Token Smart Contract
The code below is an example and requires further refinement for specific business tasks.
Interface BasicStandard is necessary to create a token (implementation is mandatory and provided below).
public interface BasicStandard {
String getName();
String getSymbol();
int getDecimal();
boolean setFrozen(boolean frozen);
String totalSupply();
String balanceOf(String owner);
String allowance(String owner, String spender);
boolean transfer(String to, String amount);
boolean transferFrom(String from, String to, String amount);
void approve(String spender, String amount);
boolean burn(String amount);
}As well as interface ExtensionStandard (Implementation is not mandatory, but recommended and is provided below).
public interface ExtensionStandard extends BasicStandard {
void register();
boolean buyTokens(String amount);
}Further is the example of a token implementation according to SWT standard.
Examples sets the following in the class constructor:
Token name (name)
Token symbol (symbol)
Number of decimals (decimal)
Public key of the token owner (owner)
Total number of tokens (totalCoins)
Examples of implementation of Interfaces BasicStandard and ExtensionsStandard are provided below.
import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
import com.credits.scapi.annotations.*;
import com.credits.scapi.v0.*;
import static java.math.BigDecimal.ROUND_FLOOR;
import static java.math.BigDecimal.ZERO;
public class Token12 extends SmartContract implements ExtensionStandard {
private final String owner;
private final BigDecimal tokenCost;
private final int decimal;
HashMap<String, BigDecimal> balances;
private String name;
private String symbol;
private BigDecimal totalCoins;
private HashMap<String, Map<String, BigDecimal>> allowed;
private boolean frozen;
public Token12() {
super();
name = "1";
symbol = "12";
decimal = 1;
tokenCost = new BigDecimal(0).setScale(decimal, ROUND_FLOOR);
totalCoins = new BigDecimal(100).setScale(decimal, ROUND_FLOOR);
owner = initiator;
allowed = new HashMap<>();
balances = new HashMap<>();
balances.put(owner, new BigDecimal(100L).setScale(decimal, ROUND_FLOOR));
}
@Override
public int getDecimal() {
return decimal;
}
@Override
public void register() {
balances.putIfAbsent(initiator, ZERO.setScale(decimal, ROUND_FLOOR));
}
@Override
public boolean setFrozen(boolean isFrozen) {
if (!initiator.equals(owner)) {
throw new RuntimeException("unable change frozen state! The wallet "+ initiator + " is not owner");
}
this.frozen = isFrozen;
return true;
}
@Override
public String getName() {
return name;
}
@Override
public String getSymbol() {
return symbol;
}
@Override
public String totalSupply() {
return totalCoins.toString();
}
@Override
public String balanceOf(String owner) {
return getTokensBalance(owner).toString();
}
@Override
public String allowance(String owner, String spender) {
if (allowed.get(owner) == null) {
return "0";
}
BigDecimal amount = allowed.get(owner).get(spender);
return amount != null ? amount.toString() : "0";
}
@Override
public boolean transfer(String to, String amount) {
contractIsNotFrozen();
if (!to.equals(initiator)) {
BigDecimal decimalAmount = toBigDecimal(amount);
BigDecimal sourceBalance = getTokensBalance(initiator);
BigDecimal targetTokensBalance = getTokensBalance(to);
if (decimalAmount.compareTo(ZERO.setScale(decimal, ROUND_FLOOR)) < 0) {
throw new RuntimeException("invalid amount");
}
if(targetTokensBalance == null)
{
targetTokensBalance = new BigDecimal(0).setScale(decimal, ROUND_FLOOR);
}
if (sourceBalance.compareTo(decimalAmount) < 0) {
throw new RuntimeException("the wallet" + initiator + "doesn't have enough tokens to transfer");
}
balances.put(initiator, sourceBalance.subtract(decimalAmount));
balances.put(to, targetTokensBalance.add(decimalAmount));
}
return true;
}
@Override
public boolean transferFrom(String from, String to, String amount) {
contractIsNotFrozen();
if (!from.equals(to)) {
BigDecimal sourceBalance = getTokensBalance(from);
BigDecimal targetTokensBalance = getTokensBalance(to);
if(targetTokensBalance == null)
{
targetTokensBalance = new BigDecimal(0).setScale(decimal, ROUND_FLOOR);
}
BigDecimal decimalAmount = toBigDecimal(amount);
if (decimalAmount.compareTo(ZERO.setScale(decimal, ROUND_FLOOR)) < 0) {
throw new RuntimeException("invalid amount");
}
if (sourceBalance.compareTo(decimalAmount) < 0)
throw new RuntimeException("unable transfer tokens! The balance of " + from + " less then " + amount);
Map<String, BigDecimal> spender = allowed.get(from);
if (spender == null || !spender.containsKey(initiator))
throw new RuntimeException("unable transfer tokens! The wallet " + from + " not allow transfer tokens for " + to);
BigDecimal allowTokens = spender.get(initiator);
if (allowTokens.compareTo(decimalAmount) < 0) {
throw new RuntimeException("unable transfer tokens! Not enough allowed tokens. For the wallet " + initiator + " allow only " + allowTokens + " tokens");
}
spender.put(initiator, allowTokens.subtract(decimalAmount));
balances.put(from, sourceBalance.subtract(decimalAmount));
balances.put(to, targetTokensBalance.add(decimalAmount));
}
return true;
}
@Override
public void approve(String spender, String amount) {
initiatorIsRegistered();
BigDecimal decimalAmount = toBigDecimal(amount);
if (decimalAmount.compareTo(ZERO.setScale(decimal, ROUND_FLOOR)) < 0) {
throw new RuntimeException("invalid amount");
}
Map<String, BigDecimal> initiatorSpenders = allowed.get(initiator);
if (initiatorSpenders == null) {
Map<String, BigDecimal> newSpender = new HashMap<>();
newSpender.put(spender, decimalAmount);
allowed.put(initiator, newSpender);
} else {
BigDecimal spenderAmount = initiatorSpenders.get(spender);
initiatorSpenders.put(spender, spenderAmount == null ? decimalAmount : spenderAmount.add(decimalAmount));
}
}
@Override
public boolean burn(String amount) {
contractIsNotFrozen();
BigDecimal decimalAmount = toBigDecimal(amount);
if (decimalAmount.compareTo(ZERO.setScale(decimal, ROUND_FLOOR)) < 0) {
throw new RuntimeException("invalid amount");
}
if (!initiator.equals(owner))
throw new RuntimeException("can not burn tokens! The wallet " + initiator + " is not owner");
if (totalCoins.compareTo(decimalAmount) < 0) totalCoins = ZERO;
else totalCoins = totalCoins.subtract(decimalAmount);
return true;
}
public void payable(String amount, String currency) {
contractIsNotFrozen();
BigDecimal decimalAmount = toBigDecimal(amount);
if (totalCoins.compareTo(decimalAmount) < 0) throw new RuntimeException("not enough tokes to buy");
balances.put(initiator, Optional.ofNullable(balances.get(initiator)).orElse(ZERO).add(decimalAmount));
totalCoins = totalCoins.subtract(decimalAmount);
}
@Override
public boolean buyTokens(String amount) {
return false;
}
private void contractIsNotFrozen() {
if (frozen) throw new RuntimeException("unavailable action! The smart-contract is frozen");
}
private void initiatorIsRegistered() {
if (!balances.containsKey(initiator))
throw new RuntimeException("unavailable action! The wallet " + initiator + " is not registered");
}
private BigDecimal toBigDecimal(String stringValue) {
return new BigDecimal(stringValue).setScale(decimal, ROUND_FLOOR);
}
private BigDecimal getTokensBalance(String address) {
return balances.get(address);
}
}Last updated