#ifndef shared_string_hh_INCLUDED
#define shared_string_hh_INCLUDED

#include "string.hh"
#include "ref_ptr.hh"
#include "utils.hh"
#include "hash_map.hh"

#include <numeric>
#include <cstring>

namespace Kakoune
{

struct StringData : UseMemoryDomain<MemoryDomain::SharedString>
{
    uint32_t refcount;
    const int length;

    [[gnu::always_inline]]
    const char* data() const { return reinterpret_cast<const char*>(this + 1); }
    [[gnu::always_inline]]
    StringView strview() const { return {data(), length}; }

private:
    StringData(int len) : refcount(0), length(len) {}

    static constexpr uint32_t interned_flag = 1u << 31;
    static constexpr uint32_t refcount_mask = ~interned_flag;

    struct PtrPolicy
    {
        static void inc_ref(StringData* r, void*) noexcept { ++r->refcount; }
        static void dec_ref(StringData* r, void*) noexcept
        {
            if ((--r->refcount & refcount_mask) > 0)
                return;
            if (r->refcount & interned_flag)
                Registry::instance().remove(r->strview());
            auto alloc_len = sizeof(StringData) + r->length + 1;
            r->~StringData();
            operator delete(r, alloc_len);
        }
        static void ptr_moved(StringData*, void*, void*) noexcept {}
    };

public:
    using Ptr = RefPtr<StringData, PtrPolicy>;

    class Registry : public Singleton<Registry>
    {
    public:
        void debug_stats() const;
        Ptr intern(StringView str);
        Ptr intern(StringView str, size_t hash);
        void remove(StringView str);

    private:
        HashMap<StringView, StringData*, MemoryDomain::SharedString> m_strings;
    };

    static Ptr create(ConvertibleTo<StringView> auto&&... strs)
    {
        const int len = ((int)StringView{strs}.length() + ...);
        void* ptr = operator new(sizeof(StringData) + len + 1);
        auto* res = new (ptr) StringData(len);
        auto* data = reinterpret_cast<char*>(res + 1);
        auto append = [&](StringView str) {
            if (str.empty()) // memcpy(..., nullptr, 0) is UB
                return;
            memcpy(data, str.begin(), (size_t)str.length());
            data += (int)str.length();
        };
        (append(strs), ...);
        *data = 0;
        return RefPtr<StringData, PtrPolicy>{res};
    }

};

using StringDataPtr = StringData::Ptr;
using StringRegistry = StringData::Registry;

inline StringDataPtr intern(StringView str) { return StringRegistry::instance().intern(str); }
inline StringDataPtr intern(StringView str, size_t hash) { return StringRegistry::instance().intern(str, hash); }

}

#endif // shared_string_hh_INCLUDED