module CommitMsgUrlShortener
  class HookScript
    attr_reader :name

    def initialize git_path
      @name = 'commit-msg'
      @hook_path = File.expand_path File.join(git_path, ".git/hooks/#{@name}")
    end

    def append_code code
      remove_code
      open('a+b') {|file| file.puts "#{code}"}
    end

    def interpreter
      @interpreter ||= begin
        return unless exist?
        interpreter  = nil
        open('rb') do |file|
          shebang_line = ''
          file.each_line{|line| shebang_line = line if line.index '#!'}
          INTERPRETERS.each{|name| interpreter = name if shebang_line.downcase.index name}
        end
        interpreter
      end
    end
    
    def remove_code
      new_lines = []
      removed_lines = []
      return removed_lines unless exist?
      open('rb') do |file|
        file.each_line do |line| 
          unless line.downcase.index BIN_NAME.downcase
            new_lines << line
          else
            removed_lines << line
          end
        end
      end
      open('wb') do |file|
        new_lines.each{|line| file.puts line}
      end
      removed_lines
    end

    def get_used_service
      lines_call_the_gem = []
      service = nil
      return service unless exist?
      open('rb') do |file|
        file.each_line {|line| lines_call_the_gem << line if line.downcase.index(BIN_NAME.downcase)}
        if lines_call_the_gem.size > 1
          raise "It appears that there are multiple calls to #{BIN_NAME} in your #{name} hook."
        end
        unless lines_call_the_gem.empty?
          service = SERVICES.select{|s| lines_call_the_gem.first.include? s.name}.first
          raise "It appears that your are using an unknow service." unless service
        end
      end
      service
    end

    def exist?
      File.exist? @hook_path
    end

    def create
      open('wb') {|file| file.puts "#!/bin/sh"}
      @interpreter = 'sh'
      make_executable
    end

    private

    def make_executable
      command = 'chmod ug+x "'+@hook_path+'" >/dev/null 2>&1'
      system_result = system(command) rescue false
      raise "I was unable to make the file #{@hook_path} executable." unless system_result
    end

    def open mode, &block
      File.send :open, @hook_path, mode, &block
    end
  end
end