source: binary-improvements/MapRendering/Web/LogBuffer.cs@ 355

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using UnityEngine;

namespace AllocsFixes.NetConnections.Servers.Web {
        public class LogBuffer {
                private const int MAX_ENTRIES = 3000;
                private static LogBuffer instance;

                private static readonly Regex logMessageMatcher =
                        new Regex (@"^([0-9]{4}-[0-9]{2}-[0-9]{2})T([0-9]{2}:[0-9]{2}:[0-9]{2}) ([0-9]+[,.][0-9]+) [A-Z]+ (.*)$");

                private readonly List<LogEntry> logEntries = new List<LogEntry> ();

                private int listOffset;

                public static void Init () {
                        if (instance == null) {
                                instance = new LogBuffer ();
                        }
                }

                private LogBuffer () {
                        Logger.Main.LogCallbacks += LogCallback;
                }

                public static LogBuffer Instance {
                        get {
                                if (instance == null) {
                                        instance = new LogBuffer ();
                                }

                                return instance;
                        }
                }

                public int OldestLine {
                        get {
                                lock (logEntries) {
                                        return listOffset;
                                }
                        }
                }

                public int LatestLine {
                        get {
                                lock (logEntries) {
                                        return listOffset + logEntries.Count - 1;
                                }
                        }
                }

                public int StoredLines {
                        get {
                                lock (logEntries) {
                                        return logEntries.Count;
                                }
                        }
                }

                public LogEntry this [int _index] {
                        get {
                                lock (logEntries) {
                                        if (_index >= listOffset && _index < listOffset + logEntries.Count) {
                                                return logEntries [_index];
                                        }
                                }

                                return null;
                        }
                }

                private void LogCallback (string _msg, string _trace, LogType _type) {
                        LogEntry le = new LogEntry ();

                        Match match = logMessageMatcher.Match (_msg);
                        if (match.Success) {
                                le.date = match.Groups [1].Value;
                                le.time = match.Groups [2].Value;
                                le.uptime = match.Groups [3].Value;
                                le.message = match.Groups [4].Value;
                        } else {
                                DateTime dt = DateTime.Now;
                                le.date = string.Format ("{0:0000}-{1:00}-{2:00}", dt.Year, dt.Month, dt.Day);
                                le.time = string.Format ("{0:00}:{1:00}:{2:00}", dt.Hour, dt.Minute, dt.Second);
                                le.uptime = "";
                                le.message = _msg;
                        }

                        le.trace = _trace;
                        le.type = _type;

                        lock (logEntries) {
                                logEntries.Add (le);
                                if (logEntries.Count > MAX_ENTRIES) {
                                        listOffset += logEntries.Count - MAX_ENTRIES;
                                        logEntries.RemoveRange (0, logEntries.Count - MAX_ENTRIES);
                                }
                        }
                }

                private readonly List<LogEntry> emptyList = new List<LogEntry> ();

                public List<LogEntry> GetRange (ref int _start, int _count, out int _end) {
                        lock (logEntries) {
                                int index;
                                
                                if (_count < 0) {
                                        _count = -_count;
                                        
                                        if (_start >= listOffset + logEntries.Count) {
                                                _start = listOffset + logEntries.Count - 1;
                                        }

                                        _end = _start;

                                        if (_start < listOffset) {
                                                return emptyList;
                                        }
                                        
                                        _start -= _count - 1;

                                        if (_start < listOffset) {
                                                _start = listOffset;
                                        }

                                        index = _start - listOffset;
                                        _end += 1;
                                        _count = _end - _start;
                                } else {
                                        if (_start < listOffset) {
                                                _start = listOffset;
                                        }

                                        if (_start >= listOffset + logEntries.Count) {
                                                _end = _start;
                                                return emptyList;
                                        }

                                        index = _start - listOffset;

                                        if (index + _count > logEntries.Count) {
                                                _count = logEntries.Count - index;
                                        }

                                        _end = _start + _count;
                                }

                                return logEntries.GetRange (index, _count);
                        }
                }


                public class LogEntry {
                        public string date;
                        public string message;
                        public string time;
                        public string trace;
                        public LogType type;
                        public string uptime;
                }
        }
}