag': frag, 'title': target_elem.textContent})
             return
         if name is current_spine_item().name:
             self.replace_history_on_next_cfi_update = False
@@ -726,6 +727,9 @@ class IframeBoss:
         else:
             self.send_message('scroll_to_anchor', name=name, frag=frag)
 
+    def on_fake_popup_activation(self, data):
+        self.send_message('show_footnote', name=data.name, frag=data.frag, title=data.title, cols_per_screen=calc_columns_per_screen())
+
     def scroll_to_anchor(self, frag):
         if frag:
             elem = document.getElementById(frag)

src/pyj/read_book/view.pyj

@@ -1062,6 +1062,13 @@ class View:
     def on_scroll_to_anchor(self, data):
         self.show_name(data.name, initial_position={'type':'anchor', 'anchor':data.frag, 'replace_history':False})
 
+    def link_in_content_popup_activated(self, name, frag, is_popup, title):
+        self.content_popup_overlay.hide()
+        if is_popup:
+            self.iframe_wrapper.send_message('fake_popup_activation', name=name, frag=frag, title=title)
+        else:
+            self.goto_named_destination(name, frag)
+
     def goto_cfi(self, bookpos, add_to_history):
         cfiname, internal_cfi = self.parse_cfi(bookpos, self.book)
         if cfiname and internal_cfi: