Fix bug where Back navigation doesn't work properly with bangs

DuckDuckGo/Common/Extensions/StringExtension.swift

@@ -92,4 +92,20 @@ extension String {
         return hasPrefix(other) || other.hasPrefix(self)
     }
 
+    // MARK: - Search with bang
+
+    private static let searchWithBangPattern = "^.+\\?q=%21[a-zA-Z]+(?:%20[a-zA-Z]+)*$"
+
+    private static var compiledSearchWithBangRegex: NSRegularExpression? = {
+        if let newRegex = try? NSRegularExpression(pattern: searchWithBangPattern, options: .caseInsensitive) {
+            return newRegex
+        }
+        return nil
+    }()
+
+    var isSearchWithBang: Bool {
+        guard let regex = Self.compiledSearchWithBangRegex else { return false }
+        return self.url?.isDuckDuckGoSearch ?? false && regex.firstMatch(in: self, options: [], range: NSRange(location: 0, length: self.utf16.count)) != nil
+    }
+
 }

DuckDuckGo/NavigationBar/View/NavigationButtonMenuDelegate.swift

@@ -134,6 +134,13 @@ extension NavigationButtonMenuDelegate: NSMenuDelegate {
             }
         }
 
+        // Remove duckduckgo search with bang
+        for (index, item) in list.enumerated().reversed() {
+            if let url = item.url, url.absoluteString.isSearchWithBang {
+                list.remove(at: index)
+            }
+        }
+
         return (list, currentIndex)
     }
 

DuckDuckGo/Tab/Model/Tab.swift

@@ -670,7 +670,8 @@ protocol NewWindowPolicyDecisionMaker {
             return
         }
 
-        let canGoBack = webView.canGoBack || self.error != nil
+        let isJustOneRidirectGoingBack = webView.backForwardList.backList.count == 1 && webView.backForwardList.backItem?.url.absoluteString.contains("%21") ?? false
+        let canGoBack = (webView.canGoBack && !isJustOneRidirectGoingBack) || self.error != nil
         let canGoForward = webView.canGoForward && self.error == nil
         let canReload = (self.content.urlForWebView?.scheme ?? URL.NavigationalScheme.about.rawValue) != URL.NavigationalScheme.about.rawValue
 
@@ -700,13 +701,29 @@ protocol NewWindowPolicyDecisionMaker {
         }
 
         userInteractionDialog = nil
+
+        // If search with bang go back of 2 spaces (to avoid redirect)
+        if let urlString = webView.backForwardList.backItem?.url.absoluteString, urlString.isSearchWithBang {
+            if let item =  webView.backForwardList.item(at: -2) {
+                return webView.navigator()?.go(to: item)
+            }
+        }
+
         return webView.navigator()?.goBack(withExpectedNavigationType: .backForward(distance: -1))
     }
 
     @MainActor
     @discardableResult
     func goForward() -> ExpectedNavigation? {
         guard canGoForward else { return nil }
+
+        // If search with bang go forward of 2 spaces (to avoid redirect)
+        if let urlString = webView.backForwardList.forwardItem?.url.absoluteString, urlString.isSearchWithBang {
+            if let item =  webView.backForwardList.item(at: +2) {
+                return webView.navigator()?.go(to: item)
+            }
+        }
+
         return webView.navigator()?.goForward(withExpectedNavigationType: .backForward(distance: 1))
     }
 

UnitTests/Tab/TabStringExtensionTests.swift

@@ -0,0 +1,46 @@
+//
+//  TabUrlExtensionTests.swift
+//
+//  Copyright © 2023 DuckDuckGo. All rights reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//  http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+
+import XCTest
+@testable import DuckDuckGo_Privacy_Browser
+
+final class TabStringExtensionTests: XCTestCase {
+
+    func testSearchWithBangDetection() {
+        let searchWithBang: [String] = [
+            "https://duckduckgo.com/?q=%21Hello",
+            "https://duckduckgo.com/?q=%21Hello%20World",
+            "https://duckduckgo.com/?q=%21Search%20With%20Bang"
+        ]
+
+        let nonSearchWithBang: [String] = [
+            "https://duckduckgo.com/?q=%21",
+            "https://duckduckgo.com/?q=%21%20",
+            "https://duckduckgo.com/?q=%21%20test",
+            "https://duckduckgo.com/?q=test%21test",
+        ]
+
+            for url in searchWithBang {
+                XCTAssertTrue(url.isSearchWithBang, "\(url) should be detected as a search with bang")
+            }
+
+            for url in nonSearchWithBang {
+                XCTAssertFalse(url.isSearchWithBang, "\(url) should not be detected as search with bang")
+            }
+        }
+}