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.
 */
struct db_entry {
	unsigned int dbe_index; /* The db_entry's position in the database. */

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

	/**
	 * 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;
};


struct db_ops {
	/* Allocate a new struct db_entry from a given key. */
	struct db_entry *(*dbe_alloc)(const gchar *);

	/* Free a struct db_entry. */
	void (*dbe_free)(struct db_entry *);

	/* Read a single struct db_entry from disk. */
	struct db_entry *(*dbe_read)(struct file *);

	/* Set up a struct db_entry after adding to the database. */
	void (*dbe_setup)(struct db_entry *);

	/* Write a single struct db_entry to disk. */
	void (*dbe_write)(struct file *, struct db_entry *);
};


/**
 * 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.   */

	const struct db_ops *db_ops; /* The database's operations vector.     */
	std::vector<T *> db_entries;
	std::map<const std::string, unsigned int> db_keys;
};


/*
 * Initialize a database using filepath as a location on disk to store data
 * and autosave as a hint for if this database should be automatically saved.
 */
template <class T>
void db_init(struct database<T> *, const char *, bool, const struct db_ops *);

/* Called to prevent memory leaks by freeing all remaining database entries. */
template <class T>
void db_deinit(struct database<T> *);


/* 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);

/* Returns the database item with the specified key. */
template <class T>
T *db_get(struct database<T> *, const gchar *);

/*
 * Similar to db_get(), but allocate and return a new item if the
 * database doesn't contain an item with the specified key.
 */
template <class T>
T *db_find(struct database<T> *, const gchar *);

/* Returns the first valid database item. */
template <class T>
T *db_first(const struct database<T> *);

/* Returns the next valid database item. */
template <class T>
T *db_next(const struct database<T> *, T *);


#define db_for_each(ent, next, db)				\
	for (ent = db_first(db), next = db_next(db, ent);	\
	     ent != NULL;					\
	     ent = next, next = db_next(db, ent))


#include "database.hpp"

#endif /* OCARINA_CORE_DATABASE_H */