// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_DATABASE_STRING_TABLE_H_
#define CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_DATABASE_STRING_TABLE_H_
#include <map>
#include <string>
#include "base/basictypes.h"
#include "base/gtest_prod_util.h"
namespace sql {
class Connection;
} // namespace sql
namespace extensions {
// A class for maintaining a persistent mapping between strings and integers.
// This is used to help compress the contents of the activity log database on
// disk by replacing repeated strings by smaller integers.
//
// The mapping from integers to strings is maintained in a database table, but
// the mapping is also cached in memory.
//
// The database table used to store the strings is configurable, but its layout
// is fixed: it always consists of just two columns, "id" and "value".
//
// All calls to DatabaseStringTable must occur on the database thread.
class DatabaseStringTable {
public:
explicit DatabaseStringTable(const std::string& table);
~DatabaseStringTable();
// Initialize the database table. This will create the table if it does not
// exist. Returns true on success; false on error.
bool Initialize(sql::Connection* connection);
// Interns a string in the database table and sets *id to the corresponding
// integer. If the string already exists, the existing number is returned;
// otherwise, new database row is inserted with the new string. Returns true
// on success and false on database error.
bool StringToInt(sql::Connection* connection,
const std::string& value,
int64* id);
// Looks up an integer value and converts it to a string (which is stored in
// *value). Returns true on success. A false return does not necessarily
// indicate a database error; it might simply be that the value cannot be
// found.
bool IntToString(sql::Connection* connection, int64 id, std::string* value);
// Clears the in-memory cache; this should be called if the underlying
// database table has been manipulated and the cache may be stale.
void ClearCache();
private:
// Reduces the size of the cache if too many entries are held in it.
void PruneCache();
// In-memory caches of recently accessed values.
std::map<int64, std::string> id_to_value_;
std::map<std::string, int64> value_to_id_;
// The name of the database table where the mapping is stored.
std::string table_;
FRIEND_TEST_ALL_PREFIXES(DatabaseStringTableTest, Prune);
DISALLOW_COPY_AND_ASSIGN(DatabaseStringTable);
};
} // namespace extensions
#endif // CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_DATABASE_STRING_TABLE_H_