[NT-330] Set initial amount from Backing

KsApi/models/Backing.swift

@@ -69,3 +69,13 @@ extension Backing: EncodableType {
 }
 
 extension Backing.Status: Argo.Decodable {}
+
+extension Backing {
+  /// Returns the pledge amount subtracting the shipping amount
+  public var pledgeAmount: Double {
+    let shippingAmount = Double(self.shippingAmount ?? 0)
+    let pledgeAmount = Decimal(amount) - Decimal(shippingAmount)
+
+    return (pledgeAmount as NSDecimalNumber).doubleValue
+  }
+}

KsApi/models/BackingTests.swift

@@ -1,4 +1,5 @@
 @testable import KsApi
+import Prelude
 import XCTest
 
 final class BackingTests: XCTestCase {
@@ -43,4 +44,15 @@ final class BackingTests: XCTestCase {
     XCTAssertEqual(1, backing.value?.sequence)
     XCTAssertEqual(Backing.Status.pledged, backing.value?.status)
   }
+
+  func testPledgeAmount() {
+    let backing = Backing.template
+      |> Backing.lens.reward .~ Reward.postcards
+      |> Backing.lens.rewardId .~ Reward.postcards.id
+      |> Backing.lens.shippingAmount .~ 100
+      |> Backing.lens.amount .~ 700.50
+
+    XCTAssertEqual(backing.amount, 700.50)
+    XCTAssertEqual(backing.pledgeAmount, 600.50)
+  }
 }

Library/ViewModels/ManagePledgeSummaryViewModel.swift

@@ -39,22 +39,24 @@ public class ManagePledgeSummaryViewModel: ManagePledgeSummaryViewModelType,
       .map(formattedPledgeDate)
 
     self.pledgeAmountText = projectAndBacking
-      .map { attributedCurrency(with: $0.0, amount: $0.1.amount) }
+      .map { project, backing in
+        attributedCurrency(with: project, amount: backing.pledgeAmount)
+      }
       .skipNil()
 
     let shippingAmount = backing
       .map { Double($0.shippingAmount ?? 0) }
 
     self.shippingAmountText = self.projectSignal
       .combineLatest(with: shippingAmount)
-      .map { shippingValue(with: $0.0, with: $0.1) }
+      .map { project, shippingAmount in
+        shippingValue(with: project, with: shippingAmount)
+      }
       .skipNil()
 
     self.totalAmountText = projectAndBacking
-      .combineLatest(with: shippingAmount)
-      .map(unpack)
-      .map { project, backing, shippingAmount in
-        attributedCurrency(with: project, amount: backing.amount + shippingAmount)
+      .map { project, backing in
+        attributedCurrency(with: project, amount: backing.amount)
       }
       .skipNil()
 

Library/ViewModels/ManagePledgeSummaryViewModelTests.swift

@@ -47,10 +47,10 @@ final class ManagePledgeSummaryViewModelTests: TestCase {
 
     self.backerNumberText.assertValue("Backer #999")
     self.backingDateText.assertValue("As of September 16, 2019")
-    self.pledgeAmountText.assertValue("$30.00")
+    self.pledgeAmountText.assertValue("$23.00")
     self.shippingAmountText.assertValue("+$7.00")
     self.shippingLocationText.assertValue("Shipping: United States")
-    self.totalAmountText.assertValue("$37.00")
+    self.totalAmountText.assertValue("$30.00")
   }
 
   func testShippingLocationStackViewIsHidden_isFalse_WithShippableRewards() {

Library/ViewModels/PledgeAmountViewModel.swift

@@ -67,8 +67,15 @@ public final class PledgeAmountViewModel: PledgeAmountViewModelType,
       .skipNil()
       .map(rounded)
 
+    let initialValue = Signal.combineLatest(
+      project
+        .map { $0.personalization.backing?.pledgeAmount },
+      minValue
+    )
+    .map { backedAmount, minValue in backedAmount ?? minValue }
+
     let stepperValue = Signal.merge(
-      minValue,
+      initialValue,
       textFieldInputValue,
       self.stepperValueProperty.signal
     )

Library/ViewModels/PledgeAmountViewModelTests.swift

@@ -43,6 +43,29 @@ internal final class PledgeAmountViewModelTests: TestCase {
     self.vm.outputs.textFieldValue.observe(self.textFieldValue.observer)
   }
 
+  func testAmountCurrencyAndStepper_FromBacking() {
+    let project = Project.template
+      |> Project.lens.personalization.isBacking .~ true
+      |> Project.lens.personalization.backing .~ (
+        .template
+          |> Backing.lens.reward .~ Reward.postcards
+          |> Backing.lens.rewardId .~ Reward.postcards.id
+          |> Backing.lens.shippingAmount .~ 10
+          |> Backing.lens.amount .~ 700
+      )
+
+    self.vm.inputs.configureWith(project: project, reward: Reward.postcards)
+
+    self.amountIsValid.assertValues([true])
+    self.amountValue.assertValues([690])
+    self.currency.assertValues(["$"])
+    self.stepperMinValue.assertValue(PledgeAmountStepperConstants.min)
+    self.stepperMaxValue.assertValue(PledgeAmountStepperConstants.max)
+    self.stepperStepValue.assertValue(6)
+    self.stepperValue.assertValues([6, 690])
+    self.textFieldValue.assertValues(["690"])
+  }
+
   func testAmountCurrencyAndStepper_NoReward() {
     self.vm.inputs.configureWith(project: .template, reward: Reward.noReward)