using System.Globalization;
using Nonemm.Core;

namespace Nonemm.Spotting;

/// Reads the `DX de` lines a cluster node sends.
public static class SpotLine
{
    private const string Marker = "DX de ";

    /// Null for any other traffic from the node, which the packet window shows
    /// as it arrived.
    public static Spot? Parse(string line, DateTime nowUtc)
    {
        int start = line.IndexOf(Marker, StringComparison.OrdinalIgnoreCase);
        if (start < 0)
        {
            return null;
        }
        string body = line[(start + Marker.Length)..];
        int colon = body.IndexOf(':');
        string[] parts = (colon < 0 ? body : body[(colon + 1)..])
            .Split(' ', StringSplitOptions.RemoveEmptyEntries);
        if (parts.Length < 2)
        {
            return null;
        }
        // without a colon the spotter is the first word and the frequency follows
        string spotter = colon >= 0 ? body[..colon].Trim() : parts[0];
        string[] fields = colon >= 0 ? parts : parts[1..];
        if (fields.Length < 2
            || !double.TryParse(fields[0], NumberStyles.Float, CultureInfo.InvariantCulture, out double kilohertz))
        {
            return null;
        }
        string[] tail = fields[2..];
        int stamp = LastTimeStamp(tail);
        Frequency where = Frequency.FromKilohertz(kilohertz);
        string comment = string.Join(' ', stamp < 0 ? tail : tail[..stamp]).Trim();
        return new Spot(
            Callsign.Parse(fields[1]),
            where,
            stamp < 0 ? nowUtc : TimeOf(tail[stamp], nowUtc),
            SpotSource.Cluster,
            spotter,
            comment)
        {
            Qsx = Qsx.Parse(comment, where),
        };
    }

    /// The node writes the spot's time as `1234Z`. It is usually the last word,
    /// but DXSpider puts the spotter's grid or country after it.
    private static int LastTimeStamp(IReadOnlyList<string> words)
    {
        for (int at = words.Count - 1; at >= 0; at--)
        {
            if (IsTimeStamp(words[at]))
            {
                return at;
            }
        }
        return -1;
    }

    private static bool IsTimeStamp(string word) =>
        word.Length == 5
        && char.ToUpperInvariant(word[4]) == 'Z'
        && word[..4].All(char.IsAsciiDigit);

    private static DateTime TimeOf(string stamp, DateTime nowUtc)
    {
        int hour = int.Parse(stamp[..2], CultureInfo.InvariantCulture);
        int minute = int.Parse(stamp[2..4], CultureInfo.InvariantCulture);
        if (hour > 23 || minute > 59)
        {
            return nowUtc;
        }
        DateTime at = new(nowUtc.Year, nowUtc.Month, nowUtc.Day, hour, minute, 0, DateTimeKind.Utc);
        // a spot timed later than now came in just before midnight
        return at > nowUtc.AddMinutes(5) ? at.AddDays(-1) : at;
    }
}