An Implementation of Regular Expression Parser in C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using RegularExpression;

namespace Driver
{
  public partial class frmNfa : Form
  {

    RegEx m_regEx = new RegEx();
    bool m_bFirstTime = true;

    public frmNfa()
    {
      InitializeComponent();
    }

    private void btnCompile_Click(object sender, EventArgs e)
    {
      if (txtRegEx.Text.Length == 0)
      {
        MessageBox.Show("You must enter a regular expression before compiling.");
        txtRegEx.Select();
        return;
      }
      StringBuilder sb = new StringBuilder(10000);
      try
      {
        ErrorCode errCode = m_regEx.CompileWithStats(this.txtRegEx.Text, sb);
        if (errCode != ErrorCode.ERR_SUCCESS)
        {
          string sErrSubstring = txtRegEx.Text.Substring(m_regEx.GetLastErrorPosition(), m_regEx.GetLastErrorLength());
          string sFormat = "Error occured during compilation.\nCode: {0}\nAt: {1}\nSubstring: {2}";
          sFormat = String.Format(sFormat, errCode.ToString(), m_regEx.GetLastErrorPosition(), sErrSubstring );
          txtRegEx.Select(m_regEx.GetLastErrorPosition(), m_regEx.GetLastErrorLength() );
          MessageBox.Show(sFormat);
          txtRegEx.Select();
          return;
        }
        this.matchDS.Clear();
      }
      catch (Exception ex)
      {
        MessageBox.Show("Error occured during compilation.\n\n" + ex.Message);
        txtRegEx.Select();
        return;
      }
      txtStat.Text = sb.ToString();
      m_bFirstTime = true;
    }

    private void txtStat_KeyDown(object sender, KeyEventArgs e)
    {
      m_bFirstTime = true;

    }

    private void txtStat_MouseDown(object sender, MouseEventArgs e)
    {
      m_bFirstTime = true;

    }

    private void btnFindAll_Click(object sender, EventArgs e)
    {
      if (!m_regEx.IsReady())
      {
        MessageBox.Show("You must first compile a regular expression.");
        txtRegEx.Focus();
        return;
      }

      matchDS.Clear();
      matchDS.AcceptChanges();

      int nFoundStart = -1;
      int nFoundEnd = -1;
      int nStartAt = 0;
      int nMatchLength = -1;

      do
      {
        bool bFound = m_regEx.FindMatch(txtSearchString.Text, nStartAt, txtSearchString.Text.Length - 1, ref nFoundStart, ref nFoundEnd);
        if (bFound == true)
        {
          string sSubstring = "{Empty String}";
          nMatchLength = nFoundEnd - nFoundStart + 1;
          if (nMatchLength > 0)
          {
            sSubstring = txtSearchString.Text.Substring(nFoundStart, nMatchLength);
          }
          matchDS.MatchInfo.AddMatchInfoRow(sSubstring, nFoundStart, nFoundEnd, nMatchLength);
          matchDS.AcceptChanges();
          nStartAt = nFoundEnd + 1;
        }
        else
        {
          nStartAt++;
        }
      } while (nStartAt < txtSearchString.Text.Length);


    }

    private void btnFindNext_Click(object sender, EventArgs e)
    {
      if (!m_regEx.IsReady())
      {
        MessageBox.Show("You must first compile a regular expression.");
        txtRegEx.Focus();
        return;
      }
      int nFoundStart = -1;
      int nFoundEnd = -1;
      int nStartAt = -1;

      if (m_bFirstTime)
      {
        nStartAt = txtSearchString.SelectionStart;
        m_bFirstTime = false;
      }
      else
      {
        nStartAt = txtSearchString.SelectionStart + 1;
      }

      bool bFound = m_regEx.FindMatch(txtSearchString.Text, nStartAt, txtSearchString.Text.Length - 1, ref nFoundStart, ref nFoundEnd);
      if (bFound)
      {
        int nMatchLength = nFoundEnd - nFoundStart + 1;
        if (nMatchLength == 0)
        {
          MessageBox.Show("Matched an empty string at position " + nFoundStart.ToString() + ".");
        }
        else
        {
          txtSearchString.Select();
          txtSearchString.Select(nFoundStart, nMatchLength);
        }
      }
      else
      {
        MessageBox.Show("No match found.");
      }
    }

    private void grdResult_RowEnter(object sender, DataGridViewCellEventArgs e)
    {
      try
      {
        DataRowView drv = (DataRowView)grdResult.Rows[e.RowIndex].DataBoundItem;
        MatchInfoDS.MatchInfoRow r = (MatchInfoDS.MatchInfoRow)drv.Row;

        txtSearchString.Select(r.StartIndex, r.Length);
      }
      catch (Exception ex)
      {
        Console.WriteLine(ex.Message);
      }
    }

    private void txtSearchString_KeyDown(object sender, KeyEventArgs e)
    {
      m_bFirstTime = true;
    }

    private void txtSearchString_MouseDown(object sender, MouseEventArgs e)
    {
      m_bFirstTime = true;
    }


    private void txtSearchString_Enter(object sender, EventArgs e)
    {
      this.AcceptButton = btnFindAll;

    }

    private void txtRegEx_Enter(object sender, EventArgs e)
    {
      this.AcceptButton = btnCompile;

    }


    private void chkGreedy_CheckedChanged(object sender, EventArgs e)
    {
      m_regEx.UseGreedy = chkGreedy.Checked;

    }

    private void btnFindFirst_Click(object sender, EventArgs e)
    {
      if (!m_regEx.IsReady())
      {
        MessageBox.Show("You must first compile a regular expression.");
        txtRegEx.Focus();
        return;
      }
      int nFoundStart = -1;
      int nFoundEnd = -1;

      bool bFound = m_regEx.FindMatch(txtSearchString.Text, 0, txtSearchString.Text.Length - 1, ref nFoundStart, ref nFoundEnd);
      if (bFound)
      {
        int nMatchLength = nFoundEnd - nFoundStart + 1;
        if (nMatchLength == 0)
        {
          MessageBox.Show("Matched an empty string at position " + nFoundStart.ToString() + ".");
        }
        else
        {
          txtSearchString.Select();
          txtSearchString.Select(nFoundStart, nMatchLength);
        }
      }
      else
      {
        MessageBox.Show("No match found.");
      }
    }

    private void TestMatch()
    {
      RegEx re = new RegEx();
      string sPattern = "a_*p";
      ErrorCode errCode = re.Compile(sPattern);

      if (errCode != ErrorCode.ERR_SUCCESS)
      {
        string sErrSubstring = sPattern.Substring(re.GetLastErrorPosition(), re.GetLastErrorLength());
        string sFormat = "Error occured during compilation.\nCode: {0}\nAt: {1}\nSubstring: {2}";
        sFormat = String.Format(sFormat, errCode.ToString(), m_regEx.GetLastErrorPosition(), sErrSubstring);
        MessageBox.Show(sFormat);
        return;
      }

      int nFoundStart = -1;
      int nFoundEnd = -1;
      string sToSearch = "appleandpotato";

      bool bFound = m_regEx.FindMatch(sToSearch, 0, sToSearch.Length - 1, ref nFoundStart, ref nFoundEnd);
      if (bFound)
      {
        int nMatchLength = nFoundEnd - nFoundStart + 1;
        if (nMatchLength == 0)
        {
          MessageBox.Show("Matched an empty string at position " + nFoundStart.ToString() + ".");
        }
        else
        {
          string sMatchString = sToSearch.Substring(nFoundStart, nMatchLength);

          MessageBox.Show("Match found at: " + nFoundStart.ToString() + "\n" + sMatchString);          
        }
      }
      else
      {
        MessageBox.Show("No match found.");
      }

    }
  }
}