/**
 * lisp-compiler: Compiles LISP using LLVM.
 * Copyright (C) 2022  Clyne Sullivan
 *
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @file parser.hpp
 * @brief Source code parser to produce AST.
 */

#ifndef PARSER_HPP
#define PARSER_HPP

#include "ast.hpp"

#include <deque>
#include <optional>
#include <string>
#include <variant>

class Parser {
public:
    enum Error {
        ExpectedProcedureCallOpen,
        ExpectedIdentifier,
        ExpectedProcedureCallClose,
        ExpectedArgumentList,
        UnknownIdentifier,
        InvalidExpression,
        InvalidOperand,
        InvalidCondition,
        InvalidThenBranch,
        InvalidElseBranch,
        InvalidInitializer,
        InvalidAssignValue,
        InvalidArgumentName,
        InvalidLambdaBody
    };

    /**
     * Appends the given string to the end of the text queue.
     * Call parse() after adding text to produce the AST.
     */
    void addString(const std::string&);

    /**
     * Attempts to parse all text in the text queue, stopping if there is an
     * error.
     * @return An iterable collection of produced AST nodes.
     */
    std::deque<AST::Node *> parse();

    std::string describeErrors() noexcept;

    bool hasErrors() const noexcept {
        return !errors.empty();
    }

private:
    std::deque<char> text;
    std::deque<Error> errors;

    /**
     * Advances through the text queue until a non-whitespace character is
     * found.
     */
    void consumeWhitespace() noexcept;
    /**
     * Attempts to consume an identifier from the text queue.
     * @return A string containing the identifier if one is found.
     */
    std::optional<std::string> consumeIdentifier() noexcept;
    /**
     * Attempts to consume a literal number from the text queue.
     * @return The number if one is found: an integer if there is no decimal
     * point; otherwise, a double.
     * TODO Ensure and add noexcept.
     */
    std::optional<std::variant<int, double>> consumeLiteralNumber();

    AST::Node *parseExpression();
    AST::Node *parseProcedureCall();
    AST::Node *parseConditional();
    AST::Node *parseDefinition();
    AST::Node *parseAssignment();
    AST::Node *parseLambdaExpression();
};

#endif // PARSER_HPP