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

namespace Paca.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 (소문자/언더스코어 포함)
    private static readonly Regex AttrRe =
        new(@"(?<k>[A-Za-z0-9_\-]+)=(\""(?<q>[^""]*)\"")|(?<k2>[A-Za-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;
        long? initByteRangeLen = null;
        long? initByteRangeOff = null;
        bool isMaster = false;

        if (baseUrl == null || string.IsNullOrWhiteSpace(text) || !text.Contains("#EXTM3U", StringComparison.OrdinalIgnoreCase))
        {
            return new ParsedPlaylist
            {
                Type = PlaylistType.Media,
                Variants = variants,
                Segments = segments,
                InitSegment = init,
                InitByteRangeLength = initByteRangeLen,
                InitByteRangeOffset = initByteRangeOff,
            };
        }

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

        long? pendingByteRangeLength = null;
        long? pendingByteRangeOffset = null;
        long prevByteRangeOffset = 0;
        long prevByteRangeLength = 0;

        using var reader = new StringReader(text);
        string? raw;
        while ((raw = reader.ReadLine()) != null)
        {
            var line = raw.Trim();
            if (string.IsNullOrEmpty(line)) continue;

            if (line.StartsWith("#EXT-X-STREAM-INF:", StringComparison.OrdinalIgnoreCase))
            {
                pendingVariant = ParseAttrs(line.Substring("#EXT-X-STREAM-INF:".Length));
                continue;
            }
            if (line.StartsWith("#EXT-X-MEDIA-SEQUENCE:", StringComparison.OrdinalIgnoreCase))
            {
                var parts = line.Split(':', 2);
                if (parts.Length > 1 && long.TryParse(parts[1].Trim(), out var s) && s >= 0) seq = s;
                continue;
            }
            if (line.StartsWith("#EXT-X-KEY:", StringComparison.OrdinalIgnoreCase))
            {
                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) && Uri.TryCreate(baseUrl, u.Trim('"'), out var ku) ? ku : null,
                        a.GetValue("IV"))
                    : null;
                continue;
            }
            if (line.StartsWith("#EXT-X-BYTERANGE:", StringComparison.OrdinalIgnoreCase))
            {
                var val = line.Substring("#EXT-X-BYTERANGE:".Length).Trim();
                var parts = val.Split('@', 2);
                if (long.TryParse(parts[0].Trim(), out var len) && len > 0)
                {
                    pendingByteRangeLength = len;
                    if (parts.Length > 1 && long.TryParse(parts[1].Trim(), out var off) && off >= 0)
                    {
                        pendingByteRangeOffset = off;
                        prevByteRangeOffset = off;
                    }
                    else
                    {
                        pendingByteRangeOffset = prevByteRangeOffset + prevByteRangeLength;
                        prevByteRangeOffset = pendingByteRangeOffset.Value;
                    }
                    prevByteRangeLength = len;
                }
                continue;
            }
            if (line.StartsWith("#EXT-X-MAP:", StringComparison.OrdinalIgnoreCase))
            {
                var a = ParseAttrs(line.Substring("#EXT-X-MAP:".Length));
                if (a.TryGetValue("URI", out var u) && !string.IsNullOrEmpty(u) && Uri.TryCreate(baseUrl, u.Trim('"'), out var mu))
                    init = mu;

                if (a.TryGetValue("BYTERANGE", out var br) && !string.IsNullOrEmpty(br))
                {
                    var cleanBr = br.Trim('"');
                    var brParts = cleanBr.Split('@', 2);
                    if (long.TryParse(brParts[0].Trim(), out var bLen) && bLen > 0)
                    {
                        initByteRangeLen = bLen;
                        if (brParts.Length > 1 && long.TryParse(brParts[1].Trim(), out var bOff) && bOff >= 0)
                        {
                            initByteRangeOff = bOff;
                        }
                    }
                }
                continue;
            }
            if (line.StartsWith("#")) continue;

            // URL 라인
            if (!Uri.TryCreate(baseUrl, line, out var abs)) continue;

            if (pendingVariant != null)
            {
                int.TryParse(pendingVariant.GetValue("BANDWIDTH", "0"), out var bw);
                variants.Add(new Variant(abs, Math.Max(0, bw),
                    pendingVariant.GetValue("RESOLUTION"), pendingVariant.GetValue("CODECS")));
                pendingVariant = null;
                isMaster = true;
            }
            else
            {
                segments.Add(new Segment(abs, idx, seq, curKey, pendingByteRangeLength, pendingByteRangeOffset));
                pendingByteRangeLength = null;
                pendingByteRangeOffset = null;
                idx++;
                if (seq < long.MaxValue) seq++;
            }
        }

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