package ellipsoid

// Written in Go by Stefan Schroeder, New York, 2013
// Version 1.0 based on Geo::Ellipsoid Version 1.12.
// Version 1.1 Added ECEF functions.
// Version 1.2 Replaced Fabs with Abs.
// Version 1.3 Added Displacement function

/*

SYNOPSIS

See hello-world.go example.

DESCRIPTION

ellipsoid performs geometrical calculations on the surface of
an ellipsoid. An ellipsoid is a three-dimension object formed from
the rotation of an ellipse about one of its axes. The approximate
shape of the earth is an ellipsoid, so ellipsoid can accurately
calculate distance and bearing between two widely-separated locations
on the earth's surface.

The shape of an ellipsoid is defined by the lengths of its
semi-major and semi-minor axes. The shape may also be specifed by
the flattening ratio f as:

    f = ( semi-major - semi-minor ) / semi-major

which, since f is a small number, is normally given as the reciprocal
of the flattening 1/f.

The shape of the earth has been surveyed and estimated differently
at different times over the years. The two most common sets of values
used to describe the size and shape of the earth in the United States
are 'NAD27', dating from 1927, and 'WGS84', from 1984. United States
Geological Survey topographical maps, for example, use one or the
other of these values, and commonly-available Global Positioning
System (GPS) units can be set to use one or the other.
See "DEFINED ELLIPSOIDS" below for the ellipsoid survey values
that may be selected for use by ellipsoid.

*/

import "math"
import "fmt"

const (
	pi           = math.Pi
	twopi        = math.Pi * 2.0
	maxLoopCount = 20
	eps          = 1.0e-23
	debug        = false
	// Meter is one of the output/input units.
	Meter = 0 //    1.0    meter
	// Foot is one of the output/input units.
	Foot = 1 //    0.3048 meter are a foot
	// Kilometer is one of the output/input units.
	Kilometer = 2 // 1000.0    meter are a kilometer
	// Mile is one of the output/input units.
	Mile = 3 // 1609.344  meter are a mile
	// Nm (nautical mile) is one of the output/input units.
	Nm = 4 // 1852.0    meter are a nautical mile,
	// Degrees is one of the possible angle units for input/output.
	Degrees = iota
	// Radians is one of the possible angle units for input/output.
	Radians = iota
	// LongitudeIsSymmetric determines that the output longitude shall be symmetric.
	LongitudeIsSymmetric = true
	// LongitudeNotSymmetric determines that the output longitude shall not be symmetric.
	LongitudeNotSymmetric = false
	// BearingIsSymmetric determines that the output bearing shall be symmetric.
	BearingIsSymmetric = true
	// BearingNotSymmetric determines that the output bearing shall not be symmetric.
	BearingNotSymmetric = false
)

// Ellipsoid is the main object to store information about one ellispoid.
type Ellipsoid struct {
	Ellipse            ellipse
	Units              int
	DistanceUnits      int
	LongitudeSymmetric bool
	BearingSymmetry    bool
	DistanceFactor     float64
	// Having the DistanceFactor AND the DistanceUnits in this struct is redundant
	// but it looks nicer in the code.
}

type ellipse struct {
	Equatorial    float64
	InvFlattening float64
}

// Location is one coordinate in LLA.
type Location struct {
	Lat float64
	Lon float64
	Ele float64
}

func deg2rad(d float64) (r float64) {
	return d * pi / 180.0
}
func rad2deg(d float64) (r float64) {
	return d * 180.0 / pi
}

/* Init

The Init constructor must be called with a list of parameters to set
the value of the ellipsoid to be used, the value of the units to be
used for angles and distances, and whether or not the output range
of longitudes and bearing angles should be symmetric around zero
or always greater than zero. There is no default constructor, all
arguments are required; they may not be abbreviated.

Example:

	geo := ellipsoid.Init(
		"WGS84",  // for possible values see below.
		ellipsoid.Degrees, // possible values: Degrees or Radians
		ellipsoid.Meter,   // possible values: Meter, Kilometer,
				   // Foot, Nm, Mile
		ellipsoid.LongitudeIsSymmetric, // possible values
						  // LongitudeIsSymmetric or
						  // LongitudeNotSymmetric
		ellipsoid.BearingIsSymmetric    // possible
						  // values BearingIsSymmetric or
						  // BearingNotSymmetric
	)

*/
func Init(name string, units int, distUnits int, longSym bool, bearSym bool) (e Ellipsoid) {
	m := map[string]ellipse{
		"AIRY":                  {6377563.396, 299.3249646},
		"AIRY-MODIFIED":         {6377340.189, 299.3249646},
		"AUSTRALIAN":            {6378160.0, 298.25},
		"BESSEL-1841":           {6377397.155, 299.1528128},
		"BESSEL-1841-NAMIBIA":   {6377483.865, 299.152813},
		"CLARKE-1866":           {6378206.400, 294.978698},
		"CLARKE-1880":           {6378249.145, 293.465},
		"EVEREST-1830":          {6377276.345, 300.8017},
		"EVEREST-1948":          {6377304.063, 300.8017},
		"EVEREST-SABAH-SARAWAK": {6377298.556, 300.801700},
		"EVEREST-1956":          {6377301.243, 300.801700},
		"EVEREST-1969":          {6377295.664, 300.801700},
		"FISHER-1960":           {6378166.0, 298.3},
		"FISCHER-1960-MODIFIED": {6378155.000, 298.300000},
		"FISHER-1968":           {6378150.0, 298.3},
		"GRS80":                 {6378137.0, 298.25722210088},
		"HELMERT-1906":          {6378200.000, 298.300000},
		"HOUGH-1956":            {6378270.0, 297.0},
		"HAYFORD":               {6378388.0, 297.0},
		"IAU76":                 {6378140.0, 298.257},
		"INTERNATIONAL":         {6378388.000, 297.000000},
		"KRASSOVSKY-1938":       {6378245.0, 298.3},
		"NAD27":                 {6378206.4, 294.9786982138},
		"NWL-9D":                {6378145.0, 298.25},
		"SGS85":                 {6378136.000, 298.257000},
		"SOUTHAMERICAN-1969":    {6378160.0, 298.25},
		"SOVIET-1985":           {6378136.0, 298.257},
		"WGS60":                 {6378165.000, 298.300000},
		"WGS66":                 {6378145.000, 298.250000},
		"WGS72":                 {6378135.0, 298.26},
		"WGS84":                 {6378137.0, 298.257223563},
	}

	e2, ok := m[name]
	if !ok {
		fmt.Printf("ellipsoid.go: Warning: Invalid ellipse type '%v'\n", name)
	}

	//                      m    ft      km      mi        nm
	conversion := []float64{1.0, 0.3048, 1000.0, 1609.344, 1852.0}
	ellipsoid := Ellipsoid{e2, units, distUnits, longSym, bearSym, conversion[distUnits]}
	return ellipsoid
}

/* Intermediate

Takes two coordinates with longitude and latitude; and a step count and
returns range and bearing and an array with the lons and lats of intermediate
points on a straight line (whatever that is on an ellipsoid), INCLUDING the
start and the endpoint.

So if you put in point1 and point2 with step count 4, the output will be
(you make 4 hops, right?)

	point1
	i1
	i2
	i3
	point2

Each point is two float64 values, lat and lon, thus you have an array
with 4*2 + 2 = 5*2 cells.

steps shall not be 0.

I havent tested the upper limit for steps.

*/
func (ellipsoid Ellipsoid) Intermediate(lat1, lon1, lat2, lon2 float64, steps int) (distance, bearing float64, arr []float64) {
	if steps == 0 {
		return
	}
	r, phi := ellipsoid.To(lat1, lon1, lat2, lon2)
	v := make([]float64, steps*2+2)
	for i := 0; i <= steps; i++ {
		a, b := ellipsoid.At(lat1, lon1, r*float64(i)/float64(steps), phi)
		v[i*2], v[i*2+1] = a, b
	}
	arr = v
	return r, phi, arr

}

/* To returns range, bearing between two specified locations.

   dist, theta  = geo.To( lat1, lon1, lat2, lon2 )

*/
func (ellipsoid Ellipsoid) To(lat1, lon1, lat2, lon2 float64) (distance, bearing float64) {

	if ellipsoid.Units == Degrees {
		lat1 = deg2rad(lat1)
		lon1 = deg2rad(lon1)
		lat2 = deg2rad(lat2)
		lon2 = deg2rad(lon2)
	}

	distance, bearing = ellipsoid.calculateBearing(lat1, lon1, lat2, lon2)
	if ellipsoid.Units == Degrees {
		bearing = rad2deg(bearing)
	}

	distance /= ellipsoid.DistanceFactor

	return
}

/* At returns the list latitude,longitude in degrees or radians that is a
specified range and bearing from a given location.

    lat2, lon2  = geo.At( lat1, lon1, range, bearing )

*/
func (ellipsoid Ellipsoid) At(lat1, lon1, distance, bearing float64) (lat2, lon2 float64) {

	if ellipsoid.Units == Degrees {
		lat1 = deg2rad(lat1)
		lon1 = deg2rad(lon1)
		bearing = deg2rad(bearing)
	}

	lat2, lon2 = ellipsoid.calculateTargetlocation(lat1, lon1, distance, bearing)

	if ellipsoid.LongitudeSymmetric == LongitudeIsSymmetric {
		if lon2 > pi {
			lon2 -= twopi
		}
	}
	if ellipsoid.LongitudeSymmetric == LongitudeNotSymmetric {
		if lon2 < 0.0 {
			lon2 += twopi
		}
	}

	if ellipsoid.Units == Degrees {
		lat2 = rad2deg(lat2)
		lon2 = rad2deg(lon2)
	}

	return
}

/* Displacement returns the (x,y) displacement in distance units between the two specified
locations.

    x, y  = geo.Displacement( lat1, lon1, lat2, lon2 )

NOTE: The x and y displacements are only approximations and only valid
between two locations that are fairly near to each other. Beyond 10 kilometers
or more, the concept of X and Y on a curved surface loses its meaning.

*/
func (ellipsoid Ellipsoid) Displacement(lat1, lon1, lat2, lon2 float64) (x, y float64) {
	// FIXME: Normalize!!! before use.
	r, bearing := ellipsoid.To(lat1, lon1, lat2, lon2)

	if ellipsoid.Units == Degrees {
		bearing = deg2rad(bearing)
	}

	x = r * math.Sin(bearing)
	y = r * math.Cos(bearing)
	return x, y
}

/* Location returns the list (latitude,longitude) of a location at a given (x,y)
displacement from a given location.

	lat2, lon2 = geo.Location( lat1, lon1, x, y )

The note from Displacement applies.

*/
func (ellipsoid Ellipsoid) Location(lat1, lon1, x, y float64) (lat, lon float64) {
	degreesPerRadian := 180.0 / math.Pi

	range1 := math.Sqrt(x*x + y*y)
	bearing1 := math.Atan2(x, y)

	if ellipsoid.Units == Degrees {
		bearing1 *= degreesPerRadian
	}

	return ellipsoid.At(lat1, lon1, range1, bearing1)
}

func (ellipsoid Ellipsoid) calculateTargetlocation(lat1, lon1, distance, bearing float64) (lat2, lon2 float64) {

	if debug == true {
		fmt.Printf("_forward(lat1=%v,lon1=%v,range=%v,bearing=%v)\n", lat1, lon1, distance, bearing)
	}

	eps := 0.5e-13

	a := ellipsoid.Ellipse.Equatorial
	f := 1.0 / ellipsoid.Ellipse.InvFlattening
	r := 1.0 - f

	clat1 := math.Cos(lat1)
	if clat1 == 0 {
		fmt.Printf("WARNING: Division by Zero in ellipsoid.go.\n")
		return 0.0, 0.0
	}
	tu := r * math.Sin(lat1) / clat1
	faz := bearing

	s := ellipsoid.DistanceFactor * distance

	sf := math.Sin(faz)
	cf := math.Cos(faz)

	baz := 0.0
	if cf != 0.0 {
		baz = 2.0 * math.Atan2(tu, cf)
	}

	cu := 1.0 / math.Sqrt(1.0+tu*tu)
	su := tu * cu
	sa := cu * sf
	c2a := 1.0 - (sa * sa)
	x := 1.0 + math.Sqrt((((1.0/(r*r))-1.0)*c2a)+1.0)
	x = (x - 2.0) / x
	c := 1.0 - x
	c = (((x * x) / 4.0) + 1.0) / c
	d := x * ((0.375 * x * x) - 1.0)
	tu = ((s / r) / a) / c
	y := tu

	if debug == true {
		fmt.Printf("r=%.8f, tu=%.8f, faz=%.8f\n", r, tu, faz)
		fmt.Printf("baz=%.8f, sf=%.8f, cf=%.8f\n", baz, sf, cf)
		fmt.Printf("cu=%.8f, su=%.8f, sa=%.8f\n", cu, su, sa)
		fmt.Printf("x=%.8f, c=%.8f, y=%.8f\n", x, c, y)
	}

	var cy, cz, e, sy float64
	for true {
		sy = math.Sin(y)
		cy = math.Cos(y)
		cz = math.Cos(baz + y)
		e = (2.0 * cz * cz) - 1.0
		c = y
		x = e * cy
		y = (2.0 * e) - 1.0
		y = (((((((((sy * sy * 4.0) - 3.0) * y * cz * d) / 6.0) + x) * d) / 4.0) - cz) * sy * d) + tu

		if math.Abs(y-c) <= eps {
			break
		}
	}
	baz = (cu * cy * cf) - (su * sy)
	c = r * math.Sqrt((sa*sa)+(baz*baz))
	d = su*cy + cu*sy*cf
	lat2 = math.Atan2(d, c)
	c = cu*cy - su*sy*cf
	x = math.Atan2(sy*sf, c)
	c = (((((-3.0 * c2a) + 4.0) * f) + 4.0) * c2a * f) / 16.0
	d = ((((e * cy * c) + cz) * sy * c) + y) * sa
	lon2 = lon1 + x - (1.0-c)*d*f

	if debug == true {
		fmt.Printf("returns(lat2=%v,lon2=%v)\n", lat2, lon2)
	}
	return lat2, lon2
}

func (ellipsoid Ellipsoid) calculateBearing(lat1, lon1, lat2, lon2 float64) (distance, bearing float64) {
	a := ellipsoid.Ellipse.Equatorial
	f := 1 / ellipsoid.Ellipse.InvFlattening

	if lon1 < 0 {
		lon1 += twopi
	}
	if lon2 < 0 {
		lon2 += twopi
	}

	r := 1.0 - f
	clat1 := math.Cos(lat1)
	if clat1 == 0 {
		fmt.Printf("WARNING: Division by Zero in ellipsoid.go.\n")
		return 0.0, 0.0
	}
	clat2 := math.Cos(lat2)
	if clat2 == 0 {
		fmt.Printf("WARNING: Division by Zero in ellipsoid.go.\n")
		return 0.0, 0.0
	}
	tu1 := r * math.Sin(lat1) / clat1
	tu2 := r * math.Sin(lat2) / clat2
	cu1 := 1.0 / (math.Sqrt((tu1 * tu1) + 1.0))
	su1 := cu1 * tu1
	cu2 := 1.0 / (math.Sqrt((tu2 * tu2) + 1.0))
	s := cu1 * cu2
	baz := s * tu2
	faz := baz * tu1
	dlon := lon2 - lon1

	if debug == true {
		fmt.Printf("a=%v, f=%v\n", a, f)
		fmt.Printf("lat1=%v, lon1=%v\n", lat1, lon1)
		fmt.Printf("lat2=%v, lon2=%v\n", lat2, lon2)

		fmt.Printf("r=%v, tu1=%v, tu2=%v\n", r, tu1, tu2)
		fmt.Printf("faz=%.8f, dlon=%.8f, su1=%v\n", faz, dlon, su1)
	}

	x := dlon
	cnt := 0

	var c2a, c, cx, cy, cz, d, del, e, sx, sy, y float64
	// This originally was a do-while loop. Exit condition is at end of loop.
	for true {
		if debug == true {
			fmt.Printf("  x=%.8f\n", x)
		}
		sx = math.Sin(x)
		cx = math.Cos(x)
		tu1 = cu2 * sx
		tu2 = baz - (su1 * cu2 * cx)

		if debug == true {
			fmt.Printf("    sx=%.8f, cx=%.8f, tu1=%.8f, tu2=%.8f\n", sx, cx, tu1, tu2)
		}

		sy = math.Sqrt(tu1*tu1 + tu2*tu2)
		cy = s*cx + faz
		y = math.Atan2(sy, cy)
		var sa float64
		if sy == 0.0 {
			sa = 1.0
		} else {
			sa = (s * sx) / sy
		}

		if debug == true {
			fmt.Printf("    sy=%.8f, cy=%.8f, y=%.8f, sa=%.8f\n", sy, cy, y, sa)
		}

		c2a = 1.0 - (sa * sa)
		cz = faz + faz
		if c2a > 0.0 {
			cz = ((-cz) / c2a) + cy
		}
		e = (2.0 * cz * cz) - 1.0
		c = (((((-3.0 * c2a) + 4.0) * f) + 4.0) * c2a * f) / 16.0
		d = x
		x = ((e*cy*c+cz)*sy*c + y) * sa
		x = (1.0-c)*x*f + dlon
		del = d - x

		if debug == true {
			fmt.Printf("    c2a=%.8f, cz=%.8f\n", c2a, cz)
			fmt.Printf("    e=%.8f, d=%.8f\n", e, d)
			fmt.Printf("    (d-x)=%.8g\n", del)
		}
		if math.Abs(del) <= eps {
			break
		}
		cnt++
		if cnt > maxLoopCount {
			break
		}

	}

	faz = math.Atan2(tu1, tu2)
	baz = math.Atan2(cu1*sx, (baz*cx-su1*cu2)) + pi
	x = math.Sqrt(((1.0/(r*r))-1.0)*c2a+1.0) + 1.0
	x = (x - 2.0) / x
	c = 1.0 - x
	c = ((x*x)/4.0 + 1.0) / c
	d = ((0.375 * x * x) - 1.0) * x
	x = e * cy

	if debug == true {
		fmt.Printf("e=%.8f, cy=%.8f, x=%.8f\n", e, cy, x)
		fmt.Printf("sy=%.8f, c=%.8f, d=%.8f\n", sy, c, d)
		fmt.Printf("cz=%.8f, a=%.8f, r=%.8f\n", cz, a, r)
	}

	s = 1.0 - e - e
	s = ((((((((sy * sy * 4.0) - 3.0) * s * cz * d / 6.0) - x) * d / 4.0) + cz) * sy * d) + y) * c * a * r

	if debug == true {
		fmt.Printf("s=%.8f\n", s)
	}

	// adjust azimuth to (0,360) or (-180,180) as specified
	if ellipsoid.BearingSymmetry == BearingIsSymmetric {
		if faz < -(pi) {
			faz += twopi
		}
		if faz >= pi {
			faz -= twopi
		}
	} else {
		if faz < 0 {
			faz += twopi
		}
		if faz >= twopi {
			faz -= twopi
		}
	}

	distance, bearing = s, faz
	return
}

/* ToLLA takes three cartesian coordinates x, y, z and returns
the latitude, longitude, elevation list.

FIXME: This algorithm cannot handle x==0, although this is a valid value.
WARNING: I put in an if condition to catch this. Is it still necessary?

*/
func (ellipsoid Ellipsoid) ToLLA(x, y, z float64) (lat1, lon1, alt1 float64) {

	if x == 0 {
		fmt.Printf("FATAL: Caught x==0 (div by zero).\n")
		return
	}

	a := ellipsoid.Ellipse.Equatorial
	f := 1 / ellipsoid.Ellipse.InvFlattening

	b := a * (1.0 - f)
	e := math.Sqrt((a*a - b*b) / (a * a))
	e2 := math.Sqrt((a*a - b*b) / (b * b)) // e'
	esq := e * e                           // e squared
	e2sq := e2 * e2                        // e' squared
	p := math.Sqrt(x*x + y*y)

	theta := math.Atan2(z*a, p*b)
	stheta3 := math.Sin(theta) * math.Sin(theta) * math.Sin(theta)
	ctheta3 := math.Cos(theta) * math.Cos(theta) * math.Cos(theta)

	lon1 = math.Atan2(y, x)
	phi := math.Atan2(z+e2sq*b*stheta3, p-esq*a*ctheta3)
	lat1 = phi

	sphisq := math.Sin(phi) * math.Sin(phi)
	N := a / (math.Sqrt(1 - esq*sphisq))
	alt1 = p/math.Cos(phi) - N

	if ellipsoid.LongitudeSymmetric == LongitudeIsSymmetric {
		if lon1 > pi {
			lon1 -= twopi
		}
	}
	if ellipsoid.LongitudeSymmetric == LongitudeNotSymmetric {
		if lon1 < 0.0 {
			lon1 += twopi
		}
	}

	if ellipsoid.Units == Degrees {
		lat1 = rad2deg(lat1)
		lon1 = rad2deg(lon1)
	}
	return lat1, lon1, alt1
}

/* ToECEF takes the latitude, longitude, elevation list and
   returns three cartesian coordinates x, y, z */
func (ellipsoid Ellipsoid) ToECEF(lat1, lon1, alt1 float64) (x, y, z float64) {
	a := ellipsoid.Ellipse.Equatorial
	f := 1 / ellipsoid.Ellipse.InvFlattening

	b := a * (1.0 - f)
	e := math.Sqrt((a*a - b*b) / (a * a))
	esq := e * e // e squared

	if ellipsoid.Units == Degrees {
		lat1 = deg2rad(lat1)
		lon1 = deg2rad(lon1)
	}

	h := alt1 // renamed for convenience
	phi := lat1
	lambda := lon1

	cphi := math.Cos(phi)
	sphi := math.Sin(phi)
	sphisq := sphi * sphi
	clam := math.Cos(lambda)
	slam := math.Sin(lambda)
	N := a / (math.Sqrt(1 - esq*sphisq))
	x = (N + h) * cphi * clam
	y = (N + h) * cphi * slam
	z = ((b*b*N)/(a*a) + h) * sphi

	return x, y, z
}

/*
 DEFINED ELLIPSOIDS

The following ellipsoids are defined in Geo::Ellipsoid, with the
semi-major axis in meters and the reciprocal flattening as shown.


    Ellipsoid        Semi-Major Axis (m.)     1/Flattening
    ---------        -------------------     ---------------
    AIRY                 6377563.396         299.3249646
    AIRY-MODIFIED        6377340.189         299.3249646
    AUSTRALIAN           6378160.0           298.25
    BESSEL-1841          6377397.155         299.1528128
    CLARKE-1880          6378249.145         293.465
    EVEREST-1830         6377276.345         290.8017
    EVEREST-MODIFIED     6377304.063         290.8017
    FISHER-1960          6378166.0           298.3
    FISHER-1968          6378150.0           298.3
    GRS80                6378137.0           298.25722210088
    HOUGH-1956           6378270.0           297.0
    HAYFORD              6378388.0           297.0
    IAU76                6378140.0           298.257
    KRASSOVSKY-1938      6378245.0           298.3
    NAD27                6378206.4           294.9786982138
    NWL-9D               6378145.0           298.25
    SOUTHAMERICAN-1969   6378160.0           298.25
    SOVIET-1985          6378136.0           298.257
    WGS72                6378135.0           298.26
    WGS84                6378137.0           298.257223563

plus a few more ...

 LIMITATIONS

The methods should not be used on points which are too near the poles
(above or below 89 degrees), and should not be used on points which
are antipodal, i.e., exactly on opposite sides of the ellipsoid. The
methods will not return valid results in these cases.

The Go-version does not support all features of the Perl module. If you
need advanced features, like defining your own ellipses at runtime,
calculating x,y dislocations, etc, please refer to the package on CPAN

Geo::Ellipsoid

http://search.cpan.org/~jgibson/Geo-Ellipsoid-1.12/lib/Geo/Ellipsoid.pm

FIXME: Add more checks for div by 0.

 ACKNOWLEDGEMENTS

The conversion algorithms used here are Perl translations of Fortran
routines written by LCDR L. Pfeifer NGS Rockville MD that implement
T. Vincenty's Modified Rainsford's method with Helmert's elliptical
terms as published in "Direct and Inverse Solutions of Ellipsoid on
the Ellipsoid with Application of Nested Equations", T. Vincenty,
Survey Review, April 1975.

The Fortran source code files inverse.for and forward.for
may be obtained from

    ftp://ftp.ngs.noaa.gov/pub/pcsoft/for_inv.3d/source/

 AUTHOR

Jim Gibson, <Jim@Gibson.org> (Perl version)
Stefan Schroeder <ondekoza@gmail.com> (Port from Perl to Golang)

 BUGS

See LIMITATIONS, above.

Please report any bugs or feature requests to
the author.

COPYRIGHT & LICENSE

Copyright 2005-2008 Jim Gibson, all rights reserved.

This program is free software; you can redistribute it and/or modify it
under the same terms as Perl.

*/