//! Manage ZFS datasets and snapshots using the `zfs` executable on `PATH`.
//!
//! ```no_run
//! for snapshot in zfs::list_snapshots("pool/home")? {
//!     println!("{snapshot}");
//! }
//! # Ok::<(), anyhow::Error>(())
//! ```

use std::process::Command;

use anyhow::{Context, Result, bail};

const ZFS_EXECUTABLE: &str = "zfs";

fn zfs_command(args: &[&str]) -> Result<String> {
    let output = Command::new(ZFS_EXECUTABLE)
        .args(args)
        .env("LC_ALL", "C")
        .output()
        .context("Failed to execute zfs")?;
    if !output.status.success() {
        let message = if output.stderr.is_empty() {
            &output.stdout
        } else {
            &output.stderr
        };
        bail!(
            "zfs {} failed ({}): {}",
            args.join(" "),
            output.status,
            String::from_utf8_lossy(message).trim()
        );
    }
    String::from_utf8(output.stdout).context("zfs returned invalid UTF-8")
}

/// List filesystem datasets, excluding pool roots.
///
/// # Errors
///
/// Returns an error if executing ZFS or decoding its output fails.
pub fn list_datasets() -> Result<Vec<String>> {
    let output = zfs_command(&["list", "-Hp", "-t", "filesystem", "-o", "name"])?;
    Ok(output
        .lines()
        .filter(|name| name.contains('/'))
        .map(String::from)
        .collect())
}

/// List snapshot names belonging directly to `dataset`, excluding child datasets.
///
/// Returned names omit the `dataset@` prefix.
///
/// # Errors
///
/// Returns an error if executing ZFS or decoding its output fails.
pub fn list_snapshots(dataset: &str) -> Result<Vec<String>> {
    let output = zfs_command(&[
        "list", "-Hp", "-t", "snapshot", "-o", "name", "-d", "1", dataset,
    ])?;
    Ok(output
        .lines()
        .filter_map(|name| {
            let (owner, snapshot) = name.split_once('@')?;
            (owner == dataset).then(|| snapshot.to_owned())
        })
        .collect())
}

/// Create `dataset@snapshot`.
///
/// # Errors
///
/// Returns an error if executing ZFS or decoding its output fails.
pub fn create_snapshot(dataset: &str, snapshot: &str) -> Result<()> {
    zfs_command(&["snapshot", &format!("{dataset}@{snapshot}")])?;
    Ok(())
}

/// Delete `dataset@snapshot`.
///
/// Returns `None` on success, or `Some("snapshot has dependent clones")` when
/// dependent clones prevent deletion.
///
/// # Errors
///
/// Returns an error for other ZFS failures, execution failures, or invalid UTF-8 output.
pub fn delete_snapshot(dataset: &str, snapshot: &str) -> Result<Option<&'static str>> {
    if let Err(error) = zfs_command(&["destroy", &format!("{dataset}@{snapshot}")]) {
        if error.to_string().contains(&format!(
            "cannot destroy '{dataset}@{snapshot}': snapshot has dependent clones"
        )) {
            return Ok(Some("snapshot has dependent clones"));
        }
        return Err(error);
    }
    Ok(None)
}