AusPostCode/Barcode.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

namespace AusPostCode {
	public class Barcode {
		public enum BarcodeFragment {
			FormatControlCode,
			SortingCode,
			CustomerInformation,
			ErrorCorrection,
		}

		public enum EncodingFormat {
			N,
			C,
			BarToDecimal,
		}

		private int _formatCode;

		public Dictionary<int, string> FormatTable = new Dictionary<int, string> {
			[0] = "Null Customer Barcode",
			[11] = "Standard Customer Barcode",
			[52] = "Customer Business Reply Paid",
			[59] = "Customer Barcode 2",
			[62] = "Customer Barcode 3",
			[67] = "Customer Business Reply Paid",
			[72] = "International Business Reply Paid",
			[77] = "International Business Reply Paid",
		};

		public Barcode(string code) {
			Code = code;
			// - check for start and end bars
			if (Code.Substring(0, 2) != "13") {
				Warnings.Add("Couldn't find Start Bars");
				Code = $"13{Code}";
			}

			if (Code.Substring(Code.Length - 3, 2) != "13") {
				Warnings.Add("Couldn't find End Bars");
				Code = $"{Code}13";
			}

			// process Format Control Code
			_formatCode = int.Parse(Decode(GetFragment(BarcodeFragment.FormatControlCode), EncodingFormat.N));
			Console.WriteLine(Format);

			// process Sorting Code Field
			SortingCode = int.Parse(Decode(GetFragment(BarcodeFragment.SortingCode), EncodingFormat.N));
			Console.WriteLine($"Sorting code: {SortingCode}");
		}

		public int SortingCode { get; set; }
		public int CustomerInformation { get; set; }
		public string Format => FormatTable.ContainsKey(_formatCode) ? FormatTable[_formatCode] : $"Unknown ({_formatCode})";
		private List<string> Warnings { get; set; } = new List<string>();
		private string Code { get; set; }

		private string GetFragment(BarcodeFragment barcodeFragment) {
			return barcodeFragment switch {
				BarcodeFragment.FormatControlCode => Code.Substring(2, 4),
				BarcodeFragment.SortingCode => Code.Substring(6, 16),
				BarcodeFragment.CustomerInformation when _formatCode == 59 => Code.Substring(22, 16),
				BarcodeFragment.CustomerInformation when _formatCode == 62 => Code.Substring(22, 31),
				BarcodeFragment.CustomerInformation => null, // format doesn't support the customer information field
				BarcodeFragment.ErrorCorrection => Code.Substring(Code.Length - 15,
					12), // the error correction bars are always immediately before the stop bars
				_ => throw new ArgumentOutOfRangeException(nameof(barcodeFragment), barcodeFragment, null),
			};
		}

		private static string Decode(string input, EncodingFormat format) {
			// bool badData;
			var chunkLength = format == EncodingFormat.N ? 2 : 3;
			if (input.Length % 2 != 0) {
				throw new ArgumentException($"Input length must be a multiple of {chunkLength}.", nameof(input));
			}

			var rx = new Regex("^[0123]+$");
			if (!rx.IsMatch(input)) {
				throw new ArgumentException("Input length must be a quaternary number.", nameof(input));
			}

			var sb = new StringBuilder();
			for (var i = 0; i < input.Length; i += chunkLength) {
				var chunk = input.Substring(i, chunkLength);

				switch (format) {
					case EncodingFormat.N:
						// format N supports the digits 0 through 9, and nothing else.
						// digits 0 through 8 are stored as their ternary representations, while 9 is stored as "30".

						if (chunk == "30") {
							sb.Append(9);
						}
						else if (chunk.Contains("3")) {
							// not a ternary number
							throw new ArgumentException($"{chunk} is not a valid identifier for format {format.ToString()}.");
						}
						else {
							sb.Append(BaseConversion.FromBase(chunk, 3));
						}
						break;

					case EncodingFormat.C:
						break;

					case EncodingFormat.BarToDecimal:
						break;

					default:
						throw new ArgumentOutOfRangeException(nameof(format), format, null);
				}
			}

			return sb.ToString();
		}
	}
}