///
/// Copyright (c) 2017 Sensus Metering Systems
///
using System;
using System.Diagnostics;

namespace TBF.BenchControl.Network.Telnet
{
    /// <summary>
    /// Virtual terminal (an array of characters).
    /// This class is thread safe under these circumstances:
    ///   - ClearScreen() and WriteVt() methods called from one thread only
    ///   - properties Text, etc. can be safely read from an arbitrary thread
    /// </summary>
    public class VirtualTerminal : IVirtualTerminal
    {
		const uint DefaultVtRowsCount = 80;		/// Default VT height (number of rows)
		const uint DefaultVtColumnsCount = 132;	/// Default VT width (number of columns)

		/// <summary>
        /// Virtual terminal special characters.
        /// <seealso cref = http://support.microsoft.com/kb/231866 />
        /// </summary>
        enum SpecialChar
        {
            BS = 8,     ///  8 = Backspace (move one position to the left)
            HT,         ///  9 = Horizontal tab
            LF,         /// 10 = Line feed
            VT,         /// 11 = Vertical tab
            FF,         /// 12 = Form feed (on visual displays most commonly clears the screen)
            CR          /// 13 = Carriage return
        }


		///
		/// Public properties
		///
		public uint Rows { get { return vtRows; } }
		public uint Columns { get { return vtColumns; } }
		public uint CurRow { get { return curRow; } }
		public uint CurColumn { get { return curColumn; } }

		/// <summary>
		/// Virtual terminal text buffer as a single string. To be printed out using monospaced font.
		/// </summary>
		public string Text
		{
			get
			{
				string result = "";
				char[] oneRow = new char[vtColumns];

				for (int row = 0; row < vtRows; row++)
				{
					for (int column = 0; column < vtColumns; column++)
					{
						oneRow[column] = vt[row, column];
					}
					result += new String(oneRow);

					/// New line at the end of each line except of the last one
					if (row < vtRows - 1) result += System.Environment.NewLine;
				}
				return result;
			}
		}


        ///
        /// Private fields
        ///
        char[,] vt;                         /// Virtual terminal text buffer
        uint    vtRows = 0;                 /// VT height (number of rows)
        uint    vtColumns = 0;              /// VT width (number of columns)
        uint    curRow = 0;                 /// Current row (cursor position)
        uint    curColumn = 0;              /// Current column (cursor position)


        /// <summary>
        /// Default constructor.
        /// </summary>
        public VirtualTerminal()
	    {
            vt = new char[DefaultVtRowsCount, DefaultVtColumnsCount];
            if (vt != null)
            {
                vtRows = DefaultVtRowsCount;
                vtColumns = DefaultVtColumnsCount;
                ClearScreen();
            }
	    }

        /// <summary>
        /// Arbitrary VT size constructor.
        /// </summary>
        public VirtualTerminal(uint nrRows, uint nrColumns)
        {
            vt = new char[nrRows, nrColumns];
            if (vt != null)
            {
                vtRows = nrRows;
                vtColumns = nrColumns;
                ClearScreen();
            }
        }

        /// <summary>
        /// Clear VT.
        /// </summary>
        public void ClearScreen()
        {
            for (uint row = 0; row < vtRows; row++)
            {
                for (uint column = 0; column < vtColumns; column++)
                {
                    vt[row, column] = ' ';
                }
            }
            curRow = 0;
            curColumn = 0;
        }

        /// <summary>
        /// Scroll VT one line up and clear the bottom line.
        /// </summary>
        void ScrollUp()
        {
            for (uint row = 0; row < vtRows - 1; row++)
            {
                for (uint column = 0; column < vtColumns; column++)
                {
                    vt[row, column] = vt[row + 1, column];
                }
            }
            for (uint column = 0; column < vtColumns; column++)
            {
                vt[vtRows - 1, column] = ' ';
            }
        }

        /// <summary>
        /// Write one regular printable character to VC.
        /// </summary>
        void WritePrintableChar(char c)
        {
            vt[curRow, curColumn] = c;
            if (curColumn < vtColumns - 1)
            {
                curColumn++;
            }
            else if (curRow < vtRows - 1)
            {
                curRow++;
                curColumn = 0;
            }
            else
            {
                ScrollUp();
                curRow = vtRows - 1;
                curColumn = 0;
            }
        }

        /// <summary>
        /// Write one character to VT (regular or special).
        /// </summary>
        public void WriteVt(char c)
        {
            if (c >= 32 && c <= 127)
            {
                WritePrintableChar(c);
            }
            else
            {
                switch ((SpecialChar)c)
                {
                    /// Carriage return
                    case SpecialChar.CR:
                        curColumn = 0;
                        break;

                    /// Line feed
                    case SpecialChar.LF:
                        if (curRow < vtRows - 1)
                        {
                            curRow++;
                        }
                        else
                        {
                            ScrollUp();
                            curRow = vtRows - 1;
                        }
                        break;

                    /// Form feed (= clear screen) 
                    case SpecialChar.FF:
                        ClearScreen();
                        break;

                    /// Backspace
                    case SpecialChar.BS:
                        if (curColumn > 0)
                        {
                            vt[curRow, --curColumn] = ' ';
                        }
                        else if (curRow > 0)
                        {
                            curColumn = vtColumns - 1;
                            vt[--curRow, curColumn] = ' ';
                        }
                        break;

                    default:
                        break;
                }
            }
        }

        /// <summary>
        /// Write a string to VT.
        /// </summary>
        public void WriteVt(string txt)
        {
            if (txt != null)
            {
                for (int i = 0; i < txt.Length; i++)
                {
                    WriteVt(txt[i]);
                }
            }
        }
    }
}