120 lines
3.1 KiB
C#
120 lines
3.1 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Text;
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using log4net;
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namespace bsmd.AISService.AIS
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{
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internal abstract class NMEA
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{
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protected string type = "";
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protected string data;
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protected string[] elements = null;
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protected static ILog _log = LogManager.GetLogger(typeof(NMEA));
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public enum Status
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{
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OK,
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UNKNOWN_TYPE,
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CHECKSUM,
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ILLEGAL_ARGUMENT
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}
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protected abstract void Decode();
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public static NMEA Decode(string data, ref Status status)
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{
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try
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{
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if (data == null)
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{
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status = Status.ILLEGAL_ARGUMENT;
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return null;
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}
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if (data[0] != '$' && data[0] != '!')
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{
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status = Status.ILLEGAL_ARGUMENT;
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return null; // no NMEA sentence
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}
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string[] elements = data.Trim().Substring(1).Split(',');
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NMEA sentence = NMEA.CreateNMEAElement(elements[0]);
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if (sentence == null)
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{
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status = Status.UNKNOWN_TYPE;
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return null;
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}
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sentence.elements = elements;
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sentence.data = data.Trim(); ;
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if (!sentence.IsChecksumOK)
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{
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status = Status.CHECKSUM;
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return null;
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}
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sentence.Decode();
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return sentence;
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}
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catch (Exception ex)
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{
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_log.ErrorFormat("Error decoding sentence: {0}, {1}", ex.Message, ex.StackTrace);
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return null;
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}
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}
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/// <summary>
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/// Factory method for nmea types
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/// </summary>
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protected static NMEA CreateNMEAElement(string type)
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{
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NMEA result = null;
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switch (type.ToUpper())
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{
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case "AIVDM":
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result = new NMEA_AIS_Sentence();
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break;
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case "PNMLS":
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result = new NMEA_PNMLS_Sentence();
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break;
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default:
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break;
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}
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if (result != null)
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result.type = type.ToUpper();
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return result;
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}
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protected bool IsChecksumOK
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{
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get
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{
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return this.data.Substring(this.data.IndexOf('*') + 1) == this.CalculateChecksum();
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}
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}
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private string CalculateChecksum()
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{
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int checksum = Convert.ToByte(this.data[1]);
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for (int i = 2; i < this.data.IndexOf('*'); i++)
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{
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checksum ^= Convert.ToByte(this.data[i]);
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}
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return checksum.ToString("X2");
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}
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}
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}
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