package config

import (
	"fmt"
	"os"
	"path/filepath"
)

// AtomicWrite writes data to the target path atomically by writing to a temp file
// in the same directory, fsyncing, then renaming over the target.
func AtomicWrite(path string, data []byte, perm os.FileMode) error {
	dir := filepath.Dir(path)

	if err := os.MkdirAll(dir, 0o755); err != nil {
		return fmt.Errorf("create directory: %w", err)
	}

	tmp, err := os.CreateTemp(dir, ".tmp-*")
	if err != nil {
		return fmt.Errorf("create temp file: %w", err)
	}
	tmpName := tmp.Name()

	cleanup := func() {
		tmp.Close()
		os.Remove(tmpName)
	}

	if _, err := tmp.Write(data); err != nil {
		cleanup()
		return fmt.Errorf("write temp file: %w", err)
	}

	if err := tmp.Sync(); err != nil {
		cleanup()
		return fmt.Errorf("fsync temp file: %w", err)
	}

	if err := tmp.Close(); err != nil {
		os.Remove(tmpName)
		return fmt.Errorf("close temp file: %w", err)
	}

	if err := os.Chmod(tmpName, perm); err != nil {
		os.Remove(tmpName)
		return fmt.Errorf("chmod temp file: %w", err)
	}

	if err := os.Rename(tmpName, path); err != nil {
		os.Remove(tmpName)
		return fmt.Errorf("rename temp to target: %w", err)
	}

	return nil
}