using System.Diagnostics;
using MeetingAssistant.Calendar;

namespace MeetingAssistant.MeetingNotes;

public sealed class OutlookClassicMeetingMetadataProvider : IMeetingMetadataProvider, IMeetingMetadataDiagnosticProvider
{
    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 OutlookClassicCom.RunStaAsync(
                () => GetCurrentMeeting(startedAt),
                cancellationToken,
                "Meeting Assistant Outlook COM Lookup");
        }
        catch (Exception exception) when (exception is not OperationCanceledException)
        {
            logger.LogDebug(exception, "Outlook Classic meeting metadata was not available");
            return Task.FromResult<MeetingMetadata?>(null);
        }
    }

    public async Task<MeetingMetadataDiagnosticResult> DiagnoseCurrentMeetingAsync(
        DateTimeOffset startedAt,
        TimeSpan timeout,
        CancellationToken cancellationToken)
    {
        var stopwatch = Stopwatch.StartNew();
        try
        {
            var lookup = OutlookClassicCom.RunStaAsync(
                () => GetCurrentMeeting(startedAt),
                cancellationToken,
                "Meeting Assistant Outlook COM Lookup");
            var metadata = timeout > TimeSpan.Zero
                ? await lookup.WaitAsync(timeout, cancellationToken)
                : await lookup.WaitAsync(cancellationToken);
            stopwatch.Stop();
            return new MeetingMetadataDiagnosticResult(
                nameof(OutlookClassicMeetingMetadataProvider),
                startedAt,
                metadata is not null,
                false,
                stopwatch.ElapsedMilliseconds,
                metadata,
                metadata is null ? "No matching Teams appointment was found." : null);
        }
        catch (TimeoutException exception)
        {
            stopwatch.Stop();
            return new MeetingMetadataDiagnosticResult(
                nameof(OutlookClassicMeetingMetadataProvider),
                startedAt,
                false,
                true,
                stopwatch.ElapsedMilliseconds,
                null,
                exception.Message);
        }
        catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
        {
            throw;
        }
        catch (Exception exception)
        {
            stopwatch.Stop();
            return new MeetingMetadataDiagnosticResult(
                nameof(OutlookClassicMeetingMetadataProvider),
                startedAt,
                false,
                false,
                stopwatch.ElapsedMilliseconds,
                null,
                exception.Message);
        }
    }

    private MeetingMetadata? GetCurrentMeeting(DateTimeOffset startedAt)
    {
        using var calendar = OutlookClassicCom.OpenDefaultCalendar(logger, "metadata lookup");
        if (calendar is null)
        {
            return null;
        }

        var startedLocal = startedAt.LocalDateTime;
        var windowStart = startedLocal.AddHours(-4);
        var windowEnd = startedLocal.AddMinutes(5);

        var candidates = new List<OutlookAppointmentCandidate>();
        foreach (var item in OutlookClassicCom.EnumerateItems(calendar.Items))
        {
            if (item is null)
            {
                continue;
            }

            var keepAppointment = false;
            try
            {
                if (!OutlookClassicCom.IsAppointment(item))
                {
                    continue;
                }

                var start = Convert.ToDateTime(OutlookClassicCom.GetProperty(item, "Start"));
                if (start > windowEnd)
                {
                    break;
                }

                var end = Convert.ToDateTime(OutlookClassicCom.GetProperty(item, "End"));
                if (end < windowStart || !IsTeamsAppointment(item))
                {
                    continue;
                }

                candidates.Add(new OutlookAppointmentCandidate(item, start, end));
                keepAppointment = true;
            }
            finally
            {
                if (!keepAppointment)
                {
                    OutlookClassicCom.ReleaseComObject(item);
                }
            }
        }

        try
        {
            var selected = OutlookMeetingCandidateSelector.Select(
                candidates,
                startedLocal,
                candidate => candidate.Start,
                candidate => candidate.End);
            if (selected is null)
            {
                return null;
            }

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

    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 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 TeamsMeetingMarkerDetector.ContainsTeamsMarker(line);
    }

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

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

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

        return NormalizeAttendees(attendees);
    }

    internal static IReadOnlyList<string> NormalizeAttendees(IEnumerable<string> attendees)
    {
        return attendees
            .Select(NormalizeAttendee)
            .Where(attendee => !string.IsNullOrWhiteSpace(attendee))
            .GroupBy(GetAttendeeDeduplicationKey, StringComparer.OrdinalIgnoreCase)
            .Select(group => group
                .OrderByDescending(attendee => attendee.Contains('<', StringComparison.Ordinal))
                .ThenBy(attendee => attendee.Length)
                .First())
            .ToList();
    }

    private static string NormalizeAttendee(string attendee)
    {
        var normalized = attendee.Trim();
        var mailtoPrefix = "mailto:";
        normalized = normalized.Replace(mailtoPrefix, "", StringComparison.OrdinalIgnoreCase);
        while (normalized.Contains("  ", StringComparison.Ordinal))
        {
            normalized = normalized.Replace("  ", " ", StringComparison.Ordinal);
        }

        var emailStart = normalized.IndexOf('<', StringComparison.Ordinal);
        var emailEnd = normalized.LastIndexOf('>');
        if (emailStart > 0 && emailEnd > emailStart)
        {
            var name = normalized[..emailStart].Trim();
            var email = normalized[(emailStart + 1)..emailEnd].Trim();
            if (name.Equals(email, StringComparison.OrdinalIgnoreCase))
            {
                return email;
            }

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

        return normalized;
    }

    private static string GetAttendeeDeduplicationKey(string attendee)
    {
        var emailStart = attendee.IndexOf('<', StringComparison.Ordinal);
        var emailEnd = attendee.LastIndexOf('>');
        if (emailStart > 0 && emailEnd > emailStart)
        {
            return attendee[(emailStart + 1)..emailEnd].Trim();
        }

        return attendee.Trim();
    }

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

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

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

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