/*
Implementing the "Two-line element set (TLE)", a data format encoding orbital elements of Earth-orbiting objects.

More information can be found here:
- https://en.wikipedia.org/wiki/Two-line_element_set
- https://spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/JavaSSOP/SSOP_Help/tle_def.html

*/

package TLE

// TLE defines the lines contained in a Two-Line-Element
type TLE struct {
	TitleLine TitleLine `json:"titleline"`
	LineOne   LineOne   `json:"lineone"`
	LineTwo   LineTwo   `json:"linetwo"`
}

// TitleLine defines the first line in the the TLE
// It contains the name of the satellite
type TitleLine struct {
	Satname string `json:"satname"`
}

// LineOne defines the first line in the TLE
type LineOne struct {
	Linenumber int `json:"linenumber"`

	// Catalog number defined by USSPACECOM
	// A "U" indicates an unclassified object
	SatelliteNumber int    `json:"satellitenumber"`
	Classification  string `json:"classification"`

	// International  Designator containing information about the launch
	InternationalDesignator InternationalDesignator `json:"internationaldesignator"`

	// Epoch defining from when the TLE is
	Epoch Epoch `json:"epoch"`

	// First Time Derivative of the Mean Motion divided by two
	// Unit: revs / day
	// "catch all" drag term used in SGP4 USSPACECOM predictor
	Firstderiv float64 `json:"firstderiv"`

	// Second Time Derivative of Mean Motion divided by six (decimal point assumed)
	// second order drag term in the SGP4
	// Unit: revs / day^3
	// A leading decimal must be applied to this value
	// The last two characters define an applicable power of 10 (12345-5 = 0.0000012345)
	Secondderiv float64 `json:"secondderiv"`

	// Drag Term
	// (67960-4 = 0.000067960)
	// Unit: earth radii^-1
	// The last two characters define an applicable power of 10
	BSTAR float64 `json:"BSTAR"`

	// The number 0 (originally this should have been "Ephemeris type")
	Numberzero int `json:"numberzero"`

	// Element set number. Incremented when a new TLE is generated for this object.
	ElementSetNumber int `json:"elementesetnumber"`

	// Checksum (modulo 10)
	Checksum int `json:"checksum"`
}

// InternationalDesignator stores information about the satellite such as when it launched
type InternationalDesignator struct {

	// Last two digits of launch year
	Launchyear int `json:"launchyear"`

	// Launch number of the year
	Launchnumber int `json:"launchnumber"`

	// Piece of the launch
	Launchpiece string `json:"launchpiece"`
}

// Epoch defines a moment in time
type Epoch struct {

	// Last two digits of the year
	Year int `json:"year"`

	// day of the year and fractional portion of the day
	Dayfraction float64 `json:"dayfraction"`
}

type LineTwo struct {
	Linenumber int `json:"linenumber"`

	// Catalog number defined by USSPACECOM
	Satellitenumber int `json:"satellitenumber"`

	// Inclination
	// Unit: degrees
	// Angle between the equator and the orbit plane
	Inclination float64 `json:"inclination"`

	// Right Ascension of the Ascending Node
	// Unit: degrees
	// Angle between vernal equinox and the point where the orbit crosses the equitorial plane (going north).
	RightAscensionOfTheAscendingNode float64 `json:"rightascensionoftheascendingnode"`

	// Eccentricity
	// Constant defining the shape of the orbit (0=circular, Less than 1=elliptical).
	// The value provided is the mean eccentricity.
	// A leading decimal must be applied to this value
	Eccentricity float64 `json:"eccentricity"`

	// Argument of perigee
	// Unit: degrees
	// The angle between the ascending node and the orbit's point of closest approach of the earth (perigee)
	ArgumentOfPerigee float64 `json:"argumentofperigee"`

	// Mean Anomaly
	// Unit: degrees
	// The angle, measured from perigee, of the satellite location in the orbit referenced to a circular orbit
	// with radius equal to the semi-major axis.
	MeanAnomaly float64 `json:"meananomaly"`

	// Mean Motion
	// The value is the mean number of orbits per day the object completes. There are 8 digits after the decimal,
	// leaving no trailing space(s) when the following element exceeds 9999.
	MeanMotion float64 `json:"meanmotion"`

	// The orbit number at Epoch Time. This time is chosen very near the time of true ascending node passage as
	// a matter of routine. The last digit is the check sum for line 2.
	RevolutionNumberAtEpoch int `json:"revolutionnumberatepoch"`

	// Checksum (modulo 10)
	Checksum int `json:"checksum"`
}