1
From the Solidity documentation:
A contract can have at most one fallback function, declared using fallback () external [payable] (without the function keyword). This function cannot have arguments, cannot return anything and must have external visibility. It is executed on a call to the contract if none of the other functions match the given function ...
1
Since you are passing value > 0 in:
contract.methods.main(amount, guess).send({value: amountWei, ...}, ...)
You need to declare function main as payable.
1
It's not easy to conjure up a trivial example. Based on the comments, I think the main concerns are approximately:
Clean up expired information responsibly and capture the gas refund offered for releasing unneeded storage.
Avoid iteration. https://blog.b9lab.com/getting-loopy-with-solidity-1d51794622ad
Access information in O(1), by user, by epoch, globally ...
Only top voted, non community-wiki answers of a minimum length are eligible
