ocarina/include/core/database.h

/**
 * Copyright 2013 (c) Anna Schumaker.
 */
#ifndef OCARINA_CORE_DATABASE_H
#define OCARINA_CORE_DATABASE_H

extern "C" {
#include <core/file.h>
}

#include <map>
#include <string>
#include <vector>

/**
 * The DatabaseEntry class is the base class for storing
 * generic data inside a Database.
 */
class DatabaseEntry {
public:
	unsigned int _index; /**< The location of an item in the Database. */

	DatabaseEntry();		/**< Initialize _index to 0. */
	virtual ~DatabaseEntry() = 0;	/**< Virtual destructor */

	/**
	 * Called to access a DatabaseEntry's index.
	 *
	 * @return DatabaseEntry::_index
	 */
	const unsigned int index();

	/**
	 * The primary key of a DatabaseEntry is a unique string representing
	 * a single DatabaseEntry instance.  This is used for preventing
	 * duplicate entries in a Database.  The primary key is not expected
	 * to change once a DatabaseEntry has been initialized.
	 *
	 * @return A unique string identifying a DatabaseEntry instance.
	 */
	virtual const std::string primary_key() const = 0;

	/**
	 * This function is called by the Database to write a specific
	 * DatabaseEntry instance to disk.
	 *
	 * @param  file  File to use when writing data.
	 */
	virtual void write(file &) = 0;

	/**
	 * This function is called by the Database to read a single
	 * DatabaseEntry instance from disk.
	 *
	 * @param  file  File to use when reading data.
	 */
	virtual void read(file &) = 0;
};


/**
 * Databases are a generic store for information used by Ocarina.  Users
 * need to inherit from a DatabaseEntry class to properly use a Database.
 *
 * When writing a Database to disk, Databases need to store their size in
 * addition to values and valid bits at each index.  For example, let's say
 * we have a Database with the following values:  { 1, 2, NULL, 4 }.  On
 * disk this would look like:
 *
 * 	4
 * 	0 true 1
 * 	1 true 2
 * 	2 false
 * 	3 true 4
 * 	<index>	<valid>	<data>
 *
 * The Database class will add a newline after each DatabaseEntry.
 */
template <class T>
struct database {
	unsigned int db_size;     /* The database's count of valid entries.   */
	bool         db_autosave; /* True if the database saves when changed. */
	struct file  db_file;     /* The database's associated file object.   */

	std::vector<T *> db_entries;
	std::map<const std::string, unsigned int> db_keys;

	/** Iterator access for our backing std::vector */
	typedef typename std::vector<T *>::iterator iterator;
	/** Const iterator access for our backing std::vector */
	typedef typename std::vector<T *>::const_iterator const_iterator;

	/**
	 * Initialize a Database using filepath as a location to store data
	 * on disk.
	 *
	 * @param  filepath  File on disk that will be written to.
	 * @param  autosave  Set to True if the Database should be saved upon
	 *                   every insertion and deletion.  If this is set
	 *                   to False then the Database will have to be saved
	 *                   manually.
	 */
	database(std::string, bool);

	/**
	 * Deletes all remaining entries in a Database to prevent memory leaks.
	 */
	~database();


	/**
	 * @return An iterator pointing to the first valid entry in the Database.
	 * @return Return Database::end() if there are no valid entries.
	 */
	iterator begin();

	/**
	 * @return An iterator pointing past the end of the database.
	 */
	iterator end();

	/**
	 * @return An iterator pointing to the next valid item in the database.
	 */
	iterator next(iterator &);

	/**
	 * Find a DatabaseItem with a specific primary key.
	 *
	 * @param  key  The key to search for.
	 * @return A pointer to the requested DatabaseEntry.
	 * @return NULL if there is no matching DatabaseEntry.
	 */
	T *find(const std::string &);
};


/* Called to write the database to disk. */
template <class T>
void db_save(struct database<T> *);

/* Save the database to disk iff database->db_autosave is set to True */
template <class T>
void db_autosave(struct database<T> *);

/* Called to read the database from disk. */
template <class T>
void db_load(struct database<T> *);

/* Returns the size of the backing std::vector. */
template <class T>
unsigned int db_actual_size(const struct database<T> *);


/*
 * Called to add a new item to the database.  The caller MUST check if the
 * database already contains a similar item before calling this function.
 */
template <class T>
T *db_insert(struct database<T> *, T *);

/* Called to remove an item from the database. */
template <class T>
void db_remove(struct database<T> *, T *);


/* Returns the database item at the requested index. */
template <class T>
T *db_at(struct database<T> *, unsigned int);

#include "database.hpp"

#endif /* OCARINA_CORE_DATABASE_H */