ladybird/Libraries/LibJS/Runtime/DeclarativeEnvironment.h

/*
 * Copyright (c) 2020-2021, Andreas Kling <andreas@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/Bitmap.h>
#include <AK/HashMap.h>
#include <AK/OwnPtr.h>
#include <AK/Utf16FlyString.h>
#include <LibJS/Export.h>
#include <LibJS/Runtime/AbstractOperations.h>
#include <LibJS/Runtime/Completion.h>
#include <LibJS/Runtime/Environment.h>
#include <LibJS/Runtime/EnvironmentShape.h>
#include <LibJS/Runtime/Value.h>

namespace JS {

class JS_API DeclarativeEnvironment : public Environment {
    JS_ENVIRONMENT(DeclarativeEnvironment, Environment);
    GC_DECLARE_ALLOCATOR(DeclarativeEnvironment);

    struct Binding {
        Utf16FlyString name;
        Value value;
        bool strict { false };
        bool mutable_ { false };
        bool can_be_deleted { false };
        bool initialized { false };
    };

public:
    virtual ~DeclarativeEnvironment() override = default;

    virtual bool is_catch_environment() const override;
    void set_is_catch_environment(bool);

    virtual ThrowCompletionOr<bool> has_binding(Utf16FlyString const& name, Optional<size_t>* = nullptr) const override final;
    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, Utf16FlyString const& name, bool can_be_deleted) override final;
    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, Utf16FlyString const& name, bool strict) override final;
    virtual ThrowCompletionOr<void> initialize_binding(VM&, Utf16FlyString const& name, Value, InitializeBindingHint) override final;
    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, Utf16FlyString const& name, Value, bool strict) override final;
    virtual ThrowCompletionOr<Value> get_binding_value(VM&, Utf16FlyString const& name, bool strict) override;
    virtual ThrowCompletionOr<bool> delete_binding(VM&, Utf16FlyString const& name) override;

    ThrowCompletionOr<void> initialize_or_set_mutable_binding(VM&, Utf16FlyString const& name, Value value);

    // This is not a method defined in the spec! Do not use this in any LibJS (or other spec related) code.
    [[nodiscard]] Vector<Utf16FlyString> bindings() const
    {
        Vector<Utf16FlyString> names;
        names.ensure_capacity(binding_count());

        auto shape_bindings_to_visit = shape_binding_count();
        if (shape_bindings_to_visit > binding_count())
            shape_bindings_to_visit = binding_count();

        for (size_t i = 0; i < shape_bindings_to_visit; ++i) {
            auto const& name = m_shape->binding_name(i);
            if (!binding_is_deleted(i) && !name.is_empty())
                names.unchecked_append(name);
        }

        if (m_rare_data) {
            for (auto const& name : m_rare_data->m_binding_names) {
                if (!name.is_empty())
                    names.unchecked_append(name);
            }
        }

        return names;
    }

    ThrowCompletionOr<void> initialize_binding_direct(VM&, size_t index, Value, InitializeBindingHint);
    ThrowCompletionOr<void> set_mutable_binding_direct(VM&, size_t index, Value, bool strict);
    ThrowCompletionOr<Value> get_binding_value_direct(VM&, size_t index) const;
    Value get_initialized_binding_value_direct(size_t index) const { return m_binding_values[index]; }

    void shrink_to_fit();
    void set_environment_shape_cache(GC::Ptr<EnvironmentShape>&, size_t expected_binding_count);

    void ensure_capacity(size_t needed_capacity)
    {
        m_binding_values.ensure_capacity(needed_capacity);
        if (m_shape || needed_capacity == 0)
            return;

        auto& rare_data = ensure_rare_data();
        rare_data.m_binding_names.ensure_capacity(needed_capacity);
        rare_data.m_binding_flags.ensure_capacity(needed_capacity);
    }

    [[nodiscard]] u64 environment_serial_number() const;

    DisposeCapability const& dispose_capability() const;
    DisposeCapability& dispose_capability();
    DisposeCapability* dispose_capability_if_exists();

private:
    struct RareData {
        void visit_edges(Visitor&) const;
        [[nodiscard]] size_t external_memory_size() const;
        [[nodiscard]] bool is_empty() const;

        Vector<Utf16FlyString> m_binding_names;
        Vector<u8> m_binding_flags;
        Bitmap m_deleted_bindings;
        HashMap<Utf16FlyString, size_t> m_bindings_assoc;
        DisposeCapability m_dispose_capability;
        GC::Ptr<EnvironmentShape>* m_environment_shape_cache { nullptr };
        size_t m_expected_binding_count { 0 };
        u64 m_environment_serial_number { 0 };
        bool m_is_catch_environment { false };
    };

    static constexpr u8 BindingFlagStrict = EnvironmentShape::BindingFlagStrict;
    static constexpr u8 BindingFlagMutable = EnvironmentShape::BindingFlagMutable;
    static constexpr u8 BindingFlagCanBeDeleted = EnvironmentShape::BindingFlagCanBeDeleted;

    [[nodiscard]] size_t shape_binding_count() const { return m_shape ? m_shape->size() : 0; }
    [[nodiscard]] size_t binding_count() const { return m_binding_values.size(); }
    [[nodiscard]] size_t local_binding_index(size_t index) const { return index - shape_binding_count(); }
    void append_binding(Binding);
    void clear_binding(Utf16FlyString const& name, size_t index);
    void ensure_deleted_bindings_capacity(size_t needed_capacity)
    {
        auto& rare_data = ensure_rare_data();
        if (needed_capacity <= rare_data.m_deleted_bindings.size())
            return;
        rare_data.m_deleted_bindings.grow(ceil_div(needed_capacity, static_cast<size_t>(8)) * 8, false);
    }
    RareData& ensure_rare_data();
    void drop_rare_data_if_empty();
    void increment_environment_serial_number();
    void maybe_finalize_environment_shape(VM&);
    void set_environment_shape(GC::Ref<EnvironmentShape>);
    Binding binding_at(size_t index) const;
    Utf16FlyString const& binding_name(size_t index) const
    {
        if (index < shape_binding_count())
            return m_shape->binding_name(index);
        VERIFY(m_rare_data);
        return m_rare_data->m_binding_names[local_binding_index(index)];
    }
    u8 binding_flags(size_t index) const
    {
        if (index < shape_binding_count())
            return m_shape->binding_flags(index);
        VERIFY(m_rare_data);
        return m_rare_data->m_binding_flags[local_binding_index(index)];
    }
    bool binding_is_strict(size_t index) const { return (binding_flags(index) & BindingFlagStrict) != 0; }
    bool binding_is_mutable(size_t index) const { return (binding_flags(index) & BindingFlagMutable) != 0; }
    bool binding_can_be_deleted(size_t index) const { return (binding_flags(index) & BindingFlagCanBeDeleted) != 0; }
    bool binding_is_initialized(size_t index) const { return !m_binding_values[index].is_special_empty_value(); }
    bool binding_is_deleted(size_t index) const { return m_rare_data && !m_rare_data->m_deleted_bindings.is_null() && m_rare_data->m_deleted_bindings.get(index); }

    ThrowCompletionOr<Value> get_binding_value_direct(VM&, Binding const&) const;
    ThrowCompletionOr<void> set_mutable_binding_direct(VM&, Binding&, Value, bool strict);

protected:
    DeclarativeEnvironment();
    explicit DeclarativeEnvironment(Environment* parent_environment);
    DeclarativeEnvironment(Environment* parent_environment, ReadonlySpan<Binding> bindings);

    virtual void visit_edges(Visitor&) override;
    virtual size_t external_memory_size() const override;

    class BindingAndIndex {
    public:
        Binding binding() const
        {
            if (m_referenced_environment)
                return m_referenced_environment->binding_at(m_index.value());
            return m_temporary_binding;
        }

        BindingAndIndex(DeclarativeEnvironment const& environment, size_t index)
            : m_referenced_environment(&environment)
            , m_index(index)
        {
        }

        explicit BindingAndIndex(Binding temporary_binding)
            : m_temporary_binding(move(temporary_binding))
        {
        }

        Optional<size_t> const& index() const { return m_index; }

    private:
        GC::Ptr<DeclarativeEnvironment const> m_referenced_environment;
        Binding m_temporary_binding {};
        Optional<size_t> m_index;
    };

    friend class ModuleEnvironment;

    virtual Optional<BindingAndIndex> find_binding_and_index(Utf16FlyString const& name) const
    {
        if (m_shape) {
            auto index = m_shape->find_binding(name);
            if (index.has_value() && *index < binding_count() && !binding_is_deleted(*index))
                return BindingAndIndex { *this, *index };
        }

        if (m_rare_data) {
            if (auto it = m_rare_data->m_bindings_assoc.find(name); it != m_rare_data->m_bindings_assoc.end())
                return BindingAndIndex { *this, it->value };
        }

        return {};
    }

private:
    GC::Ptr<EnvironmentShape> m_shape;
    Vector<Value> m_binding_values;
    OwnPtr<RareData> m_rare_data;
};

inline ThrowCompletionOr<Value> DeclarativeEnvironment::get_binding_value_direct(VM& vm, size_t index) const
{
    if (!binding_is_initialized(index))
        return vm.throw_completion<ReferenceError>(ErrorType::BindingNotInitialized, binding_name(index));

    return m_binding_values[index];
}

inline ThrowCompletionOr<Value> DeclarativeEnvironment::get_binding_value_direct(VM&, Binding const& binding) const
{
    // 2. If the binding for N in envRec is an uninitialized binding, throw a ReferenceError exception.
    if (!binding.initialized)
        return vm().throw_completion<ReferenceError>(ErrorType::BindingNotInitialized, binding.name);

    // 3. Return the value currently bound to N in envRec.
    return binding.value;
}

template<>
inline bool Environment::fast_is<DeclarativeEnvironment>() const { return is_declarative_environment(); }

}