#!/usr/bin/env python
import json
import numpy as np
import unittest

# constants
FILENAME = 'customers.json'
INTERCOM_COORDS = [53.339428,-6.257664]
WITHIN_DISTANCE = 100
EARTH_RADIUS = 6367

def read_file_as_json(filename):
    """reads a json file and returns an object"""
    with open(filename, 'r') as json_file:
        data = json.load(json_file)
    return data

def haversine(coord1, coord2):
    """calculates the great-circle distance between two coordinates using haversine formula and
    returns the distance in km."""
    lat1, lon1 = map(np.deg2rad, coord1)
    lat2, lon2 = map(np.deg2rad, coord2)

    delta_lat = abs(lat2 - lat1)
    delta_lon = abs(lon2 - lon1)

    a = np.sin(delta_lat / 2.0)**2 + np.cos(lat1) * np.cos(lat2) * np.sin(delta_lon / 2.0)**2

    central_angle = 2 * np.arcsin(np.sqrt(a))
    distance = EARTH_RADIUS * central_angle
    return distance

def in_distance(coord1, coord2, distance):
    """checks whether two coordinates within a given distance"""
    return haversine(coord1, coord2) <= distance

def customer_coords(customer):
    """returns a list containing longitude and latitude of given customer"""
    return map(float, [customer['latitude'], customer['longitude']])

def customers_in_distance(customers):
    """returns the names and user ids of customers within 100km, sorted by User ID"""
    customers = [(c['name'], c['user_id']) for c in customers if in_distance(INTERCOM_COORDS, customer_coords(c), WITHIN_DISTANCE)]
    customers = sorted(customers, key=lambda tup: tup[1])
    return customers

def print_customers(customers):
    """prints names and user ids of customers within 100 km from Intercom office."""
    for customer in customers:
        print "{0} - {1}".format(customer[0], customer[1])

class TestCustomers(unittest.TestCase):
    def setUp(self):
        self.json = read_file_as_json(FILENAME)

    def test_read_file_as_json(self):
        self.assertEqual(len(self.json), 32)

    def test_haversine(self):
        self.assertEqual(haversine([0,0], [0,0]), 0)
        self.assertEqual(int(haversine(INTERCOM_COORDS, [51.92893,-10.27699])), 313)

    def test_in_distance(self):
        self.assertEqual(in_distance([0,0], [0,0], 0), True)
        self.assertEqual(in_distance(INTERCOM_COORDS, [51.92893,-10.27699], WITHIN_DISTANCE), False)

    def test_customer_coords(self):
        first_customer_coords = customer_coords(self.json[0])
        self.assertEqual(first_customer_coords, [52.986375, -6.043701])

    def test_customers_in_distance(self):
        customers = customers_in_distance(self.json)
        self.assertEqual(len(customers), 16)

    def test_print_customers(self):
        customers = customers_in_distance(self.json)
        print '\n'
        print_customers(customers)

if __name__ == "__main__":
    unittest.main()