using global::Android.Views;

namespace DodoSSH.Client.Android.Platform;

/// <summary>
/// Hands native focus back to the terminal's WebView after Avalonia chrome took it.
/// </summary>
/// <remarks>
/// <para>
/// <b>The sibling of <see cref="SoftKeyboard"/>, and it exists for the same reason that one does:</b> the
/// keyboard over a terminal belongs to the WebView's own native view, which Avalonia's focus manager does
/// not own. The accessory row's keys are already <c>Focusable=false</c> — see TerminalScreen — so Avalonia's
/// idea of focus never leaves the terminal when one is tapped. What still moves is <em>Android's</em>: the
/// tap lands on Avalonia's own input view, which is focusable-in-touch-mode because Avalonia's text boxes
/// need it to be, and the platform hands that view focus on the way to delivering the touch. The WebView's
/// input connection dies with its focus, the keyboard swaps to the layout it shows an editor that takes no
/// text, and the inset churn that follows can leave it sitting on top of the very row that was tapped.
/// </para>
/// <para>
/// So each accessory key hands focus straight back once its byte is on the wire. The page inside the
/// WebView never noticed anything — its own DOM focus never moved — so regaining native focus re-establishes
/// the same input connection and the keyboard settles back to what it was. Skipped when the WebView is still
/// focused, which makes the call free on any platform arrangement where the steal never happened.
/// </para>
/// <para>
/// Found by walking the decor view rather than asked of the <c>NativeWebView</c> control, because the
/// control does not expose its platform child and this application only ever has the one WebView — the
/// walk's first match is necessarily the terminal. Every step is allowed to be absent, exactly as
/// <see cref="SoftKeyboard.Hide"/>'s are: no activity while backgrounded, no WebView while the terminal
/// surface has never been shown, and nothing to do in either case.
/// </para>
/// </remarks>
internal static class TerminalFocus
{
    public static void Return()
    {
        if (PhoneEnvironment.CurrentActivity?.Window?.DecorView is not ViewGroup decor)
        {
            return;
        }

        if (FindWebView(decor) is { IsFocused: false } webView)
        {
            webView.RequestFocus();
        }
    }

    private static View? FindWebView(ViewGroup parent)
    {
        for (var i = 0; i < parent.ChildCount; i++)
        {
            switch (parent.GetChildAt(i))
            {
                case global::Android.Webkit.WebView webView:
                    return webView;

                case ViewGroup child when FindWebView(child) is { } found:
                    return found;
            }
        }

        return null;
    }
}