# @version 0.2.15
"""
@title Voting Escrow
@author Curve Finance
@license MIT
@notice Votes have a weight depending on time, so that users are
        committed to the future of (whatever they are voting for)
@dev Vote weight decays linearly over time. Lock time cannot be
     more than `MAXTIME` (4 years).
"""

# Voting escrow to have time-weighted votes
# Votes have a weight depending on time, so that users are committed
# to the future of (whatever they are voting for).
# The weight in this implementation is linear, and lock cannot be more than maxtime:
# w ^
# 1 +        /
#   |      /
#   |    /
#   |  /
#   |/
# 0 +--------+------> time
#       maxtime (4 years?)

struct Point:
    bias: int128
    slope: int128  # - dweight / dt
    ts: uint256
    blk: uint256  # block
# We cannot really do block numbers per se b/c slope is per time, not per block
# and per block could be fairly bad b/c Ethereum changes blocktimes.
# What we can do is to extrapolate ***At functions

struct LockedBalance:
    amount: int128
    end: uint256


interface ERC20:
    def decimals() -> uint256: view
    def name() -> String[64]: view
    def symbol() -> String[32]: view
    def transfer(to: address, amount: uint256) -> bool: nonpayable
    def transferFrom(spender: address, to: address, amount: uint256) -> bool: nonpayable


# Interface for checking whether address belongs to a whitelisted
# type of a smart wallet.
# When new types are added - the whole contract is changed
# The check() method is modifying to be able to use caching
# for individual wallet addresses
interface SmartWalletChecker:
    def check(addr: address) -> bool: nonpayable

DEPOSIT_FOR_TYPE: constant(int128) = 0
CREATE_LOCK_TYPE: constant(int128) = 1
INCREASE_LOCK_AMOUNT: constant(int128) = 2
INCREASE_UNLOCK_TIME: constant(int128) = 3


event CommitOwnership:
    admin: address

event ApplyOwnership:
    admin: address

event Deposit:
    provider: indexed(address)
    value: uint256
    locktime: indexed(uint256)
    type: int128
    ts: uint256

event Withdraw:
    provider: indexed(address)
    value: uint256
    ts: uint256

event Supply:
    prevSupply: uint256
    supply: uint256

event NewDelegation:
    delegator: indexed(address)
    gauge: indexed(address)
    receiver: indexed(address)
    pct: uint256
    cancel_time: uint256
    expire_time: uint256

event CancelledDelegation:
    delegator: indexed(address)
    gauge: indexed(address)
    receiver: indexed(address)
    cancelled_by: address

struct ReceivedBoost:
    length: uint256
    data: uint256[10]


WEEK: constant(uint256) = 7 * 86400  # all future times are rounded by week
MAXTIME: constant(uint256) = 4 * 365 * 86400  # 4 years
MULTIPLIER: constant(uint256) = 10 ** 18

token: public(address)
supply: public(uint256)

locked: public(HashMap[address, LockedBalance])

epoch: public(uint256)
point_history: public(Point[100000000000000000000000000000])  # epoch -> unsigned point
user_point_history: public(HashMap[address, Point[1000000000]])  # user -> Point[user_epoch]
user_point_epoch: public(HashMap[address, uint256])
slope_changes: public(HashMap[uint256, int128])  # time -> signed slope change

# Aragon's view methods for compatibility
controller: public(address)
transfersEnabled: public(bool)

name: public(String[64])
symbol: public(String[32])
version: public(String[32])
decimals: public(uint256)

# Checker for whitelisted (smart contract) wallets which are allowed to deposit
# The goal is to prevent tokenizing the escrow
future_smart_wallet_checker: public(address)
smart_wallet_checker: public(address)

admin: public(address)  # Can and will be a smart contract
future_admin: public(address)

# user -> number of active boost delegations
delegation_count: public(HashMap[address, uint256])

# user -> gauge -> data on boosts delegated to user
# tightly packed as [address][uint16 pct][uint40 cancel time][uint40 expire time]
delegation_data: HashMap[address, HashMap[address, ReceivedBoost]]

# user -> gauge -> data about delegation user has made for this gauge
delegated_to: HashMap[address, HashMap[address, uint256]]

operator_of: public(HashMap[address, address])

MIN_VE: constant(uint256) = 2500 * 10**18


@external
def __init__(token_addr: address, _name: String[64], _symbol: String[32], _version: String[32]):
    """
    @notice Contract constructor
    @param token_addr `ERC20CRV` token address
    @param _name Token name
    @param _symbol Token symbol
    @param _version Contract version - required for Aragon compatibility
    """
    self.admin = msg.sender
    self.token = token_addr
    self.point_history[0].blk = block.number
    self.point_history[0].ts = block.timestamp
    self.controller = msg.sender
    self.transfersEnabled = True

    _decimals: uint256 = ERC20(token_addr).decimals()
    assert _decimals <= 255
    self.decimals = _decimals

    self.name = _name
    self.symbol = _symbol
    self.version = _version


@external
def commit_transfer_ownership(addr: address):
    """
    @notice Transfer ownership of VotingEscrow contract 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 apply_transfer_ownership():
    """
    @notice Apply ownership transfer
    """
    assert msg.sender == self.admin  # dev: admin only
    _admin: address = self.future_admin
    assert _admin != ZERO_ADDRESS  # dev: admin not set
    self.admin = _admin
    log ApplyOwnership(_admin)


@external
def commit_smart_wallet_checker(addr: address):
    """
    @notice Set an external contract to check for approved smart contract wallets
    @param addr Address of Smart contract checker
    """
    assert msg.sender == self.admin
    self.future_smart_wallet_checker = addr


@external
def apply_smart_wallet_checker():
    """
    @notice Apply setting external contract to check approved smart contract wallets
    """
    assert msg.sender == self.admin
    self.smart_wallet_checker = self.future_smart_wallet_checker


@internal
def assert_not_contract(addr: address):
    """
    @notice Check if the call is from a whitelisted smart contract, revert if not
    @param addr Address to be checked
    """
    if addr != tx.origin:
        checker: address = self.smart_wallet_checker
        if checker != ZERO_ADDRESS:
            if SmartWalletChecker(checker).check(addr):
                return
        raise "Smart contract depositors not allowed"


@external
@view
def get_last_user_slope(addr: address) -> int128:
    """
    @notice Get the most recently recorded rate of voting power decrease for `addr`
    @param addr Address of the user wallet
    @return Value of the slope
    """
    uepoch: uint256 = self.user_point_epoch[addr]
    return self.user_point_history[addr][uepoch].slope


@external
@view
def user_point_history__ts(_addr: address, _idx: uint256) -> uint256:
    """
    @notice Get the timestamp for checkpoint `_idx` for `_addr`
    @param _addr User wallet address
    @param _idx User epoch number
    @return Epoch time of the checkpoint
    """
    return self.user_point_history[_addr][_idx].ts


@external
@view
def locked__end(_addr: address) -> uint256:
    """
    @notice Get timestamp when `_addr`'s lock finishes
    @param _addr User wallet
    @return Epoch time of the lock end
    """
    return self.locked[_addr].end


@internal
def _checkpoint(addr: address, old_locked: LockedBalance, new_locked: LockedBalance):
    """
    @notice Record global and per-user data to checkpoint
    @param addr User's wallet address. No user checkpoint if 0x0
    @param old_locked Pevious locked amount / end lock time for the user
    @param new_locked New locked amount / end lock time for the user
    """
    u_old: Point = empty(Point)
    u_new: Point = empty(Point)
    old_dslope: int128 = 0
    new_dslope: int128 = 0
    _epoch: uint256 = self.epoch

    if addr != ZERO_ADDRESS:
        # Calculate slopes and biases
        # Kept at zero when they have to
        if old_locked.end > block.timestamp and old_locked.amount > 0:
            u_old.slope = old_locked.amount / MAXTIME
            u_old.bias = u_old.slope * convert(old_locked.end - block.timestamp, int128)
        if new_locked.end > block.timestamp and new_locked.amount > 0:
            u_new.slope = new_locked.amount / MAXTIME
            u_new.bias = u_new.slope * convert(new_locked.end - block.timestamp, int128)

        # Read values of scheduled changes in the slope
        # old_locked.end can be in the past and in the future
        # new_locked.end can ONLY by in the FUTURE unless everything expired: than zeros
        old_dslope = self.slope_changes[old_locked.end]
        if new_locked.end != 0:
            if new_locked.end == old_locked.end:
                new_dslope = old_dslope
            else:
                new_dslope = self.slope_changes[new_locked.end]

    last_point: Point = Point({bias: 0, slope: 0, ts: block.timestamp, blk: block.number})
    if _epoch > 0:
        last_point = self.point_history[_epoch]
    last_checkpoint: uint256 = last_point.ts
    # initial_last_point is used for extrapolation to calculate block number
    # (approximately, for *At methods) and save them
    # as we cannot figure that out exactly from inside the contract
    initial_last_point: Point = last_point
    block_slope: uint256 = 0  # dblock/dt
    if block.timestamp > last_point.ts:
        block_slope = MULTIPLIER * (block.number - last_point.blk) / (block.timestamp - last_point.ts)
    # If last point is already recorded in this block, slope=0
    # But that's ok b/c we know the block in such case

    # Go over weeks to fill history and calculate what the current point is
    t_i: uint256 = (last_checkpoint / WEEK) * WEEK
    for i in range(255):
        # Hopefully it won't happen that this won't get used in 5 years!
        # If it does, users will be able to withdraw but vote weight will be broken
        t_i += WEEK
        d_slope: int128 = 0
        if t_i > block.timestamp:
            t_i = block.timestamp
        else:
            d_slope = self.slope_changes[t_i]
        last_point.bias -= last_point.slope * convert(t_i - last_checkpoint, int128)
        last_point.slope += d_slope
        if last_point.bias < 0:  # This can happen
            last_point.bias = 0
        if last_point.slope < 0:  # This cannot happen - just in case
            last_point.slope = 0
        last_checkpoint = t_i
        last_point.ts = t_i
        last_point.blk = initial_last_point.blk + block_slope * (t_i - initial_last_point.ts) / MULTIPLIER
        _epoch += 1
        if t_i == block.timestamp:
            last_point.blk = block.number
            break
        else:
            self.point_history[_epoch] = last_point

    self.epoch = _epoch
    # Now point_history is filled until t=now

    if addr != ZERO_ADDRESS:
        # If last point was in this block, the slope change has been applied already
        # But in such case we have 0 slope(s)
        last_point.slope += (u_new.slope - u_old.slope)
        last_point.bias += (u_new.bias - u_old.bias)
        if last_point.slope < 0:
            last_point.slope = 0
        if last_point.bias < 0:
            last_point.bias = 0

    # Record the changed point into history
    self.point_history[_epoch] = last_point

    if addr != ZERO_ADDRESS:
        # Schedule the slope changes (slope is going down)
        # We subtract new_user_slope from [new_locked.end]
        # and add old_user_slope to [old_locked.end]
        if old_locked.end > block.timestamp:
            # old_dslope was <something> - u_old.slope, so we cancel that
            old_dslope += u_old.slope
            if new_locked.end == old_locked.end:
                old_dslope -= u_new.slope  # It was a new deposit, not extension
            self.slope_changes[old_locked.end] = old_dslope

        if new_locked.end > block.timestamp:
            if new_locked.end > old_locked.end:
                new_dslope -= u_new.slope  # old slope disappeared at this point
                self.slope_changes[new_locked.end] = new_dslope
            # else: we recorded it already in old_dslope

        # Now handle user history
        user_epoch: uint256 = self.user_point_epoch[addr] + 1

        self.user_point_epoch[addr] = user_epoch
        u_new.ts = block.timestamp
        u_new.blk = block.number
        self.user_point_history[addr][user_epoch] = u_new


@internal
def _deposit_for(_from: address, _addr: address, _value: uint256, unlock_time: uint256, locked_balance: LockedBalance, type: int128):
    """
    @notice Deposit and lock tokens for a user
    @param _addr User's wallet address
    @param _value Amount to deposit
    @param unlock_time New time when to unlock the tokens, or 0 if unchanged
    @param locked_balance Previous locked amount / timestamp
    """
    _locked: LockedBalance = locked_balance
    supply_before: uint256 = self.supply

    self.supply = supply_before + _value
    old_locked: LockedBalance = _locked
    # Adding to existing lock, or if a lock is expired - creating a new one
    _locked.amount += convert(_value, int128)
    if unlock_time != 0:
        _locked.end = unlock_time
    self.locked[_addr] = _locked

    # Possibilities:
    # Both old_locked.end could be current or expired (>/< block.timestamp)
    # value == 0 (extend lock) or value > 0 (add to lock or extend lock)
    # _locked.end > block.timestamp (always)
    self._checkpoint(_addr, old_locked, _locked)

    if _value != 0:
        assert ERC20(self.token).transferFrom(_from, self, _value)

    log Deposit(_addr, _value, _locked.end, type, block.timestamp)
    log Supply(supply_before, supply_before + _value)


@external
def checkpoint():
    """
    @notice Record global data to checkpoint
    """
    self._checkpoint(ZERO_ADDRESS, empty(LockedBalance), empty(LockedBalance))


@external
@nonreentrant('lock')
def deposit_for(_addr: address, _value: uint256):
    """
    @notice Deposit `_value` tokens for `_addr` and add to the lock
    @dev Anyone (even a smart contract) can deposit for someone else, but
         cannot extend their locktime and deposit for a brand new user
    @param _addr User's wallet address
    @param _value Amount to add to user's lock
    """
    _locked: LockedBalance = self.locked[_addr]

    assert _value > 0  # dev: need non-zero value
    assert _locked.amount > 0, "No existing lock found"
    assert _locked.end > block.timestamp, "Cannot add to expired lock. Withdraw"

    self._deposit_for(msg.sender, _addr, _value, 0, self.locked[_addr], DEPOSIT_FOR_TYPE)


@external
@nonreentrant('lock')
def create_lock(_value: uint256, _unlock_time: uint256):
    """
    @notice Deposit `_value` tokens for `msg.sender` and lock until `_unlock_time`
    @param _value Amount to deposit
    @param _unlock_time Epoch time when tokens unlock, rounded down to whole weeks
    """
    self.assert_not_contract(msg.sender)
    unlock_time: uint256 = (_unlock_time / WEEK) * WEEK  # Locktime is rounded down to weeks
    _locked: LockedBalance = self.locked[msg.sender]

    assert _value > 0  # dev: need non-zero value
    assert _locked.amount == 0, "Withdraw old tokens first"
    assert unlock_time > block.timestamp, "Can only lock until time in the future"
    assert unlock_time <= block.timestamp + MAXTIME, "Voting lock can be 4 years max"

    self._deposit_for(msg.sender, msg.sender, _value, unlock_time, _locked, CREATE_LOCK_TYPE)


@external
@nonreentrant('lock')
def increase_amount(_value: uint256):
    """
    @notice Deposit `_value` additional tokens for `msg.sender`
            without modifying the unlock time
    @param _value Amount of tokens to deposit and add to the lock
    """
    self.assert_not_contract(msg.sender)
    _locked: LockedBalance = self.locked[msg.sender]

    assert _value > 0  # dev: need non-zero value
    assert _locked.amount > 0, "No existing lock found"
    assert _locked.end > block.timestamp, "Cannot add to expired lock. Withdraw"

    self._deposit_for(msg.sender, msg.sender, _value, 0, _locked, INCREASE_LOCK_AMOUNT)


@external
@nonreentrant('lock')
def increase_unlock_time(_unlock_time: uint256):
    """
    @notice Extend the unlock time for `msg.sender` to `_unlock_time`
    @param _unlock_time New epoch time for unlocking
    """
    self.assert_not_contract(msg.sender)
    _locked: LockedBalance = self.locked[msg.sender]
    unlock_time: uint256 = (_unlock_time / WEEK) * WEEK  # Locktime is rounded down to weeks

    assert _locked.end > block.timestamp, "Lock expired"
    assert _locked.amount > 0, "Nothing is locked"
    assert unlock_time > _locked.end, "Can only increase lock duration"
    assert unlock_time <= block.timestamp + MAXTIME, "Voting lock can be 4 years max"

    self._deposit_for(msg.sender, msg.sender, 0, unlock_time, _locked, INCREASE_UNLOCK_TIME)


@external
@nonreentrant('lock')
def withdraw():
    """
    @notice Withdraw all tokens for `msg.sender`
    @dev Only possible if the lock has expired
    """
    _locked: LockedBalance = self.locked[msg.sender]
    assert block.timestamp >= _locked.end, "The lock didn't expire"
    value: uint256 = convert(_locked.amount, uint256)

    old_locked: LockedBalance = _locked
    _locked.end = 0
    _locked.amount = 0
    self.locked[msg.sender] = _locked
    supply_before: uint256 = self.supply
    self.supply = supply_before - value

    # old_locked can have either expired <= timestamp or zero end
    # _locked has only 0 end
    # Both can have >= 0 amount
    self._checkpoint(msg.sender, old_locked, _locked)

    assert ERC20(self.token).transfer(msg.sender, value)

    log Withdraw(msg.sender, value, block.timestamp)
    log Supply(supply_before, supply_before - value)


# The following ERC20/minime-compatible methods are not real balanceOf and supply!
# They measure the weights for the purpose of voting, so they don't represent
# real coins.

@internal
@view
def find_block_epoch(_block: uint256, max_epoch: uint256) -> uint256:
    """
    @notice Binary search to estimate timestamp for block number
    @param _block Block to find
    @param max_epoch Don't go beyond this epoch
    @return Approximate timestamp for block
    """
    # Binary search
    _min: uint256 = 0
    _max: uint256 = max_epoch
    for i in range(128):  # Will be always enough for 128-bit numbers
        if _min >= _max:
            break
        _mid: uint256 = (_min + _max + 1) / 2
        if self.point_history[_mid].blk <= _block:
            _min = _mid
        else:
            _max = _mid - 1
    return _min

@internal
@view
def _balanceOf(addr: address, _t: uint256 = block.timestamp) -> uint256:
    """
    @notice Get the current voting power for `msg.sender`
    @dev Adheres to the ERC20 `balanceOf` interface for Aragon compatibility
    @param addr User wallet address
    @param _t Epoch time to return voting power at
    @return User voting power
    """
    _epoch: uint256 = self.user_point_epoch[addr]
    if _epoch == 0:
        return 0
    else:
        last_point: Point = self.user_point_history[addr][_epoch]
        last_point.bias -= last_point.slope * convert(_t - last_point.ts, int128)
        if last_point.bias < 0:
            last_point.bias = 0
        return convert(last_point.bias, uint256)

@external
@view
def balanceOf(addr: address, _t: uint256 = block.timestamp) -> uint256:
    """
    @notice Get the current voting power for `msg.sender`
    @dev Adheres to the ERC20 `balanceOf` interface for Aragon compatibility
    @param addr User wallet address
    @param _t Epoch time to return voting power at
    @return User voting power
    """
    return self._balanceOf(addr, _t)

@external
@view
def balanceOfAt(addr: address, _block: uint256) -> uint256:
    """
    @notice Measure voting power of `addr` at block height `_block`
    @dev Adheres to MiniMe `balanceOfAt` interface: https://github.com/Giveth/minime
    @param addr User's wallet address
    @param _block Block to calculate the voting power at
    @return Voting power
    """
    # Copying and pasting totalSupply code because Vyper cannot pass by
    # reference yet
    assert _block <= block.number

    # Binary search
    _min: uint256 = 0
    _max: uint256 = self.user_point_epoch[addr]
    for i in range(128):  # Will be always enough for 128-bit numbers
        if _min >= _max:
            break
        _mid: uint256 = (_min + _max + 1) / 2
        if self.user_point_history[addr][_mid].blk <= _block:
            _min = _mid
        else:
            _max = _mid - 1

    upoint: Point = self.user_point_history[addr][_min]

    max_epoch: uint256 = self.epoch
    _epoch: uint256 = self.find_block_epoch(_block, max_epoch)
    point_0: Point = self.point_history[_epoch]
    d_block: uint256 = 0
    d_t: uint256 = 0
    if _epoch < max_epoch:
        point_1: Point = self.point_history[_epoch + 1]
        d_block = point_1.blk - point_0.blk
        d_t = point_1.ts - point_0.ts
    else:
        d_block = block.number - point_0.blk
        d_t = block.timestamp - point_0.ts
    block_time: uint256 = point_0.ts
    if d_block != 0:
        block_time += d_t * (_block - point_0.blk) / d_block

    upoint.bias -= upoint.slope * convert(block_time - upoint.ts, int128)
    if upoint.bias >= 0:
        return convert(upoint.bias, uint256)
    else:
        return 0


@internal
@view
def supply_at(point: Point, t: uint256) -> uint256:
    """
    @notice Calculate total voting power at some point in the past
    @param point The point (bias/slope) to start search from
    @param t Time to calculate the total voting power at
    @return Total voting power at that time
    """
    last_point: Point = point
    t_i: uint256 = (last_point.ts / WEEK) * WEEK
    for i in range(255):
        t_i += WEEK
        d_slope: int128 = 0
        if t_i > t:
            t_i = t
        else:
            d_slope = self.slope_changes[t_i]
        last_point.bias -= last_point.slope * convert(t_i - last_point.ts, int128)
        if t_i == t:
            break
        last_point.slope += d_slope
        last_point.ts = t_i

    if last_point.bias < 0:
        last_point.bias = 0
    return convert(last_point.bias, uint256)


@external
@view
def totalSupply(t: uint256 = block.timestamp) -> uint256:
    """
    @notice Calculate total voting power
    @dev Adheres to the ERC20 `totalSupply` interface for Aragon compatibility
    @return Total voting power
    """
    _epoch: uint256 = self.epoch
    last_point: Point = self.point_history[_epoch]
    return self.supply_at(last_point, t)


@external
@view
def totalSupplyAt(_block: uint256) -> uint256:
    """
    @notice Calculate total voting power at some point in the past
    @param _block Block to calculate the total voting power at
    @return Total voting power at `_block`
    """
    assert _block <= block.number
    _epoch: uint256 = self.epoch
    target_epoch: uint256 = self.find_block_epoch(_block, _epoch)

    point: Point = self.point_history[target_epoch]
    dt: uint256 = 0
    if target_epoch < _epoch:
        point_next: Point = self.point_history[target_epoch + 1]
        if point.blk != point_next.blk:
            dt = (_block - point.blk) * (point_next.ts - point.ts) / (point_next.blk - point.blk)
    else:
        if point.blk != block.number:
            dt = (_block - point.blk) * (block.timestamp - point.ts) / (block.number - point.blk)
    # Now dt contains info on how far are we beyond point

    return self.supply_at(point, point.ts + dt)


# Dummy methods for compatibility with Aragon

@external
def changeController(_newController: address):
    """
    @dev Dummy method required for Aragon compatibility
    """
    assert msg.sender == self.controller
    self.controller = _newController

@view
@external
def get_delegated_to(_delegator: address, _gauge: address) -> (address, uint256, uint256, uint256):
    """
    @notice Get data about an accounts's boost delegation
    @param _delegator Address to query delegation data for
    @param _gauge Gauge address to query. Use ZERO_ADDRESS for global delegation.
    @return address receiving the delegated boost
            delegated boost pct (out of 10000)
            cancellable timestamp
            expiry timestamp
    """
    data: uint256 = self.delegated_to[_delegator][_gauge]
    return (
        convert(shift(data, 96), address),
        shift(data, 80) % 2**16,
        shift(data, 40) % 2**40,
        data % 2**40
    )


@view
@external
def get_delegation_data(
    _receiver: address,
    _gauge: address,
    _idx: uint256
) -> (address, uint256, uint256, uint256):
    """
    @notice Get data delegation toward an account
    @param _receiver Address to query delegation data for
    @param _gauge Gauge address to query. Use ZERO_ADDRESS for global delegation.
    @param _idx Data index. Each account can receive a max of 10 delegations per pool.
    @return address of the delegator
            delegated boost pct (out of 10000)
            cancellable timestamp
            expiry timestamp
    """
    data: uint256 = self.delegation_data[_receiver][_gauge].data[_idx]
    return (
        convert(shift(data, 96), address),
        shift(data, 80) % 2**16,
        shift(data, 40) % 2**40,
        data % 2**40
    )


@external
def set_operator(_operator: address) -> bool:
    """
    @notice Set the authorized operator for an address
    @dev An operator can delegate boost, including creating delegations that
         cannot be cancelled. This permission should only be given to trusted
         3rd parties and smart contracts where the contract behavior is known
         to be not malicious.
    @param _operator Approved operator address. Set to `ZERO_ADDRESS` to revoke
                     the currently active approval.
    @return bool success
    """
    self.operator_of[msg.sender] = _operator
    return True


@internal
def _delete_delegation_data(_delegator: address, _gauge: address, _delegation_data: uint256):
    # delete record for the delegator
    self.delegated_to[_delegator][_gauge] = 0
    self.delegation_count[_delegator] -= 1

    receiver: address = convert(shift(_delegation_data, 96), address)
    length: uint256 = self.delegation_data[receiver][_gauge].length

    # delete record for the receiver
    for i in range(10):
        if i == length - 1:
            self.delegation_data[receiver][_gauge].data[i] = 0
            break
        if self.delegation_data[receiver][_gauge].data[i] == _delegation_data:
            self.delegation_data[receiver][_gauge].data[i] = self.delegation_data[receiver][_gauge].data[length-1]
            self.delegation_data[receiver][_gauge].data[length-1] = 0


@external
def delegate_boost(
    _delegator: address,
    _gauge: address,
    _receiver: address,
    _pct: uint256,
    _cancel_time: uint256,
    _expire_time: uint256
) -> bool:
    """
    @notice Delegate per-gauge or global boost to another account
    @param _delegator Address of the user delegating boost. The caller must be the
                      delegator or the approved operator of the delegator.
    @param _gauge Address of the gauge to delegate for. Set as ZERO_ADDRESS for
                  global delegation. Global delegation is not possible if there is
                  also one or more active per-gauge delegations.
    @param _receiver Address to delegate boost to.
    @param _pct Percentage of boost to delegate. 100% is expressed as 10000.
    @param _cancel_time Delegation cannot be cancelled before this time.
    @param _expire_time Delegation automatically expires at this time.
    @return bool success
    """
    assert msg.sender in [_delegator, self.operator_of[_delegator]], "Only owner or operator"

    assert _delegator != _receiver, "Cannot delegate to self"
    assert _pct >= 100, "Percent too low"
    assert _pct <= 10000, "Percent too high"
    assert _expire_time < 2**40, "Expiry time too high"
    assert _expire_time > block.timestamp, "Already expired"
    assert _cancel_time <= _expire_time, "Cancel time after expiry time"

    # check for minimum ve- balance, used to prevent 0 ve- delegation spam
    assert self._balanceOf(_delegator) >= MIN_VE, "Insufficient ve- to delegate"

    # check for an existing, expired delegation
    data: uint256 = self.delegated_to[_delegator][_gauge]
    if data != 0:
        assert data % 2**40 <= block.timestamp, "Existing delegation has not expired"
        self._delete_delegation_data(_delegator, _gauge, data)

    if _gauge == ZERO_ADDRESS:
        assert self.delegation_count[_delegator] == 0, "Cannot delegate globally while per-gauge is active"
    else:
        assert self.delegated_to[_delegator][ZERO_ADDRESS] == 0, "Cannot delegate per-gauge while global is active"

    # tightly pack the delegation data
    # [address][uint16 pct][uint40 cancel time][uint40 expire time]
    data = shift(_pct, -80) + shift(_cancel_time, -40) + _expire_time
    idx: uint256 = self.delegation_data[_receiver][_gauge].length

    self.delegation_data[_receiver][_gauge].data[idx] = data + shift(convert(_delegator, uint256), -96)
    self.delegated_to[_delegator][_gauge] = data + shift(convert(_receiver, uint256), -96)
    self.delegation_data[_receiver][_gauge].length = idx + 1

    log NewDelegation(_delegator, _gauge, _receiver, _pct, _cancel_time, _expire_time)
    return True


@external
def cancel_delegation(_delegator: address, _gauge: address) -> bool:
    """
    @notice Cancel an existing boost delegation
    @param _delegator Address of the user delegating boost. The caller can be the
                      delegator, the receiver, the approved operator of the delegator
                      or receiver. The delegator can cancel after the cancel time
                      has passed, the receiver can cancel at any time.
    @param _gauge Address of the gauge to cancel delegattion for. Set as ZERO_ADDRESS
                  for global delegation.
    @return bool success
    """
    data: uint256 = self.delegated_to[_delegator][_gauge]
    assert data != 0, "No delegation for this pool"

    receiver: address = convert(shift(data, 96), address)
    if msg.sender not in [receiver, self.operator_of[receiver]]:
        assert msg.sender in [receiver, self.operator_of[receiver]], "Only owner or operator"
        assert shift(data, 40) % 2**40 <= block.timestamp, "Not yet cancellable"

    self._delete_delegation_data(_delegator, _gauge, data)

    log CancelledDelegation(_delegator, _gauge, receiver, msg.sender)
    return True


@view
@external
def get_adjusted_ve_balance(_user: address, _gauge: address) -> uint256:
    """
    @notice Get the adjusted ve- balance of an account after delegation
    @param _user Address to query a ve- balance for
    @param _gauge Gauge address
    @return Adjusted ve- balance after delegation
    """
    # query the initial ve balance for `_user`
    voting_balance: uint256 = self._balanceOf(_user)

    # check if the user has delegated any ve and reduce the voting balance
    delegation_count: uint256 = self.delegation_count[_user]
    if delegation_count != 0:
        is_global: bool = False
        # apply global delegation
        if delegation_count == 1:
            data: uint256 = self.delegated_to[_user][ZERO_ADDRESS]
            if data % 2**40 > block.timestamp:
                voting_balance = voting_balance * (10000 - shift(data, 80) % 2**16) / 10000
                is_global = True
        # apply pool-specific delegation
        if not is_global:
            data: uint256 = self.delegated_to[_user][_gauge]
            if data % 2**40 > block.timestamp:
                voting_balance = voting_balance * (10000 - shift(data, 80) % 2**16) / 10000

    # check for other ve delegated to `_user` and increase the voting balance
    for target in [_gauge, ZERO_ADDRESS]:
        length: uint256 = self.delegation_data[_user][target].length
        if length > 0:
            for i in range(10):
                if i == length:
                    break
                data: uint256 = self.delegation_data[_user][target].data[i]
                if data % 2**40 > block.timestamp:
                    delegator: address = convert(shift(data, 96), address)
                    delegator_balance: uint256 = self._balanceOf(delegator)
                    voting_balance += delegator_balance * (shift(data, 80) % 2**16) / 10000

    return voting_balance


@external
def update_delegation_records(_user: address, _gauge: address) -> bool:
    """
    @notice Remove data about any expired delegations for a user.
    @dev Reduces gas costs when calling `get_adjusted_ve_balance` on
         an address with expired delegations.
    @param _user Address to update records for.
    @param _gauge Gauge address. Use `ZERO_ADDRESS` for global delegations.
    """
    length: uint256 = self.delegation_data[_user][_gauge].length - 1
    adjusted_length: uint256 = length

    # iterate in reverse over `delegation_data` and remove expired records
    for i in range(10):
        if i > length:
            break
        idx: uint256 = length - i
        data: uint256 = self.delegation_data[_user][_gauge].data[idx]
        if data % 2**40 <= block.timestamp:
            # delete record for the delegator
            delegator: address = convert(shift(data, 96), address)
            self.delegated_to[delegator][_gauge] = 0
            self.delegation_count[delegator] -= 1

            # delete record for the receiver
            if idx == adjusted_length:
                self.delegation_data[_user][_gauge].data[idx] = 0
            else:
                self.delegation_data[_user][_gauge].data[idx] = self.delegation_data[_user][_gauge].data[adjusted_length]
            adjusted_length -= 1

    return True