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

#ifndef _LIB9P_INTERNAL_H_
#define _LIB9P_INTERNAL_H_

#include <assert.h>
#include <stddef.h> /* for size_t */
#include <limits.h> /* for SSIZE_MAX */

#include <lib9p/9p.h>

#define USE_CONFIG_9P
#define USE_CONFIG_COROUTINE
#include "config.h"
static_assert(CONFIG_9P_MAX_ERR_SIZE <= UINT16_MAX);
static_assert(CONFIG_9P_MAX_MSG_SIZE <= SSIZE_MAX);
static_assert(CONFIG_9P_MAX_ERR_SIZE + CONFIG_9P_MAX_MSG_SIZE + 2*CONFIG_9P_MAX_HOSTMSG_SIZE < CONFIG_COROUTINE_DEFAULT_STACK_SIZE);

/* C language *****************************************************************/

#define UNUSED(name) /* name __attribute__ ((unused)) */

/* types **********************************************************************/

/* NB: We declare this here instead of in the public <lib9p/9p.h>
 * because we don't want to include "config.h" from public headers,
 * and I want the MAX_ERR_SIZE to be configurable.  */
struct lib9p_ctx {
	/* negotiated */
	enum lib9p_version      version;
	uint32_t                max_msg_size;

	/* state */
	uint32_t                err_num;
	char                    err_msg[CONFIG_9P_MAX_ERR_SIZE];
};

/* vtables ********************************************************************/

struct _checksize_ctx {
	struct lib9p_ctx        *ctx;
	uint32_t                 net_size;
	uint8_t                 *net_bytes;

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

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

	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 {
	struct lib9p_ctx        *ctx;

	uint8_t                 *net_bytes;
	uint32_t                 net_offset;
};
typedef bool (*_marshal_fn_t)(struct _marshal_ctx *ctx, void *host_val);

struct _vtable_msg {
	size_t                  unmarshal_basesize;
	_checksize_fn_t         unmarshal_extrasize;
	_unmarshal_fn_t         unmarshal;
	_marshal_fn_t           marshal;
};

struct _vtable_version {
	struct _vtable_msg      msgs[0xFF];
};

extern struct _vtable_version _lib9p_vtables[LIB9P_VER_NUM];

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

static inline uint8_t decode_u8le(uint8_t *in) {
	return in[0];
}
static inline uint16_t decode_u16le(uint8_t *in) {
	return (((uint16_t)(in[0])) <<	0)
	     | (((uint16_t)(in[1])) <<	8)
	     ;
}
static inline uint32_t decode_u32le(uint8_t *in) {
	return (((uint32_t)(in[0])) <<	0)
	     | (((uint32_t)(in[1])) <<	8)
	     | (((uint32_t)(in[2])) << 16)
	     | (((uint32_t)(in[3])) << 24)
	     ;
}
static inline uint64_t decode_u64le(uint8_t *in) {
	return (((uint64_t)(in[0])) <<	0)
	     | (((uint64_t)(in[1])) <<	8)
	     | (((uint64_t)(in[2])) << 16)
	     | (((uint64_t)(in[3])) << 24)
	     | (((uint64_t)(in[4])) << 32)
	     | (((uint64_t)(in[5])) << 40)
	     | (((uint64_t)(in[6])) << 48)
	     | (((uint64_t)(in[7])) << 56)
	     ;
}

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)

/* marshal utilities **********************************************************/

static inline void encode_u8le(uint8_t in, uint8_t *out) {
	out[0] = in;
}
static inline void encode_u16le(uint16_t in, uint8_t *out) {
	out[0] = (uint8_t)((in >>  0) & 0xFF);
	out[1] = (uint8_t)((in >>  8) & 0xFF);
}
static inline void encode_u32le(uint32_t in, uint8_t *out) {
	out[0] = (uint8_t)((in >>  0) & 0xFF);
	out[1] = (uint8_t)((in >>  8) & 0xFF);
	out[2] = (uint8_t)((in >> 16) & 0xFF);
	out[3] = (uint8_t)((in >> 24) & 0xFF);
}
static inline void encode_u64le(uint64_t in, uint8_t *out) {
	out[0] = (uint8_t)((in >>  0) & 0xFF);
	out[1] = (uint8_t)((in >>  8) & 0xFF);
	out[2] = (uint8_t)((in >> 16) & 0xFF);
	out[3] = (uint8_t)((in >> 24) & 0xFF);
	out[4] = (uint8_t)((in >> 32) & 0xFF);
	out[5] = (uint8_t)((in >> 40) & 0xFF);
	out[6] = (uint8_t)((in >> 48) & 0xFF);
	out[7] = (uint8_t)((in >> 56) & 0xFF);
}

#endif /* _LIB9P_INTERNAL_H_ */