[documentation] extract DocumentationBrowserHistory from DocumentationBrowser

GitOrigin-RevId: 6fec825c39845dfbd548f11cb456e2128c159423

platform/lang-impl/src/com/intellij/lang/documentation/ide/impl/DocumentationBrowser.kt

@@ -22,7 +22,6 @@ import com.intellij.openapi.project.IndexNotReadyException
 import com.intellij.openapi.project.Project
 import com.intellij.openapi.roots.OrderEntry
 import com.intellij.openapi.roots.ui.configuration.ProjectSettingsService
-import com.intellij.util.containers.Stack
 import com.intellij.util.lateinitVal
 import com.intellij.util.ui.EDT
 import kotlinx.coroutines.*
@@ -40,14 +39,11 @@ internal class DocumentationBrowser private constructor(
   private lateinit var state: BrowserState
 
   private val stateListeners = ArrayList<BrowserStateListener>(2)
-  private val backStack = Stack<HistorySnapshot>()
-  private val forwardStack = Stack<HistorySnapshot>()
 
   override fun dispose() {
     cs.cancel()
     stateListeners.clear()
-    backStack.clear()
-    forwardStack.clear()
+    myHistory.clear()
   }
 
   var ui: DocumentationUI by lateinitVal()
@@ -79,8 +75,7 @@ internal class DocumentationBrowser private constructor(
   fun resetBrowser(request: DocumentationRequest) {
     cs.coroutineContext.cancelChildren()
     cs.launch(Dispatchers.EDT) {
-      backStack.clear()
-      forwardStack.clear()
+      myHistory.clear()
       browseDocumentation(request)
     }
   }
@@ -127,8 +122,7 @@ internal class DocumentationBrowser private constructor(
         }
       }
       is InternalLinkResult.Request -> {
-        backStack.push(historySnapshot())
-        forwardStack.clear()
+        myHistory.nextPage()
         browseDocumentation(internalResult.request)
       }
       is InternalLinkResult.Updater -> {
@@ -154,6 +148,10 @@ internal class DocumentationBrowser private constructor(
     return result.getCompleted()?.links?.externalUrl
   }
 
+  val history: DocumentationHistory get() = myHistory
+
+  private val myHistory = DocumentationBrowserHistory(::historySnapshot, ::restore)
+
   private class HistorySnapshot(
     val state: BrowserState,
     val ui: UISnapshot,
@@ -196,27 +194,6 @@ internal class DocumentationBrowser private constructor(
     }
   }
 
-  val history: DocumentationHistory = object : DocumentationHistory {
-
-    override fun canBackward(): Boolean {
-      return !backStack.isEmpty()
-    }
-
-    override fun backward() {
-      forwardStack.push(historySnapshot())
-      restore(backStack.pop())
-    }
-
-    override fun canForward(): Boolean {
-      return !forwardStack.isEmpty()
-    }
-
-    override fun forward() {
-      backStack.push(historySnapshot())
-      restore(forwardStack.pop())
-    }
-  }
-
   companion object {
 
     fun createBrowser(project: Project, initialRequest: DocumentationRequest): DocumentationBrowser {

platform/lang-impl/src/com/intellij/lang/documentation/ide/impl/DocumentationBrowserHistory.kt

@@ -0,0 +1,48 @@
+// Copyright 2000-2022 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package com.intellij.lang.documentation.ide.impl
+
+import com.intellij.util.containers.Stack
+import com.intellij.util.ui.EDT
+
+internal class DocumentationBrowserHistory<T>(
+  private val snapshot: () -> T,
+  private val restore: (T) -> Unit,
+) : DocumentationHistory {
+
+  private val backStack = Stack<T>()
+  private val forwardStack = Stack<T>()
+
+  override fun canBackward(): Boolean {
+    EDT.assertIsEdt()
+    return !backStack.isEmpty()
+  }
+
+  override fun backward() {
+    EDT.assertIsEdt()
+    forwardStack.push(snapshot())
+    restore(backStack.pop())
+  }
+
+  override fun canForward(): Boolean {
+    EDT.assertIsEdt()
+    return !forwardStack.isEmpty()
+  }
+
+  override fun forward() {
+    EDT.assertIsEdt()
+    backStack.push(snapshot())
+    restore(forwardStack.pop())
+  }
+
+  fun clear() {
+    EDT.assertIsEdt()
+    backStack.clear()
+    forwardStack.clear()
+  }
+
+  fun nextPage() {
+    EDT.assertIsEdt()
+    backStack.push(snapshot())
+    forwardStack.clear()
+  }
+}