package brainfstest

import (
	"fmt"
	"os"
	"path/filepath"
	"runtime"
	"syscall"
	"testing"
	"time"
)

// recordingTB stands in for the test under AssertNoLeakFrom so a fatal
// there can be observed instead of failing this test. Fatalf ends the
// calling goroutine the way testing.T does.
type recordingTB struct {
	testing.TB
	failed bool
	msg    string
}

func (r *recordingTB) Fatalf(format string, args ...any) {
	r.failed, r.msg = true, fmt.Sprintf(format, args...)
	runtime.Goexit()
}

func runAssert(t *testing.T, path, target string, read func() string) *recordingTB {
	t.Helper()
	r := &recordingTB{TB: t}
	done := make(chan struct{})
	go func() {
		defer close(done)
		AssertNoLeakFrom(r, path, "inside", target, 200*time.Millisecond, read)
	}()
	<-done
	return r
}

// hyperguild#177: with every swap failing, no leak can occur, so the leak
// assertion passed without testing anything.
func TestAssertNoLeakFromFailsWhenNoSymlinkSwapSucceeds(t *testing.T) {
	path := filepath.Join(t.TempDir(), "missing-dir", "r.md")
	r := runAssert(t, path, Outside(t), func() string { return "inside" })
	if !r.failed {
		t.Fatal("AssertNoLeakFrom passed with zero successful symlink swaps")
	}
}

// hyperguild#177: a reader that always errors returns nothing, so it never
// leaks either.
func TestAssertNoLeakFromFailsWhenNoReadReturnsTheInsideNote(t *testing.T) {
	path := filepath.Join(t.TempDir(), "r.md")
	r := runAssert(t, path, Outside(t), func() string { return "" })
	if !r.failed {
		t.Fatal("AssertNoLeakFrom passed with zero reads returning the inside note")
	}
}

// Positive control: a reader that refuses symlinks and reads regular files
// passes, so the floors do not fail a working reader.
func TestAssertNoLeakFromPassesAReaderThatRefusesSymlinks(t *testing.T) {
	path := filepath.Join(t.TempDir(), "r.md")
	read := func() string {
		f, err := os.OpenFile(path, os.O_RDONLY|noFollow, 0)
		if err != nil {
			return ""
		}
		defer func() { _ = f.Close() }()
		b := make([]byte, 64)
		n, _ := f.Read(b)
		return string(b[:n])
	}
	r := runAssert(t, path, Outside(t), read)
	if r.failed {
		t.Fatalf("a symlink-refusing reader failed: %s", r.msg)
	}
}

const noFollow = syscall.O_NOFOLLOW