From d7a413d5e74703640aa6a6f74f220d8dd50f239b Mon Sep 17 00:00:00 2001
From: James Turner <zakalawe@mac.com>
Date: Fri, 29 Jun 2018 13:28:02 +0100
Subject: [PATCH] Lat-lon parsing: allow lon,lat order, and detect order

Flightplan/route-manager defaults to lon,lat order. Allow the parser
to detect the correct order when NSEW suffixes are provided and
consistent.
---
 simgear/misc/strutils.cxx      | 37 ++++++++++++++++++++++++++++------
 simgear/misc/strutils.hxx      | 13 +++++++++++-
 simgear/misc/strutils_test.cxx | 22 ++++++++++++++++++++
 3 files changed, 65 insertions(+), 7 deletions(-)

diff --git a/simgear/misc/strutils.cxx b/simgear/misc/strutils.cxx
index 8c0ff464..1de78be5 100644
--- a/simgear/misc/strutils.cxx
+++ b/simgear/misc/strutils.cxx
@@ -1179,7 +1179,21 @@ bool parseStringAsLatLonValue(const std::string& s, double& degrees)
     return true;
 }
         
-bool parseStringAsGeod(const std::string& s, SGGeod* result)
+namespace {
+    bool isLatString(const std::string &s)
+    {
+        const char lastChar = ::toupper(s.back());
+        return (lastChar == 'N') || (lastChar == 'S');
+    }
+    
+    bool isLonString(const std::string &s)
+    {
+        const char lastChar = ::toupper(s.back());
+        return (lastChar == 'E') || (lastChar == 'W');
+    }
+} // of anonymous namespace
+        
+bool parseStringAsGeod(const std::string& s, SGGeod* result, bool assumeLonLatOrder)
 {
     if (s.empty())
         return false;
@@ -1189,16 +1203,27 @@ bool parseStringAsGeod(const std::string& s, SGGeod* result)
         return false;
     }
     
-    double lat, lon;
-    if (!parseStringAsLatLonValue(s.substr(0, commaPos), lat) ||
-        !parseStringAsLatLonValue(s.substr(commaPos+1), lon))
-    {
+    auto termA = simplify(s.substr(0, commaPos)),
+        termB = simplify(s.substr(commaPos+1));
+    double valueA, valueB;
+    if (!parseStringAsLatLonValue(termA, valueA) || !parseStringAsLatLonValue(termB, valueB)) {
         return false;
     }
     
     if (result) {
-        *result = SGGeod::fromDeg(lon, lat);
+        // explicit ordering
+        if (isLatString(termA) && isLonString(termB)) {
+            *result = SGGeod::fromDeg(valueB, valueA);
+        } else if (isLonString(termA) && isLatString(termB)) {
+            *result = SGGeod::fromDeg(valueA, valueB);
+        } else {
+            // implicit ordering
+            // SGGeod wants longitude, latitude
+            *result = assumeLonLatOrder ? SGGeod::fromDeg(valueA, valueB)
+                                        : SGGeod::fromDeg(valueB, valueA);
+        }
     }
+    
     return true;
 }
         
diff --git a/simgear/misc/strutils.hxx b/simgear/misc/strutils.hxx
index cc735982..f4b14558 100644
--- a/simgear/misc/strutils.hxx
+++ b/simgear/misc/strutils.hxx
@@ -367,8 +367,19 @@ namespace simgear {
        *
        * Supported formats:
        *   <signed decimal degrees latitude>,<signed decimal degress longitude>
+       *   <unsigned decimal degrees>[NS],<unsigned decimal degrees>[EW]
+       *   <degrees>*<decimal minutes>'[NS],<degrees>*<decimal minutes>'[EW]
+       *
+       * Latitude and longitude are parsed seperately so the formats for each
+       * do not need to agree. Latitude is assumed to precede longitude
+       * unless assumeLonLatOrder = true
+       *
+       * When NSEW characters are used, the order can be swapped and will be
+       * fixed correctly (longitude then latitude).
        */
-      bool parseStringAsGeod(const std::string& string, SGGeod* result = nullptr);
+      bool parseStringAsGeod(const std::string& string,
+                             SGGeod* result = nullptr,
+                             bool assumeLonLatOrder = false);
       
       // enum values here correspond to existing lon-lat format codes inside
       // FlightGear (property: /sim/lon-lat-format )
diff --git a/simgear/misc/strutils_test.cxx b/simgear/misc/strutils_test.cxx
index e321f13b..07ff8c1c 100644
--- a/simgear/misc/strutils_test.cxx
+++ b/simgear/misc/strutils_test.cxx
@@ -654,6 +654,28 @@ void test_parseGeod()
     
     SG_VERIFY(strutils::parseStringAsGeod("") == false);
     SG_VERIFY(strutils::parseStringAsGeod("aaaaaaaa") == false);
+    
+    // ordering tests
+    
+    // normal default order, but explicitly pass as lon,lat
+    // (should work)
+    SG_VERIFY(strutils::parseStringAsGeod("3.12345678w, 56.12345678s", &a));
+    SG_CHECK_EQUAL_EP(a.getLongitudeDeg(), -3.12345678);
+    SG_CHECK_EQUAL_EP(a.getLatitudeDeg(), -56.12345678);
+    
+
+    // different default order
+    // also some embedded whitespace for fun
+    SG_VERIFY(strutils::parseStringAsGeod(" -12 34.56,\n-45 27.89 ", &a, true));
+    SG_CHECK_EQUAL_EP(a.getLongitudeDeg(), -12.576);
+    SG_CHECK_EQUAL_EP(a.getLatitudeDeg(), -45.464833333);
+    
+    
+    // differnet default order, but still set explicitly so should
+    // use the lat,lon order
+    SG_VERIFY(strutils::parseStringAsGeod("\t40 30'50\"S,  12 34'56\"W ", &a, true));
+    SG_CHECK_EQUAL_EP(a.getLongitudeDeg(), -12.58222222);
+    SG_CHECK_EQUAL_EP(a.getLatitudeDeg(), -40.5138888);
 }
 
 void test_formatGeod()