Add g:fzf_grep_preview_window for enabling Ag/grep preview

Close #225

README.md

@@ -150,6 +150,11 @@ let g:fzf_tags_command = 'ctags -R'
 
 " [Commands] --expect expression for directly executing the command
 let g:fzf_commands_expect = 'alt-enter,ctrl-x'
+
+" [Ag / fzf#vim#grep] Command to preview the content
+"   - Requires Ruby
+"   - Install Highlight or CodeRay for syntax highlighting
+let g:fzf_grep_preview_window = 'right:50%'
 ```
 
 #### Advanced customization using autoload functions

autoload/fzf/vim.vim

@@ -29,6 +29,7 @@ set cpo&vim
 " ------------------------------------------------------------------
 
 let s:layout_keys = ['window', 'up', 'down', 'left', 'right']
+let s:bin = { 'preview': expand('<sfile>:h:h:h').'/bin/preview.rb' }
 let s:TYPE = {'dict': type({}), 'funcref': type(function('call')), 'string': type('')}
 
 function s:remove_layout(opts)
@@ -587,12 +588,18 @@ function! fzf#vim#grep(grep_command, with_column, ...)
   let name    = join(words, '-')
   let capname = join(map(words, 'toupper(v:val[0]).v:val[1:]'), '')
   let textcol = a:with_column ? '4..' : '3..'
+  let preview = ''
+  if executable('ruby') && exists('g:fzf_grep_preview_window')
+    let preview = printf(' --preview-window %s --preview "%s"\ {1}\ {2}\ %d',
+          \ g:fzf_grep_preview_window,
+          \ shellescape(s:bin.preview), g:fzf_grep_preview_window =~ 'up\|down')
+  endif
   let opts = {
   \ 'source':  a:grep_command,
   \ 'column':  a:with_column,
   \ 'options': '--ansi --delimiter : --nth '.textcol.',.. --prompt "'.capname.'> " '.
   \            '--multi --bind alt-a:select-all,alt-d:deselect-all '.
-  \            '--color hl:68,hl+:110'
+  \            '--color hl:68,hl+:110'.preview
   \}
   function! opts.sink(lines)
     return s:ag_handler(a:lines, self.column)

bin/preview.rb

@@ -0,0 +1,26 @@
+#!/usr/bin/env ruby
+#
+# usage: ./preview.rb FILENAME LINENO VSPLIT(0|1)
+
+require 'shellwords'
+
+COMMAND = %[(highlight -O ansi -l {} || coderay {} || cat {}) 2> /dev/null]
+ANSI    = /\x1b\[[0-9;]*m/
+REVERSE = "\x1b[7m"
+RESET   = "\x1b[m"
+
+file, center, split = ARGV.fetch(0), ARGV.fetch(1).to_i, ARGV.fetch(2) == '1'
+height = File.readable?('/dev/tty') ? `stty size < /dev/tty`.split.first.to_i : 40
+height /= 2 if split
+height -= 2 # preview border
+offset = [1, center - height / 3].max
+
+IO.popen(['sh', '-c', COMMAND.gsub('{}', Shellwords.shellescape(file))]) do |io|
+  io.each_line.drop(offset - 1).take(height).each_with_index do |line, lno|
+    if lno + offset == center
+      puts REVERSE + line.chomp.gsub(ANSI) { |m| m + REVERSE } + RESET
+    else
+      puts line
+    end
+  end
+end