/* lib9p/internal.h - TODO
 *
 * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */

#ifndef _LIB9P_INTERNAL_H_
#define _LIB9P_INTERNAL_H_

#include <stddef.h> /* for size_t */
#include <limits.h> /* for SSIZE_MAX, not set by newlib */
#ifndef SSIZE_MAX
#define SSIZE_MAX (SIZE_MAX >> 1)
#endif

#include <libmisc/endian.h>
#include <libmisc/macro.h>

#include <lib9p/9p.h>

/* configuration **************************************************************/

#include "config.h"

#ifndef CONFIG_9P_MAX_MSG_SIZE
	#error config.h must define CONFIG_9P_MAX_MSG_SIZE
#endif
#ifndef CONFIG_9P_MAX_HOSTMSG_SIZE
	#error config.h must define CONFIG_9P_MAX_HOSTMSG_SIZE
#endif
#ifndef CONFIG_9P_MAX_ERR_SIZE
	#error config.h must define CONFIG_9P_MAX_ERR_SIZE
#endif

static_assert(CONFIG_9P_MAX_ERR_SIZE <= UINT16_MAX);
static_assert(CONFIG_9P_MAX_MSG_SIZE <= CONFIG_9P_MAX_HOSTMSG_SIZE);
static_assert(CONFIG_9P_MAX_HOSTMSG_SIZE <= SSIZE_MAX);

/* specialized contexts *******************************************************/

struct _validate_ctx {
	/* input */
	struct lib9p_ctx        *ctx;
	uint32_t                 net_size;
	uint8_t                 *net_bytes;

	/* output */
	uint32_t                 net_offset;
	/* Increment `host_extra` to pre-allocate space that is
	 * "extra" beyond sizeof().  */
	size_t                   host_extra;
};
typedef bool (*_validate_fn_t)(struct _validate_ctx *ctx);

struct _unmarshal_ctx {
	/* input */
	struct lib9p_ctx        *ctx;
	uint8_t                 *net_bytes;

	/* output */
	uint32_t                 net_offset;
	/* `extra` points to the beginning of unallocated space.  */
	void                    *extra;
};
typedef void (*_unmarshal_fn_t)(struct _unmarshal_ctx *ctx, void *out);

struct _marshal_ctx {
	/* input */
	struct lib9p_ctx        *ctx;

	/* output */
	size_t                   net_iov_cnt;
	struct iovec            *net_iov;
	size_t                   net_copied_size;
	uint8_t                 *net_copied;
};
typedef bool (*_marshal_fn_t)(struct _marshal_ctx *ctx, void *host_val);

/* tables / exports ***********************************************************/

struct _lib9p_recv_tentry {
	size_t                  basesize;
	_validate_fn_t          validate;
	_unmarshal_fn_t         unmarshal;
};

struct _lib9p_send_tentry {
	_marshal_fn_t           marshal;
};

extern const char *const _lib9p_table_ver_name[LIB9P_VER_NUM];
extern const char *const _lib9p_table_msg_name[LIB9P_VER_NUM][0x100];
extern const uint32_t _lib9p_table_msg_min_size[LIB9P_VER_NUM];
extern const struct _lib9p_recv_tentry _lib9p_table_Tmsg_recv[LIB9P_VER_NUM][0x80];
extern const struct _lib9p_recv_tentry _lib9p_table_Rmsg_recv[LIB9P_VER_NUM][0x80];
extern const struct _lib9p_send_tentry _lib9p_table_Tmsg_send[LIB9P_VER_NUM][0x80];
extern const struct _lib9p_send_tentry _lib9p_table_Rmsg_send[LIB9P_VER_NUM][0x80];

bool _lib9p_stat_validate(struct _validate_ctx *ctx);
void _lib9p_stat_unmarshal(struct _unmarshal_ctx *ctx, struct lib9p_stat *out);
bool _lib9p_stat_marshal(struct _marshal_ctx *ctx, struct lib9p_stat *val);

/* unmarshal utilities ********************************************************/

static inline bool _is_valid_utf8(uint8_t *str, size_t len, bool forbid_nul) {
	uint32_t ch;
	uint8_t chlen;
	assert(str);
	for (size_t pos = 0; pos < len;) {
		if      ((str[pos] & 0b10000000) == 0b00000000) { ch = str[pos] & 0b01111111; chlen = 1; }
		else if ((str[pos] & 0b11100000) == 0b11000000) { ch = str[pos] & 0b00011111; chlen = 2; }
		else if ((str[pos] & 0b11110000) == 0b11100000) { ch = str[pos] & 0b00001111; chlen = 3; }
		else if ((str[pos] & 0b11111000) == 0b11110000) { ch = str[pos] & 0b00000111; chlen = 4; }
		else return false;
		if ((ch == 0 && (chlen != 1 || forbid_nul)) || pos + chlen > len) return false;
		for (uint8_t i = 1; i < chlen; i++) {
			if ((str[pos+i] & 0b11000000) != 0b10000000) return false;
			ch = (ch << 6) | (str[pos+i] & 0b00111111);
		}
		if (ch > 0x10FFFF) return false;
		pos += chlen;
	}
	return true;
}

#define is_valid_utf8(str, len)                 _is_valid_utf8(str, len, false)
#define is_valid_utf8_without_nul(str, len)     _is_valid_utf8(str, len, true)

#endif /* _LIB9P_INTERNAL_H_ */