/// <summary>
/// Get a new page segment for this length content using fixed index
/// </summary>
private BufferSlice InternalInsert(ushort bytesLength, ref byte index)
{
var isNewInsert = index == byte.MaxValue;
ENSURE(_buffer.ShareCounter == BUFFER_WRITABLE, "page must be writable to support changes");
ENSURE(bytesLength > 0, "must insert more than 0 bytes");
ENSURE(this.FreeBytes >= bytesLength + (isNewInsert ? SLOT_SIZE : 0), "length must be always lower than current free space");
ENSURE(this.ItemsCount < byte.MaxValue, "page full");
ENSURE(this.FreeBytes >= this.FragmentedBytes, "fragmented bytes must be at most free bytes");
if (!(this.FreeBytes >= bytesLength + (isNewInsert ? SLOT_SIZE : 0)))
{
throw LiteException.InvalidFreeSpacePage(this.PageID, this.FreeBytes, bytesLength + (isNewInsert ? SLOT_SIZE : 0));
}
// calculate how many continuous bytes are avaiable in this page
var continuousBlocks = this.FreeBytes - this.FragmentedBytes - (isNewInsert ? SLOT_SIZE : 0);
ENSURE(continuousBlocks == PAGE_SIZE - this.NextFreePosition - this.FooterSize - (isNewInsert ? SLOT_SIZE : 0), "continuousBlock must be same as from NextFreePosition");
// if continuous blocks are not enough for this data, must run page defrag
if (bytesLength > continuousBlocks)
{
this.Defrag();
}
// if index is new insert segment, must request for new Index
if (index == byte.MaxValue)
{
// get new free index must run after defrag
index = this.GetFreeIndex();
}
if (index > this.HighestIndex || this.HighestIndex == byte.MaxValue)
{
ENSURE(index == (byte)(this.HighestIndex + 1), "new index must be next highest index");
this.HighestIndex = index;
}
// get segment addresses
var positionAddr = CalcPositionAddr(index);
var lengthAddr = CalcLengthAddr(index);
ENSURE(_buffer.ReadUInt16(positionAddr) == 0, "slot position must be empty before use");
ENSURE(_buffer.ReadUInt16(lengthAddr) == 0, "slot length must be empty before use");
// get next free position in page
var position = this.NextFreePosition;
// write this page position in my position address
_buffer.Write(position, positionAddr);
// write page segment length in my length address
_buffer.Write(bytesLength, lengthAddr);
// update next free position and counters
this.ItemsCount++;
this.UsedBytes += bytesLength;
this.NextFreePosition += bytesLength;
this.IsDirty = true;
ENSURE(position + bytesLength <= (PAGE_SIZE - (this.HighestIndex + 1) * SLOT_SIZE), "new buffer slice could not override footer area");
// create page segment based new inserted segment
return(_buffer.Slice(position, bytesLength));
}