mtgban/arbit: Add a Profitability index value

Replace Price Ratio in the csv column since it's unused.

Author: kodawah

mtgban/arbit.go

@@ -1,6 +1,7 @@
 package mtgban
 
 import (
+	"math"
 	"strconv"
 	"strings"
 
@@ -72,6 +73,10 @@ type ArbitOpts struct {
 	// It returns a custom factor to be applied on the buylist price,
 	// and whether the entry shoul be skipped
 	CustomCardFilter func(co *mtgmatcher.CardObject) (float64, bool)
+
+	// Constant used to offset prices (the higher the value, the less impactful
+	// lower prices will be)
+	ProfitabilityConstant float64
 }
 
 type ArbitEntry struct {
@@ -98,13 +103,18 @@ type ArbitEntry struct {
 
 	// Amount of cards that can be applied
 	Quantity int
+
+	// The higher the number the better the arbit is. Using this formula
+	// Profitability Index (PI) = (Difference / (Sell Price + 10)) * log(1 + Spread) * sqrt(Units)
+	Profitability float64
 }
 
 func Arbit(opts *ArbitOpts, vendor Vendor, seller Seller) (result []ArbitEntry, err error) {
 	minDiff := 0.0
 	minSpread := 0.0
 	useTrades := false
 	rate := 1.0
+	profitabilityConstant := 10.0
 
 	minPrice := 0.0
 	minBuyPrice := 0.0
@@ -134,6 +144,9 @@ func Arbit(opts *ArbitOpts, vendor Vendor, seller Seller) (result []ArbitEntry,
 		if opts.Rate != 0 {
 			rate = opts.Rate
 		}
+		if opts.ProfitabilityConstant > 0 {
+			profitabilityConstant = opts.ProfitabilityConstant
+		}
 		useTrades = opts.UseTrades
 
 		minPrice = opts.MinPrice
@@ -306,6 +319,11 @@ func Arbit(opts *ArbitOpts, vendor Vendor, seller Seller) (result []ArbitEntry,
 				}
 			}
 
+			profitability := (difference / (price + profitabilityConstant)) * math.Log(1+spread)
+			if qty > 1 {
+				profitability *= math.Sqrt(float64(qty))
+			}
+
 			res := ArbitEntry{
 				CardId:             cardId,
 				BuylistEntry:       blEntry,
@@ -314,6 +332,7 @@ func Arbit(opts *ArbitOpts, vendor Vendor, seller Seller) (result []ArbitEntry,
 				AbsoluteDifference: difference * float64(qty),
 				Spread:             spread,
 				Quantity:           qty,
+				Profitability:      profitability,
 			}
 			result = append(result, res)
 		}
@@ -417,6 +436,7 @@ func Mismatch(opts *ArbitOpts, reference Seller, probe Seller) (result []ArbitEn
 	maxSpread := 0.0
 	minPrice := 0.0
 	minQty := 0
+	profitabilityConstant := 10.0
 	filterFoil := false
 	filterOnlyFoil := false
 	filterRLOnly := false
@@ -434,6 +454,9 @@ func Mismatch(opts *ArbitOpts, reference Seller, probe Seller) (result []ArbitEn
 		if opts.MinSpread != 0 {
 			minSpread = opts.MinSpread
 		}
+		if opts.ProfitabilityConstant > 0 {
+			profitabilityConstant = opts.ProfitabilityConstant
+		}
 
 		minPrice = opts.MinPrice
 		maxSpread = opts.MaxSpread
@@ -559,13 +582,19 @@ func Mismatch(opts *ArbitOpts, reference Seller, probe Seller) (result []ArbitEn
 					}
 				}
 
+				profitability := (difference / (price + profitabilityConstant)) * math.Log(1+spread)
+				if qty > 1 {
+					profitability *= math.Sqrt(float64(qty))
+				}
+
 				res := ArbitEntry{
 					CardId:         cardId,
 					InventoryEntry: invEntry,
 					ReferenceEntry: refEntry,
 					Difference:     difference,
 					Spread:         spread,
 					Quantity:       qty,
+					Profitability:  profitability,
 				}
 				result = append(result, res)
 			}

mtgban/csv.go

@@ -28,7 +28,7 @@ var (
 	// The canonical header that will be present in all buylist files
 	BuylistHeader = append(CardHeader, "Conditions", "Buy Price", "Trade Price", "Quantity", "Price Ratio", "URL", "Vendor")
 
-	ArbitHeader = append(CardHeader, "Conditions", "Available", "Sell Price", "Buy Price", "Trade Price", "Difference", "Spread", "Abs Difference", "Price Ratio")
+	ArbitHeader = append(CardHeader, "Conditions", "Available", "Sell Price", "Buy Price", "Trade Price", "Difference", "Spread", "Abs Difference", "Profitability")
 
 	MismatchHeader = append(CardHeader, "Conditions", "Price", "Reference", "Difference", "Spread")
 
@@ -463,7 +463,7 @@ func WriteArbitrageToCSV(arbitrage []ArbitEntry, w io.Writer) error {
 			fmt.Sprintf("%0.2f", entry.Difference),
 			fmt.Sprintf("%0.2f", entry.Spread),
 			fmt.Sprintf("%0.2f", entry.AbsoluteDifference),
-			fmt.Sprintf("%0.2f", bl.PriceRatio),
+			fmt.Sprintf("%0.2f", entry.Profitability),
 		)
 		if hasExtraSeller {
 			record = append(record, inv.SellerName)