/*
 * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Hyra nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NSTP LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NSTP LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR STPHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef STP_SESSION_H_
#define STP_SESSION_H_

#include <ostp/crypto/aes.h>
#include <ostp/defs.h>
#include <stdint.h>

#define MAX_USERNAME_LEN 64
#define MAX_PASSWORD_LEN 256

/*
 * 2^12 (4096) bytes is a common page size on
 * modern systems, this could lead to potential
 * optimizations.
 */
#define MESSAGE_SIZE (1 << 12)

/* Session Request option bits */
#define SESSION_REQ_USER BIT(0)
#define SESSION_REQ_P2P  BIT(1)

/*
 * For ACKing/TRUNCing packets e.g.,
 * peer blocks
 */
#define ACK_WORD 0xAC7E
#define TRUNC_WORD 0x782C

#define PB_N_PEERS 16
#define PB_N_BLOCKS 16

/*
 * The Session Request is sent from the client to the
 * server and contains options, public key and some
 * optional padding.
 *
 * @options: Flags/options
 * @pubkey: Ephemeral public key.
 * @pad: Random padding used to obsecure message length
 *       (can be 8 to 32 bytes, optional)
 *
 * -- Option/flag bits --
 *
 *                         Bit number
 *                        /
 *           0 1 2 3 4 5 6
 *           ~ ~ ~ ~ ~ ~ ~
 *           U P R R R R R
 *                        \
 *                         Purpose
 *
 * U: User auth.
 * P: Peer-to-peer.
 * R: Reserved, keep zero.
 */
struct session_request {
    uint8_t options;
    uint8_t pubkey[32];
    uint8_t pad[8];
} PACKED;

/*
 * The `peer' structure describes a peer on
 * an OSTP server running in peer-to-peer mode.
 *
 * @pad: Must be all 1s, treat invalid otherwise
 * @port: Port peer accepts connections on
 * @host: Host peer is at
 */
struct peer {
    uint8_t pad[1];
    uint16_t port;
    char host[IP_LEN_MAX];
};

/*
 * If P2P is enabled and supported, the OCS
 * sends one or more peer blocks in a consecutive
 * manner. Each peer block can list up to 16 peers
 * max. If the `seq' field is greater than zero and
 * the list of peers within the current block is full,
 * the client may either request the next peer block by
 * sending an ACK packet or terminating the connection
 * by sending a TRUNC packet.
 *
 * @peers: List of available peers within this block
 * @seq: Descending one-based block sequence number (0=invalid)
 */
struct peer_block {
    struct peer peers[PB_N_PEERS];
    uint8_t seq;
} PACKED;

/* Peer/block counts must be powers of two */
CTASSERT((PB_N_PEERS & 1) == 0, "PB_N_PEERS not power-of-two!");
CTASSERT((PB_N_BLOCKS & 1) == 0, "PB_N_BLOCKS not power-of-two!");

/*
 * Structure containing user information
 * for password protected channels.
 */
struct session_auth {
    char username[MAX_USERNAME_LEN];
    char password[MAX_PASSWORD_LEN];
    uint8_t code;
};

/*
 * OSTP Message Frame containing an IV, AES
 * GCM tag, payload length and payload
 * with encrypted data.
 */
struct msg_frame {
    uint8_t iv[AES_IV_SIZE];
    uint8_t tag[AES_GCM_TAG_SIZE];
    uint16_t len;
    uint8_t payload[MESSAGE_SIZE];
};

int send_frame(int client_fd, void *data, size_t len,
    const unsigned char *session_key);
int recv_frame(int client_fd, size_t len, const unsigned char *session_key,
    void *res);

#endif  /* STP_SESSION_H_ */