From db4b3e57313be9b935677932b2cfc8c450490b44 Mon Sep 17 00:00:00 2001
From: Veloman Yunkan <veloman.yunkan@gmail.com>
Date: Wed, 27 Jul 2022 19:20:27 +0400
Subject: [PATCH] Added Entry::getRedirectEntryIndex()

`Entry::getRedirectEntryIndex()` is functionally equivalent to
`Entry::getRedirectEntry().getIndex()`. However, the latter involves
access to the dirent of the target entry. When only the index of the
target entry is of interest, unnecessarily loading the target dirent may
turn sequential disk IO (when iterating entries by their native order)
to somewhat random disk IO. The new method is devoid of that drawback.
---
 include/zim/entry.h | 10 +++++++++-
 src/entry.cpp       |  8 ++++++--
 test/archive.cpp    |  4 ++++
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/include/zim/entry.h b/include/zim/entry.h
index a3e72e7d2..6944aa6a3 100644
--- a/include/zim/entry.h
+++ b/include/zim/entry.h
@@ -69,10 +69,18 @@ namespace zim
       /** Get the Entry targeted by the entry.
        *
        * @return The entry directly targeted by this redirect entry.
-       * @exception InvalidEntry in the entry is not a redirection.
+       * @exception InvalidEntry if the entry is not a redirection.
        */
       Entry getRedirectEntry() const;
 
+      /** Get the index of the Entry targeted by the entry.
+       *
+       * @return The index of the entry directly targeted by this redirect
+       *         entry.
+       * @exception InvalidEntry if the entry is not a redirection.
+       */
+      entry_index_type getRedirectEntryIndex() const;
+
       entry_index_type getIndex() const   { return m_idx; }
 
     private:
diff --git a/src/entry.cpp b/src/entry.cpp
index b469c833e..717d45e9a 100644
--- a/src/entry.cpp
+++ b/src/entry.cpp
@@ -80,11 +80,15 @@ Item Entry::getRedirect() const {
   return nextEntry.getItem(false);
 }
 
-Entry Entry::getRedirectEntry() const  {
+entry_index_type Entry::getRedirectEntryIndex() const  {
   if (!isRedirect()) {
     std::ostringstream sstream;
     sstream << "Entry " << getPath() << " is not a redirect entry.";
     throw InvalidType(sstream.str());
   }
-  return Entry(m_file, static_cast<entry_index_type>(m_dirent->getRedirectIndex()));
+  return m_dirent->getRedirectIndex().v;
+}
+
+Entry Entry::getRedirectEntry() const  {
+  return Entry(m_file, getRedirectEntryIndex());
 }
diff --git a/test/archive.cpp b/test/archive.cpp
index 933170010..0a7123f15 100644
--- a/test/archive.cpp
+++ b/test/archive.cpp
@@ -204,6 +204,8 @@ TEST(ZimArchive, openCreatedArchive)
   ASSERT_EQ(foo.getPath(), "foo");
   ASSERT_EQ(foo.getTitle(), "Foo");
   ASSERT_EQ(std::string(foo.getItem().getData()), "FooContent");
+  ASSERT_THROW(foo.getRedirectEntry(), zim::InvalidType);
+  ASSERT_THROW(foo.getRedirectEntryIndex(), zim::InvalidType);
 
   auto foo2 = archive.getEntryByPath("foo2");
   ASSERT_EQ(foo2.getPath(), "foo2");
@@ -215,10 +217,12 @@ TEST(ZimArchive, openCreatedArchive)
   ASSERT_EQ(foo3.getTitle(), "FooRedirection");
   ASSERT_TRUE(foo3.isRedirect());
   ASSERT_EQ(foo3.getRedirectEntry().getIndex(), foo.getIndex());
+  ASSERT_EQ(foo3.getRedirectEntryIndex(), foo.getIndex());
 
   auto main = archive.getMainEntry();
   ASSERT_TRUE(main.isRedirect());
   ASSERT_EQ(main.getRedirectEntry().getIndex(), foo.getIndex());
+  ASSERT_EQ(main.getRedirectEntryIndex(), foo.getIndex());
   ASSERT_EQ(archive.getMainEntryIndex(), main.getIndex());
 }