text: // Copyright 2011 The Kyua Authors.
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  //   notice, this list of conditions and the following disclaimer.
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  //   may be used to endorse or promote products derived from this software
  //   without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #include "store/metadata.hpp"
  
  #include "store/exceptions.hpp"
  #include "utils/format/macros.hpp"
  #include "utils/sanity.hpp"
  #include "utils/sqlite/database.hpp"
  #include "utils/sqlite/exceptions.hpp"
  #include "utils/sqlite/statement.ipp"
  
  namespace sqlite = utils::sqlite;
  
  
  namespace {
  
  
  /// Fetches an integer column from a statement of the 'metadata' table.
  ///
  /// \param stmt The statement from which to get the column value.
  /// \param column The name of the column to retrieve.
  ///
  /// \return The value of the column.
  ///
  /// \throw store::integrity_error If there is a problem fetching the value
  ///     caused by an invalid schema or data.
  static int64_t
  int64_column(sqlite::statement& stmt, const char* column)
  {
      int index;
      try {
          index = stmt.column_id(column);
      } catch (const sqlite::invalid_column_error& e) {
          UNREACHABLE_MSG("Invalid column specification; the SELECT statement "
                          "should have caught this");
      }
      if (stmt.column_type(index) != sqlite::type_integer)
          throw store::integrity_error(F("The '%s' column in 'metadata' table "
                                         "has an invalid type") % column);
      return stmt.column_int64(index);
  }
  
  
  }  // anonymous namespace
  
  
  /// Constructs a new metadata object.
  ///
  /// \param schema_version_ The schema version.
  /// \param timestamp_ The time at which this version was created.
  store::metadata::metadata(const int schema_version_, const int64_t timestamp_) :
      _schema_version(schema_version_),
      _timestamp(timestamp_)
  {
  }
  
  
  /// Returns the timestamp of this entry.
  ///
  /// \return The timestamp in this metadata entry.
  int64_t
  store::metadata::timestamp(void) const
  {
      return _timestamp;
  }
  
  
  /// Returns the schema version.
  ///
  /// \return The schema version in this metadata entry.
  int
  store::metadata::schema_version(void) const
  {
      return _schema_version;
  }
  
  
  /// Reads the latest metadata entry from the database.
  ///
  /// \param db The database from which to read the metadata from.
  ///
  /// \return The current metadata of the database.  It is not OK for the metadata
  /// table to be empty, so this is guaranteed to return a value unless there is
  /// an error.
  ///
  /// \throw store::integrity_error If the metadata in the database is empty,
  ///     has an invalid schema or its contents are bogus.
  store::metadata
  store::metadata::fetch_latest(sqlite::database& db)
  {
      try {
          sqlite::statement stmt = db.create_statement(
              "SELECT schema_version, timestamp FROM metadata "
              "ORDER BY schema_version DESC LIMIT 1");
          if (!stmt.step())
              throw store::integrity_error("The 'metadata' table is empty");
  
          const int schema_version_ =
              static_cast< int >(int64_column(stmt, "schema_version"));
          const int64_t timestamp_ = int64_column(stmt, "timestamp");
  
          if (stmt.step())
              UNREACHABLE_MSG("Got more than one result from a query that "
                              "does not permit this; any pragmas defined?");
  
          return metadata(schema_version_, timestamp_);
      } catch (const sqlite::error& e) {
          throw store::integrity_error(F("Invalid metadata schema: %s") %
                                       e.what());
      }
  }
  