game-of-life/GameOfLife/IO/RleDecoder.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using GameOfLife.Entities;

namespace GameOfLife.IO
{
    public class RleDecoder
    {
        public Pattern Pattern { get; }
        public PatternMetadata Metadata { get; }

        public RleDecoder(string filename) : this(new FileInfo(filename)) { }

        public RleDecoder(FileSystemInfo fi) : this(GetLines(fi)) { }

        public RleDecoder(IEnumerable<string> encodedRle)
        {
            var groups =
                (from line in encodedRle
                    let trimmed = line.Trim()
                    where
                        !string.IsNullOrEmpty(trimmed)
                    group line by line.StartsWith("#") into g
                    select g
                ).ToArray();

            var comments = groups.First(g => g.Key);
            var nonComments = groups.First(g => !g.Key).ToArray();

            Metadata = new RlePatternMetaData(nonComments.First(), comments);
            var rleData = string.Join("", nonComments.Skip(1));
            Pattern = Pattern.Extract(ExpandRle(rleData).ToArray());
        }

        /// <summary>
        /// Returns RLE encoded string into decoded expansion, breaking lines into an enumeration
        /// </summary>
        private static IEnumerable<string> ExpandRle(string rleData)
        {
            if (!rleData.Contains("!"))
                throw new ArgumentException("RLE pattern did not contain terminating character '!'");

            var encodedRle
                = rleData.Substring(0, rleData.IndexOf("!", StringComparison.Ordinal));

            var rleDecodingRegex = new Regex(@"(?<count>\d*)(?<char>[a-z$])");

            var matches = rleDecodingRegex.Matches(encodedRle);
            var decoded = string.Empty;
            foreach (Match match in matches)
            {
                var countStr = match.Groups["count"].Value;
                var count = string.IsNullOrEmpty(countStr) ? 1 : int.Parse(countStr);
                var c = match.Groups["char"].Value.First();
                for (var i = 0; i < count; i++)
                {
                    switch (c)
                    {
                        case '$':
                            yield return decoded;
                            decoded = string.Empty;
                            break;
                        default:
                            decoded += c;
                            break;
                    }
                }
            }
            yield return decoded;
        }

        private static IEnumerable<string> GetLines(FileSystemInfo fi)
        {
            if (!fi.Exists)
                throw new FileNotFoundException(fi.FullName);
            return File.ReadAllLines(fi.FullName);
        }
    }
}