LibPDF: Parse page structures

This commit introduces the ability to parse the document catalog dict,
as well as the page tree and individual pages. Pages obviously aren't
fully parsed, as we won't care about most of the fields until we
start actually rendering PDFs.

One of the primary benefits of the PDF format is laziness. PDFs are
not meant to be parsed all at once, and the same is true for pages.
When a Document is constructed, it builds a map of page number to
object index, but it does not fetch and parse any of the pages. A page
is only parsed when a caller requests that particular page (and is
cached going forwards).

Additionally, this commit also adds an object_cast function which
logs bad casts if DEBUG_PDF is set. Additionally, utility functions
were added to ArrayObject and DictObject to get all types of objects
from the collections to avoid having to manually cast.

1 files changed, 24 insertions, 0 deletions

diff --git a/Userland/Libraries/LibPDF/Object.cpp b/Userland/Libraries/LibPDF/Object.cpp
index 4fca01a497..3cd861cb61 100644
--- a/Userland/Libraries/LibPDF/Object.cpp
+++ b/Userland/Libraries/LibPDF/Object.cpp
@@ -5,10 +5,34 @@
  */
 
 #include <AK/Hex.h>
+#include <LibPDF/Document.h>
 #include <LibPDF/Object.h>
 
 namespace PDF {
 
+NonnullRefPtr<Object> ArrayObject::get_object_at(Document* document, size_t index) const
+{
+    return document->resolve_to<Object>(m_elements[index]);
+}
+
+NonnullRefPtr<Object> DictObject::get_object(Document* document, const FlyString& key) const
+{
+    return document->resolve_to<Object>(get_value(key));
+}
+
+#define DEFINE_ACCESSORS(class_name, snake_name)                                                           \
+    NonnullRefPtr<class_name> ArrayObject::get_##snake_name##_at(Document* document, size_t index) const   \
+    {                                                                                                      \
+        return document->resolve_to<class_name>(m_elements[index]);                                        \
+    }                                                                                                      \
+                                                                                                           \
+    NonnullRefPtr<class_name> DictObject::get_##snake_name(Document* document, const FlyString& key) const \
+    {                                                                                                      \
+        return document->resolve_to<class_name>(get(key).value());                                         \
+    }
+ENUMERATE_DIRECT_OBJECT_TYPES(DEFINE_ACCESSORS)
+#undef DEFINE_INDEXER
+
 static void append_indent(StringBuilder& builder, int indent)
 {
     for (int i = 0; i < indent; i++)