AusPostCode/Barcode.cs

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

namespace AusPostCode {
	public class Barcode {
		private readonly struct BarcodeFragment {
			public EncodingFormat TypicalFormat { get; }
			public int Length { get;}
			public int Offset { get; }

			public BarcodeFragment(EncodingFormat typicalFormat, int length, int offset) {
				TypicalFormat = typicalFormat;
				Length = length;
				Offset = offset;
			}
		}

		private readonly Dictionary<string, BarcodeFragment> _fragments = new Dictionary<string, BarcodeFragment> {
			["FormatControlCode"] = new BarcodeFragment(EncodingFormat.N, 4, 2),
			["SortingCode"] = new BarcodeFragment(EncodingFormat.N, 16, 6),
			["CustomerInformation2"] = new BarcodeFragment(EncodingFormat.C, 16, 22),
			["CustomerInformation3"] = new BarcodeFragment(EncodingFormat.C, 31, 22),
			["ErrorCorrection"] = new BarcodeFragment(EncodingFormat.BarToDecimal, 12, - 16),
		};

		private enum EncodingFormat {
			N,
			C,
			BarToDecimal,
		}

		private int _formatCode;

		private readonly 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(GetFragment(_fragments["FormatControlCode"]));
			Console.WriteLine(Format);

			// process Sorting Code Field
			SortingCode = int.Parse(GetFragment(_fragments["SortingCode"]));
			Console.WriteLine($"Sorting code: {SortingCode}");

			// process Customer Information, if necessary
			// TODO: actually do this, and get a code to test it on. also, ensure that customer codes are the right length
			if (_formatCode == 59) {
				Console.WriteLine("This code has a Customer Information field, but I don't know how to process that yet 0uo");
			} else if (_formatCode == 62) {
				Console.WriteLine("This code has a Customer Information field, but I don't know how to process that yet 0uo");
			}

			// process Reed-Solomon Error Correction Bars
			// TODO: actually validate the barcode
			Console.WriteLine(BaseConversion.FromBase(GetFragment(_fragments["ErrorCorrection"]), 64));

		}

		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; } = new List<string>();
		private string Code { get; }

		private string GetFragment(BarcodeFragment fragment, bool decode = true) {
			var data = Code.Substring(fragment.Offset < 0 ? Code.Length + fragment.Offset : fragment.Offset, fragment.Length);

			if (!decode) {
				return data;
			}

			// bool badData;
			var chunkLength = fragment.TypicalFormat == EncodingFormat.N ? 2 : 3;
			var rx = new Regex("^[0123]+$");
			var sb = new StringBuilder();
			if (!rx.IsMatch(data)) {
				throw new ArgumentException("Input length must be a quaternary number.", nameof(data));
			}

			for (var i = 0; i < data.Length; i += chunkLength) {
				var chunk = data.Substring(i, chunkLength);

				switch (fragment.TypicalFormat) {
					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 {data.ToString()}.");
						}
						else {
							sb.Append(BaseConversion.FromBase(chunk, 3));
						}
						break;

					case EncodingFormat.C:
						break;

					case EncodingFormat.BarToDecimal:
						var digitInt = BaseConversion.FromBase(chunk, 4);
						sb.Insert(0, BaseConversion.ToBase(digitInt, 64));
						break;

					default:
						throw new ArgumentOutOfRangeException(nameof(fragment.TypicalFormat), fragment.TypicalFormat, null);
				}
			}

			return sb.ToString();
		}

		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();
		}
	}
}