using System;

namespace Microsoft.PowerShell
{
    public partial class PSConsoleReadLine
    {
        /// <summary>
        /// Moves the cursor to the beginning of the first logical line
        /// of a multi-line buffer.
        /// </summary>
        /// <param name="key" />
        /// <param name="arg" />
        public void MoveToFirstLine(ConsoleKeyInfo? key = null, object arg = null)
        {
            if (!LineIsMultiLine())
            {
                Ding(key, arg);
                return;
            }

            var currentLine =  GetLogicalLineNumber(); 

            var pos = ConvertOffsetToPoint(_singleton._current);

            pos.Y -= currentLine -1;

            var newCurrent = ConvertLineAndColumnToOffset(pos);
            var position = GetBeginningOfLinePos(newCurrent);

            _singleton.MoveCursor(position);
        }

        /// <summary>
        /// Moves the cursor to the beginning of the last logical logical line.
        /// of a multi-line buffer.
        /// </summary>
        /// <param name="key" />
        /// <param name="arg" />
        public void MoveToLastLine(ConsoleKeyInfo? key = null, object arg = null)
        {
            var count = GetLogicalLineCount();
            if (count == 1)
            {
                Ding(key, arg);
                return;
            }

            var currentLine = GetLogicalLineNumber();

            var pos = ConvertOffsetToPoint(_singleton._current);

            pos.Y += (count - currentLine);

            var newCurrent = ConvertLineAndColumnToOffset(pos);
            var position = GetBeginningOfLinePos(newCurrent);

            _singleton.MoveCursor(position);
        }

        private void ViMoveToLine(int lineOffset)
        {
            // When moving up or down in a buffer in VI mode
            // the cursor wants to be positioned at a desired column number, which is:
            // - either a specified column number, the 0-based offset from the start of the logical line.
            // - or the end of the line
            //
            // Only one of those desired position is available at any given time.
            //
            // If the desired column number is specified, the cursor will be positioned at
            // the specified offset in the target logical line, or at the end of the line as appropriate.
            // The fact that a logical line is shorter than the desired column number *does not*
            // change its value. If a subsequent move to another logical line is performed, the
            // desired column number will take effect.
            //
            // If the desired column number is the end of the line, the cursor will be positioned at
            // the end of the target logical line.

            const int endOfLine = int.MaxValue;

            _moveToLineCommandCount += 1;

            // if this is the first "move to line" command
            // record the desired column number from the current position
            // on the logical line

            if (_moveToLineCommandCount == 1 && _moveToLineDesiredColumn == -1)
            {
                var startOfLine = GetBeginningOfLinePos(_current);
                _moveToLineDesiredColumn = _current - startOfLine;
            }

            // Nothing needs to be done when:
            //  - actually not moving the line, or
            //  - moving the line down when it's at the end of the last logical line.
            if (lineOffset == 0 || (lineOffset > 0 && _current == _buffer.Length))
            {
                return;
            }

            int targetLineOffset;

            var currentLineIndex = _singleton.GetLogicalLineNumber() - 1;

            if (lineOffset < 0)
            {
                targetLineOffset = Math.Max(0, currentLineIndex + lineOffset);
            }
            else
            {
                var lastLineIndex = _singleton.GetLogicalLineCount() - 1;
                targetLineOffset = Math.Min(lastLineIndex, currentLineIndex + lineOffset);
            }

            var startOfTargetLinePos = GetBeginningOfNthLinePos(targetLineOffset);
            var endOfTargetLinePos = GetEndOfLogicalLinePos(startOfTargetLinePos);

            var newCurrent = _moveToLineDesiredColumn == endOfLine
                ? endOfTargetLinePos
                : Math.Min(startOfTargetLinePos + _moveToLineDesiredColumn, endOfTargetLinePos);

            MoveCursor(newCurrent);
        }
    }
}