Normalize known Matroska tag fields so they can be recognized despite different casing

* Do this by default with an opt-out; changing only known fields should not
  be very intrusive
* Fix recognizing known fields when only the case differs, see
  https://github.com/Martchus/tageditor/issues/72

generictagfield.h

@@ -38,6 +38,7 @@ public:
     TagField(const IdentifierType &id, const TagValue &value);
     ~TagField();
 
+    IdentifierType &id();
     const IdentifierType &id() const;
     std::string idToString() const;
     void setId(const IdentifierType &id);
@@ -110,6 +111,14 @@ template <class ImplementationType> TagField<ImplementationType>::~TagField()
 {
 }
 
+/*!
+ * \brief Returns the id of the current TagField.
+ */
+template <class ImplementationType> inline typename TagField<ImplementationType>::IdentifierType &TagField<ImplementationType>::id()
+{
+    return m_id;
+}
+
 /*!
  * \brief Returns the id of the current TagField.
  */

matroska/matroskacontainer.cpp

@@ -663,7 +663,11 @@ void MatroskaContainer::internalParseTags(Diagnostics &diag, AbortableProgressFe
     CPP_UTILITIES_UNUSED(progress)
 
     static const string context("parsing tags of Matroska container");
-    for (EbmlElement *element : m_tagsElements) {
+    auto flags = MatroskaTagFlags::None;
+    if (fileInfo().fileHandlingFlags() & MediaFileHandlingFlags::NormalizeKnownTagFieldIds) {
+        flags += MatroskaTagFlags::NormalizeKnownFieldIds;
+    }
+    for (EbmlElement *const element : m_tagsElements) {
         try {
             element->parse(diag);
             for (EbmlElement *subElement = element->firstChild(); subElement; subElement = subElement->nextSibling()) {
@@ -672,7 +676,7 @@ void MatroskaContainer::internalParseTags(Diagnostics &diag, AbortableProgressFe
                 case MatroskaIds::Tag:
                     m_tags.emplace_back(make_unique<MatroskaTag>());
                     try {
-                        m_tags.back()->parse(*subElement, diag);
+                        m_tags.back()->parse2(*subElement, flags, diag);
                     } catch (const NoDataFoundException &) {
                         m_tags.pop_back();
                     } catch (const Failure &) {

matroska/matroskatag.cpp

@@ -108,6 +108,18 @@ KnownField MatroskaTag::internallyGetKnownField(const IdentifierType &id) const
  *         error occurs.
  */
 void MatroskaTag::parse(EbmlElement &tagElement, Diagnostics &diag)
+{
+    parse2(tagElement, MatroskaTagFlags::None, diag);
+}
+
+/*!
+ * \brief Parses tag information from the specified \a tagElement.
+ *
+ * \throws Throws std::ios_base::failure when an IO error occurs.
+ * \throws Throws TagParser::Failure or a derived exception when a parsing
+ *         error occurs.
+ */
+void MatroskaTag::parse2(EbmlElement &tagElement, MatroskaTagFlags flags, Diagnostics &diag)
 {
     static const string context("parsing Matroska tag");
     m_size = tagElement.totalSize();
@@ -117,15 +129,24 @@ void MatroskaTag::parse(EbmlElement &tagElement, Diagnostics &diag)
         diag.emplace_back(DiagLevel::Critical, "Matroska tag is too big.", context);
         throw NotImplementedException();
     }
+    const auto normalize = flags & MatroskaTagFlags::NormalizeKnownFieldIds;
     for (EbmlElement *child = tagElement.firstChild(); child; child = child->nextSibling()) {
         child->parse(diag);
         switch (child->id()) {
         case MatroskaIds::SimpleTag:
             try {
-                MatroskaTagField field;
+                auto field = MatroskaTagField();
                 field.reparse(*child, diag, true);
-                fields().emplace(field.id(), move(field));
+                if (normalize) {
+                    auto normalizedId = field.id();
+                    MatroskaTagField::normalizeId(normalizedId);
+                    if (internallyGetKnownField(normalizedId) != KnownField::Invalid) {
+                        field.id() = std::move(normalizedId);
+                    }
+                }
+                fields().emplace(field.id(), std::move(field));
             } catch (const Failure &) {
+                // message will be added to diag anyways
             }
             break;
         case MatroskaIds::Targets:

matroska/matroskatag.h

@@ -11,6 +11,20 @@ namespace TagParser {
 class EbmlElement;
 class MatroskaTag;
 
+/*!
+ * \brief The MatroskaTagFlags enum specifies flags which controls parsing and making of Matroska tags.
+ */
+enum class MatroskaTagFlags : std::uint64_t {
+    None = 0x0, /**< Regular parsing/making. */
+    NormalizeKnownFieldIds = 0x1, /**< Normalize known field IDs when parsing. */
+};
+
+} // namespace TagParser
+
+CPP_UTILITIES_MARK_FLAG_ENUM_CLASS(TagParser, TagParser::MatroskaTagFlags)
+
+namespace TagParser {
+
 class TAG_PARSER_EXPORT MatroskaTagMaker {
     friend class MatroskaTag;
 
@@ -70,6 +84,7 @@ public:
     TagTargetLevel targetLevel() const override;
 
     void parse(EbmlElement &tagElement, Diagnostics &diag);
+    void parse2(EbmlElement &tagElement, MatroskaTagFlags flags, Diagnostics &diag);
     MatroskaTagMaker prepareMaking(Diagnostics &diag);
     void make(std::ostream &stream, Diagnostics &diag);
 

matroska/matroskatagfield.cpp

@@ -176,6 +176,19 @@ void MatroskaTagField::make(ostream &stream, Diagnostics &diag)
     prepareMaking(diag).make(stream);
 }
 
+/*!
+ * \brief Ensures the specified \a id is upper-case as recommended by the Matroska spec.
+ * \sa https://matroska.org/technical/tagging.html#tag-formatting
+ */
+void MatroskaTagField::normalizeId(std::string &id)
+{
+    for (auto &c : id) {
+        if (c >= 'a' && c <= 'z') {
+            c -= 'a' - 'A';
+        }
+    }
+}
+
 /*!
  * \class TagParser::MatroskaTagFieldMaker
  * \brief The MatroskaTagFieldMaker class helps making tag fields.

matroska/matroskatagfield.h

@@ -79,6 +79,7 @@ public:
 
     static typename std::string fieldIdFromString(std::string_view idString);
     static std::string fieldIdToString(const std::string &id);
+    static void normalizeId(std::string &id);
 };
 
 /*!

mediafileinfo.cpp

@@ -90,8 +90,8 @@ MediaFileInfo::MediaFileInfo(std::string &&path)
     , m_preferredPadding(0)
     , m_tagPosition(ElementPosition::BeforeData)
     , m_indexPosition(ElementPosition::BeforeData)
-    , m_fileHandlingFlags(
-          MediaFileHandlingFlags::ForceRewrite | MediaFileHandlingFlags::ForceTagPosition | MediaFileHandlingFlags::ForceIndexPosition)
+    , m_fileHandlingFlags(MediaFileHandlingFlags::ForceRewrite | MediaFileHandlingFlags::ForceTagPosition | MediaFileHandlingFlags::ForceIndexPosition
+          | MediaFileHandlingFlags::NormalizeKnownTagFieldIds)
 {
 }
 

mediafileinfo.h

@@ -62,6 +62,7 @@ enum class MediaFileHandlingFlags : std::uint64_t {
     ForceRewrite = (1 << 1), /**< enforces a re-write of the file when applying changes */
     ForceTagPosition = (1 << 2), /**< enforces the tag position when applying changes, see remarks of MediaFileInfo::setTagPosition() */
     ForceIndexPosition = (1 << 3), /**< enforces the index position when applying changes, see remarks of MediaFileInfo::setIndexPosition() */
+    NormalizeKnownTagFieldIds = (1 << 4), /**< normalizes known tag field IDs when parsing to match the tag specification's recommendations */
 };
 
 } // namespace TagParser
@@ -162,6 +163,8 @@ public:
     void setSaveFilePath(std::string &&saveFilePath);
     const std::string &writingApplication() const;
     void setWritingApplication(std::string_view writingApplication);
+    MediaFileHandlingFlags fileHandlingFlags();
+    void setFileHandlingFlags(MediaFileHandlingFlags flags);
     bool isForcingFullParse() const;
     void setForceFullParse(bool forceFullParse);
     bool isForcingRewrite() const;
@@ -472,6 +475,22 @@ inline AbstractContainer *MediaFileInfo::container() const
     return m_container.get();
 }
 
+/*!
+ * \brief Returns the currently configured file handling flags.
+ */
+inline MediaFileHandlingFlags MediaFileInfo::fileHandlingFlags()
+{
+    return m_fileHandlingFlags;
+}
+
+/*!
+ * \brief Replaces all currently configured file handling flags with the specified \a flags.
+ */
+inline void MediaFileInfo::setFileHandlingFlags(MediaFileHandlingFlags flags)
+{
+    m_fileHandlingFlags = flags;
+}
+
 /*!
  * \brief Returns an indication whether forcing a full parse is enabled.
  *