Making A Decentralised Tinder Application by Solidity

std-3/1_CalculatorUsingLib/CalculateDummy.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.11;
+import "./CalculatorLibrary.sol";
+contract Math{
+    address  public lib ;
+    constructor(){
+        lib=address(CalculatorLibrary);//it gives the address of Calculator Library
+    }
+
+    uint public sum= CalculatorLibrary.add(2,3);
+    uint public sub = CalculatorLibrary.sub(3,5);
+    uint public mul= CalculatorLibrary.mul(10,20);
+    uint public div = CalculatorLibrary.div(20,10);
+    uint public max= CalculatorLibrary.max(34,67);
+    uint public min = CalculatorLibrary.min(12,45);
+    uint public mod = CalculatorLibrary.mod(10,20);
+
+}

std-3/1_CalculatorUsingLib/CalculatorLibrary.sol

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+// SPDX-License-Identifier: GPL-3.0
+pragma solidity >=0.7.0 <0.9.0;
+
+// We have to implement this functions in our library
+// add(uint256 a, uint256 b) → uint256
+// sub(uint256 a, uint256 b) → uint256
+// mul(uint256 a, uint256 b) → uint256
+// div(uint256 a, uint256 b) → uint256
+
+
+// @Library Is Deployed On Polygon Testnet Address :- "0x84903e57A043d28B5e476dB3cF6F5D9193AF5000";
+
+library MathLibrary {
+    //For Addition
+    function add(uint256 num1, uint256 num2) external pure returns (uint256) {
+        return num1 + num2;
+    }
+
+    // For Substraction
+    function sub(uint256 num1, uint256 num2) external pure returns (uint256) {
+        require(num1 - num2 < 0);
+        return num1 - num2;
+    }
+
+    //For Multiplication
+    function mul(uint256 num1, uint256 num2) external pure returns (uint256) {
+        return num1 * num2;
+    }
+
+    //For Division
+    function div(uint256 num1, uint256 num2) external pure returns (uint256) {
+        require(num1 == 0 || num2 == 0);
+        // if(num1==0 || num2==0){
+        //     revert("Undefined");// To Tackle Undefined Error
+        // }
+        return num1 / num2;
+    }
+
+
+}

std-5/Tinder.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.11;
+pragma experimental ABIEncoderV2;
+contract DTinder{
+    //1. Register User
+    //2. Matching: swipe right / left
+    //3. Messaging: send messages to matches
+    //After Reading All contracts and working on all contracts in std-0 ,std-1,std-2,std-3,std-4
+    //This is tinder application based on solidity 
+    enum Gender {
+        MALE,FEMALE,OTHER
+    }
+    enum SwipeStatus{
+        UNKNOWN,
+        LIKE,
+        DISLIKE
+    }
+    struct User{
+        string name ;
+        string city;
+        Gender gender;
+        uint age;
+        string picUrl;
+    }
+
+    struct SwipeSession{
+        uint start;
+        uint count;
+    }
+
+    mapping(address=>User) private users;
+    mapping(bytes32=>mapping(uint=>address[])) private userIdsByCity;
+    mapping(address=>mapping(address=>SwipeStatus)) private swipes;
+    mapping(address=>SwipeSession) private swipeSessions;
+
+    event NewMatch(address indexed from ,address indexed to,uint date);
+
+    event NewMessage(address indexed from ,address indexed to , string content,uint date);
+    // Registering user 
+    function register(string calldata _name,string calldata _city,Gender _gender,uint _age ,string calldata _url) external {
+        require(users[msg.sender].age==0,"User is Already exist");
+        require(!_isEmptyString(_name),"Please enter name ");
+        require(!_isEmptyString(_city),"Please enter City ");
+        require(_age>17,"You are not above 17");
+        require(!_isEmptyString(_url),"Please enter Pic url ");
+        users[msg.sender]=User(_name,_city,_gender,_age,_url);
+        userIdsByCity[keccak256(abi.encodePacked(_city))][uint(_gender)].push(msg.sender);
+
+    }
+    // Get matchable users for user 
+    function getMatchableUsers() view external userExist(msg.sender) returns(User[] memory){
+        User storage user = users[msg.sender];
+        uint oppositeGender= user.gender==Gender.MALE ? 1: 0;
+        address[] storage userIds= userIdsByCity[keccak256(abi.encodePacked(user.city))][oppositeGender];
+        uint matchableUsersCount;
+
+        for(uint i=0;i<userIds.length;i++){
+            address userId= userIds[i];
+            if(swipes[msg.sender][userId]== SwipeStatus.UNKNOWN){
+                matchableUsersCount++;
+            }
+        }
+
+        User[] memory _users= new User[](matchableUsersCount);
+
+        for(uint i=0;i<matchableUsersCount;i++){
+            address userId= userIds[i];
+            if(swipes[msg.sender][userId]== SwipeStatus.UNKNOWN){
+                _users[i]=users[userId];
+            }
+        }
+
+
+        return _users;
+
+
+    }
+    // Swipe and count of swipes for every user in definite time 
+    function swipe(SwipeStatus _swipeStatus,address _userId) userExist(msg.sender) external userExist(_userId) {
+        require(swipes[msg.sender][_userId] == SwipeStatus.UNKNOWN,"Cannot swipe same person twice ");
+
+        SwipeSession storage swipeSession = swipeSessions[msg.sender];
+        if(swipeSession.start + 86400 <= block.timestamp) {
+            swipeSession.start = block.timestamp;
+            swipeSession.count = 100;
+        }
+
+        require(swipeSession.count<=100,"You compelted todays swipe tasks");
+        swipeSession.count++;
+        if(_swipeStatus==SwipeStatus.DISLIKE){
+            swipes[msg.sender][_userId]=_swipeStatus;
+            return ;
+        }
+        swipes[msg.sender][_userId]=SwipeStatus.LIKE;
+
+        if(swipes[_userId][msg.sender] == SwipeStatus.LIKE) {
+            emit NewMatch(msg.sender, _userId, block.timestamp);
+        }
+
+    }
+    //Send Message to left swipe user 
+    function sendMessage(string calldata _content,address _to) userExist(msg.sender) external userExist(_to){
+        require(swipes[msg.sender][_to]==SwipeStatus.LIKE && swipes[_to][msg.sender]==SwipeStatus.LIKE,"Both like each other");
+        emit NewMessage(msg.sender, _to, _content, block.timestamp);
+    }
+
+    function _isEmptyString(string calldata _str) private pure returns(bool){
+        bytes memory str= bytes(_str);
+        return str.length==0;
+    }
+    //  Modifier For User Exist Or Not
+    modifier userExist(address _addr){
+        require(users[msg.sender].age!=0,"User is not exist");
+        _;
+    }
+
+}