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

namespace elna::source
{
    using source_position = elna::source::position;
    using source_error = elna::source::error;
    using source_result = elna::source::result<std::vector<token>>;

    std::pair<text_iterator, text_iterator> text_iterators(const std::string &buffer)
    {
        return std::make_pair<>(text_iterator(std::cbegin(buffer)),
                text_iterator(std::cend(buffer), position{0, 0}));
    }

    text_iterator::text_iterator(std::string::const_iterator buffer,
            const source_position start_position)
        : m_buffer(buffer), m_position(start_position)
    {
    }

    const source_position& text_iterator::position() const noexcept
    {
        return this->m_position;
    }

    text_iterator::reference text_iterator::operator*() const noexcept
    {
        return *m_buffer;
    }

    text_iterator::pointer text_iterator::operator->() const noexcept
    {
        return m_buffer.base();
    }

    text_iterator& text_iterator::operator++()
    {
        if (*this->m_buffer == '\n')
        {
            this->m_position.column = 1;
            ++this->m_position.line;
        }
        else
        {
            ++this->m_position.column;
        }
        std::advance(this->m_buffer, 1);

        return *this;
    }

    text_iterator& text_iterator::operator++(int)
    {
        auto tmp = *this;
        ++(*this);
        return *this;
    }

    bool text_iterator::operator==(const text_iterator& that) const noexcept
    {
        return this->m_buffer == that.m_buffer;
    }

    bool text_iterator::operator!=(const text_iterator& that) const noexcept
    {
        return !(*this == that);
    }

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

    token::token(const token& that)
        : m_type(that.of()), m_position(that.position())
    {
        *this = that;
    }

    token::token(token&& that)
        : m_type(that.of()), m_position(that.position())
    {
        *this = std::move(that);
    }

    token::~token()
    {
        if (m_type == type::identifier || m_type == type::term_operator || m_type == type::factor_operator)
        {
            m_value.identifier.~basic_string();
        }
    }

    token& token::operator=(const token& that)
    {
        m_type = that.of();
        m_position = that.position();
        if (that.has_identifier())
        {
            m_value.identifier = that.identifier();
        }
        else if (that.of() == type::number)
        {
            m_value.number = that.number();
        }
        else
        {
            m_value.nil = nullptr;
        }
        return *this;
    }

    token& token::operator=(token&& that)
    {
        m_type = that.of();
        m_position = that.position();
        if (that.has_identifier())
        {
            m_value.identifier = std::move(that.identifier());
        }
        else if (that.of() == type::number)
        {
            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 (of() != type::number)
        {
            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;
    }

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

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

        ss << character << "'";

        return ss.str();
    }

    source_result lex(const std::string& buffer)
    {
        std::vector<token> tokens;
        auto [iterator, text_end] = text_iterators(buffer);

        while (iterator != text_end)
        {
            if (*iterator == ' ' || *iterator == '\n')
            {
            }
            else if (std::isdigit(*iterator))
            {
                tokens.emplace_back(
                        token::type::number,
                        static_cast<std::int32_t>(*iterator - '0'),
                        iterator.position()
                );
            }
            else if (*iterator == '=')
            {
                tokens.emplace_back(token::type::equals, iterator.position());
            }
            else if (*iterator == '(')
            {
                tokens.emplace_back(token::type::left_paren, iterator.position());
            }
            else if (*iterator == ')')
            {
                tokens.emplace_back(token::type::right_paren, iterator.position());
            }
            else if (*iterator == ';')
            {
                tokens.emplace_back(token::type::semicolon, iterator.position());
            }
            else if (*iterator == ',')
            {
                tokens.emplace_back(token::type::comma, iterator.position());
            }
            else if (*iterator == '!')
            {
                tokens.emplace_back(token::type::bang, iterator.position());
            }
            else if (*iterator == '.')
            {
                tokens.emplace_back(token::type::dot, iterator.position());
            }
            else if (std::isalpha(*iterator))
            {
                std::string word;
                auto i = iterator;
                while (i != text_end && std::isalpha(*i))
                {
                    word.push_back(*i);
                    ++i;
                }
                if (word == "const")
                {
                    tokens.emplace_back(token::type::let, iterator.position());
                }
                else if (word == "var")
                {
                    tokens.emplace_back(token::type::var, iterator.position());
                }
                else
                {
                    tokens.emplace_back(token::type::identifier, word.c_str(), iterator.position());
                }
                iterator = i;
                continue;
            }
            else if (*iterator == '+' || *iterator == '-')
            {
                std::string _operator{ *iterator };

                tokens.emplace_back(token::type::term_operator, _operator.c_str(), iterator.position());
            }
            else if (*iterator == '*' || *iterator == '/')
            {
                std::string _operator{ *iterator };

                tokens.emplace_back(token::type::factor_operator, _operator.c_str(), iterator.position());
            }
            else
            {
                return source_result(unexpected_character{ std::string{ *iterator }, iterator.position() });
            }
            ++iterator;
        }
        return source_result(std::move(tokens));
    }
}