#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>

#include "bakeware.h"

#define BW_TRAILER_V1_LENGTH          48
#define BW_TRAILER_V1_MAGIC           (BW_TRAILER_V1_LENGTH - 4)
#define BW_TRAILER_V1_TRAILER_VERSION (BW_TRAILER_V1_LENGTH - 5)
#define BW_TRAILER_V1_COMPRESSION     (BW_TRAILER_V1_LENGTH - 6)
#define BW_TRAILER_V1_FLAGS           (BW_TRAILER_V1_LENGTH - 8)
#define BW_TRAILER_V1_CONTENTS_OFFSET (BW_TRAILER_V1_LENGTH - 12)
#define BW_TRAILER_V1_CONTENTS_LENGTH (BW_TRAILER_V1_LENGTH - 16)
#define BW_TRAILER_V1_START_COMMAND   (BW_TRAILER_V1_LENGTH - 28)
#define BW_TRAILER_V1_SHA1            (BW_TRAILER_V1_LENGTH - 48)

static uint32_t read_be32(const uint8_t *buffer)
{
    return (buffer[0] << 24) + (buffer[1] << 16) + (buffer[2] << 8) + buffer[3];
}

static uint16_t read_be16(const uint8_t *buffer)
{
    return (buffer[0] << 8) + buffer[1];
}

static void sha1_to_ascii(const uint8_t *input, char *output)
{
    bw_bin_to_hex(input, output, 20);
}

int bw_read_trailer(int fd, struct bakeware_trailer *trailer)
{
    memset(trailer, 0, sizeof(struct bakeware_trailer));
    if (lseek(fd, -BW_TRAILER_V1_LENGTH, SEEK_END) < 0) {
        bw_warn("lseek");
        return -1;
    }

    uint8_t buffer[BW_TRAILER_V1_LENGTH];
    if (read(fd, buffer, BW_TRAILER_V1_LENGTH) != BW_TRAILER_V1_LENGTH) {
        bw_warn("read");
        return -1;
    }

    if (memcmp(&buffer[BW_TRAILER_V1_MAGIC], "BAKE", 4) != 0) {
        bw_warnx("Incorrect Bakeware magic %d %d %d %d",
            buffer[BW_TRAILER_V1_MAGIC], buffer[BW_TRAILER_V1_MAGIC+1], buffer[BW_TRAILER_V1_MAGIC+2], buffer[BW_TRAILER_V1_MAGIC+3]);
        return -1;
    }

    trailer->trailer_version = buffer[BW_TRAILER_V1_TRAILER_VERSION];
    trailer->compression = buffer[BW_TRAILER_V1_COMPRESSION];
    trailer->flags = read_be16(&buffer[BW_TRAILER_V1_FLAGS]);
    trailer->contents_offset = read_be32(&buffer[BW_TRAILER_V1_CONTENTS_OFFSET]);
    trailer->contents_length = read_be32(&buffer[BW_TRAILER_V1_CONTENTS_LENGTH]);
    memcpy(trailer->sha1, &buffer[BW_TRAILER_V1_SHA1], sizeof(trailer->sha1));
    sha1_to_ascii(trailer->sha1, trailer->sha1_ascii);
    memcpy(trailer->start_command, &buffer[BW_TRAILER_V1_START_COMMAND], BAKEWARE_MAX_START_COMMAND_LEN);
    trailer->start_command[BAKEWARE_MAX_START_COMMAND_LEN] = 0;

    return 0;
}