refactor: improve codeium#Accept function and related mappings

Author: chenxuan520

autoload/codeium.vim

@@ -87,9 +87,22 @@ function! s:CompletionInserter(current_completion, insert_text) abort
   return delete_range . insert_text . cursor_text
 endfunction
 
-function! codeium#Accept() abort
+function! codeium#Accept(...) abort
   let current_completion = s:GetCurrentCompletionItem()
-  return s:CompletionInserter(current_completion, current_completion is v:null ? '' : current_completion.completion.text)
+  if current_completion is v:null
+    let default =  pumvisible() ? "\<C-N>" : "\t"
+    if a:0 > 0 && type(a:1) == v:t_func
+      try
+        return call(a:1, [])
+      catch
+        return default
+      endtry
+    else
+      return default
+    endif
+  else
+    return s:CompletionInserter(current_completion, current_completion is v:null ? '' : current_completion.completion.text)
+  endif
 endfunction
 
 function! codeium#AcceptNextWord() abort

autoload/codeium/server.vim

@@ -260,7 +260,7 @@ function! s:UnzipAndStart(status) abort
     call system('chmod +x ' . s:bin)
   endif
   if !filereadable(s:bin)
-    call codeium#log#Error('Failed to download language server binary.')
+    call codeium#log#Error('Failed to download language server binary. In '.s:bin)
     return ''
   endif
   call s:ActuallyStart()

plugin/codeium.vim

@@ -20,7 +20,22 @@ endfunction
 
 function! s:MapTab() abort
   if !get(g:, 'codeium_no_map_tab', v:false) && !get(g:, 'codeium_disable_bindings')
-    imap <script><silent><nowait><expr> <Tab> codeium#Accept()
+    let tab_map = maparg('<Tab>', 'i', 0, 1)
+    if !has_key(tab_map, 'rhs')
+      imap <script><silent><nowait><expr> <Tab> codeium#Accept()
+    elseif tab_map.rhs !~# 'codeium'
+      if tab_map.expr
+        let tab_fallback = '{ -> ' . tab_map.rhs . ' }'
+      else
+        let tab_fallback = substitute(json_encode(tab_map.rhs), '<', '\\<', 'g')
+      endif
+      let tab_fallback = substitute(tab_fallback, '<SID>', '<SNR>' . get(tab_map, 'sid') . '_', 'g')
+      if get(tab_map, 'noremap') || get(tab_map, 'script') || mapcheck('<Left>', 'i') || mapcheck('<Del>', 'i')
+        exe 'imap <script><silent><nowait><expr> <Tab> codeium#Accept(' . tab_fallback . ')'
+      else
+        exe 'imap <silent><nowait><expr>         <Tab> codeium#Accept(' . tab_fallback . ')'
+      endif
+    endif
   endif
 endfunction
 
@@ -66,6 +81,7 @@ if !get(g:, 'codeium_disable_bindings')
   endif
 endif
 
+call s:MapTab()
 call s:SetStyle()
 
 let s:dir = expand('<sfile>:h:h')