SubtitleEdit: Merge subtitles

namespace Nikse.SubtitleEdit.Extensions
{
    public static class SubtitleExtensions
    {
        public static void Merge(this Subtitle subtitle, IEnumerable<Paragraph> paragraphs)
        {
            var mergingParagraphs = paragraphs.OrderBy(p => p.Number).ToArray();
            if (mergingParagraphs.Length < 2)
            {
                return;
            }

            // check if sequential
            if (!IsSequential(paragraphs))
            {
                return;
            }

            // Array.Sort(paragraphs, (p, other) => p.Number.CompareTo(other.Number));
            var pivotParagraph = mergingParagraphs.First();
            pivotParagraph.EndTime = mergingParagraphs.Last().EndTime;
            pivotParagraph.Text = Utilities.AutoBreakLine(string.Join(Environment.NewLine, mergingParagraphs.Select(p => p.Text)));

            // note: this required that the paragraph number is sequential and starting from 1
            subtitle.Paragraphs.RemoveRange(pivotParagraph.Number - 1, mergingParagraphs.Skip(1).Count());

            bool IsSequential(IEnumerable<Paragraph> sequentialParagraphs)
            {
                int sequenceStart = sequentialParagraphs.First().Number;
                var range = Enumerable.Range(sequenceStart, sequentialParagraphs.Count());
                var indexedParagraph = sequentialParagraphs.Zip(range, (p, i) => new ValueTuple<int, Paragraph>(i, p));
                return sequentialParagraphs.Skip(1).All(p => p.Number == sequenceStart + 1);
            }
        }
    }
}