# Special cases of String where all the characters are ASCII-based
#
# Optimizes access operations to O(1) complexity.
private class ASCIIFlatString
	super FlatString

	init full_data(items: CString, byte_length, from, length: Int) do
		self._items = items
		self._length = length
		self._byte_length = byte_length
		_first_byte = from
		_bytepos = from
	end

	redef fun [](idx) do
		assert idx < _byte_length and idx >= 0
		return _items[idx + _first_byte].code_point
	end

	redef fun substring(from, count) do
		var ln = _length
		if count <= 0 then return ""
		if (count + from) > ln then count = ln - from
		if count <= 0 then return ""
		if from < 0 then
			count += from
			if count <= 0 then return ""
			from = 0
		end
		return new ASCIIFlatString.full_data(_items, count, from + _first_byte, count)
	end

	redef fun reversed do
		var b = new FlatBuffer.with_capacity(_byte_length + 1)
		var i = _length - 1
		while i >= 0 do
			b.add self[i]
			i -= 1
		end
		var s = b.to_s.as(FlatString)
		return s
	end

	redef fun char_to_byte_index(index) do return index + _first_byte

	redef fun substring_impl(from, count, end_index) do
		return new ASCIIFlatString.full_data(_items, count, from + _first_byte, count)
	end

	redef fun fetch_char_at(i) do return _items[i + _first_byte].code_point
end