Scintilla's CellBuffer buffer's data management

cellbuffer_insert.c

void CellBuffer::BasicInsertString(int position, const char *s, int insertLength) {
	if (insertLength == 0)
		return;
	PLATFORM_ASSERT(insertLength > 0);

	substance.InsertFromArray(position, s, 0, insertLength);
	style.InsertValue(position, insertLength, 0);

	int lineInsert = lv.LineFromPosition(position) + 1;
	bool atLineStart = lv.LineStart(lineInsert-1) == position;
	// Point all the lines after the insertion point further along in the buffer
	lv.InsertText(lineInsert-1, insertLength);
	char chPrev = substance.ValueAt(position - 1);
	char chAfter = substance.ValueAt(position + insertLength);
	if (chPrev == '\r' && chAfter == '\n') {
		// Splitting up a crlf pair at position
		InsertLine(lineInsert, position, false);
		lineInsert++;
	}
	char ch = ' ';
	for (int i = 0; i < insertLength; i++) {
		ch = s[i];
		if (ch == '\r') {
			InsertLine(lineInsert, (position + i) + 1, atLineStart);
			lineInsert++;
		} else if (ch == '\n') {
			if (chPrev == '\r') {
				// Patch up what was end of line
				lv.SetLineStart(lineInsert - 1, (position + i) + 1);
			} else {
				InsertLine(lineInsert, (position + i) + 1, atLineStart);
				lineInsert++;
			}
		}
		chPrev = ch;
	}
	// Joining two lines where last insertion is cr and following substance starts with lf
	if (chAfter == '\n') {
		if (ch == '\r') {
			// End of line already in buffer so drop the newly created one
			RemoveLine(lineInsert - 1);
		}
	}
}