From 262e13845cd2c41abb9030b694a193ae3e30e273 Mon Sep 17 00:00:00 2001
From: Veloman Yunkan <veloman.yunkan@gmail.com>
Date: Sun, 28 Nov 2021 20:40:52 +0400
Subject: [PATCH] Enter Library::removeBooksNotUpdatedSince()

---
 include/library.h | 33 ++++++++++++++++++++++++++++++++-
 src/library.cpp   | 32 +++++++++++++++++++++++++++++++-
 test/library.cpp  | 31 +++++++++++++++++++++++++++++++
 3 files changed, 94 insertions(+), 2 deletions(-)

diff --git a/include/library.h b/include/library.h
index 3ef7b5248..c5054dcc7 100644
--- a/include/library.h
+++ b/include/library.h
@@ -147,8 +147,20 @@ private: // functions
  */
 class LibraryBase
 {
+protected: // types
+  typedef uint64_t LibraryRevision;
+
+  struct Entry : Book
+  {
+    LibraryRevision lastUpdatedRevision = 0;
+
+    // May also keep the Archive and Reader pointers here and get
+    // rid of the m_readers and m_archives data members in Library
+  };
+
 protected: // data
-  std::map<std::string, kiwix::Book> m_books;
+  LibraryRevision m_revision;
+  std::map<std::string, Entry> m_books;
   std::map<std::string, std::shared_ptr<Reader>> m_readers;
   std::map<std::string, std::shared_ptr<zim::Archive>> m_archives;
   std::vector<kiwix::Bookmark> m_bookmarks;
@@ -172,6 +184,7 @@ class Library : private LibraryBase
   mutable std::mutex m_mutex;
 
  public:
+  typedef LibraryRevision Revision;
   typedef std::vector<std::string> BookIdCollection;
   typedef std::map<std::string, int> AttributeCounts;
 
@@ -368,6 +381,24 @@ class Library : private LibraryBase
     const std::vector<std::string>& tags = {},
     size_t maxSize = 0) const;
 
+  /**
+   * Return the current revision of the library.
+   *
+   * The revision of the library is updated (incremented by one) only by
+   * the addBook() operation.
+   *
+   * @return Current revision of the library.
+   */
+  LibraryRevision getRevision() const;
+
+  /**
+   * Remove books that have not been updated since the specified revision.
+   *
+   * @param  rev the library revision to use
+   * @return Count of books that were removed by this operation.
+   */
+  uint32_t removeBooksNotUpdatedSince(LibraryRevision rev);
+
   friend class OPDSDumper;
   friend class libXMLDumper;
 
diff --git a/src/library.cpp b/src/library.cpp
index 3518e2b0c..79ccbf044 100644
--- a/src/library.cpp
+++ b/src/library.cpp
@@ -101,6 +101,7 @@ Library::~Library()
 bool Library::addBook(const Book& book)
 {
   std::lock_guard<std::mutex> lock(m_mutex);
+  ++m_revision;
   /* Try to find it */
   updateBookDB(book);
   try {
@@ -111,9 +112,12 @@ bool Library::addBook(const Book& book)
     oldbook.update(book); // XXX: This may have no effect if oldbook is readonly
                           // XXX: Then m_bookDB will become out-of-sync with
                           // XXX: the real contents of the library.
+    oldbook.lastUpdatedRevision = m_revision;
     return false;
   } catch (std::out_of_range&) {
-    m_books[book.getId()] = book;
+    Entry& newEntry = m_books[book.getId()];
+    static_cast<Book&>(newEntry) = book;
+    newEntry.lastUpdatedRevision = m_revision;
     return true;
   }
 }
@@ -151,6 +155,32 @@ bool Library::removeBookById(const std::string& id)
   return m_books.erase(id) == 1;
 }
 
+Library::Revision Library::getRevision() const
+{
+  std::lock_guard<std::mutex> lock(m_mutex);
+  return m_revision;
+}
+
+uint32_t Library::removeBooksNotUpdatedSince(LibraryRevision libraryRevision)
+{
+  BookIdCollection booksToRemove;
+  {
+    std::lock_guard<std::mutex> lock(m_mutex);
+    for ( const auto& entry : m_books) {
+      if ( entry.second.lastUpdatedRevision <= libraryRevision ) {
+        booksToRemove.push_back(entry.first);
+      }
+    }
+  }
+
+  uint32_t countOfRemovedBooks = 0;
+  for ( const auto& id : booksToRemove ) {
+    if ( removeBookById(id) )
+      ++countOfRemovedBooks;
+  }
+  return countOfRemovedBooks;
+}
+
 const Book& Library::getBookById(const std::string& id) const
 {
   // XXX: Doesn't make sense to lock this operation since it cannot
diff --git a/test/library.cpp b/test/library.cpp
index e06026318..a8d99e896 100644
--- a/test/library.cpp
+++ b/test/library.cpp
@@ -707,4 +707,35 @@ TEST_F(LibraryTest, removeBookByIdUpdatesTheSearchDB)
   EXPECT_THROW(lib.getBookById("raycharles"), std::out_of_range);
 };
 
+TEST_F(LibraryTest, removeBooksNotUpdatedSince)
+{
+  EXPECT_FILTER_RESULTS(kiwix::Filter(),
+    "An example ZIM archive",
+    "Encyclopédie de la Tunisie",
+    "Granblue Fantasy Wiki",
+    "Géographie par Wikipédia",
+    "Islam Stack Exchange",
+    "Mathématiques",
+    "Movies & TV Stack Exchange",
+    "Mythology & Folklore Stack Exchange",
+    "Ray Charles",
+    "TED talks - Business",
+    "Tania Louis",
+    "Wikiquote"
+  );
+
+  const uint64_t rev = lib.getRevision();
+  for ( const auto& id : lib.filter(kiwix::Filter().query("exchange")) ) {
+    lib.addBook(lib.getBookByIdThreadSafe(id));
+  }
+
+  EXPECT_EQ(9u, lib.removeBooksNotUpdatedSince(rev));
+
+  EXPECT_FILTER_RESULTS(kiwix::Filter(),
+    "Islam Stack Exchange",
+    "Movies & TV Stack Exchange",
+    "Mythology & Folklore Stack Exchange",
+  );
+};
+
 };