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

namespace N_m3u8DL_RE.Common.Entity;

public partial class WebVttSub
{
    [GeneratedRegex("X-TIMESTAMP-MAP.*")]
    private static partial Regex TSMapRegex();
    [GeneratedRegex("MPEGTS:(\\d+)")]
    private static partial Regex TSValueRegex();
    [GeneratedRegex("\\s")]
    private static partial Regex SplitRegex();
    [GeneratedRegex(@"<c\..*?>([\s\S]*?)<\/c>")]
    private static partial Regex VttClassRegex();

    public List<SubCue> Cues { get; set; } = [];
    public long MpegtsTimestamp { get; set; } = 0L;

    /// <summary>
    /// 从字节数组解析WEBVTT
    /// </summary>
    /// <param name="textBytes"></param>
    /// <returns></returns>
    public static WebVttSub Parse(byte[] textBytes, long BaseTimestamp = 0L)
    {
        return Parse(Encoding.UTF8.GetString(textBytes), BaseTimestamp);
    }

    /// <summary>
    /// 从字节数组解析WEBVTT
    /// </summary>
    /// <param name="textBytes"></param>
    /// <param name="encoding"></param>
    /// <returns></returns>
    public static WebVttSub Parse(byte[] textBytes, Encoding encoding, long BaseTimestamp = 0L)
    {
        return Parse(encoding.GetString(textBytes), BaseTimestamp);
    }

    /// <summary>
    /// 从字符串解析WEBVTT
    /// </summary>
    /// <param name="text"></param>
    /// <returns></returns>
    public static WebVttSub Parse(string text, long BaseTimestamp = 0L)
    {
        if (!text.Trim().StartsWith("WEBVTT"))
            throw new Exception("Bad vtt!");

        text += Environment.NewLine;

        var webSub = new WebVttSub();
        var needPayload = false;
        var timeLine = "";
        var regex1 = TSMapRegex();

        if (regex1.IsMatch(text))
        {
            var timestamp = TSValueRegex().Match(regex1.Match(text).Value).Groups[1].Value;
            webSub.MpegtsTimestamp = Convert.ToInt64(timestamp);
        }

        var payloads = new List<string>();
        foreach (var line in text.Split('\n'))
        {
            if (line.Contains(" --> "))
            {
                needPayload = true;
                timeLine = line.Trim();
                continue;
            }

            if (!needPayload) continue;
            
            if (string.IsNullOrEmpty(line.Trim()))
            {
                var payload = string.Join(Environment.NewLine, payloads);
                if (string.IsNullOrEmpty(payload.Trim())) continue; // 没获取到payload 跳过添加

                var arr = SplitRegex().Split(timeLine.Replace("-->", "")).Where(s => !string.IsNullOrEmpty(s)).ToList();
                var startTime = ConvertToTS(arr[0]);
                var endTime = ConvertToTS(arr[1]);
                var style = arr.Count > 2 ? string.Join(" ", arr.Skip(2)) : "";
                webSub.Cues.Add(new SubCue()
                {
                    StartTime = startTime,
                    EndTime = endTime,
                    Payload = RemoveClassTag(string.Join("", payload.Where(c => c != 8203))), // Remove Zero Width Space!
                    Settings = style
                });
                payloads.Clear();
                needPayload = false;
            }
            else
            {
                payloads.Add(line.Trim());
            }
        }

        if (BaseTimestamp == 0) return webSub;
        
        foreach (var item in webSub.Cues)
        {
            if (item.StartTime.TotalMilliseconds - BaseTimestamp >= 0)
            {
                item.StartTime = TimeSpan.FromMilliseconds(item.StartTime.TotalMilliseconds - BaseTimestamp);
                item.EndTime = TimeSpan.FromMilliseconds(item.EndTime.TotalMilliseconds - BaseTimestamp);
            }
            else
            {
                break;
            }
        }

        return webSub;
    }

    private static string RemoveClassTag(string text)
    {
        if (VttClassRegex().IsMatch(text))
        {
            return string.Join(Environment.NewLine, text.Split('\n').Select(line => line.TrimEnd()).Select(line =>
            {
                return string.Concat(VttClassRegex().Matches(line).Select(x => x.Groups[1].Value + " "));
            })).TrimEnd();
        }
        return text;
    }

    /// <summary>
    /// 从另一个字幕中获取所有Cue，并加载此字幕中，且自动修正偏移
    /// </summary>
    /// <param name="webSub"></param>
    /// <returns></returns>
    public WebVttSub AddCuesFromOne(WebVttSub webSub)
    {
        FixTimestamp(webSub, this.MpegtsTimestamp);
        foreach (var item in webSub.Cues)
        {
            if (this.Cues.Contains(item)) continue;
            
            // 如果相差只有1ms，且payload相同，则拼接
            var last = this.Cues.LastOrDefault();
            if (last != null && this.Cues.Count > 0 && (item.StartTime - last.EndTime).TotalMilliseconds <= 1 && item.Payload == last.Payload) 
            {
                last.EndTime = item.EndTime;
            }
            else
            {
                this.Cues.Add(item);
            }
        }
        return this;
    }

    private void FixTimestamp(WebVttSub sub, long baseTimestamp)
    {
        if (sub.MpegtsTimestamp == 0)
        {
            return;
        }

        // 确实存在时间轴错误的情况，才修复
        if ((this.Cues.Count > 0 && sub.Cues.Count > 0 && sub.Cues.First().StartTime < this.Cues.Last().EndTime && sub.Cues.First().EndTime != this.Cues.Last().EndTime) || this.Cues.Count == 0)
        {
            // The MPEG2 transport stream clocks (PCR, PTS, DTS) all have units of 1/90000 second
            var seconds = (sub.MpegtsTimestamp - baseTimestamp) / 90000;
            var offset = TimeSpan.FromSeconds(seconds);
            // 当前预添加的字幕的起始时间小于实际上已经走过的时间(如offset已经是100秒，而字幕起始却是2秒)，才修复
            if (sub.Cues.Count > 0 && sub.Cues.First().StartTime < offset)
            {
                foreach (var subCue in sub.Cues)
                {
                    subCue.StartTime += offset;
                    subCue.EndTime += offset;
                }
            }
        }
    }

    private IEnumerable<SubCue> GetCues()
    {
        return this.Cues.Where(c => !string.IsNullOrEmpty(c.Payload));
    }

    private static TimeSpan ConvertToTS(string str)
    {
        // 17.0s
        if (str.EndsWith('s'))
        {
            double sec = Convert.ToDouble(str[..^1]);
            return TimeSpan.FromSeconds(sec);
        }

        str = str.Replace(',', '.');
        long time = 0;
        string[] parts = str.Split('.');
        if (parts.Length > 1)
        {
            time += Convert.ToInt32(parts.Last().PadRight(3, '0'));
            str = parts.First();
        }
        var t = str.Split(':').Reverse().ToList();
        for (int i = 0; i < t.Count; i++)
        {
            time += (long)Math.Pow(60, i) * Convert.ToInt32(t[i]) * 1000;
        }
        return TimeSpan.FromMilliseconds(time);
    }

    public override string ToString()
    {
        var sb = new StringBuilder();
        foreach (var c in GetCues())  // 输出时去除空串
        {
            sb.AppendLine(c.StartTime.ToString(@"hh\:mm\:ss\.fff") + " --> " + c.EndTime.ToString(@"hh\:mm\:ss\.fff") + " " + c.Settings);
            sb.AppendLine(c.Payload);
            sb.AppendLine();
        }
        sb.AppendLine();
        return sb.ToString();
    }

    /// <summary>
    /// 字幕向前平移指定时间
    /// </summary>
    /// <param name="time"></param>
    public void LeftShiftTime(TimeSpan time)
    {
        foreach (var cue in this.Cues)
        {
            if (cue.StartTime.TotalSeconds - time.TotalSeconds > 0) cue.StartTime -= time;
            else cue.StartTime = TimeSpan.FromSeconds(0);

            if (cue.EndTime.TotalSeconds - time.TotalSeconds > 0) cue.EndTime -= time;
            else cue.EndTime = TimeSpan.FromSeconds(0);
        }
    }

    public string ToVtt()
    {
        return "WEBVTT" + Environment.NewLine + Environment.NewLine + ToString();
    }

    public string ToSrt()
    {
        StringBuilder sb = new StringBuilder();
        int index = 1;
        foreach (var c in GetCues())
        {
            sb.AppendLine($"{index++}");
            sb.AppendLine(c.StartTime.ToString(@"hh\:mm\:ss\,fff") + " --> " + c.EndTime.ToString(@"hh\:mm\:ss\,fff"));
            sb.AppendLine(c.Payload);
            sb.AppendLine();
        }
        sb.AppendLine();

        var srt = sb.ToString();

        if (string.IsNullOrEmpty(srt.Trim()))
        {
            srt = "1\r\n00:00:00,000 --> 00:00:01,000"; // 空字幕
        }

        return srt;
    }
}