From 277d4bdf815f0b6dbe5d127a34825e2b612ed626 Mon Sep 17 00:00:00 2001
From: alanwatsonforster <68709385+alanwatsonforster@users.noreply.github.com>
Date: Fri, 22 Sep 2023 18:05:18 -0600
Subject: [PATCH] Rework altitude.

---
 airpower/aircraft.py | 14 ++++++------
 airpower/altitude.py | 51 +++++++++++++++++++++++++++++++++-----------
 2 files changed, 46 insertions(+), 19 deletions(-)

diff --git a/airpower/aircraft.py b/airpower/aircraft.py
index 9cb7da45..237c7f17 100644
--- a/airpower/aircraft.py
+++ b/airpower/aircraft.py
@@ -13,7 +13,7 @@ def __init__(self, name, hexcode, azimuth, altitude):
     x, y = aphexcode.toxy(hexcode)
     facing = apazimuth.tofacing(azimuth)
 
-    apaltitude._checkaltitude(altitude)
+    apaltitude.checkisvalidaltitude(altitude)
     aphex.checkisvalidfacing(x, y, facing)
 
     self._turn          = 0
@@ -80,13 +80,13 @@ def _reportstatus(self, when):
     if when != "start":
        self._report("%d HFPs and %d VFPs used." % (self._ihfp, self._ivfp))
 
-    altitudeband = apaltitude._altitudeband(self._altitude)
+    altitudeband = apaltitude.altitudeband(self._altitude)
 
     if when == "start":
       self._reportposition("")
 
     if when != "start":
-      self._report("altitude carry is %s." % apaltitude._formataltitudecarry(self._altitudecarry))
+      self._report("altitude carry is %s." % apaltitude.formataltitudecarry(self._altitudecarry))
 
     if when == "start":
       self._initialaltitudeband = altitudeband
@@ -177,10 +177,10 @@ def _L(self, facingchange):
     self._facing = (self._facing + facingchange) % 360
 
   def _D(self, altitudechange):
-    self._altitude, self._altitudecarry = apaltitude._adjustaltitude(self._altitude, self._altitudecarry, -altitudechange)
+    self._altitude, self._altitudecarry = apaltitude.adjustaltitude(self._altitude, self._altitudecarry, -altitudechange)
 
   def _C(self, altitudechange):
-    self._altitude, self._altitudecarry = apaltitude._adjustaltitude(self._altitude, self._altitudecarry, +altitudechange)
+    self._altitude, self._altitudecarry = apaltitude.adjustaltitude(self._altitude, self._altitudecarry, +altitudechange)
 
   def _K(self):
     self._reportfp("killed.")
@@ -190,7 +190,7 @@ def _A(self, what):
     self._reportfp("attack with %s." % what)
 
   def checkforterraincollision(self):
-    altitudeofterrain = apaltitude._altitudeofterrain()
+    altitudeofterrain = apaltitude.terrainaltitude()
     if self._altitude <= altitudeofterrain:
       self._altitude = altitudeofterrain
       self._altitudecarry = 0
@@ -357,7 +357,7 @@ def next(self, actions):
     assert self._ifp <= self._nfp
     aphex.checkiscenteroredge(self._x, self._y)
     aphex.checkisvalidfacing(self._x, self._y, self._facing)
-    apaltitude._checkaltitude(self._altitude)
+    apaltitude.checkisvalidaltitude(self._altitude)
 
     if self._ifp == self._nfp:
 
diff --git a/airpower/altitude.py b/airpower/altitude.py
index c0f631e5..87afb9e8 100644
--- a/airpower/altitude.py
+++ b/airpower/altitude.py
@@ -1,13 +1,28 @@
-import math
-
 # _altitudequantum must be 1 over an integral power of 2.
 _altitudequantum = 1/8
 
-def _checkaltitude(altitude):
-  if not isinstance(altitude, (int, float)) or altitude % 1 != 0 or altitude < 1:
-    raise ValueError("invalid altitude %s." % altitude)
+def isvalidaltitude(altitude):
+
+  """
+  Return True if altitude is a valid altitude.
+  """
+  return isinstance(altitude, (int, float)) and altitude % 1 == 0 and altitude >= 0
+
+def checkisvalidaltitude(altitude):
+
+  """
+  Raise a ValueError exception if z is not a valid altitude.
+  """
+
+  if not isvalidaltitude(altitude):
+    raise ValueError("%s is not a valid altitude." % altitude)
+
+def adjustaltitude(altitude, altitudecarry, altitudechange):
 
-def _adjustaltitude(altitude, altitudecarry, altitudechange):
+    """
+    Adjust altitude by altitudechange, taking into account altitudecarry. 
+    Return the new altitude and altitudecarry. 
+    """
 
     # Here we do altitude arithmetic, ensuring that _altitude stays as an
     # non-negative integer and keeping track of fractions in _altitudecarry. 
@@ -19,9 +34,9 @@ def _adjustaltitude(altitude, altitudecarry, altitudechange):
 
     altitude = altitude + altitudecarry + altitudechange
     if altitudechange >= 0:
-      altitudecarry = altitude - math.floor(altitude)
+      altitudecarry = altitude % +1
     else:
-      altitudecarry = altitude - math.ceil(altitude)
+      altitudecarry = altitude % -1
     altitude = altitude - altitudecarry
 
     if altitude < 0:
@@ -33,7 +48,11 @@ def _adjustaltitude(altitude, altitudecarry, altitudechange):
 
     return altitude, altitudecarry
 
-def _formataltitudecarry(altitudecarry):
+def formataltitudecarry(altitudecarry):
+
+  """
+  Return altitudecarry formatted as a signed fraction.
+  """
 
   assert abs(altitudecarry) < 1 and altitudecarry % _altitudequantum == 0
 
@@ -48,7 +67,11 @@ def _formataltitudecarry(altitudecarry):
     m = m / 2
   return "%+d/%d" % (n, m)
   
-def _altitudeband(altitude):
+def altitudeband(altitude):
+
+  """
+  Return the altitude band corresponding to altitude.
+  """
 
   assert altitude % 1 == 0 and altitude >= 0
 
@@ -67,6 +90,10 @@ def _altitudeband(altitude):
   else:
     return "UH"
 
-def _altitudeofterrain():
-  return 0
+def terrainaltitude():
 
+  """
+  Return the altitude of the terrain.
+  """
+
+  return 0