using System;
using System.Data;

namespace DataStreams.ETL
{
	/// <summary>
	///		Allows quick lookups on DataTables based on column values instead of using the super
	///		slow Select method of a DataTable.
	/// </summary>
	public class DataTableIndex
	{
		private DataView lookupTable = null;

		public DataTableIndex(DataTable data, params DataColumn[] index)
		{
			bool first = true;
			string sort = "";

			// create a comma separated list of sort columns
			foreach (DataColumn column in index)
			{
				if (!first)
				{
					sort += ",";
				}

				first = false;

				// use brackets to handle column names with spaces, etc
				sort += "[" + column.ColumnName + "]";
			}

			// use a DataView because it internally creates an index to cover the sort criteria
			lookupTable = new DataView(
				data, 
				null, 
				sort, 
				DataViewRowState.CurrentRows);
		}

		/// <summary>
		///		Searches for DataRow's using an indexed lookup.
		/// </summary>
		/// <param name="value">
		///		Value order must directly match the order of the columns passed in to the constructor.
		/// </param>
		/// <returns>
		///		The matching DataRow's.
		/// </returns>
		public DataRow[] Find(params object[] value)
		{
			DataRowView[] found = lookupTable.FindRows(value);

			DataRow[] matchingRows = new DataRow[found.Length];

			for (int i = 0; i < found.Length; i++)
			{
				matchingRows[i] = found[i].Row;
			}

			return matchingRows;
		}
	}
}