/* Name analysis.
   Copyright (C) 2025 Free Software Foundation, Inc.

GCC 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, or (at your option)
any later version.

GCC 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 GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "elna/boot/semantic.h"

#include <algorithm>

namespace elna::boot
{
    declaration_error::declaration_error(const kind error_kind,
            const std::string& identifier, const struct position position)
        : error(position), identifier(identifier), error_kind(error_kind)
    {
    }

    std::string declaration_error::what() const
    {
        switch (this->error_kind)
        {
            case kind::undeclared:
                return "Type '" + identifier + "' not declared";
            case kind::already:
                return "Symbol '" + identifier + "' has been already declared";
            case kind::local_export:
                return "Local symbol '" + this->identifier + "' cannot be exported";
            default:
                __builtin_unreachable();
        }
    }

    type_expectation_error::type_expectation_error(const kind error_kind, const struct position position)
        : error(position), error_kind(error_kind)
    {
    }

    std::string type_expectation_error::what() const
    {
        switch (this->error_kind)
        {
            case kind::assignment:
                return "Assinging an incompatible type";
            case kind::result:
                return "Procedure return type and type of the return expression are not compatible";
            case kind::argument:
                return "Argument type does not match parameter";
            default:
                __builtin_unreachable();
        }
    }

    field_duplication_error::field_duplication_error(const std::string& field_name, const struct position position)
        : error(position), field_name(field_name)
    {
    }

    std::string field_duplication_error::what() const
    {
        return "Repeated field name '" + field_name + "'";
    }

    cyclic_declaration_error::cyclic_declaration_error(const std::vector<std::string>& cycle,
            const struct position position)
        : error(position), cycle(cycle)
    {
    }

    std::string cyclic_declaration_error::what() const
    {
        auto segment = std::cbegin(this->cycle);
        std::string message = "Type declaration forms a cycle: " + *segment;

        ++segment;
        for (; segment != std::cend(this->cycle); ++segment)
        {
            message += " -> " + *segment;
        }
        return message;
    }

    return_error::return_error(const std::string& identifier, const struct position position)
        : error(position), identifier(identifier)
    {
    }

    std::string return_error::what() const
    {
        return "Procedure '" + this->identifier + "' is expected to return, but does not have a return statement";
    }

    base_type_error::base_type_error(const std::string& base, const struct position position)
        : error(position), base(base)
    {
    }

    std::string base_type_error::what() const
    {
        return "Record base type '" + this->base + "' is not a record.";
    }

    argument_count_error::argument_count_error(std::size_t expected, std::size_t actual,
            const struct position position)
        : error(position), expected(expected), actual(actual)
    {
    }

    std::string argument_count_error::what() const
    {
        if (actual > expected)
        {
            return "Too many arguments, expected " + std::to_string(expected)
                + ", got " + std::to_string(actual);
        }
        else
        {
            return "Too few arguments, expected " + std::to_string(expected)
                + ", got " + std::to_string(actual);
        }
    }

    type_analysis_visitor::type_analysis_visitor(symbol_bag bag)
        : error_container(), bag(bag)
    {
    }

    void type_analysis_visitor::visit(procedure_declaration *declaration)
    {
        this->current_procedure = this->bag.lookup(declaration->identifier.name)->is_procedure();

        if (declaration->body.has_value())
        {
            this->bag.enter(this->current_procedure->scope);
        }
        walking_visitor::visit(declaration);

        if (declaration->body.has_value())
        {
            if (declaration->body.value().return_expression != nullptr)
            {
                expression *return_expr = declaration->body.value().return_expression;
                type return_type = this->current_procedure->symbol.return_type.proper_type;

                if (!return_type.empty())
                {
                    if (!is_assignable_from(return_type, return_expr->type_decoration))
                    {
                        add_error<type_expectation_error>(type_expectation_error::kind::result, return_expr->position());
                    }
                }
                else
                {
                    add_error<type_expectation_error>(type_expectation_error::kind::result, return_expr->position());
                }
            }
            else if (declaration->heading().return_type.proper_type != nullptr)
            {
                add_error<return_error>(declaration->identifier.name, declaration->position());
            }
            this->bag.leave();
        }
        this->current_procedure.reset();
    }

    void type_analysis_visitor::visit(unit *unit)
    {
        walking_visitor::visit(unit);

        if (unit->has_body())
        {
            if (unit->return_expression != nullptr)
            {
                type return_type = this->bag.lookup("Int")->is_type()->symbol;

                if (!is_assignable_from(return_type, unit->return_expression->type_decoration))
                {
                    add_error<type_expectation_error>(type_expectation_error::kind::result,
                            unit->return_expression->position());
                }
            }
            else
            {
                add_error<return_error>("module", unit->position());
            }
        }
    }

    void type_analysis_visitor::visit(assign_statement *statement)
    {
        walking_visitor::visit(statement);

        if (!is_assignable_from(statement->lvalue().type_decoration, statement->rvalue().type_decoration))
        {
            add_error<type_expectation_error>(type_expectation_error::kind::assignment, statement->position());
        }
    }

    void type_analysis_visitor::visit(variable_declaration *declaration)
    {
        walking_visitor::visit(declaration);

        if (declaration->initializer == nullptr)
        {
            return;
        }
        for (const identifier_definition& variable_identifier : declaration->identifiers)
        {
            auto variable_symbol = this->bag.lookup(variable_identifier.name)->is_variable();
            if (!is_assignable_from(variable_symbol->symbol, declaration->initializer->type_decoration))
            {
                add_error<type_expectation_error>(type_expectation_error::kind::assignment,
                        declaration->initializer->position());
            }
        }
    }

    void type_analysis_visitor::visit(case_statement *statement)
    {
        walking_visitor::visit(statement);
        type condition_type = inner_aliased_type(statement->condition().type_decoration);

        for (const switch_case& case_block : statement->cases)
        {
            for (expression *const case_label : case_block.labels)
            {
                if (!is_assignable_from(condition_type, case_label->type_decoration))
                {
                    add_error<type_expectation_error>(type_expectation_error::kind::assignment,
                            case_label->position());
                }
            }
        }
    }

    bool type_analysis_visitor::check_unresolved_symbol(std::shared_ptr<alias_type> alias,
            std::vector<std::string>& alias_path)
    {
        if (std::find(std::cbegin(alias_path), std::cend(alias_path), alias->name) != std::cend(alias_path))
        {
            return false;
        }
        alias_path.push_back(alias->name);

        if (auto another_alias = alias->reference.get<alias_type>())
        {
            return check_unresolved_symbol(another_alias, alias_path);
        }
        return true;
    }

    void type_analysis_visitor::visit(type_declaration *declaration)
    {
        std::vector<std::string> alias_path;
        auto unresolved_type = this->bag.lookup(declaration->identifier.name)->is_type()->symbol.get<alias_type>();

        if (!check_unresolved_symbol(unresolved_type, alias_path))
        {
            add_error<cyclic_declaration_error>(alias_path, declaration->position());
        }
        else
        {
            walking_visitor::visit(declaration);
        }
    }

    void type_analysis_visitor::visit(record_type_expression *expression)
    {
        if (expression->base.has_value())
        {
            type base_type = inner_aliased_type(this->bag.lookup(expression->base.value())->is_type()->symbol);
            if (base_type.get<record_type>() == nullptr)
            {
                add_error<base_type_error>(expression->base.value(), expression->position());
            }
        }
        walking_visitor::visit(expression);
    }

    void type_analysis_visitor::visit(procedure_call *call)
    {
        call->callable().accept(this);

        if (auto procedure = call->callable().type_decoration.get<procedure_type>())
        {
            std::vector<expression *>::const_iterator argument_iterator = std::cbegin(call->arguments);
            std::vector<type>::const_iterator type_iterator = std::cbegin(procedure->parameters);

            while (argument_iterator != std::cend(call->arguments)
                    && type_iterator != std::cend(procedure->parameters))
            {
                (*argument_iterator)->accept(this);
                if (!is_assignable_from(*type_iterator, (*argument_iterator)->type_decoration))
                {
                    add_error<type_expectation_error>(type_expectation_error::kind::argument,
                            (*argument_iterator)->position());
                }
                ++argument_iterator;
                ++type_iterator;
            }
            if (call->arguments.size() != procedure->parameters.size())
            {
                add_error<argument_count_error>(procedure->parameters.size(),
                        call->arguments.size(), call->position());
            }
        }
    }

    void type_analysis_visitor::visit(record_constructor_expression *expression)
    {
        auto record = inner_aliased_type(expression->type_decoration).get<record_type>();

        if (record == nullptr)
        {
            add_error<type_expectation_error>(type_expectation_error::kind::result, expression->position());
            return;
        }
        for (const field_initializer& initializer : expression->field_initializers)
        {
            for (const type_field& field : record->fields)
            {
                if (field.first == initializer.name)
                {
                    if (!is_assignable_from(field.second, initializer.value->type_decoration))
                    {
                        add_error<type_expectation_error>(type_expectation_error::kind::argument,
                                initializer.value->position());
                    }
                    break;
                }
            }
        }
    }

    void type_analysis_visitor::visit(array_constructor_expression *expression)
    {
        auto array = inner_aliased_type(expression->type_decoration).get<array_type>();

        if (array == nullptr)
        {
            add_error<type_expectation_error>(type_expectation_error::kind::result, expression->position());
            return;
        }
        if (expression->elements.size() > array->size)
        {
            add_error<argument_count_error>(array->size, expression->elements.size(),
                    expression->position());
            return;
        }
        for (auto element : expression->elements)
        {
            if (!is_assignable_from(array->base, element->type_decoration))
            {
                add_error<type_expectation_error>(type_expectation_error::kind::argument,
                        element->position());
            }
        }
    }

    name_analysis_visitor::name_analysis_visitor(symbol_bag bag)
        : error_container(), bag(bag)
    {
    }

    std::pair<procedure_type, std::vector<std::string>> name_analysis_visitor::build_procedure(
            procedure_type_expression& expression)
    {
        procedure_type::return_t result_return;

        if (expression.return_type.no_return)
        {
            result_return = procedure_type::return_t(std::monostate{});
        }
        else if (expression.return_type.proper_type != nullptr)
        {
            expression.return_type.proper_type->accept(this);
            result_return = procedure_type::return_t(this->current_type);
        }
        else
        {
            result_return = procedure_type::return_t();
        }
        std::pair<procedure_type, std::vector<std::string>> result_type{
            procedure_type(result_return), std::vector<std::string>()
        };
        for (auto& [parameter_names, parameters_type] : expression.parameters)
        {
            parameters_type->accept(this);
            for (auto& parameter_name : parameter_names)
            {
                result_type.first.parameters.push_back(this->current_type);
                result_type.second.push_back(parameter_name);
            }
        }
        return result_type;
    }

    type name_analysis_visitor::lookup_primitive_type(const std::string& name)
    {
        return this->bag.lookup(name)->is_type()->symbol;
    }

    type name_analysis_visitor::type_of_constant(const constant_info::variant& value)
    {
        return std::visit([this](auto&& arg) -> type {
            using T = std::decay_t<decltype(arg)>;

            if constexpr (std::is_same_v<T, std::int32_t>)
            {
                return lookup_primitive_type("Int");
            }
            else if constexpr (std::is_same_v<T, std::uint32_t>)
            {
                return lookup_primitive_type("Word");
            }
            else if constexpr (std::is_same_v<T, double>)
            {
                return lookup_primitive_type("Float");
            }
            else if constexpr (std::is_same_v<T, bool>)
            {
                return lookup_primitive_type("Bool");
            }
            else if constexpr (std::is_same_v<T, unsigned char>)
            {
                return lookup_primitive_type("Char");
            }
            else if constexpr (std::is_same_v<T, std::nullptr_t>)
            {
                return lookup_primitive_type("Pointer");
            }
            else if constexpr (std::is_same_v<T, std::string>)
            {
                return lookup_primitive_type("String");
            }
            else
            {
                static_assert(!sizeof(T*), "Unhandled constant type");
            }
        }, value);
    }

    type name_analysis_visitor::lookup_field(const type& composite_type, const std::string& field_name)
    {
        type resolved_type = inner_aliased_type(composite_type);

        if (auto record = resolved_type.get<record_type>())
        {
            for (auto& field : record->fields)
            {
                if (field.first == field_name)
                {
                    return field.second;
                }
            }
            if (!record->base.empty())
            {
                return lookup_field(record->base, field_name);
            }
        }
        else if (auto primitive = resolved_type.get<primitive_type>(); primitive != nullptr && primitive->identifier == "String")
        {
            if (field_name == "length")
            {
                return lookup_primitive_type("Word");
            }
            else if (field_name == "ptr")
            {
                return type(std::make_shared<pointer_type>(lookup_primitive_type("Char")));
            }
        }
        return type();
    }

    void name_analysis_visitor::visit(type_declaration *declaration)
    {
        walking_visitor::visit(declaration);
        auto resolved = this->bag.resolve(declaration->identifier.name, this->current_type);
        auto info = std::make_shared<type_info>(type(resolved));

        info->exported = declaration->identifier.exported;
        this->bag.enter(declaration->identifier.name, info);
    }

    void name_analysis_visitor::visit(pointer_type_expression *expression)
    {
        walking_visitor::visit(expression);
        this->current_type = type(std::make_shared<pointer_type>(this->current_type));
    }

    void name_analysis_visitor::visit(array_type_expression *expression)
    {
        walking_visitor::visit(expression);
        auto result_type = std::make_shared<array_type>(this->current_type, expression->size);

        this->current_type = type(result_type);
    }

    /**
     * Collects field names from a record type recursively, base first.
     */
    static void collect_field_names(const type& composite_type, std::set<std::string>& names)
    {
        auto record = inner_aliased_type(composite_type).get<record_type>();
        if (record == nullptr)
        {
            return;
        }
        if (!record->base.empty())
        {
            collect_field_names(record->base, names);
        }
        for (auto& field : record->fields)
        {
            names.insert(field.first);
        }
    }

    std::vector<type_field> name_analysis_visitor::build_composite_type(
            const std::vector<field_declaration>& fields, std::set<std::string>& field_names)
    {
        std::vector<type_field> result;

        for (auto& field : fields)
        {
            field.second->accept(this);
            for (auto& field_name : field.first)
            {
                if (!field_names.insert(field_name).second)
                {
                    add_error<field_duplication_error>(field_name, field.second->position());
                }
                else
                {
                    result.push_back(std::make_pair(field_name, this->current_type));
                }
            }
        }
        return result;
    }

    void name_analysis_visitor::visit(record_type_expression *expression)
    {
        std::shared_ptr<record_type> result_type;
        if (expression->base.has_value())
        {
            if (auto unresolved_alias = this->bag.declared(expression->base.value()))
            {
                result_type = std::make_shared<record_type>(type(unresolved_alias));
            }
            else if (auto base_symbol = this->bag.lookup(expression->base.value()))
            {
                if (auto base_type_info = base_symbol->is_type())
                {
                    result_type = std::make_shared<record_type>(base_type_info->symbol);
                }
                else
                {
                    add_error<base_type_error>(expression->base.value(), expression->position());
                    this->current_type = type();
                    return;
                }
            }
            else
            {
                add_error<declaration_error>(declaration_error::kind::undeclared,
                        expression->base.value(), expression->position());
                this->current_type = type();
                return;
            }
        }
        else
        {
            result_type = std::make_shared<record_type>();
        }

        std::set<std::string> field_names;
        collect_field_names(result_type->base, field_names);
        result_type->fields = build_composite_type(expression->fields, field_names);

        this->current_type = type(result_type);
    }

    void name_analysis_visitor::visit(record_constructor_expression *expression)
    {
        if (auto type_symbol = this->bag.lookup(expression->type_name))
        {
            if (auto type_info = type_symbol->is_type())
            {
                expression->type_decoration = type_info->symbol;
            }
        }
        for (const field_initializer& initializer : expression->field_initializers)
        {
            initializer.value->accept(this);
            if (!expression->type_decoration.empty()
                    && lookup_field(expression->type_decoration, initializer.name).empty())
            {
                add_error<declaration_error>(declaration_error::kind::undeclared,
                        initializer.name, expression->position());
            }
        }
    }

    void name_analysis_visitor::visit(array_constructor_expression *expression)
    {
        expression->m_element_type->accept(this);
        auto element_type = this->current_type;
        for (auto element : expression->elements)
        {
            element->accept(this);
        }
        expression->type_decoration = type(std::make_shared<array_type>(element_type, expression->size));
    }

    void name_analysis_visitor::visit(procedure_type_expression *expression)
    {
        std::shared_ptr<procedure_type> result_type =
            std::make_shared<procedure_type>(std::move(build_procedure(*expression).first));

        this->current_type = type(result_type);
    }

    void name_analysis_visitor::visit(enumeration_type_expression *expression)
    {
        std::shared_ptr<enumeration_type> result_type = std::make_shared<enumeration_type>(expression->members);

        this->current_type = type(result_type);
    }

    std::shared_ptr<variable_info> name_analysis_visitor::register_variable(const std::string& name,
            const bool is_extern, const struct position position)
    {
        auto variable_symbol = std::make_shared<variable_info>(this->current_type, is_extern);

        if (!this->bag.enter(name, variable_symbol))
        {
            add_error<declaration_error>(declaration_error::kind::already, name, position);
        }
        return variable_symbol;
    }

    void name_analysis_visitor::visit(variable_declaration *declaration)
    {
        declaration->variable_type().accept(this);
        auto variable_type = this->current_type;
        if (declaration->initializer != nullptr)
        {
            declaration->initializer->accept(this);
            this->current_type = variable_type;
        }
        for (const identifier_definition& variable_identifier : declaration->identifiers)
        {
            auto variable_symbol = register_variable(variable_identifier.name, declaration->is_extern,
                    declaration->position());
            variable_symbol->exported = variable_identifier.exported;
        }
    }

    void name_analysis_visitor::visit(constant_declaration *declaration)
    {
        walking_visitor::visit(declaration);
        auto constant_symbol = std::make_shared<constant_info>(this->current_literal);

        constant_symbol->exported = declaration->identifier.exported;
        this->bag.enter(declaration->identifier.name, constant_symbol);
    }

    void name_analysis_visitor::visit(procedure_declaration *declaration)
    {
        std::shared_ptr<procedure_info> info;
        auto [heading, parameter_names] = build_procedure(declaration->heading());

        if (declaration->body.has_value())
        {
            info = std::make_shared<procedure_info>(heading, std::move(parameter_names), this->bag.enter());
            auto name_iterator = std::cbegin(info->names);
            auto type_iterator = std::cbegin(heading.parameters);

            while (name_iterator != std::cend(info->names) && type_iterator != std::cend(heading.parameters))
            {
                this->current_type = *type_iterator;
                auto variable_symbol = register_variable(*name_iterator, false, declaration->heading().position());
                variable_symbol->exported = false;

                ++name_iterator;
                ++type_iterator;
            }
            for (constant_declaration *const constant : declaration->body.value().constants)
            {
                constant->accept(this);
            }
            for (variable_declaration *const variable : declaration->body.value().variables)
            {
                variable->accept(this);
            }
            for (statement *const statement : declaration->body.value().entry_point)
            {
                statement->accept(this);
            }
            if (declaration->body.value().return_expression != nullptr)
            {
                declaration->body.value().return_expression->accept(this);
            }
            this->bag.leave();
        }
        else
        {
            info = std::make_shared<procedure_info>(heading, std::move(parameter_names));
        }
        info->exported = declaration->identifier.exported;
        this->bag.enter(declaration->identifier.name, info);
    }

    void name_analysis_visitor::visit(procedure_call *call)
    {
        call->callable().accept(this);
        if (auto procedure = call->callable().type_decoration.get<procedure_type>())
        {
            call->type_decoration = procedure->return_type.proper_type;
        }
        else if (call->callable().is_named() != nullptr)
        {
            call->type_decoration = this->current_type;
        }
        for (expression *const argument : call->arguments)
        {
            argument->accept(this);
        }
    }

    void name_analysis_visitor::visit(unit *unit)
    {
        for (type_declaration *const type : unit->types)
        {
            type->accept(this);
        }
        for (variable_declaration *const variable : unit->variables)
        {
            variable->accept(this);
        }
        for (constant_declaration *const constant : unit->constants)
        {
            constant->accept(this);
        }
        for (procedure_declaration *const procedure : unit->procedures)
        {
            procedure->accept(this);
        }
        if (unit->has_body())
        {
            this->bag.enter();
            auto variable_type = lookup_primitive_type("Int");
            this->bag.enter("count", std::make_shared<variable_info>(variable_type, false));

            variable_type = lookup_primitive_type("Char");
            variable_type = type(std::make_shared<pointer_type>(variable_type));
            variable_type = type(std::make_shared<pointer_type>(variable_type));
            this->bag.enter("parameters", std::make_shared<variable_info>(variable_type, false));

            for (statement *const statement : unit->entry_point)
            {
                statement->accept(this);
            }
            if (unit->return_expression != nullptr)
            {
                unit->return_expression->accept(this);
            }
            this->bag.leave();
        }
    }

    void name_analysis_visitor::visit(traits_expression *trait)
    {
        if (!trait->parameters.empty())
        {
            trait->parameters.front()->accept(this);
            trait->types.push_back(this->current_type);
        }

        if (trait->name == "size" || trait->name == "alignment" || trait->name == "offset")
        {
            trait->type_decoration = lookup_primitive_type("Word");
        }
        else if (trait->name == "min" || trait->name == "max")
        {
            trait->type_decoration = trait->types.empty() ? type() : trait->types.front();
        }
    }

    void name_analysis_visitor::visit(binary_expression *expression)
    {
        walking_visitor::visit(expression);

        switch (expression->operation())
        {
            case binary_operator::equals:
            case binary_operator::not_equals:
            case binary_operator::less:
            case binary_operator::greater:
            case binary_operator::less_equal:
            case binary_operator::greater_equal:
                expression->type_decoration = lookup_primitive_type("Bool");
                break;
            case binary_operator::subtraction:
                if (expression->lhs().type_decoration.get<pointer_type>()
                        && expression->rhs().type_decoration.get<pointer_type>())
                {
                    expression->type_decoration = lookup_primitive_type("Int");
                }
                else
                {
                    expression->type_decoration = expression->lhs().type_decoration;
                }
                break;
            default:
                expression->type_decoration = expression->lhs().type_decoration;
                break;
        }
    }

    void name_analysis_visitor::visit(unary_expression *expression)
    {
        walking_visitor::visit(expression);

        if (expression->operation() == unary_operator::reference)
        {
            expression->type_decoration = this->current_type
                = type(std::make_shared<pointer_type>(expression->operand().type_decoration));
        }
        else
        {
            expression->type_decoration = expression->operand().type_decoration;
        }
    }

    void name_analysis_visitor::visit(array_access_expression *expression)
    {
        walking_visitor::visit(expression);
        auto resolved_base= inner_aliased_type(expression->base().type_decoration);

        if (auto array = resolved_base.get<array_type>())
        {
            expression->type_decoration = array->base;
        }
        else if (resolved_base == lookup_primitive_type("String"))
        {
            expression->type_decoration = lookup_primitive_type("Char");
        }
    }

    void name_analysis_visitor::visit(field_access_expression *expression)
    {
        walking_visitor::visit(expression);
        expression->type_decoration = lookup_field(expression->base().type_decoration, expression->field());
        auto is_designator = expression->base().is_designator();

        if (expression->type_decoration.empty() && is_designator != nullptr && is_designator->is_named() != nullptr)
        {
            expression->type_decoration = this->current_type;
        }
    }

    void name_analysis_visitor::visit(dereference_expression *expression)
    {
        walking_visitor::visit(expression);

        if (auto pointer = inner_aliased_type(expression->base().type_decoration).get<pointer_type>())
        {
            expression->type_decoration = pointer->base;
        }
    }

    void name_analysis_visitor::visit(cast_expression *expression)
    {
        walking_visitor::visit(expression);
        expression->type_decoration = this->current_type;
    }

    void name_analysis_visitor::visit(named_expression *expression)
    {
        this->current_type = type();

        if (auto unresolved_alias = this->bag.declared(expression->name))
        {
            this->current_type = type(unresolved_alias);
        }
        else if (auto from_symbol_table = this->bag.lookup(expression->name))
        {
            if (auto type_symbol = from_symbol_table->is_type())
            {
                this->current_type = type_symbol->symbol;
            }
            else if (auto variable_symbol = from_symbol_table->is_variable())
            {
                expression->type_decoration = variable_symbol->symbol;
            }
            else if (auto constant_symbol = from_symbol_table->is_constant())
            {
                expression->type_decoration = type_of_constant(constant_symbol->symbol);
            }
            else if (auto procedure_symbol = from_symbol_table->is_procedure())
            {
                expression->type_decoration = type(std::make_shared<procedure_type>(procedure_symbol->symbol));
            }
        }
        else
        {
            add_error<declaration_error>(declaration_error::kind::undeclared,
                    expression->name, expression->position());
        }
    }

    void name_analysis_visitor::visit(literal<std::int32_t> *literal)
    {
        this->current_literal = literal->value;
        literal->type_decoration = lookup_primitive_type("Int");
    }

    void name_analysis_visitor::visit(literal<std::uint32_t> *literal)
    {
        this->current_literal = literal->value;
        literal->type_decoration = lookup_primitive_type("Word");
    }

    void name_analysis_visitor::visit(literal<double> *literal)
    {
        this->current_literal = literal->value;
        literal->type_decoration = lookup_primitive_type("Float");
    }

    void name_analysis_visitor::visit(literal<bool> *literal)
    {
        this->current_literal = literal->value;
        literal->type_decoration = lookup_primitive_type("Bool");
    }

    void name_analysis_visitor::visit(literal<unsigned char> *literal)
    {
        this->current_literal = literal->value;
        literal->type_decoration = lookup_primitive_type("Char");
    }

    void name_analysis_visitor::visit(literal<std::nullptr_t> *literal)
    {
        this->current_literal = literal->value;
        literal->type_decoration = lookup_primitive_type("Pointer");
    }

    void name_analysis_visitor::visit(literal<std::string> *literal)
    {
        this->current_literal = literal->value;
        literal->type_decoration = lookup_primitive_type("String");
    }

    declaration_visitor::declaration_visitor()
        : error_container()
    {
    }

    void declaration_visitor::visit(import_declaration *)
    {
    }

    void declaration_visitor::visit(unit *unit)
    {
        for (import_declaration *const _import : unit->imports)
        {
            _import->accept(this);
        }
        for (type_declaration *const type : unit->types)
        {
            type->accept(this);
        }
        for (procedure_declaration *const procedure : unit->procedures)
        {
            procedure->accept(this);
        }
    }

    void declaration_visitor::visit(type_declaration *declaration)
    {
        const std::string& type_identifier = declaration->identifier.name;

        if (!this->unresolved.insert({ type_identifier, std::make_shared<alias_type>(type_identifier) }).second)
        {
            add_error<declaration_error>(declaration_error::kind::already,
                    declaration->identifier.name, declaration->position());
        }
    }

    void declaration_visitor::visit(procedure_declaration *declaration)
    {
        if (!declaration->body.has_value())
        {
            return;
        }
        for (constant_declaration *const constant : declaration->body.value().constants)
        {
            constant->accept(this);
        }
        for (variable_declaration *const variable : declaration->body.value().variables)
        {
            variable->accept(this);
        }
    }

    void declaration_visitor::visit(variable_declaration *declaration)
    {
        for (const identifier_definition& variable_identifier : declaration->identifiers)
        {
            if (variable_identifier.exported)
            {
                add_error<declaration_error>(declaration_error::kind::local_export,
                        variable_identifier.name, declaration->position());
            }
        }
    }

    void declaration_visitor::visit(constant_declaration *declaration)
    {
        if (declaration->identifier.exported)
        {
                add_error<declaration_error>(declaration_error::kind::local_export,
                        declaration->identifier.name, declaration->position());
        }
    }

    bool is_base_of(std::shared_ptr<record_type> base, std::shared_ptr<record_type> derived)
    {
        type current = derived->base;

        while (!current.empty())
        {
            auto current_record = inner_aliased_type(current).get<record_type>();
            if (current_record == nullptr)
            {
                return false;
            }
            if (current_record == base)
            {
                return true;
            }
            current = current_record->base;
        }
        return false;
    }

    bool are_compatible_pointers(type lhs_type, type rhs_type)
    {
        std::shared_ptr<primitive_type> lhs_primitive = lhs_type.get<primitive_type>();
        std::shared_ptr<primitive_type> rhs_primitive = rhs_type.get<primitive_type>();

        bool lhs_is_primitive_pointer = lhs_primitive != nullptr && lhs_primitive->identifier == "Pointer";
        bool rhs_is_primitive_pointer = rhs_primitive != nullptr && rhs_primitive->identifier == "Pointer";

        return (lhs_is_primitive_pointer && rhs_type.get<pointer_type>() != nullptr)
            || (rhs_is_primitive_pointer && lhs_type.get<pointer_type>() != nullptr)
            || (lhs_is_primitive_pointer && rhs_type.get<procedure_type>() != nullptr)
            || (rhs_is_primitive_pointer && lhs_type.get<procedure_type>() != nullptr)
            || (lhs_is_primitive_pointer && rhs_is_primitive_pointer);
    }

    bool is_assignable_from(const type& assignee, const type& assignment)
    {
        type resolved_assignee = inner_aliased_type(assignee);
        type resolved_assignment = inner_aliased_type(assignment);

        if (resolved_assignee == resolved_assignment)
        {
            return true;
        }
        // If the types do not match, only some pointers can be assigned.
        if (are_compatible_pointers(resolved_assignee, resolved_assignment))
        {
            return true;
        }
        std::shared_ptr<pointer_type> assignee_pointer = resolved_assignee.get<pointer_type>();
        std::shared_ptr<pointer_type> assignment_pointer = resolved_assignment.get<pointer_type>();

        if (assignee_pointer == nullptr || assignment_pointer == nullptr)
        {
            return false;
        }
        // A pointer to a record can be assigned to a pointer to its base type.
        type assignee_pointee = inner_aliased_type(assignee_pointer->base);
        type assignment_pointee = inner_aliased_type(assignment_pointer->base);
        std::shared_ptr<record_type> assignee_record = assignee_pointee.get<record_type>();
        std::shared_ptr<record_type> assignment_record = assignment_pointee.get<record_type>();

        return assignee_record != nullptr && assignment_record != nullptr
            && is_base_of(assignee_record, assignment_record);
    }
}