/*

 * Copyright (C) the libgit2 contributors. All rights reserved.

 *

 * This file is part of libgit2, distributed under the GNU GPL v2 with

 * a Linking Exception. For full terms see the included COPYING file.

 */

#ifndef INCLUDE_sys_git_odb_backend_h__

#define INCLUDE_sys_git_odb_backend_h__

#include "git2/common.h"

#include "git2/types.h"

#include "git2/oid.h"

#include "git2/odb.h"

/**

 * @file git2/sys/backend.h

 * @brief Git custom backend implementors functions

 * @defgroup git_backend Git custom backend APIs

 * @ingroup Git

 * @{

 */

GIT_BEGIN_DECL

/**

 * An instance for a custom backend

 */

struct git_odb_backend {

	unsigned int version;

	git_odb *odb;

	/* read and read_prefix each return to libgit2 a buffer which

	 * will be freed later. The buffer should be allocated using

	 * the function git_odb_backend_malloc to ensure that it can

	 * be safely freed later. */

	int (* read)(

		void **, size_t *, git_otype *, git_odb_backend *, const git_oid *);

	/* To find a unique object given a prefix of its oid.  The oid given

	 * must be so that the remaining (GIT_OID_HEXSZ - len)*4 bits are 0s.

	 */

	int (* read_prefix)(

		git_oid *, void **, size_t *, git_otype *,

		git_odb_backend *, const git_oid *, size_t);

	int (* read_header)(

		size_t *, git_otype *, git_odb_backend *, const git_oid *);

	/**

	 * Write an object into the backend. The id of the object has

	 * already been calculated and is passed in.

	 */

	int (* write)(

		git_odb_backend *, const git_oid *, const void *, size_t, git_otype);

	int (* writestream)(

		git_odb_stream **, git_odb_backend *, git_off_t, git_otype);

	int (* readstream)(

		git_odb_stream **, git_odb_backend *, const git_oid *);

	int (* exists)(

		git_odb_backend *, const git_oid *);

	int (* exists_prefix)(

		git_oid *, git_odb_backend *, const git_oid *, size_t);

	/**

	 * If the backend implements a refreshing mechanism, it should be exposed

	 * through this endpoint. Each call to `git_odb_refresh()` will invoke it.

	 *

	 * However, the backend implementation should try to stay up-to-date as much

	 * as possible by itself as libgit2 will not automatically invoke

	 * `git_odb_refresh()`. For instance, a potential strategy for the backend

	 * implementation to achieve this could be to internally invoke this

	 * endpoint on failed lookups (ie. `exists()`, `read()`, `read_header()`).

	 */

	int (* refresh)(git_odb_backend *);

	int (* foreach)(

		git_odb_backend *, git_odb_foreach_cb cb, void *payload);

	int (* writepack)(

		git_odb_writepack **, git_odb_backend *, git_odb *odb,

		git_transfer_progress_cb progress_cb, void *progress_payload);

	/**

	 * "Freshens" an already existing object, updating its last-used

	 * time.  This occurs when `git_odb_write` was called, but the

	 * object already existed (and will not be re-written).  The

	 * underlying implementation may want to update last-used timestamps.

	 *

	 * If callers implement this, they should return `0` if the object

	 * exists and was freshened, and non-zero otherwise.

	 */

	int (* freshen)(git_odb_backend *, const git_oid *);

	/**

	 * Frees any resources held by the odb (including the `git_odb_backend`

	 * itself). An odb backend implementation must provide this function.

	 */

	void (* free)(git_odb_backend *);

};

#define GIT_ODB_BACKEND_VERSION 1

#define GIT_ODB_BACKEND_INIT {GIT_ODB_BACKEND_VERSION}

/**

 * Initializes a `git_odb_backend` with default values. Equivalent to

 * creating an instance with GIT_ODB_BACKEND_INIT.

 *

 * @param backend the `git_odb_backend` struct to initialize.

 * @param version Version the struct; pass `GIT_ODB_BACKEND_VERSION`

 * @return Zero on success; -1 on failure.

 */

GIT_EXTERN(int) git_odb_init_backend(

	git_odb_backend *backend,

	unsigned int version);

GIT_EXTERN(void *) git_odb_backend_malloc(git_odb_backend *backend, size_t len);

GIT_END_DECL

#endif