package notes

import (
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"testing"

	"github.com/stretchr/testify/require"
)

// lockChild runs inside a re-executed test binary: it takes the note's edit
// lock N times and, while holding it, creates an O_EXCL marker. Finding the
// marker already there means another process holds the "same" lock: mutual
// exclusion failed. It prints the overlap count.
func lockChild(brainDir string, rounds int) {
	t, err := Resolve(brainDir, "wiki/w/facts/n.md", ScopeNotes)
	if err != nil {
		fmt.Println("resolve:", err)
		os.Exit(2)
	}
	marker := filepath.Join(brainDir, "marker")
	overlaps := 0
	for i := 0; i < rounds; i++ {
		unlock, err := flockFile(t)
		if err != nil {
			fmt.Println("lock:", err)
			os.Exit(2)
		}
		f, err := os.OpenFile(marker, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o644)
		if errors.Is(err, os.ErrExist) {
			overlaps++
		} else if err == nil {
			_ = f.Close()
			_ = os.Remove(marker)
		}
		unlock()
	}
	fmt.Println(overlaps)
	os.Exit(0)
}

func TestMain(m *testing.M) {
	if dir := os.Getenv("NOTES_LOCK_CHILD"); dir != "" {
		n, _ := strconv.Atoi(os.Getenv("NOTES_LOCK_ROUNDS"))
		lockChild(dir, n)
	}
	os.Exit(m.Run())
}

// hyperguild#192: the edit lock must exclude other processes (two ingestion
// pods share the hostPath brain during a RollingUpdate). Unlock removes the
// lock file, so without re-checking that the locked file is still the one at
// the path, a waiter and the next caller each held a lock (measured on main:
// hundreds of overlaps in 2000 rounds).
func TestEditLockExcludesOtherProcesses(t *testing.T) {
	brain := t.TempDir()
	require.NoError(t, os.MkdirAll(filepath.Join(brain, "wiki", "w", "facts"), 0o755))
	require.NoError(t, os.WriteFile(filepath.Join(brain, "wiki", "w", "facts", "n.md"), []byte("x"), 0o644))
	const procs, rounds = 3, 400
	cmds := make([]*exec.Cmd, procs)
	outs := make([]*strings.Builder, procs)
	for i := range cmds {
		outs[i] = &strings.Builder{}
		cmds[i] = exec.Command(os.Args[0], "-test.run=^$")
		cmds[i].Env = append(os.Environ(), "NOTES_LOCK_CHILD="+brain, "NOTES_LOCK_ROUNDS="+strconv.Itoa(rounds))
		cmds[i].Stdout, cmds[i].Stderr = outs[i], outs[i]
		require.NoError(t, cmds[i].Start())
	}
	total := 0
	for i, c := range cmds {
		require.NoError(t, c.Wait(), "child %d: %s", i, outs[i].String())
		n, err := strconv.Atoi(strings.TrimSpace(outs[i].String()))
		require.NoError(t, err, "child %d output: %q", i, outs[i].String())
		total += n
	}
	require.Zero(t, total, "processes held the edit lock at the same time")
}