[Stablestake]: Fix USDC earn amount and borrow ratio (#830)

* add account interest migration

* add migration

x/stablestake/keeper/begin_blocker.go

@@ -19,7 +19,6 @@ func (k Keeper) BeginBlocker(ctx sdk.Context) {
 		k.SetParams(ctx, params)
 	}
 	k.SetInterest(ctx, uint64(ctx.BlockHeight()), types.InterestBlock{InterestRate: params.InterestRate, BlockTime: ctx.BlockTime().Unix(), BlockHeight: uint64(ctx.BlockHeight())})
-
 	// Remove old data, should keep data of 2 years
 	if numBlocks < int(ctx.BlockHeight()) {
 		delBlock := ctx.BlockHeight() - int64(numBlocks)

x/stablestake/keeper/debt.go

@@ -260,3 +260,28 @@ func (k Keeper) DeleteAllInterest(ctx sdk.Context) {
 		store.Delete(iterator.Key())
 	}
 }
+
+func (k Keeper) AccountInterest(ctx sdk.Context) []types.Debt {
+	store := ctx.KVStore(k.storeKey)
+	params := k.GetParams(ctx)
+
+	iterator := sdk.KVStorePrefixIterator(store, types.DebtPrefixKey)
+	defer iterator.Close()
+
+	debts := []types.Debt{}
+	for ; iterator.Valid(); iterator.Next() {
+		debt := types.Debt{}
+		k.cdc.MustUnmarshal(iterator.Value(), &debt)
+
+		// Set to 17% (as it couldn't be more over period of ~6 months)
+		// Note: These interest values were inflated due to a migration issue
+		val := sdk.NewDecFromInt(debt.Borrowed).Mul(sdk.NewDecWithPrec(17, 2))
+		if debt.InterestStacked.GT(val.TruncateInt()) {
+			sub := debt.InterestStacked.Sub(val.TruncateInt())
+			params.TotalValue = params.TotalValue.Sub(sub)
+			debt.InterestStacked = val.TruncateInt()
+		}
+	}
+	k.SetParams(ctx, params)
+	return debts
+}

x/stablestake/migrations/v6_migration.go

@@ -0,0 +1,12 @@
+package migrations
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+func (m Migrator) V6Migration(ctx sdk.Context) error {
+
+	m.keeper.AccountInterest(ctx)
+
+	return nil
+}

x/stablestake/module.go

@@ -117,7 +117,7 @@ func (am AppModule) RegisterServices(cfg module.Configurator) {
 	types.RegisterMsgServer(cfg.MsgServer(), keeper.NewMsgServerImpl(am.keeper))
 	types.RegisterQueryServer(cfg.QueryServer(), am.keeper)
 	m := migrations.NewMigrator(am.keeper)
-	err := cfg.RegisterMigration(types.ModuleName, 4, m.V5Migration)
+	err := cfg.RegisterMigration(types.ModuleName, 5, m.V6Migration)
 	if err != nil {
 		panic(err)
 	}
@@ -144,7 +144,7 @@ func (am AppModule) ExportGenesis(ctx sdk.Context, cdc codec.JSONCodec) json.Raw
 }
 
 // ConsensusVersion is a sequence number for state-breaking change of the module. It should be incremented on each consensus-breaking change introduced by the module. To avoid wrong/empty versions, the initial version should be set to 1
-func (AppModule) ConsensusVersion() uint64 { return 5 }
+func (AppModule) ConsensusVersion() uint64 { return 6 }
 
 // BeginBlock contains the logic that is automatically triggered at the beginning of each block
 func (am AppModule) BeginBlock(ctx sdk.Context, _ abci.RequestBeginBlock) {