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contracts...Ticketing_System.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

// Group 43 Members:
// Amogh Bharadwaj [2019A7PS0086H]
// Anish Kacham [2019A7PS0091H]
// Kevin Kevin Biju Kizhake Kanichery [2019A7PS0045H]

contract Ticketing_System {
    
    // Initialising values
    uint256 tokenPrice;
    
    // Mapping in Solidity: we can associate a field with the sender's address.
    // This allows us to store the number of RETs an address possesses.
    mapping(address => uint256) EntryBalance;
    mapping(address => uint256) TokenBalance;
  
    
    address customer; 
    
    // 'payable' keyword implies we can send ether to this object(address in this case).
    address Dexter = payable(0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2); 
    
    constructor() payable {
        customer = msg.sender;
        EntryBalance[customer] = customer.balance;
        tokenPrice = 3;
        TokenBalance[customer]=0;
    }
     
    
    //Public, payable function for users to buy Royal Entry Tokens.
    function BuyTokens (uint256 amount) public payable returns (string memory, uint256){
        
        
        // Edge case : Only the owner of the contract can perform transactions.
        if(customer != msg.sender) return ("Unauthorised.",0);
        
        uint256 total_price = tokenPrice * amount;
        
        // Checking if customer can afford the purchase.
        if (EntryBalance[customer] < total_price) {
            return ("Insufficient balance.",0);
        } 
        
        // Executing the transaction.
        EntryBalance[customer] = EntryBalance[customer] - total_price;
        EntryBalance[Dexter] = EntryBalance[Dexter] + total_price;
        
        // Updating the token count of the address.
        TokenBalance[customer] = TokenBalance[customer] + amount;
        
        return ("Successful purchase.Token balance below",TokenBalance[customer]); // Decoded output shows updated token balance.
    }
    
    // Public function which allows users to use a given amount of tokens to enter the shop.
    function UseTokens (uint256 amount) public returns(string memory,uint256){
        
        // Edge case : Only the owner of the contract can perform transactions.
        if(customer != msg.sender) return ("Unauthorised.",0);
        
        // Edge case: Checking to see if customer has that many tokens.
        if (TokenBalance[customer] < amount){
            return ("Insufficient tokens possessed.",0);
        }
        
        // Deducting from token balance
        TokenBalance[customer] = TokenBalance[customer] - amount;
        
        return ("Successfully spent. Token balance below.",TokenBalance[customer]); 
    }
    
    // Public, payable function to sell a given amount RETs.
    function SellTokens (uint256 amount) public payable returns (string memory,uint256){
        
        // Edge case : Only the owner of the contract can perform transactions.
        if(customer != msg.sender) return ("Unauthorised.",0);

        // Edge case: Checking to see if customer has that many tokens.
        if (TokenBalance[customer] < amount){
            return ("Insufficient tokens possessed.",0);
        }
        
        uint256 selling_price = tokenPrice * amount;
        
        // Edge case: Checking to see if Dexter can afford this.
        if (EntryBalance[Dexter] < selling_price){
            return ("Insufficient balance at Dexter's address.",0);
        }
        
        // Executing the transaction.
        EntryBalance[customer] = EntryBalance[customer] + selling_price;
        EntryBalance[Dexter] = EntryBalance[Dexter] - selling_price;
        
        //Deducting tokens
        TokenBalance[customer] = TokenBalance[customer]-amount;
        
        return ("Successfully sold. Token balance below.",TokenBalance[customer]);
    }
    
    
}