library-ts/browser/text/Levehshtein.ts

export class LevenshteinFuzzyMatch
{
  lowestDistance:number;
  index:number;
}

export class LevenshteinDistance
{   
  protected static getMatrix( aLength:number, bLength:number )
  {
    let matrix:number[][] = [];

    for ( let i = 0; i < aLength + 1; i++ )
    {
      let bArray = [];

      for ( let j = 0; j < bLength + 1; j++ )
      {
        bArray.push( 0 );
      }

      matrix.push( bArray );
    }

    for ( let i = 0; i <= aLength; i++ )
    {
      matrix[ i ][ 0 ] = i;
    }

    for ( let j = 0; j <= bLength; j++ )
    {
      matrix[ 0 ][ j ] = j;
    }

    return matrix;
  }

  static computeFuzzyMatch( value:string, matcher:string )
  {
    let result = new LevenshteinFuzzyMatch();

    if ( matcher.length >= value.length )
    {
      result.index = 0;
      result.lowestDistance = LevenshteinDistance.compute( value, matcher );
      
    }
    else
    {
      let offsets = value.length - matcher.length;

      for ( let i = 0; i < offsets; i++ )
      {
        let subValue = value.substring( i, i + matcher.length );
        let distance = LevenshteinDistance.compute( subValue, matcher );

        if ( i === 0 )
        {
          result.index = 0;
          result.lowestDistance = distance;
          continue;
        }

        if ( distance < result.lowestDistance )
        {
          result.index = i;
          result.lowestDistance = distance;
        }
        
      }
    }


    return result;
  }


  static compute( a:string, b:string ):number
  {
    let aLength = a.length;
    let bLength = b.length;

    if ( aLength == 0 ) { return bLength; }
    if ( bLength == 0 ) { return aLength; }

    let evaluationMatrix = LevenshteinDistance.getMatrix( aLength, bLength );        
      
    for ( let i = 1; i <= aLength; i++ )
    {          
      for ( let j = 1; j <= bLength; j++ )
      {            
        let isSame = b[ j - 1 ] === a[ i - 1 ];

        let isDifferentCost = isSame ? 0 : 1;

        let insertionCost    = evaluationMatrix[ i - 1][ j ] + 1;
        let deletionCost     = evaluationMatrix[ i ][ j - 1 ] + 1;
        let substitutionCost = evaluationMatrix[ i - 1][ j - 1 ] + isDifferentCost;
          
        evaluationMatrix[ i ][ j ] = Math.min( insertionCost, deletionCost, substitutionCost );
      }
    }
      
    return evaluationMatrix[ aLength][ bLength ];
  }
}