nep.py

"""
NEP5 Token
===================================
A simplified version of the original authored by: 
.. moduleauthor:: Thomas Saunders <tom@cityofzion.io>
..modifiedby:: Tyler Adams <tyler@coz.io>
"""

from boa.interop.Neo.Runtime import GetTrigger, CheckWitness
from boa.interop.Neo.Action import RegisterAction
from boa.interop.Neo.TriggerType import Application, Verification
from boa.interop.Neo.Storage import GetContext, Get, Put, Delete
from boa.builtins import concat

# -------------------------------------------
# TOKEN SETTINGS
# -------------------------------------------

OWNER = b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
# Script hash of the contract owner

# Name of the Token
TOKEN_NAME = 'NEP5 Standard'

# Symbol of the Token
TOKEN_SYMBOL = 'NEP5'

# Number of decimal places
TOKEN_DECIMALS = 8

# Total Supply of tokens in the system
TOKEN_TOTAL_SUPPLY = 10000000 * 100000000  # 10m total supply * 10^8 ( decimals)

ctx = GetContext()

# -------------------------------------------
# Events
# -------------------------------------------

OnTransfer = RegisterAction('transfer', 'addr_from', 'addr_to', 'amount')
OnApprove = RegisterAction('approve', 'addr_from', 'addr_to', 'amount')


def Main(operation, args):
    """
    This is the main entry point for the Smart Contract
    :param operation: the operation to be performed ( eg `balanceOf`, `transfer`, etc)
    :type operation: str
    :param args: a list of arguments ( which may be empty, but not absent )
    :type args: list
    :return: indicating the successful execution of the smart contract
    :rtype: bool
    """

    # The trigger determines whether this smart contract is being
    # run in 'verification' mode or 'application'

    trigger = GetTrigger()

    # 'Verification' mode is used when trying to spend assets ( eg NEO, Gas)
    # on behalf of this contract's address
    if trigger == Verification():

        # if the script that sent this is the owner
        # we allow the spend
        is_owner = CheckWitness(OWNER)

        if is_owner:

            return True

        return False

    # 'Application' mode is the main body of the smart contract
    elif trigger == Application():

        if operation == 'name':
            return TOKEN_NAME

        elif operation == 'decimals':
            return TOKEN_DECIMALS

        elif operation == 'symbol':
            return TOKEN_SYMBOL

        elif operation == 'totalSupply':
            return TOKEN_TOTAL_SUPPLY

        elif operation == 'balanceOf':
            if len(args) == 1:
                account = args[0]
                return do_balance_of(ctx, account)

        elif operation == 'transfer':
            if len(args) == 3:
                t_from = args[0]
                t_to = args[1]
                t_amount = args[2]
                return do_transfer(ctx, t_from, t_to, t_amount)
            else:
                return False

        return 'unknown operation'

    return False


def do_balance_of(ctx, account):
    """
    Method to return the current balance of an address
    :param account: the account address to retrieve the balance for
    :type account: bytearray
    :return: the current balance of an address
    :rtype: int
    """

    if len(account) != 20:
        return 0

    return Get(ctx, account)


def do_transfer(ctx, t_from, t_to, amount):
    """
    Method to transfer NEP5 tokens of a specified amount from one account to another
    :param t_from: the address to transfer from
    :type t_from: bytearray
    :param t_to: the address to transfer to
    :type t_to: bytearray
    :param amount: the amount of NEP5 tokens to transfer
    :type amount: int
    :return: whether the transfer was successful
    :rtype: bool
    """

    if amount <= 0:
        return False

    if len(t_from) != 20:
        return False

    if len(t_to) != 20:
        return False

    if CheckWitness(t_from):

        if t_from == t_to:
            print("transfer to self!")
            return True

        from_val = Get(ctx, t_from)

        if from_val < amount:
            print("insufficient funds")
            return False

        if from_val == amount:
            Delete(ctx, t_from)

        else:
            difference = from_val - amount
            Put(ctx, t_from, difference)

        to_value = Get(ctx, t_to)

        to_total = to_value + amount

        Put(ctx, t_to, to_total)

        OnTransfer(t_from, t_to, amount)

        return True
    else:
        print("from address is not the tx sender")

    return False