Transformation from one position scale of notation to another

How can I transform from one scale of notation to another using my custom function by C#.

abstract string Convert(string value, string fromBase, string toBase);

value - string representation scale of notation in basic notation

fromBase - string represent the base of numeric

toBase - string representation the base of numeric which you must to transform

P.S. string which represents the base position scale开发者_如何学运维 of notation can include any symbols for represent numeral ascending order

For example

Value = “GSAK”

   fromBase = “A,S,G,K” – four(4) is the base scale of notation (If write arabic figures:  0,1,2,3)
   toBase= “0,1,2,3,4,5,6,7,8,9” – ten(10) is the base scale of notation
   return value = “147”

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I would first translate the input value to one of the numeric data types (i.e. long), and then encode into the target format. Draft implementation of a class to do the parsing and encoding (untested and certainly not optimal):

public class Formatter
{
  List<char> symbols;
  int base;

  public Formatter(string format)
  {
    string[] splitted = format.Split(",");
    symbols = splitted.Select(x => x[0]).ToList();
    base = symbols.Size;
  }

  public long Parse(string value)
  {
    long result = 0;
    foreach(char c in value)
    {
      long n = symbols.IndexOf(c);
      result = result*base+n;
    }
    return result;
  }

  public string Encode(long value)
  {
    StringBuilder sb = new StringBuilder();
    while(value>0)
    {
      long n = value % base;
      value /= base;
      sb.Insert(0, symbols[n]);
    }
    return sb.ToString();
  }
}