package wal

import (
	"fmt"
	"os"
)

// dirFsyncFn is the package-level indirection over dirFsync so tests can
// inject failures without interface plumbing in production code.
//
// NOT PARALLEL-SAFE: tests that override this must not use t.Parallel().
// All existing wal tests run serially within the package.
var dirFsyncFn = dirFsync

// dirFsync opens the directory and fsyncs it. Required for durable-ready
// state per design §3.2 line 258. This is a hard requirement, not
// best-effort: rename is atomic in memory but not guaranteed to survive
// power loss without a directory fsync.
//
// Order: os.Open → f.Stat → IsDir → f.Sync. The open-then-stat sequence
// avoids the TOCTOU window between a separate os.Stat and os.Open, and
// ensures IsDir is checked against the actually-opened file.
func dirFsync(dir string) error {
	f, err := os.Open(dir)
	if err != nil {
		return fmt.Errorf("open dir %q: %w", dir, err)
	}
	defer f.Close()

	info, err := f.Stat()
	if err != nil {
		return fmt.Errorf("stat dir %q: %w", dir, err)
	}
	if !info.IsDir() {
		return fmt.Errorf("path %q is not a directory", dir)
	}

	if err := f.Sync(); err != nil {
		return fmt.Errorf("fsync dir %q: %w", dir, err)
	}
	return nil
}