Fix TUI details viewport scrolling

apps/tui/src/viewer.rs

@@ -1,6 +1,6 @@
 //! Secret-aware presentation state for one storage-owned entry document.
 
-use std::fmt;
+use std::{cell::Cell, fmt};
 
 use ironstorage::{
     document::{DocumentError, EntryDocument, EntryField, EntryFieldId, EntrySensitivity},
@@ -15,7 +15,7 @@ pub struct EntryViewer {
     document: EntryDocument,
     focused: usize,
     revealed: Option<EntryFieldId>,
-    scroll: usize,
+    scroll: Cell<usize>,
 }
 
 impl EntryViewer {
@@ -24,7 +24,7 @@ impl EntryViewer {
             document,
             focused: 0,
             revealed: None,
-            scroll: 0,
+            scroll: Cell::new(0),
         }
     }
 
@@ -52,7 +52,6 @@ impl EntryViewer {
         self.hide_revealed();
         if !self.document.fields().is_empty() {
             self.focused = (self.focused + 1) % self.document.fields().len();
-            self.scroll = self.focused;
         }
     }
 
@@ -63,7 +62,6 @@ impl EntryViewer {
                 .focused
                 .checked_sub(1)
                 .unwrap_or(self.document.fields().len() - 1);
-            self.scroll = self.focused;
         }
     }
 
@@ -90,23 +88,56 @@ impl EntryViewer {
     }
 
     pub fn scroll(&self) -> usize {
-        self.scroll
+        self.scroll.get()
+    }
+
+    /// Keep the focused rendered row range inside the supplied viewport while
+    /// retaining the current offset whenever it is already visible.
+    pub fn ensure_focus_visible(
+        &self,
+        focused_start: usize,
+        focused_height: usize,
+        total_rows: usize,
+        viewport_rows: usize,
+    ) -> usize {
+        if self.document.fields().is_empty() || total_rows == 0 {
+            self.scroll.set(0);
+            return 0;
+        }
+        if viewport_rows == 0 {
+            let scroll = self.scroll.get().min(total_rows.saturating_sub(1));
+            self.scroll.set(scroll);
+            return scroll;
+        }
+        let maximum = total_rows.saturating_sub(viewport_rows);
+        let mut scroll = self.scroll.get().min(maximum);
+        let focused_height = focused_height.max(1);
+        let focused_end = focused_start.saturating_add(focused_height);
+        let viewport_end = scroll.saturating_add(viewport_rows);
+        if focused_height > viewport_rows {
+            if focused_end <= scroll {
+                scroll = focused_end.saturating_sub(1);
+            } else if focused_start >= viewport_end {
+                scroll = focused_start;
+            }
+        } else if focused_start < scroll {
+            scroll = focused_start;
+        } else {
+            if focused_end > viewport_end {
+                scroll = focused_end.saturating_sub(viewport_rows);
+            }
+        }
+        scroll = scroll.min(maximum);
+        self.scroll.set(scroll);
+        scroll
     }
 
     pub fn scroll_down(&mut self, rows: usize) {
-        self.scroll = self.scroll.saturating_add(rows).min(self.scroll_limit());
+        self.scroll.set(self.scroll.get().saturating_add(rows));
     }
 
     pub fn scroll_up(&mut self, rows: usize) {
-        self.scroll = self.scroll.saturating_sub(rows);
-    }
-
-    fn scroll_limit(&self) -> usize {
-        self.document
-            .fields()
-            .iter()
-            .map(|field| field.value().len().saturating_add(1))
-            .sum()
+        self.scroll.set(self.scroll.get().saturating_sub(rows));
     }
 }
 
@@ -117,7 +148,7 @@ impl fmt::Debug for EntryViewer {
             .field("document", &self.document)
             .field("focused", &self.focused)
             .field("revealed", &self.revealed.map(|_| "[REDACTED]"))
-            .field("scroll", &self.scroll)
+            .field("scroll", &self.scroll.get())
             .finish()
     }
 }
@@ -201,4 +232,69 @@ mod tests {
         viewer.scroll_up(usize::MAX);
         assert_eq!(viewer.scroll(), 0);
     }
+
+    #[test]
+    fn focus_only_scrolls_when_it_crosses_a_viewport_edge() {
+        let mut viewer = EntryViewer::new(fixture_document("email/personal"));
+        assert_eq!(viewer.document().fields().len(), 3);
+
+        assert_eq!(viewer.ensure_focus_visible(0, 1, 3, 3), 0);
+        viewer.focus_next();
+        assert_eq!(viewer.ensure_focus_visible(1, 1, 3, 3), 0);
+        viewer.focus_next();
+        assert_eq!(viewer.ensure_focus_visible(2, 1, 3, 3), 0);
+        viewer.focus_next();
+        assert_eq!(viewer.ensure_focus_visible(0, 1, 3, 3), 0);
+
+        viewer.focus_previous();
+        assert_eq!(viewer.focused_index(), Some(2));
+        assert_eq!(viewer.ensure_focus_visible(2, 1, 3, 2), 1);
+        viewer.focus_previous();
+        assert_eq!(viewer.focused_index(), Some(1));
+        assert_eq!(viewer.ensure_focus_visible(1, 1, 3, 2), 1);
+        viewer.focus_previous();
+        assert_eq!(viewer.focused_index(), Some(0));
+        assert_eq!(viewer.ensure_focus_visible(0, 1, 3, 2), 0);
+    }
+
+    #[test]
+    fn viewport_resize_clamps_then_minimally_reveals_the_focus() {
+        let mut viewer = EntryViewer::new(fixture_document("email/personal"));
+        viewer.focus_next();
+        viewer.focus_next();
+        assert_eq!(viewer.ensure_focus_visible(2, 1, 3, 1), 2);
+        assert_eq!(viewer.ensure_focus_visible(2, 1, 3, 2), 1);
+        assert_eq!(viewer.ensure_focus_visible(2, 1, 3, 3), 0);
+        assert_eq!(viewer.ensure_focus_visible(2, 1, 3, 1), 2);
+
+        viewer.focus_previous();
+        assert_eq!(viewer.ensure_focus_visible(1, 1, 3, 1), 1);
+        viewer.focus_previous();
+        assert_eq!(viewer.ensure_focus_visible(0, 1, 3, 1), 0);
+    }
+
+    #[test]
+    fn wrapped_fields_use_rendered_row_ranges_for_minimal_scrolling() {
+        let mut viewer = EntryViewer::new(fixture_document("email/personal"));
+        viewer.focus_next();
+        viewer.focus_next();
+
+        assert_eq!(viewer.ensure_focus_visible(4, 2, 6, 4), 2);
+        viewer.focus_previous();
+        assert_eq!(viewer.ensure_focus_visible(2, 2, 6, 4), 2);
+        viewer.focus_previous();
+        assert_eq!(viewer.ensure_focus_visible(0, 2, 6, 4), 0);
+    }
+
+    #[test]
+    fn a_field_taller_than_the_viewport_allows_needed_manual_scrolling() {
+        let mut viewer = EntryViewer::new(fixture_document("email/personal"));
+        viewer.focus_next();
+
+        assert_eq!(viewer.ensure_focus_visible(1, 5, 7, 3), 0);
+        viewer.scroll_down(2);
+        assert_eq!(viewer.ensure_focus_visible(1, 5, 7, 3), 2);
+        viewer.scroll_down(usize::MAX);
+        assert_eq!(viewer.ensure_focus_visible(1, 5, 7, 3), 4);
+    }
 }