#include "elna/source/lexer.hpp"
#include <cassert>
#include <variant>

namespace elna::source
{
    using source_position = elna::source::position;
    using source_error = elna::source::error;

    token::value::value()
        : nil(nullptr)
    {
    }

    token::value::value(std::int32_t value)
        : number(value)
    {
    }

    token::value::value(const std::string& value)
        : identifier(value)
    {
    }

    token::value::~value()
    {
    }

    token::token(const type of, const std::string& value, const source_position position)
        : m_type(of), m_value(value), m_position(position)
    {
    }

    token::token(const type of, std::int32_t number, const source_position position)
        : m_type(of), m_value(number), m_position(position)
    {
    }

    token::token(type of, value&& value, const elna::source::position position)
        : m_type(of), m_position(position)
    {
        if (has_identifier())
        {
            new((void *) &m_value.identifier) std::string(std::move(value.identifier));
        }
        else if (is_numeric())
        {
            m_value.number = value.number;
        }
        else
        {
            m_value.nil = nullptr;
        }
    }

    token::token(const type of, source_position position)
        : m_type(of), m_position(position)
    {
    }

    token::token(const token& that)
    {
        *this = that;
    }

    token::token(token&& that)
    {
        *this = std::move(that);
    }

    token::~token()
    {
        if (has_identifier())
        {
            m_value.identifier.~basic_string();
        }
    }

    token& token::operator=(const token& that)
    {
        if (has_identifier())
        {
            m_value.identifier.~basic_string();
        }
        m_type = that.of();
        m_position = that.position();
        if (that.has_identifier())
        {
            new((void *) &m_value.identifier) std::string(that.identifier());
        }
        else if (that.is_numeric())
        {
            m_value.number = that.number();
        }
        else
        {
            m_value.nil = nullptr;
        }
        return *this;
    }

    token& token::operator=(token&& that)
    {
        if (has_identifier())
        {
            m_value.identifier.~basic_string();
        }
        m_type = that.of();
        m_position = that.position();
        if (that.has_identifier())
        {
            new((void *) &m_value.identifier) std::string(std::move(that.identifier()));
        }
        else if (that.is_numeric())
        {
            m_value.number = that.number();
        }
        else
        {
            m_value.nil = nullptr;
        }
        return *this;
    }

    token::type token::of() const noexcept
    {
        return m_type;
    }

    const std::string& token::identifier() const
    {
        if (!has_identifier())
        {
            throw std::bad_variant_access();
        }
        return m_value.identifier;
    }

    std::int32_t token::number() const
    {
        if (!is_numeric())
        {
            throw std::bad_variant_access();
        }
        return m_value.number;
    }

    const source_position& token::position() const noexcept
    {
        return m_position;
    }

    bool token::has_identifier() const noexcept
    {
        return of() == type::identifier
            || of() == type::term_operator
            || of() == type::factor_operator
            || of() == type::comparison_operator;
    }

    bool token::is_numeric() const noexcept
    {
        return of() == type::number
            || of() == type::boolean;
    }

    std::string token::to_string() const
    {
        switch (this->m_type)
        {
            case type::number:
                return "«number»";
            case type::boolean:
                return "«boolean»";
            case type::term_operator:
                return "«term_operator»";
            case type::let:
                return "«const»";
            case type::identifier:
                return "«identifier»";
            case type::equals:
                return "«=»";
            case type::var:
                return "«var»";
            case type::semicolon:
                return "«;»";
            case type::left_paren:
                return "«(»";
            case type::right_paren:
                return "«)»";
            case type::dot:
                return "«)»";
            case type::comma:
                return "«,»";
            case type::factor_operator:
                return "«*»";
            case type::eof:
                return "«EOF»";
            case type::begin:
                return "«begin»";
            case type::end:
                return "«end»";
            case type::assignment:
                return "«:=»";
            case type::colon:
                return "«:»";
            case type::when:
                return "«if»";
            case type::then:
                return "«then»";
            case type::loop:
                return "«while»";
            case type::_do:
                return "«do»";
            case type::procedure:
                return "«proc»";
            case type::comparison_operator:
                return "«comparison_operator»";
        };
        assert(false);
    }

    unexpected_character::unexpected_character(const std::string& character, const std::filesystem::path& path,
            const source::position position)
        : error(path, position), character(character)
    {
    }

    std::string unexpected_character::what() const
    {
        std::string ss{ "Unexpected character '" };

        ss.insert(ss.cend(), character.cbegin(), character.cend());
        ss.push_back('\'');

        return ss;
    }

    unexpected_token::unexpected_token(const token& token, const std::filesystem::path& path)
        : error(path, token.position()), m_token(token)
    {
    }

    std::string unexpected_token::what() const
    {
        return "Unexpected token " + m_token.to_string();
    }

    lexer::lexer(std::vector<token>&& tokens, const position last_position, const std::filesystem::path& path)
        : tokens(std::move(tokens)), iterator(this->tokens.cbegin()), eof(token(token::type::eof, last_position)),
        source_file(path)
    {
    }

    lexer& lexer::operator++()
    {
        ++iterator;
        return *this;
    }

    const token& lexer::operator*() const
    {
        return *iterator;
    }

    const token *lexer::operator->() const
    {
        return iterator.base();
    }

    const token& lexer::current() const noexcept
    {
        if (iterator == tokens.cend())
        {
            return this->eof;
        }
        return *iterator;
    }

    bool lexer::current(const token::type token_type) const noexcept
    {
        return current().of() == token_type;
    }

    void lexer::add_error(const token& expected)
    {
        m_errors.push_back(std::make_unique<unexpected_token>(expected, this->source_file));
    }

    std::optional<std::reference_wrapper<const token>> lexer::advance(const token::type token_type)
    {
        if (iterator != tokens.cend() && iterator->of() == token_type)
        {
            return std::make_optional<>(std::cref(*iterator++));
        }
        add_error(current());
        return std::optional<std::reference_wrapper<const token>>();
    }

    const token& lexer::look_ahead() const
    {
        auto tmp = iterator;
        ++tmp;
        if (iterator == tokens.cend() || tmp == tokens.cend())
        {
            return eof;
        }
        return *tmp;
    }

    bool lexer::look_ahead(const token::type token_type) const
    {
        return look_ahead().of() == token_type;
    }

    bool lexer::skip(const token::type token_type)
    {
        return advance(token_type).has_value();
    }

    const std::list<std::unique_ptr<error>>& lexer::errors() const noexcept
    {
        return m_errors;
    }
}