Add scrolling context to StatusBar

- Whenever a scrolling context is entered/exited, send a ScrollUpdate event.
- StatusBar maintains a stack of scrolling contexts and displays the
last one, if it exists. Each context is associated with a ComponentId.
- To handle dangling contexts after their Components aren't visible
anymore, send a VisibilityChange event in situations where that scenario
is possible.

src/components.rs

@@ -66,6 +66,22 @@ pub enum PageMovement {
     End,
 }
 
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct ScrollContext {
+    shown_lines: usize,
+    total_lines: usize,
+    has_more_lines: bool,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum ScrollUpdate {
+    End(ComponentId),
+    Update {
+        id: ComponentId,
+        context: ScrollContext,
+    },
+}
+
 /// Types implementing this Trait can draw on the terminal and receive events.
 /// If a type wants to skip drawing if it has not changed anything, it can hold some flag in its
 /// fields (eg self.dirty = false) and act upon that in their `draw` implementation.

src/components/contacts/contact_list.rs

@@ -414,6 +414,27 @@ impl ContactList {
 
         let top_idx = page_no * rows;
 
+        if self.length >= rows {
+            context
+                .replies
+                .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                    ScrollUpdate::Update {
+                        id: self.id,
+                        context: ScrollContext {
+                            shown_lines: top_idx + rows,
+                            total_lines: self.length,
+                            has_more_lines: false,
+                        },
+                    },
+                )));
+        } else {
+            context
+                .replies
+                .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                    ScrollUpdate::End(self.id),
+                )));
+        }
+
         /* If cursor position has changed, remove the highlight from the previous position and
          * apply it in the new one. */
         if self.cursor_pos != self.new_cursor_pos && prev_page_no == page_no {
@@ -621,6 +642,11 @@ impl Component for ContactList {
 
                     self.mode = ViewMode::View(manager.id());
                     self.view = Some(manager);
+                    context
+                        .replies
+                        .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                            ScrollUpdate::End(self.id),
+                        )));
 
                     return true;
                 }
@@ -639,6 +665,11 @@ impl Component for ContactList {
 
                     self.mode = ViewMode::View(manager.id());
                     self.view = Some(manager);
+                    context
+                        .replies
+                        .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                            ScrollUpdate::End(self.id),
+                        )));
 
                     return true;
                 }

src/components/mail/compose.rs

@@ -925,6 +925,9 @@ impl Component for Composer {
     }
 
     fn process_event(&mut self, mut event: &mut UIEvent, context: &mut Context) -> bool {
+        if let UIEvent::VisibilityChange(_) = event {
+            self.pager.process_event(event, context);
+        }
         let shortcuts = self.get_shortcuts(context);
         match (&mut self.mode, &mut event) {
             (ViewMode::Edit, _) => {

src/components/mail/listing.rs

@@ -703,6 +703,8 @@ impl Component for Listing {
                     fallback = *cur;
                 }
                 if self.component.coordinates() == (*account_hash, *mailbox_hash) {
+                    self.component
+                        .process_event(&mut UIEvent::VisibilityChange(false), context);
                     self.component.set_coordinates((
                         self.accounts[self.cursor_pos.0].hash,
                         self.accounts[self.cursor_pos.0].entries[fallback].3,
@@ -730,6 +732,8 @@ impl Component for Listing {
                     let account_hash = self.accounts[self.cursor_pos.0].hash;
                     self.cursor_pos.1 = MenuEntryCursor::Mailbox(*idx);
                     self.status = None;
+                    self.component
+                        .process_event(&mut UIEvent::VisibilityChange(false), context);
                     self.component
                         .set_coordinates((account_hash, *mailbox_hash));
                     self.menu_content.empty();
@@ -1148,6 +1152,11 @@ impl Component for Listing {
             match *event {
                 UIEvent::Input(Key::Right) => {
                     self.focus = ListingFocus::Mailbox;
+                    context
+                        .replies
+                        .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                            ScrollUpdate::End(self.id),
+                        )));
                     self.ratio = 90;
                     self.set_dirty(true);
                     return true;
@@ -1161,6 +1170,11 @@ impl Component for Listing {
                     self.set_dirty(true);
                     self.focus = ListingFocus::Mailbox;
                     self.ratio = 90;
+                    context
+                        .replies
+                        .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                            ScrollUpdate::End(self.id),
+                        )));
                     return true;
                 }
                 UIEvent::Input(ref k)
@@ -1171,6 +1185,11 @@ impl Component for Listing {
                     self.focus = ListingFocus::Mailbox;
                     self.ratio = 90;
                     self.set_dirty(true);
+                    context
+                        .replies
+                        .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                            ScrollUpdate::End(self.id),
+                        )));
                     context
                         .replies
                         .push_back(UIEvent::StatusEvent(StatusEvent::UpdateStatus(
@@ -1650,6 +1669,20 @@ impl Listing {
             ),
         );
         if self.show_menu_scrollbar == ShowMenuScrollbar::True && total_height > rows {
+            if self.focus == ListingFocus::Menu {
+                context
+                    .replies
+                    .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                        ScrollUpdate::Update {
+                            id: self.id,
+                            context: ScrollContext {
+                                shown_lines: skip_offset + rows,
+                                total_lines: total_height,
+                                has_more_lines: false,
+                            },
+                        },
+                    )));
+            }
             ScrollBar::default().set_show_arrows(true).draw(
                 grid,
                 (
@@ -1664,6 +1697,12 @@ impl Listing {
                 /* length */
                 total_height,
             );
+        } else if total_height < rows {
+            context
+                .replies
+                .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                    ScrollUpdate::End(self.id),
+                )));
         }
 
         context.dirty_areas.push_back(area);
@@ -1964,6 +2003,8 @@ impl Listing {
                 if let Some((_, _, _, mailbox_hash)) =
                     self.accounts[self.cursor_pos.0].entries.get(idx)
                 {
+                    self.component
+                        .process_event(&mut UIEvent::VisibilityChange(false), context);
                     self.component
                         .set_coordinates((account_hash, *mailbox_hash));
                     /* Check if per-mailbox configuration overrides general configuration */

src/components/mail/listing/compact.rs

@@ -1627,6 +1627,8 @@ impl Component for CompactListing {
                         ) =>
                 {
                     self.unfocused = false;
+                    self.view
+                        .process_event(&mut UIEvent::VisibilityChange(false), context);
                     self.dirty = true;
                     /* If self.row_updates is not empty and we exit a thread, the row_update events
                      * will be performed but the list will not be drawn. So force a draw in any case.

src/components/mail/listing/conversations.rs

@@ -1491,6 +1491,8 @@ impl Component for ConversationsListing {
                         ) =>
                 {
                     self.unfocused = false;
+                    self.view
+                        .process_event(&mut UIEvent::VisibilityChange(false), context);
                     self.dirty = true;
                     /* If self.row_updates is not empty and we exit a thread, the row_update events
                      * will be performed but the list will not be drawn. So force a draw in any case.

src/components/mail/listing/plain.rs

@@ -1146,6 +1146,8 @@ impl Component for PlainListing {
                         && shortcut!(k == shortcuts[PlainListing::DESCRIPTION]["exit_thread"]) =>
                 {
                     self.unfocused = false;
+                    self.view
+                        .process_event(&mut UIEvent::VisibilityChange(false), context);
                     self.dirty = true;
                     /* If self.row_updates is not empty and we exit a thread, the row_update events
                      * will be performed but the list will not be drawn. So force a draw in any case.

src/components/mail/listing/thread.rs

@@ -1224,6 +1224,9 @@ impl Component for ThreadListing {
             }
             UIEvent::Input(Key::Char('i')) if self.unfocused => {
                 self.unfocused = false;
+                if let Some(ref mut s) = self.view {
+                    s.process_event(&mut UIEvent::VisibilityChange(false), context);
+                }
                 self.dirty = true;
                 self.view = None;
                 return true;

src/components/utilities.rs

@@ -64,6 +64,7 @@ pub struct StatusBar {
     progress_spinner: ProgressSpinner,
     in_progress_jobs: HashSet<JobId>,
     done_jobs: HashSet<JobId>,
+    scroll_contexts: IndexMap<ComponentId, ScrollContext>,
 
     auto_complete: AutoComplete,
     cmd_history: Vec<String>,
@@ -104,6 +105,7 @@ impl StatusBar {
             progress_spinner,
             in_progress_jobs: HashSet::default(),
             done_jobs: HashSet::default(),
+            scroll_contexts: IndexMap::default(),
             cmd_history: crate::command::history::old_cmd_history(),
         }
     }
@@ -140,6 +142,33 @@ impl StatusBar {
                 grid[(x, y)].set_attrs(attribute.attrs | Attr::BOLD);
             }
         }
+        if let Some((
+            _,
+            ScrollContext {
+                shown_lines,
+                total_lines,
+                has_more_lines,
+            },
+        )) = self.scroll_contexts.last()
+        {
+            let s = format!(
+                "| {shown_percentage}% {line_desc}{shown_lines}/{total_lines}{has_more_lines}",
+                line_desc = if grid.ascii_drawing { "lines:" } else { "☰ " },
+                shown_percentage = (*shown_lines as f32 / (*total_lines as f32) * 100.0) as usize,
+                shown_lines = *shown_lines,
+                total_lines = *total_lines,
+                has_more_lines = if *has_more_lines { "(+)" } else { "" }
+            );
+            write_string_to_grid(
+                &s,
+                grid,
+                attribute.fg,
+                attribute.bg,
+                attribute.attrs,
+                ((x + 1, y), bottom_right!(area)),
+                None,
+            );
+        }
 
         let (mut x, y) = bottom_right!(area);
         if self.progress_spinner.is_active() {
@@ -706,6 +735,21 @@ impl Component for StatusBar {
                 self.progress_spinner.set_dirty(true);
                 self.in_progress_jobs.insert(*job_id);
             }
+            UIEvent::StatusEvent(StatusEvent::ScrollUpdate(ScrollUpdate::End(component_id))) => {
+                if self.scroll_contexts.remove(component_id).is_some() {
+                    self.dirty = true;
+                }
+                return true;
+            }
+            UIEvent::StatusEvent(StatusEvent::ScrollUpdate(ScrollUpdate::Update {
+                id,
+                context,
+            })) => {
+                if self.scroll_contexts.insert(*id, *context) != Some(*context) {
+                    self.dirty = true;
+                }
+                return true;
+            }
             UIEvent::Timer(_) => {
                 if self.progress_spinner.process_event(event, context) {
                     return true;
@@ -975,6 +1019,21 @@ impl Component for Tabbed {
                     ),
                 );
                 if height.wrapping_div(rows + 1) > 0 || width.wrapping_div(cols + 1) > 0 {
+                    context
+                        .replies
+                        .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                            ScrollUpdate::Update {
+                                id: self.id,
+                                context: ScrollContext {
+                                    shown_lines: std::cmp::min(
+                                        (height).saturating_sub(rows + 1),
+                                        self.help_screen_cursor.1,
+                                    ) + rows,
+                                    total_lines: height,
+                                    has_more_lines: false,
+                                },
+                            },
+                        )));
                     ScrollBar::default().set_show_arrows(true).draw(
                         grid,
                         (
@@ -989,6 +1048,12 @@ impl Component for Tabbed {
                         /* length */
                         height,
                     );
+                } else {
+                    context
+                        .replies
+                        .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                            ScrollUpdate::End(self.id),
+                        )));
                 }
                 self.dirty = false;
                 return;
@@ -1192,6 +1257,21 @@ impl Component for Tabbed {
                 ),
             );
             if height.wrapping_div(rows + 1) > 0 || width.wrapping_div(cols + 1) > 0 {
+                context
+                    .replies
+                    .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                        ScrollUpdate::Update {
+                            id: self.id,
+                            context: ScrollContext {
+                                shown_lines: std::cmp::min(
+                                    (height).saturating_sub(rows),
+                                    self.help_screen_cursor.1,
+                                ) + rows,
+                                total_lines: height,
+                                has_more_lines: false,
+                            },
+                        },
+                    )));
                 ScrollBar::default().set_show_arrows(true).draw(
                     grid,
                     (
@@ -1206,6 +1286,12 @@ impl Component for Tabbed {
                     /* length */
                     height,
                 );
+            } else {
+                context
+                    .replies
+                    .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                        ScrollUpdate::End(self.id),
+                    )));
             }
         }
         self.dirty = false;
@@ -1250,6 +1336,11 @@ impl Component for Tabbed {
                 if self.show_shortcuts {
                     /* children below the shortcut overlay must be redrawn */
                     self.set_dirty(true);
+                    context
+                        .replies
+                        .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                            ScrollUpdate::End(self.id),
+                        )));
                 }
                 self.show_shortcuts = !self.show_shortcuts;
                 self.dirty = true;
@@ -1281,6 +1372,8 @@ impl Component for Tabbed {
                     return true;
                 }
                 if let Some(c_idx) = self.children.iter().position(|x| x.id() == *id) {
+                    self.children[c_idx]
+                        .process_event(&mut UIEvent::VisibilityChange(false), context);
                     self.children.remove(c_idx);
                     self.cursor_pos = 0;
                     self.set_dirty(true);

src/components/utilities/pager.rs

@@ -533,28 +533,30 @@ impl Component for Pager {
         }
         if (rows < height) || self.search.is_some() {
             const RESULTS_STR: &str = "Results for ";
-            let shown_percentage =
-                ((self.cursor.1 + rows) as f32 / (height as f32) * 100.0) as usize;
             let shown_lines = self.cursor.1 + rows;
             let total_lines = height;
-            let scrolling = if rows < height {
+            if rows < height {
-                format!(
+                context
-                    "{shown_percentage}% {line_desc}{shown_lines}/{total_lines}{has_more_lines}",
+                    .replies
-                    line_desc = if grid.ascii_drawing { "lines:" } else { "☰ " },
+                    .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
-                    shown_percentage = shown_percentage,
+                        ScrollUpdate::Update {
-                    shown_lines = shown_lines,
+                            id: self.id,
-                    total_lines = total_lines,
+                            context: ScrollContext {
-                    has_more_lines = if self.line_breaker.is_finished() {
+                                shown_lines,
-                        ""
+                                total_lines,
-                    } else {
+                                has_more_lines: !self.line_breaker.is_finished(),
-                        "(+)"
+                            },
-                    }
+                        },
-                )
+                    )));
             } else {
-                String::new()
+                context
+                    .replies
+                    .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                        ScrollUpdate::End(self.id),
+                    )));
             };
-            let search_results = if let Some(ref search) = self.search {
+            if let Some(ref search) = self.search {
-                format!(
+                let status_message = format!(
                     "{results_str}{search_pattern}: {current_pos}/{total_results}{has_more_lines}",
                     results_str = RESULTS_STR,
                     search_pattern = &search.pattern,
@@ -569,39 +571,29 @@ impl Component for Pager {
                     } else {
                         "(+)"
                     }
-                )
+                );
-            } else {
+                let mut attribute = crate::conf::value(context, "status.bar");
-                String::new()
+                if !context.settings.terminal.use_color() {
-            };
+                    attribute.attrs |= Attr::REVERSE;
-            let status_message = format!(
+                }
-                "{search_results}{divider}{scrolling}",
+                let (_, y) = write_string_to_grid(
-                search_results = search_results,
+                    &status_message,
-                divider = if self.search.is_some() { " " } else { "" },
+                    grid,
-                scrolling = scrolling,
+                    attribute.fg,
-            );
+                    attribute.bg,
-            let mut attribute = crate::conf::value(context, "status.bar");
+                    attribute.attrs,
-            if !context.settings.terminal.use_color() {
+                    (
-                attribute.attrs |= Attr::REVERSE;
+                        set_y(upper_left!(area), get_y(bottom_right!(area))),
-            }
+                        bottom_right!(area),
-            let (_, y) = write_string_to_grid(
+                    ),
-                &status_message,
+                    None,
-                grid,
+                );
-                attribute.fg,
+                /* set search pattern to italics */
-                attribute.bg,
-                attribute.attrs,
-                (
-                    set_y(upper_left!(area), get_y(bottom_right!(area))),
-                    bottom_right!(area),
-                ),
-                None,
-            );
-            /* set search pattern to italics */
-            if let Some(ref search) = self.search {
                 let start_x = get_x(upper_left!(area)) + RESULTS_STR.len();
                 for c in grid.row_iter(start_x..(start_x + search.pattern.grapheme_width()), y) {
                     grid[c].set_attrs(attribute.attrs | Attr::ITALICS);
                 }
-            }
+            };
         }
         context.dirty_areas.push_back(area);
     }
@@ -746,6 +738,13 @@ impl Component for Pager {
                 self.initialised = false;
                 self.dirty = true;
             }
+            UIEvent::VisibilityChange(false) => {
+                context
+                    .replies
+                    .push_back(UIEvent::StatusEvent(StatusEvent::ScrollUpdate(
+                        ScrollUpdate::End(self.id),
+                    )));
+            }
             _ => {}
         }
         false

src/types.rs

@@ -38,7 +38,7 @@ pub use self::helpers::*;
 use super::command::Action;
 use super::jobs::{JobExecutor, JobId};
 use super::terminal::*;
-use crate::components::{Component, ComponentId};
+use crate::components::{Component, ComponentId, ScrollUpdate};
 use std::sync::Arc;
 
 use melib::backends::{AccountHash, BackendEvent, MailboxHash};
@@ -57,6 +57,7 @@ pub enum StatusEvent {
     JobFinished(JobId),
     JobCanceled(JobId),
     SetMouse(bool),
+    ScrollUpdate(ScrollUpdate),
 }
 
 /// `ThreadEvent` encapsulates all of the possible values we need to transfer between our threads
@@ -149,6 +150,7 @@ pub enum UIEvent {
     ConfigReload {
         old_settings: crate::conf::Settings,
     },
+    VisibilityChange(bool),
 }
 
 pub struct CallbackFn(pub Box<dyn FnOnce(&mut crate::Context) -> () + Send + 'static>);