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//! File manifests.
//!
//! This crate defines the [`ManifestEntry`] struct to represent an
//! entry in a file manifest. The entry contains data about each file.
//! A manifest can be produced of some data, and later, a new manifest
//! can be produced and compared with the original. If the manifests
//! have changed, the data has changed. If they haven't changed, the
//! data has probably not changed.
//!
//! Such manifests can be used, for example, to verify that data that
//! has been restored from a backup is the same as what was backed up.
//!
//! This crate uses Linux metadata of files.
//!
//! ~~~
//! let m = std::fs::metadata(".").unwrap();
//! let e = summain::ManifestEntry(m);
//! println!("{}", serde_yaml::to_string(e).unwrap());
//! ~~~
//!
//! The output is something like:
//!
//! ~~~yaml
//! path: "."
//! atime: 1606565868
//! atime_nsec: 824368155
//! mode: drwxrwxr-x
//! mtime: 1606565867
//! mtime_nsec: 500355545
//! nlink: 6
//! size: ~
//! ~~~

use serde::Serialize;
use std::fs::Metadata;
use std::os::linux::fs::MetadataExt;
use std::path::{Path, PathBuf};

/// An entry in a file manifest.
#[derive(Serialize, Debug)]
pub struct ManifestEntry {
    path: PathBuf,
    atime: i64,
    atime_nsec: i64,
    #[serde(with = "mode")]
    mode: u32,
    mtime: i64,
    mtime_nsec: i64,
    nlink: u64,
    size: Option<u64>,
}

impl ManifestEntry {
    /// Create a new manifest entry.
    ///
    /// The pathname of the file and the metadata are passed in by the
    /// caller. This function doesn't query the system for it.
    ///
    /// The structure can be serialized using serde.
    pub fn new(path: &Path, m: Metadata) -> Self {
        Self {
            path: path.to_path_buf(),
            atime: m.st_atime(),
            atime_nsec: m.st_atime_nsec(),
            mode: m.st_mode(),
            mtime: m.st_mtime(),
            mtime_nsec: m.st_mtime_nsec(),
            nlink: m.st_nlink(),
            size: if m.is_dir() { None } else { Some(m.st_size()) },
        }
    }
}

mod mode {
    use serde::{self, Serializer};

    pub fn serialize<S>(mode: &u32, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let s = unix_mode::to_string(*mode);
        serializer.serialize_str(&s)
    }
}