Fix decimal point issue

Summary:
We observed that sometimes when logging the value of a transaction, it was logged with an excess number of decimal points (i.e. 4.99 was 4.9900000000000002 or 1.99 was 1.9899999999999998). This can hurt the event quality.

The root cause is because doubles do not have as much precision as decimals and when converting the price from a decimal to a double, we lost precision. To fix it, we first round the number to 3 decimal places (this is the most any currency has) and then we log it as an ```NSDecimalNumber``` as opposed to a ```Double``` to maintain precision.

Reviewed By: jjiang10

Differential Revision: D64154628

fbshipit-source-id: 9d15b2eb1d94e3631731403fb9ad4a49293f90cd

FBSDKCoreKit/FBSDKCoreKit/AppEvents/Internal/IAP/IAPTransactionLogger.swift

@@ -77,7 +77,7 @@ extension IAPTransactionLogger {
       if event.hasIntroductoryOffer {
         parameters[.hasFreeTrial] = event.hasFreeTrial ? "1" : "0"
         parameters[.trialPeriod] = durationOfSubscriptionPeriod(event.introductoryOfferSubscriptionPeriod)
-        parameters[.trialPrice] = event.introductoryOfferPrice?.doubleValue
+        parameters[.trialPrice] = event.introductoryOfferPrice?.currencyNumber
       }
     } else {
       parameters[.inAppPurchaseType] = IAPType.product.rawValue
@@ -106,7 +106,7 @@ extension IAPTransactionLogger {
     let parameters = getParameters(for: event)
     logImplicitTransactionEvent(
       eventName: event.eventName,
-      valueToSum: event.amount.doubleValue,
+      valueToSum: event.amount,
       parameters: parameters
     )
   }
@@ -119,7 +119,7 @@ extension IAPTransactionLogger {
     let parameters = getParameters(for: event)
     logImplicitTransactionEvent(
       eventName: event.eventName,
-      valueToSum: event.amount.doubleValue,
+      valueToSum: event.amount,
       parameters: parameters
     )
   }
@@ -128,20 +128,25 @@ extension IAPTransactionLogger {
     let parameters = getParameters(for: event)
     logImplicitTransactionEvent(
       eventName: event.eventName,
-      valueToSum: event.amount.doubleValue,
+      valueToSum: event.amount,
       parameters: parameters
     )
   }
 
   private func logImplicitTransactionEvent(
     eventName: AppEvents.Name,
-    valueToSum: Double,
+    valueToSum: Decimal,
     parameters: [AppEvents.ParameterName: Any]
   ) {
     guard let dependencies = try? Self.getDependencies() else {
       return
     }
-    dependencies.eventLogger.logEvent(eventName, valueToSum: valueToSum, parameters: parameters)
+    dependencies.eventLogger.logEvent(
+      eventName,
+      valueToSum: valueToSum.currencyNumber,
+      parameters: parameters,
+      accessToken: nil
+    )
     if dependencies.eventLogger.flushBehavior != .explicitOnly {
       dependencies.eventLogger.flush(for: .eagerlyFlushingEvent)
     }
@@ -207,7 +212,17 @@ enum IAPType: String {
 // MARK: - Decimal
 
 extension Decimal {
-  var doubleValue: Double {
-    NSDecimalNumber(decimal: self).doubleValue
+  var currencyNumber: NSDecimalNumber {
+    var decimalNumber = NSDecimalNumber(decimal: self)
+    let behavior = NSDecimalNumberHandler(
+      roundingMode: .plain,
+      scale: 3,
+      raiseOnExactness: false,
+      raiseOnOverflow: false,
+      raiseOnUnderflow: false,
+      raiseOnDivideByZero: false
+    )
+    decimalNumber = decimalNumber.rounding(accordingToBehavior: behavior)
+    return decimalNumber
   }
 }

FBSDKCoreKit/FBSDKCoreKit/include/FBSDKEventLogging.h

@@ -39,6 +39,11 @@ NS_SWIFT_NAME(EventLogging)
       valueToSum:(double)valueToSum
       parameters:(nullable NSDictionary<FBSDKAppEventParameterName, id> *)parameters;
 
+- (void)logEvent:(FBSDKAppEventName)eventName
+      valueToSum:(nullable NSNumber *)valueToSum
+      parameters:(nullable NSDictionary<FBSDKAppEventParameterName, id> *)parameters
+     accessToken:(nullable FBSDKAccessToken *)accessToken;
+
 - (void)logInternalEvent:(FBSDKAppEventName)eventName
       isImplicitlyLogged:(BOOL)isImplicitlyLogged;
 

TestTools/TestTools/TestEventLogger.swift

@@ -74,4 +74,15 @@ open class TestEventLogger: NSObject, EventLogging { // swiftlint:disable:this p
   ) {
     capturedEventName = eventName
   }
+
+  public func logEvent(
+    _ eventName: AppEvents.Name,
+    valueToSum: NSNumber?,
+    parameters: [AppEvents.ParameterName: Any]?,
+    accessToken: AccessToken?
+  ) {
+    capturedEventName = eventName
+    capturedValueToSum = valueToSum?.doubleValue
+    capturedParameters = parameters
+  }
 }