using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

namespace Alkami.Ops.Common.Extensions
{
    public static class StringExtensions
    {
        private static readonly Regex Base64Regex = new Regex(
            @"^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}[AEIMQUYcgkosw048]=|[A-Za-z0-9+/][AQgw]==)?$",
            RegexOptions.Compiled | RegexOptions.CultureInvariant);

        /// <summary>
        /// Determines if a string is base 64
        /// </summary>
        /// <param name="s"></param>
        /// <returns></returns>
        public static bool IsBase64String(this string s)
        {
            if (string.IsNullOrEmpty(s))
            {
                return false;
            }

            return (Base64Regex.IsMatch(s) && s.Length % 4 == 0);
        }


        /// <summary>
        /// Removes characters that are invalid for a filename from a string
        /// </summary>
        /// <param name="fileName"></param>
        /// <returns></returns>
        public static string GetSanitizedFileName(this string fileName)
        {
            var invalidChars = Regex.Escape(new string(Path.GetInvalidFileNameChars()));
            var invalidReStr = string.Format(@"[{0}]+", invalidChars);

            var reservedWords = new[]
            {
                "CON", "PRN", "AUX", "CLOCK$", "NUL", "COM0", "COM1", "COM2", "COM3", "COM4",
                "COM5", "COM6", "COM7", "COM8", "COM9", "LPT0", "LPT1", "LPT2", "LPT3", "LPT4",
                "LPT5", "LPT6", "LPT7", "LPT8", "LPT9"
            };

            var sanitisedNamePart = Regex.Replace(fileName, invalidReStr, "_");

            return reservedWords.Select(reservedWord => string.Format("^{0}\\.", reservedWord))
                .Aggregate(sanitisedNamePart,
                    (current, reservedWordPattern) => Regex.Replace(current, reservedWordPattern, "_reservedWord_.", RegexOptions.IgnoreCase));
        }
    }
}