Database: Add forward/reverse iterator

This allows the database to be treated as a single collection of strings, but
can be used to avoid loading the entire database when only interested in recent
entries.

Related to issue #245.

src/Database.cpp

@@ -24,6 +24,7 @@
 //
 ////////////////////////////////////////////////////////////////////////////////
 
+#include <cassert>
 #include <Database.h>
 #include <format.h>
 #include <JSON.h>
@@ -32,6 +33,191 @@
 #include <shared.h>
 #include <timew.h>
 
+////////////////////////////////////////////////////////////////////////////////
+Database::iterator::iterator (files_iterator fbegin, files_iterator fend) :
+          files_it(fbegin),
+          files_end(fend)
+{
+    if (files_end != files_it) {
+      auto &lines = files_it->allLines ();
+      lines_it = lines.begin ();
+      lines_end = lines.end ();
+      while ((lines_it == lines_end) && (files_it != files_end))
+        ++files_it;
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+Database::iterator& Database::iterator::operator++()
+{
+  if (files_it != files_end)
+  {
+    if (lines_it != lines_end)
+    {
+      ++lines_it;
+
+      // If we are at the end of the current file, we will need to advance to
+      // the next file here. A file may be empty, which is why we need to wait
+      // until we are pointing at a valid line.
+      while ((lines_it == lines_end) && (files_it != files_end))
+      {
+        ++files_it;
+        if (files_it != files_end)
+        {
+          auto& lines = files_it->allLines ();
+          lines_it = lines.begin ();
+          lines_end = lines.end ();
+        }
+      }
+    }
+  }
+  return *this;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+bool Database::iterator::operator==(const iterator & other) const
+{
+  return (other.files_it == other.files_end) ?
+          files_it == files_end :
+         ((files_it == other.files_it) &&
+          (files_end == other.files_end) &&
+          (lines_it == other.lines_it) &&
+          (lines_end == other.lines_end));
+}
+
+////////////////////////////////////////////////////////////////////////////////
+bool Database::iterator::operator!=(const iterator & other) const
+{
+  return ! (*this == other);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+const std::string& Database::iterator::operator*() const
+{
+  assert(lines_it != lines_end);
+  return *lines_it;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+const std::string* Database::iterator::operator->() const
+{
+  assert(lines_it != lines_end);
+  return &(*lines_it);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+Database::reverse_iterator::reverse_iterator (files_iterator fbegin,
+                                              files_iterator fend) :
+          files_it(fbegin),
+          files_end(fend)
+{
+    if (files_end != files_it)
+    {
+      lines_it = files_it->allLines ().rbegin ();
+      lines_end = files_it->allLines ().rend ();
+      while ((lines_it == lines_end) && (files_it != files_end))
+        ++files_it;
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+Database::reverse_iterator& Database::reverse_iterator::operator++()
+{
+  if (files_it != files_end)
+  {
+    if (lines_it != lines_end)
+    {
+      ++lines_it;
+
+      // If we are at the end of the current file, we will need to advance to
+      // the next file here. A file may be empty, which is why we need to wait
+      // until we are pointing at a valid line.
+      while ((lines_it == lines_end) && (files_it != files_end))
+      {
+        ++files_it;
+        if (files_it != files_end)
+        {
+          lines_it = files_it->allLines ().rbegin ();
+          lines_end = files_it->allLines ().rend ();
+        }
+      }
+    }
+  }
+  return *this;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+bool
+Database::reverse_iterator::operator==(const reverse_iterator & other) const
+{
+  return (other.files_it == other.files_end) ?
+          files_it == files_end :
+         ((files_it == other.files_it) &&
+          (files_end == other.files_end) &&
+          (lines_it == other.lines_it) &&
+          (lines_end == other.lines_end));
+}
+
+////////////////////////////////////////////////////////////////////////////////
+bool
+Database::reverse_iterator::operator!=(const reverse_iterator & other) const
+{
+  return ! (*this == other);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+const std::string& Database::reverse_iterator::operator*() const
+{
+  assert (lines_it != lines_end);
+  return *lines_it;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+const std::string* Database::reverse_iterator::operator->() const
+{
+  return &operator*();
+}
+
+////////////////////////////////////////////////////////////////////////////////
+Database::iterator Database::begin ()
+{
+  if (_files.empty ())
+  {
+    initializeDatafiles ();
+  }
+
+  return iterator(_files.begin (), _files.end ());
+}
+
+////////////////////////////////////////////////////////////////////////////////
+Database::iterator Database::end ()
+{
+  return iterator (_files.end (), _files.end ());
+}
+
+
+////////////////////////////////////////////////////////////////////////////////
+Database::reverse_iterator Database::rbegin ()
+{
+  if (_files.empty ())
+  {
+    initializeDatafiles ();
+  }
+
+  return reverse_iterator (_files.rbegin (), _files.rend ());
+}
+
+////////////////////////////////////////////////////////////////////////////////
+Database::reverse_iterator Database::rend ()
+{
+  if (_files.empty ())
+  {
+    initializeDatafiles ();
+  }
+
+  return reverse_iterator (_files.rend (), _files.rend ());
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 void Database::initialize (const std::string& location, Journal& journal)
 {

src/Database.h

@@ -38,6 +38,60 @@
 
 class Database
 {
+public:
+
+  class iterator
+  {
+  private:
+    friend class Database;
+    typedef std::vector <Datafile>::iterator files_iterator;
+    typedef std::vector <std::string>::const_iterator lines_iterator;
+    typedef std::string value_type;
+
+    files_iterator files_it;
+    files_iterator files_end;
+
+    lines_iterator lines_it;
+    lines_iterator lines_end;
+
+    iterator (files_iterator fbegin, files_iterator fend);
+
+  public:
+    iterator& operator++ ();
+    iterator& operator++ (int);
+    iterator& operator-- ();
+    bool operator== (const iterator & other) const;
+    bool operator!= (const iterator & other) const;
+    const value_type& operator* () const;
+    const value_type* operator-> () const;
+  };
+
+  class reverse_iterator
+  {
+  private:
+    friend class Database;
+    typedef std::vector <Datafile>::reverse_iterator files_iterator;
+    typedef std::vector <std::string>::const_reverse_iterator lines_iterator;
+    typedef std::string value_type;
+
+    files_iterator files_it;
+    files_iterator files_end;
+
+    lines_iterator lines_it;
+    lines_iterator lines_end;
+
+    reverse_iterator(files_iterator fbegin, files_iterator fend);
+
+  public:
+    reverse_iterator& operator++ ();
+    reverse_iterator& operator++ (int);
+    reverse_iterator& operator-- ();
+    bool operator== (const reverse_iterator & other) const;
+    bool operator!= (const reverse_iterator & other) const;
+    const value_type& operator* () const;
+    const value_type* operator-> () const;
+  };
+
 public:
   Database () = default;
   void initialize (const std::string&, Journal& journal);
@@ -53,6 +107,11 @@ public:
 
   std::string dump () const;
 
+  iterator begin ();
+  iterator end ();
+  reverse_iterator rbegin ();
+  reverse_iterator rend ();
+
 private:
   unsigned int getDatafile (int, int);
   std::vector <Range> segmentRange (const Range&);