From bbe4e21f52ea47057ee11991c4ad9fedb48c5520 Mon Sep 17 00:00:00 2001
From: Adam Harrison <adamdharrison@gmail.com>
Date: Sun, 29 Aug 2021 17:54:57 -0400
Subject: [PATCH] Fixed cursors moving around with removal and inserts with
 cursors. Also fixed drawing line highlights with multicursors.

---
 data/core/doc/init.lua | 19 +++++++++++++++++++
 data/core/docview.lua  | 10 +++++++---
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/data/core/doc/init.lua b/data/core/doc/init.lua
index d05d9d45..2165ed83 100644
--- a/data/core/doc/init.lua
+++ b/data/core/doc/init.lua
@@ -309,6 +309,7 @@ end
 function Doc:raw_insert(line, col, text, undo_stack, time)
   -- split text into lines and merge with line at insertion point
   local lines = split_lines(text)
+  local len = #lines[#lines]
   local before = self.lines[line]:sub(1, col - 1)
   local after = self.lines[line]:sub(col)
   for i = 1, #lines - 1 do
@@ -325,6 +326,15 @@ function Doc:raw_insert(line, col, text, undo_stack, time)
   push_undo(undo_stack, time, "selection", unpack(self.selections))
   push_undo(undo_stack, time, "remove", line, col, line2, col2)
 
+  -- keep cursors where they should be
+  for idx, cline1, ccol1, cline2, ccol2 in self:get_selections(true) do
+    if cline1 >= line then 
+      local line_addition = line > cline1 or ccol1 > col and #lines - 1 or 0
+      local column_addition = line == cline1 and ccol1 > col and len or 0
+      self:set_selections(idx, cline1 + line_addition, ccol1 + column_addition, cline2 + line_addition, ccol2 + column_addition)
+    end
+  end
+
   -- update highlighter and assure selection is in bounds
   self.highlighter:invalidate(line)
   self:sanitize_selection()
@@ -343,6 +353,15 @@ function Doc:raw_remove(line1, col1, line2, col2, undo_stack, time)
 
   -- splice line into line array
   common.splice(self.lines, line1, line2 - line1 + 1, { before .. after })
+  
+  -- move all cursors back if they share a line with the removed text
+  for idx, cline1, ccol1, cline2, ccol2 in self:get_selections(true) do
+    if cline1 >= line2 then
+      local line_removal = line2 - line1
+      local column_removal = line2 == cline2 and col2 < ccol1 and (line2 == line1 and col2 - col1 or col2) or 0
+      self:set_selections(idx, cline1 - line_removal, ccol1 - column_removal, cline2 - line_removal, ccol2 - column_removal)
+    end
+  end
 
   -- update highlighter and assure selection is in bounds
   self.highlighter:invalidate(line1)
diff --git a/data/core/docview.lua b/data/core/docview.lua
index 89da8190..54eec575 100644
--- a/data/core/docview.lua
+++ b/data/core/docview.lua
@@ -366,16 +366,20 @@ function DocView:draw_line_body(idx, x, y)
       local x1 = x + self:get_col_x_offset(idx, col1)
       local x2 = x + self:get_col_x_offset(idx, col2)
       local lh = self:get_line_height()
-      renderer.draw_rect(x1, y, x2 - x1, lh, style.selection)
+      if x1 ~= x2 then
+        renderer.draw_rect(x1, y, x2 - x1, lh, style.selection)
+      end
     end
   end
+  local draw_highlight = nil
   for lidx, line1, col1, line2, col2 in self.doc:get_selections(true) do
     -- draw line highlight if caret is on this line
-    if config.highlight_current_line and (line1 == line2 and col1 == col2)
+    if draw_highlight ~= false and config.highlight_current_line
     and line1 == idx and core.active_view == self then
-      self:draw_line_highlight(x + self.scroll.x, y)
+      draw_highlight = (line1 == line2 and col1 == col2)
     end
   end
+  if draw_highlight then self:draw_line_highlight(x + self.scroll.x, y) end
 
   -- draw line's text
   self:draw_line_text(idx, x, y)