[Protocol3] Improved maintenance mode

[Brechtpd]

Implements #206.

Tests still need to be updated.

[dong77]

can this be written as:
uint costLRC = S.getDowntimeCostLRC(numMinutesToPurchase);

[Brechtpd]

That doesn't seem possible because it's a function in the same library. If you do something like this:

library ExchangeAdmins
{
    using ExchangeAdmins for ExchangeData.State;
    ...
}

then this strangely compiles, but cannot be deployed because it references itself.

[dong77]

Fair enough.

[dong77]

use block.timestamp instead of now

[Brechtpd]

Any reason for this? now is exactly the same as block.timestamp:
https://solidity.readthedocs.io/en/develop/units-and-global-variables.html?highlight=block.timestamp#block-and-transaction-properties

All other code uses now.

[dong77]

Ok, there is a lint warning we should use block.timestamp instead of now. But if you don't see it, it means we disabled that rule. Then stick to now for consistence then.

[dong77]

@Brechtpd can we add a totalDowntime per exchange. Maybe also have a view method called

getTotalDowntimeBips to return totalDowntime * 100 / totalExchangeLifetime, this will be a good indicator of the exchange's quality of service.

In future versions, we may want to give a different downtime price per minute, for example:

function getDowntimePricePerMinute() {
  uint multipler = getTotalDowntimeBips() / 100;
  if (totalDowntimeMin < 30 days || multipler == 0) {
    multipler = 1;
  } else if (multipler > 5) {
    multipler = 5;
  }
   return downtimePriceLRCPerMinute * multipler;
}

** UPDATE **

After a second thought, maybe we should still use constant price for the downtime. We should not set up any barrier for a DEX to operate? @Brechtpd ?

[Brechtpd]

@Brechtpd can we add a totalDowntime per exchange. Maybe also have a view method called

getTotalDowntimeBips to return totalDowntime * 100 / totalExchangeLifetime, this will be a good indicator of the exchange's quality of service.

Good idea. I exposed getTotalTimeInMaintenanceSeconds and getExchangeCreationTimestamp which allows doing this.

[dong77]

LGTM.

[dong77]

please merge once tests pass.

[Brechtpd]

After a second thought, maybe we should still use constant price for the downtime. We should not set up any barrier for a DEX to operate? @Brechtpd ?

Maintenance mode needs to be expensive because users cannot withdraw anything in maintenance. If it's cheap the exchange can hold user funds hostage for a long time. Making maintenance mode even more expensive if it's used a lot could make sense, other parameters like total user funds stored in the exchange, ... could also be used.