From f1cb574733b17d292fdcacf80f52b27abf8ce00e Mon Sep 17 00:00:00 2001
From: Michael Tsitrin <michael@dymension.xyz>
Date: Tue, 21 Jan 2025 11:08:00 +0200
Subject: [PATCH] first sell tokens, than charge fee

---
 x/iro/keeper/trade.go        | 16 ++++++++--------
 x/iro/types/bonding_curve.go |  4 ++--
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/x/iro/keeper/trade.go b/x/iro/keeper/trade.go
index 6c5124ba9..9beab62cb 100644
--- a/x/iro/keeper/trade.go
+++ b/x/iro/keeper/trade.go
@@ -215,14 +215,6 @@ func (k Keeper) Sell(ctx sdk.Context, planId string, seller sdk.AccAddress, amou
 		return errorsmod.Wrapf(types.ErrInvalidMinCost, "minCost: %s, cost: %s, fee: %s", minIncomeAmt.String(), costAmt.String(), takerFeeAmt.String())
 	}
 
-	// Charge taker fee
-	takerFee := sdk.NewCoin(appparams.BaseDenom, takerFeeAmt)
-	owner := k.rk.MustGetRollappOwner(ctx, plan.RollappId)
-	err = k.chargeTakerFee(ctx, takerFee, seller, &owner)
-	if err != nil {
-		return err
-	}
-
 	// send allocated tokens from seller to the plan
 	err = k.BK.SendCoinsFromAccountToModule(ctx, seller, types.ModuleName, sdk.NewCoins(sdk.NewCoin(plan.TotalAllocation.Denom, amountTokensToSell)))
 	if err != nil {
@@ -240,6 +232,14 @@ func (k Keeper) Sell(ctx sdk.Context, planId string, seller sdk.AccAddress, amou
 	plan.SoldAmt = plan.SoldAmt.Sub(amountTokensToSell)
 	k.SetPlan(ctx, *plan)
 
+	// Charge taker fee
+	takerFee := sdk.NewCoin(appparams.BaseDenom, takerFeeAmt)
+	owner := k.rk.MustGetRollappOwner(ctx, plan.RollappId)
+	err = k.chargeTakerFee(ctx, takerFee, seller, &owner)
+	if err != nil {
+		return err
+	}
+
 	// Emit event
 	err = uevent.EmitTypedEvent(ctx, &types.EventSell{
 		Seller:       seller.String(),
diff --git a/x/iro/types/bonding_curve.go b/x/iro/types/bonding_curve.go
index 2b2ea8210..f97adaf90 100644
--- a/x/iro/types/bonding_curve.go
+++ b/x/iro/types/bonding_curve.go
@@ -164,13 +164,13 @@ func (lbc BondingCurve) TokensApproximation(startingX, spendTokens math.LegacyDe
 	// Newton-Raphson iteration
 	epsilonDec := math.LegacyNewDecWithPrec(1, epsilonPrecision)
 	for i := 0; i < maxIterations; i++ {
-		fx := f(x)
+		fx := f(x) // diff between spendTokens and the actual cost to get to x
 		// If the function converges, return the result
 		if fx.Abs().LT(epsilonDec) {
 			return x, i, nil
 		}
 		prevX := x
-		fPrimex := fPrime(x)
+		fPrimex := fPrime(x) // price for new X
 
 		// defensive check to avoid division by zero
 		// not supposed to happen, as spotPriceInternal should never return 0