jsmin.rb

#--
# jsmin.rb - Ruby implementation of Douglas Crockford's JSMin.
#
# This is a port of jsmin.c, and is distributed under the same terms, which are
# as follows:
#
# Copyright (c) 2002 Douglas Crockford  (www.crockford.com)
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
# 
# The Software shall be used for Good, not Evil.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
#++

require 'strscan'

# = JSMin
#
# Ruby implementation of Douglas Crockford's JavaScript minifier, JSMin.
#
# Author::    Ryan Grove (mailto:ryan@wonko.com)
# Version::   1.0.0 (2008-03-22)
# Copyright:: Copyright (c) 2008 Ryan Grove. All rights reserved.
# Website::   http://github.com/rgrove/jsmin/
#
# == Example
#
#   require 'rubygems'
#   require 'jsmin'
#
#   File.open('example.js', 'r') {|file| puts JSMin.minify(file) }
#
module JSMin
  ORD_LF    = "\n"[0].freeze
  ORD_SPACE = ' '[0].freeze
  
  class << self
    
    # Reads JavaScript from +input+ (which can be a String or an IO object) and
    # returns a String containing minified JS.
    def minify(input)
      @js = StringScanner.new(input.is_a?(IO) ? input.read : input.to_s)

      @a         = "\n"
      @b         = nil
      @lookahead = nil
      @output    = ''
      
      action_get
      
      while !@a.nil? do
        case @a
        when ' '
          if alphanum?(@b)
            action_output
          else
            action_copy
          end
          
        when "\n"
          if @b == ' '
            action_get
          elsif @b =~ /[{\[\(+-]/
            action_output
          else
            if alphanum?(@b)
              action_output
            else
              action_copy
            end
          end
          
        else
          if @b == ' '
            if alphanum?(@a)
              action_output
            else
              action_get
            end
          elsif @b == "\n"
            if @a =~ /[}\]\)\\"+-]/
              action_output
            else
              if alphanum?(@a)
                action_output
              else
                action_get
              end
            end
          else
            action_output
          end
        end
      end
      
      @output
    end
    
    private
    
    # Corresponds to action(1) in jsmin.c.
    def action_output
      @output << @a
      action_copy
    end
    
    # Corresponds to action(2) in jsmin.c.
    def action_copy
      @a = @b
      
      if @a == '\'' || @a == '"'
        loop do
          @output << @a
          @a = get
          
          break if @a == @b
          
          if @a[0] <= ORD_LF
            raise "JSMin parse error: unterminated string literal: #{@a}"
          end
          
          if @a == '\\'
            @output << @a
            @a = get
            
            if @a[0] <= ORD_LF
              raise "JSMin parse error: unterminated string literal: #{@a}"
            end
          end
        end
      end
      
      action_get
    end
    
    # Corresponds to action(3) in jsmin.c.
    def action_get
      @b = nextchar
      
      if @b == '/' && (@a == "\n" || @a =~ /[\(,=:\[!&|?{};]/)
        @output << @a
        @output << @b
        
        loop do
          @a = get
          
          if @a == '/'
            break
          elsif @a == '\\'
            @output << @a
            @a = get
          elsif @a[0] <= ORD_LF
            raise "JSMin parse error: unterminated regular expression " +
                "literal: #{@a}"
          end
          
          @output << @a
        end
        
        @b = nextchar
      end
    end
    
    # Returns true if +c+ is a letter, digit, underscore, dollar sign,
    # backslash, or non-ASCII character.
    def alphanum?(c)
      c.is_a?(String) && !c.empty? && (c[0] > 126 || c =~ /[0-9a-z_$\\]/i)
    end
    
    # Returns the next character from the input. If the character is a control
    # character, it will be translated to a space or linefeed.
    def get
      c = @lookahead.nil? ? @js.getch : @lookahead
      @lookahead = nil

      return c if c.nil? || c == "\n" || c[0] >= ORD_SPACE
      return "\n" if c == "\r"
      return ' '
    end
    
    # Gets the next character, excluding comments.
    def nextchar
      c = get
      return c unless c == '/'
      
      case peek
      when '/'
        loop do
          c = get
          return c if c[0] <= ORD_LF
        end
      
      when '*'
        get
        loop do
          case get
          when '*'
            if peek == '/'
              get
              return ' '
            end
          
          when nil
            raise 'JSMin parse error: unterminated comment'
          end
        end
      
      else
        return c
      end
    end
    
    # Gets the next character without getting it.
    def peek
      @lookahead = get
    end
  end
end