/*
 * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Enumerate.h>
#include <AK/SaturatingMath.h>
#include <LibCore/System.h>
#include <LibWasm/AbstractMachine/AbstractMachine.h>
#include <LibWasm/AbstractMachine/BytecodeInterpreter.h>
#include <LibWasm/AbstractMachine/Configuration.h>
#include <LibWasm/AbstractMachine/Interpreter.h>
#include <LibWasm/AbstractMachine/Validator.h>
#include <LibWasm/Types.h>

namespace Wasm {

MemoryBuffer::~MemoryBuffer()
{
    clear();
}

MemoryBuffer::MemoryBuffer(MemoryBuffer&& other)
    : m_size(exchange(other.m_size, 0))
    , m_reserved_capacity(exchange(other.m_reserved_capacity, 0))
    , m_mapping_size(exchange(other.m_mapping_size, 0))
    , m_host_page_size(exchange(other.m_host_page_size, 0))
    , m_mapping_base(exchange(other.m_mapping_base, nullptr))
    , m_data(exchange(other.m_data, nullptr))
    , m_fallback(move(other.m_fallback))
{
}

MemoryBuffer& MemoryBuffer::operator=(MemoryBuffer&& other)
{
    if (this != &other) {
        clear();
        m_size = exchange(other.m_size, 0);
        m_reserved_capacity = exchange(other.m_reserved_capacity, 0);
        m_mapping_size = exchange(other.m_mapping_size, 0);
        m_host_page_size = exchange(other.m_host_page_size, 0);
        m_mapping_base = exchange(other.m_mapping_base, nullptr);
        m_data = exchange(other.m_data, nullptr);
        m_fallback = move(other.m_fallback);
    }
    return *this;
}

void MemoryBuffer::clear()
{
    if (m_mapping_base) {
        VERIFY(m_reserved_capacity);
        VERIFY(m_mapping_size);
        VERIFY(m_host_page_size);
        auto reservation_size = m_mapping_size + 2 * m_host_page_size;
        [[maybe_unused]] auto result = Core::System::release_address_space(m_mapping_base, reservation_size);
        VERIFY(!result.is_error());
    }
    m_mapping_base = nullptr;
    m_data = nullptr;
    m_reserved_capacity = 0;
    m_mapping_size = 0;
    m_host_page_size = 0;
    m_size = 0;
    m_fallback.clear();
}

void MemoryBuffer::try_reserve_wasm32_address_space()
{
    if (m_mapping_base)
        return;

    auto host_page_size = static_cast<size_t>(PAGE_SIZE);
    auto reserved_capacity = static_cast<size_t>(Constants::page_size) * 65536;
    auto mapping_size = reserved_capacity * 2;
    auto reservation_size = mapping_size + 2 * host_page_size;

    auto mapping_or_error = Core::System::reserve_address_space(reservation_size);
    if (mapping_or_error.is_error())
        return;

    m_mapping_base = mapping_or_error.value();
    m_data = reinterpret_cast<u8*>(m_mapping_base) + host_page_size;
    m_reserved_capacity = reserved_capacity;
    m_mapping_size = mapping_size;
    m_host_page_size = host_page_size;
}

ErrorOr<void> MemoryBuffer::try_resize(size_t new_size)
{
    if (m_data) {
        VERIFY(new_size >= m_size);
        VERIFY(m_host_page_size);
        if (new_size > m_reserved_capacity)
            return Error::from_errno(ENOMEM);
        if (new_size == m_size)
            return {};

        auto* grow_base = m_data + m_size;
        auto grow_size = new_size - m_size;
        TRY(Core::System::commit_memory(grow_base, grow_size));

        m_size = new_size;
        return {};
    }

    TRY(m_fallback.try_resize(new_size));
    m_size = m_fallback.size();
    return {};
}

bool MemoryBuffer::contains_virtual_address(void const* address) const
{
    if (!m_mapping_base)
        return false;

    auto fault_address = bit_cast<FlatPtr>(address);
    auto base = bit_cast<FlatPtr>(m_data);
    return fault_address >= base && fault_address < base + m_mapping_size;
}

ErrorOr<MemoryInstance> MemoryInstance::create(MemoryType const& type)
{
    MemoryInstance instance { type };

    if (!instance.grow(type.limits().min() * Constants::page_size, GrowType::No))
        return Error::from_string_literal("Failed to grow to requested size");

    return { move(instance) };
}

MemoryInstance::MemoryInstance(MemoryType const& type)
    : m_type(type)
{
    if (type.limits().address_type() == AddressType::I32)
        m_data.try_reserve_wasm32_address_space();
}

bool MemoryInstance::grow(size_t size_to_grow, GrowType grow_type, InhibitGrowCallback inhibit_callback)
{
    if (size_to_grow == 0)
        return true;
    u64 new_size = m_data.size() + size_to_grow;
    if (new_size >= Constants::page_size * 65536)
        return false;
    if (auto max = m_type.limits().max(); max.has_value()) {
        if (max.value() * Constants::page_size < new_size)
            return false;
    }

    auto previous_size = m_data.size();
    if (m_data.try_resize(new_size).is_error())
        return false;
    if (!m_data.is_virtual())
        m_data.span().slice(previous_size, size_to_grow).fill(0);

    if (inhibit_callback == InhibitGrowCallback::No && successful_grow_hook)
        successful_grow_hook();

    if (grow_type == GrowType::Yes)
        m_type = MemoryType { Limits(m_type.limits().address_type(), m_type.limits().min() + size_to_grow / Constants::page_size, m_type.limits().max()) };

    return true;
}

Optional<FunctionAddress> Store::allocate(ModuleInstance& instance, Module const& module, CodeSection::Code const& code, TypeIndex type_index)
{
    FunctionAddress address { m_functions.size() };
    if (type_index.value() >= instance.types().size())
        return {};

    auto& type = instance.types()[type_index.value()].function();
    m_functions.empend(WasmFunction { type, instance, module, code });
    return address;
}

Optional<FunctionAddress> Store::allocate(HostFunction&& function)
{
    FunctionAddress address { m_functions.size() };
    m_functions.empend(HostFunction { move(function) });
    return address;
}

Optional<TableAddress> Store::allocate(TableType const& type)
{
    if (type.limits().min() > Constants::max_allowed_table_size)
        return {};

    TableAddress address { m_tables.size() };
    Vector<Reference> elements;
    elements.ensure_capacity(type.limits().min());
    for (size_t i = 0; i < type.limits().min(); i++)
        elements.append(Wasm::Reference { Wasm::Reference::Null { type.element_type() } });
    elements.resize(type.limits().min());
    m_tables.empend(TableInstance { type, move(elements) });
    return address;
}

Optional<MemoryAddress> Store::allocate(MemoryType const& type)
{
    MemoryAddress address { m_memories.size() };
    auto instance = MemoryInstance::create(type);
    if (instance.is_error())
        return {};

    m_memories.append(make<MemoryInstance>(instance.release_value()));
    return address;
}

Optional<GlobalAddress> Store::allocate(GlobalType const& type, Value value)
{
    GlobalAddress address { m_globals.size() };
    m_globals.append(GlobalInstance { value, type.is_mutable(), type.type() });
    return address;
}

Optional<DataAddress> Store::allocate_data(Vector<u8> initializer)
{
    DataAddress address { m_datas.size() };
    m_datas.append(DataInstance { move(initializer) });
    return address;
}

Optional<ElementAddress> Store::allocate(ValueType const& type, Vector<Reference> references)
{
    ElementAddress address { m_elements.size() };
    m_elements.append(ElementInstance { type, move(references) });
    return address;
}

Optional<TagAddress> Store::allocate(FunctionType const& type, TagType::Flags flags)
{
    TagAddress address { m_tags.size() };
    m_tags.append({ type, flags });
    return address;
}

Optional<ExceptionAddress> Store::allocate(TagInstance const& tag_instance, Vector<Value> params)
{
    ExceptionAddress address { m_exceptions.size() };
    m_exceptions.append(ExceptionInstance { tag_instance, move(params) });
    return address;
}

FunctionInstance* Store::get(FunctionAddress address)
{
    auto value = address.value();
    if (m_functions.size() <= value)
        return nullptr;
    auto& instance = m_functions[value];
    if (auto const* wasm = instance.get_pointer<WasmFunction>()) {
        if (!wasm->try_module())
            return nullptr;
    }
    return &instance;
}

Module const* Store::get_module_for(Wasm::FunctionAddress address)
{
    auto* function = get(address);
    if (!function || function->has<HostFunction>())
        return nullptr;
    return function->get<WasmFunction>().module_ref().ptr();
}

RefPtr<ModuleInstance const> Store::get_module_instance_for(FunctionAddress address)
{
    auto* function = get(address);
    if (!function || function->has<HostFunction>())
        return nullptr;
    return function->get<WasmFunction>().try_module();
}

TableInstance* Store::get(TableAddress address)
{
    auto value = address.value();
    if (m_tables.size() <= value)
        return nullptr;
    return &m_tables[value];
}

MemoryInstance* Store::get(MemoryAddress address)
{
    auto value = address.value();
    if (m_memories.size() <= value)
        return nullptr;
    return m_memories[value].ptr();
}

GlobalInstance* Store::get(GlobalAddress address)
{
    auto value = address.value();
    if (m_globals.size() <= value)
        return nullptr;
    return &m_globals[value];
}

ElementInstance* Store::get(ElementAddress address)
{
    auto value = address.value();
    if (m_elements.size() <= value)
        return nullptr;
    return &m_elements[value];
}

DataInstance* Store::get(DataAddress address)
{
    auto value = address.value();
    if (m_datas.size() <= value)
        return nullptr;
    return &m_datas[value];
}

TagInstance* Store::get(TagAddress address)
{
    auto value = address.value();
    if (m_tags.size() <= value)
        return nullptr;
    return &m_tags[value];
}

ExceptionInstance* Store::get(ExceptionAddress address)
{
    auto value = address.value();
    if (m_exceptions.size() <= value)
        return nullptr;
    return &m_exceptions[value];
}

ErrorOr<void, ValidationError> AbstractMachine::validate(Module& module)
{
    if (module.validation_status() != Module::ValidationStatus::Unchecked) {
        if (module.validation_status() == Module::ValidationStatus::Valid)
            return {};

        return ValidationError { module.validation_error() };
    }

    auto result = Validator {}.validate(module);
    if (result.is_error()) {
        module.set_validation_error(result.error().error_string);
        return result.release_error();
    }

    return {};
}
InstantiationResult AbstractMachine::instantiate(Module const& module, Vector<ExternValue> externs)
{
    if (auto result = validate(const_cast<Module&>(module)); result.is_error())
        return InstantiationError { ByteString::formatted("Validation failed: {}", result.error()) };

    auto main_module_instance_pointer = adopt_ref(*new ModuleInstance);
    main_module_instance_pointer->cached_minimum_call_record_allocation_size = module.minimum_call_record_allocation_size();
    auto& main_module_instance = *main_module_instance_pointer;

    main_module_instance.types() = module.type_section().types();

    Vector<Value> global_values;
    Vector<Vector<Reference>> elements;
    auto auxiliary_instance_ptr = adopt_ref(*new ModuleInstance);
    auto& auxiliary_instance = *auxiliary_instance_ptr;

    auxiliary_instance.cached_minimum_call_record_allocation_size = module.minimum_call_record_allocation_size();

    for (auto [i, import_] : enumerate(module.import_section().imports())) {
        auto extern_ = externs.at(i);
        auto invalid = import_.description().visit(
            [&](MemoryType const& mem_type) -> Optional<ByteString> {
                if (!extern_.has<MemoryAddress>())
                    return "Expected memory import"sv;
                auto other_mem_type = m_store.get(extern_.get<MemoryAddress>())->type();
                if (other_mem_type.limits().is_subset_of(mem_type.limits()))
                    return {};
                return ByteString::formatted("Memory import and extern do not match: {}-{} vs {}-{}", mem_type.limits().min(), mem_type.limits().max(), other_mem_type.limits().min(), other_mem_type.limits().max());
            },
            [&](TableType const& table_type) -> Optional<ByteString> {
                if (!extern_.has<TableAddress>())
                    return "Expected table import"sv;
                auto other_table_type = m_store.get(extern_.get<TableAddress>())->type();
                if (table_type.element_type() == other_table_type.element_type()
                    && other_table_type.limits().is_subset_of(table_type.limits()))
                    return {};

                return ByteString::formatted("Table import and extern do not match: {}-{} vs {}-{}", table_type.limits().min(), table_type.limits().max(), other_table_type.limits().min(), other_table_type.limits().max());
            },
            [&](GlobalType const& global_type) -> Optional<ByteString> {
                if (!extern_.has<GlobalAddress>())
                    return "Expected global import"sv;
                auto other_global_type = m_store.get(extern_.get<GlobalAddress>())->type();
                if (global_type.type() == other_global_type.type()
                    && global_type.is_mutable() == other_global_type.is_mutable())
                    return {};
                return "Global import and extern do not match"sv;
            },
            [&](FunctionType const& type) -> Optional<ByteString> {
                if (!extern_.has<FunctionAddress>())
                    return "Expected function import"sv;
                auto other_type = m_store.get(extern_.get<FunctionAddress>())->visit([&](WasmFunction const& wasm_func) { return wasm_func.type(); }, [&](HostFunction const& host_func) { return host_func.type(); });
                if (type.results() != other_type.results())
                    return ByteString::formatted("Function import and extern do not match, results: {} vs {}", type.results(), other_type.results());
                if (type.parameters() != other_type.parameters())
                    return ByteString::formatted("Function import and extern do not match, parameters: {} vs {}", type.parameters(), other_type.parameters());
                return {};
            },
            [&](TagType const& type) -> Optional<ByteString> {
                if (!extern_.has<TagAddress>())
                    return "Expected tag import"sv;
                auto other_tag_instance = m_store.get(extern_.get<TagAddress>());
                if (other_tag_instance->flags() != type.flags())
                    return "Tag import and extern do not match"sv;

                auto& this_type = module.type_section().types()[type.type().value()];

                if (other_tag_instance->type().parameters() != this_type.function().parameters())
                    return "Tag import and extern do not match"sv;
                return {};
            },
            [&](TypeIndex type_index) -> Optional<ByteString> {
                if (!extern_.has<FunctionAddress>())
                    return "Expected function import"sv;
                auto other_type = m_store.get(extern_.get<FunctionAddress>())->visit([&](WasmFunction const& wasm_func) { return wasm_func.type(); }, [&](HostFunction const& host_func) { return host_func.type(); });
                auto& type = module.type_section().types()[type_index.value()].function();
                if (type.results() != other_type.results())
                    return ByteString::formatted("Function import and extern do not match, results: {} vs {}", type.results(), other_type.results());
                if (type.parameters() != other_type.parameters())
                    return ByteString::formatted("Function import and extern do not match, parameters: {} vs {}", type.parameters(), other_type.parameters());
                return {};
            });
        if (invalid.has_value())
            return InstantiationError { ByteString::formatted("{}::{}: {}", import_.module(), import_.name(), invalid.release_value()) };
    }

    for (auto& entry : externs) {
        if (auto* ptr = entry.get_pointer<GlobalAddress>())
            auxiliary_instance.globals().append(*ptr);
        else if (auto* ptr = entry.get_pointer<FunctionAddress>())
            auxiliary_instance.functions().append(*ptr);
    }

    Vector<FunctionAddress> module_functions;
    module_functions.ensure_capacity(module.function_section().types().size());

    size_t i = 0;
    for (auto& code : module.code_section().functions()) {
        auto type_index = module.function_section().types()[i];
        auto address = m_store.allocate(main_module_instance, module, code, type_index);
        VERIFY(address.has_value());
        auxiliary_instance.functions().append(*address);
        module_functions.append(*address);
        ++i;
    }

    BytecodeInterpreter interpreter(m_stack_info);
    auto handle = register_scoped(interpreter);

    for (auto& entry : module.global_section().entries()) {
        Configuration config { m_store };
        if (m_should_limit_instruction_count)
            config.enable_instruction_count_limit();
        config.set_frame(IsTailcall::No,
            auxiliary_instance,
            Vector<Value, ArgumentsStaticSize> {},
            entry.expression(),
            1uz);
        auto result = config.execute(interpreter);
        if (result.is_trap())
            return InstantiationError { "Global instantiation trapped", move(result.trap()) };
        global_values.append(result.values().first());
        auto addr = m_store.allocate(entry.type(), result.values().first()).release_value();
        auxiliary_instance.globals().append(addr);
    }

    if (auto result = allocate_all_initial_phase(module, main_module_instance, externs, global_values, module_functions); result.has_value())
        return result.release_value();

    for (auto& segment : module.element_section().segments()) {
        Vector<Reference> references;
        for (auto& entry : segment.init) {
            Configuration config { m_store };
            if (m_should_limit_instruction_count)
                config.enable_instruction_count_limit();
            config.set_frame(IsTailcall::No,
                main_module_instance,
                Vector<Value, ArgumentsStaticSize> {},
                entry,
                entry.instructions().size() - 1);
            auto result = config.execute(interpreter);
            if (result.is_trap())
                return InstantiationError { "Element section initialisation trapped", move(result.trap()) };

            for (auto& value : result.values()) {
                auto reference = value.to<Reference>();
                references.append(reference);
            }
        }
        elements.append(move(references));
    }

    if (auto result = allocate_all_final_phase(module, main_module_instance, elements); result.has_value())
        return result.release_value();

    size_t index = 0;
    for (auto& segment : module.element_section().segments()) {
        auto current_index = index;
        ++index;
        auto active_ptr = segment.mode.get_pointer<ElementSection::Active>();
        auto elem_instance = m_store.get(main_module_instance.elements()[current_index]);
        if (!active_ptr) {
            if (segment.mode.has<ElementSection::Declarative>())
                *elem_instance = ElementInstance(elem_instance->type(), {});
            continue;
        }
        Configuration config { m_store };
        if (m_should_limit_instruction_count)
            config.enable_instruction_count_limit();
        config.set_frame(IsTailcall::No,
            main_module_instance,
            Vector<Value, ArgumentsStaticSize> {},
            active_ptr->expression,
            1uz);
        auto result = config.execute(interpreter);
        if (result.is_trap())
            return InstantiationError { "Element section initialisation trapped", move(result.trap()) };
        auto d = result.values().first().to<i32>();
        auto table_instance = m_store.get(main_module_instance.tables()[active_ptr->index.value()]);
        if (current_index >= main_module_instance.elements().size())
            return InstantiationError { "Invalid element referenced by active element segment" };
        if (!table_instance || !elem_instance)
            return InstantiationError { "Invalid element referenced by active element segment" };

        auto total_size = saturating_add(elem_instance->references().size(), static_cast<size_t>(d));

        if (total_size > table_instance->elements().size())
            return InstantiationError { "Table instantiation out of bounds" };

        size_t i = 0;
        for (auto it = elem_instance->references().begin(); it < elem_instance->references().end(); ++i, ++it) {
            RefPtr<ModuleInstance const> anchor;
            if (auto const* func = it->ref().template get_pointer<Reference::Func>())
                anchor = m_store.get_module_instance_for(func->address);
            table_instance->set_element(i + d, *it, move(anchor));
        }
        // Drop element
        *m_store.get(main_module_instance.elements()[current_index]) = ElementInstance(elem_instance->type(), {});
    }

    for (auto& segment : module.data_section().data()) {
        Optional<InstantiationError> result = segment.value().visit(
            [&](DataSection::Data::Active const& data) -> Optional<InstantiationError> {
                Configuration config { m_store };
                if (m_should_limit_instruction_count)
                    config.enable_instruction_count_limit();
                config.set_frame(IsTailcall::No,
                    main_module_instance,
                    Vector<Value, ArgumentsStaticSize> {},
                    data.offset,
                    1uz);
                auto result = config.execute(interpreter);
                if (result.is_trap())
                    return InstantiationError { "Data section initialisation trapped", move(result.trap()) };
                size_t offset = result.values().first().to<u64>();
                if (main_module_instance.memories().size() <= data.index.value()) {
                    return InstantiationError {
                        ByteString::formatted("Data segment referenced out-of-bounds memory ({}) of max {} entries",
                            data.index.value(), main_module_instance.memories().size())
                    };
                }
                auto maybe_data_address = m_store.allocate_data(data.init);
                if (!maybe_data_address.has_value()) {
                    return InstantiationError { "Failed to allocate a data instance for an active data segment"sv };
                }
                main_module_instance.datas().append(*maybe_data_address);

                auto address = main_module_instance.memories()[data.index.value()];
                auto instance = m_store.get(address);
                Checked<size_t> checked_offset = data.init.size();
                checked_offset += offset;
                if (checked_offset.has_overflow() || checked_offset > instance->size()) {
                    return InstantiationError {
                        ByteString::formatted("Data segment attempted to write to out-of-bounds memory ({}) in memory of size {}",
                            offset, instance->size())
                    };
                }
                if (!data.init.is_empty())
                    instance->data().overwrite(offset, data.init.data(), data.init.size());
                return {};
            },
            [&](DataSection::Data::Passive const& passive) -> Optional<InstantiationError> {
                auto maybe_data_address = m_store.allocate_data(passive.init);
                if (!maybe_data_address.has_value()) {
                    return InstantiationError { "Failed to allocate a data instance for a passive data segment"sv };
                }
                main_module_instance.datas().append(*maybe_data_address);
                return {};
            });
        if (result.has_value())
            return result.release_value();
    }

    if (module.start_section().function().has_value()) {
        auto& functions = main_module_instance.functions();
        auto index = module.start_section().function()->index();
        if (functions.size() <= index.value())
            return InstantiationError { ByteString::formatted("Start section function referenced invalid index {} of max {} entries", index.value(), functions.size()) };
        auto result = invoke(functions[index.value()], {});
        if (result.is_trap())
            return InstantiationError { "Start function trapped", move(result.trap()), InstantiationErrorSource::StartFunction };
    }

    return InstantiationResult { move(main_module_instance_pointer) };
}

Optional<InstantiationError> AbstractMachine::allocate_all_initial_phase(Module const& module, ModuleInstance& module_instance, Vector<ExternValue>& externs, Vector<Value>& global_values, Vector<FunctionAddress>& own_functions)
{
    Optional<InstantiationError> result;

    for (auto& entry : externs) {
        entry.visit(
            [&](FunctionAddress const& address) { module_instance.functions().append(address); },
            [&](TableAddress const& address) { module_instance.tables().append(address); },
            [&](MemoryAddress const& address) { module_instance.memories().append(address); },
            [&](GlobalAddress const& address) { module_instance.globals().append(address); },
            [&](TagAddress const& address) { module_instance.tags().append(address); });
    }

    module_instance.functions().extend(own_functions);

    // FIXME: What if this fails?

    for (auto& table : module.table_section().tables()) {
        auto table_address = m_store.allocate(table.type());
        if (table_address.has_value()) {
            module_instance.tables().append(*table_address);
        }
    }

    for (auto& memory : module.memory_section().memories()) {
        auto memory_address = m_store.allocate(memory.type());
        if (memory_address.has_value()) {
            module_instance.memories().append(*memory_address);
        }
    }

    size_t index = 0;
    for (auto& entry : module.global_section().entries()) {
        auto address = m_store.allocate(entry.type(), move(global_values[index]));
        VERIFY(address.has_value());
        module_instance.globals().append(*address);
        index++;
    }

    for (auto& entry : module.tag_section().tags()) {
        auto& type = module.type_section().types()[entry.type().value()];
        auto address = m_store.allocate(type.function(), entry.flags());
        VERIFY(address.has_value());
        module_instance.tags().append(*address);
    }

    for (auto& entry : module.export_section().entries()) {
        Variant<FunctionAddress, TableAddress, MemoryAddress, GlobalAddress, TagAddress, Empty> address {};
        entry.description().visit(
            [&](FunctionIndex const& index) {
                if (module_instance.functions().size() > index.value())
                    address = FunctionAddress { module_instance.functions()[index.value()] };
                else
                    dbgln("Failed to export '{}', the exported address ({}) was out of bounds (min: 0, max: {})", entry.name(), index.value(), module_instance.functions().size());
            },
            [&](TableIndex const& index) {
                if (module_instance.tables().size() > index.value())
                    address = TableAddress { module_instance.tables()[index.value()] };
                else
                    dbgln("Failed to export '{}', the exported address ({}) was out of bounds (min: 0, max: {})", entry.name(), index.value(), module_instance.tables().size());
            },
            [&](MemoryIndex const& index) {
                if (module_instance.memories().size() > index.value())
                    address = MemoryAddress { module_instance.memories()[index.value()] };
                else
                    dbgln("Failed to export '{}', the exported address ({}) was out of bounds (min: 0, max: {})", entry.name(), index.value(), module_instance.memories().size());
            },
            [&](GlobalIndex const& index) {
                if (module_instance.globals().size() > index.value())
                    address = GlobalAddress { module_instance.globals()[index.value()] };
                else
                    dbgln("Failed to export '{}', the exported address ({}) was out of bounds (min: 0, max: {})", entry.name(), index.value(), module_instance.globals().size());
            },
            [&](TagIndex const& index) {
                if (module_instance.tags().size() > index.value())
                    address = TagAddress { module_instance.tags()[index.value()] };
                else
                    dbgln("Failed to export '{}', the exported address ({}) was out of bounds (min: 0, max: {})", entry.name(), index.value(), module_instance.tags().size());
            });

        if (address.has<Empty>()) {
            result = InstantiationError { "An export could not be resolved" };
            continue;
        }

        module_instance.exports().append(ExportInstance {
            entry.name(),
            move(address).downcast<FunctionAddress, TableAddress, MemoryAddress, GlobalAddress, TagAddress>(),
        });
    }

    return result;
}

Optional<InstantiationError> AbstractMachine::allocate_all_final_phase(Module const& module, ModuleInstance& module_instance, Vector<Vector<Reference>>& elements)
{
    size_t index = 0;
    for (auto& segment : module.element_section().segments()) {
        auto address = m_store.allocate(segment.type, move(elements[index]));
        VERIFY(address.has_value());
        module_instance.elements().append(*address);
        index++;
    }

    return {};
}

Result AbstractMachine::invoke(FunctionAddress address, Vector<Value> arguments)
{
    BytecodeInterpreter interpreter(m_stack_info);
    auto handle = register_scoped(interpreter);
    return invoke(interpreter, address, move(arguments));
}

Result AbstractMachine::invoke(Interpreter& interpreter, FunctionAddress address, Vector<Value> arguments)
{
    Configuration configuration { m_store };
    if (m_should_limit_instruction_count)
        configuration.enable_instruction_count_limit();

    Vector<Value, ArgumentsStaticSize> args = move(arguments);
    return configuration.call(interpreter, address, args);
}

void Linker::link(ModuleInstance const& instance)
{
    populate();
    if (m_unresolved_imports.is_empty())
        return;

    HashTable<Name> resolved_imports;
    for (auto& import_ : m_unresolved_imports) {
        auto it = instance.exports().find_if([&](auto& export_) { return export_.name() == import_.name; });
        if (!it.is_end()) {
            resolved_imports.set(import_);
            m_resolved_imports.set(import_, it->value());
        }
    }

    for (auto& entry : resolved_imports)
        m_unresolved_imports.remove(entry);
}

void Linker::link(HashMap<Linker::Name, ExternValue> const& exports)
{
    populate();
    if (m_unresolved_imports.is_empty())
        return;

    if (exports.is_empty())
        return;

    HashTable<Name> resolved_imports;
    for (auto& import_ : m_unresolved_imports) {
        auto export_ = exports.get(import_);
        if (export_.has_value()) {
            resolved_imports.set(import_);
            m_resolved_imports.set(import_, export_.value());
        }
    }

    for (auto& entry : resolved_imports)
        m_unresolved_imports.remove(entry);
}

AK::ErrorOr<Vector<ExternValue>, LinkError> Linker::finish()
{
    populate();
    if (!m_unresolved_imports.is_empty()) {
        if (!m_error.has_value())
            m_error = LinkError {};
        for (auto& entry : m_unresolved_imports)
            m_error->missing_imports.append(entry.name);
        return *m_error;
    }

    if (m_error.has_value())
        return *m_error;

    // Result must be in the same order as the module imports
    Vector<ExternValue> exports;
    exports.ensure_capacity(m_ordered_imports.size());
    for (auto& import_ : m_ordered_imports)
        exports.unchecked_append(*m_resolved_imports.get(import_));
    return exports;
}

void Linker::populate()
{
    if (!m_ordered_imports.is_empty())
        return;

    for (auto& import_ : m_module.import_section().imports()) {
        m_ordered_imports.append({ import_.module(), import_.name(), import_.description() });
        m_unresolved_imports.set(m_ordered_imports.last());
    }
}

void AbstractMachine::visit_external_resources(HostVisitOps const& host)
{
    for (auto interpreter_ptr : m_active_interpreters)
        interpreter_ptr->visit_external_resources(host);
}

}