//! Power-loss simulation tests (0.7.0 stress expansion).
//!
//! Extension of the 0.5.0 crash-test harness. The 0.5.0 tests
//! simulate process death (SIGKILL) at three kill points
//! (PreSyscall / MidSyscall / PostSyscall). Process death is a
//! *partial* approximation of power loss: the kernel keeps
//! running, the page cache survives, and any data already in the
//! page cache (but not flushed to media) is later flushed by the
//! kernel.
//!
//! Real power loss kills the kernel mid-cycle. Anything in the
//! page cache that hasn't reached stable storage is lost. Tests
//! that pass under SIGKILL but fail under real power loss are a
//! correctness gap.
//!
//! ## Approximation strategy
//!
//! Without an actual power-loss event, the closest approximation
//! is **forced unmount mid-write** — `umount -f` while a write is
//! in flight. The kernel discards anything in the page cache for
//! the unmounted filesystem; subsequent reads (after remount) see
//! only what was actually flushed to media before the unmount.
//!
//! This is still an approximation (the unmount waits for active
//! references to drain in some scenarios), but it's stricter than
//! SIGKILL.
//!
//! ## Operating model
//!
//! These tests require:
//! - A loopback-mounted filesystem the test can `umount -f`
//!   without affecting the host.
//! - Root or `CAP_SYS_ADMIN` to perform the unmount.
//!
//! Most CI runners cannot satisfy both. The tests detect the
//! requirements via the env var `FSYS_TEST_LOOP_DEV` and
//! `FSYS_TEST_MOUNT_POINT`; if either is unset, the test skips.
//!
//! Tier-3 release-prep humans run these tests on a workstation
//! with a pre-prepared loopback mount. The harness compiles in
//! every CI environment and the skip path is exercised.

use std::path::PathBuf;

fn loopback_mount_point() -> Option<(PathBuf, String)> {
    let dev = std::env::var("FSYS_TEST_LOOP_DEV").ok()?;
    let mount = std::env::var_os("FSYS_TEST_MOUNT_POINT")?;
    let mount_path = PathBuf::from(mount);
    if !mount_path.is_dir() {
        eprintln!("[power_loss_sim] FSYS_TEST_MOUNT_POINT is not a directory; skipping");
        return None;
    }
    Some((mount_path, dev))
}

#[test]
#[cfg(target_os = "linux")]
fn forced_unmount_during_write_preserves_atomic_replace_invariant() {
    let Some((mount_path, loop_dev)) = loopback_mount_point() else {
        eprintln!(
            "[power_loss_sim] FSYS_TEST_LOOP_DEV and FSYS_TEST_MOUNT_POINT not set; \
             skipping (release-prep tier-3 only)"
        );
        return;
    };

    // The harness scaffold:
    //   1. Establish initial state on the loopback fs.
    //   2. Spawn a write thread that issues fs.write() in a loop.
    //   3. After 200 ms of writes, force-unmount the loopback fs.
    //   4. Re-mount, scan the file's state.
    //   5. Verify the atomic-replace invariant: file is either
    //      entirely the old payload or entirely the new payload —
    //      never torn.
    //
    // This test is a stub: full implementation requires running
    // `umount -f` and `mount` as root, plus careful orchestration
    // of the write-loop thread. The release-prep human runs the
    // implementation manually with their preferred test
    // orchestration.
    eprintln!(
        "[power_loss_sim] scaffold present; full implementation deferred to \
         tier-3 release-prep run on {mount_path:?} via {loop_dev}"
    );
}

#[test]
fn power_loss_test_compiles_without_admin_privileges() {
    // Compile-time gate: ensures the harness builds even when
    // env vars aren't set. The other tests in this file are
    // gated on `loopback_mount_point()` returning Some(…), which
    // they don't on a normal CI run.
    let _ = loopback_mount_point();
}
