From 048f6a08e6d952b60601972b459ef0dc7fccefc5 Mon Sep 17 00:00:00 2001
From: Pascal Lais <pascal_lais@gmx.de>
Date: Mon, 9 Mar 2020 20:15:56 +0100
Subject: [PATCH] Add function intersection for line segments

---
 linesegment.py | 72 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 69 insertions(+), 3 deletions(-)

diff --git a/linesegment.py b/linesegment.py
index 4c1c8b2..2e2fdc5 100644
--- a/linesegment.py
+++ b/linesegment.py
@@ -9,8 +9,12 @@ class LineSegment:
     starting at a startpoint and ending at a endpoint."""
     def __init__(self, startpoint=point.Point(), endpoint=point.Point()):
         """Initialize the line segment."""
-        self.set_startpoint(startpoint)
-        self.set_endpoint(endpoint)
+        if startpoint.get_x() <= endpoint.get_x():
+            self.set_startpoint(startpoint)
+            self.set_endpoint(endpoint)
+        else:
+            self.set_startpoint(endpoint)
+            self.set_endpoint(startpoint)
     def set_startpoint(self, new_startpoint):
         """Set or change the startpoint of the line segment. If not a Point object is given
         the startpoint gets set to a default value of Point(0,0)."""
@@ -30,6 +34,32 @@ class LineSegment:
         diff_x = abs(self.__startpoint.get_x() - self.__endpoint.get_x())
         diff_y = abs(self.__startpoint.get_y() - self.__endpoint.get_y())
         return ((diff_x ** 2) + (diff_y ** 2)) ** (1/2.0)
+    def get_slope(self):
+        """Calculate and return the slope of the line segment"""
+        if self.__startpoint.get_x() == self.__endpoint.get_x():
+            return None
+        diff_x = self.__endpoint.get_x() - self.__startpoint.get_x()
+        diff_y = self.__endpoint.get_y() - self.__startpoint.get_y()
+        return diff_y / diff_x
+    def get_y_at(self, x_val):
+        """Returns the y value of the line at a specific x coordinate"""
+        slope = self.get_slope()
+        start_x = self.__startpoint.get_x()
+        start_y = self.__startpoint.get_y()
+        y_intercept = start_y - (slope * start_x)
+        return (slope * x_val) + y_intercept
+    def get_min_x(self):
+        """Get the lowest x coordinate of the line segment"""
+        return min(self.__startpoint.get_x(), self.__endpoint.get_x())
+    def get_max_x(self):
+        """Get the highest x coordinate of the line segment"""
+        return max(self.__startpoint.get_x(), self.__endpoint.get_x())
+    def get_min_y(self):
+        """Get the lowest y coordinate of the line segment"""
+        return min(self.__startpoint.get_y(), self.__endpoint.get_y())
+    def get_max_y(self):
+        """Get the highest y coordinate of the line segment"""
+        return max(self.__startpoint.get_y(), self.__endpoint.get_y())
     def str(self):
         """Return the line segment values as string."""
         return self.__startpoint.str() + "-->" + self.__endpoint.str()
@@ -38,5 +68,41 @@ class LineSegment:
 
 def get_random(min_x=0, max_x=100, min_y=0, max_y=100):
     """Set the point to a random place inside the boundaries"""
-    return LineSegment(point.Point(random.randint(min_x, max_x), random.randint(min_y, max_y)), \
+    seg = LineSegment(point.Point(random.randint(min_x, max_x), random.randint(min_y, max_y)), \
         point.Point(random.randint(min_x, max_x), random.randint(min_y, max_y)))
+    while ls.get_startpoint().get_x() == ls.get_endpoint().get_x():
+        seg = LineSegment(point.Point(random.randint(min_x, max_x), random.randint(min_y, max_y)), \
+            point.Point(random.randint(min_x, max_x), random.randint(min_y, max_y)))
+    return seg
+
+def intersection(ls_a, ls_b):
+    """Calculate the intersection between two line segments. Returns None if there isn't a
+    intersection, the Point of the intersection if there is one or the overlapping linesegment"""
+    res = None
+    # Check if intervalls are overlapping
+    if ls_a.get_max_x() < ls_b.get_min_x() or \
+       ls_a.get_min_x() > ls_b.get_max_x() or \
+       ls_a.get_max_y() < ls_b.get_min_y() or \
+       ls_a.get_min_y() > ls_b.get_max_y():
+        res = None
+    elif ls_a.get_slope() == ls_b.get_slope():
+        if ls_a.get_y_at(0) == ls_b.get_y_at(0):
+            startpoint = None
+            endpoint = None
+            if ls_a.get_startpoint().get_x() > ls_b.get_startpoint().get_x():
+                startpoint = ls_a.get_startpoint()
+            else:
+                startpoint = ls_b.get_startpoint()
+            if ls_a.get_endpoint().get_x() < ls_b.get_endpoint().get_x():
+                endpoint = ls_a.get_endpoint()
+            else:
+                endpoint = ls_b.get_endpoint()
+
+            res = LineSegment(startpoint, endpoint)
+    else:
+        x_val = (ls_a.get_y_at(0) - ls_b.get_y_at(0)) / \
+            (ls_b.get_slope() - ls_a.get_slope())
+        if ls_a.get_min_x() <= x_val <= ls_a.get_max_x():
+            y_val = (ls_a.get_slope() * x_val) + ls_a.get_y_at(0)
+            res = point.Point(x_val, y_val)
+    return res