package infra

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

// ResolveRegistryRoot returns the absolute path of the fn_registry root
// (the directory that contains registry.db), or an error if not found.
//
// Resolution order:
//  1. FN_REGISTRY_ROOT env var — if set and <dir>/registry.db exists, return it.
//  2. Walk up from the executable's directory — up to 6 levels; first dir
//     that contains registry.db wins. Covers binaries at <root>/fn and at
//     <root>/apps/<x>/<bin>.
//  3. $HOME/fn_registry — if <$HOME>/fn_registry/registry.db exists.
//  4. Error — no method found a valid registry root.
func ResolveRegistryRoot() (string, error) {
	// 1. Env var
	if envDir := os.Getenv("FN_REGISTRY_ROOT"); envDir != "" {
		if nonEmptyFile(filepath.Join(envDir, "registry.db")) {
			return filepath.Clean(envDir), nil
		}
	}

	// 2. Walk up from executable
	if exe, err := os.Executable(); err == nil {
		dir := filepath.Dir(exe)
		for i := 0; i < 6; i++ {
			if nonEmptyFile(filepath.Join(dir, "registry.db")) {
				return dir, nil
			}
			parent := filepath.Dir(dir)
			if parent == dir {
				// Reached filesystem root
				break
			}
			dir = parent
		}
	}

	// 3. $HOME/fn_registry
	if home, err := os.UserHomeDir(); err == nil {
		candidate := filepath.Join(home, "fn_registry")
		if nonEmptyFile(filepath.Join(candidate, "registry.db")) {
			return candidate, nil
		}
	}

	return "", fmt.Errorf("resolve_registry_root: no se encontro registry.db (set FN_REGISTRY_ROOT)")
}

// nonEmptyFile reports whether path is an existing, non-empty regular file.
// A zero-byte registry.db — which sql.Open silently creates when handed a
// mis-resolved path — must NOT count as a valid registry root, otherwise such
// a shadow file would hijack the walk-up and mask the real database.
func nonEmptyFile(path string) bool {
	fi, err := os.Stat(path)
	return err == nil && fi.Mode().IsRegular() && fi.Size() > 0
}