using System;
using System.Collections.Generic;
using System.Linq;
using MediaBrowser.Controller.LiveTv;

namespace Jellyfin.Plugin.Enigma2;

/// <summary>Keep saved native channels playable after a receiver bouquet migration.</summary>
public static class ChannelReferenceResolver
{
    public static string Resolve(string reference, IEnumerable<ChannelInfo> channels, Func<string> previousName)
    {
        var current = channels.Where(c => !string.IsNullOrWhiteSpace(c.Id)).ToArray();
        var exact = current.FirstOrDefault(c => string.Equals(c.Id, reference, StringComparison.OrdinalIgnoreCase));
        if (exact != null) return exact.Id;

        // A changed Enigma service type does not change the DVB service identity.
        var identity = Identity(reference);
        var matches = current.Where(c => identity != null && Identity(c.Id) == identity)
            .Select(c => c.Id).Distinct(StringComparer.OrdinalIgnoreCase).ToArray();
        if (matches.Length == 1) return matches[0];
        if (matches.Length > 1) return reference;

        // A moved service has a new SID/TSID. Use only a unique exact historical
        // name; never guess between HD/SD, regional or alternative services.
        var name = previousName()?.Trim();
        if (string.IsNullOrEmpty(name)) return reference;
        matches = current.Where(c => string.Equals(c.Name?.Trim(), name, StringComparison.OrdinalIgnoreCase))
            .Select(c => c.Id).Distinct(StringComparer.OrdinalIgnoreCase).ToArray();
        return matches.Length == 1 ? matches[0] : reference;
    }

    private static string Identity(string reference)
    {
        var fields = reference?.TrimEnd(':').Split(':');
        if (fields == null || fields.Length != 10 || fields[0] != "1" || fields[1] != "0") return null;
        // No URLs, labels or non-DVB references participate in this fallback.
        if (fields.Any(f => f.Length == 0 || !f.All(Uri.IsHexDigit))) return null;
        fields[2] = "";
        return string.Join(':', fields).ToUpperInvariant();
    }
}