LiquidtyGaugeUpgrade

LiquidityGaugeV4.vy

# @version 0.2.16
"""
@title Liquidity Gauge v4
@author Angle Protocol
@license MIT
"""

# Original idea and credit:
# Curve Finance's LiquidityGaugeV4
# https://github.com/curvefi/curve-dao-contracts/blob/master/contracts/gauges/LiquidityGaugeV4.vy

from vyper.interfaces import ERC20

implements: ERC20


interface CRV20:
    def future_epoch_time_write() -> uint256: nonpayable
    def rate() -> uint256: view

interface Controller:
    def period() -> int128: view
    def period_write() -> int128: nonpayable
    def period_timestamp(p: int128) -> uint256: view
    def gauge_relative_weight(addr: address, time: uint256) -> uint256: view
    def voting_escrow() -> address: view
    def checkpoint(): nonpayable
    def checkpoint_gauge(addr: address): nonpayable

interface Minter:
    def token() -> address: view
    def controller() -> address: view
    def minted(user: address, gauge: address) -> uint256: view

interface VotingEscrow:
    def user_point_epoch(addr: address) -> uint256: view
    def user_point_history__ts(addr: address, epoch: uint256) -> uint256: view

interface VotingEscrowBoost:
    def adjusted_balance_of(_account: address) -> uint256: view

interface ERC20Extended:
    def symbol() -> String[26]: view


event Deposit:
    provider: indexed(address)
    value: uint256

event Withdraw:
    provider: indexed(address)
    value: uint256

event UpdateLiquidityLimit:
    user: address
    original_balance: uint256
    original_supply: uint256
    working_balance: uint256
    working_supply: uint256

event UpdateLiquidityLimitRewards:
    user: address
    token: address
    original_balance: uint256
    original_supply: uint256
    working_balance: uint256
    working_supply: uint256

event CommitOwnership:
    admin: address

event ApplyOwnership:
    admin: address

event Transfer:
    _from: indexed(address)
    _to: indexed(address)
    _value: uint256

event Approval:
    _owner: indexed(address)
    _spender: indexed(address)
    _value: uint256

event RewardDataUpdate:
    _token: indexed(address)
    _amount: uint256

struct OldReward:
    token: address
    distributor: address
    period_finish: uint256
    rate: uint256
    last_update: uint256
    integral: uint256

struct Reward:
    distributor: address
    ve: address
    veBoost: address
    period_finish: uint256
    rate: uint256
    last_update: uint256
    integral: uint256

MAX_REWARDS: constant(uint256) = 8
TOKENLESS_PRODUCTION: constant(uint256) = 40
WEEK: constant(uint256) = 604800

token: public(address)
voting_escrow: public(address)
veBoost_proxy: public(address)

lp_token: public(address)
decimal_staking_token: public(uint256)

balanceOf: public(HashMap[address, uint256])
totalSupply: public(uint256)
allowance: public(HashMap[address, HashMap[address, uint256]])

name: public(String[64])
symbol: public(String[32])

old_working_balances: public(HashMap[address, uint256])
old_working_supply: public(uint256)

old_integrate_checkpoint_of: public(HashMap[address, uint256])

# For tracking external rewards
reward_count: public(uint256)
reward_tokens: public(address[MAX_REWARDS])

old_reward_data: public(HashMap[address, OldReward])

# claimant -> default reward receiver
rewards_receiver: public(HashMap[address, address])

# reward token -> claiming address -> integral
reward_integral_for: public(HashMap[address, HashMap[address, uint256]])

# user -> [uint128 claimable amount][uint128 claimed amount]
claim_data: HashMap[address, HashMap[address, uint256]]

admin: public(address)
future_admin: public(address)

initialized: public(bool)

### NEW STATE VARS
minter: public(address)
gauge_controller: public(address)

future_epoch_time: public(uint256)

working_balances: public(HashMap[address, uint256])
working_supply: public(uint256)

working_balances_rewards: public(HashMap[address, HashMap[address, uint256]])
working_supply_rewards: public(HashMap[address, uint256])

integrate_checkpoint_of_rewards: public(HashMap[address, HashMap[address, uint256]])

# The goal is to be able to calculate ∫(rate * balance / totalSupply dt) from 0 till checkpoint
# All values are kept in units of being multiplied by 1e18
period: public(int128)
period_timestamp: public(uint256[100000000000000000000000000000])

# 1e18 * ∫(rate(t) / totalSupply(t) dt) from 0 till checkpoint
integrate_inv_supply: public(uint256[100000000000000000000000000000])  # bump epoch when rate() changes

# 1e18 * ∫(rate(t) / totalSupply(t) dt) from (last_action) till checkpoint
integrate_inv_supply_of: public(HashMap[address, uint256])
integrate_checkpoint_of: public(HashMap[address, uint256])

# ∫(balance * rate(t) / totalSupply(t) dt) from 0 till checkpoint
# Units: rate * t = already number of coins per address to issue
integrate_fraction: public(HashMap[address, uint256])

inflation_rate: public(uint256)

# For tracking external rewards
reward_data: public(HashMap[address, Reward])

is_killed: public(bool)
reinitialized: public(bool)


@external
def __init__():
    """
    @notice Contract constructor
    """

    assert self.reinitialized == False #dev: contract is already initialized
    self.reinitialized = True

@external
def initialize(_lp_token: address, _minter: address, _veBoost_proxy: address):
    assert self.reinitialized == False #dev: contract is already initialized
    self.reinitialized = True

    _angle: address = self.token
    assert _angle != ZERO_ADDRESS

    _controller: address = Minter(_minter).controller()
    _token: address = Minter(_minter).token()
    _ve: address = Controller(_controller).voting_escrow()

    self.reward_data[_angle].distributor = self.old_reward_data[_angle].distributor
    self.reward_data[_angle].ve = self.voting_escrow
    self.reward_data[_angle].veBoost = self.veBoost_proxy
    self.reward_data[_angle].period_finish = self.old_reward_data[_angle].period_finish
    self.reward_data[_angle].rate = self.old_reward_data[_angle].rate
    self.reward_data[_angle].last_update = self.old_reward_data[_angle].last_update
    self.reward_data[_angle].integral = self.old_reward_data[_angle].integral

    self.working_balances_rewards[_angle] = self.old_working_balances
    self.working_supply_rewards[_angle] = self.old_working_supply
    self.integrate_checkpoint_of_rewards[_angle] = self.old_integrate_checkpoint_of

    self.lp_token = _lp_token
    self.minter = _minter
    self.gauge_controller = _controller
    self.token = _token
    self.voting_escrow = _ve
    self.veBoost_proxy = _veBoost_proxy

    # symbol: String[26] = ERC20Extended(_lp_token).symbol()
    # self.name = concat(symbol, " Spice Harvester Deposit")
    # self.symbol = concat("st", symbol)

    self.period_timestamp[0] = block.timestamp
    self.inflation_rate = CRV20(_token).rate()
    self.future_epoch_time = CRV20(_token).future_epoch_time_write()


@view
@external
def decimals() -> uint256:
    """
    @notice Get the number of decimals for this token
    @dev Implemented as a view method to reduce gas costs
    @return uint256 decimal places
    """
    return 18


@view
@external
def integrate_checkpoint() -> uint256:
    return self.period_timestamp[self.period]


@internal
def _update_liquidity_limit(addr: address, l: uint256, L: uint256):
    """
    @notice Calculate limits which depend on the amount of CRV token per-user.
            Effectively it calculates working balances to apply amplification
            of CRV production by CRV
    @param addr User address
    @param l User's amount of liquidity (LP tokens)
    @param L Total amount of liquidity (LP tokens)
    """
    # To be called after totalSupply is updated
    voting_balance: uint256 = VotingEscrowBoost(self.veBoost_proxy).adjusted_balance_of(addr)
    voting_total: uint256 = ERC20(self.voting_escrow).totalSupply()

    lim: uint256 = l * TOKENLESS_PRODUCTION / 100
    if voting_total > 0:
        lim += L * voting_balance / voting_total * (100 - TOKENLESS_PRODUCTION) / 100

    lim = min(l, lim)
    old_bal: uint256 = self.working_balances[addr]
    self.working_balances[addr] = lim
    _working_supply: uint256 = self.working_supply + lim - old_bal
    self.working_supply = _working_supply

    log UpdateLiquidityLimit(addr, l, L, lim, _working_supply)

@internal
def _update_liquidity_limit_rewards(addr: address, l: uint256, L: uint256, token: address):
    """
    @notice Calculate limits which depend on the amount of TOKEN token per-user.
            Effectively it calculates working balances to apply amplification
            of TOKEN production
    @param addr User address
    @param l User's amount of liquidity (LP tokens)
    @param L Total amount of liquidity (LP tokens)
    """
    # To be called after totalSupply is updated
    veBoost: address = self.reward_data[token].veBoost
    ve: address = self.reward_data[token].ve
    voting_balance: uint256 = VotingEscrowBoost(veBoost).adjusted_balance_of(addr)
    voting_total: uint256 = ERC20(ve).totalSupply()

    lim: uint256 = l * TOKENLESS_PRODUCTION / 100
    if voting_total > 0:
        lim += L * voting_balance / voting_total * (100 - TOKENLESS_PRODUCTION) / 100

    lim = min(l, lim)
    old_bal: uint256 = self.working_balances_rewards[token][addr]
    self.working_balances_rewards[token][addr] = lim
    _working_supply: uint256 = self.working_supply_rewards[token] + lim - old_bal
    self.working_supply_rewards[token] = _working_supply

    log UpdateLiquidityLimitRewards(addr, token, l, L, lim, _working_supply)


@internal
def _checkpoint_reward(_user: address, token: address, _total_supply: uint256, _user_balance: uint256, _claim: bool, receiver: address):
    """
    @notice Claim pending rewards and checkpoint rewards for a user
    """
    total_supply: uint256 = _total_supply
    user_balance: uint256 = _user_balance
    if self.reward_data[token].ve != ZERO_ADDRESS: 
        total_supply = self.working_supply_rewards[token]
        user_balance = self.working_balances_rewards[token][_user]
        self.integrate_checkpoint_of_rewards[token][_user] = block.timestamp

    integral: uint256 = self.reward_data[token].integral
    last_update: uint256 = min(block.timestamp, self.reward_data[token].period_finish)
    duration: uint256 = last_update - self.reward_data[token].last_update
    if duration != 0:
        self.reward_data[token].last_update = last_update
        if total_supply != 0:
            integral += duration * self.reward_data[token].rate * 10**18 / total_supply
            self.reward_data[token].integral = integral

    if _user != ZERO_ADDRESS:
        integral_for: uint256 = self.reward_integral_for[token][_user]
        new_claimable: uint256 = 0

        if integral_for < integral:
            self.reward_integral_for[token][_user] = integral
            new_claimable = user_balance * (integral - integral_for) / 10**18

        claim_data: uint256 = self.claim_data[_user][token]
        total_claimable: uint256 = shift(claim_data, -128) + new_claimable
        if total_claimable > 0:
            total_claimed: uint256 = claim_data % 2**128
            if _claim:
                response: Bytes[32] = raw_call(
                    token,
                    concat(
                        method_id("transfer(address,uint256)"),
                        convert(receiver, bytes32),
                        convert(total_claimable, bytes32),
                    ),
                    max_outsize=32,
                )
                if len(response) != 0:
                    assert convert(response, bool)
                self.claim_data[_user][token] = total_claimed + total_claimable
            elif new_claimable > 0:
                self.claim_data[_user][token] = total_claimed + shift(total_claimable, 128)


@internal
def _checkpoint_rewards(_user: address, _total_supply: uint256, _claim: bool, _receiver: address):
    """
    @notice Claim pending rewards and checkpoint rewards for a user
    """

    receiver: address = _receiver
    user_balance: uint256 = 0
    if _user != ZERO_ADDRESS:
        user_balance = self.balanceOf[_user]
        if _claim and _receiver == ZERO_ADDRESS:
            # if receiver is not explicitly declared, check if a default receiver is set
            receiver = self.rewards_receiver[_user]
            if receiver == ZERO_ADDRESS:
                # if no default receiver is set, direct claims to the user
                receiver = _user

    reward_count: uint256 = self.reward_count
    for i in range(MAX_REWARDS):
        if i == reward_count:
            break
        token: address = self.reward_tokens[i]
        self._checkpoint_reward(_user, token, _total_supply, user_balance, _claim, receiver)


@internal
def _checkpoint(addr: address):
    """
    @notice Checkpoint for a user
    @param addr User address
    """
    _period: int128 = self.period
    _period_time: uint256 = self.period_timestamp[_period]
    _integrate_inv_supply: uint256 = self.integrate_inv_supply[_period]
    rate: uint256 = self.inflation_rate
    new_rate: uint256 = rate
    prev_future_epoch: uint256 = self.future_epoch_time
    if prev_future_epoch >= _period_time:
        _token: address = self.token
        self.future_epoch_time = CRV20(_token).future_epoch_time_write()
        new_rate = CRV20(_token).rate()
        self.inflation_rate = new_rate

    if self.is_killed:
        # Stop distributing inflation as soon as killed
        rate = 0

    # Update integral of 1/supply
    if block.timestamp > _period_time:
        _working_supply: uint256 = self.working_supply
        _controller: address = self.gauge_controller
        Controller(_controller).checkpoint_gauge(self)
        prev_week_time: uint256 = _period_time
        week_time: uint256 = min((_period_time + WEEK) / WEEK * WEEK, block.timestamp)

        for i in range(500):
            dt: uint256 = week_time - prev_week_time
            w: uint256 = Controller(_controller).gauge_relative_weight(self, prev_week_time / WEEK * WEEK)

            if _working_supply > 0:
                if prev_future_epoch >= prev_week_time and prev_future_epoch < week_time:
                    # If we went across one or multiple epochs, apply the rate
                    # of the first epoch until it ends, and then the rate of
                    # the last epoch.
                    # If more than one epoch is crossed - the gauge gets less,
                    # but that'd meen it wasn't called for more than 1 year
                    _integrate_inv_supply += rate * w * (prev_future_epoch - prev_week_time) / _working_supply
                    rate = new_rate
                    _integrate_inv_supply += rate * w * (week_time - prev_future_epoch) / _working_supply
                else:
                    _integrate_inv_supply += rate * w * dt / _working_supply
                # On precisions of the calculation
                # rate ~= 10e18
                # last_weight > 0.01 * 1e18 = 1e16 (if pool weight is 1%)
                # _working_supply ~= TVL * 1e18 ~= 1e26 ($100M for example)
                # The largest loss is at dt = 1
                # Loss is 1e-9 - acceptable

            if week_time == block.timestamp:
                break
            prev_week_time = week_time
            week_time = min(week_time + WEEK, block.timestamp)

    _period += 1
    self.period = _period
    self.period_timestamp[_period] = block.timestamp
    self.integrate_inv_supply[_period] = _integrate_inv_supply

    # Update user-specific integrals
    _working_balance: uint256 = self.working_balances[addr]
    self.integrate_fraction[addr] += _working_balance * (_integrate_inv_supply - self.integrate_inv_supply_of[addr]) / 10 ** 18
    self.integrate_inv_supply_of[addr] = _integrate_inv_supply
    self.integrate_checkpoint_of[addr] = block.timestamp


@external
def user_checkpoint(addr: address) -> bool:
    """
    @notice Record a checkpoint for `addr`
    @param addr User address
    @return bool success
    """
    assert msg.sender in [addr, self.minter]  # dev: unauthorized
    _total_supply: uint256 = self.totalSupply
    user_balance: uint256 = self.balanceOf[addr]
    self._checkpoint(addr)
    self._update_liquidity_limit(addr, user_balance, _total_supply)
    if msg.sender == addr:
        reward_count: uint256 = self.reward_count
        for i in range(MAX_REWARDS):
            if i == reward_count:
                break
            token: address = self.reward_tokens[i]
            if self.reward_data[token].ve != ZERO_ADDRESS:
                self._checkpoint_reward(addr, token, _total_supply, user_balance, False, ZERO_ADDRESS)
                self._update_liquidity_limit_rewards(addr, user_balance, _total_supply, token)
    return True


@external
def claimable_tokens(addr: address) -> uint256:
    """
    @notice Get the number of claimable tokens per user
    @dev This function should be manually changed to "view" in the ABI
    @return uint256 number of claimable tokens per user
    """
    self._checkpoint(addr)
    return self.integrate_fraction[addr] - Minter(self.minter).minted(addr, self)


@view
@external
def claimed_reward(_addr: address, _token: address) -> uint256:
    """
    @notice Get the number of already-claimed reward tokens for a user
    @param _addr Account to get reward amount for
    @param _token Token to get reward amount for
    @return uint256 Total amount of `_token` already claimed by `_addr`
    """
    return self.claim_data[_addr][_token] % 2**128


@view
@external
def claimable_reward(_user: address, _reward_token: address) -> uint256:
    """
    @notice Get the number of claimable reward tokens for a user
    @param _user Account to get reward amount for
    @param _reward_token Token to get reward amount for
    @return uint256 Claimable reward token amount
    """
    integral: uint256 = self.reward_data[_reward_token].integral
    total_supply: uint256 = self.totalSupply
    user_balance: uint256 = self.balanceOf[_user]
    if self.reward_data[_reward_token].ve != ZERO_ADDRESS: 
        total_supply = self.working_supply_rewards[_reward_token]
        user_balance = self.working_balances_rewards[_reward_token][_user]
        
    if total_supply != 0:
        last_update: uint256 = min(block.timestamp, self.reward_data[_reward_token].period_finish)
        duration: uint256 = last_update - self.reward_data[_reward_token].last_update
        integral += (duration * self.reward_data[_reward_token].rate * 10**18 / total_supply)

    integral_for: uint256 = self.reward_integral_for[_reward_token][_user]
    new_claimable: uint256 = user_balance * (integral - integral_for) / 10**18

    return shift(self.claim_data[_user][_reward_token], -128) + new_claimable


@external
def set_rewards_receiver(_receiver: address):
    """
    @notice Set the default reward receiver for the caller.
    @dev When set to ZERO_ADDRESS, rewards are sent to the caller
    @param _receiver Receiver address for any rewards claimed via `claim_rewards`
    """
    self.rewards_receiver[msg.sender] = _receiver


@external
@nonreentrant('lock')
def claim_rewards(_addr: address = msg.sender, _receiver: address = ZERO_ADDRESS):
    """
    @notice Claim available reward tokens for `_addr`
    @param _addr Address to claim for
    @param _receiver Address to transfer rewards to - if set to
                     ZERO_ADDRESS, uses the default reward receiver
                     for the caller
    """
    if _receiver != ZERO_ADDRESS:
        assert _addr == msg.sender  # dev: cannot redirect when claiming for another user
    self._checkpoint_rewards(_addr, self.totalSupply, True, _receiver)


@external
def kick(addr: address):
    """
    @notice Kick `addr` for abusing their boost
    @dev Only if either they had another voting event, or their voting escrow lock expired
    @param addr Address to kick
    """
    t_last: uint256 = self.integrate_checkpoint_of[addr]
    _ve: address = self.voting_escrow
    t_ve: uint256 = VotingEscrow(_ve).user_point_history__ts(
        addr, VotingEscrow(_ve).user_point_epoch(addr)
    )
    _balance: uint256 = self.balanceOf[addr]

    assert ERC20(_ve).balanceOf(addr) == 0 or t_ve > t_last # dev: kick not allowed
    assert self.working_balances[addr] > _balance * TOKENLESS_PRODUCTION / 100  # dev: kick not needed

    self._checkpoint(addr)
    self._update_liquidity_limit(addr, self.balanceOf[addr], self.totalSupply)

@external
def kick_rewards(addr: address, token: address):
    """
    @notice Kick `addr` for abusing their boost
    @dev Only if either they had another voting event, or their voting escrow lock expired
    @param addr Address to kick
    """
    ve: address = self.reward_data[token].ve
    assert ve != ZERO_ADDRESS
    t_last: uint256 = self.integrate_checkpoint_of_rewards[token][addr]
    t_ve: uint256 = VotingEscrow(ve).user_point_history__ts(
        addr, VotingEscrow(ve).user_point_epoch(addr)
    )
    _balance: uint256 = self.balanceOf[addr]

    assert ERC20(ve).balanceOf(addr) == 0 or t_ve > t_last # dev: kick not allowed
    assert self.working_balances_rewards[token][addr] > _balance * TOKENLESS_PRODUCTION / 100  # dev: kick not needed

    total_supply: uint256 = self.totalSupply
    self._checkpoint_reward(addr, token, total_supply, _balance, False, ZERO_ADDRESS)
    self._update_liquidity_limit_rewards(addr, _balance, total_supply, token)

@external
@nonreentrant('lock')
def deposit(_value: uint256, _addr: address = msg.sender, _claim_rewards: bool = False):
    """
    @notice Deposit `_value` LP tokens
    @dev Depositing also claims pending reward tokens
    @param _value Number of tokens to deposit
    @param _addr Address to deposit for
    """

    self._checkpoint(_addr)

    if _value != 0:
        total_supply: uint256 = self.totalSupply
        reward_count: uint256 = self.reward_count
        if reward_count > 0:
            self._checkpoint_rewards(_addr, total_supply, _claim_rewards, ZERO_ADDRESS)

        total_supply += _value
        new_balance: uint256 = self.balanceOf[_addr] + _value
        self.balanceOf[_addr] = new_balance
        self.totalSupply = total_supply

        self._update_liquidity_limit(_addr, new_balance, total_supply)
        for i in range(MAX_REWARDS):
            if i == reward_count:
                break
            token: address = self.reward_tokens[i]
            if self.reward_data[token].ve != ZERO_ADDRESS:
                self._update_liquidity_limit_rewards(_addr, new_balance, total_supply, token)

        ERC20(self.lp_token).transferFrom(msg.sender, self, _value)

    log Deposit(_addr, _value)
    log Transfer(ZERO_ADDRESS, _addr, _value)


@external
@nonreentrant('lock')
def withdraw(_value: uint256, _claim_rewards: bool = False):
    """
    @notice Withdraw `_value` LP tokens
    @dev Withdrawing also claims pending reward tokens
    @param _value Number of tokens to withdraw
    """
    self._checkpoint(msg.sender)

    if _value != 0:
        total_supply: uint256 = self.totalSupply
        reward_count: uint256 = self.reward_count
        if reward_count > 0:
            self._checkpoint_rewards(msg.sender, total_supply, _claim_rewards, ZERO_ADDRESS)

        total_supply -= _value
        new_balance: uint256 = self.balanceOf[msg.sender] - _value
        self.balanceOf[msg.sender] = new_balance
        self.totalSupply = total_supply

        self._update_liquidity_limit(msg.sender, new_balance, total_supply)
        for i in range(MAX_REWARDS):
            if i == reward_count:
                break
            token: address = self.reward_tokens[i]
            if self.reward_data[token].ve != ZERO_ADDRESS:
                self._update_liquidity_limit_rewards(msg.sender, new_balance, total_supply, token)

        ERC20(self.lp_token).transfer(msg.sender, _value)

    log Withdraw(msg.sender, _value)
    log Transfer(msg.sender, ZERO_ADDRESS, _value)


@internal
def _transfer(_from: address, _to: address, _value: uint256):
    self._checkpoint(_from)
    self._checkpoint(_to)

    if _value != 0:
        total_supply: uint256 = self.totalSupply
        reward_count: uint256 = self.reward_count
        if reward_count > 0:
            self._checkpoint_rewards(_from, total_supply, False, ZERO_ADDRESS)
        new_balance_from: uint256 = self.balanceOf[_from] - _value
        self.balanceOf[_from] = new_balance_from
        self._update_liquidity_limit(_from, new_balance_from, total_supply)

        if reward_count > 0:
            self._checkpoint_rewards(_to, total_supply, False, ZERO_ADDRESS)
        new_balance_to: uint256 = self.balanceOf[_to] + _value
        self.balanceOf[_to] = new_balance_to
        self._update_liquidity_limit(_to, new_balance_to, total_supply)
        for i in range(MAX_REWARDS):
            if i == reward_count:
                break
            token: address = self.reward_tokens[i]
            if self.reward_data[token].ve != ZERO_ADDRESS:
                self._update_liquidity_limit_rewards(_from, new_balance_from, total_supply, token)
                self._update_liquidity_limit_rewards(_to, new_balance_to, total_supply, token)

    log Transfer(_from, _to, _value)


@external
@nonreentrant('lock')
def transfer(_to : address, _value : uint256) -> bool:
    """
    @notice Transfer token for a specified address
    @dev Transferring claims pending reward tokens for the sender and receiver
    @param _to The address to transfer to.
    @param _value The amount to be transferred.
    """
    self._transfer(msg.sender, _to, _value)

    return True


@external
@nonreentrant('lock')
def transferFrom(_from : address, _to : address, _value : uint256) -> bool:
    """
     @notice Transfer tokens from one address to another.
     @dev Transferring claims pending reward tokens for the sender and receiver
     @param _from address The address which you want to send tokens from
     @param _to address The address which you want to transfer to
     @param _value uint256 the amount of tokens to be transferred
    """
    _allowance: uint256 = self.allowance[_from][msg.sender]
    if _allowance != MAX_UINT256:
        self.allowance[_from][msg.sender] = _allowance - _value

    self._transfer(_from, _to, _value)

    return True


@external
def approve(_spender : address, _value : uint256) -> bool:
    """
    @notice Approve the passed address to transfer the specified amount of
            tokens on behalf of msg.sender
    @dev Beware that changing an allowance via this method brings the risk
         that someone may use both the old and new allowance by unfortunate
         transaction ordering. This may be mitigated with the use of
         {incraseAllowance} and {decreaseAllowance}.
         https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
    @param _spender The address which will transfer the funds
    @param _value The amount of tokens that may be transferred
    @return bool success
    """
    self.allowance[msg.sender][_spender] = _value
    log Approval(msg.sender, _spender, _value)

    return True


@external
def increaseAllowance(_spender: address, _added_value: uint256) -> bool:
    """
    @notice Increase the allowance granted to `_spender` by the caller
    @dev This is alternative to {approve} that can be used as a mitigation for
         the potential race condition
    @param _spender The address which will transfer the funds
    @param _added_value The amount of to increase the allowance
    @return bool success
    """
    allowance: uint256 = self.allowance[msg.sender][_spender] + _added_value
    self.allowance[msg.sender][_spender] = allowance

    log Approval(msg.sender, _spender, allowance)

    return True


@external
def decreaseAllowance(_spender: address, _subtracted_value: uint256) -> bool:
    """
    @notice Decrease the allowance granted to `_spender` by the caller
    @dev This is alternative to {approve} that can be used as a mitigation for
         the potential race condition
    @param _spender The address which will transfer the funds
    @param _subtracted_value The amount of to decrease the allowance
    @return bool success
    """
    allowance: uint256 = self.allowance[msg.sender][_spender] - _subtracted_value
    self.allowance[msg.sender][_spender] = allowance

    log Approval(msg.sender, _spender, allowance)

    return True


@external
def add_reward(_reward_token: address, _distributor: address, _ve: address, _veBoost: address):
    """
    @notice Set the active reward contract
    """
    assert msg.sender == self.admin  # dev: only owner
    assert _distributor != ZERO_ADDRESS

    reward_count: uint256 = self.reward_count
    assert reward_count < MAX_REWARDS
    assert self.reward_data[_reward_token].distributor == ZERO_ADDRESS

    self.reward_data[_reward_token].distributor = _distributor
    self.reward_data[_reward_token].ve = _ve
    self.reward_data[_reward_token].veBoost = _veBoost
    self.reward_tokens[reward_count] = _reward_token
    self.reward_count = reward_count + 1


@external
def set_reward_distributor(_reward_token: address, _distributor: address):
    current_distributor: address = self.reward_data[_reward_token].distributor

    assert msg.sender == current_distributor or msg.sender == self.admin
    assert current_distributor != ZERO_ADDRESS
    assert _distributor != ZERO_ADDRESS

    self.reward_data[_reward_token].distributor = _distributor

@external
def set_reward_voting_escrow(_reward_token: address, _ve: address, _veBoost: address):
    assert msg.sender == self.admin # dev: only owner
    self.reward_data[_reward_token].ve = _ve
    self.reward_data[_reward_token].veBoost = _veBoost

@external
@nonreentrant("lock")
def deposit_reward_token(_reward_token: address, _amount: uint256):
    assert msg.sender == self.reward_data[_reward_token].distributor

    self._checkpoint_rewards(ZERO_ADDRESS, self.totalSupply, False, ZERO_ADDRESS)

    response: Bytes[32] = raw_call(
        _reward_token,
        concat(
            method_id("transferFrom(address,address,uint256)"),
            convert(msg.sender, bytes32),
            convert(self, bytes32),
            convert(_amount, bytes32),
        ),
        max_outsize=32,
    )
    if len(response) != 0:
        assert convert(response, bool)

    period_finish: uint256 = self.reward_data[_reward_token].period_finish
    if block.timestamp >= period_finish:
        self.reward_data[_reward_token].rate = _amount / WEEK
    else:
        remaining: uint256 = period_finish - block.timestamp
        leftover: uint256 = remaining * self.reward_data[_reward_token].rate
        self.reward_data[_reward_token].rate = (_amount + leftover) / WEEK

    self.reward_data[_reward_token].last_update = block.timestamp
    self.reward_data[_reward_token].period_finish = block.timestamp + WEEK


@external
def set_killed(_is_killed: bool):
    """
    @notice Set the killed status for this contract
    @dev When killed, the gauge always yields a rate of 0 and so cannot mint CRV
    @param _is_killed Killed status to set
    """
    assert msg.sender == self.admin

    self.is_killed = _is_killed


@external
def commit_transfer_ownership(addr: address):
    """
    @notice Transfer ownership of GaugeController to `addr`
    @param addr Address to have ownership transferred to
    """
    assert msg.sender == self.admin  # dev: admin only

    self.future_admin = addr
    log CommitOwnership(addr)


@external
def accept_transfer_ownership():
    """
    @notice Accept a pending ownership transfer
    """
    _admin: address = self.future_admin
    assert msg.sender == _admin  # dev: future admin only

    self.admin = _admin
    log ApplyOwnership(_admin)