Backport turbo-ios PR #181

Source/Turbo/Session/Session.swift

@@ -37,6 +37,7 @@ public class Session: NSObject {
 
     private var currentVisit: Visit?
     private var topmostVisit: Visit?
+    private var disappearingVisitForSnapshotting: Visit?
 
     /// The topmost visitable is the visitable that has most recently completed a visit
     public var topmostVisitable: Visitable? {
@@ -227,6 +228,9 @@ extension Session: VisitDelegate {
 
 extension Session: VisitableDelegate {
     public func visitableViewWillAppear(_ visitable: Visitable) {
+        let lastDisappearingVisit = disappearingVisitForSnapshotting
+        disappearingVisitForSnapshotting = nil
+
         guard let topmostVisit = topmostVisit, let currentVisit = currentVisit else { return }
 
         if isSnapshotCacheStale {
@@ -247,7 +251,7 @@ extension Session: VisitableDelegate {
         } else if visitable === currentVisit.visitable && currentVisit.state == .started {
             // Navigating forward - complete navigation early
             completeNavigationForCurrentVisit()
-        } else if visitable !== topmostVisit.visitable {
+        } else if visitable !== topmostVisit.visitable || visitable === lastDisappearingVisit?.visitable {
             // Navigating backward
             visit(visitable, action: .restore)
         }
@@ -266,6 +270,15 @@ extension Session: VisitableDelegate {
         }
     }
 
+    public func visitableViewWillDisappear(_ visitable: Visitable) {
+        disappearingVisitForSnapshotting = topmostVisit
+    }
+
+    public func visitableViewDidDisappear(_ visitable: Visitable) {
+        disappearingVisitForSnapshotting?.cacheSnapshot()
+        deactivateVisitable(visitable)
+    }
+
     public func visitableDidRequestReload(_ visitable: Visitable) {
         guard visitable === topmostVisitable else { return }
         reload()

Source/Turbo/Visit/Visit.swift

@@ -68,6 +68,10 @@ class Visit: NSObject {
         delegate?.visitDidFinish(self)
     }
 
+    func cacheSnapshot() {
+        bridge.cacheSnapshot()
+    }
+
     func startVisit() {}
     func cancelVisit() {}
     func completeVisit() {}

Source/Turbo/Visitable/Visitable.swift

@@ -4,6 +4,8 @@ import WebKit
 public protocol VisitableDelegate: AnyObject {
     func visitableViewWillAppear(_ visitable: Visitable)
     func visitableViewDidAppear(_ visitable: Visitable)
+    func visitableViewWillDisappear(_ visitable: Visitable)
+    func visitableViewDidDisappear(_ visitable: Visitable)
     func visitableDidRequestReload(_ visitable: Visitable)
     func visitableDidRequestRefresh(_ visitable: Visitable)
 }

Source/Turbo/Visitable/VisitableViewController.swift

@@ -28,6 +28,16 @@ open class VisitableViewController: UIViewController, Visitable {
         visitableDelegate?.visitableViewDidAppear(self)
     }
 
+    override open func viewWillDisappear(_ animated: Bool) {
+        super.viewWillDisappear(animated)
+        visitableDelegate?.visitableViewWillDisappear(self)
+    }
+
+    override open func viewDidDisappear(_ animated: Bool) {
+        super.viewDidDisappear(animated)
+        visitableDelegate?.visitableViewDidDisappear(self)
+    }
+
     // MARK: Visitable
 
     open func visitableDidRender() {

Source/Turbo/WebView/WebViewBridge.swift

@@ -68,6 +68,10 @@ final class WebViewBridge {
         callJavaScript(function: "window.turboNative.clearSnapshotCache")
     }
 
+    func cacheSnapshot() {
+        callJavaScript(function: "window.turboNative.cacheSnapshot")
+    }
+
     func cancelVisit(withIdentifier identifier: String) {
         callJavaScript(function: "window.turboNative.cancelVisitWithIdentifier", arguments: [identifier])
     }

Source/Turbo/WebView/turbo.js

@@ -57,13 +57,19 @@
         }
       }
     }
-      
+
     clearSnapshotCache() {
       if (window.Turbo) {
         Turbo.session.clearCache()
       }
     }
 
+    cacheSnapshot() {
+      if (window.Turbo) {
+        Turbo.session.view.cacheSnapshot()
+      }
+    }
+
     // Current visit
 
     issueRequestForVisitWithIdentifier(identifier) {
@@ -150,7 +156,7 @@
     visitCompleted(visit) {
       this.postMessage("visitCompleted", { identifier: visit.identifier, restorationIdentifier: visit.restorationIdentifier })
     }
-      
+
     formSubmissionStarted(formSubmission) {
       this.postMessage("formSubmissionStarted", { location: formSubmission.location.toString() })
     }