require 'spreadsheet'

module XlsExporter
  class Exporter
    def self.export(&block)
      exporter = new
      exporter.instance_exec(&block)
      exporter.save!
    end

    def initialize
      @book     = Spreadsheet::Workbook.new
    end

    def add_sheet(sheet_name = nil)
      save_sheet! if @sheet
      @headers = []
      @body    = []
      @sheet   = @book.create_worksheet

      @sheet.name = sheet_name
    end

    def filename(new_filename)
      @filename = new_filename
    end

    def headers(*args)
      @headers = args
    end

    def body(new_body)
      @body = new_body
    end

    def humanize_columns(columns)
      columns.map do |column|
        column = column.keys.first if column.is_a? Hash
        column.to_s.humanize
      end
    end

    def export_models(scope, *columns)
      headers(*humanize_columns(columns))
      to_body = scope.map do |instance|
        columns.map do |column|
          column = column.values.first if column.is_a? Hash
          if column.is_a? Proc
            instance.instance_exec(&column)
          elsif column.is_a? Symbol
            instance.send column
          end
        end
      end
      body to_body
    end

    def save_sheet!
      @sheet.row(0).concat(@headers)
      @body.each_with_index do |row, index|
        @sheet.row(index + 1).concat(row)
      end
    end

    def save!
      save_sheet!
      if @filename.present?
        filename = "./#{@filename}_#{Time.now.to_i}.xls"
        @book.write(filename)
        puts "Report has been saved as #{filename}"
      else
        @book
      end
    end
  end
end