using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using StardewModdingAPI.Web.Framework.LogParsing.Models;

namespace StardewModdingAPI.Web.Framework.LogParsing
{
    /// <summary>Parses SMAPI log files.</summary>
    public class LogParser
    {
        /*********
        ** Properties
        *********/
        /// <summary>A regex pattern matching the start of a SMAPI message.</summary>
        private readonly Regex MessageHeaderPattern = new Regex(@"^\[(?<time>\d\d:\d\d:\d\d) (?<level>[a-z]+) +(?<modName>[^\]]+)\] ", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        /// <summary>A regex pattern matching SMAPI's initial platform info message.</summary>
        private readonly Regex InfoLinePattern = new Regex(@"^SMAPI (?<apiVersion>.+) with Stardew Valley (?<gameVersion>.+) on (?<os>.+)", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        /// <summary>A regex pattern matching SMAPI's mod folder path line.</summary>
        private readonly Regex ModPathPattern = new Regex(@"^Mods go here: (?<path>.+)", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        /// <summary>A regex pattern matching SMAPI's log timestamp line.</summary>
        private readonly Regex LogStartedAtPattern = new Regex(@"^Log started at (?<timestamp>.+) UTC", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        /// <summary>A regex pattern matching the start of SMAPI's mod list.</summary>
        private readonly Regex ModListStartPattern = new Regex(@"^Loaded \d+ mods:$", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        /// <summary>A regex pattern matching an entry in SMAPI's mod list.</summary>
        private readonly Regex ModListEntryPattern = new Regex(@"^   (?<name>.+) (?<version>.+) by (?<author>.+) \| (?<description>.+)$", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        /// <summary>A regex pattern matching the start of SMAPI's content pack list.</summary>
        private readonly Regex ContentPackListStartPattern = new Regex(@"^Loaded \d+ content packs:$", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        /// <summary>A regex pattern matching an entry in SMAPI's content pack list.</summary>
        private readonly Regex ContentPackListEntryPattern = new Regex(@"^   (?<name>.+) (?<version>.+) by (?<author>.+) \| for (?<for>.+?) \| (?<description>.+)$", RegexOptions.Compiled | RegexOptions.IgnoreCase);


        /*********
        ** Public methods
        *********/
        /// <summary>Parse SMAPI log text.</summary>
        /// <param name="logText">The SMAPI log text.</param>
        public ParsedLog Parse(string logText)
        {
            try
            {
                // skip if empty
                if (string.IsNullOrWhiteSpace(logText))
                {
                    return new ParsedLog
                    {
                        IsValid = false,
                        Error = "The log is empty."
                    };
                }

                // init log
                ParsedLog log = new ParsedLog
                {
                    IsValid = true,
                    Messages = this.CollapseRepeats(this.GetMessages(logText)).ToArray(),
                };

                // parse log messages
                LogModInfo smapiMod = new LogModInfo { Name = "SMAPI", Author = "Pathoschild", Description = "" };
                IDictionary<string, LogModInfo> mods = new Dictionary<string, LogModInfo>();
                bool inModList = false;
                bool inContentPackList = false;
                foreach (LogMessage message in log.Messages)
                {
                    // collect stats
                    if (message.Level == LogLevel.Error)
                    {
                        if (message.Mod == "SMAPI")
                            smapiMod.Errors++;
                        else if (mods.ContainsKey(message.Mod))
                            mods[message.Mod].Errors++;
                    }

                    // collect SMAPI metadata
                    if (message.Mod == "SMAPI")
                    {
                        // update flags
                        if (inModList && !this.ModListEntryPattern.IsMatch(message.Text))
                            inModList = false;
                        if (inContentPackList && !this.ContentPackListEntryPattern.IsMatch(message.Text))
                            inContentPackList = false;

                        // mod list
                        if (!inModList && message.Level == LogLevel.Info && this.ModListStartPattern.IsMatch(message.Text))
                            inModList = true;
                        else if (inModList)
                        {
                            Match match = this.ModListEntryPattern.Match(message.Text);
                            string name = match.Groups["name"].Value;
                            string version = match.Groups["version"].Value;
                            string author = match.Groups["author"].Value;
                            string description = match.Groups["description"].Value;
                            mods[name] = new LogModInfo { Name = name, Author = author, Version = version, Description = description };
                        }

                        // content pack list
                        else if (!inContentPackList && message.Level == LogLevel.Info && this.ContentPackListStartPattern.IsMatch(message.Text))
                            inContentPackList = true;
                        else if (inContentPackList)
                        {
                            Match match = this.ContentPackListEntryPattern.Match(message.Text);
                            string name = match.Groups["name"].Value;
                            string version = match.Groups["version"].Value;
                            string author = match.Groups["author"].Value;
                            string description = match.Groups["description"].Value;
                            string forMod = match.Groups["for"].Value;
                            mods[name] = new LogModInfo { Name = name, Author = author, Version = version, Description = description, ContentPackFor = forMod };
                        }

                        // platform info line
                        else if (message.Level == LogLevel.Info && this.InfoLinePattern.IsMatch(message.Text))
                        {
                            Match match = this.InfoLinePattern.Match(message.Text);
                            log.ApiVersion = match.Groups["apiVersion"].Value;
                            log.GameVersion = match.Groups["gameVersion"].Value;
                            log.OperatingSystem = match.Groups["os"].Value;
                            smapiMod.Version = log.ApiVersion;
                        }

                        // mod path line
                        else if (message.Level == LogLevel.Debug && this.ModPathPattern.IsMatch(message.Text))
                        {
                            Match match = this.ModPathPattern.Match(message.Text);
                            log.ModPath = match.Groups["path"].Value;
                        }

                        // log UTC timestamp line
                        else if (message.Level == LogLevel.Trace && this.LogStartedAtPattern.IsMatch(message.Text))
                        {
                            Match match = this.LogStartedAtPattern.Match(message.Text);
                            log.Timestamp = DateTime.Parse(match.Groups["timestamp"].Value + "Z");
                        }
                    }
                }

                // finalise log
                log.Mods = new[] { smapiMod }.Concat(mods.Values.OrderBy(p => p.Name)).ToArray();
                return log;
            }
            catch (LogParseException ex)
            {
                return new ParsedLog
                {
                    IsValid = false,
                    Error = ex.Message,
                    RawTextIfError = logText
                };
            }
            catch (Exception ex)
            {
                return new ParsedLog
                {
                    IsValid = false,
                    Error = $"Parsing the log file failed. Technical details:\n{ex}",
                    RawTextIfError = logText
                };
            }
        }


        /*********
        ** Private methods
        *********/
        /// <summary>Collapse consecutive repeats into the previous message.</summary>
        /// <param name="messages">The messages to filter.</param>
        private IEnumerable<LogMessage> CollapseRepeats(IEnumerable<LogMessage> messages)
        {
            LogMessage next = null;
            foreach (LogMessage message in messages)
            {
                // new message
                if (next == null)
                {
                    next = message;
                    continue;
                }

                // repeat
                if (next.Level == message.Level && next.Mod == message.Mod && next.Text == message.Text)
                {
                    next.Repeated++;
                    continue;
                }

                // non-repeat message
                yield return next;
                next = message;
            }
            yield return next;
        }

        /// <summary>Split a SMAPI log into individual log messages.</summary>
        /// <param name="logText">The SMAPI log text.</param>
        /// <exception cref="LogParseException">The log text can't be parsed successfully.</exception>
        private IEnumerable<LogMessage> GetMessages(string logText)
        {
            LogMessage message = new LogMessage();
            using (StringReader reader = new StringReader(logText))
            {
                while (true)
                {
                    // read data
                    string line = reader.ReadLine();
                    if (line == null)
                        break;
                    Match header = this.MessageHeaderPattern.Match(line);

                    // validate
                    if (message.Text == null && !header.Success)
                        throw new LogParseException("Found a log message with no SMAPI metadata. Is this a SMAPI log file?");

                    // start or continue message
                    if (header.Success)
                    {
                        if (message.Text != null)
                            yield return message;

                        message = new LogMessage
                        {
                            Time = header.Groups["time"].Value,
                            Level = Enum.Parse<LogLevel>(header.Groups["level"].Value, ignoreCase: true),
                            Mod = header.Groups["modName"].Value,
                            Text = line.Substring(header.Length)
                        };
                    }
                    else
                        message.Text += "\n" + line;
                }

                // end last message
                if (message.Text != null)
                    yield return message;
            }
        }
    }
}