separate wkt visitor from wkb directly

include/geopackage/wkb/wkt.hpp

@@ -0,0 +1,93 @@
+#ifndef NGEN_GEOPACKAGE_WKB_VISITOR_WKT_H
+#define NGEN_GEOPACKAGE_WKB_VISITOR_WKT_H
+
+#include "reader.hpp"
+
+namespace geopackage {
+namespace wkb {
+
+class wkt_visitor : public boost::static_visitor<std::string>
+{
+  public:
+
+    /**
+    * @brief Get the WKT form from WKB structs
+    * 
+    * @tparam T WKB geometry struct type
+    * @param g geometry object
+    * @return std::string @param{g} in WKT form
+    */
+    template<typename T>
+    std::string operator()(T& g) const
+    {
+        return std::string(this->wkt_type(g)) + " " + this->wkt_coords(g);
+    }
+
+  private:
+    constexpr const char* wkt_type(const wkb_point&)           const { return "POINT";           }
+    constexpr const char* wkt_type(const wkb_linestring&)      const { return "LINESTRING";      }
+    constexpr const char* wkt_type(const wkb_polygon&)         const { return "POLYGON";         }
+    constexpr const char* wkt_type(const wkb_multipoint&)      const { return "MULTIPOINT";      }
+    constexpr const char* wkt_type(const wkb_multilinestring&) const { return "MULTILINESTRING"; }
+    constexpr const char* wkt_type(const wkb_multipolygon&)    const { return "MULTIPOLYGON";    }
+
+    std::string wkt_coords(const wkb_point& g) const
+    {
+        std::ostringstream out;
+        out.precision(3);
+        out << std::fixed << g.x << " " << g.y;
+        return std::move(out).str();
+    } 
+
+    std::string wkt_coords(const wkb_linestring& g) const
+    {
+        return "(" + std::accumulate(
+            std::next(g.points.begin()),
+            g.points.end(),
+            wkt_coords(g.points[0]),
+            [this](const std::string& a, const wkb_point b) { return a + "," + this->wkt_coords(b); }
+        ) + ")";
+    }
+
+    std::string wkt_coords(const wkb_multipoint& g) const
+    {
+        return "(" + std::accumulate(
+            std::next(g.points.begin()),
+            g.points.end(),
+            wkt_coords(g.points[0]),
+            [this](const std::string& a, const wkb_point b) { return a + "," + this->wkt_coords(b); }
+        ) + ")";
+    }
+
+    std::string wkt_coords(const wkb_polygon& g) const
+    {
+        std::string output;
+        for (const auto& gg : g.rings) {
+            output += "(" + wkt_coords(gg) + ")";
+        }
+        return output;
+    }
+
+    std::string wkt_coords(const wkb_multilinestring& g) const
+    {
+        std::string output;
+        for (const auto& gg : g.lines) {
+            output += "(" + wkt_coords(gg) + ")";
+        }
+        return output;
+    }
+
+    std::string wkt_coords(const wkb_multipolygon& g) const
+    {
+        std::string output;
+        for (const auto& gg : g.polygons) {
+            output += "(" + wkt_coords(gg) + ")";
+        }
+        return output;
+    }
+};
+
+} // namespace wkb
+} // namespace geopackage
+
+#endif // NGEN_GEOPACKAGE_WKB_VISITOR_WKT_H