CmdPal: Add custom search engine option to Web Search extension (#43941)

## Summary of the Pull Request

This PR allows user to customize a search query in Command Palette's Web
Search built-in extension. This will also solve a problem with some
browser that doesn't handle argument in form "? <query>" as it will
allow user to specify the complete URI.

- Introduces a new text box in Web Search extension settings for
specifying a custom search engine URI
- If the text box is non-empty, the provided URI is used for queries
- If left empty, the extension defaults to previous behavior, sending
queries in the format "? query"

## Pictures? Pictures!

<img width="825" height="566" alt="image"
src="https://github.com/user-attachments/assets/fbf3d3a5-ebfe-4c16-a5f1-0d044b6f9047"
/>

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## PR Checklist

- [x] Closes: #43940 
- [x] Closes: #42867 
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

Author: jiripolasek

src/modules/cmdpal/Tests/Microsoft.CmdPal.Ext.WebSearch.UnitTests/MockSettingsInterface.cs

@@ -18,6 +18,8 @@ public class MockSettingsInterface : ISettingsInterface
 
     public int HistoryItemCount { get; set; }
 
+    public string CustomSearchUri { get; }
+
     public IReadOnlyList<HistoryItem> HistoryItems => _historyItems;
 
     public MockSettingsInterface(int historyItemCount = 0, bool globalIfUri = true, List<HistoryItem> mockHistory = null)

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WebSearch/Commands/SearchWebCommand.cs

@@ -28,17 +28,44 @@ internal SearchWebCommand(string arguments, ISettingsInterface settingsManager,
 
     public override CommandResult Invoke()
     {
-        if (!_browserInfoService.Open($"? {Arguments}"))
+        var uri = BuildUri();
+
+        if (!_browserInfoService.Open(uri))
         {
             // TODO GH# 138 --> actually display feedback from the extension somewhere.
             return CommandResult.KeepOpen();
         }
 
+        // remember only the query, not the full URI
         if (_settingsManager.HistoryItemCount != 0)
         {
             _settingsManager.AddHistoryItem(new HistoryItem(Arguments, DateTime.Now));
         }
 
         return CommandResult.Dismiss();
     }
+
+    private string BuildUri()
+    {
+        if (string.IsNullOrWhiteSpace(_settingsManager.CustomSearchUri))
+        {
+            return $"? " + Arguments;
+        }
+
+        // if the custom search URI contains query placeholder, replace it with the actual query
+        // otherwise append the query to the end of the URI
+        // support {query}, %query% or %s as placeholder
+        var placeholderVariants = new[] { "{query}", "%query%", "%s" };
+        foreach (var placeholder in placeholderVariants)
+        {
+            if (_settingsManager.CustomSearchUri.Contains(placeholder, StringComparison.OrdinalIgnoreCase))
+            {
+                return _settingsManager.CustomSearchUri.Replace(placeholder, Uri.EscapeDataString(Arguments), StringComparison.OrdinalIgnoreCase);
+            }
+        }
+
+        // is this too smart?
+        var separator = _settingsManager.CustomSearchUri.Contains('?') ? '&' : '?';
+        return $"{_settingsManager.CustomSearchUri}{separator}q={Uri.EscapeDataString(Arguments)}";
+    }
 }

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WebSearch/Helpers/ISettingsInterface.cs

@@ -18,5 +18,7 @@ public interface ISettingsInterface
 
     public IReadOnlyList<HistoryItem> HistoryItems { get; }
 
+    string CustomSearchUri { get; }
+
     public void AddHistoryItem(HistoryItem historyItem);
 }

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WebSearch/Helpers/SettingsManager.cs

@@ -41,6 +41,15 @@ public event EventHandler? HistoryChanged
         Resources.plugin_global_if_uri,
         false);
 
+    private readonly TextSetting _customSearchUri = new(
+        Namespaced(nameof(CustomSearchUri)),
+        Resources.plugin_custom_search_uri,
+        Resources.plugin_custom_search_uri,
+        string.Empty)
+    {
+        Placeholder = Resources.plugin_custom_search_uri_placeholder,
+    };
+
     private readonly ChoiceSetSetting _historyItemCount = new(
         Namespaced(HistoryItemCountLegacySettingsKey),
         Resources.plugin_history_item_count,
@@ -51,6 +60,8 @@ public event EventHandler? HistoryChanged
 
     public int HistoryItemCount => int.TryParse(_historyItemCount.Value, out var value) && value >= 0 ? value : 0;
 
+    public string CustomSearchUri => _customSearchUri.Value ?? string.Empty;
+
     public IReadOnlyList<HistoryItem> HistoryItems => _history.HistoryItems;
 
     public SettingsManager()
@@ -59,6 +70,7 @@ public SettingsManager()
 
         Settings.Add(_globalIfURI);
         Settings.Add(_historyItemCount);
+        Settings.Add(_customSearchUri);
 
         LoadSettings();
 

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WebSearch/Properties/Resources.Designer.cs

@@ -187,4 +187,10 @@
   <data name="default_browser" xml:space="preserve">
     <value>default browser</value>
   </data>
+  <data name="plugin_custom_search_uri" xml:space="preserve">
+    <value>Custom search engine URL</value>
+  </data>
+  <data name="plugin_custom_search_uri_placeholder" xml:space="preserve">
+    <value>Use {query} or %s as the search query placeholder; e.g. https://www.bing.com/search?q={query}</value>
+  </data>
 </root>