feat: CSS selectors

css.lua

@@ -0,0 +1,176 @@
+local M = {}
+
+local function trim(str)
+	return str:match("^%s*(.-)%s*$")
+end
+
+
+local COMBINATORS = {
+	DESCENDANT = {},
+	DIRECT_DESCENDANT = {},
+	NEXT_SIBLING = {},
+	SUBSEQUENT_SIBLING = {},
+}
+M.COMBINATORS = COMBINATORS
+
+local COMBINATOR_CHARS = {
+	[">"] = COMBINATORS.DIRECT_DESCENDANT,
+	["+"] = COMBINATORS.NEXT_SIBLING,
+	["~"] = COMBINATORS.SUBSEQUENT_SIBLING
+}
+
+
+
+
+
+
+local function create_tokeniser(input)
+	local pos = 1
+	local len = #input
+
+	local function peek()
+		if pos > len then return nil end
+		return input:sub(pos, pos)
+	end
+
+	local function next()
+		local char = peek()
+		if char then pos = pos + 1 end
+		return char
+	end
+
+	local function read_identifier()
+		local result = ""
+		while pos <= len do
+			local char = peek()
+			if char and char:match("[%w-]") then
+				result = result .. next()
+			else
+				break
+			end
+		end
+		return result
+	end
+
+	return {
+		peek = peek,
+		next = next,
+		read_identifier = read_identifier,
+		pos = function() return pos end
+	}
+end
+
+
+local function parse_compound_selector( tokeniser )
+	local selector = {
+		tag_name = nil,
+		id = nil,
+		class = {},
+		attributes = {},
+	}
+
+	--local selectors = {}
+
+	-- Parse first part (type or universal)
+	local char = tokeniser.peek()
+	if char == "*" then
+		tokeniser.next()
+		--table.insert(selectors, {type = "universal"})
+		selector.tag_name = "*"
+	elseif char and char:match("[%w-]") then
+		local name = tokeniser.read_identifier()
+		if name ~= "" then
+			--table.insert(selectors, {type = "type", value = name})
+			selector.tag_name = name
+		end
+	end
+
+	-- Parse additional class or ID selectors
+	while true do
+		char = tokeniser.peek()
+		if not char then break end
+
+		if char == "." then
+			tokeniser.next() -- consume '.'
+			local name = tokeniser.read_identifier()
+			if name == "" then
+				error("Expected class name at position " .. tokeniser.pos())
+			end
+			--table.insert(selectors, {type = "class", value = name})
+			table.insert( selector.class, name )
+		elseif char == "#" then
+			tokeniser.next() -- consume '#'
+			local name = tokeniser.read_identifier()
+			if name == "" then
+				error("Expected id at position " .. tokeniser.pos())
+			end
+			--table.insert(selectors, {type = "id", value = name})
+			selector.id = name
+		else
+			break
+		end
+	end
+
+	return selector
+end
+
+
+local function parse_combinator( tokeniser )
+	-- Skip leading whitespace
+	while tokeniser.peek() and tokeniser.peek():match("%s") do
+		tokeniser.next()
+	end
+
+	local char = tokeniser.peek()
+	if not char then return nil end
+
+	if char == ">" or char == "+" or char == "~" then
+		tokeniser.next()
+		-- Skip trailing whitespace
+		while tokeniser.peek() and tokeniser.peek():match("%s") do
+			tokeniser.next()
+		end
+		return COMBINATOR_CHARS[char]
+	else
+		-- Make sure next character isn't an explicit combinator
+		char = tokeniser.peek()
+		if char and not (char == ">" or char == "+" or char == "~") then
+			return COMBINATORS.DESCENDANT
+		end
+	end
+
+	return nil
+end
+
+
+
+
+function M.parse( input )
+	input = trim( input )
+
+	local tokeniser = create_tokeniser( input )
+
+	local output = { selector = parse_compound_selector( tokeniser ) }
+	local current = output
+
+	-- Parse combinations of combinators and compound selectors
+	while true do
+		local combinator = parse_combinator( tokeniser )
+		if not combinator then
+			current.combinator = nil
+			current.next = nil
+			break
+		end
+
+		local next_selector = parse_compound_selector( tokeniser )
+		current.combinator = combinator
+		current.next = { selector = next_selector }
+		current = current.next
+	end
+
+	return output
+end
+
+
+return M
+