/*-------------------------------------------------------------------------
 *
 * rewind_source.h
 *	  Abstraction for fetching from source server.
 *
 * The source server can be either a libpq connection to a live system,
 * or a local data directory. The 'rewind_source' struct abstracts the
 * operations to fetch data from the source system, so that the rest of
 * the code doesn't need to care what kind of a source its dealing with.
 *
 * Copyright (c) 2013-2025, PostgreSQL Global Development Group
 *
 *-------------------------------------------------------------------------
 */
#ifndef REWIND_SOURCE_H
#define REWIND_SOURCE_H

#include "access/xlogdefs.h"
#include "file_ops.h"
#include "filemap.h"
#include "libpq-fe.h"

typedef struct rewind_source
{
	/*
	 * Traverse all files in the source data directory, and call 'callback' on
	 * each file.
	 */
	void		(*traverse_files) (struct rewind_source *,
								   process_file_callback_t callback);

	/*
	 * Fetch a single file into a malloc'd buffer. The file size is returned
	 * in *filesize. The returned buffer is always zero-terminated, which is
	 * handy for text files.
	 */
	char	   *(*fetch_file) (struct rewind_source *, const char *path,
							   size_t *filesize);

	/*
	 * Request to fetch (part of) a file in the source system, specified by an
	 * offset and length, and write it to the same offset in the corresponding
	 * target file. The source implementation may queue up the request and
	 * execute it later when convenient. Call finish_fetch() to flush the
	 * queue and execute all requests.
	 */
	void		(*queue_fetch_range) (struct rewind_source *, const char *path,
									  off_t offset, size_t len);

	/*
	 * Like queue_fetch_range(), but requests replacing the whole local file
	 * from the source system. 'len' is the expected length of the file,
	 * although when the source is a live server, the file may change
	 * concurrently. The implementation is not obliged to copy more than 'len'
	 * bytes, even if the file is larger. However, to avoid copying a
	 * truncated version of the file, which can cause trouble if e.g. a
	 * configuration file is modified concurrently, the implementation should
	 * try to copy the whole file, even if it's larger than expected.
	 */
	void		(*queue_fetch_file) (struct rewind_source *, const char *path,
									 size_t len);

	/*
	 * Execute all requests queued up with queue_fetch_range().
	 */
	void		(*finish_fetch) (struct rewind_source *);

	/*
	 * Get the current WAL insert position in the source system.
	 */
	XLogRecPtr	(*get_current_wal_insert_lsn) (struct rewind_source *);

	/*
	 * Free this rewind_source object.
	 */
	void		(*destroy) (struct rewind_source *);

} rewind_source;

/* in libpq_source.c */
extern rewind_source *init_libpq_source(PGconn *conn);

/* in local_source.c */
extern rewind_source *init_local_source(const char *datadir);

#endif							/* REWIND_SOURCE_H */
