using System.Text.RegularExpressions;
using VideoDownloader.Core.Models;

namespace VideoDownloader.Core.Hls;

/// <summary>m3u8(마스터/미디어) 재생목록 파서. Python parse_m3u8 의 C# 포팅.</summary>
public static class M3u8Parser
{
    // KEY="VAL",KEY2=VAL  형태 속성 파싱
    private static readonly Regex AttrRe =
        new(@"(?<k>[A-Z0-9\-]+)=(\""(?<q>[^""]*)\"")|(?<k2>[A-Z0-9\-]+)=(?<v>[^,]*)",
            RegexOptions.Compiled);

    private static Dictionary<string, string> ParseAttrs(string s)
    {
        var d = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        foreach (Match m in AttrRe.Matches(s))
        {
            var key = m.Groups["k"].Success ? m.Groups["k"].Value : m.Groups["k2"].Value;
            var val = m.Groups["q"].Success ? m.Groups["q"].Value : m.Groups["v"].Value;
            d[key] = val;
        }
        return d;
    }

    private static string GetValue(this Dictionary<string, string> d, string key, string def = "") =>
        d.TryGetValue(key, out var v) ? v : def;

    public static ParsedPlaylist Parse(string text, Uri baseUrl)
    {
        var variants = new List<Variant>();
        var segments = new List<Segment>();
        Uri? init = null;
        bool isMaster = false;

        Dictionary<string, string>? pendingVariant = null;
        KeyInfo? curKey = null;
        long seq = 0;
        int idx = 0;

        foreach (var raw in text.Split('\n'))
        {
            var line = raw.Trim();
            if (string.IsNullOrEmpty(line)) continue;

            if (line.StartsWith("#EXT-X-STREAM-INF:"))
            {
                pendingVariant = ParseAttrs(line.Substring("#EXT-X-STREAM-INF:".Length));
                continue;
            }
            if (line.StartsWith("#EXT-X-MEDIA-SEQUENCE:"))
            {
                if (long.TryParse(line.Split(':', 2)[1].Trim(), out var s)) seq = s;
                continue;
            }
            if (line.StartsWith("#EXT-X-KEY:"))
            {
                var a = ParseAttrs(line.Substring("#EXT-X-KEY:".Length));
                var method = a.GetValue("METHOD", "NONE").ToUpperInvariant();
                curKey = method == "AES-128"
                    ? new KeyInfo(
                        a.TryGetValue("URI", out var u) && !string.IsNullOrEmpty(u) ? new Uri(baseUrl, u) : null,
                        a.GetValue("IV"))
                    : null;
                continue;
            }
            if (line.StartsWith("#EXT-X-MAP:"))
            {
                var a = ParseAttrs(line.Substring("#EXT-X-MAP:".Length));
                if (a.TryGetValue("URI", out var u) && !string.IsNullOrEmpty(u))
                    init = new Uri(baseUrl, u);
                continue;
            }
            if (line.StartsWith("#")) continue;

            // URL 라인
            var abs = new Uri(baseUrl, line);
            if (pendingVariant != null)
            {
                int.TryParse(pendingVariant.GetValue("BANDWIDTH", "0"), out var bw);
                variants.Add(new Variant(abs, bw,
                    pendingVariant.GetValue("RESOLUTION"), pendingVariant.GetValue("CODECS")));
                pendingVariant = null;
                isMaster = true;
            }
            else
            {
                segments.Add(new Segment(abs, idx, seq, curKey));
                idx++; seq++;
            }
        }

        return new ParsedPlaylist
        {
            Type = isMaster ? PlaylistType.Master : PlaylistType.Media,
            Variants = variants,
            Segments = segments,
            InitSegment = init,
        };
    }
}