fix insertText completion when issued with the cursor on a newline

New algorithm:
	1. check if the cursor is on a word which is a prefix of the completion
	2. if not try to decrement the position because it is common than the
	   cursor is behind the token to complete "fooba┃"
	3. if found a match in 1. or 2. delete it
	4. insert the new text at the current pos or the start of the deleted token

Hopefully this is good enough to work in all possible corner cases

1 files changed, 36 insertions, 14 deletions

diff --git a/init.lua b/init.lua
index 89034c2..1a36fa8 100644
--- a/init.lua
+++ b/init.lua
@@ -412,8 +412,6 @@ local function lspc_handle_completion_method_response(win, result, old_pos)
   end
 
   if completion.insertText then
-    lspc.log(string.format('Completion old_pos=%d', old_pos))
-
     -- Does our current state correspont to the state when the completion method
     -- was called.
     -- Otherwise we don't have a good way to apply the 'insertText' completion
@@ -422,25 +420,49 @@ local function lspc_handle_completion_method_response(win, result, old_pos)
     end
 
     local new_word = completion.insertText
-
     local old_word_range = win.file:text_object_word(old_pos)
     local old_word = win.file:content(old_word_range)
 
-    -- our curser is behind the token to complete
-    if old_word_range.finish - old_word_range.start == 1 then
-      if not new_word:sub(string.len(old_word)) ~= old_word then
-        lspc.log('Have to adjust the cursor position')
-      end
+    lspc.log(string.format(
+                 'Completion old_pos=%d, old_range={start=%d, finish=%d}, old_word=%s',
+                 old_pos, old_word_range.start, old_word_range.finish,
+                 old_word:gsub('\n', '\\n')))
+
+    -- update old_word_range and old_word and return if old_word is a prefix of the completion
+    local function does_completion_apply_to_pos(pos)
+      old_word_range = win.file:text_object_word(pos)
+      old_word = win.file:content(old_word_range)
+
+      local is_prefix = new_word:sub(1, string.len(old_word)) == old_word
+      return is_prefix
+    end
+
+    -- search for a possible completion token which we should replace with this insertText
+    local matches = does_completion_apply_to_pos(old_pos)
+    if not matches then
+      lspc.log('Cursor looks like its not on the completion token')
 
-      old_pos = old_pos - 1
-      old_word_range = win.file:text_object_word(old_pos)
+      -- try the common case the cursor is behind its completion token: fooba┃
+      local next_pos_candidate = old_pos - 1
+      matches = does_completion_apply_to_pos(next_pos_candidate)
+      if matches then
+        old_pos = next_pos_candidate
+      end
     end
 
+    local completion_start
+    -- we found a completion token -> replace it
+    if matches then
+      lspc.log('replace the token: ' .. old_word ..
+                   '  we found being a prefix of the completion')
+      win.file:delete(old_word_range)
+      completion_start = old_word_range.start
+    else
+      completion_start = old_pos
+    end
     -- apply insertText
-    win.file:delete(old_word_range)
-    local completion_start = old_word_range.start
-    win.file:insert(completion_start, completion.insertText)
-    win.selection.pos = completion_start + string.len(completion.insertText)
+    win.file:insert(completion_start, new_word)
+    win.selection.pos = completion_start + string.len(new_word)
     win:draw()
     return
   end