February 13, 2018

Example of the Visitor Pattern


A simple but non-contrived example of the Visitor pattern. Here are the main classes.

// Interface for the visiting system permit populator
public interface IPopulatorVisitor
{
    void PopulateVisit(ISet<int> permitSystemsSet);
}

public interface IPermitSystems
{
    void AcceptPopulator(IPopulatorVisitor populatorVisitor);

    bool PermitRequired(int systemId);
}

// This is the Visitor target
// It stores a set of systems that require a permit for entry
public class PermitSystems : IPermitSystems
{
    HashSet<int> _permitRequiredSystemIds = new HashSet<int>();

    // Accept Visitors here
    public void AcceptPopulator(IPopulatorVisitor populatorVisitor)
    {
        populatorVisitor.PopulateVisit(_permitRequiredSystemIds);
    }

    public bool PermitRequired(int systemId)
    {
        bool res = _permitRequiredSystemIds.Contains(systemId);
        return res;
    }
}

The Visitor class, this has removed the responsibility for deserialising the permit data from the the PermitSystems class. In this case the data is stored in 'JSonl' form, but it could be stored in other formats and a different visitor would be provided

public class PermitSystemsJsonlDeserialiserVisitor 
    : IPopulatorVisitor
{
    FileInfo _jsonlFilePath;

    public void Initialise(string jsonlFilePath)
    {
        _jsonlFilePath = new FileInfo(jsonlFilePath);
    }

    public void PopulateVisit(ISet<int> permitSystemsSet)
    {
        List permitReqdSystems;
        if (_jsonlFilePath.TryLoadFromJson(out permitReqdSystems))
        {
            if (permitReqdSystems != null)
            {
                PopulateImpl(permitSystemsSet, permitReqdSystems);
            }
        }
    }

    private static void PopulateImpl(ISet<int> permitSystemsSet, 
        List permitReqdSystems)
    {
        foreach (var sys in permitReqdSystems)
        {
            Trace.WriteLine(" Permit required for id=" + sys.id + " name=" + sys.name +
                            " permitRequired=" + sys.permitRequired);
            permitSystemsSet.Add(sys.id);
        }
    }
}
Some sample code to bring it all together
[Test]
public void PermitSystemsExperiment()
{
    IPermitSystems permitSystems = new PermitSystems();
    PermitSystemsJsonlDeserialiserVisitor jdv = new PermitSystemsJsonlDeserialiserVisitor();
    jdv.Initialise(TestFilePaths.PermitRequiredSystemsJSonFilePath);
    permitSystems.AcceptPopulator(jdv);

    Assert.That(true == permitSystems.PermitRequired(19054));
    Assert.That(false == permitSystems.PermitRequired(26));
}

September 13, 2017

CSV Files with Linq

An example of using Linq to parse a CSV file and write data to a TSV file. The beauty of the approach shown here is the file is read one line at a time when parsing, you do not have to load the whole file to process the data, and written one line at a time when writing. Here is a sample piece of the CSV file (note the first line is a header line not a data line):
id,edsm_id,name,x,y,z,population,is_populated,government_id,government,allegiance_id,allegiance,state_id,state,security_id,security,primary_economy_id,primary_economy,power,power_state,power_state_id,needs_permit,updated_at,simbad_ref,controlling_minor_faction_id,controlling_minor_faction,reserve_type_id,reserve_type
17,60,"10 Ursae Majoris",0.03125,34.90625,-39.09375,0,0,176,None,5,None,80,None,16,Low,10,None,,,,0,1497906646,"10 Ursae Majoris",,,,
24,12009,"11 Bootis",-49.40625,285.25,65.21875,0,0,176,None,5,None,80,None,16,Low,10,None,,,,0,1474116394,"11 Bootis",,,,
26,13308,"11 Mu Aurigae",-30,0.75,-150.03125,0,0,176,None,5,None,80,None,16,Low,10,None,,,,0,1497806946,,,,,


Want to parse some of these lines into this structure:
public class BaseSystemRaw
{
    public int id { get; set; }
    public string name { get; set; }
    public float x { get; set; }
    public float y { get; set; }
    public float z { get; set; }

    public override string ToString()
    {
        return "id=" + id + ", name=" + name + 
               ", location=( " + x + ", " + y + ", " + z + " )";
    }
}
Here is a test harness:
[ TestFixture ]
class ParseCsvFilesWithLinqTests
{
    [ Test ]
    public void ParseCsvFileTest()
    {
        // Skip(1) will skip the header line
        // This commented out version will only use the first 10 lines,
        // great for debugging
        // var baseSystemRaws = File.ReadLines(TestFilePaths.SystemsFilePath).
        //     Take(10).Skip(1).Select(line => ExtractBaseSystemRaw(line));
        var baseSystemRaws = File.ReadLines( TestFilePaths.SystemsFilePath ).
                Skip( 1 ).Select( line => ExtractBaseSystemRaw( line ) );
        DoSomethingWith( baseSystemRaws );
    }

    BaseSystemRaw ExtractBaseSystemRaw(
        string line )
    {
        var parts = line.Split( ',' );
        var sysRaw = new BaseSystemRaw();
        int tmp;
        if ( int.TryParse( parts[ 0 ], out tmp ) )
        {
            sysRaw.id = tmp;
        }
        // Ignore parts[1] edsm_id
        sysRaw.name = parts[ 2 ].Trim().Replace( "\"", "" );
        float ftmp;
        if ( float.TryParse( parts[ 3 ], out ftmp ) )
        {
            sysRaw.x = ftmp;
        }
        if ( float.TryParse( parts[ 4 ], out ftmp ) )
        {
            sysRaw.y = ftmp;
        }
        if ( float.TryParse( parts[ 5 ], out ftmp ) )
        {
            sysRaw.z = ftmp;
        }
        // Ignore other parts
        return sysRaw;
    }

    private void DoSomethingWith(
        IEnumerable<BaseSystemRaw> baseSystemRaws )
    {
        foreach ( var entry in baseSystemRaws )
        {
            Trace.WriteLine( entry );
        }
    }
}
Now write the data to a TSV file.
[ TestFixture ]
class WriteTsvFilesWithLinqTests
{
    [ Test ]
    public void WriteTsvFileTest()
    {
        const string separator = "\t";
        var headers = new[] { "Id", "System", "x", "y", "z" };
        // Skip(1) will skip the header line
        // This version will only use the first 4 lines, great for debugging, 
        // remove the Take(4) to process the whole file
        var baseSystemRaws = File.ReadLines( TestFilePaths.SystemsFilePath ).
            Take(4).Skip(1).Select( line => ExtractBaseSystemRaw( line ) );
        
        // Use Enumerable.Concat to add the header string
        File.WriteAllLines( TestFilePaths.BaseSystemsTsvFilePath,
            Enumerable.Concat( new[] { string.Join( separator, headers ) },
                baseSystemRaws.Select(sys => sys != null ? 
                    CoreSystemRawToTsv( separator, sys ) : "")));
    }

    private string CoreSystemRawToTsv(
        BaseSystemRaw sys )
    {
        string line = string.Join( "\t", sys.id, sys.name, sys.x.ToString( "0.0000" ),
            sys.y.ToString( "0.0000" ), sys.z.ToString( "0.0000" ) );
        return line;
    }
}

September 5, 2017

C# HashSet

Best to demonstrate what some of the methods do with some unit tests. In particular what does 'SymmetricExceptWith' do?
[ TestFixture ]
public class HashSetTests
{
    private HashSet<int> integerSet1;
    private HashSet<int> integerSet1Copy;
    private HashSet<int> integerSet2;

    [ SetUp ]
    public void Setup()
    {
        integerSet1 = new HashSet<int> { 1, 2, 3 };
        integerSet2 = new HashSet<int> { 2, 3, 4 };
        integerSet1Copy = new HashSet<int> { 2, 3, 1 };
    }

    [ Test ]
    // The SetEquals method ignores duplicate entries and 
    // the order of elements in the other parameter.
    public void SetEqualsTest()
    {
        var integerList = new List<int> { 2, 3, 1, 3, 2 };

        Assert.That( !integerSet1.SetEquals( integerSet2 ) );
        Assert.That( integerSet1.SetEquals( integerSet1Copy ) );
        Assert.That( integerSet1.SetEquals( integerList ) );
    }

    [ Test ]
    public void IntersectWithTest() // All elements common to both sets
    {
        integerSet1.IntersectWith( integerSet2 );
        Assert.That( !integerSet1.Contains( 1 ) );
        Assert.That( integerSet1.Contains( 2 ) );
        Assert.That( integerSet1.Contains( 3 ) );
        Assert.That( !integerSet1.Contains( 4 ) );
    }

    [ Test ]
    public void UnionWithTest() // All elements in both sets
    {
        integerSet1.UnionWith( integerSet2 );
        Assert.That( integerSet1.Contains( 1 ) );
        Assert.That( integerSet1.Contains( 2 ) );
        Assert.That( integerSet1.Contains( 3 ) );
        Assert.That( integerSet1.Contains( 4 ) );
    }

    [ Test ]
    public void SymmetricExceptWithTest() // All elements not common to both sets
    {
        integerSet1.SymmetricExceptWith( integerSet2 );
        Assert.That( integerSet1.Contains( 1 ) );
        Assert.That( !integerSet1.Contains( 2 ) );
        Assert.That( !integerSet1.Contains( 3 ) );
        Assert.That( integerSet1.Contains( 4 ) );
    }
}

July 28, 2017

An Alternative Queue Class

Here is an alternative generic Queue class. I created it as I constantly found when using a queue class that Enqueue and Dequeue were never enough. There was always a need for a remove an item and a need to iterate through all the items in a queue. The original basic source for the queue class is here.
public class Node< T >
{
    public T Data { get; set; }
    public Node<T> Next { get; set; }

    public Node( T data )
    {
        this.Data = data;
    }
}

public class Queue2< T >
{
    private Node<T> _head;
    private Node<T> _tail;
    private int _count;
    private readonly IEqualityComparer<T> _comparator;

    public Queue2()
    {
        _comparator = EqualityComparer<T>.Default;
    }

    public Queue2( IEqualityComparer<T> comparator )
    {
        _comparator = comparator;
    }

    public void Enqueue(
        T data )
    {
        Node<T> _newNode = new Node<T>( data );
        if ( _head == null )
        {
            _head = _newNode;
            _tail = _head;
        }
        else
        {
            _tail.Next = _newNode;
            _tail = _tail.Next;
        }
        _count++;
    }

    public T Dequeue()
    {
        if ( _head == null )
        {
            throw new Exception( "Queue is Empty" );
        }
        T _result = _head.Data;
        _head = _head.Next;
        return _result;
    }

    public void Remove(
        T item )
    {
        Node<T> previous = null, cursor = _head;
        bool found = false;
        while ( ( cursor != null ) && !found )
        {
            found = _comparator.Equals( cursor.Data, item );
            if ( found )
            {
                if ( previous == null )
                {
                    _head = cursor.Next;
                }
                else
                {
                    previous.Next = cursor.Next;
                }
            }
            else
            {
                previous = cursor;
                cursor = cursor.Next;
            }
        }
    }

    public void Clear()
    {
        _head = _tail = null;
    }

    public IEnumerable<T> GetEnumerator()
    {
        Node<T> cursor = _head;
        while ( cursor != null )
        {
            yield return cursor.Data;
            cursor = cursor.Next;
        }
    }

    public int Count
    {
        get { return this._count; }
    }
}

July 20, 2017

A String.Split() That Returns An IEnumerable

A version of Split string that returns an IEnumerable<string> rather than an array. Only single separate string is allowed, it is very rare that an array of separator strings is required.
  
public static class StringSplitExtensions
{
  
  public static IEnumerable<string> Split2(
    this string targetStr,
    string separator )
  {
    if ( targetStr == null )
      yield break;

    if ( string.IsNullOrEmpty( separator ) )
    {
      yield return targetStr;
    }
    else
    {
      string str = targetStr;
      bool finished = false;
      int startIx = 0;
      int sepLength = separator.Length;
      while ( !finished )
      {
        var ix = str.IndexOf( separator, 
            StringComparison.OrdinalIgnoreCase );
        if ( ix == -1 )
        {
          finished = true;
          yield return str;
        }
        else
        {
          string res = str.Substring( 0, ix );
          yield return res;
          startIx = ix + sepLength;
          str = str.Substring( startIx, str.Length - startIx );
        }
      }
    }
  }
}



[ Test ]
public void SplitTest()
{
  string test = "012 3456\t7890\ta  aaa\tbbbb\t";

  var res2 = test.Split2( "\t" ).ToArray();
  var norm2 = test.Split( '\t' );
  Assert.IsTrue( AreTheSame( res2, norm2 ) );

  var res3 = "".Split2( "\t" ).ToArray();
  var norm3 = "".Split( '\t' );
  Assert.IsTrue( AreTheSame( res3, norm3 ) );

  var res4 = "\t".Split2( "\t" ).ToArray();
  var norm4 = "\t".Split( '\t' );
  Assert.IsTrue( AreTheSame( res4, norm4 ) );

  var res5 = "\t\t".Split2( "\t" ).ToArray();
  var norm5 = "\t\t".Split( '\t' );
  Assert.IsTrue( AreTheSame( res5, norm5 ) );

  var res6 = "a\t".Split2( "\t" ).ToArray();
  var norm6 = "a\t".Split( '\t' );
  Assert.IsTrue( AreTheSame( res6, norm6 ) );

  var res7 = "\ta".Split2( "\t" ).ToArray();
  var norm7 = "\ta".Split( '\t' );
  Assert.IsTrue( AreTheSame( res7, norm7 ) );

  // Works the same as a standard Split string except in 
  // the case where the Splitter string is an empty string
  var norm8 = test.Split();
  var res8 = test.Split2( "" ).ToArray();
  Assert.IsFalse( AreTheSame( res8, norm8 ) );
}


// Checks whether 2 string arrays are exactly the same, ie. they have
// the same length and the same values at each array entry
public static bool AreTheSame(
string[] stringArray1,
string[] stringArray2)
{
  bool areTheSame = (stringArray1.Length == stringArray2.Length);
  for (int ix = 0; (ix < stringArray1.Length) && areTheSame; ix++)
  {
    areTheSame = stringArray1[ix].Equals(stringArray2[ix], StringComparison.CurrentCulture);
  }
  return areTheSame;
}

June 29, 2017

Case Insensitive Dictionary


Very easy to implement in C#, just pass 'StringComparer.OrdinalIgnoreCase' in the constructor, for example:
Dictionary nameToIdTable = new Dictionary(StringComparer.OrdinalIgnoreCase);
Here is an an example in action:
[ Test ]
public void CaseInsenstiveDictionaryTest()
{
  var dictionary = new Dictionary(StringComparer.OrdinalIgnoreCase)
  {
    { "Mbukuravi", 1 },
    { "Liaedin", 2 },
  };

  Assert.That( dictionary[ "Liaedin" ] == 2 );
  Assert.That( dictionary[ "LiAEdin" ] == 2 );
  Assert.That( dictionary[ "LiaeDIn" ] == 2 );
  Assert.That( dictionary[ "LIAEDIN" ] == 2 );
}

June 14, 2017

A ConcurrentStreamWriter Class

A class for writing to a stream from multiple threads:

public interface IConcurrentStreamWriter
{
    void WriteStream(
        string theStringToWrite);
}

/// <summary>
///     A concurrent stream writer. Allows concurrent/queued writes to a stream
/// </summary>
///
/// <seealso cref="T:ASM.DEK.Printer.Micron.PrintEngine.Timing.Timers.IConcurrentStreamWriter"/>
/// <seealso cref="T:System.IDisposable"/>
public class ConcurrentStreamWriter : IConcurrentStreamWriter, IDisposable
{
    private readonly Func<StreamWriter> _streamWriterProvider;
    private readonly ConcurrentQueue<string> queuedWrites = new ConcurrentQueue<string>();
    private readonly AutoResetEvent _autoResetEvent = new AutoResetEvent(false);

    private bool _exit;

    public ConcurrentStreamWriter(
        Func<StreamWriter> streamWriterProvider)
    {
        Contract.Requires<ArgumentNullException>(
            streamWriterProvider != null);

        _streamWriterProvider = streamWriterProvider;

        Task.Factory.StartNew(
            WriteQueueThreadRoutine, 
            TaskCreationOptions.LongRunning);
    }

    public void WriteStream(
        string theStringToWrite)
    {
        if (!string.IsNullOrEmpty(theStringToWrite))
        {
            queuedWrites.Enqueue(theStringToWrite);
            _autoResetEvent.Set();
        }
    }

    #region private

    private void WriteQueueThreadRoutine()
    {
        using (var stream = _streamWriterProvider())
        {
            while (!_exit)
            {
                _autoResetEvent.WaitOne();
                if (queuedWrites.Count > 0)
                {
                    WriteQueueImpl(stream);
                }
            }
        }
        _autoResetEvent.Dispose();
    }

    private void WriteQueueImpl(
        StreamWriter stream)
    {
        try
        {
            string stringToWrite = "";
            do
            {
                if (queuedWrites.TryDequeue(out stringToWrite))
                {
                    stream.WriteLine(stringToWrite);
                }
            } while (queuedWrites.Count > 0);
            stream.Flush();
        }
        catch (IOException ioex)
        {
            Trace.WriteLine("IOException caught: " + ioex);
        }
    }

    #endregion private

    #region Dispose Implementation

    // Use C# destructor syntax for finalization code.
    ~ConcurrentStreamWriter()
    {
        Dispose(false);
        Debug.Assert(false, "Detected ConcurrentStreamWriter object was undisposed");
    }

    private bool _isDisposed;

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(
        bool disposing)
    {
        if (_isDisposed)
            return;

        if (disposing)
        {
            _exit = true;
            _autoResetEvent.Set();
        }

        _isDisposed = true;
    }

    #endregion Dispose Implementation
}
It uses a ConcurrentQueue object to queue the stream requests up and an AutoResetEvent to release a writer on a separate thread to actually output the stream contents.