/********************************************************************++
Copyright (c) Microsoft Corporation.  All rights reserved.
--********************************************************************/

using System;
using Microsoft.PowerShell.Internal;

namespace Microsoft.PowerShell
{
    public partial class PSConsoleReadLine
    {
        private class DisplayBlockBase
        {
            internal PSConsoleReadLine Singleton;
            internal int Top;

            protected void MoveCursorDown(int cnt)
            {
                IConsole console = Singleton._console;
                while (cnt-- > 0)
                {
                    console.Write("\n");
                }
            }

            protected void AdjustForActualScroll(int scrollCnt)
            {
                if (scrollCnt > 0)
                {
                    Top -= scrollCnt;
                    _singleton._initialY -= scrollCnt;
                    _savedCursorTop -= scrollCnt;
                }
            }

            protected void AdjustForPossibleScroll(int cnt)
            {
                IConsole console = Singleton._console;
                var scrollCnt = console.CursorTop + cnt + 1 - console.BufferHeight;
                if (scrollCnt > 0)
                {
                    Top -= scrollCnt;
                    _singleton._initialY -= scrollCnt;
                    _savedCursorTop -= scrollCnt;
                }
            }

            protected void MoveCursorToStartDrawingPosition(IConsole console)
            {
                // Calculate the coord to place the cursor at the end of current input.
                Point bufferEndPoint = Singleton.ConvertOffsetToPoint(Singleton._buffer.Length);
                // Top must be initialized before any possible adjustment by 'AdjustForPossibleScroll' or 'AdjustForActualScroll',
                // otherwise its value would be corrupted and cause rendering issue.
                Top = bufferEndPoint.Y + 1;

                if (bufferEndPoint.Y == console.BufferHeight)
                {
                    // The input happens to end at the very last cell of the current buffer, so 'bufferEndPoint' is pointing to
                    // the first cell at one line below the current buffer, and thus we need to scroll up the buffer.
                    console.SetCursorPosition(console.BufferWidth - 1, console.BufferHeight - 1);
                    // We scroll the buffer by 2 lines here, so the cursor is placed at the start of the first line after 'bufferEndPoint'.
                    MoveCursorDown(2);
                    bufferEndPoint.Y -= 2;
                    AdjustForActualScroll(2);
                }
                else
                {
                    // Move the cursor to the end of our input.
                    console.SetCursorPosition(bufferEndPoint.X, bufferEndPoint.Y);
                    // Move cursor to the start of the first line after our input (after 'bufferEndPoint').
                    AdjustForPossibleScroll(1);
                    MoveCursorDown(1);
                }
            }

            private int _savedCursorLeft;
            private int _savedCursorTop;

            public void SaveCursor()
            {
                IConsole console = Singleton._console;
                _savedCursorLeft = console.CursorLeft;
                _savedCursorTop = console.CursorTop;
            }

            public void RestoreCursor() => Singleton._console.SetCursorPosition(_savedCursorLeft, _savedCursorTop);
        }
    }
}