Add fzf#vim#with_preview function for previewing search result

Close #225

README.md

@@ -152,18 +152,40 @@ let g:fzf_tags_command = 'ctags -R'
 let g:fzf_commands_expect = 'alt-enter,ctrl-x'
 ```
 
-#### Advanced customization using autoload functions
+#### Advanced customization
 
 You can use autoload functions to define your own commands.
 
 ```vim
-" git grep
+" Command for git grep
+" - fzf#vim#grep(command, with_column, [options], [fullscreen])
 command! -bang -nargs=* GGrep
   \ call fzf#vim#grep('git grep --line-number '.shellescape(<q-args>), 0, <bang>0)
 
 " We use VimEnter event so that the code is run after fzf.vim is loaded
-autocmd VimEnter * command! Colors
-  \ call fzf#vim#colors({'left': '15%', 'options': '--reverse --margin 30%,0'})
+autocmd VimEnter * command! -bang Colors
+  \ call fzf#vim#colors({'left': '15%', 'options': '--reverse --margin 30%,0'}, <bang>0)
+
+" Augmenting Ag command using fzf#vim#with_preview function
+"   * fzf#vim#with_preview([[options], preview window, [toggle keys...]])
+"   * Preview script requires Ruby
+"   * Install Highlight or CodeRay to enable syntax highlighting
+"
+"   :Ag  - Start fzf with hidden preview window that can be enabled with "?" key
+"   :Ag! - Start fzf in fullscreen and display the preview window above
+autocmd VimEnter * command! -bang -nargs=* Ag
+  \ call fzf#vim#ag(<q-args>,
+  \                 <bang>0 ? fzf#vim#with_preview('up:60%')
+  \                         : fzf#vim#with_preview('right:50%:hidden', '?'),
+  \                 <bang>0)
+
+" Similarly, we can apply it to fzf#vim#grep. To use ripgrep instead of ag:
+command! -bang -nargs=* Rg
+  \ call fzf#vim#grep(
+  \   'rg --column --line-number --no-heading --color=always '.shellescape(<q-args>), 1,
+  \   <bang>0 ? fzf#vim#with_preview('up:60%')
+  \           : fzf#vim#with_preview('right:50%:hidden', '?'),
+  \   <bang>0)
 ```
 
 Mappings

autoload/fzf/vim.vim

@@ -29,9 +29,47 @@ 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)
+" [[options to wrap], preview window expression, [toggle-preview keys...]]
+function! fzf#vim#with_preview(...)
+  " Default options
+  let options = {}
+  let window = 'right'
+
+  let args = copy(a:000)
+
+  " Options to wrap
+  if len(args) && type(args[0]) == s:TYPE.dict
+    let options = copy(args[0])
+    call remove(args, 0)
+  endif
+
+  " Preview window
+  if len(args) && type(args[0]) == s:TYPE.string
+    if args[0] !~# '^\(up\|down\|left\|right\)'
+      throw 'invalid preview window: '.args[0]
+    endif
+    let window = args[0]
+    call remove(args, 0)
+  endif
+
+  if !executable('ruby')
+    return options
+  endif
+
+  let preview = printf(' --preview-window %s --preview "%s"\ %s\ {}',
+        \ window,
+        \ shellescape(s:bin.preview), window =~ 'up\|down' ? '-v' : '')
+  if len(args)
+    let preview .= ' --bind '.join(map(args, 'v:val.":toggle-preview"'), ',')
+  endif
+  let options.options = get(options, 'options', '').preview
+  return options
+endfunction
+
+function! s:remove_layout(opts)
   for key in s:layout_keys
     if has_key(a:opts, key)
       call remove(a:opts, key)

bin/preview.rb

@@ -0,0 +1,40 @@
+#!/usr/bin/env ruby
+#
+# usage: ./preview.rb [-v] FILENAME[:LINE][:IGNORED]
+
+require 'shellwords'
+
+COMMAND = %[(highlight -O ansi -l {} || coderay {} || cat {}) 2> /dev/null]
+ANSI    = /\x1b\[[0-9;]*m/
+REVERSE = "\x1b[7m"
+RESET   = "\x1b[m"
+
+split = ARGV.delete('-v')
+
+if ARGV.empty?
+  puts "usage: #$0 [-v] FILENAME[:LINENO][:IGNORED]"
+  exit 1
+end
+
+file, center = ARGV.first.split(':')
+
+unless File.readable? file
+  puts "File not found: #{file}"
+  exit 1
+end
+
+center = (center || 0).to_i
+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