#include "elna/source/parser.hpp"
#include <stdexcept>

namespace elna::source
{
    /**
     * AST node.
     */
    void node::accept(parser_visitor *)
    {
    }

    declaration::declaration(const std::string& identifier)
        : m_identifier(identifier)
    {
    }

    std::string& declaration::identifier() noexcept
    {
        return m_identifier;
    }

    definition::definition(const std::string& identifier, std::unique_ptr<integer_literal>&& body)
        : m_identifier(std::move(identifier)), m_body(std::move(body))
    {
    }

    void declaration::accept(parser_visitor *visitor)
    {
        visitor->visit(this);
    }

    void definition::accept(parser_visitor *visitor)
    {
        visitor->visit(this);
    }

    std::string& definition::identifier() noexcept
    {
        return m_identifier;
    }

    integer_literal& definition::body()
    {
        return *m_body;
    }

    block::block(std::vector<std::unique_ptr<definition>>&& definitions,
            std::vector<std::unique_ptr<declaration>>&& declarations,
            std::unique_ptr<statement>&& body)
        : m_definitions(std::move(definitions)), m_declarations(std::move(declarations)), m_body(std::move(body))
    {
    }

    void block::accept(parser_visitor *visitor)
    {
        visitor->visit(this);
    }

    statement& block::body()
    {
        return *m_body;
    }

    std::vector<std::unique_ptr<definition>>& block::definitions() noexcept
    {
        return m_definitions;
    }

    std::vector<std::unique_ptr<declaration>>& block::declarations() noexcept
    {
        return m_declarations;
    }

    integer_literal::integer_literal(const std::int32_t value)
        : m_number(value)
    {
    }

    void integer_literal::accept(parser_visitor *visitor)
    {
        visitor->visit(this);
    }

    std::int32_t integer_literal::number() const noexcept
    {
        return m_number;
    }

    variable_expression::variable_expression(const std::string& name)
        : m_name(name)
    {
    }

    void variable_expression::accept(parser_visitor *visitor)
    {
        visitor->visit(this);
    }

    const std::string& variable_expression::name() const noexcept
    {
        return m_name;
    }

    binary_expression::binary_expression(std::unique_ptr<expression>&& lhs,
            std::unique_ptr<expression>&& rhs, const unsigned char operation)
        : m_lhs(std::move(lhs)), m_rhs(std::move(rhs))
    {
        switch (operation)
        {
            case '+':
                this->m_operator = binary_operator::sum;
                break;
            case '-': 
                this->m_operator = binary_operator::subtraction;
                break;
            case '*':
                this->m_operator = binary_operator::multiplication;
                break;
            case '/':
                this->m_operator = binary_operator::division;
                break;
            default:
                throw std::logic_error("Invalid binary operator");
        }
    }

    void binary_expression::accept(parser_visitor *visitor)
    {
        visitor->visit(this);
    }

    expression& binary_expression::lhs()
    {
        return *m_lhs;
    }

    expression& binary_expression::rhs()
    {
        return *m_rhs;
    }

    binary_operator binary_expression::operation() const noexcept
    {
        return m_operator;
    }

    bang_statement::bang_statement(std::unique_ptr<expression>&& body)
        : m_body(std::move(body))
    {
    }

    void bang_statement::accept(parser_visitor *visitor)
    {
        visitor->visit(this);
    }

    expression& bang_statement::body()
    {
        return *m_body;
    }

    compound_statement::compound_statement(std::vector<std::unique_ptr<statement>>&& statements)
        : m_statements(std::move(statements))
    {
    }

    void compound_statement::accept(parser_visitor *visitor)
    {
        visitor->visit(this);
    }

    std::vector<std::unique_ptr<statement>>& compound_statement::statements()
    {
        return m_statements;
    }

    parser::parser(const std::vector<token>& tokens)
        : tokens(tokens.cbegin()), end(tokens.cend())
    {
    }

    std::unique_ptr<block> parser::parse()
    {
        return parse_block();
    }

    std::unique_ptr<expression> parser::parse_factor()
    {
        if (tokens->of() == source::token::type::identifier)
        {
            auto result = std::make_unique<variable_expression>(tokens->identifier());
            ++tokens;
            return result;
        }
        else if (tokens->of() == source::token::token::type::number)
        {
            auto result = std::make_unique<integer_literal>(tokens->number());
            ++tokens;
            return result;
        }
        else if (tokens->of() == source::token::type::left_paren)
        {
            ++tokens;

            auto expression = parse_expression();

            ++tokens;

            return expression;
        }
        return nullptr;
    }

    std::unique_ptr<expression> parser::parse_term()
    {
        auto lhs = parse_factor();
        if (lhs == nullptr || tokens == end || tokens->of() != source::token::type::factor_operator)
        {
            return lhs;
        }
        while (tokens->of() == source::token::type::factor_operator)
        {
            auto _operator = tokens->identifier()[0];
            ++tokens;

            auto rhs = parse_factor();
            lhs = std::make_unique<binary_expression>(std::move(lhs),
                    std::move(rhs), _operator);
        }
        return lhs;
    }

    std::unique_ptr<expression> parser::parse_expression()
    {
        auto term = parse_term();
        if (term == nullptr || tokens == end || tokens->of() != source::token::type::term_operator)
        {
            return term;
        }
        while (tokens->of() == source::token::type::term_operator)
        {
            auto _operator = tokens->identifier()[0];
            ++tokens;

            auto rhs = parse_term();
            term = std::make_unique<binary_expression>(std::move(term),
                    std::move(rhs), _operator);
        }
        return term;
    }

    std::unique_ptr<definition> parser::parse_definition()
    {
        auto definition_identifier = advance(token::type::identifier);

        if (!definition_identifier.has_value())
        {
            return nullptr;
        }
        if (!skip(token::type::equals))
        {
            return nullptr;
        }

        if (tokens->of() == source::token::type::number)
        {
            auto result = std::make_unique<definition>(definition_identifier.value().get().identifier(),
                    std::make_unique<integer_literal>(tokens->number()));
            ++tokens;
            return result;
        }
        return nullptr;
    }

    std::unique_ptr<declaration> parser::parse_declaration()
    {
        auto declaration_identifier = advance(token::type::identifier);

        if (!declaration_identifier.has_value())
        {
            return nullptr;
        }
        return std::make_unique<declaration>(declaration_identifier.value().get().identifier());
    }

    std::unique_ptr<statement> parser::parse_statement()
    {
        if (tokens->of() == source::token::type::bang)
        {
            return parse_bang_statement();
        }
        else if (tokens->of() == source::token::type::begin)
        {
            return parse_compound_statement();
        }
        errors.push_back(std::make_unique<unexpected_token>(unexpected_token{ *tokens }));
        return nullptr;
    }

    std::unique_ptr<bang_statement> parser::parse_bang_statement()
    {
        if (!advance(token::type::bang))
        {
            return nullptr;
        }
        auto bang_body = parse_expression();

        if (bang_body != nullptr)
        {
            return std::make_unique<bang_statement>(std::move(bang_body));
        }

        return nullptr;
    }

    std::unique_ptr<compound_statement> parser::parse_compound_statement()
    {
        if (!advance(token::type::begin))
        {
            return nullptr;
        }
        auto result = std::make_unique<compound_statement>();
        std::unique_ptr<statement> next_statement;

        do
        {
            if ((next_statement = parse_statement()) == nullptr)
            {
                return nullptr;
            }
            result->statements().push_back(std::move(next_statement));
        }
        while (tokens->of() != token::type::end);
        ++tokens;

        return result;
    }

    std::vector<std::unique_ptr<definition>> parser::parse_definitions()
    {
        std::vector<std::unique_ptr<definition>> definitions;

        if (tokens->of() != token::type::let)
        {
            return definitions;
        }
        ++tokens; // Skip const.

        std::unique_ptr<definition> parsed_definition;
        while ((parsed_definition = parse_definition()) != nullptr)
        {
            definitions.push_back(std::move(parsed_definition));

            if (tokens->of() == source::token::type::comma)
            {
                ++tokens;
            }
            else if (tokens->of() == source::token::type::semicolon)
            {
                ++tokens;
                break;
            }
            else
            {
                errors.push_back(std::make_unique<unexpected_token>(*tokens));
                break;
            }
        }
        return definitions;
    }

    std::vector<std::unique_ptr<declaration>> parser::parse_declarations()
    {
        std::vector<std::unique_ptr<declaration>> declarations;

        if (tokens->of() != token::type::var)
        {
            return declarations;
        }
        ++tokens; // Skip var.

        std::unique_ptr<declaration> parsed_declaration;
        while ((parsed_declaration = parse_declaration()) != nullptr)
        {
            declarations.push_back(std::move(parsed_declaration));

            if (tokens->of() == token::type::comma)
            {
                ++tokens;
            }
            else if (tokens->of() == token::type::semicolon)
            {
                ++tokens;
                break;
            }
            else
            {
                errors.push_back(std::make_unique<unexpected_token>(*tokens));
                break;
            }
        }
        return declarations;
    }

    std::unique_ptr<block> parser::parse_block()
    {
        auto definitions = parse_definitions();
        auto declarations = parse_declarations();
        auto parsed_statement = parse_statement();

        if (parsed_statement == nullptr)
        {
            return nullptr;
        }
        return std::make_unique<block>(std::move(definitions),
                std::move(declarations), std::move(parsed_statement));
    }

    std::optional<std::reference_wrapper<const token>> parser::advance(const token::type token_type)
    {
        if (tokens->of() == token_type)
        {
            return std::make_optional<>(std::cref(*tokens++));
        }
        errors.push_back(std::make_unique<unexpected_token>(*tokens));
        return std::optional<std::reference_wrapper<const token>>();
    }

    bool parser::skip(const token::type token_type)
    {
        if (tokens->of() == token_type)
        {
            ++tokens;
            return true;
        }
        errors.push_back(std::make_unique<unexpected_token>(*tokens));
        return false;
    }
}