previewer: Add title_align option

change alignment of the preview title

default is left

README.md

@@ -370,6 +370,7 @@ require'fzf-lua'.setup {
       flip_columns   = 120,             -- #cols to switch to horizontal on flex
       -- Only used with the builtin previewer:
       title          = true,            -- preview border title (file/buf)?
+      title_align    = "left",         -- left|center|right, preview title alignment (file/buf)?
       scrollbar      = 'float',         -- `false` or string:'float|border'
                                         -- float:  in-window floating border
                                         -- border: in-border chars (see below)

lua/fzf-lua/config.lua

@@ -61,6 +61,7 @@ M.globals = {
       layout              = 'flex',
       flip_columns        = 120,
       title               = true,
+      title_align         = "left",
       scrollbar           = 'border',
       scrolloff           = '-2',
       scrollchar          = '',
@@ -838,6 +839,7 @@ function M.normalize_opts(opts, defaults)
     ['winopts.hl.cursorline']         = 'previewers.builtin.hl_cursorline',
     ['winopts.preview.delay']         = 'previewers.builtin.delay',
     ['winopts.preview.title']         = 'previewers.builtin.title',
+    ['winopts.preview.title_align']   = 'previewers.builtin.title_align',
     ['winopts.preview.scrollbar']     = 'previewers.builtin.scrollbar',
     ['winopts.preview.scrollchar']    = 'previewers.builtin.scrollchar',
     -- Diagnostics & LSP symbols separation options

lua/fzf-lua/previewer/builtin.lua

@@ -24,6 +24,7 @@ function Previewer.base:new(o, opts, fzf_win)
   self.win = fzf_win
   self.delay = self.win.winopts.preview.delay or 100
   self.title = self.win.winopts.preview.title
+  self.title_align = self.win.winopts.preview.title_align
   self.winopts = self.win.winopts.preview.winopts
   self.syntax = default(o.syntax, true)
   self.syntax_delay = default(o.syntax_delay, 0)

lua/fzf-lua/win.lua

@@ -884,7 +884,7 @@ end
 function FzfWin:set_title_hl()
   if self.winopts.__hl.title and self._title_len and self._title_len>0 then
     pcall(vim.api.nvim_win_call, self.border_winid, function()
-      fn.matchaddpos(self.winopts.__hl.title, {{1, 9, self._title_len+1}}, 11)
+      fn.matchaddpos(self.winopts.__hl.title, {{1, self._title_position, self._title_len+1}}, 11)
     end)
   end
 end
@@ -1056,10 +1056,19 @@ function FzfWin:update_title(title)
   end
   -- save for set_title_hl
   self._title_len = #title
+  local width_title = fn.strwidth(title)
   local prefix = fn.strcharpart(top, 0, 3)
-  local suffix = fn.strcharpart(top, fn.strwidth(title) + 3, fn.strwidth(top))
+  if self.winopts.preview.title_align == "center" then
+    prefix = fn.strcharpart(top, 0, utils.round((width - width_title)/2))
+  elseif self.winopts.preview.title_align == "right" then
+    prefix = fn.strcharpart(top, 0, width - (width_title + 3))
+  end
+
+  local suffix = fn.strcharpart(top, width_title + fn.strwidth(prefix), width)
   title = ('%s%s%s'):format(prefix, title, suffix)
   api.nvim_buf_set_lines(border_buf, 0, 1, 1, {title})
+  -- will be used later in set_title_hl()
+  self._title_position = #prefix
   self:set_title_hl()
 end