//go:build linux

package safeio

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

func TestReadCanonicalRegularRejectsReplacementDuringRead(t *testing.T) {
	root := t.TempDir()
	path := filepath.Join(root, "schema.sql")
	replacement := filepath.Join(root, "replacement.sql")
	parked := filepath.Join(root, "parked.sql")
	contents := make([]byte, 64<<20)
	if err := os.WriteFile(path, contents, 0o600); err != nil {
		t.Fatal(err)
	}
	if err := os.WriteFile(replacement, contents, 0o600); err != nil {
		t.Fatal(err)
	}

	entered := make(chan struct{})
	proceed := make(chan struct{})
	beforeBoundedRead = func() {
		close(entered)
		<-proceed
	}
	t.Cleanup(func() { beforeBoundedRead = nil })
	result := make(chan error, 1)
	go func() { _, err := ReadCanonicalRegular(path, int64(len(contents))); result <- err }()
	<-entered
	if err := os.Rename(path, parked); err != nil {
		t.Fatal(err)
	}
	if err := os.Rename(replacement, path); err != nil {
		t.Fatal(err)
	}
	close(proceed)
	err := <-result
	if !errors.Is(err, ErrUnsafeFile) {
		t.Fatalf("replacement during read error = %v, want ErrUnsafeFile", err)
	}
}