path: root/libs/litehtml/src/css_parser.cpp

#include "html.h"
#include "css_parser.h"

namespace litehtml
{

// https://www.w3.org/TR/css-syntax-3/#css-filter-code-points
void filter_code_points(string& input)
{
	const char* xFFFD = "\xEF\xBF\xBD";

	size_t null_count = std::count(input.begin(), input.end(), 0);

	string result(input.size() + 2 * null_count, 0);

	for (int i = 0, j = 0; i < (int)input.size(); i++)
	{
		switch (input[i])
		{
		case '\r':
			result[j++] = '\n';
			if (i + 1 < (int)input.size() && input[i + 1] == '\n') i++; // skip \n after \r
			break;
		case '\f':
			result[j++] = '\n';
			break;
		case 0:
			memcpy(&result[j], xFFFD, 3);
			j += 3;
			break;
		default:
			result[j++] = input[i];
		}
	}

	// trim trailing NULs
	result.resize(strlen(result.c_str()));
	input = result;
}

void remove_whitespace(css_token_vector& tokens, keep_whitespace_fn keep_whitespace)
{
	for (int i = 0; i < (int)tokens.size(); i++)
	{
		auto& tok = tokens[i];
		if (tok.type == ' ')
		{
			const auto& left = i > 0 ? tokens[i - 1] : css_token();
			const auto& right = at(tokens, i + 1);
			bool keep = keep_whitespace && keep_whitespace(left, right);
			if (!keep) remove(tokens, i), i--;
		}
		else if (tok.is_component_value())
			remove_whitespace(tok.value, keep_whitespace);
	}
}

void componentize(css_token_vector& tokens)
{
	css_parser parser(tokens);
	css_token_vector result;
	while (true)
	{
		css_token tok = parser.consume_component_value();
		if (tok.type == EOF) break;
		result.push_back(tok);
	}
	tokens = result;
}

// https://www.w3.org/TR/css-syntax-3/#normalize-into-a-token-stream
template<>
css_token_vector normalize(css_token_vector input, int options, keep_whitespace_fn keep_whitespace)
{
	if (options & f_componentize) componentize(input);
	if (options & f_remove_whitespace) remove_whitespace(input, keep_whitespace);
	return input;
}
template<>
css_token_vector normalize(string input, int options, keep_whitespace_fn keep_whitespace)
{
	filter_code_points(input);
	auto tokens = tokenize(input);
	return normalize(tokens, options, keep_whitespace);
}

// https://www.w3.org/TR/css-syntax-3/#parse-stylesheet
// I don't create a stylesheet because its only perpose is to pass a list of rules to 
// parse_css_stylesheet. I just return the list of rules directly instead.
raw_rule::vector css_parser::parse_stylesheet(const string& input, bool top_level)
{
	// 1. If input is a byte stream for stylesheet, decode bytes from input, and set input to the result.
	// not implemented, utf-8 is always assumed
	string str = decode(input, encoding::utf_8); // decoding potentially broken UTF-8 into valid UTF-8
	
	// 2. Normalize input, and set input to the result.
	auto tokens = normalize(str);
	
	return parse_stylesheet(tokens, top_level);
}
raw_rule::vector css_parser::parse_stylesheet(const css_token_vector& input, bool top_level)
{
	// 3. Create a new stylesheet, with its location set to location.
	// 4. Consume a list of rules from input, with the top-level flag set, and set the stylesheet’s value to the result.
	// 5. Return the stylesheet.
	return css_parser(input).consume_list_of_rules(top_level);
}

// https://www.w3.org/TR/css-syntax-3/#consume-the-next-input-token
css_token css_parser::next_token()
{
	if (m_index == (int)m_tokens.size())
		return css_token_type(EOF);
	else
		return m_tokens[m_index++];
}

css_token css_parser::peek_token()
{
	if (m_index == (int)m_tokens.size())
		return css_token_type(EOF);
	else
		return m_tokens[m_index];
}

// https://www.w3.org/TR/css-syntax-3/#consume-list-of-rules
raw_rule::vector css_parser::consume_list_of_rules(bool top_level)
{
	raw_rule::vector rules;
	raw_rule::ptr rule;

	while (true)
	{
		// Repeatedly consume the next input token:
		css_token token = next_token();

		switch (token.type)
		{
		case WHITESPACE:
			break; // Do nothing.

		case EOF:
			return rules; // Return the list of rules.

		case CDO:
		case CDC:
			// If the top-level flag is set, do nothing.
			if (top_level) break;

			// Otherwise, reconsume the current input token. Consume a qualified rule. 
			// If anything is returned, append it to the list of rules.
			m_index--;
			rule = consume_qualified_rule();
			if (rule) rules.push_back(rule);
			break;

		case AT_KEYWORD:
			// Reconsume the current input token. Consume an at-rule, and append the returned value to the list of rules.
			m_index--;
			rule = consume_at_rule();
			if (rule) rules.push_back(rule);
			break;

		default:
			// Reconsume the current input token. Consume a qualified rule. If anything is returned, append it to the list of rules.
			m_index--;
			rule = consume_qualified_rule();
			if (rule) rules.push_back(rule);
			break;
		}
	}
}

// https://www.w3.org/TR/css-syntax-3/#consume-qualified-rule
raw_rule::ptr css_parser::consume_qualified_rule()
{
	// Create a new qualified rule with its prelude initially set to an empty list, and its value initially set to nothing.
	raw_rule::ptr rule = make_shared<raw_rule>(raw_rule::qualified);

	while (true)
	{
		// Repeatedly consume the next input token:
		css_token token = next_token();

		switch (token.type)
		{
		case EOF:
			// This is a parse error. Return nothing.
			css_parse_error("eof in qualified rule");
			return nullptr;
		case '{':
			// Consume a simple block and assign it to the qualified rule’s block. Return the qualified rule.
			rule->block = consume_simple_block('{');
			return rule;
		case CURLY_BLOCK:
			// Assign the block to the qualified rule’s block. Return the qualified rule.
			rule->block = token;
			return rule;
		default:
			// Reconsume the current input token. Consume a component value. Append the returned value to the qualified rule’s prelude.
			m_index--;
			css_token value = consume_component_value();
			rule->prelude.push_back(value);
		}
	}
}

// https://www.w3.org/TR/css-syntax-3/#consume-at-rule
raw_rule::ptr css_parser::consume_at_rule()
{
	// Consume the next input token. Create a new at-rule with its name set to the value of the current input token, 
	// its prelude initially set to an empty list, and its value initially set to nothing.
	css_token token = next_token();
	raw_rule::ptr rule = make_shared<raw_rule>(raw_rule::at, token.str);

	while (true)
	{
		// Repeatedly consume the next input token:
		token = next_token();

		switch (token.type)
		{
		case ';':
			return rule;
		case EOF:
			// This is a parse error. Return the at-rule.
			css_parse_error("eof in at-rule");
			return rule;
		case '{':
			// Consume a simple block and assign it to the at-rule’s block. Return the at-rule.
			rule->block = consume_simple_block('{');
			return rule;
		case CURLY_BLOCK:
			// Assign the block to the at-rule’s block. Return the at-rule.
			rule->block = token;
			return rule;
		default:
			// Reconsume the current input token. Consume a component value. Append the returned value to the at-rule’s prelude.
			m_index--;
			css_token value = consume_component_value();
			rule->prelude.push_back(value);
		}
	}
}

char mirror(char c);

// https://www.w3.org/TR/css-syntax-3/#consume-simple-block
css_token css_parser::consume_simple_block(char opening_bracket)
{
	// Create a simple block with its associated token set to the current input token and with its value initially set to an empty list.
	auto block_type = css_token_type(-100 - opening_bracket); // see css_token_type
	css_token block(block_type);
	
	char closing_bracket = mirror(opening_bracket);

	while (true)
	{
		// Repeatedly consume the next input token and process it as follows:
		css_token token = next_token();

		if (token.type == closing_bracket)
		{
			return block;
		}
		else if (token.type == EOF)
		{
			css_parse_error("eof in simple block");
			return block;
		}
		else
		{
			// Reconsume the current input token. Consume a component value and append it to the value of the block.
			m_index--;
			css_token val = consume_component_value();
			block.value.push_back(val);
		}
	}
}

// https://www.w3.org/TR/css-syntax-3/#consume-component-value
css_token css_parser::consume_component_value()
{
	// Consume the next input token.
	css_token token = next_token();

	switch (token.type)
	{
		// If the current input token is a <{-token>, <[-token>, or <(-token>, consume a simple block and return it.
	case '{': case '[': case '(':
		return consume_simple_block((char)token.ch);
		
		// Otherwise, if the current input token is a <function-token>, consume a function and return it.
	case FUNCTION:
		return consume_function(token.name);
		
		// Otherwise, return the current input token.
	default:
		return token;
	}
}

// https://www.w3.org/TR/css-syntax-3/#consume-function
css_token css_parser::consume_function(const string& name)
{
	// Create a function with its name equal to the value of the current input token and with its value initially set to an empty list.
	css_token function(CV_FUNCTION, name);

	while (true)
	{
		// Repeatedly consume the next input token and process it as follows:
		css_token token = next_token();

		switch (token.type)
		{
		case ')':
			return function;

		case EOF:
			css_parse_error("eof in function");
			return function;

		default:
			// Reconsume the current input token. Consume a component value and append the returned value to the function’s value.
			m_index--;
			css_token val = consume_component_value();
			function.value.push_back(val);
		}
	}
}


///////////////////////////////////////////////////////////////////////////////////////////////////////////////////


void trim_whitespace(css_token_vector& tokens)
{
	while (at(tokens, 0).type == ' ')  remove(tokens, 0);
	while (at(tokens, -1).type == ' ') remove(tokens, -1);
}

// https://www.w3.org/TR/css-syntax-3/#consume-declaration
// next token is guaranteed to be IDENT
raw_declaration css_parser::consume_declaration()
{
	// Consume the next input token. Create a new declaration with its name set to the value of 
	// the current input token and its value initially set to an empty list.
	css_token token = next_token();
	raw_declaration decl = {token.name};
	auto& value = decl.value;

	// 1. While the next input token is a <whitespace-token>, consume the next input token.
	while (peek_token().type == ' ') next_token();

	// 2. If the next input token is anything other than a <colon-token>, this is a parse error. Return nothing.
	if (peek_token().ch != ':')
	{
		css_parse_error("consume_declaration: ':' not found");
		return {};
	}
	//    Otherwise, consume the next input token.
	next_token();

	// 3. While the next input token is a <whitespace-token>, consume the next input token.
	while (peek_token().type == ' ') next_token();

	// 4. As long as the next input token is anything other than an <EOF-token>, 
	//    consume a component value and append it to the declaration’s value.
	while (peek_token().type != EOF)
		value.push_back(consume_component_value());

	// 5. If the last two non-<whitespace-token>s in the declaration’s value are a <delim-token> with the value "!" 
	//    followed by an <ident-token> with a value that is an ASCII case-insensitive match for "important", 
	//    remove them from the declaration’s value and set the declaration’s important flag to true.

	trim_whitespace(value); // deviation from standard: removing leading whitespace as well

	if (at(value, -1).ident() == "important" && at(value, -2).ch == '!')
	{
		remove(value, -2, 2);
		decl.important = true;
	}

	// 6. While the last token in the declaration’s value is a <whitespace-token>, remove that token.
	trim_whitespace(value);

	// 7. Return the declaration.
	return decl;
}

// https://www.w3.org/TR/css-syntax-3/#consume-style-block
void css_parser::consume_style_block_contents(/*out*/ raw_declaration::vector& decls, /*out*/ raw_rule::vector& rules)
{
	while (true)
	{
		// Repeatedly consume the next input token:
		css_token token = next_token();

		switch (token.type)
		{
		case WHITESPACE:
		case ';':
			break; // Do nothing.

		case EOF:
			// "Extend decls with rules, then return decls."
			// NOTE: I just return decls and rules separately
			return;

		case AT_KEYWORD: {
			// Reconsume the current input token. Consume an at-rule, and append the result to rules.
			m_index--;
			auto rule = consume_at_rule();
			if (rule) rules.push_back(rule);
			break;
		}
		case IDENT: {
			// Initialize a temporary list initially filled with the current input token.
			css_token_vector temp = { token };
			// As long as the next input token is anything other than a <semicolon-token> or <EOF-token>, 
			// consume a component value and append it to the temporary list.
			while (!is_one_of(peek_token().type, ';', EOF))
				temp.push_back(consume_component_value());

			css_parser parser(temp);
			// Consume a declaration from the temporary list.
			auto decl = parser.consume_declaration();
			// If anything was returned, append it to decls.
			if (decl) decls.push_back(decl);
			break;
		}
		case '&': {
			// Reconsume the current input token. Consume a qualified rule. If anything was returned, append it to rules.
			m_index--;
			auto rule = consume_qualified_rule();
			if (rule) rules.push_back(rule);
			break;
		}
		default:
			// This is a parse error. Reconsume the current input token. As long as the next input token is 
			// anything other than a <;> or <EOF>, consume a component value and throw away the returned value.
			css_parse_error("unexpected token in a style block");
			m_index--;
			while (!is_one_of(peek_token().type, ';', EOF))
				consume_component_value();
			break;
		}
	}
}


// https://www.w3.org/TR/css-syntax-3/#parse-comma-separated-list-of-component-values
// Note: result is never empty. If input is empty result is {{}}.
vector<css_token_vector> parse_comma_separated_list(const css_token_vector& tokens)
{
	vector<css_token_vector> result;

	css_token_vector list;
	for (auto& tok : tokens)
	{
		if (tok.type == ',')  // Note: EOF token is not stored in arrays
		{
			result.push_back(list);
			list.clear();
			continue;
		}
		list.push_back(tok);
	}
	result.push_back(list);

	return result;
}

// https://drafts.csswg.org/css-syntax-3/#typedef-any-value
// assumes that tokens have been componentized
bool is_any_value(const css_token_vector& tokens)
{
	if (tokens.empty()) return false;
	for (auto& tok : tokens)
	{
		if (is_one_of(tok.type, BAD_STRING, BAD_URL, ')', ']', '}'))
			return false;
		else if (tok.is_component_value() && !is_any_value(tok.value))
			return false;
	}
	return true;
}

// https://drafts.csswg.org/css-syntax-3/#typedef-declaration-value
// assumes that tokens have been componentized
bool is_declaration_value(const css_token_vector& tokens, int index)
{
	if (index >= (int)tokens.size()) return false;
	for (int i = index; i < (int)tokens.size(); i++)
	{
		auto& tok = tokens[i];
		if (is_one_of(tok.type, BAD_STRING, BAD_URL, ')', ']', '}', ';', '!'))
			return false;
		// Note: ';' '!' inside component values are allowed, so using is_any_value here.
		else if (tok.is_component_value() && !is_any_value(tok.value))
			return false;
	}
	return true;
}

// Note: it is possible to have several whitespace tokens in a row: "  /**/  /**/   "
bool skip_whitespace(const css_token_vector& tokens, int& index)
{
	int start = index;
	while (at(tokens, index).type == ' ') index++;
	return index != start;
}

} // namespace litehtml