#!/usr/bin/env python2
import random
import math
import optparse

#######################################################################
# Begining of the main program.
def main():
    (events, pdgCode, options) = ParseOptions()

    v = Vector()
    for c in range(events):
        v.random()
        v.unit()
        energy = options.energy
        if options.energyRange > 0:
            energy += random.uniform(0.0,options.energyRange)
        print " $ begin"
        print " $ vertex %0.3f %0.3f %0.3f %0.3f" % ( 0, 0, 0, 0)
        print " $ track %s %0.2f %f %f %f %d %d" \
              % (pdgCode, energy,v.x, v.y, v.z, 0, 0)
        print " $ end"
    print " $ stop"
    return None

class Vector:
    def __init__(self):
        self.x = 0
        self.y = 0
        self.z = 0
    def random(self):
        ct = random.uniform(0.5,1)
        st = math.sqrt(1.0-ct*ct)
        phi = random.uniform(0.0,2*math.pi)
        self.x = math.cos(phi)*st
        self.y = math.sin(phi)*st
        self.z = ct
    def unit(self):
        r = math.pow(self.x,2) + math.pow(self.y,2) + math.pow(self.z,2)
        r = math.sqrt(r)
        self.x /= r
        self.y /= r
        self.z /= r

def ParseOptions():
    """ Parse the command line and return the options and arguments.

    """

    usage = """make-particle.py <events> <pdg-code>

    Generate <events> with a single particle that is determined by <pdg-code>.
    """
    
    parser = optparse.OptionParser(usage=usage)
    parser.add_option("-e", "--energy", dest="energy",
                      action="store",type="float",default=100)
    parser.add_option("-r", "--energy-range", dest="energyRange",
                      action="store",type="float",default=0)

    (options, args) = parser.parse_args()

    if len(args)<2:
        parser.error("Must specify <events> and <pdgCode>")
    if len(args)<1:
        parser.error("Must specify <pdg-code>")

    events = int(args[0])
    pdgCode = args[1]
    
    return (events, pdgCode, options)

# Magic to run the program from the command line.
if __name__ == "__main__": main()