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SpeedBumpPriceGate.sol
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SpeedBumpPriceGate.sol
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// SPDX-License-Identifier: GPL-3.0-only
pragma solidity 0.8.9;
import "../interfaces/IPriceGate.sol";
/// @title A factory pattern for a price gate whose price increases exponentially on purchase and decays linearly thereafter
/// @author metapriest, adrian.wachel, marek.babiarz, radoslaw.gorecki
/// @notice This contract has no management key, anyone can add a gate
/// @dev Note passing thru the gate forwards all gas, so beneficiary can be a contract, possibly malicious
contract SpeedBumpPriceGate is IPriceGate {
// this represents a single gate
struct Gate {
uint priceIncreaseFactor;
uint priceIncreaseDenominator;
uint lastPrice;
uint decayFactor;
uint priceFloor;
uint lastPurchaseBlock;
address beneficiary;
}
// array-like mapping of gate structs
mapping (uint => Gate) public gates;
// count the gates as they come in!
uint public numGates;
/// @notice Add a price gate to the list of available price gates
/// @dev Anyone can call this, but it must be connected to MerkleIdentity via priceGateIndex to be used
/// @dev The price increase factor is split into numerator and denominator to enable fractions (wow! I love fractions!)
/// @param priceFloor the starting price and the lowest price that can be reached via decay
/// @param priceDecay the per-block rate at which the price reduces until it hits the price floor
/// @param priceIncrease the numerator of the factor by which the price multiplies when a purchase occurs
/// @param priceIncreaseDenominator the denominator of the price increase factor
/// @param beneficiary who receives the proceeds from a purchase
function addGate(uint priceFloor, uint priceDecay, uint priceIncrease, uint priceIncreaseDenominator, address beneficiary) external {
// prefix operator increments then evaluates
Gate storage gate = gates[++numGates];
gate.priceFloor = priceFloor;
gate.decayFactor = priceDecay;
gate.priceIncreaseFactor = priceIncrease;
gate.priceIncreaseDenominator = priceIncreaseDenominator;
gate.beneficiary = beneficiary;
}
/// @notice Get the cost of passing thru this gate
/// @param index which gate are we talking about?
/// @return _ethCost the amount of ether required to pass thru this gate
function getCost(uint index) override public view returns (uint _ethCost) {
Gate memory gate = gates[index];
// compute the linear decay
uint decay = gate.decayFactor * (block.number - gate.lastPurchaseBlock);
// gate.lastPrice - decay < gate.priceFloor (left side could underflow)
if (gate.lastPrice < decay + gate.priceFloor) {
return gate.priceFloor;
} else {
return gate.lastPrice - decay;
}
}
/// @notice Pass thru this gate, should be called by MerkleIndex
/// @dev This can be called by anyone, devs can call it to test it on mainnet
/// @param index which gate are we passing thru?
function passThruGate(uint index, address) override external payable {
uint price = getCost(index);
require(msg.value >= price, 'Please send more ETH');
// bump up the price
Gate storage gate = gates[index];
// multiply by the price increase factor
gate.lastPrice = (price * gate.priceIncreaseFactor) / gate.priceIncreaseDenominator;
// move up the reference
gate.lastPurchaseBlock = block.number;
// pass thru the ether
if (msg.value > 0) {
// use .call so we can send to contracts, for example gnosis safe, re-entrance is not a threat here
(bool sent, bytes memory data) = gate.beneficiary.call{value: msg.value}("");
require(sent, 'ETH transfer failed');
}
}
}