module Eco
  class CSV
    class Split
      include Eco::Language::AuxiliarLogger

      attr_reader :filename

      def initialize(filename, max_rows:, start_at: nil, **kargs)
        msg = "File '#{filename}' does not exist"
        raise ArgumentError, msg unless ::File.exist?(filename)

        @filename = filename
        @max_rows = max_rows
        @start_at = start_at
        @params   = kargs
        init
      end

      # @yield [idx, file] a block to spot the filename
      # @yieldparam idx [Integer] the number of the file
      # @yieldparam file [String] the default name of the file
      # @yieldreturn [String] the filename of the file `idx`.
      #   - If `nil` it will create its own filename convention
      # @return [Array<String>] names of the generated files
      def call(&block)
        stream.for_each(start_at_idx: start_at) do |row, ridx|
          copy_row(row, ridx, &block)
        end
        out_files
      ensure
        puts "Close at row #{row_idx}"
        @csv&.close
      end

      private

      attr_reader :params
      attr_reader :idx, :max_rows, :start_at
      attr_reader :headers, :row_idx

      attr_accessor :exception

      def copy_row(row, ridx, &block)
        @headers ||= row.headers
        @row_idx   = ridx

        current_csv(ridx) do |csv, fidx, file_out|
          included   = true
          included &&= !block || yield(row, ridx, fidx, file_out)
          next unless included

          csv << row.fields
        end
      end

      def current_csv(ridx)
        if split?(ridx) || @csv.nil?
          puts "Split at row #{row_idx}"
          @csv&.close

          out_filename = generate_name(next_idx)
          @csv         = ::CSV.open(out_filename, "w")
          @csv        << headers
          out_files   << out_filename
        end

        yield(@csv, idx, out_files.last) if block_given?

        @csv
      end

      def split?(ridx)
        ((ridx + 1) % max_rows).zero?
      end

      def next_idx
        idx.tap { @idx += 1 }
      end

      def init
        @idx ||= 0 # rubocop:disable Naming/MemoizedInstanceVariableName
      end

      def stream
        @stream ||= Eco::CSV::Stream.new(filename, **params)
      end

      def generate_name(fidx)
        File.join(input_dir, "#{input_name}_#{file_number(fidx)}#{input_ext}")
      end

      def file_number(num)
        "#{zeroed}#{num}"[-5..]
      end

      def zeroed
        "0" * 5
      end

      def out_files
        @out_files ||= []
      end

      def input_name
        @input_name ||= File.basename(input_basename, input_ext)
      end

      def input_ext
        @input_ext ||= input_basename.split('.')[1..].join('.').then do |name|
          ".#{name}"
        end
      end

      def input_basename
        @input_basename ||= File.basename(input_full_filename)
      end

      def input_dir
        @input_dir = File.dirname(input_full_filename)
      end

      def input_full_filename
        @input_full_filename ||= File.expand_path(filename)
      end
    end
  end
end