// Package atomicfile persists bounded service snapshots without exposing a
// partially written destination after a process crash.
package atomicfile

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

func Write(path string, content []byte, mode os.FileMode) error {
	if path == "" {
		return errors.New("atomic file path must not be empty")
	}
	path = filepath.Clean(path)
	if info, err := os.Lstat(path); err == nil {
		if info.Mode()&os.ModeSymlink != 0 {
			return errors.New("refusing to replace a symbolic-link store path")
		}
		if !info.Mode().IsRegular() {
			return errors.New("refusing to replace a non-regular store path")
		}
	} else if !os.IsNotExist(err) {
		return fmt.Errorf("inspect store path: %w", err)
	}

	directory := filepath.Dir(path)
	temporary, err := os.CreateTemp(directory, ".tera-store-*")
	if err != nil {
		return fmt.Errorf("create temporary store: %w", err)
	}
	temporaryPath := temporary.Name()
	renamed := false
	defer func() {
		_ = temporary.Close()
		if !renamed {
			_ = os.Remove(temporaryPath)
		}
	}()
	if err := temporary.Chmod(mode.Perm()); err != nil {
		return fmt.Errorf("protect temporary store: %w", err)
	}
	if _, err := temporary.Write(content); err != nil {
		return fmt.Errorf("write temporary store: %w", err)
	}
	if err := temporary.Sync(); err != nil {
		return fmt.Errorf("sync temporary store: %w", err)
	}
	if err := temporary.Close(); err != nil {
		return fmt.Errorf("close temporary store: %w", err)
	}
	if err := os.Rename(temporaryPath, path); err != nil {
		return fmt.Errorf("replace store: %w", err)
	}
	renamed = true
	if err := syncDirectory(directory); err != nil {
		return fmt.Errorf("sync store directory: %w", err)
	}
	return nil
}