Conflict during migration with data in the contract

[olga24912]

Do I understand correctly the migration mechanism:

• First we create and init contract
• Migrate the data

In that case, we already have some data in the contract. For example, we register the current_account_id and owner_id and change accounts_counter https://github.com/aurora-is-near/aurora-eth-connector/blob/master/eth-connector/src/lib.rs#L197

After migration, we don't delete the current_account_id and owner_id from the accounts list, but rewrite account_counter, as a result, it can become incorrect. https://github.com/aurora-is-near/aurora-eth-connector/blob/master/eth-connector/src/lib.rs#L625

Moreover, we don't check at the end of the migration that the data is consistent:

• account_counter == self.ft.account.size();
• ft.total_supply == sum(ft.accounts.amount)
• ft.account_storage_usage == ???

And we don't migrate metadata

I propose checking before migration that all the data is empty and don't register anything in new function.

Or presenting more clear guarantee for the migration. For example, merge the data instead of rewriting it.

[mrLSD]

I think it's one major mistake here. Data should be the same as migrated data from the Engine. It means:

1. ft.total_supply == total_supply from migration
2. ft.accounts != accounts count from migration. But all accounts from migration should exist in eth-connector
3. ft.account_counter > self.ft.account.size();

But about account_counter field. May be good idea just recalculate it, yes.

Other data look consistent, and checked with method check_migration_correctness

[mrLSD]

We shouldn't migrate metadata. It's constant data, and it's initialized with contract.

[mrLSD]

Refactored at #56