026-subcurrency-crypto-tokens.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

/**
 * Crypto Tokens
 *
 * The contract allows only its creator to create new coins(different issuance schemes are possible)
 *
 * Anyone can send coins to each other without the need for regictering
 * with username and password, all you need is an Etherium keypair
 *
 */

contract CryptoTokensAndMinting {
    // REMINDER: The keyword public is used in
    // making the variables accessible from other contracts

    address public minter;

    // bonus rate only configurable by the contract owner
    // set to an initial value of 0
    uint256 bonusRate = 0;

    // account balances
    mapping(address => uint256) public balances;

    // bonuses --each client account will be entitled to a bonus
    // depending on hopw they work.
    mapping(address => uint256) public bonuses;

    // our clients can react to specific
    // contract changes you declare

    // Event is an inheritable member of a contract. An event is emmited
    // it stores the arguments passed in the transaction logs.

    // These logs are stored on the blockchain and are accessible using the
    // address of the contract untill the contract is present on the blockchain.
    event Sent(address from, address to, uint256 amount);

    // create a constructor
    // REMINDER: The constructor only runs when we deploy the contract
    constructor() {
        minter = msg.sender;
    }

    // want to make new coins and send to an address
    // only the owner can do this
    function mint(address receiver, uint256 amount) public {
        // make sure its the minter
        require(msg.sender == minter, "Access Denied");

        // add amount to the receiver's previous balance
        balances[receiver] += amount;
    }

    // set a bonus rate
    // only by the contract owner
    function setBonusRate(uint256 bonus) public {
        require(msg.sender == minter, "Access Denied");

        // set a bonus rate
        bonusRate = bonus;
    }

    // check set bonus rate
    function checkBonusRate() public view returns (uint256) {
        return bonusRate;
    }

    // add eligible clients to benefit from bonus rate
    function setEligibility(address _addr) public {
        require(msg.sender == minter, "Access Denied");

        // add client to map of eligible clients
        bonuses[_addr] = bonusRate;
    }

    // error function to handle error in transactions
    error insufficientBalance(uint256 requested, uint256 available);

    // send any amount of coins to an existing address
    function send(address receiver, uint256 amount) public {
        // require the senders balance to be greater that or equal to the amount to be sent
        if (balances[msg.sender] < amount) {
            // revert keyword will cancel the transaction
            revert insufficientBalance({
                requested: amount,
                available: balances[msg.sender]
            });
        }

        // the sender has a reduction in amount of coins in possession
        // while the receiver has an increase in amount of coins in posesssion
        balances[msg.sender] -= amount;
        balances[receiver] += amount;

        // emit the event with the required details
        emit Sent(msg.sender, receiver, amount);
    }

    // check availability of a bonus for current account
    function requestMyBonus() public view returns (uint256) {
        if (bonusRate > 0) return bonuses[msg.sender];
        return 0;
    }

    // request transfer of the current account's bonus to balances account
    function requestToTransferMyBonus() public returns (string memory) {
        if (bonuses[msg.sender] > 0) {
            // add bonus to the requested account
            balances[msg.sender] += bonusRate;

            // reset account bonus to zero
            bonuses[msg.sender] = 0;
            return "Coins successfully transfered!";
        }

        return
            "Transfer could not be established! Please check you bonus value and try again.";
    }
}