LibLine: Properly paginate suggestions in XtermSuggestionDisplay

This commit adds back suggestion pagination, and makes it 10x better.
Also adds a "< page m of n >" indicator at the bottom if there are more
suggestions than would fit in a page.
It properly handles cycling forwards and backwards :^)

4 files changed, 95 insertions, 4 deletions

diff --git a/Libraries/LibLine/Editor.cpp b/Libraries/LibLine/Editor.cpp
index db63696561..18d691eb44 100644
--- a/Libraries/LibLine/Editor.cpp
+++ b/Libraries/LibLine/Editor.cpp
@@ -566,6 +566,7 @@ String Editor::get_line(const String& prompt)
                     suggest(0, 0, Span::CodepointOriented);
                     m_times_tab_pressed = 0;
                     m_suggestion_manager.reset();
+                    m_suggestion_display->finish();
                 }
                 continue;
             }
@@ -582,6 +583,7 @@ String Editor::get_line(const String& prompt)
                 }
                 m_suggestion_manager.reset();
                 suggest(0, 0, Span::CodepointOriented);
+                m_suggestion_display->finish();
             }
             m_times_tab_pressed = 0; // Safe to say if we get here, the user didn't press TAB
 
diff --git a/Libraries/LibLine/SuggestionDisplay.h b/Libraries/LibLine/SuggestionDisplay.h
index 77393c0641..a6c56a6a76 100644
--- a/Libraries/LibLine/SuggestionDisplay.h
+++ b/Libraries/LibLine/SuggestionDisplay.h
@@ -39,6 +39,7 @@ public:
     virtual ~SuggestionDisplay() { }
     virtual void display(const SuggestionManager&) = 0;
     virtual bool cleanup() = 0;
+    virtual void finish() = 0;
     virtual void set_initial_prompt_lines(size_t) = 0;
 
     virtual void set_vt_size(size_t lines, size_t columns) = 0;
@@ -67,6 +68,10 @@ public:
     virtual ~XtermSuggestionDisplay() override { }
     virtual void display(const SuggestionManager&) override;
     virtual bool cleanup() override;
+    virtual void finish() override
+    {
+        m_pages.clear();
+    }
 
     virtual void set_initial_prompt_lines(size_t lines) override
     {
@@ -77,14 +82,22 @@ public:
     {
         m_num_lines = lines;
         m_num_columns = columns;
+        m_pages.clear();
     }
 
 private:
+    size_t fit_to_page_boundary(size_t selection_index);
     size_t m_lines_used_for_last_suggestions { 0 };
     size_t m_num_lines { 0 };
     size_t m_num_columns { 0 };
     size_t m_prompt_lines_at_suggestion_initiation { 0 };
     size_t m_prompt_length { 0 };
+
+    struct PageRange {
+        size_t start;
+        size_t end;
+    };
+    Vector<PageRange> m_pages;
 };
 
 }
diff --git a/Libraries/LibLine/SuggestionManager.h b/Libraries/LibLine/SuggestionManager.h
index 47821b6bb0..cdc201d90b 100644
--- a/Libraries/LibLine/SuggestionManager.h
+++ b/Libraries/LibLine/SuggestionManager.h
@@ -83,12 +83,13 @@ class SuggestionManager {
 
 public:
     void set_suggestions(Vector<CompletionSuggestion>&& suggestions);
-    void set_current_suggestion_initiation_index(size_t index);
+    void set_current_suggestion_initiation_index(size_t start_index);
 
     size_t count() const { return m_suggestions.size(); }
     size_t display_length() const { return m_last_shown_suggestion_display_length; }
-    size_t index() const { return m_last_displayed_suggestion_index; }
+    size_t start_index() const { return m_last_displayed_suggestion_index; }
     size_t next_index() const { return m_next_suggestion_index; }
+    void set_start_index(size_t index) const { m_last_displayed_suggestion_index = index; }
 
     size_t for_each_suggestion(Function<IterationDecision(const CompletionSuggestion&, size_t)>) const;
 
@@ -151,7 +152,7 @@ private:
     mutable size_t m_next_suggestion_invariant_offset { 0 };
     mutable size_t m_next_suggestion_static_offset { 0 };
     size_t m_largest_common_suggestion_prefix_length { 0 };
-    size_t m_last_displayed_suggestion_index { 0 };
+    mutable size_t m_last_displayed_suggestion_index { 0 };
     size_t m_selected_suggestion_index { 0 };
 };
 
diff --git a/Libraries/LibLine/XtermSuggestionDisplay.cpp b/Libraries/LibLine/XtermSuggestionDisplay.cpp
index 3cd02f6c85..b4e8527b09 100644
--- a/Libraries/LibLine/XtermSuggestionDisplay.cpp
+++ b/Libraries/LibLine/XtermSuggestionDisplay.cpp
@@ -24,7 +24,9 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/BinarySearch.h>
 #include <AK/Function.h>
+#include <AK/StringBuilder.h>
 #include <LibLine/SuggestionDisplay.h>
 #include <LibLine/VT.h>
 #include <stdio.h>
@@ -43,7 +45,7 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
     });
 
     size_t num_printed = 0;
-    size_t lines_used { 1 };
+    size_t lines_used = 1;
 
     VT::save_cursor();
     VT::clear_lines(0, m_lines_used_for_last_suggestions);
@@ -62,8 +64,45 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
         lines_used += max_line_count;
         longest_suggestion_length = 0;
     }
+
     VT::move_absolute(max_line_count + m_origin_x, 1);
 
+    if (m_pages.is_empty()) {
+        size_t num_printed = 0;
+        size_t lines_used = 1;
+        // cache the pages
+        manager.set_start_index(0);
+        size_t page_start = 0;
+        manager.for_each_suggestion([&](auto& suggestion, auto index) {
+            size_t next_column = num_printed + suggestion.text_view.length() + longest_suggestion_length + 2;
+            if (next_column > m_num_columns) {
+                auto lines = (suggestion.text_view.length() + m_num_columns - 1) / m_num_columns;
+                lines_used += lines;
+                num_printed = 0;
+            }
+
+            if (lines_used + m_prompt_lines_at_suggestion_initiation >= m_num_lines) {
+                m_pages.append({ page_start, index });
+                page_start = index;
+                lines_used = 1;
+                num_printed = 0;
+            }
+
+            if (spans_entire_line)
+                num_printed += m_num_columns;
+            else
+                num_printed += longest_suggestion_length + 2;
+
+            return IterationDecision::Continue;
+        });
+        // last page
+        m_pages.append({ page_start, manager.count() });
+    }
+
+    auto page_index = fit_to_page_boundary(manager.next_index());
+
+    manager.set_start_index(m_pages[page_index].start);
+
     manager.for_each_suggestion([&](auto& suggestion, auto index) {
         size_t next_column = num_printed + suggestion.text_view.length() + longest_suggestion_length + 2;
 
@@ -106,6 +145,23 @@ void XtermSuggestionDisplay::display(const SuggestionManager& manager)
     if (m_origin_x + lines_used >= m_num_lines) {
         m_origin_x = m_num_lines - lines_used;
     }
+
+    if (m_pages.size() > 1) {
+        auto left_arrow = page_index > 0 ? '<' : ' ';
+        auto right_arrow = page_index < m_pages.size() - 1 ? '>' : ' ';
+        auto string = String::format("%c page %d of %d %c", left_arrow, page_index + 1, m_pages.size(), right_arrow);
+
+        if (string.length() > m_num_columns - 1) {
+            // this would overflow into the next line, so just don't print an indicator
+            return;
+        }
+
+        VT::move_absolute(m_origin_x + lines_used, m_num_columns - string.length() - 1);
+        VT::apply_style({ Style::Background(Style::XtermColor::Green) });
+        fputs(string.characters(), stdout);
+        VT::apply_style(Style::reset_style());
+        fflush(stdout);
+    }
 }
 
 bool XtermSuggestionDisplay::cleanup()
@@ -119,4 +175,23 @@ bool XtermSuggestionDisplay::cleanup()
     return false;
 }
 
+size_t XtermSuggestionDisplay::fit_to_page_boundary(size_t selection_index)
+{
+    ASSERT(m_pages.size() > 0);
+    int index = 0;
+
+    auto* match = binary_search(
+        m_pages.data(), m_pages.size(), { selection_index, selection_index }, [](auto& a, auto& b) -> int {
+            if (a.start >= b.start && a.start < b.end)
+                return 0;
+            return a.start - b.start;
+        },
+        &index);
+
+    if (!match)
+        return m_pages.size() - 1;
+
+    return index;
+}
+
 }