usage.rs

use std::ffi::CString;
use std::fmt;
use std::io;
use std::mem;
use std::path::Path;

use heim_common::prelude::*;
use heim_common::units::{information, ratio, Information, Ratio};

use crate::os::unix::Flags;

pub struct Usage(libc::statvfs);

// Why there are `u64::from()` everywhere -- to mitigate the differences
// between `libc::statvfs` for x86 and `libc::statvfs` for x86_64,
// fields can be either `u32` or `u64`.
#[allow(clippy::useless_conversion)]
impl Usage {
    pub fn total(&self) -> Information {
        let value = u64::from(self.0.f_blocks) * u64::from(self.0.f_frsize);

        Information::new::<information::byte>(value)
    }

    pub fn used(&self) -> Information {
        let avail_to_root = u64::from(self.0.f_bfree) * u64::from(self.0.f_frsize);

        self.total() - Information::new::<information::byte>(avail_to_root)
    }

    pub fn free(&self) -> Information {
        let value = u64::from(self.0.f_bavail) * u64::from(self.0.f_frsize);

        Information::new::<information::byte>(value)
    }

    pub fn ratio(&self) -> Ratio {
        // FIXME: Possible value truncation while casting into f64.
        // Lucky us, it is a 2019 and we are good for the next couple of decades
        let used = self.used().get::<information::byte>() as f32;
        let avail_to_user = u64::from(self.0.f_bavail) * u64::from(self.0.f_frsize);
        let total_user = used + avail_to_user as f32;

        Ratio::new::<ratio::ratio>(used / total_user)
    }

    pub fn flags(&self) -> Flags {
        Flags::from_bits_truncate(self.0.f_flag)
    }
}

// TODO: Stub
impl fmt::Debug for Usage {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Usage").finish()
    }
}

// TODO: It is an internal function, we could monomorphize it and accept `path: &Path`
pub async fn usage<T: AsRef<Path>>(path: T) -> Result<Usage> {
    let path = path
        .as_ref()
        .to_str()
        .ok_or_else(|| io::Error::from(io::ErrorKind::InvalidInput))
        .and_then(|string| {
            CString::new(string).map_err(|_| io::Error::from(io::ErrorKind::InvalidInput))
        })
        .map_err(|e| Error::from(e).with_message("Invalid path"))?;

    let mut vfs = mem::MaybeUninit::<libc::statvfs>::uninit();
    let result = unsafe { libc::statvfs(path.as_ptr(), vfs.as_mut_ptr()) };

    if result == 0 {
        let vfs = unsafe { vfs.assume_init() };
        Ok(Usage(vfs))
    } else {
        Err(Error::last_os_error().with_ffi("statvfs"))
    }
}