pgLab/core/SqlParser.h

#ifndef SQLPARSER_H
#define SQLPARSER_H

#include "SqlLexer.h"
#include "SqlAstNode.h"
#include <memory>
#include <optional>

enum class Keyword {
	NotAKeyword,
	As,
	By,
	Delete,
	From,
	Group,
	Insert,
	Order,
	Select,
	Update,
	Where,

};

namespace SqlAst {

	class Node;
	class Select;
	class SelectList;

}
// The parsing works by calling functions that know either a global part
// or a smaller specific part and is thus recursive. At certain points a function parsing something specific
// will reach a point where it is in a valid terminal state and it encounters something that cannot be a continuation
// of what it is parsing and thus returns succesfully or it is in a non terminal state and encounters something unexpected
// In both cases it will return hoping that one of the functions above can continue (and recover from the error if needed)

class SqlParser
{
public:
	explicit SqlParser(SqlLexer &lexer);

	std::shared_ptr<SqlAst::Node> parse();

	/** Checks to see if the next token is the expected keyword.
	 *
	 * If it is the token is consumed and the function returns true.
	 * Otherwise false is returned
	 */
	std::optional<SqlToken> expectKeyword(Keyword kw);
	std::optional<SqlToken> expectSymbol();
	std::optional<SqlToken> expectToken(BasicTokenType tt);

	/** If the next token is Keyword kw consume it otherwise do nothing.
	 * In some cases the return value is unimportant as the keyword is completely optional
	 * in other cases the optional keywords presence might force the next token to be something specific
	 *
	 * \return true if the token was found
	 */
	bool consumeOptionalKeyword(Keyword kw);
private:

	//using TokenStack = std::stack<SqlToken>;

	//TokenStack tokenStack;

	SqlLexer &lexer;

	//bool try_reduce(SqkToken token);


};


#endif // SQLPARSER_H