serenity/Userland/Libraries/LibPDF/Document.cpp

/*
 * Copyright (c) 2021, Matthew Olsson <mattco@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibPDF/Document.h>
#include <LibPDF/Parser.h>

namespace PDF {

Document::Document(const ReadonlyBytes& bytes)
    : m_parser(Parser({}, bytes))
{
    VERIFY(m_parser.perform_validation());
    auto [xref_table, trailer] = m_parser.parse_last_xref_table_and_trailer();

    m_xref_table = xref_table;
    m_trailer = trailer;

    m_catalog = m_trailer->get_dict(this, "Root");
    build_page_tree();
}

Value Document::get_or_load_value(u32 index)
{
    auto value = get_value(index);
    if (value)
        return value;

    VERIFY(m_xref_table.has_object(index));
    auto byte_offset = m_xref_table.byte_offset_for_object(index);
    auto indirect_value = m_parser.parse_indirect_value_at_offset(byte_offset);
    VERIFY(indirect_value->index() == index);
    value = indirect_value->value();
    m_values.set(index, value);
    return value;
}

u32 Document::get_first_page_index() const
{
    // FIXME: A PDF can have a different default first page, which
    // should be fetched and returned here
    return 0;
}

u32 Document::get_page_count() const
{
    return m_page_object_indices.size();
}

Page Document::get_page(u32 index)
{
    VERIFY(index < m_page_object_indices.size());

    auto cached_page = m_pages.get(index);
    if (cached_page.has_value())
        return cached_page.value();

    auto page_object_index = m_page_object_indices[index];
    auto raw_page_object = resolve_to<DictObject>(get_or_load_value(page_object_index));

    auto resources = raw_page_object->get_dict(this, "Resources");
    auto media_box_array = raw_page_object->get_array(this, "MediaBox");
    auto media_box = Rectangle {
        media_box_array->at(0).to_float(),
        media_box_array->at(1).to_float(),
        media_box_array->at(2).to_float(),
        media_box_array->at(3).to_float(),
    };
    auto contents = raw_page_object->get_object(this, "Contents");

    Page page { resources, media_box, contents };
    m_pages.set(index, page);
    return page;
}

Value Document::resolve(const Value& value)
{
    if (!value.is_object())
        return value;

    auto obj = value.as_object();

    // FIXME: Surely indirect PDF objects can't contain another indirect PDF object,
    // right? Unsure from the spec, but if they can, these return values would have
    // to be wrapped with another resolve() call.

    if (obj->is_indirect_value_ref()) {
        auto object_index = static_cast<NonnullRefPtr<IndirectValueRef>>(obj)->index();
        return get_or_load_value(object_index);
    }

    if (obj->is_indirect_value())
        return static_cast<NonnullRefPtr<IndirectValue>>(obj)->value();

    return obj;
}

template<IsValueType T>
UnwrappedValueType<T> Document::resolve_to(const Value& value)
{
    auto resolved = resolve(value);

    if constexpr (IsSame<T, bool>)
        return resolved.as_bool();
    if constexpr (IsSame<T, int>)
        return resolved.as_int();
    if constexpr (IsSame<T, float>)
        return resolved.as_float();
    if constexpr (IsObject<T>)
        return object_cast<T>(resolved.as_object());

    VERIFY_NOT_REACHED();
}

void Document::build_page_tree()
{
    auto page_tree = m_catalog->get_dict(this, "Pages");
    add_page_tree_node_to_page_tree(page_tree);
}

void Document::add_page_tree_node_to_page_tree(NonnullRefPtr<DictObject> page_tree)
{
    auto kids_array = page_tree->get_array(this, "Kids");
    auto page_count = page_tree->get("Count").value().as_int();

    if (static_cast<size_t>(page_count) != kids_array->elements().size()) {
        // This page tree contains child page trees, so we recursively add
        // these pages to the overall page tree

        for (auto& value : *kids_array) {
            auto reference = resolve_to<IndirectValueRef>(value);
            auto byte_offset = m_xref_table.byte_offset_for_object(reference->index());
            auto maybe_page_tree_node = m_parser.conditionally_parse_page_tree_node_at_offset(byte_offset);
            if (maybe_page_tree_node) {
                add_page_tree_node_to_page_tree(maybe_page_tree_node.release_nonnull());
            } else {
                m_page_object_indices.append(reference->index());
            }
        }

        return;
    }

    // We know all of the kids are leaf nodes
    for (auto& value : *kids_array) {
        auto reference = resolve_to<IndirectValueRef>(value);
        m_page_object_indices.append(reference->index());
    }
}

}