using System.Text;
using System.Text.RegularExpressions;

namespace CVRManager.Services;

public static class MlLogColours
{
    const string Esc = "\u001b[";
    const string Reset = "\u001b[0m";
    const long MaxScan = 16L << 20;

    static readonly Regex Sgr = new(@"\u001b\[([0-9;]*)m", RegexOptions.Compiled);
    static readonly Regex AnyEsc = new(@"\u001b\[[0-9;?]*[A-Za-z]", RegexOptions.Compiled);
    static readonly Regex Stamp = new(@"^\[(\d\d:\d\d:\d\d\.\d{3})\] (.*)$", RegexOptions.Compiled);

    sealed class FileIndex
    {
        public long Offset;
        public string? State;
        public readonly Dictionary<string, string> Lines = new(StringComparer.Ordinal);
    }

    static readonly Dictionary<string, FileIndex> Files = new(StringComparer.OrdinalIgnoreCase);
    static readonly object Gate = new();
    static long version;

    public static long Refresh(params string[] paths)
    {
        lock (Gate)
        {
            foreach (var path in paths) Scan(path);
            return version;
        }
    }

    static void Scan(string path)
    {
        if (!Files.TryGetValue(path, out var index)) Files[path] = index = new FileIndex();
        try
        {
            if (!File.Exists(path))
            {
                if (index.Offset != 0 || index.Lines.Count > 0) { Files[path] = new FileIndex(); version++; }
                return;
            }
            using var fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete);
            var length = fs.Length;
            if (length < index.Offset) { Files[path] = index = new FileIndex(); version++; }
            if (length == index.Offset) return;
            var start = Math.Max(index.Offset, length - MaxScan);
            var buffer = new byte[length - start];
            fs.Seek(start, SeekOrigin.Begin);
            fs.ReadExactly(buffer);
            var end = Array.LastIndexOf(buffer, (byte)'\n');
            if (end < 0) return;
            var text = Encoding.UTF8.GetString(buffer, 0, end + 1);
            if (start > index.Offset) index.State = null;
            index.Offset = start + end + 1;
            foreach (var raw in text.Split('\n')) Add(index, raw.TrimEnd('\r'));
            version++;
        }
        catch (Exception e) when (e is IOException or UnauthorizedAccessException) { }
    }

    static void Add(FileIndex index, string line)
    {
        var hasEsc = line.IndexOf('\u001b') >= 0;
        if (!hasEsc && index.State == null) return;
        var styled = index.State == null ? line : Esc + index.State + "m" + line;
        foreach (Match m in Sgr.Matches(line))
        {
            var codes = m.Groups[1].Value;
            index.State = codes is "" or "0" or "39" ? null : codes;
        }
        if (index.State != null) styled += Reset;
        var plain = AnyEsc.Replace(line, "");
        if (plain.Trim().Length > 0) index.Lines[plain] = styled;
    }

    public static string Colour(string mlText, params string[] paths)
    {
        var sb = new StringBuilder(mlText.Length * 2);
        lock (Gate)
        {
            foreach (var raw in mlText.Split('\n'))
            {
                var line = raw.TrimEnd('\r');
                string? styled = null;
                for (var i = paths.Length - 1; i >= 0 && styled == null; i--)
                    if (Files.TryGetValue(paths[i], out var index)) index.Lines.TryGetValue(line, out styled);
                if (styled == null && Stamp.Match(line) is { Success: true } m)
                    styled = $"{Esc}38;2;211;211;211m[{Reset}{Esc}38;2;50;205;50m{m.Groups[1].Value}{Reset}{Esc}38;2;211;211;211m] {m.Groups[2].Value}{Reset}";
                sb.Append(styled ?? line).Append('\n');
            }
        }
        if (sb.Length > 0 && !mlText.EndsWith('\n')) sb.Length--;
        return sb.ToString();
    }
}