package ids

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

	"github.com/google/uuid"

	"github.com/monlet/agent/internal/config"
)

// LoadOrCreateAgentID returns configured ID if non-empty, otherwise loads
// state_dir/agent_id, generating and persisting it on first run.
func LoadOrCreateAgentID(stateDir, configured string) (string, error) {
	if configured != "" {
		return configured, nil
	}
	if err := os.MkdirAll(stateDir, 0o755); err != nil {
		return "", fmt.Errorf("create state dir: %w", err)
	}
	path := filepath.Join(stateDir, "agent_id")
	b, err := os.ReadFile(path)
	if err == nil {
		id := strings.TrimSpace(string(b))
		if err := config.ValidateID("agent_id", id); err != nil {
			return "", fmt.Errorf("persisted agent_id invalid: %w", err)
		}
		return id, nil
	}
	if !os.IsNotExist(err) {
		return "", err
	}
	id := uuid.NewString()
	if err := os.WriteFile(path, []byte(id+"\n"), 0o600); err != nil {
		return "", err
	}
	return id, nil
}