package engine

import (
	"errors"
	"io/fs"
	"os"
	"path/filepath"
	"testing"
)

func TestImportLinkResolutionTracksActiveExpansions(t *testing.T) {
	root := t.TempDir()
	if err := os.Mkdir(filepath.Join(root, "parts"), 0o700); err != nil {
		t.Fatal(err)
	}
	for name, target := range map[string]string{"parts/up": "..", "self": "self", "first": "second", "second": "first"} {
		if err := os.Symlink(target, filepath.Join(root, filepath.FromSlash(name))); err != nil {
			t.Skipf("symlinks unavailable: %v", err)
		}
	}
	host, err := openHostAccess(root)
	if err != nil {
		t.Fatal(err)
	}
	defer host.close()
	filesystem := os.DirFS(root)
	links, ok := filesystem.(fs.ReadLinkFS)
	if !ok {
		t.Fatal("native directory filesystem does not expose link inspection")
	}
	native := newNativeAccess(filesystem, ".", &namespaceToken{})
	for name, resolve := range map[string]func(string) (string, error){
		"host":   func(name string) (string, error) { return resolveHostImportPath(host, name) },
		"native": func(name string) (string, error) { return resolveNativeImportPath(native, links, name) },
	} {
		t.Run(name, func(t *testing.T) {
			if got, err := resolve("parts/up/parts/up/parts"); err != nil || got != "parts" {
				t.Errorf("finite link reuse = %q, %v", got, err)
			}
			for _, cycle := range []string{"self", "first"} {
				if _, err := resolve(cycle); !errors.Is(err, errImportDirectoryLinkCycle) {
					t.Errorf("%s cycle = %v", cycle, err)
				}
			}
		})
	}
}