/* Nanopb input streams for writing/reading data from the GPRS unit.
 * These implement this simple packet format:
 * LEN LEN MSGTYPE PAYLOAD CHECKSUM
 * 
 * LEN LEN is 16-bit length of the rest of the message, big-endian.
 * MSGTYPE is 8-bit byte corresponding to RPCCommand enumeration in .proto
 * CHECKSUM is 0xFF xorred with each byte after LEN.
 */

#pragma once

#include <stdio.h>
#include <pb.h>
#include <pb_encode.h>
#include <pb_decode.h>
#include "paatti.pb.h"

typedef struct {
    pb_istream_t stream;
    FILE *file;
    RPCCommand msgtype;
    uint8_t checksum;
} rpc_istream_t;

// Reads a packet header from the input stream.
// You must call this function prior to using the stream for reading.
// After that, you can read stream->msgtype.
// stream->file must be set before calling this.
// Returns false if read fails or packet header is invalid.
bool rpc_istream_start(rpc_istream_t *stream);

// Read the packet to end (if not already read) and verify checksum.
// Returns false if read fails or checksum is invalid.
bool rpc_istream_end(rpc_istream_t *stream);

typedef struct {
    pb_ostream_t stream;
    FILE *file;
    uint8_t checksum;
} rpc_ostream_t;

// Writes a packet header.
// stream->file must be set before calling this.
// length is the length to be written in the packet header, i.e. payload + 2
bool rpc_ostream_start(rpc_ostream_t *stream, RPCCommand msgtype, size_t length);

// Writes packet CRC
// Returns false if actual written length was different than expected or
// if write failed.
bool rpc_ostream_end(rpc_ostream_t *stream);