Negative coin error fix (#390)

* Adding the condition which avoids negative coin error.

* Adding condition to return error when undelegation tokens are more than delegated tokens.

* Adding big test cases for delegate and undelegate validator-amount generation.

* Using sdk errors to report insufficient funds to undelegate.

* Changing the way of sorting WeightedAddressAmounts.

Author: arhamchordia

x/lscosmos/keeper/delegation_strategy.go

@@ -91,23 +91,33 @@ func (k Keeper) UndelegateMsgs(ctx sdk.Context, amount sdk.Int, denom string, de
 
 // FetchValidatorsToDelegate gives a list of all validators having weighted amount for few and 1uatom for rest in order to auto claim all rewards accumulated in current epoch
 func FetchValidatorsToDelegate(valList types.AllowListedValidators, delegationState types.DelegationState, amount sdk.Coin) (types.ValAddressAmounts, error) {
-	curDiffDistribution := GetIdealCurrentDelegations(valList, delegationState, amount, false)
+	curDiffDistribution, err := GetIdealCurrentDelegations(valList, delegationState, amount, false)
+	if err != nil {
+		return nil, err
+	}
 	sort.Sort(sort.Reverse(curDiffDistribution))
 
 	return DivideAmountIntoValidatorSet(curDiffDistribution, amount)
 }
 
 // FetchValidatorsToUndelegate gives a list of all validators having weighted amount for few and 1uatom for rest in order to auto claim all rewards accumulated in current epoch
 func FetchValidatorsToUndelegate(valList types.AllowListedValidators, delegationState types.DelegationState, amount sdk.Coin) (types.ValAddressAmounts, error) {
-	currDiffDistribution := GetIdealCurrentDelegations(valList, delegationState, amount, true)
+	currDiffDistribution, err := GetIdealCurrentDelegations(valList, delegationState, amount, true)
+	if err != nil {
+		return nil, err
+	}
 	sort.Sort(sort.Reverse(currDiffDistribution))
 	return DivideUndelegateAmountIntoValidatorSet(currDiffDistribution, amount)
 }
 
 // GetIdealCurrentDelegations returns ideal amount of delegations to validators on host chain
-func GetIdealCurrentDelegations(valList types.AllowListedValidators, delegationState types.DelegationState, amt sdk.Coin, reverse bool) types.WeightedAddressAmounts {
+func GetIdealCurrentDelegations(valList types.AllowListedValidators, delegationState types.DelegationState, amt sdk.Coin, reverse bool) (types.WeightedAddressAmounts, error) {
 	totalDelegations := delegationState.TotalDelegations(amt.Denom)
 
+	if reverse && totalDelegations.IsLT(amt) {
+		return nil, sdkerrors.Wrapf(types.ErrInsufficientFundsToUndelegate, "staked:  %s, undelegate : %s", totalDelegations, amt)
+	}
+
 	curDiffDistribution := types.WeightedAddressAmounts{}
 	delegationMap := types.GetHostAccountDelegationMap(delegationState.HostAccountDelegations)
 	var idealTokens, curTokens sdk.Int
@@ -135,7 +145,7 @@ func GetIdealCurrentDelegations(valList types.AllowListedValidators, delegationS
 		})
 	}
 
-	return curDiffDistribution
+	return curDiffDistribution, nil
 }
 
 // divideAmountWeightedSet : divides amount to be delegated or undelegated w.r.t weights.
@@ -168,8 +178,14 @@ func distributeCoinsAmongstValSet(ws types.WeightedAddressAmounts, coin sdk.Coin
 			valAddrAmts = append(valAddrAmts, types.ValAddressAmount{ValidatorAddr: w.Address, Amount: coin})
 			return valAddrAmts, sdk.NewInt64Coin(coin.Denom, 0)
 		}
-		valAddrAmts = append(valAddrAmts, types.ValAddressAmount{ValidatorAddr: w.Address, Amount: w.Coin()})
-		coin = coin.SubAmount(w.Amount)
+
+		tempAmount := w.Amount
+		if w.Amount.IsNegative() {
+			tempAmount = sdk.ZeroInt()
+		}
+
+		valAddrAmts = append(valAddrAmts, types.ValAddressAmount{ValidatorAddr: w.Address, Amount: sdk.NewCoin(w.Denom, tempAmount)})
+		coin = coin.SubAmount(tempAmount)
 	}
 
 	return valAddrAmts, coin