class CSVParser

# File app/lib/csv_parser.rb, line 21
def self.call(...) = new(...).call

private_class_method :new

Field =
  Struct.new("Field", :value, :column, :row, :header) do
    delegate :blank?, :present?, to: :value

    alias_method :to_s, :value

    def cell = "#{column}#{row}"

    def to_i
      Integer(value)
    rescue ArgumentError, TypeError
      nil
    end

    def to_date
      return nil if blank?

      parsed_values =
        DATE_FORMATS.lazy.filter_map do |format|
          date = Date.strptime(value, format)
          date.year >= 1000 ? date : nil
        rescue ArgumentError, TypeError
          nil
        end

      parsed_values.first
    end

    def to_postcode
      if present?
        postcode = UKPostcode.parse(value)
        postcode.to_s if PostcodeValidator.postcode_valid?(postcode)
      end
    end

    def to_time
      return nil if blank?

      parsed_values =
        TIME_FORMATS.lazy.filter_map do |format|
          # We change the date to 2000-01-01 as this is what Rails uses when
          #  it's reading from a `TIME` column.
          Time
            .zone
            .strptime(value, format)
            .change(year: 2000, month: 1, day: 1)
        rescue ArgumentError, TypeError
          nil
        end

      parsed_values.first
    end
  end

private

attr_reader :data

ALPHABET = ("A".."Z").to_a.freeze
COLUMNS = ALPHABET + ALPHABET.product(ALPHABET).map { _1 + _2 }

DATE_FORMATS = %w[%Y%m%d %Y-%m-%d %d/%m/%Y].freeze
TIME_FORMATS = %w[%H:%M:%S %H:%M %H%M%S %H%M %H].freeze

def unconverted_headers
  @unconverted_headers ||=
    CSV.parse_line(data.lines.first, encoding:, strip: true)
end

def encoding
  "#{detect_encoding}:UTF-8" if detect_encoding
end

def detect_encoding
  @detect_encoding ||=
    begin
      return nil if data.blank?

      encoding = CharlockHolmes::EncodingDetector.detect(data)
      return nil if encoding.nil?

      encoding[:ruby_encoding]
    end
end

def converters
  proc do |value, info|
    column = COLUMNS[info.index]
    row = info.line
    header = unconverted_headers[info.index]

    Field.new(value&.normalise_whitespace, column, row, header)
  end
end

def header_converters
  proc do |value|
    value.downcase.normalise_whitespace.tr("-", "_").tr(" ", "_").to_sym
  end
end

# File app/lib/csv_parser.rb, line 4
def initialize(data)
  @data = data
end

# File app/lib/csv_parser.rb, line 8
def call
  CSV.parse(
    data,
    converters:,
    empty_value: nil,
    encoding:,
    header_converters:,
    headers: true,
    skip_blanks: true,
    strip: true
  )
end