Flexible Rake task

I would like to use the following Rake task for multiple directories. And each directory would need slightly different constants defined. How can I handle this and stay DRY?

namespace :assets do
  EXT     = 'js'
  OBJDIR  = 'public/javascripts'
  LIBFILE = "#{OBJDIR}/packaged.#{EXT}"
  SRC     = FileList["#{OBJDIR}/*.#{EXT}"].select {|file| !file.match(/\.min\.#{EXT}|packaged\.#{EXT}/)}
  OBJ     = SRC.collect {|fn| File.join(OBJDIR, File.basename(fn).ext("min.#{EXT}"))}
  MINE    = %w(4sq app fb mbp).collect {|x| x + ".#{EXT}"}

  desc "Build #{LIBFILE}"
  task :build => LIBFILE

  desc "Remove minified files"
  task :clean do
    rm_f OBJ
  end      

  desc "Remove #{LIBFILE}"
  task :clobber do
    rm_f LIBFILE
  end

  file LIBFILE => OBJ do
    sh "cat #{OBJ} >> #{LIBFILE}"
  end

  rule ".m开发者_开发问答in.#{EXT}" => lambda{ |objfile| find_source(objfile) } do |t|
    if EXT == 'js'
      if MINE.include?(File.basename(t.source))
        sh "closure --js #{t.source} --js_output_file #{t.name}"
      else
        sh "closure --warning_level QUIET --third_party --js #{t.source} --js_output_file #{t.name}"
      end
    elsif EXT == 'css'
      sh "yuicompressor #{t.source} -o #{t.name}"
    end
  end

  def find_source(objfile)
    base = File.basename(objfile, ".min.#{EXT}")
    SRC.find {|s| File.basename(s, ".#{EXT}") == base}
  end
end

First you must replace the constants by variables. The next problem is to set the variables. Task can get variables.

Example:

namespace :assets do |x1,x2|
  task :doit, :ext, :objdir do |tsk, args|
    puts tsk
    p args
  end
end

You can call it with:

  rake assets:doit[js,objdir]

Result:

assets:doit called with {:ext=>"js", :objdir=>"objdir"}

If you want to avoid to set the variables for each of your task, you may add a 'set' task:

namespace :assets2 do |x1,x2|
  task :set, :ext, :objdir do |tsk, args|
    @args = args
    puts "#{tsk} set: #{@args.inspect}"
  end
  task :doit do |tsk|
    puts "#{tsk} called with #{@args.inspect}"
  end
end

Call: rake assets2:set[js,objdir] assets2:doit

Result:

assets2:set set: {:ext=>"js", :objdir=>"objdir"}
assets2:doit called with {:ext=>"js", :objdir=>"objdir"}

Instead of setting all parameters, you may define a configuration file.

There is one disadvantage. The following task would not work:

rake assets:doit[js,objdir] assets:doit[c,objdir2]

assets:doit would be called once. the second call is ignored, the task is already executed. there is no check for different parameters (One solution for this: perhaps you could reset the task)

Edit: I found and tested a 'reset'-method: You just need to add tsk.reenable

namespace :assets do |x1,x2|
  task :doit, :ext, :objdir do |tsk, args|
    puts "#{tsk} called with #{args.inspect}"
    tsk.reenable
  end
end

Another problem: If your parameters contains spaces. you may get trouble.

============== Code for generic generation of rule: (see comments)

namespace :assets3 do |x1,x2|
  task :set, :ext, :objdir do |tsk, args|
    @args = args
    @src =   FileList["*.rb"]

    puts "#{tsk} set: #{@args.inspect}"

    #Define rule, when extension is set.
    rule ".min.#{@args[:ext]}" => lambda{ |objfile| find_source(objfile) } do |t|
      puts "#{t} called with #{@args.inspect}"
    end

  end

  task :doit do |tsk|
    puts "#{tsk} called with #{@args.inspect}"
  end

  def find_source(objfile)
    base = File.basename(objfile, ".min.#{@args[:ext]}")
    #If nothing is found, rake will abort with 'can't convert nil into String (TypeError)'
    #If I return '' in this case, I get 'Don't know how to build task 'test.min.js' (RuntimeError)'
    @src.find {|s| File.basename(s, ".#{@args[:ext]}") == base} || ''
  end

end

With your help I finally figured it out. Here's what's working for me so far:

namespace :assets do
  task :set, [:ext, :objdir] do |t, args|
    @ext    = args.ext
    @objdir = args.objdir
    @bundle = "#{@objdir}/bundle.#{@ext}"
    @src    = FileList["#{@objdir}/*.#{@ext}"].select {|file| !file.match(/\.min\.#{@ext}|#{Regexp.escape(@bundle)}/)}
    @min    = @src.collect {|fn| File.join(@objdir, File.basename(fn).ext("min.#{@ext}"))}

    Rake::Task.define_task 'assets:build' => @bundle

    Rake::FileTask.define_task @bundle =>  @min do
      sh "cat #{@min} > #{@bundle}"
    end

    Rake::Task.create_rule ".min.#{@ext}" => lambda{ |objfile| find_source(objfile) } do |t|
      if @ext == 'js'
        if @mine.include?(File.basename(t.source))
          sh "closure --js #{t.source} --js_output_file #{t.name}"
        else
          sh "closure --warning_level QUIET --third_party --js #{t.source} --js_output_file #{t.name}"
        end
      elsif @ext == 'css'
        sh "yuicompressor #{t.source} -o #{t.name}"
      end
    end
  end

  desc "Remove minified files"
  task :clean do
    rm_f @min
  end      

  desc "Remove bundle"
  task :clobber do
    rm_f @bundle
  end

  def find_source(objfile)
    base = File.basename(objfile, ".min.#{@ext}")
    @src.find {|s| File.basename(s, ".#{@ext}") == base}
  end
end