using GeoVLog.Core.Models;
using System;
using System.Globalization;
using System.Text;

namespace GeoVLog.Core.Parsers;

/// <summary>
/// Parser for Geometrics G-823A magnetometer ASCII frames
/// of the form "$ 30614.050,1521". Validates basic structure
/// and extracts the magnetic field and ADC value.
/// </summary>
internal static class MagParser
{
    public static bool TryParse(ReadOnlySpan<byte> msg, DateTime arrivalUtc, out MagReading parsed)
    {
        parsed = default!;
        var line = Encoding.ASCII.GetString(msg).Trim();
        if (line.Length == 0 || line[0] != '$')
            return false;

        var body = line.Substring(1).TrimStart();
        int comma = body.IndexOf(',');
        if (comma <= 0 || comma >= body.Length - 1)
            return false;

        string fieldPart = body.Substring(0, comma);
        string adcPart = body.Substring(comma + 1);
        if (!double.TryParse(fieldPart, NumberStyles.Float, CultureInfo.InvariantCulture, out double field))
            return false;
        if (!int.TryParse(adcPart, NumberStyles.Integer, CultureInfo.InvariantCulture, out int adc))
            return false;

        parsed = new MagReading
        {
            TimestampUtc = arrivalUtc,
            RawLine = line,
            MagneticFieldNT = field,
            SignalLevel = adc,
            Channel = 0 // default; caller can override
        };
        return true;
    }
}