meeting-assistant/MeetingAssistant/Recording/MicrophoneSwitchMonitor.cs

namespace MeetingAssistant.Recording;

public sealed class MicrophoneSwitchMonitor
{
    private readonly IMicrophoneDeviceProvider devices;
    private readonly IMicrophoneSwitchPromptService prompts;
    private readonly ILogger<MicrophoneSwitchMonitor> logger;
    private readonly TimeSpan pollInterval;
    private readonly TimeSpan promptLifetime;

    public MicrophoneSwitchMonitor(
        IMicrophoneDeviceProvider devices,
        IMicrophoneSwitchPromptService prompts,
        ILogger<MicrophoneSwitchMonitor> logger)
        : this(devices, prompts, logger, TimeSpan.FromSeconds(1), TimeSpan.FromMinutes(1))
    {
    }

    internal MicrophoneSwitchMonitor(
        IMicrophoneDeviceProvider devices,
        IMicrophoneSwitchPromptService prompts,
        ILogger<MicrophoneSwitchMonitor> logger,
        TimeSpan pollInterval,
        TimeSpan promptLifetime)
    {
        this.devices = devices;
        this.prompts = prompts;
        this.logger = logger;
        this.pollInterval = pollInterval;
        this.promptLifetime = promptLifetime;
    }

    public async Task RunAsync(Action<MicrophoneDevice, CancellationToken> switchMicrophone, CancellationToken cancellationToken)
    {
        var known = (ReadDevices() ?? []).Select(device => device.Id).ToHashSet(StringComparer.OrdinalIgnoreCase);
        var pending = new Dictionary<string, PendingPrompt>(StringComparer.OrdinalIgnoreCase);
        try
        {
            while (true)
            {
                await Task.Delay(pollInterval, cancellationToken);
                var available = ReadDevices();
                if (available is null) continue;
                var availableIds = available.Select(device => device.Id).ToHashSet(StringComparer.OrdinalIgnoreCase);
                foreach (var (id, prompt) in pending.ToArray())
                {
                    if (!availableIds.Contains(id)) await prompt.Cancellation.CancelAsync();
                    if (prompt.Task.IsCompleted)
                    {
                        prompt.Cancellation.Dispose();
                        pending.Remove(id);
                    }
                }

                foreach (var device in available)
                {
                    if (known.Add(device.Id))
                    {
                        var promptCancellation = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
                        promptCancellation.CancelAfter(promptLifetime);
                        pending.Add(device.Id, new PendingPrompt(promptCancellation,
                            OfferAsync(device, switchMicrophone, promptCancellation.Token)));
                    }
                }
            }
        }
        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
        {
        }
        finally
        {
            foreach (var prompt in pending.Values) await prompt.Cancellation.CancelAsync();
            await Task.WhenAll(pending.Values.Select(prompt => prompt.Task));
            foreach (var prompt in pending.Values) prompt.Cancellation.Dispose();
        }
    }

    private async Task OfferAsync(MicrophoneDevice device, Action<MicrophoneDevice, CancellationToken> switchMicrophone,
        CancellationToken cancellationToken)
    {
        try
        {
            if (await prompts.ConfirmSwitchAsync(device, cancellationToken)
                && !cancellationToken.IsCancellationRequested
                && ReadDevices()?.Any(current => current.Id.Equals(device.Id, StringComparison.OrdinalIgnoreCase)) == true
                && !cancellationToken.IsCancellationRequested)
            {
                switchMicrophone(device, cancellationToken);
            }
        }
        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
        {
        }
        catch (Exception exception)
        {
            logger.LogWarning(exception, "Could not offer microphone {MicrophoneName}", device.Name);
        }
    }

    private IReadOnlyList<MicrophoneDevice>? ReadDevices()
    {
        try
        {
            return devices.GetAvailableMicrophones();
        }
        catch (Exception exception)
        {
            logger.LogWarning(exception, "Could not check for newly available microphones");
            return null;
        }
    }

    private sealed record PendingPrompt(CancellationTokenSource Cancellation, Task Task);
}