From 360959dab103c7e88a094a9e03e1633f3c3974f3 Mon Sep 17 00:00:00 2001
From: Andrew <andy@tensixtyone.com>
Date: Mon, 11 Nov 2013 21:26:21 +0000
Subject: [PATCH] Added function to calculate the distance between systems.

---
 evesde/models/locations.py | 13 ++++++++++++-
 evesde/utils.py            |  6 ++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 evesde/utils.py

diff --git a/evesde/models/locations.py b/evesde/models/locations.py
index 9a17619..8a2c430 100644
--- a/evesde/models/locations.py
+++ b/evesde/models/locations.py
@@ -1,5 +1,8 @@
+from math import sqrt
 from django.db import models
-from .utils import InheritanceQuerySet
+from evesde.utils import euclidean_distance
+from evesde.app_defines import DISTANCE_LIGHT_YEAR
+from evesde.models.utils import InheritanceQuerySet
 
 
 class LocationManager(models.Manager):
@@ -132,6 +135,14 @@ class System(Location):
     def moons(self):
         return Moon.objects.filter(planet__in=self.planets.all())
 
+    def distance_to(self, destination):
+        """Calculates the ly distance between the two systems"""
+        if not isinstance(destination, System):
+            raise ValueError('Provided destination is not a System.')
+        origin = (self.x, self.y, self.z)
+        destination = (destination.x, destination.y, destination.z)
+        return euclidean_distance(origin, destination) / DISTANCE_LIGHT_YEAR
+
     class Meta:
         app_label = 'evesde'
         ordering = ['name']
diff --git a/evesde/utils.py b/evesde/utils.py
new file mode 100644
index 0000000..ab4db39
--- /dev/null
+++ b/evesde/utils.py
@@ -0,0 +1,6 @@
+from math import sqrt
+
+
+def euclidean_distance(origin, destination):
+    """Calculates the Euclidean distance of two sets of x/y/z tuples"""
+    return sqrt(sum((a - b)**2 for a, b in zip(origin, destination)))