/*
 * Copyright © 2024 Nick Bowler
 *
 * getline-like function which removes trailing newline (if any).
 *
 * If HAVE_GETLINE is not defined (or defined to 0) then a standard C
 * implementation is used.  Othewrise, the POSIX getline function
 * is called.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
#ifndef DX_GETLINE_H_
#define DX_GETLINE_H_

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>

/*
 * Size of the initial buffer allocated internally by the fallback
 * implementation when *linebuf is NULL.
 */
#ifndef DX_GETLINE_INITIAL_ALLOC
#  define DX_GETLINE_INITIAL_ALLOC 75
#endif

enum {
	DX_GETLINE_OK     =  1,
	DX_GETLINE_EOF    =  0,
	DX_GETLINE_ERROR  = -1,
	DX_GETLINE_ENOMEM = -2
};

/*
 * Wrapper around getline with standard C fallback.
 *
 * Note that for portability to some getline implementations (e.g., FreeBSD)
 * both *linebuf and *n should be set to zero on the initial call.
 *
 * If pre-allocating a buffer, ensure that its size is more than 1 byte,
 * otherwise AIX 7.2 getline fails to work correctly.
 *
 * Returns 1 (DX_GETLINE_OK) if a line was read or 0 (DX_GETLINE_EOF) if
 * no line could be read because the end of file was reached.
 *
 * On failure, returns a negative value.  If the C library input call failed
 * then the return value is DX_GETLINE_ERROR and the reason for the failure
 * should be available in errno.
 *
 * For the standard C fallback only, a return value of DX_GETLINE_ENOMEM
 * indicates that the buffer allocation could not be expanded to fit the
 * input line.
 */
static inline int dx_getline(char **linebuf, size_t *n, FILE *f)
{
#if HAVE_GETLINE
	ssize_t rc;

	if ((rc = getline(linebuf, n, f)) < 0) {
		if (ferror(f))
			return DX_GETLINE_ERROR;
		return DX_GETLINE_EOF;
	}

	if (rc-- && (*linebuf)[rc] == '\n')
		(*linebuf)[rc] = '\0';

	return DX_GETLINE_OK;
#else
	char *work = *linebuf;
	size_t pos = 0;
	size_t sz;

	if (!work) {
		sz = DX_GETLINE_INITIAL_ALLOC;
		goto initial_alloc;
	}

	for (sz = *n;;) {
		if (!fgets(&work[pos], sz - pos, f)) {
			if (ferror(f))
				return DX_GETLINE_ERROR;

			return pos ? DX_GETLINE_OK : DX_GETLINE_EOF;
		}

		pos += strlen(&work[pos]);
		if (work[pos-1] == '\n') {
			work[pos-1] = '\0';
			return DX_GETLINE_OK;
		}

		if (sz > INT_MAX/2 || sz > ((size_t)-1)/4)
			break;

		sz = ((sz*4) + 2) / 3;
initial_alloc:
		work = realloc(work, sz);
		if (!work)
			break;
		*linebuf = work;
		*n = sz;
	}

	return DX_GETLINE_ENOMEM;
#endif
}

#endif