Some features require the user to pay a certain amount of MANA for execution. These features include:
Publishing a collection, which charges the user a fixed amount of MANA depending on the rarities of the items being published with the collection
Claiming a name, where the user is charged a fixed amount of MANA to claim.
Purchasing Third Party item slots, which are charged according to the number of slots bought.
Lately, The community has been using the DAO to define the price in MANA but pegged to the USD dollar. For example, the price per item for publishing a collection has been reduced from 500 MANA to 100 MANA to achieve it.
Chainlink MANA/USD Data Feed allows our contracts to obtain the rate of MANA in USD on both the Ethereum and Polygon chains. This can be used, given an original price in USD, to calculate how much MANA is required by the user to perform a certain transaction.
For more information about Chainlink go check their homepage or their whitepaper.
In summary, Chainlink is a solution in which via Oracles, one can obtain off-chain data in a tamper-proof and still decentralized manner to be used on-chain.
To implement these price feeds we will create a new contract ChainlinkOracle with
a getRate function. This oracle will be consumed by other contracts which require
the rate of MANA/USD to reflect a price accordingly. This ChainlinkOracle will
receive both a Data Feed (Represented as an
AggregatorV3Interface
by the Chainlink
docs).
A contract consuming this oracle can then do the following calculation to obtain and use/return and amount of MANA converted from USD.
uint256 priceInUSD = 100000000000000000000; // 100 USD
uint256 rate = oracle.getRate(); // 5000000000000000000 -> 5 USD per MANA
uint256 finalPrice = priceInUSD.mul(1 ether).div(rate); // 20000000000000000000 -> 20 MANA
0x56a4857acbcfe3a66965c251628B1c9f1c408C19
0xA1CbF3Fe43BC3501e3Fc4b573e822c70e76A7512