module MJ; module Tools

    module SubProcess

        module ClassMethods

            # Executes command
            #
            # Executes the given command and yields each line of output.
            # Returns +$?+ .
            def execute( command, wd = nil, env = nil )
                cwd ||= Dir.getwd
                $log.cmd( "(#{wd}) > #{command} 2>&1" )
                if !$noop
                    adjust_environment( wd, env ) {
                        IO.popen( "#{command} 2>&1" ) {
                            |f|
                            begin
                                while
                                    line = f.readline
                                    $log.cmdout( line.chomp )
                                    yield line if block_given?
                                end
                            rescue EOFError:
                                # Expected. Do nothing
                            end
                        }
                        $log.cmdout( "= #{$?}" )
                        return $?
                    }
                else
                    $log.cmdout( "= 0 # noop" )
                    return 0
                end

            end

        #########
        protected
        #########

            # Helper method to adjust LANG to "C"
            def adjust_environment( wd=nil, env=nil, lang="C" )
                if wd
                    cwd = Dir.getwd
                    Dir.chdir(wd)
                end
                # Set the environment the user wants
                oldenv = Hash.new
                if env
                    env.each do |var, value|
                        oldenv[var] = ENV[var]
                        $log.debug "#{var} = #{value}"
                        ENV[var] = value
                    end
                end
                # Save old LANG setting and switch to 'C'
                oldlang = ENV['LANG']
                ENV['LANG'] = lang
                yield
                # Reset the old LANG setting
                ENV['LANG'] = oldlang
                # Reset our changes to ENV
                oldenv.each do |var, value|
                    ENV[var] = value
                end
                # Reset the current working directory
                if wd
                    Dir.chdir(cwd)
                end
            end
        end

        def self.included( klass )
            klass.extend( ClassMethods )
        end


    end


end; end