LibWebView: Add facilities to ask the user for a download directory

If the Downloads directory exists, we will use it (note that this will
respect the XDG_DOWNLOAD_DIR environment variable).

Otherwise, we will ask the UI layer to retrieve a download directory
from the user. This directory is not saved, so it will be re-prompted
every time. Once a proper settings UI is complete, we will of course
integrate with that for persistent settings.

Userland/Libraries/LibWebView/Application.cpp

@@ -7,7 +7,9 @@
 #include <AK/Debug.h>
 #include <LibCore/ArgsParser.h>
 #include <LibCore/Environment.h>
+#include <LibCore/StandardPaths.h>
 #include <LibCore/TimeZoneWatcher.h>
+#include <LibFileSystem/FileSystem.h>
 #include <LibImageDecoderClient/Client.h>
 #include <LibWebView/Application.h>
 #include <LibWebView/URL.h>
@@ -207,4 +209,22 @@ void Application::process_did_exit(Process&& process)
     }
 }
 
+ErrorOr<LexicalPath> Application::path_for_downloaded_file(StringView file) const
+{
+    auto downloads_directory = Core::StandardPaths::downloads_directory();
+
+    if (!FileSystem::is_directory(downloads_directory)) {
+        auto maybe_downloads_directory = ask_user_for_download_folder();
+        if (!maybe_downloads_directory.has_value())
+            return Error::from_errno(ECANCELED);
+
+        downloads_directory = maybe_downloads_directory.release_value();
+    }
+
+    if (!FileSystem::is_directory(downloads_directory))
+        return Error::from_errno(ENOENT);
+
+    return LexicalPath::join(downloads_directory, file);
+}
+
 }

Userland/Libraries/LibWebView/Application.h

@@ -7,6 +7,9 @@
 #pragma once
 
 #include <AK/Badge.h>
+#include <AK/ByteString.h>
+#include <AK/LexicalPath.h>
+#include <AK/Optional.h>
 #include <AK/Swift.h>
 #include <LibCore/EventLoop.h>
 #include <LibCore/Forward.h>
@@ -45,6 +48,8 @@ public:
     void update_process_statistics();
     String generate_process_statistics_html();
 
+    ErrorOr<LexicalPath> path_for_downloaded_file(StringView file) const;
+
 protected:
     template<DerivedFrom<Application> ApplicationType>
     static NonnullOwnPtr<ApplicationType> create(Main::Arguments& arguments, URL::URL new_tab_page_url)
@@ -62,6 +67,8 @@ protected:
     virtual void create_platform_arguments(Core::ArgsParser&) { }
     virtual void create_platform_options(ChromeOptions&, WebContentOptions&) { }
 
+    virtual Optional<ByteString> ask_user_for_download_folder() const { return {}; }
+
 private:
     void initialize(Main::Arguments const& arguments, URL::URL new_tab_page_url);