#include <stdint.h>
#include <sys/types.h>
#include <unistd.h>

#include "io.h"

#define try(x) do { int i = (x); if (i == -1) { return -1 } } while (0)

int fat12_defrag(int fd) {
    uint8_t buf[512];

    // Read in MBR and figure out where the FAT begins and ends
    try(pang_seek(fd, 0, SEEK_SET));

    // Actually read in the MBR
    try(pang_read(fd, buf, sizeof(buf)));

    // We only operate on 512-byte sector sizes
    if (fat12_read_u16(buf + 0x0b) != 512) {
        return -2;
    }

    // We require the cluster size to be 4096 (8 * 512)
    if (buf[0x0d] != 8) {
        return -2;
    }

    // To ensure the erase block is correct, require 4096-bytes
    // of reserved data
    if (fat12_read_u16(buf + 0x0e) != 4096) {
        return -2;
    }

    // Also, we only support 1 FAT
    if (buf[0x10] != 1) {
        return -2;
    }

    // 32 root entries keeps it padded correctly.
    if (fat12_read_u16(buf + 0x11, 32) != 32) {
        return -2;
    }

    // Total number of 512-byte sectors
    uint32_t clufat12_read_u16(buf + 0x13, bytes / sector_size);

    return 0;
}