SHADE_Y3/SHADE_Engine/src/Resource/SparseSet.hpp

/************************************************************************************//*!
\file           SparseSet.h
\author         Tng Kah Wei, kahwei.tng, 390009620
\par            email: kahwei.tng\@digipen.edu
\date           Jul 30, 2021
\brief          Contains the declaration and template implementation of a generic
                SparseSet.
 
Copyright (C) 2021 DigiPen Institute of Technology.
Reproduction or disclosure of this file or its contents without the prior written consent 
of DigiPen Institute of Technology is prohibited.
*//*************************************************************************************/
#pragma once

// Primary Header
#include "SparseSet.h"

namespace SHADE
{
    /*---------------------------------------------------------------------------------*/
    /* SparseSet: Constructor                                                          */
    /*---------------------------------------------------------------------------------*/
    template<typename T>
    SparseSet<T>::SparseSet()
    {        
        static_assert(std::is_move_assignable_v<T>, "Objects stored by the SparseSet must be move-assignable.");
        static_assert(std::is_move_constructible_v<T>, "Objects stored by the SparseSet must be move-constructible.");
    }
    /*---------------------------------------------------------------------------------*/
    /* SparseSet: Usage Functions                                                      */
    /*---------------------------------------------------------------------------------*/
    template<typename T>
    T& SparseSet<T>::get(index_type idx)
    {
        return at(idx);
    }

    template<typename T>
    const T& SparseSet<T>::get(index_type idx) const
    {
        return at(idx);
    }

    template<typename T>
    bool SparseSet<T>::contains(index_type idx) const
    {
        if (idx >= sparseArray.size())
            return false;
        return sparseArray[idx] != INVALID;
    }

    template<typename T>
    void SparseSet<T>::erase(index_type idx)
    {		
        if (idx >= sparseArray.size() || !contains(idx)) 
            throw std::invalid_argument("An element at this index does not exist!");

        // Swap with the last element
        const int BACK_IDX = denseArray.size() - 1;
        std::swap(denseArray[sparseArray[idx]], denseArray.back());
        denseArray.pop_back();
        // Update the sparse set by swapping the indices
        sparseArray[inverseSparseArray[BACK_IDX]] = sparseArray[idx];
        inverseSparseArray[sparseArray[idx]] = inverseSparseArray[BACK_IDX];
        // Mark the "removed" values as invalid
        sparseArray[idx] = INVALID;
        inverseSparseArray[BACK_IDX] = INVALID;

        // Reset the dense array value
    }

    template<typename T>
    SparseSet<T>::reference SparseSet<T>::at(index_type idx)
    {
        return const_cast<reference>(static_cast<const SparseSet<T>&>(*this).at(idx));
    }

    template<typename T>
    SparseSet<T>::const_reference SparseSet<T>::at(index_type idx) const
    {
        // Range Check
        if (idx >= sparseArray.size() || !contains(idx))
            throw std::out_of_range("An element at this index does not exist!");
        return denseArray[sparseArray[idx]];
    }
    template<typename T>
    SparseSet<T>::size_type SparseSet<T>::size() const
    {
        return denseArray.size();
    }
    template<typename T>
    bool SparseSet<T>::empty() const
    {
        return denseArray.empty();
    }
    template<typename T>
    void SparseSet<T>::clear()
    {
        // Default initialize
        denseArray.clear();

        // Invalidate the sparse array
        std::fill(sparseArray.begin(), sparseArray.end(), INVALID);		
        std::fill(inverseSparseArray.begin(), inverseSparseArray.end(), INVALID);
    }
    template<typename T>
    template<typename ...Args>
    SparseSet<T>::reference SparseSet<T>::insert(index_type idx, Args && ...args)
    {
        // We need to resize the array
        if (idx >= sparseArray.size())
        {
            const int NEW_SIZE = idx + 1;
            sparseArray.resize(NEW_SIZE, INVALID);
            inverseSparseArray.resize(NEW_SIZE, INVALID);
        }
        else if (contains(idx))
        {
            throw std::invalid_argument("An element at this index already exists!");
        }

        // Insert to the back
        auto& insertedElem = denseArray.emplace_back(std::forward<Args>(args) ...);

        // Update sparse and inverse sparse arrays
        const index_type DENSE_IDX = denseArray.size() - 1;
        sparseArray[idx] = DENSE_IDX;
        inverseSparseArray[DENSE_IDX] = idx;

        return insertedElem;
    }
    
    /*---------------------------------------------------------------------------------*/
    /* Convenience Operator Functions                                                  */
    /*---------------------------------------------------------------------------------*/
    template<typename T>
    inline typename SparseSet<T>::reference SparseSet<T>::operator[](index_type idx)
    {
        return at(idx);
    }
    template<typename T>
    inline typename SparseSet<T>::const_reference SparseSet<T>::operator[](index_type idx) const
    {
        return at(idx);
    }
}