#define _GNU_SOURCE

#include <stdint.h>
#include <assert.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <error.h>

#include <libgen.h>
#include <err.h>
#include <ctype.h>
#include <errno.h>
#include <stdlib.h>
#include <math.h>

#include <sys/statvfs.h>

uint64_t max_size(const char *path)
{
  struct statvfs stat;
  
  int ret = statvfs(path, &stat);

  assert(ret == 0);

  return (uint64_t)stat.f_bsize * stat.f_bavail;
}

#define qemu_toupper(c)     toupper((unsigned char)(c)) 

static int64_t suffix_mul(char suffix, int64_t unit)                             
{                                                                                
    switch (qemu_toupper(suffix)) {                                              
    case 'B':                                                                    
        return 1;                                                                
    case 'K':                                                                    
        return unit;                                                             
    case 'M':                                                                    
        return unit * unit;                                                      
    case 'G':                                                                    
        return unit * unit * unit;                                               
    case 'T':                                                                    
        return unit * unit * unit * unit;                                        
    case 'P':                                                                    
        return unit * unit * unit * unit * unit;                                 
    case 'E':                                                                    
        return unit * unit * unit * unit * unit * unit;                          
    }                                                                            
    return -1;                                                                   
}

/*                                                                               
 * Convert string to bytes, allowing either B/b for bytes, K/k for KB,           
 * M/m for MB, G/g for GB or T/t for TB. End pointer will be returned            
 * in *end, if not NULL. Return -ERANGE on overflow, Return -EINVAL on           
 * other error.                                                                  
 */                                                                              
static int do_strtosz(const char *nptr, char **end,                              
                      const char default_suffix, int64_t unit,                   
                      uint64_t *result)                                          
{                                                                                
    int retval;                                                                  
    char *endptr;                                                                
    unsigned char c;                                                             
    int mul_required = 0;                                                        
    double val, mul, integral, fraction;                                         
                                                                                 
    errno = 0;                                                                   
    val = strtod(nptr, &endptr);                                                 
    if (isnan(val) || endptr == nptr || errno != 0) {                            
        retval = -EINVAL;                                                        
        goto out;                                                                
    }                                                                            
    fraction = modf(val, &integral);                                             
    if (fraction != 0) {                                                         
        mul_required = 1;                                                        
    }                                                                            
    c = *endptr;                                                                 
    mul = suffix_mul(c, unit);                                                   
    if (mul >= 0) {                                                              
        endptr++;                                                                
    } else {                                                                     
        mul = suffix_mul(default_suffix, unit);                                  
        assert(mul >= 0);                                                        
    }                                                                            
    if (mul == 1 && mul_required) {                                              
        retval = -EINVAL;                                                        
        goto out;                                                                
    }                                                                            
    /*                                                                           
     * Values >= 0xfffffffffffffc00 overflow uint64_t after their trip           
     * through double (53 bits of precision).                                    
     */                                                                          
    if ((val * mul >= 0xfffffffffffffc00) || val < 0) {                          
        retval = -ERANGE;                                                        
        goto out;                                                                
    }                                                                            
    *result = val * mul;                                                         
    retval = 0;                                                                  
out:                                                                             
    if (end) {                                                                   
        *end = endptr;                                                           
    } else if (*endptr) {                                                        
        retval = -EINVAL;                                                        
    }                                                                            
                                                                                 
    return retval;                                                               
}


int qemu_strtosz(const char *nptr, char **end, uint64_t *result)                 
{                                                                                
    return do_strtosz(nptr, end, 'B', 1024, result);                             
}   

static int64_t cvtnum(const char *s)
{
    int err;
    uint64_t value;                                                              
                                                                               
    err = qemu_strtosz(s, NULL, &value);
    if (err < 0) {
        return err;
    }
    if (value > INT64_MAX) {
        return -ERANGE;
    }
    return value;
}

int balloon_fd;

int create_balloon(const char *filename)
{
    int fd = open(filename, O_RDWR);
    uint64_t sz = max_size(filename);

    printf("%ld\n", sz);
}

int main(int argc, char *argv[])
{
    int ret = 0;
    int fd = -1;
    struct statvfs stat;
    const char *filename = argv[1];
    int64_t len = cvtnum(argv[2]), disk_len, off;
    char *dir;
    int64_t block = 64 * 1024, try;
    int64_t flen;

    char *buf[block];

    dir = strdup(filename);
    dirname(dir);
    ret = statvfs(dir, &stat);
    if (ret < 0) {
        perror("Can not get fs stats");
        goto fail;
    }
    disk_len = (uint64_t)stat.f_bsize * stat.f_bavail;
    if (disk_len < len) {
        perror("Not enough space on disk");
        goto fail;
    }

    fd = open(filename, O_CREAT | O_RDWR);
    if (fd < 0) {
        perror("Can not open file for RW");
        goto fail;
    }

    sync();

    printf("fallocating max space. You can monitor progress by 'watch -d \"df -h %s\"'\n", dir);

    flen = len;
    try = (disk_len - 10 * block) / 2 / block * block;
    while (try >= block) {
        ret = statvfs(dir, &stat);
        if (ret < 0) {
            perror("Can not get fs stats");
            goto fail;
        }
        disk_len = (uint64_t)stat.f_bsize * stat.f_bavail;

        try = disk_len / 2 / block * block;
        if (try < 10 * block) {
            break;
        }
        ret = fallocate(fd, 0, flen, try);
        if (ret >= 0) {
            flen += try;
        } else {
            break;
        }
    }

    ret = statvfs(dir, &stat);
    if (ret < 0) {
        perror("Can not get fs stats");
        goto fail;
    }
    disk_len = (uint64_t)stat.f_bsize * stat.f_bavail;
    printf("done (remaining space %ld).\n\n", disk_len);

    printf("reallocating final blocks:\n");
    for (off = 0; off < len; off += block) {
        while (fallocate(fd, 0, off, block) < 0) {
            ret = ftruncate(fd, flen - block);
            if (ret < 0) {
                error(0, errno, "Failed to punch hole for block %ld", off / block);
                goto fail;
            }
            flen -= block;
        }

        lseek(fd, off, SEEK_SET);
        write(fd, buf, block);

        printf("done bytes: %ld/%ld                \r", off, len);
    }
    printf("done.                                                              \n\n");

    printf("truncating file to final size\n");
    ret = ftruncate(fd, len);
    if (ret < 0) {
        perror("Failed to truncate to final size");
        goto fail;
    }

fail:
    free(dir);

    if (fd >= 0) {
        close(fd);
        if (ret < 0) {
            unlink(filename);
        }
    }

    return -ret;
}