# @version 0.2.16
"""
@title Root-Chain Gauge
@author Curve Finance
@license MIT
@notice Calculates total allocated weekly CRV emission
        mints and sends across a sidechain bridge
"""

from vyper.interfaces import ERC20


interface HarmonyBridge:
    def lockToken(ethTokenAddr: address, amount: uint256, recipient: address): nonpayable

interface CRV20:
    def start_epoch_time_write() -> uint256: nonpayable
    def rate() -> uint256: view

interface Controller:
    def period() -> int128: view
    def gauge_relative_weight(addr: address, time: uint256) -> uint256: 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
    def mint(gauge: address): nonpayable


event PeriodEmission:
    period_start: uint256
    mint_amount: uint256

event CommitOwnership:
    admin: address

event ApplyOwnership:
    admin: address


WEEK: constant(uint256) = 604800
YEAR: constant(uint256) = 86400 * 365
RATE_DENOMINATOR: constant(uint256) = 10 ** 18
RATE_REDUCTION_COEFFICIENT: constant(uint256) = 1189207115002721024  # 2 ** (1/4) * 1e18
RATE_REDUCTION_TIME: constant(uint256) = YEAR
HARMONY_BRIDGE: constant(address) = 0x2dCCDB493827E15a5dC8f8b72147E6c4A5620857


minter: public(address)
crv_token: public(address)
controller: public(address)
start_epoch_time: public(uint256)

period: public(uint256)
emissions: public(uint256)
inflation_rate: public(uint256)

admin: public(address)
future_admin: public(address)  # Can and will be a smart contract
checkpoint_admin: public(address)
is_killed: public(bool)


@external
def __init__(_minter: address, _admin: address):
    """
    @notice Contract constructor
    @param _minter Minter contract address
    @param _admin Admin who can kill the gauge
    """

    crv_token: address = Minter(_minter).token()

    self.minter = _minter
    self.admin = _admin
    self.crv_token = crv_token
    self.controller = Minter(_minter).controller()

    # because we calculate the rate locally, this gauge cannot
    # be used prior to the start of the first emission period
    rate: uint256 = CRV20(crv_token).rate()
    assert rate != 0
    self.inflation_rate = rate

    self.period = block.timestamp / WEEK - 1
    self.start_epoch_time = CRV20(crv_token).start_epoch_time_write()

    ERC20(crv_token).approve(HARMONY_BRIDGE, MAX_UINT256)


@external
def checkpoint() -> bool:
    """
    @notice Mint all allocated CRV emissions and transfer across the bridge
    @dev Should be called once per week, after the new epoch period has begun
    """
    assert self.checkpoint_admin in [ZERO_ADDRESS, msg.sender]
    last_period: uint256 = self.period
    current_period: uint256 = block.timestamp / WEEK - 1

    if last_period < current_period:
        controller: address = self.controller
        Controller(controller).checkpoint_gauge(self)

        rate: uint256 = self.inflation_rate
        new_emissions: uint256 = 0
        last_period += 1
        next_epoch_time: uint256 = self.start_epoch_time + RATE_REDUCTION_TIME
        for i in range(last_period, last_period + 255):
            if i > current_period:
                break
            period_time: uint256 = i * WEEK
            period_emission: uint256 = 0
            gauge_weight: uint256 = Controller(controller).gauge_relative_weight(self, i * WEEK)

            if next_epoch_time >= period_time and next_epoch_time < period_time + WEEK:
                # If the period crosses an epoch, we calculate a reduction in the rate
                # using the same formula as used in `ERC20CRV`. We perform the calculation
                # locally instead of calling to `ERC20CRV.rate()` because we are generating
                # the emissions for the upcoming week, so there is a possibility the new
                # rate has not yet been applied.
                period_emission = gauge_weight * rate * (next_epoch_time - period_time) / 10**18
                rate = rate * RATE_DENOMINATOR / RATE_REDUCTION_COEFFICIENT
                period_emission += gauge_weight * rate * (period_time + WEEK - next_epoch_time) / 10**18

                self.inflation_rate = rate
                self.start_epoch_time = next_epoch_time
                next_epoch_time += RATE_REDUCTION_TIME
            else:
                period_emission = gauge_weight * rate * WEEK / 10**18

            log PeriodEmission(period_time, period_emission)
            new_emissions += period_emission

        self.period = current_period
        self.emissions += new_emissions
        if new_emissions > 0 and not self.is_killed:
            Minter(self.minter).mint(self)
            HarmonyBridge(HARMONY_BRIDGE).lockToken(self.crv_token, new_emissions, self)

    return True


@view
@external
def future_epoch_time() -> uint256:
    return self.start_epoch_time + YEAR


@view
@external
def user_checkpoint(addr: address) -> bool:
    return True


@view
@external
def integrate_fraction(addr: address) -> uint256:
    assert addr == self, "Gauge can only mint for itself"
    return self.emissions


@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  # dev: admin only

    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)


@external
def set_checkpoint_admin(_admin: address):
    """
    @notice Set the checkpoint admin address
    @dev Setting to ZERO_ADDRESS allows anyone to call `checkpoint`
    @param _admin Address of the checkpoint admin
    """
    assert msg.sender == self.admin  # dev: admin only

    self.checkpoint_admin = _admin