Proof-of-concept of JSON export limited to PrimeMeridian (refs #1545)

4 files changed, 87 insertions, 2 deletions

diff --git a/include/proj/common.hpp b/include/proj/common.hpp
index 7940f4fc..d857dafd 100644
--- a/include/proj/common.hpp
+++ b/include/proj/common.hpp
@@ -104,6 +104,9 @@ class PROJ_GCC_DLL UnitOfMeasure : public util::BaseObject {
                                     const std::string &unitType = std::string())
         const; // throw(io::FormattingException)
 
+    PROJ_INTERNAL void _exportToJSON(
+        io::JSONFormatter *formatter) const; // throw(io::FormattingException)
+
     PROJ_INTERNAL std::string exportToPROJString() const;
 
     PROJ_INTERNAL bool
@@ -329,6 +332,8 @@ class PROJ_GCC_DLL IdentifiedObject : public util::BaseObject,
         formatID(io::WKTFormatter *formatter) const;
     PROJ_INTERNAL void formatRemarks(io::WKTFormatter *formatter) const;
 
+    PROJ_INTERNAL void formatID(io::JSONFormatter *formatter) const;
+
     PROJ_INTERNAL bool
     _isEquivalentTo(const util::IComparable *other,
                     util::IComparable::Criterion criterion =
diff --git a/include/proj/datum.hpp b/include/proj/datum.hpp
index b7416497..47bab4a0 100644
--- a/include/proj/datum.hpp
+++ b/include/proj/datum.hpp
@@ -171,7 +171,8 @@ using PrimeMeridianNNPtr = util::nn<PrimeMeridianPtr>;
  * \remark Implements PrimeMeridian from \ref ISO_19111_2019
  */
 class PROJ_GCC_DLL PrimeMeridian final : public common::IdentifiedObject,
-                                         public io::IPROJStringExportable {
+                                         public io::IPROJStringExportable,
+                                         public io::IJSONExportable {
   public:
     //! @cond Doxygen_Suppress
     PROJ_DLL ~PrimeMeridian() override;
@@ -198,6 +199,9 @@ class PROJ_GCC_DLL PrimeMeridian final : public common::IdentifiedObject,
     PROJ_INTERNAL void _exportToWKT(io::WKTFormatter *formatter)
         const override; // throw(io::FormattingException)
 
+    PROJ_INTERNAL void _exportToJSON(io::JSONFormatter *formatter)
+        const override; // throw(io::FormattingException)
+
     PROJ_INTERNAL bool
     _isEquivalentTo(const util::IComparable *other,
                     util::IComparable::Criterion criterion =
diff --git a/include/proj/io.hpp b/include/proj/io.hpp
index c553598d..71a6430d 100644
--- a/include/proj/io.hpp
+++ b/include/proj/io.hpp
@@ -38,6 +38,7 @@
 
 #include "proj.h"
 
+#include "proj_json_streaming_writer.hpp"
 #include "util.hpp"
 
 NS_PROJ_START
@@ -455,6 +456,77 @@ class PROJ_GCC_DLL PROJStringFormatter {
 
 // ---------------------------------------------------------------------------
 
+class JSONFormatter;
+/** JSONFormatter unique pointer. */
+using JSONFormatterPtr = std::unique_ptr<JSONFormatter>;
+/** Non-null JSONFormatter unique pointer. */
+using JSONFormatterNNPtr = util::nn<JSONFormatterPtr>;
+
+/** \brief Formatter to JSON strings.
+ *
+ * An instance of this class can only be used by a single
+ * thread at a time.
+ */
+class PROJ_GCC_DLL JSONFormatter {
+  public:
+    PROJ_DLL static JSONFormatterNNPtr
+    create(DatabaseContextPtr dbContext = nullptr);
+    //! @cond Doxygen_Suppress
+    PROJ_DLL ~JSONFormatter();
+    //! @endcond
+
+    PROJ_DLL JSONFormatter &setMultiLine(bool multiLine) noexcept;
+    PROJ_DLL JSONFormatter &setIndentationWidth(int width) noexcept;
+
+    PROJ_DLL const std::string &toString() const;
+
+    PROJ_PRIVATE :
+
+        //! @cond Doxygen_Suppress
+        PROJ_INTERNAL PROJ::CPLJSonStreamingWriter &
+        writer() const;
+
+    // cppcheck-suppress functionStatic
+    PROJ_INTERNAL bool outputId() const;
+
+    //! @endcond
+
+  protected:
+    //! @cond Doxygen_Suppress
+    PROJ_INTERNAL explicit JSONFormatter();
+    JSONFormatter(const JSONFormatter &other) = delete;
+
+    INLINED_MAKE_UNIQUE
+    //! @endcond
+
+  private:
+    PROJ_OPAQUE_PRIVATE_DATA
+};
+
+// ---------------------------------------------------------------------------
+
+/** \brief Interface for an object that can be exported to JSON. */
+class PROJ_GCC_DLL IJSONExportable {
+  public:
+    //! @cond Doxygen_Suppress
+    PROJ_DLL virtual ~IJSONExportable();
+    //! @endcond
+
+    /** Builds a JSON representation. May throw a FormattingException */
+    PROJ_DLL std::string
+    exportToJSON(JSONFormatter *formatter) const; // throw(FormattingException)
+
+    PROJ_PRIVATE :
+
+        //! @cond Doxygen_Suppress
+        PROJ_INTERNAL virtual void
+        _exportToJSON(
+            JSONFormatter *formatter) const = 0; // throw(FormattingException)
+    //! @endcond
+};
+
+// ---------------------------------------------------------------------------
+
 /** \brief Exception possibly thrown by IWKTExportable::exportToWKT() or
  * IPROJStringExportable::exportToPROJString(). */
 class PROJ_GCC_DLL FormattingException : public util::Exception {
diff --git a/include/proj/metadata.hpp b/include/proj/metadata.hpp
index d32996fb..37241e6f 100644
--- a/include/proj/metadata.hpp
+++ b/include/proj/metadata.hpp
@@ -361,7 +361,8 @@ using IdentifierNNPtr = util::nn<IdentifierPtr>;
  * originates from \ref ISO_19115
  */
 class PROJ_GCC_DLL Identifier : public util::BaseObject,
-                                public io::IWKTExportable {
+                                public io::IWKTExportable,
+                                public io::IJSONExportable {
   public:
     //! @cond Doxygen_Suppress
     PROJ_DLL Identifier(const Identifier &other);
@@ -401,6 +402,9 @@ class PROJ_GCC_DLL Identifier : public util::BaseObject,
     PROJ_INTERNAL void _exportToWKT(io::WKTFormatter *formatter)
         const override; // throw(io::FormattingException)
 
+    PROJ_INTERNAL void _exportToJSON(io::JSONFormatter *formatter)
+        const override; // throw(io::FormattingException)
+
     //! @endcond
 
   protected: