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contracts...MyNFTCharity.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.15;

import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract MyNFTCharity is ERC721URIStorage{

    // address of the owner
    address payable owner; 

    // pause minting
    bool public paused = false;
    constructor() ERC721 ("My Charity Tokens", "MCT"){
        owner = payable(msg.sender);
    }

    // Counters from library
    using Counters for Counters.Counter;

    // to count the number of collections
    Counters.Counter private _collectionCount;

    // to count the number of tokens in the contract
    Counters.Counter private _tokenCount;

    // access to tht owner
    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }

    // to pause minting of NFTs
    function pause(bool _state) public onlyOwner {
        paused = _state;
    }

    // struct of NFT token
    struct CharityItem{
        uint256 tokenId;
        uint collectionId;
        address payable owner;
        uint256 price;
    }

    // struct of a collection
    struct Collection{
        uint256 collectionId;
        address payable charityAddress;
        uint[] tokensMinted;
    }

    // event that gets called on minting an NFT
    event Donated (
        uint indexed collectionId,
        uint indexed tokenId,
        uint indexed price
    );

    // maps charity token to its tokenId, collectionId, owner and price
    mapping ( uint256 => CharityItem ) public idToCharityToken;

    // maps collection to its collectionId, charity address, tokensMinted
    mapping ( uint256 => Collection ) public idToCollection;

    function createCollection ( address payable _charity ) public {
        require ( msg.sender == owner );
        uint256 currentCollectionId = _collectionCount.current();
        uint[] memory tempArr;
        idToCollection[currentCollectionId] = Collection(
            currentCollectionId,
            _charity,
            tempArr
        );
    }

    function mintCharityToken(string memory tokenURI, uint _collectionId, uint _price ) external payable {
    
    require ( msg.value == _price );
    _tokenCount.increment();
    uint256 newTokenId = _tokenCount.current();
    _safeMint(msg.sender, newTokenId);

    idToCollection[_collectionId].tokensMinted.push(newTokenId);

    _setTokenURI(newTokenId, tokenURI);

    idToCharityToken[newTokenId] = CharityItem(
        newTokenId,
        _collectionId,
        payable(msg.sender),
        _price
    );

    // transfers money to charity address
    payable(idToCollection[_collectionId].charityAddress).transfer(_price);

    emit Donated ( _collectionId, newTokenId, _price );
  }
  
}