Create a patterned encoder

Author: colinangusmackay

src/.idea/.idea.Stravaig.ShortCode/.idea/riderModule.iml

@@ -0,0 +1,33 @@
+using NUnit.Framework;
+
+namespace Stravaig.ShortCode.Tests
+{
+    [TestFixture]
+    public class PatternedEncoderTests
+    {
+        [TestCase(1UL, ExpectedResult = "AA-00-ab")]
+        [TestCase(27UL, ExpectedResult = "AA-00-bb")]
+        [TestCase(675UL, ExpectedResult = "AA-00-zz")]
+        [TestCase(676UL, ExpectedResult = "AA-01-aa")]
+        [TestCase(677UL, ExpectedResult = "AA-01-ab")]
+        [TestCase(6760UL, ExpectedResult = "AA-10-aa")]
+        [TestCase(6761UL, ExpectedResult = "AA-10-ab")]
+        [TestCase(67600UL, ExpectedResult = "AB-00-aa")]
+        [TestCase(1757600UL, ExpectedResult = "BA-00-aa")]
+        [TestCase(45697599UL, ExpectedResult = "ZZ-99-zz")]
+        [TestCase(45697600UL, ExpectedResult = "AA-00-aa")]
+        public string ConvertPattern(ulong code)
+        {
+            PatternedEncoder encoder = new PatternedEncoder(new[]
+            {
+                new PatternPart(NamedCharacterSpaces.UpperLatinLetters, 2),
+                new PatternPart("-"),
+                new PatternPart(NamedCharacterSpaces.Digits, 2),
+                new PatternPart("-"),
+                new PatternPart(NamedCharacterSpaces.LowerLatinLetters, 2),
+            });
+
+            return encoder.Convert(code);
+        }
+    }
+}

src/Stravaig.ShortCode.Tests/PatternedEncoderTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Security.Cryptography.X509Certificates;
 
 namespace Stravaig.ShortCode
 {

src/Stravaig.ShortCode/Encoder.cs

@@ -0,0 +1,23 @@
+namespace Stravaig.ShortCode
+{
+    public class PatternPart
+    {
+        public string Pattern { get; set; }
+        public PatternType Type { get; set; }
+        public int Length { get; set; }
+
+        public PatternPart(string fixedChars)
+        {
+            Pattern = fixedChars;
+            Type = PatternType.Fixed;
+            Length = fixedChars.Length;
+        }
+
+        public PatternPart(string characterSpace, int length)
+        {
+            Pattern = characterSpace;
+            Type = PatternType.EncodeIntoCharacterSpace;
+            Length = length;
+        }
+    }
+}

src/Stravaig.ShortCode/PatternPart.cs

@@ -0,0 +1,8 @@
+namespace Stravaig.ShortCode
+{
+    public enum PatternType
+    {
+        Fixed,
+        EncodeIntoCharacterSpace,
+    }
+}

src/Stravaig.ShortCode/PatternType.cs

@@ -0,0 +1,72 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Stravaig.ShortCode
+{
+    public class PatternedEncoder : IEncoder
+    {
+        private readonly PatternPart[] _parts;
+        private readonly int _length;
+
+        public PatternedEncoder(IEnumerable<PatternPart> parts)
+        {
+            _parts = parts.ToArray();
+            _length = _parts.Sum(p => p.Length);
+        }
+
+        public string Convert(ulong fullCode, int? fixedChars = null, int maxChars = Int32.MaxValue)
+        {
+            if (fullCode == 0) 
+                throw new ArgumentOutOfRangeException(nameof(fullCode), $"Must be greater than zero.");
+
+            char[] result = new char[_length];
+            ulong code = fullCode;
+            int position = _length;
+            for (int i = _parts.Length - 1; i >= 0; i--)
+            {
+                var part = _parts[i];
+                position -= part.Length;
+                code = BuildShortCode(code, part, result, position);
+            }
+
+            return new string(result);
+        }
+        
+        private ulong BuildShortCode(ulong fullCode, PatternPart part, char[] code, int position)
+        {
+            if (part.Type == PatternType.Fixed)
+            {
+                for (int i = 0; i < part.Length; i++)
+                    code[position + i] = part.Pattern[i];
+                return fullCode;
+            }
+
+            ulong divisor = (ulong) part.Pattern.Length;
+            for (int i = (position + part.Length - 1); i >= position; i--)
+            {
+                ulong remainder = fullCode % divisor;
+                code[i] = part.Pattern[(int) remainder];
+                fullCode = (fullCode - remainder) / divisor;
+            }
+
+            return fullCode;
+        }
+
+        public ulong RangeRequired(int numChars)
+        {
+            throw new NotImplementedException();
+        }
+
+        public int MaxLength()
+        {
+            throw new NotImplementedException();
+        }
+
+        public string NamedCharacterSpace =>
+            throw new InvalidOperationException($"{nameof(NamedCharacterSpace)} is not applicable to this encoder.");
+
+        public string CharacterSpace =>
+            throw new InvalidOperationException($"{nameof(CharacterSpace)} is not applicable to this encoding.");
+    }
+}

src/Stravaig.ShortCode/PatternedEncoder.cs

@@ -1,11 +1,13 @@
 using System;
+using System.Collections.Generic;
 
 namespace Stravaig.ShortCode
 {
     public static class ShortCode
     {
         private static int _defaultLength;
         private static Encoder _encoder;
+        private static PatternedEncoder _patternedEncoder;
         private static SequentialCodeGenerator _sequentialCodeGenerator;
         private static IShortCodeGenerator _randomGenerator;
 
@@ -15,6 +17,14 @@ static ShortCode()
             _encoder = new Encoder(NamedCharacterSpaces.LettersAndDigits);
             _sequentialCodeGenerator = new SequentialCodeGenerator();
             _randomGenerator = new CryptographicallyRandomCodeGenerator();
+            _patternedEncoder = new PatternedEncoder(new[]
+            {
+                new PatternPart(NamedCharacterSpaces.ReducedAmbiguity, 3),
+                new PatternPart("-"),
+                new PatternPart(NamedCharacterSpaces.ReducedAmbiguity, 3),
+                new PatternPart("-"),
+                new PatternPart(NamedCharacterSpaces.ReducedAmbiguity, 3),
+            });
         }
 
         public static string GenerateSequentialShortCode(int? length = null)
@@ -51,5 +61,10 @@ public static void SetDefaultLength(int length)
         {
             _randomGenerator = new TGenerator();
         }
+
+        public static void SetPattern(IEnumerable<PatternPart> patternParts)
+        {
+            _patternedEncoder = new PatternedEncoder(patternParts);
+        }
     }
 }