// SPDX-License-Identifier: MIT
/**
  ______ _____   _____ ______ ___  __ _  _  _ 
 |  ____|  __ \ / ____|____  |__ \/_ | || || |
 | |__  | |__) | |        / /   ) || | \| |/ |
 |  __| |  _  /| |       / /   / / | |\_   _/ 
 | |____| | \ \| |____  / /   / /_ | |  | |   
 |______|_|  \_\\_____|/_/   |____||_|  |_|   
                                              
                                            
 */
pragma solidity ^0.8.0;

import "solidity-bits/contracts/BitMaps.sol";
import "../ERC721PsiUpgradeable.sol";


abstract contract ERC721PsiBurnableUpgradeable is ERC721PsiUpgradeable {
    using BitMaps for BitMaps.BitMap;
    BitMaps.BitMap private _burnedToken;

    /**
     * @dev Destroys `tokenId`.
     * The approval is cleared when the token is burned.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     *
     * Emits a {Transfer} event.
     */
    function _burn(uint256 tokenId) internal virtual {
        address from = ownerOf(tokenId);
        _beforeTokenTransfers(from, address(0), tokenId, 1);
        _burnedToken.set(tokenId);
        
        emit Transfer(from, address(0), tokenId);

        _afterTokenTransfers(from, address(0), tokenId, 1);
    }

    /**
     * @dev Returns whether `tokenId` exists.
     *
     * Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
     *
     * Tokens start existing when they are minted (`_mint`),
     * and stop existing when they are burned (`_burn`).
     */
    function _exists(uint256 tokenId) internal view override virtual returns (bool){
        if(_burnedToken.get(tokenId)) {
            return false;
        } 
        return super._exists(tokenId);
    }

    /**
     * @dev See {IERC721Enumerable-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalMinted() - _burned();
    }

    /**
     * @dev Returns number of token burned.
     */
    function _burned() internal view returns (uint256 burned){
        uint256 startBucket = _startTokenId() >> 8;
        uint256 lastBucket = (_nextTokenId() >> 8) + 1;

        for(uint256 i=startBucket; i < lastBucket; i++) {
            uint256 bucket = _burnedToken.getBucket(i);
            burned += _popcount(bucket);
        }
    }

    /**
     * @dev Returns number of set bits.
     */
    function _popcount(uint256 x) private pure returns (uint256 count) {
        unchecked{
            for (count=0; x!=0; count++)
                x &= x - 1;
        }
    }
}