using MeetingAssistant.Transcription;

namespace MeetingAssistant.Speakers;

internal static class SpeakerSampleSpanSelector
{
    public static IReadOnlyList<TranscriptionSegment> SelectBestSameSpeakerSpan(
        IReadOnlyList<TranscriptionSegment> segments,
        string speaker,
        TimeSpan minimumDuration,
        TimeSpan maximumSampleDuration)
    {
        SpeakerSampleSpan? best = null;
        SpeakerSampleSpan? current = null;
        foreach (var segment in segments.OrderBy(segment => segment.Start))
        {
            if (!IsSpeaker(segment, speaker))
            {
                current = null;
                continue;
            }

            current = ExtendOrStart(current, segment, maximumSampleDuration);
            if (current is not null &&
                (best is null || current.SpeechDuration > best.SpeechDuration))
            {
                best = current;
            }
        }

        return best is not null && best.SpeechDuration >= minimumDuration
            ? best.Segments
            : [];
    }

    public static IReadOnlyList<IReadOnlyList<TranscriptionSegment>> SelectBestSameSpeakerSpans(
        IReadOnlyList<TranscriptionSegment> segments,
        string speaker,
        TimeSpan minimumDuration,
        TimeSpan maximumSampleDuration,
        int maxSpans)
    {
        if (maxSpans <= 0)
        {
            return [];
        }

        var completed = new List<SpeakerSampleSpan>();
        SpeakerSampleSpan? current = null;
        TimeSpan? lastCompletedEnd = null;
        foreach (var segment in segments.OrderBy(segment => segment.Start))
        {
            if (!IsSpeaker(segment, speaker))
            {
                current = null;
                continue;
            }

            if (lastCompletedEnd is { } end && segment.Start < end)
            {
                current = null;
                continue;
            }

            current = ExtendOrStart(current, segment, maximumSampleDuration);
            if (current is null || current.SpeechDuration < minimumDuration)
            {
                continue;
            }

            completed.Add(current);
            lastCompletedEnd = current.End;
            current = null;
        }

        return completed
            .OrderByDescending(span => span.SpeechDuration)
            .ThenBy(span => span.Start)
            .Take(maxSpans)
            .OrderBy(span => span.Start)
            .Select(span => span.Segments)
            .ToList();
    }

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

    private static SpeakerSampleSpan? ExtendOrStart(
        SpeakerSampleSpan? current,
        TranscriptionSegment segment,
        TimeSpan maximumSampleDuration)
    {
        return current is not null && current.TryExtend(segment, out var extended)
            ? extended
            : SpeakerSampleSpan.Create(segment, maximumSampleDuration);
    }

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