able to return column for given field

app/services/bulk_upload/lettings/year2022/csv_parser.rb

@@ -39,8 +39,16 @@ class BulkUpload::Lettings::Year2022::CsvParser
     @rows ||= CSV.parse(normalised_string, row_sep:)
   end
 
+  def column_for_field(field)
+    cols[headers.find_index(field) + col_offset]
+  end
+
 private
 
+  def headers
+    @headers ||= ("field_1".."field_134").to_a
+  end
+
   def with_headers?
     rows[0][0]&.match?(/\D+/)
   end

app/services/bulk_upload/lettings/year2023/csv_parser.rb

@@ -38,6 +38,10 @@ class BulkUpload::Lettings::Year2023::CsvParser
     @rows ||= CSV.parse(normalised_string, row_sep:)
   end
 
+  def column_for_field(field)
+    cols[field_numbers.find_index(field) + col_offset]
+  end
+
 private
 
   def default_field_numbers
@@ -45,7 +49,7 @@ private
   end
 
   def field_numbers
-    if with_headers?
+    @field_numbers ||= if with_headers?
                          rows[row_offset - 1][col_offset..].map { |h| h.present? ? "field_#{h}" : "field_blank" }
                        else
                          default_field_numbers

spec/services/bulk_upload/lettings/year2022/csv_parser_spec.rb

@@ -69,4 +69,29 @@ RSpec.describe BulkUpload::Lettings::Year2022::CsvParser do
       expect(service.row_parsers[0].field_12.to_i).to eql(log.age1)
     end
   end
+
+  describe "#column_for_field", aggregate_failures: true do
+    context "when headers present" do
+      it "returns correct column" do
+        expect(service.column_for_field("field_1")).to eql("B")
+        expect(service.column_for_field("field_134")).to eql("EE")
+      end
+    end
+
+    context "when no headers" do
+      let(:file) { Tempfile.new }
+      let(:path) { file.path }
+      let(:log) { build(:lettings_log, :completed) }
+
+      before do
+        file.write(BulkUpload::LogToCsv.new(log:, col_offset: 0).to_2022_csv_row)
+        file.rewind
+      end
+
+      it "returns correct column" do
+        expect(service.column_for_field("field_1")).to eql("A")
+        expect(service.column_for_field("field_134")).to eql("ED")
+      end
+    end
+  end
 end

spec/services/bulk_upload/lettings/year2023/csv_parser_spec.rb

@@ -98,4 +98,60 @@ RSpec.describe BulkUpload::Lettings::Year2023::CsvParser do
       expect(service.row_parsers[0].field_13).to eql(log.tenancycode)
     end
   end
+
+  describe "#column_for_field", aggregate_failures: true do
+    context "when with headers using default ordering" do
+      before do
+        file.write("Question\n")
+        file.write("Additional info\n")
+        file.write("Values\n")
+        file.write("Can be empty?\n")
+        file.write("Type of letting the question applies to\n")
+        file.write("Duplicate check field?\n")
+        file.write(BulkUpload::LogToCsv.new(log:).default_2023_field_numbers_row)
+        file.write(BulkUpload::LogToCsv.new(log:).to_2023_csv_row)
+        file.rewind
+      end
+
+      it "returns correct column" do
+        expect(service.column_for_field("field_5")).to eql("B")
+        expect(service.column_for_field("field_22")).to eql("EL")
+      end
+    end
+
+    context "when without headers using default ordering" do
+      before do
+        file.write(BulkUpload::LogToCsv.new(log:, col_offset: 0).to_2023_csv_row)
+        file.rewind
+      end
+
+      it "returns correct column" do
+        expect(service.column_for_field("field_5")).to eql("A")
+        expect(service.column_for_field("field_22")).to eql("EK")
+      end
+    end
+
+    context "when with headers using custom ordering" do
+      let(:seed) { 123 }
+
+      before do
+        file.write("Question\n")
+        file.write("Additional info\n")
+        file.write("Values\n")
+        file.write("Can be empty?\n")
+        file.write("Type of letting the question applies to\n")
+        file.write("Duplicate check field?\n")
+        file.write(BulkUpload::LogToCsv.new(log:).default_2023_field_numbers_row(seed:))
+        file.write(BulkUpload::LogToCsv.new(log:).to_2023_csv_row(seed:))
+        file.rewind
+      end
+
+      it "returns correct column" do
+        expect(service.column_for_field("field_5")).to eql("N")
+        expect(service.column_for_field("field_22")).to eql("O")
+        expect(service.column_for_field("field_26")).to eql("B")
+        expect(service.column_for_field("field_25")).to eql("EF")
+      end
+    end
+  end
 end