FileLogComparer.cs

using System;
using System.Collections.Generic;

namespace IisLogRotator
{
    public class FileLogComparer : IComparer<FileLogInfo>
    {
        public enum ComparisonMethod
        {
            ByNameOrdinal,
            ByNameOrdinalIgnoringUtf8Prefix,
            ByCreationTime,
            ByIisLogDate
        }

        public FileLogComparer(Folder folder)
        {
            this.Folder = folder;

            // if rotation is size-based, we order by creation date
            // other naming syntaxes are sortable patterns
            if (folder.Period == IisPeriodType.MaxSize)
            {
                this.Method = FileLogComparer.ComparisonMethod.ByCreationTime;
            }
            else
            {
                this.Method = FileLogComparer.ComparisonMethod.ByIisLogDate;
            }
        }

        public Folder Folder { get; private set; }
        public ComparisonMethod Method { get; private set; }

        public int Compare(FileLogInfo x, FileLogInfo y)
        {
            switch (this.Method)
            {
                case ComparisonMethod.ByNameOrdinal:
                    return StringComparer.Ordinal.Compare(
                        x.File.Name,
                        y.File.Name
                    );

                case ComparisonMethod.ByNameOrdinalIgnoringUtf8Prefix:
                    // TODO convert YY to YYYY to compare centuries
                    // ex.: ex990101.log must be before ex000101.log
                    // parse first two digits to integer then pass to Calendar.ToFourDigitYear(...)
                    return StringComparer.Ordinal.Compare(
                        x.File.Name.StripeUtf8Prefix(),
                        y.File.Name.StripeUtf8Prefix()
                    );

                case ComparisonMethod.ByCreationTime:
                    return DateTime.Compare(x.File.CreationTime, y.File.CreationTime);

                case ComparisonMethod.ByIisLogDate:
                    if (x.IsChild && y.IsChild)
                        return DateTime.Compare(x.Date, y.Date);
                    else if (x.IsChild)
                        return 1;
                    else if (y.IsChild)
                        return -1;
                    else
                        return 0;

                default:
                    throw new NotImplementedException("This comparison method is not yet implemented");
            }
        }
    }
}