Adding an additional function in an ERC-1155 contract that handles the issuance of the ERC-721 tokens it contains. This function would have logic to check the amount of ether being sent to a method. If it's not enough,
mint fails. If it's just enough,
mint goes through. If it's too much,
mint occurs and sends the extra back (minus tx fees) to the owner.
You will have to create an ERC-1155 collection responsible for minting the ERC-721 tokens and define custom logic for price. Any time
transferTo is called on the NFT, it must call the collection which owns it to determine if the price is enough, right, or too much.
Your logic could be rigid, and place a hard cap on price, or dynamic to allow events like discounts to take place. Since your question is vague, I'll indulge both slightly.
A collection contains many ERC-721 NFTs which may have slightly different properties; a ticket would have metadata like
This is a novel area of development and ripe for improvisation and unique solutions. I would encourage you to think outside the box while working on this project.
Unlike traditional markets, you don't need a counterparty to determine the price using this model. The price you get for an asset is determined by a formula. If I'm looking at a single source of ETH:DAI liquidity, and I want to buy all of the ETH, I could not, as each ETH purchased exponentially increases the price with zero as a limit, if either
y reach zero, the equation doesn't work, our
k value goes to zero, making the asset unbuyable.
If you want a price set in stone with no change at all, collection need only to limit the maximum number of ETH that can be sent to call the
mint function on an NFT within it, with remainder being returned to the purchasing account.
But right now, prices are not always set in stone. There are early bird specials, discounts for purchasing many tickets (e.g. company gatherings), and even discounts after an underwhelming sale to fill seats are all commonplace.
You could loosely define the value of something (arbitrarily) as:
Value = Utility + Ownership History + Future Value + Liquidity
A ticket's has high utility, low/no ownership history impact, no future value, and liquidity varies (depending on number of sold out tickets, hype surrounding the event, number of seats). Compared to a piece of art that's sold 100 times which has low utility, high ownership history, potential future value, and liquidity without an ending time.
Since ownership history and future value are not important for tickets, we have liquidity (availability) and demand.
Value = Availability / Demand
demand is dependent on
availability. Your 1155 contract would set the initial
demand value, and the
availability is determined by the number of tokens not claimed by an address in the collection leading up to the event.
A fixed price requires less code, as you simply need to set it's value in the purchasing token.
availability is not part of any equation and serves only to see the remaining number of tickets.
In the case of a fluctuating price,
demand could be represented as a floating point variable between 0-1. When tickets first go on sale,
demand starts at 1 as zero tickets have been minted. We can approach zero, but can never reach it even if there is no demand for tickets as it creates a mathematical impossibility. It is likely that
demand will remain constant: people who want to go to something want to go to something regardless. If they can afford it, they'll go. The only thing this does is reduce the price proportionally depending on the number of requests for tickets, which is not unlike tickets to events today where promoters will give discounts just to fill the seats.
Setting the equation up like this also prevents the price from going above the sale price as you cap
demand at 1 in the controlling contract. However, you could alter this and allow for some resale within a reasonable range. If it's last minute, sometimes ticket prices do go up (scalpers or not). Perhaps setting
demand to a floating point value slightly above one would make more sense.
If the NFT is controlled by an 1155 collection with custom logic, you can define any type of price issuance from fixed price to a bonding curve, or even lower the cost automatically if
N number of tickets are still unsold
X days prior to the event in order to sell out.