using MeetingAssistant.Transcription;

namespace MeetingAssistant.Speakers;

internal static class SpeakerSampleSpanSelector
{
    public static bool CanExtend(
        string currentSpeaker,
        TimeSpan currentEnd,
        TranscriptionSegment nextSegment,
        TimeSpan maximumSegmentGap)
    {
        return string.Equals(currentSpeaker, nextSegment.Speaker, StringComparison.OrdinalIgnoreCase) &&
            nextSegment.Start - currentEnd <= maximumSegmentGap;
    }

    public static IReadOnlyList<TranscriptionSegment> SelectBestContinuousSpan(
        IReadOnlyList<TranscriptionSegment> segments,
        string speaker,
        TimeSpan maximumSegmentGap,
        TimeSpan minimumDuration)
    {
        var best = new List<TranscriptionSegment>();
        var current = new List<TranscriptionSegment>();

        foreach (var segment in segments.OrderBy(segment => segment.Start))
        {
            if (current.Count == 0)
            {
                if (IsSpeaker(segment, speaker))
                {
                    current.Add(segment);
                    best = LongerSpan(current, best);
                }

                continue;
            }

            if (!CanExtend(speaker, current[^1].End, segment, maximumSegmentGap))
            {
                current.Clear();
                if (!IsSpeaker(segment, speaker))
                {
                    continue;
                }
            }

            current.Add(segment);
            best = LongerSpan(current, best);
        }

        return SpanDuration(best) >= minimumDuration
            ? best
            : [];
    }

    public static TimeSpan SpanDuration(IReadOnlyList<TranscriptionSegment> segments)
    {
        return segments.Count == 0
            ? TimeSpan.Zero
            : segments[^1].End - segments[0].Start;
    }

    private static bool IsSpeaker(
        TranscriptionSegment segment,
        string speaker)
    {
        return string.Equals(segment.Speaker, speaker, StringComparison.OrdinalIgnoreCase);
    }

    private static List<TranscriptionSegment> LongerSpan(
        List<TranscriptionSegment> current,
        List<TranscriptionSegment> best)
    {
        return SpanDuration(current) > SpanDuration(best)
            ? current.ToList()
            : best;
    }
}