#! /usr/bin/env ruby
# coding: utf-8

require "tempfile"

# Module that provide a framework for text filters.
#
# Provide basic functions for a command like below:
#   Input:
#     - Without indicating filenames like "command.rb",
#       input data is eaten from STDIN.
#     - With indicating filenames like "command.rb *.txt",
#       input data is eaten from indicated files in order.
#       When the file which is in the filenames does not exist,
#       output report to STDERR.
#
#   Output:
#     - Without indicating "--overwrite" option,
#       output to STDOUT even from many files.
#     - With indicating "--overwrite" option,
#       - With indicating input files,
#         overwrite each file.
#       - Without indicating input files,
#         output to STDOUT in one stream.
#
# If indicated file(s) not found,
# this program notify on stderr and does not throw an exception.
#
module TextFilter

	class NotRedefinedMethodError < Exception; end
	class TypeError < Exception; end

	# 保持している入力ファイル対して、順に処理を実行する。
	# filenames.size が 0 ならば STDIN からの入力を待つことになる。
	#
	# STDIN からの入力だった場合、出力先は必ず STDOUT になる。
	# STDIN からの入力ではない、すなわちファイル入力であった場合、
	#   - overwrite_flag が false ならば STDOUT に出力する。
	#   - overwrite_flag が true ならば 個々のファイルに上書きする。
	#
	# Process of each file is defined in 'process_stream' method.
	#
	def self.run(filenames, overwrite_flag = false)
		#p self; exit
		if filenames.size == 0 
			self.process_stream( $stdin, $stdout )
		else
			#p filenames
			filenames.each do |filename|
				if overwrite_flag
					tempfile = Tempfile.new("tefil", "/tmp")
					File.open(filename, "r") do |input_file|
						self.process_stream(input_file, tempfile)
					end
					tempfile.close
					tempfile.open
					File.open(filename, "w") do |output_file|
						tempfile.each { |line| output_file.puts(line) }
					end
				else
					File.open(filename, "r") do |input_file|
						self.process_stream(input_file, $stdout)
					end
				end
			end
		end
	end

	private

	# Process a file.
	# An argument 'in_io' indicates an io (file handle) for input.
	# Another argument 'out_io' indicates an io (file handle) for output.
	# This method must be redefined in a subclass or be overridden.
	# If not redefined, raise an exception TextFilter::NotRedefinedMethodError.
	def self.process_stream(in_io, out_io)
		raise NotRedefinedMethodError
	end

end