align2.rb

#!/usr/bin/ruby
#
# Assignment block tidier, version 0.1.
#
# Copyright Chris Poirier 2006.
# Licensed under the Academic Free License version 3.0.
#
# This script can be used as a command for TextMate to align all 
# of the equal signs within a block of text.  When using it with
# TextMate, set the command input to "Selected Text" or "Document",
# and the output to "Replace Selected Text".  Map it to a key 
# equivalent, and any time you want to tidy up a block, either 
# select it, or put your cursor somewhere within it; then hit the
# key equivalent.  Voila.
#
# Note that this is the first version of the script, and it hasn't
# been heavily tested.  You might encounter a bug or two. 
#
# Per the license, use of this script is ENTIRELY at your own risk.
# See the license for full details (they override anything I've 
# said here).

lines = STDIN.readlines()
selected_text = true

relevant_line_pattern = /^[^=]+[^-+<>=!%\/|&*^]=(?!=|~)/
column_search_pattern = /[\t ]*=/


#
# If called on a selection, every assignment statement
# is in the block.  If called on the document, we start on the 
# current line and look up and down for the start and end of the
# block.

if selected_text then
   block_top    = 1
   block_bottom = lines.length
else
 
   #
   # We start looking on the current line.  However, if the
   # current line doesn't match the pattern, we may be just
   # after or just before a block, and we should check.  If
   # neither, we are done.

   start_on      = 1
   block_top     = lines.length + 1
   block_bottom  = 0
   search_top    = 1
   search_bottom = lines.length
   search_failed = false

   if lines[start_on - 1] !~ relevant_line_pattern then
      if lines[start_on - 2] =~ relevant_line_pattern then
         search_bottom = start_on = start_on - 1
      elsif lines[start_on] =~ relevant_line_pattern then
         search_top = start_on = start_on
      else
         search_failed = true
      end 
   end

   #
   # Now with the search boundaries set, start looking for
   # the block top and bottom.
   
   unless search_failed
      start_on.downto(search_top) do |number|
         if lines[number-1] =~ relevant_line_pattern then
            block_top = number
         else
            break
         end
      end
      
      start_on.upto(search_bottom) do |number|
         if lines[number-1] =~ relevant_line_pattern then
            block_bottom = number
         else
            break
         end
      end
   end
end


#
# Now, iterate over the block and find the best column number
# for the = sign.  The pattern will tell us the position of the
# first bit of whitespace before the equal sign.  We put the
# equals sign to the right of the furthest-right one.  Note that
# we cannot assume every line in the block is relevant.

best_column = 0
block_top.upto(block_bottom) do |number|
   line = lines[number - 1]
   if line =~ relevant_line_pattern then
      m = column_search_pattern.match(line)
      best_column = m.begin(0) if m.begin(0) > best_column
   end
end

   
#
# Reformat the block.  Again, we cannot assume all lines in the 
# block are relevant.

block_top.upto(block_bottom) do |number|
   if lines[number-1] =~ relevant_line_pattern then
      before, after = lines[number-1].split(/[\t ]*=[\t ]*/, 2)
      lines[number-1] = [before.ljust(best_column), after].join(after[0,1] == '>' ? " =" : " = ")
   end
end


#
# Output the replacement text

lines.each do |line|
   puts line
end