// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

//go:build linux

package nfsfs

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

// cloneTestFS builds a backend over a fresh directory holding a source
// file of the given content.
func cloneTestFS(t *testing.T, content []byte) (*Local, Handle, Handle, string) {
	t.Helper()
	root := t.TempDir()
	l, err := NewLocal(root)
	if err != nil {
		t.Fatalf("NewLocal: %v", err)
	}
	if err := os.WriteFile(filepath.Join(root, "src"), content, 0o644); err != nil {
		t.Fatalf("WriteFile: %v", err)
	}
	if err := os.WriteFile(filepath.Join(root, "dst"), make([]byte, len(content)), 0o644); err != nil {
		t.Fatalf("WriteFile: %v", err)
	}
	rh, err := l.Root()
	if err != nil {
		t.Fatalf("Root: %v", err)
	}
	src, _, err := l.Lookup(rh, "src")
	if err != nil {
		t.Fatalf("Lookup src: %v", err)
	}
	dst, _, err := l.Lookup(rh, "dst")
	if err != nil {
		t.Fatalf("Lookup dst: %v", err)
	}
	return l, src, dst, filepath.Join(root, "dst")
}

// TestCopyRangeKernel drives the kernel copy and verifies the bytes
// landed. Filesystems that refuse the syscall for their files skip the
// test: the handler falls back to its userspace path either way.
func TestCopyRangeKernel(t *testing.T) {
	content := make([]byte, 1<<20)
	for i := range content {
		content[i] = byte(i * 3)
	}
	l, src, dst, dstPath := cloneTestFS(t, content)
	if err := l.CopyRange(src, 0, dst, 0, int64(len(content))); err != nil {
		if errors.Is(err, syscall.ENOSYS) || errors.Is(err, syscall.EOPNOTSUPP) ||
			errors.Is(err, syscall.EXDEV) || errors.Is(err, syscall.EINVAL) {
			t.Skipf("the filesystem refuses copy_file_range: %v", err)
		}
		t.Fatalf("CopyRange: %v", err)
	}
	got, err := os.ReadFile(dstPath)
	if err != nil {
		t.Fatalf("ReadFile: %v", err)
	}
	if !bytes.Equal(got, content) {
		t.Fatalf("the copied bytes differ: %d vs %d", len(got), len(content))
	}
}

// TestCloneRangeKernel drives the reflink where the filesystem provides
// one, and verifies the clone reads back as the source.
func TestCloneRangeKernel(t *testing.T) {
	content := make([]byte, 1<<20)
	for i := range content {
		content[i] = byte(i * 7)
	}
	l, src, dst, dstPath := cloneTestFS(t, content)
	err := l.CloneRange(src, 0, dst, 0, int64(len(content)))
	if err != nil {
		if errors.Is(err, syscall.EOPNOTSUPP) || errors.Is(err, syscall.EXDEV) ||
			errors.Is(err, syscall.EINVAL) || errors.Is(err, syscall.EBADF) {
			t.Skipf("the filesystem refuses FICLONERANGE: %v", err)
		}
		t.Fatalf("CloneRange: %v", err)
	}
	got, err := os.ReadFile(dstPath)
	if err != nil {
		t.Fatalf("ReadFile: %v", err)
	}
	if !bytes.Equal(got, content) {
		t.Fatalf("the cloned bytes differ: %d vs %d", len(got), len(content))
	}
}