src: Avoid use of `detail` folder for installable headers

This commit moves `lp/detail/*` to `lp/`, as `detail` folders should
include only private APIs that are only used during the build and cannot
be used (header files not installed) by external applications.

Change-Id: I370592819c4bc5f4016689ef7c9c5bd2cdd0eaa2
diff --git a/src/lp/field-decl.hpp b/src/lp/field-decl.hpp
new file mode 100644
index 0000000..a71aceb
--- /dev/null
+++ b/src/lp/field-decl.hpp
@@ -0,0 +1,145 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2013-2017 Regents of the University of California.
+ *
+ * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
+ *
+ * ndn-cxx library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * ndn-cxx library is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndn-cxx authors and contributors.
+ */
+
+#ifndef NDN_CXX_LP_FIELD_DECL_HPP
+#define NDN_CXX_LP_FIELD_DECL_HPP
+
+#include "field.hpp"
+#include "tlv.hpp"
+
+#include "../encoding/block-helpers.hpp"
+#include "../util/concepts.hpp"
+#include <boost/concept/requires.hpp>
+
+namespace ndn {
+namespace lp {
+
+template<typename TlvType, typename T>
+struct DecodeHelper
+{
+  static
+  BOOST_CONCEPT_REQUIRES(((WireDecodable<T>)), (T))
+  decode(const Block& wire)
+  {
+    T type;
+    type.wireDecode(wire);
+    return type;
+  }
+};
+
+template<typename TlvType>
+struct DecodeHelper<TlvType, uint64_t>
+{
+  static uint64_t
+  decode(const Block& wire)
+  {
+    return readNonNegativeInteger(wire);
+  }
+};
+
+template<typename TlvType>
+struct DecodeHelper<TlvType, std::pair<Buffer::const_iterator, Buffer::const_iterator>>
+{
+  static std::pair<Buffer::const_iterator, Buffer::const_iterator>
+  decode(const Block& wire)
+  {
+    if (wire.value_size() == 0) {
+      BOOST_THROW_EXCEPTION(ndn::tlv::Error(to_string(wire.type()) + " must not be empty"));
+    }
+
+    return std::make_pair(wire.value_begin(), wire.value_end());
+  }
+};
+
+template<typename encoding::Tag TAG, typename TlvType, typename T>
+struct EncodeHelper
+{
+  static
+  BOOST_CONCEPT_REQUIRES(((WireEncodable<T>)), (size_t))
+  encode(EncodingImpl<TAG>& encoder, const T& value)
+  {
+    return value.wireEncode(encoder);
+  }
+};
+
+template<typename encoding::Tag TAG, typename TlvType>
+struct EncodeHelper<TAG, TlvType, uint64_t>
+{
+  static size_t
+  encode(EncodingImpl<TAG>& encoder, const uint64_t value)
+  {
+    return prependNonNegativeIntegerBlock(encoder, TlvType::value, value);
+  }
+};
+
+template<typename encoding::Tag TAG, typename TlvType>
+struct EncodeHelper<TAG, TlvType, std::pair<Buffer::const_iterator, Buffer::const_iterator>>
+{
+  static size_t
+  encode(EncodingImpl<TAG>& encoder, const std::pair<Buffer::const_iterator, Buffer::const_iterator>& value)
+  {
+    size_t length = 0;
+    length += encoder.prependRange(value.first, value.second);
+    length += encoder.prependVarNumber(length);
+    length += encoder.prependVarNumber(TlvType::value);
+    return length;
+  }
+};
+
+template<typename LOCATION, typename VALUE, uint64_t TYPE, bool REPEATABLE = false>
+class FieldDecl
+{
+public:
+  typedef LOCATION FieldLocation;
+  typedef VALUE ValueType;
+  typedef std::integral_constant<uint64_t, TYPE> TlvType;
+  typedef std::integral_constant<bool, REPEATABLE> IsRepeatable;
+
+  /** \brief decodes a field
+   *  \param wire a Block with top-level type \p TYPE
+   *  \return value of the field
+   */
+  static ValueType
+  decode(const Block& wire)
+  {
+    if (wire.type() != TlvType::value) {
+      BOOST_THROW_EXCEPTION(ndn::tlv::Error("Unexpected TLV type " + to_string(wire.type())));
+    }
+
+    return DecodeHelper<TlvType, ValueType>::decode(wire);
+  }
+
+  /** \brief encodes a field and prepends to \p encoder its Block with top-level type \p TYPE
+   *  \param encoder Instance of the buffer encoder or buffer estimator
+   *  \param value value of the field
+   */
+  template<typename encoding::Tag TAG, typename T>
+  static size_t
+  encode(EncodingImpl<TAG>& encoder, const T& value)
+  {
+    return EncodeHelper<TAG, TlvType, T>::encode(encoder, value);
+  }
+};
+
+} // namespace lp
+} // namespace ndn
+
+#endif // NDN_CXX_LP_FIELD_DECL_HPP