package mining

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

// AtomicWriteFile writes data to a file atomically by writing to a temp file
// first, syncing to disk, then renaming to the target path. This prevents
// corruption if the process is interrupted during write.
func AtomicWriteFile(path string, data []byte, perm os.FileMode) error {
	dir := filepath.Dir(path)

	// Create temp file in the same directory for atomic rename
	tmpFile, err := os.CreateTemp(dir, ".tmp-*")
	if err != nil {
		return fmt.Errorf("failed to create temp file: %w", err)
	}
	tmpPath := tmpFile.Name()

	// Clean up temp file on error
	success := false
	defer func() {
		if !success {
			os.Remove(tmpPath)
		}
	}()

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

	// Sync to ensure data is flushed to disk before rename
	if err := tmpFile.Sync(); err != nil {
		tmpFile.Close()
		return fmt.Errorf("failed to sync temp file: %w", err)
	}

	if err := tmpFile.Close(); err != nil {
		return fmt.Errorf("failed to close temp file: %w", err)
	}

	// Set permissions before rename
	if err := os.Chmod(tmpPath, perm); err != nil {
		return fmt.Errorf("failed to set file permissions: %w", err)
	}

	// Atomic rename (on POSIX systems)
	if err := os.Rename(tmpPath, path); err != nil {
		return fmt.Errorf("failed to rename temp file: %w", err)
	}

	success = true
	return nil
}