Presentation

@inject Bit.Butil.Presentation presentation

@* Start opens the browser's device picker, so it needs a real user gesture. *@
<button @onclick="Start">Present</button>

@code {
    private PresentationConnectionHandle? _connection;

    private async Task Start()
    {
        _connection = await presentation.Start(["/present"],
            onMessage: message => Console.WriteLine(message.Text),
            onStateChange: state => Console.WriteLine(state));

        await _connection!.Send("{\"slide\":3}");

        // Keep it: this is the only way back in after this page navigates away or reloads.
        var savedId = _connection.ConnectionId;
    }
}

@page "/present"
@inject Bit.Butil.Presentation presentation

@* The page the second screen loads. It is an ordinary page of the same app on the same origin -
   the URL passed to Start is what the display navigates to. *@

<h1>Slide @_slide</h1>

@code {
    private int _slide;

    // A receiver page does not create connections; it finds the controllers that opened it.
    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender is false) return;

        await presentation.WatchReceiverConnections(
            onConnection: connection => Console.WriteLine($"controller {connection.ConnectionId} attached"),
            onMessage: message => InvokeAsync(() =>
            {
                _slide = JsonDocument.Parse(message.Text!).RootElement.GetProperty("slide").GetInt32();
                StateHasChanged();
            }));
    }
}

@page "/present"
@inject Bit.Butil.Presentation presentation

@code {
    // The page that runs on the second screen. Nothing here starts anything: it collects the
    // controllers that opened it, and can talk back over the same handles.
    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender is false) return;

        await presentation.WatchReceiverConnections(
            onConnection: connection => Console.WriteLine($"controller {connection.ConnectionId} attached"),
            onMessage: message => ApplyCommand(message.Text));
    }
}

@inject Bit.Butil.Presentation presentation

@code {
    // On the controlling page, so the browser's own "cast this page" menu item does something for
    // this app rather than being greyed out. It is a standing offer, not a request: no picker opens.
    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender) await presentation.SetDefaultRequest(["/present"]);
    }
}