Redesign fee market payment

[boundless-forest]

TODO

• (Update tests)
• (Remove RewardBook)

[hackfisher]

Have kind of difficulty to read the code from my point as a reviewer. There might be still spaces for the code to be more simplified/clean.

And it's a chance to review and simplify other business logic.

Request for better naming and docs.

@hujw77 @wuminzhe please review.

[hackfisher]

Maybe in another PR, need to handle the dispatch fee (message.weight)

https://github.com/darwinia-network/darwinia-messages-substrate/issues/142

[hackfisher]

V3:
{
    confirm_relayer 落在哪个Slot Index, Slot price is the relayer ask for Slot Index.

    Message surplus = Message Fee - Slot price.

    1. 
      A: Slot Offensive Slash: ?For each assigned relayer's slot index < Slot index(Confirm), slash: a) collateral_const * 20% and no reward or b) slash function(t) in expriy time (> last slot)

    Message Reward = Slot price + Slot Offensive Slash

      B. Slot Duty Reward = Message surplus * 20% -> assigned relayers which >= Slot index(Confirm)  (If no relayers match the condition, Ask reward is zero)

    Message surplus -= Slot Duty Reward

    2. Message Reward -> (delivery_relayer, confirm_relayer)

    3. Treasury: Message surplus
}

[boundless-forest]

V3:
{
    confirm_relayer 落在哪个Slot Index, Slot price is the relayer ask for Slot Index.

    Message surplus = Message Fee - Slot price.

    1. 
      A: Slot Offensive Slash: ?For each assigned relayer's slot index < Slot index(Confirm), slash: a) collateral_const * 20% and no reward or b) slash function(t) in expriy time (> last slot)

    Message Reward = Slot price + Slot Offensive Slash

      B. Slot Duty Reward = Message surplus * 20% -> assigned relayers which >= Slot index(Confirm)  (If no relayers match the condition, Ask reward is zero)

    Message surplus -= Slot Duty Reward

    2. Message Reward -> (delivery_relayer, confirm_relayer)

    3. Treasury: Message surplus
}

I find a issue while doing tests:

Assuming the fee market with 3 assigned relayers A, B, C with quota QA, QB, QC. If there is a order confirmed at the third slot, the message fee paied by user is QC in this case, the slot price is also QC when calculate rewards. Thus the message_surplus is 0, the slot duty reward for C is zero as well. That's seems make no sense. Confirmed in the third slot is still considered in-time delivery, the slot duty reward for C should not be zero. @hackfisher @hujw77

[hackfisher]

the slot duty reward for C is zero as well. That's seems make no sense

This looks good to me, C still will get incentives from the message reward.

[boundless-forest]

This looks good to me, C still will get incentives from the message reward.

It may not be the case, C may not be a message deliver or confirm relayer. Check out this test case: https://github.com/darwinia-network/darwinia-messages-substrate/blob/bear-slash-empty-relayers/modules/fee-market/src/tests.rs#L1027-L1060