#pragma once

#include <cstdint>
#include <functional>

namespace extra2d {

/**
 * @brief 轻量级资源句柄
 * 
 * 只包含 32-bit 索引和世代，类似 ECS 中的 Entity ID。
 * 不直接管理生命周期，由 AssetStorage 统一管理。
 * 
 * @tparam T 资源类型
 */
template<typename T>
class Handle {
public:
    using Index = uint32_t;
    using Generation = uint32_t;
    
    Handle() : index_(0), generation_(0) {}
    Handle(Index index, Generation generation) 
        : index_(index), generation_(generation) {}
    
    bool isValid() const { return generation_ != 0; }
    Index index() const { return index_; }
    Generation generation() const { return generation_; }
    
    bool operator==(const Handle& other) const {
        return index_ == other.index_ && generation_ == other.generation_;
    }
    bool operator!=(const Handle& other) const { return !(*this == other); }
    
    static Handle invalid() { return Handle(); }
    
private:
    Index index_;
    Generation generation_;
};

} // namespace extra2d

namespace std {
    template<typename T>
    struct hash<extra2d::Handle<T>> {
        size_t operator()(const extra2d::Handle<T>& h) const {
            return std::hash<uint64_t>{}(
                (static_cast<uint64_t>(h.index()) << 32) | h.generation()
            );
        }
    };
}