meeting-assistant/MeetingAssistant/MeetingNotes/OutlookClassicMeetingMetadataProvider.Windows.cs

using System.Runtime.InteropServices;

namespace MeetingAssistant.MeetingNotes;

public sealed class OutlookClassicMeetingMetadataProvider : IMeetingMetadataProvider
{
    private const int OutlookCalendarFolder = 9;
    private readonly ILogger<OutlookClassicMeetingMetadataProvider> logger;

    public OutlookClassicMeetingMetadataProvider(ILogger<OutlookClassicMeetingMetadataProvider> logger)
    {
        this.logger = logger;
    }

    public Task<MeetingMetadata?> GetCurrentMeetingAsync(
        DateTimeOffset startedAt,
        CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();
        try
        {
            return Task.FromResult(GetCurrentMeeting(startedAt));
        }
        catch (Exception exception) when (exception is not OperationCanceledException)
        {
            logger.LogDebug(exception, "Outlook Classic meeting metadata was not available");
            return Task.FromResult<MeetingMetadata?>(null);
        }
    }

    private MeetingMetadata? GetCurrentMeeting(DateTimeOffset startedAt)
    {
        object? application = null;
        object? session = null;
        object? calendar = null;
        object? items = null;
        object? restrictedItems = null;

        try
        {
            var applicationType = Type.GetTypeFromProgID("Outlook.Application");
            if (applicationType is null)
            {
                return null;
            }

            application = Activator.CreateInstance(applicationType);
            if (application is null)
            {
                return null;
            }

            session = GetProperty(application, "Session");
            calendar = Invoke(session!, "GetDefaultFolder", OutlookCalendarFolder);
            items = GetProperty(calendar!, "Items");
            SetProperty(items!, "IncludeRecurrences", true);
            Invoke(items!, "Sort", "[Start]");

            var startedLocal = startedAt.LocalDateTime;
            var windowStart = startedLocal.AddMinutes(-1);
            var windowEnd = startedLocal.AddMinutes(5);
            var filter =
                $"[Start] <= '{windowEnd:g}' AND [End] >= '{windowStart:g}'";
            restrictedItems = Invoke(items!, "Restrict", filter);

            var candidates = new List<OutlookAppointmentCandidate>();
            var count = Convert.ToInt32(GetProperty(restrictedItems!, "Count"));
            for (var index = 1; index <= count; index++)
            {
                var appointment = Invoke(restrictedItems!, "Item", index);
                if (appointment is not null && IsTeamsAppointment(appointment))
                {
                    candidates.Add(new OutlookAppointmentCandidate(
                        appointment,
                        Convert.ToDateTime(GetProperty(appointment, "Start")),
                        Convert.ToDateTime(GetProperty(appointment, "End"))));
                }
                else
                {
                    ReleaseComObject(appointment);
                }
            }

            var selected = OutlookMeetingCandidateSelector.Select(
                candidates,
                startedLocal,
                candidate => candidate.Start,
                candidate => candidate.End);
            if (selected is null)
            {
                foreach (var candidate in candidates)
                {
                    ReleaseComObject(candidate.Appointment);
                }

                return null;
            }

            try
            {
                var appointment = selected.Appointment;
                var title = Convert.ToString(GetProperty(appointment, "Subject")) ?? "";
                var attendees = ReadAttendees(appointment);
                var body = Convert.ToString(GetProperty(appointment, "Body")) ?? "";
                return new MeetingMetadata(
                    title.Trim(),
                    attendees,
                    ExtractAgenda(body),
                    ToLocalOffset(selected.End));
            }
            finally
            {
                foreach (var candidate in candidates)
                {
                    ReleaseComObject(candidate.Appointment);
                }
            }
        }
        finally
        {
            ReleaseComObject(restrictedItems);
            ReleaseComObject(items);
            ReleaseComObject(calendar);
            ReleaseComObject(session);
            ReleaseComObject(application);
        }
    }

    internal static string ExtractAgenda(string body)
    {
        if (string.IsNullOrWhiteSpace(body))
        {
            return "";
        }

        var lines = body.Replace("\r\n", "\n", StringComparison.Ordinal).Replace('\r', '\n').Split('\n');
        var agendaLines = new List<string>();
        foreach (var line in lines)
        {
            if (IsTeamsSeparator(line) || IsTeamsJoinLine(line))
            {
                break;
            }

            agendaLines.Add(line);
        }

        return string.Join(Environment.NewLine, agendaLines).Trim();
    }

    private static bool IsTeamsAppointment(object appointment)
    {
        var subject = Convert.ToString(GetProperty(appointment, "Subject")) ?? "";
        var location = Convert.ToString(GetProperty(appointment, "Location")) ?? "";
        var body = Convert.ToString(GetProperty(appointment, "Body")) ?? "";
        return ContainsTeamsMarker(subject) ||
            ContainsTeamsMarker(location) ||
            ContainsTeamsMarker(body);
    }

    private static bool ContainsTeamsMarker(string value)
    {
        return value.Contains("teams.microsoft.com", StringComparison.OrdinalIgnoreCase) ||
            value.Contains("Microsoft Teams", StringComparison.OrdinalIgnoreCase) ||
            value.Contains("Join the meeting now", StringComparison.OrdinalIgnoreCase) ||
            value.Contains("Join Microsoft Teams Meeting", StringComparison.OrdinalIgnoreCase);
    }

    private static bool IsTeamsSeparator(string line)
    {
        var trimmed = line.Trim();
        return trimmed.Length >= 8 &&
            trimmed.All(character => character is '_' or '-' or '*' or ' ');
    }

    private static bool IsTeamsJoinLine(string line)
    {
        return ContainsTeamsMarker(line);
    }

    private static IReadOnlyList<string> ReadAttendees(object appointment)
    {
        var attendees = new List<string>();
        var organizer = Convert.ToString(GetProperty(appointment, "Organizer"));
        if (!string.IsNullOrWhiteSpace(organizer))
        {
            attendees.Add(organizer.Trim());
        }

        object? recipients = null;
        try
        {
            recipients = GetProperty(appointment, "Recipients");
            var count = Convert.ToInt32(GetProperty(recipients!, "Count"));
            for (var index = 1; index <= count; index++)
            {
                object? recipient = null;
                try
                {
                    recipient = Invoke(recipients!, "Item", index);
                    var formatted = FormatRecipient(recipient!);
                    if (!string.IsNullOrWhiteSpace(formatted))
                    {
                        attendees.Add(formatted);
                    }
                }
                finally
                {
                    ReleaseComObject(recipient);
                }
            }
        }
        finally
        {
            ReleaseComObject(recipients);
        }

        return attendees
            .Where(attendee => !string.IsNullOrWhiteSpace(attendee))
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .ToList();
    }

    private static DateTimeOffset ToLocalOffset(DateTime value)
    {
        return new DateTimeOffset(DateTime.SpecifyKind(value, DateTimeKind.Local));
    }

    private static string FormatRecipient(object recipient)
    {
        var name = Convert.ToString(GetProperty(recipient, "Name"))?.Trim() ?? "";
        var email = Convert.ToString(GetProperty(recipient, "Address"))?.Trim() ?? "";
        if (string.IsNullOrWhiteSpace(name))
        {
            return email;
        }

        if (string.IsNullOrWhiteSpace(email) ||
            email.Contains('/'))
        {
            return name;
        }

        return $"{name} <{email}>";
    }

    private static object? GetProperty(object target, string name)
    {
        return target.GetType().InvokeMember(
            name,
            System.Reflection.BindingFlags.GetProperty,
            null,
            target,
            null);
    }

    private static void SetProperty(object target, string name, object value)
    {
        target.GetType().InvokeMember(
            name,
            System.Reflection.BindingFlags.SetProperty,
            null,
            target,
            [value]);
    }

    private static object? Invoke(object target, string name, params object[] arguments)
    {
        return target.GetType().InvokeMember(
            name,
            System.Reflection.BindingFlags.InvokeMethod,
            null,
            target,
            arguments);
    }

    private static void ReleaseComObject(object? value)
    {
        if (value is not null && Marshal.IsComObject(value))
        {
            Marshal.FinalReleaseComObject(value);
        }
    }

    private sealed record OutlookAppointmentCandidate(
        object Appointment,
        DateTime Start,
        DateTime End);
}