package session

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sync/atomic"
	"syscall"
	"testing"
	"time"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"golang.org/x/sys/unix"
)

// session_log passed the caller's session_id straight into
// filepath.Join(sessionsDir, id+".jsonl") and opened it O_CREATE|O_APPEND:
// path segments in the id created or appended files anywhere the pod could
// write. The id is now a plain name, and the open does not follow a final
// symlink.
func TestAppendRefusesSessionIDsThatAreNotPlainNames(t *testing.T) {
	root := t.TempDir()
	dir := filepath.Join(root, "sessions")
	for _, id := range []string{"../x", "a/b", "/abs", ".", "..", ".hidden", "", "a\\b", "a\x00b"} {
		assert.Error(t, Append(dir, id, Entry{SessionID: id}), "%q", id)
	}
	ents, _ := os.ReadDir(root)
	for _, e := range ents {
		assert.Equal(t, "sessions", e.Name(), "nothing created beside the sessions dir")
	}
	for _, id := range []string{"1557b2e1-bf0d-5c4f-bbe3-0754d087e356", "_routing", "2026-05-05-infra.plan", "0"} {
		require.NoError(t, Append(dir, id, Entry{SessionID: id}), "positive control: %q", id)
	}
}

func TestAppendDoesNotWriteThroughASymlinkedLog(t *testing.T) {
	root := t.TempDir()
	dir := filepath.Join(root, "sessions")
	require.NoError(t, os.MkdirAll(dir, 0o755))
	victim := filepath.Join(root, "victim.md")
	require.NoError(t, os.WriteFile(victim, []byte("untouched\n"), 0o644))
	require.NoError(t, os.Symlink(filepath.Join("..", "victim.md"), filepath.Join(dir, "s.jsonl")))
	assert.Error(t, Append(dir, "s", Entry{SessionID: "s"}))
	got, _ := os.ReadFile(victim)
	assert.Equal(t, "untouched\n", string(got))
}

func TestReadRefusesSessionIDsThatAreNotPlainNames(t *testing.T) {
	root := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(root, "x.jsonl"), []byte(`{"session_id":"x"}`+"\n"), 0o644))
	_, err := Read(filepath.Join(root, "sessions"), "../x")
	assert.Error(t, err)
}

// A name that starts plainly and then climbs out with ".." is exactly what the
// ban on "/" in the id's tail stops: filepath.Join cleans "a/../../x" to a
// path beside the sessions dir without needing sessions/a to exist. The
// assertion is on the refusal itself (ErrInvalidID), not on any error.
func TestAppendRefusesAnIDThatClimbsOutAfterAPlainPrefix(t *testing.T) {
	root := t.TempDir()
	dir := filepath.Join(root, "sessions")
	require.NoError(t, os.MkdirAll(dir, 0o755))
	for _, id := range []string{"a/../../escape", "a/../../../escape", "a/../b"} {
		err := Append(dir, id, Entry{SessionID: id})
		assert.ErrorIs(t, err, ErrInvalidID, "%q", id)
	}
	_, err := os.Lstat(filepath.Join(root, "escape.jsonl"))
	assert.True(t, errors.Is(err, os.ErrNotExist), "nothing created beside the sessions dir")
	_, err = os.Lstat(filepath.Join(dir, "b.jsonl"))
	assert.True(t, errors.Is(err, os.ErrNotExist), "no in-dir alias created either")
}

// Append does no Lstat type check, so O_NONBLOCK is the only thing that keeps
// a FIFO named <id>.jsonl with no reader from blocking session_log forever.
func TestAppendReturnsPromptlyOnAFIFOLogWithNoReader(t *testing.T) {
	dir := filepath.Join(t.TempDir(), "sessions")
	require.NoError(t, os.MkdirAll(dir, 0o755))
	fifo := filepath.Join(dir, "s.jsonl")
	require.NoError(t, syscall.Mkfifo(fifo, 0o644))
	done := make(chan error, 1)
	go func() { done <- Append(dir, "s", Entry{SessionID: "s"}) }()
	select {
	case err := <-done:
		assert.Error(t, err, "a FIFO with no reader is refused, not written")
	case <-time.After(3 * time.Second):
		// Unblock the stuck open so the goroutine and TempDir cleanup finish.
		if r, err := os.OpenFile(fifo, os.O_RDONLY|syscall.O_NONBLOCK, 0); err == nil {
			defer r.Close() //nolint:errcheck
		}
		<-done
		t.Fatal("Append blocked on a FIFO log with no reader")
	}
}

// hyperguild#173: session_log followed a symlinked sessions dir.
func TestAppendRefusesASymlinkedSessionsDir(t *testing.T) {
	root := t.TempDir()
	elsewhere := filepath.Join(root, "elsewhere")
	require.NoError(t, os.MkdirAll(elsewhere, 0o755))
	dir := filepath.Join(root, "sessions")
	require.NoError(t, os.Symlink("elsewhere", dir))
	assert.Error(t, Append(dir, "s", Entry{SessionID: "s"}))
	ents, _ := os.ReadDir(elsewhere)
	assert.Empty(t, ents, "a log was created through the symlinked dir")
}

// The sessions dir is swapped (RENAME_EXCHANGE) with a symlink to a
// directory outside the brain while Append runs. Append opens through an
// os.Root on the sessions dir's parent, so a swap can redirect it only
// inside that parent (the #167 residual), never outside it.
func TestAppendNeverCreatesALogOutsideTheParentUnderADirSwapRace(t *testing.T) {
	brain := t.TempDir()
	outside := t.TempDir()
	dir := filepath.Join(brain, "sessions")
	other := filepath.Join(brain, "sessions.link")
	require.NoError(t, os.MkdirAll(dir, 0o755))
	require.NoError(t, os.Symlink(outside, other))
	var stop atomic.Bool
	done := make(chan struct{})
	go func() {
		defer close(done)
		for !stop.Load() {
			_ = unix.Renameat2(unix.AT_FDCWD, dir, unix.AT_FDCWD, other, unix.RENAME_EXCHANGE)
		}
	}()
	ok := 0
	for i := 0; i < 20000; i++ {
		if Append(dir, fmt.Sprintf("s%d", i), Entry{SessionID: "s"}) == nil {
			ok++
		}
	}
	stop.Store(true)
	<-done
	ents, _ := os.ReadDir(outside)
	assert.Empty(t, ents, "logs were created outside the brain")
	assert.Positive(t, ok, "positive control: appends to the real dir succeed")
}

// The log file is swapped between a regular file and a symlink to another
// file in the brain while Append runs: Append writes only after confirming
// the path is the regular file it opened, so the other file never grows.
func TestAppendNeverWritesThroughALogSwappedForASymlink(t *testing.T) {
	brain := t.TempDir()
	dir := filepath.Join(brain, "sessions")
	require.NoError(t, os.MkdirAll(dir, 0o755))
	victim := filepath.Join(brain, "victim.md")
	require.NoError(t, os.WriteFile(victim, []byte("untouched\n"), 0o644))
	log := filepath.Join(dir, "s.jsonl")
	var stop atomic.Bool
	done := make(chan struct{})
	go func() {
		defer close(done)
		tmp := log + ".swap"
		for i := 0; !stop.Load(); i++ {
			_ = os.Remove(tmp)
			if i%2 == 0 {
				_ = os.WriteFile(tmp, nil, 0o644)
			} else {
				_ = os.Symlink(filepath.Join("..", "victim.md"), tmp)
			}
			_ = os.Rename(tmp, log)
		}
	}()
	ok := 0
	for i := 0; i < 20000; i++ {
		if Append(dir, "s", Entry{SessionID: "s"}) == nil {
			ok++
		}
	}
	stop.Store(true)
	<-done
	got, _ := os.ReadFile(victim)
	assert.Equal(t, "untouched\n", string(got), "a log line was written through the swapped-in symlink")
	assert.Positive(t, ok, "positive control: appends to the regular log succeed")
}