// Two-line satellite orbital element calculations.
//
// See:
//   http://celestrak.com/columns/v04n03/index.asp#FAQ01
// and
//   http://satobs.org/element.html
// and
//   http://www.zeptomoby.com/satellites/
//   
//
// Elements are of the format:
//
// SATNAME
// 1 NNNNNC NNNNNAAA NNNNN.NNNNNNNN +.NNNNNNNN +NNNNN-N +NNNNN-N N NNNNN
// 2 NNNNN NNN.NNNN NNN.NNNN NNNNNNN NNN.NNNN NNN.NNNN NN.NNNNNNNNNNNNNN
//
// A sample for the International Space Station:
//
// ISS
// 1 25544U 98067A   06153.51583746  .00020000  00000-0  20000-3 0  9003
// 2 25544  51.6326 263.0272 0009318 279.9714  80.0399 15.75882122 30853

class TLE
{
   // A human-readable name
   var name
   
   // The NORAD catalog number
   var catalogNumber

   // Security classification of satellite
   var securityClassification

   // International COSPAR identification
   var COSPAR

   // The epoch year
//   var epochYear

   // The epoch day
//   var epochDay

   // The time that the satellite crossed the equator in a northerly direction.
   var epoch

   // First derivative of the mean motion
   var meanMotion1

   // Second derivative of the mean motion
   var meanMotion2

   // BStar drag term
   var bStar

   // Ephemeris type
   var ephemerisType

   // Element number
   var elementNumber

   // Inclination angle
   var inclination

   // Right ascension of ascending node
   var rightAscension

   // Eccentricity of orbit
   var eccentricity

   // Argument of perigee
   var argumentOfPerigee

   // Mean anomaly
   var meanAnomaly

   // Revolutions per day
   var revolutionsPerDay

   // Revolution number at epoch
   var revolutionAtEpoch

   // Constructor, parses a TLE specification from strings
   new[readableName, line1, line2] :=
   {
      name = readableName

      // Parse line 1
      catalogNumber = trim[substrLen[line1, 2,5]]
      securityClassification = substrLen[line1, 7,1]
      COSPAR = trim[substrLen[line1, 9,8]]
      
      year = parseInt[substrLen[line1, 18,2]]
      if (year >= 57)
         epochYear = year + 1900
      else
         epochYear = year + 2000

      epochDay = eval[substrLen[line1, 20,12]]

      epoch = parseDate["$epochYear GMT"] + epochDay days

      meanMotion1 = eval[substrLen[line1, 33,10]]
      meanMotion2 = eval[substrLen[line1, 44, 1] + "0." + substrLen[line1, 45,5] + "*10^" + substrLen[line1, 50,2]]

      bStar = eval[substrLen[line1, 53, 1] + "0." + substrLen[line1, 54,5] + "*10^" + substrLen[line1, 59,2]]

      ephemerisType = substrLen[line1, 62,1]
      elementNumber = eval[substrLen[line1, 64,4]]

      // Parse line 2
      if (catalogNumber != trim[substrLen[line2, 2, 5]])
         println["Error!  catalog number does not match in lines 1 and 2!"]
      // TODO:  Throw an exception for the above.

      inclination = eval[substrLen[line2, 8, 8]]
      rightAscension = eval[substrLen[line2, 17, 8]]
      eccentricity = eval["0." + substrLen[line2, 26, 7]]
      argumentOfPerigee = eval[substrLen[line2, 34, 8]]
      meanAnomaly = eval[substrLen[line2, 43, 8]]
      revolutionsPerDay = eval[substrLen[line2, 52, 11]]
      revolutionAtEpoch = eval[substrLen[line2, 63, 5]]
   }

   // Returns the orbital period
   getOrbitalPeriod[] := day / revolutionsPerDay
}

  

line1Pattern = %r/1                 # Line number 1
                 \s            
                 (\d{1,5})           # Satellite number
                 (\w)                # Designation
                 \s+
                 (\d{5})             # International designator
                 (\w{1,3})           # Designator parts
                 \s+
                 (\d{2})             # Epoch year (last 2 digits)
                 (\d{3}\.\d{8})      # Epoch day
                 \s+
                 ((?:\+|\-)?\.\d{8}) # First derivative of mean motion
                 \s+
                 ((?:\+|\-)?\S+)      # Second derivative of mean motion
                 \s+
                 (\S+)               # Bstar drag term
                 /x

line2Pattern = %r/^2 /

var name
var line1
var t
for line = lines["file:tletest.txt"]
{
   if line =~ line1Pattern
      line1 = line
   else
      if line =~ line2Pattern
      {
         t = new TLE[name, line1, line]
         println[t]
         println[t.epoch -> GMT]
      } else
      name = line
}