A simple program to parse git logs and produces change statistics grouped by month

gitafterstats.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Linq;

namespace gitafterstat
{
    /// <summary>
    /// A simple program to parse git logs and produces change statistics grouped by month
    /// To run e.g. use
    /// <code>C:\src\MyProject> git log --pretty=format:nyny%cI -u --no-color -U0 --full-history --date-order --no-merges --reverse -p | gitafterstat.exe</code>
    ///
    /// notes
    /// * the cmd is much faster than running in powershell
    /// * there is a delimiter 'nyny' in the above which is hard-coded into the parser
    /// </summary>
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<DateTime, List<Commit>> changes = null;

            Console.WriteLine("");
            Time("Reading input", () => { changes = GitParser.Parse(Console.OpenStandardInput()); });

            Time("Filter", () =>
            {
                foreach (var commits in changes)
                foreach (var commit in commits.Value)
                    commit.Changes = commit.Changes.Where(x => x.Fileextension == "cs" || x.Fileextension == "fs").ToList();

                changes = changes.Where(x => x.Value.Any()).ToDictionary(x => x.Key, x => x.Value);
            });

            Console.WriteLine("");

            Console.WriteLine("CSV output");
            Console.WriteLine("----------");
            Console.WriteLine("date,delta,total,commits");
            var previousDelta = 0;
            var g = changes.GroupBy(x => FirstInMonth(x.Key));
            foreach (var month in g)
            {
                var sumDelta = month.Sum(x => x.Value.Sum(f => f.TotalDelta()));
                previousDelta += sumDelta;
                var commits = month.Sum(x => x.Value.Count);
                Console.WriteLine($"{month.Key.ToShortDateString()}, {sumDelta}, {previousDelta}, {commits}");
            }
        }

        static DateTime FirstInMonth(DateTime d) => new DateTime(d.Year, d.Month, 1);

        static void Time(string title, Action a)
        {
            var s = Stopwatch.StartNew();
            a();
            Console.WriteLine($"{title}: {s.Elapsed.ToString()}");
        }
    }

    class GitParser
    {
        const string Delimiter = "nyny";
        const char FirstDelimiter = 'n';

        public static Dictionary<DateTime, List<Commit>> Parse(Stream s)
        {
            var changes = new Dictionary<DateTime, List<Commit>>();
            var top = Console.CursorTop;

            using (var stream = new StreamReader(s))
            {
                Commit commit = null;
                FileChange fileChange = null;

                while (!stream.EndOfStream)
                {
                    var line = stream.ReadLine();
                    if (line.Length == 0)
                        continue;

                    switch (line[0])
                    {
                        case '-':
                            if (!line.StartsWith("---", StringComparison.Ordinal))
                                fileChange.DeltaLines--;
                            break;

                        case '+':
                            if (!line.StartsWith("+++", StringComparison.Ordinal))
                                fileChange.DeltaLines++;
                            break;

                        case FirstDelimiter:
                            if (line.StartsWith(Delimiter, StringComparison.Ordinal))
                            {
                                var date = GetDate(line);
                                if (!changes.ContainsKey(date))
                                {
                                    changes[date] = new List<Commit>();
                                    Console.SetCursorPosition(0, top);
                                    Console.Write(date);
                                }

                                commit = new Commit();
                                changes[date].Add(commit);
                            }
                            break;

                        case 'd':
                            const string diffGit = "diff --git ";
                            if (line.StartsWith(diffGit, StringComparison.Ordinal))
                            {
                                var posEnd = line.IndexOf(' ', diffGit.Length);
                                var posDot = line.LastIndexOf('.', posEnd - 1, 7) + 1;
                                var ext = line.Substring(posDot, posEnd - posDot);

                                fileChange = new FileChange();
                                fileChange.Fileextension = string.Intern(ext);

                                commit.Changes.Add(fileChange);
                            }
                            break;
                    }
                }
            }

            return changes;
        }

        private static DateTime GetDate(string line)
        {
            var format = "yyyy-MM-dd";
            var datepart = line.Substring(Delimiter.Length, format.Length);
            var date = DateTime.ParseExact(datepart, format, CultureInfo.InvariantCulture);

            return date;
        }
    }

    class FileChange
    {
        public int DeltaLines;
        public string Fileextension;
    }

    class Commit
    {
        public List<FileChange> Changes = new List<FileChange>();

        public int TotalDelta() => Changes.Sum(x => x.DeltaLines);
    }
}