From 428c7c5444bf6171d8ba45d1f12f023875296ce8 Mon Sep 17 00:00:00 2001
From: HugoDoyon <hugo@viawebtech.ca>
Date: Wed, 31 Jul 2019 17:29:55 -0400
Subject: [PATCH] Fix "Do not propose on chain payment if the value of the
 invoice is below..." and take care of the GAP edge case

---
 .../Bitcoin/BitcoinLikePaymentHandler.cs      | 55 ++++++++++++++-----
 1 file changed, 40 insertions(+), 15 deletions(-)

diff --git a/BTCPayServer/Payments/Bitcoin/BitcoinLikePaymentHandler.cs b/BTCPayServer/Payments/Bitcoin/BitcoinLikePaymentHandler.cs
index d553c0ba0..e2c1ad50f 100644
--- a/BTCPayServer/Payments/Bitcoin/BitcoinLikePaymentHandler.cs
+++ b/BTCPayServer/Payments/Bitcoin/BitcoinLikePaymentHandler.cs
@@ -73,37 +73,62 @@ namespace BTCPayServer.Payments.Bitcoin
         public override async Task<string> IsPaymentMethodAllowedBasedOnInvoiceAmount(StoreBlob storeBlob,
             Dictionary<CurrencyPair, Task<RateResult>> rate, Money amount, PaymentMethodId paymentMethodId)
         {
+            
             Func<Money, Money, bool> compare = null;
             CurrencyValue limitValue = null;
             string errorMessage = null;
-            if (paymentMethodId.PaymentType == PaymentTypes.LightningLike &&
-               storeBlob.LightningMaxValue != null)
+            
+            if (paymentMethodId.PaymentType == PaymentTypes.BTCLike)
             {
-                compare = (a, b) => a > b;
-                limitValue = storeBlob.LightningMaxValue;
-                errorMessage = "The amount of the invoice is too high to be paid with lightning";
-            }
-            else if (paymentMethodId.PaymentType == PaymentTypes.BTCLike &&
-               storeBlob.OnChainMinValue != null)
-            {
-                compare = (a, b) => a < b;
-                limitValue = storeBlob.OnChainMinValue;
-                errorMessage = "The amount of the invoice is too low to be paid on chain";
+                if (storeBlob.LightningMaxValue == null && 
+                    storeBlob.OnChainMinValue != null)
+                {
+                    compare = (value, limit) => value < limit;
+                    limitValue = storeBlob.OnChainMinValue;
+                    errorMessage = "The amount of the invoice is too low to be paid on chain";
+                }
+                else if (storeBlob.LightningMaxValue != null && 
+                         storeBlob.OnChainMinValue != null)
+                {
+                    if (storeBlob.LightningMaxValue.Currency == storeBlob.OnChainMinValue.Currency &&
+                        storeBlob.LightningMaxValue.Value <= storeBlob.OnChainMinValue.Value)
+                    {
+                        //Case where both fields are set but OnChainMinValue is greater
+                        // --> then use LightningMaxValue as limit
+                        compare = (value, limit) => value < limit;
+                        limitValue = storeBlob.LightningMaxValue;
+                        errorMessage = "The amount of the invoice is too low to be paid on chain";
+                    }
+                    else if (storeBlob.LightningMaxValue.Currency == storeBlob.OnChainMinValue.Currency &&
+                             storeBlob.LightningMaxValue.Value > storeBlob.OnChainMinValue.Value)
+                    {
+                        //Case where both fields are set but LightningMaxValue is greater
+                        // --> then use OnChainMinValue as limit
+                        //    (Otherwise a gap of price value with no payment method is possible) 
+                        compare = (value, limit) => value < limit;
+                        limitValue = storeBlob.OnChainMinValue;
+                        errorMessage = "The amount of the invoice is too low to be paid on chain";                        
+                    }
+                }                
             }
 
+            
             if (compare != null)
             {
-                var limitValueRate = await rate[new CurrencyPair(paymentMethodId.CryptoCode, storeBlob.OnChainMinValue.Currency)];
-                if (limitValueRate.BidAsk != null)
+                var currentRateToCrypto = await rate[new CurrencyPair(paymentMethodId.CryptoCode, limitValue.Currency)];
+                
+                if (currentRateToCrypto.BidAsk != null)
                 {
-                    var limitValueCrypto = Money.Coins(limitValue.Value / limitValueRate.BidAsk.Bid);
+                    var limitValueCrypto = Money.Coins(limitValue.Value / currentRateToCrypto.BidAsk.Bid);
                     if (compare(amount, limitValueCrypto))
                     {
                         return errorMessage;
                     }
                 }
             }
+            
             return string.Empty;
+
         }
 
         public override IEnumerable<PaymentMethodId> GetSupportedPaymentMethods()