Added support for complex metadata checks

This commit is intended to demonstrate how complex checks (involving more
than one metadata entries) can be added if required.

src/metadata.cpp

@@ -47,6 +47,59 @@ size_t getTextLength(const std::string& utf8EncodedString)
   return icu::UnicodeString::fromUTF8(utf8EncodedString).length();
 }
 
+bool checkTextLanguage(const std::string& text, const std::string& langCode)
+{
+  // TODO: check that text is in langCode's script
+  return true;
+}
+
+class MetadataComplexCheckBase
+{
+public:
+  const std::string description;
+  const MetadataComplexCheckBase* const prev;
+
+public: // functions
+  explicit MetadataComplexCheckBase(const std::string& desc)
+    : description(desc)
+    , prev(last)
+  {
+    last = this;
+  }
+
+  virtual ~MetadataComplexCheckBase() = default;
+
+  virtual bool checkMetadata(const Metadata& m) const = 0;
+
+  static const MetadataComplexCheckBase* getLastCheck() { return last; }
+
+private: // functions
+  static const MetadataComplexCheckBase* last;
+};
+
+const MetadataComplexCheckBase* MetadataComplexCheckBase::last = nullptr;
+
+#define ADD_METADATA_COMPLEX_CHECK(DESC, CLSNAME)              \
+class CLSNAME : public MetadataComplexCheckBase                \
+{                                                              \
+public:                                                        \
+  CLSNAME() : MetadataComplexCheckBase(DESC) {}                \
+  bool checkMetadata(const Metadata& data) const override;     \
+};                                                             \
+                                                               \
+const CLSNAME CONCAT(obj, CLSNAME);                            \
+                                                               \
+bool CLSNAME::checkMetadata(const Metadata& data) const        \
+/* should be followed by the check body */
+
+
+
+#define CONCAT(X, Y) X##Y
+#define GENCLSNAME(UUID) CONCAT(MetadataComplexCheck, UUID)
+
+#define METADATA_ASSERT(DESC) ADD_METADATA_COMPLEX_CHECK(DESC, GENCLSNAME(__LINE__))
+
+
 #include "metadata_constraints.cpp"
 
 } // unnamed namespace
@@ -124,13 +177,29 @@ Metadata::Errors Metadata::checkSimpleConstraints() const
   return errors;
 }
 
+Metadata::Errors Metadata::checkComplexConstraints() const
+{
+  Errors errors;
+  const MetadataComplexCheckBase* c = MetadataComplexCheckBase::getLastCheck();
+  for ( ; c != nullptr ; c = c->prev ) {
+    if ( ! c->checkMetadata(*this) ) {
+      errors.push_back(c->description);
+    }
+  }
+  return errors;
+}
+
 Metadata::Errors Metadata::check() const
 {
   Errors e = checkMandatoryMetadata();
   if ( !e.empty() )
     return e;
 
-  return checkSimpleConstraints();
+  e = checkSimpleConstraints();
+  if ( !e.empty() )
+    return e;
+
+  return checkComplexConstraints();
 }
 
 } // namespace zim

src/metadata.h

@@ -59,6 +59,7 @@ class Metadata
 private: // functions
   Errors checkMandatoryMetadata() const;
   Errors checkSimpleConstraints() const;
+  Errors checkComplexConstraints() const;
 
 private: // data
   std::map<std::string, std::string> data;

src/metadata_constraints.cpp

@@ -24,3 +24,16 @@ const Metadata::ReservedMetadataTable reservedMetadataInfoTable = {
     PNG_REGEXP
   },
 };
+
+METADATA_ASSERT("LongDescription shouldn't be shorter than Description")
+{
+  return !data.has("LongDescription")
+      || data["LongDescription"].size() >= data["Description"].size();
+}
+
+METADATA_ASSERT("Description must be in the language of the ZIM file")
+{
+  const auto lang = data["Language"];
+  const auto description = data["Description"];
+  return checkTextLanguage(description, lang);
+}

test/metadata-test.cpp

@@ -128,3 +128,16 @@ TEST(Metadata, regexpConstraints)
   m.set("Language", "fre,nch");
   ASSERT_TRUE(m.valid());
 }
+
+TEST(Metadata, complexConstraints)
+{
+  zim::Metadata m = makeValidMetadata();
+  m.set("Description",     "Short description");
+  m.set("LongDescription", "Long description");
+  ASSERT_FALSE(m.valid());
+  ASSERT_EQ(m.check(),
+      zim::Metadata::Errors({
+        "LongDescription shouldn't be shorter than Description"
+      })
+  );
+}