//nolint:testpackage // white-box tests exercise unexported internals
package cli

import (
	"bytes"
	"errors"
	"fmt"
	"math/rand"
	"os"
	"sync"
	"testing"

	"github.com/spf13/afero"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	urfcli "github.com/urfave/cli/v2"
	"sneak.berlin/go/mfer/mfer"
)

const (
	testApp         = "mfer"
	testDir         = "/testdir"
	testFile1       = "/testdir/file1.txt"
	testMF          = "/testdir/test.mf"
	testOutput      = "/output.mf"
	testOutputTmp   = "/output.mf.tmp"
	testManifest    = "/manifest.mf"
	testFlagBase    = "--base"
	testFlagNoExtra = "--no-extra-files"
)

var errSimulatedWrite = errors.New("simulated write failure")

// runMu serializes CLI runs: RunWithOptions wires the process-global
// logger to the run's I/O streams, so parallel runs would cross-wire
// captured output between tests.
//
//nolint:gochecknoglobals // guards process-global logger state in tests
var runMu sync.Mutex

// runCLI invokes RunWithOptions while holding runMu so parallel tests
// capture their own output.
func runCLI(opts *RunOptions) int {
	runMu.Lock()
	defer runMu.Unlock()

	return RunWithOptions(opts)
}

func TestMain(m *testing.M) {
	// Prevent urfave/cli from calling os.Exit during tests
	urfcli.OsExiter = func(_ int) {}

	os.Exit(m.Run())
}

func TestBuild(t *testing.T) {
	t.Parallel()

	m := &CLIApp{}
	assert.NotNil(t, m)
}

func testOpts(args []string, fs afero.Fs) *RunOptions {
	return &RunOptions{
		Appname: testApp,
		Version: "1.0.0",
		Gitrev:  "abc123",
		Args:    args,
		Stdin:   &bytes.Buffer{},
		Stdout:  &bytes.Buffer{},
		Stderr:  &bytes.Buffer{},
		Fs:      fs,
	}
}

func testStdout(t *testing.T, opts *RunOptions) string {
	t.Helper()

	buf, ok := opts.Stdout.(*bytes.Buffer)
	require.True(t, ok)

	return buf.String()
}

func testStderr(t *testing.T, opts *RunOptions) string {
	t.Helper()

	buf, ok := opts.Stderr.(*bytes.Buffer)
	require.True(t, ok)

	return buf.String()
}

func writeTestFile(t *testing.T, fs afero.Fs, path, content string) {
	t.Helper()

	require.NoError(t, afero.WriteFile(fs, path, []byte(content), 0o644))
}

func TestVersionCommand(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()
	opts := testOpts([]string{testApp, "version"}, fs)

	exitCode := runCLI(opts)

	assert.Equal(t, 0, exitCode)

	stdout := testStdout(t, opts)
	assert.Contains(t, stdout, mfer.Version)
	assert.Contains(t, stdout, "abc123")
}

func TestHelpCommand(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()
	opts := testOpts([]string{testApp, "--help"}, fs)

	exitCode := runCLI(opts)

	assert.Equal(t, 0, exitCode)

	stdout := testStdout(t, opts)
	assert.Contains(t, stdout, cmdGenerate)
	assert.Contains(t, stdout, cmdCheck)
	assert.Contains(t, stdout, "fetch")
}

func TestGenerateCommand(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test files in memory filesystem
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello world")
	writeTestFile(t, fs, "/testdir/file2.txt", "test content")

	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testMF, testDir}, fs)

	exitCode := runCLI(opts)

	assert.Equal(t, 0, exitCode, "stderr: %s", testStderr(t, opts))

	// Verify manifest was created
	exists, err := afero.Exists(fs, testMF)
	require.NoError(t, err)
	assert.True(t, exists)
}

func TestGenerateAndCheckCommand(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test files with subdirectory
	require.NoError(t, fs.MkdirAll("/testdir/subdir", 0o755))
	writeTestFile(t, fs, testFile1, "hello world")
	writeTestFile(t, fs, "/testdir/subdir/file2.txt", "test content")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testMF, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode, "generate failed: %s", testStderr(t, opts))

	// Check manifest
	opts = testOpts([]string{testApp, cmdCheck, "-q", testFlagBase, testDir, testMF}, fs)
	exitCode = runCLI(opts)
	assert.Equal(t, 0, exitCode, "check failed: %s", testStderr(t, opts))
}

func TestCheckCommandWithMissingFile(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test file
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello world")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testMF, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode, "generate failed: %s", testStderr(t, opts))

	// Delete the file
	require.NoError(t, fs.Remove(testFile1))

	// Check manifest - should fail
	opts = testOpts([]string{testApp, cmdCheck, "-q", testFlagBase, testDir, testMF}, fs)
	exitCode = runCLI(opts)
	assert.Equal(t, 1, exitCode, "check should have failed for missing file")
}

func runCheckAfterRewrite(t *testing.T, rewritten, msg string) {
	t.Helper()

	fs := afero.NewMemMapFs()

	// Create test file
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello world")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testMF, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode, "generate failed: %s", testStderr(t, opts))

	// Rewrite the file, then check the manifest - it must fail
	writeTestFile(t, fs, testFile1, rewritten)

	opts = testOpts([]string{testApp, cmdCheck, "-q", testFlagBase, testDir, testMF}, fs)
	exitCode = runCLI(opts)
	assert.Equal(t, 1, exitCode, msg)
}

func TestCheckCommandWithCorruptedFile(t *testing.T) {
	t.Parallel()

	// Corrupt the file (change content but keep same size)
	runCheckAfterRewrite(t, "HELLO WORLD",
		"check should have failed for corrupted file")
}

func TestCheckCommandWithSizeMismatch(t *testing.T) {
	t.Parallel()

	// Change file size
	runCheckAfterRewrite(t, "different size content here",
		"check should have failed for size mismatch")
}

func TestBannerOutput(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test file
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")

	// Run without -q to see banner
	opts := testOpts([]string{testApp, cmdGenerate, "-o", testMF, testDir}, fs)
	exitCode := runCLI(opts)
	assert.Equal(t, 0, exitCode)

	// Banner ASCII art should be in stdout
	stdout := testStdout(t, opts)
	assert.Contains(t, stdout, "___")
	assert.Contains(t, stdout, "\\")
}

func TestUnknownCommand(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()
	opts := testOpts([]string{testApp, "unknown"}, fs)

	exitCode := runCLI(opts)
	assert.Equal(t, 1, exitCode)
}

func TestGenerateExcludesDotfilesByDefault(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test files including dotfiles
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")
	writeTestFile(t, fs, "/testdir/.hidden", "secret")

	// Generate manifest without --include-dotfiles (default excludes dotfiles)
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testMF, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Check that manifest exists
	exists, _ := afero.Exists(fs, testMF)
	assert.True(t, exists)

	// Verify manifest only has 1 file (the non-dotfile)
	manifest, err := mfer.NewManifestFromFile(fs, testMF)
	require.NoError(t, err)
	assert.Len(t, manifest.Files(), 1)
	assert.Equal(t, "file1.txt", manifest.Files()[0].GetPath())
}

func TestGenerateWithIncludeDotfiles(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test files including dotfiles
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")
	writeTestFile(t, fs, "/testdir/.hidden", "secret")

	// Generate manifest with --include-dotfiles
	opts := testOpts([]string{
		testApp, cmdGenerate, "-q", "--include-dotfiles", "-o", testMF, testDir,
	}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Verify manifest has 2 files (including dotfile)
	manifest, err := mfer.NewManifestFromFile(fs, testMF)
	require.NoError(t, err)
	assert.Len(t, manifest.Files(), 2)
}

func TestMultipleInputPaths(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test files in multiple directories
	require.NoError(t, fs.MkdirAll("/dir1", 0o755))
	require.NoError(t, fs.MkdirAll("/dir2", 0o755))
	writeTestFile(t, fs, "/dir1/file1.txt", "content1")
	writeTestFile(t, fs, "/dir2/file2.txt", "content2")

	// Generate manifest from multiple paths
	opts := testOpts([]string{
		testApp, cmdGenerate, "-q", "-o", testOutput, "/dir1", "/dir2",
	}, fs)
	exitCode := runCLI(opts)
	assert.Equal(t, 0, exitCode, "stderr: %s", testStderr(t, opts))

	exists, _ := afero.Exists(fs, testOutput)
	assert.True(t, exists)
}

func TestNoExtraFilesPass(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test files
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")
	writeTestFile(t, fs, "/testdir/file2.txt", "world")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testManifest, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Check with --no-extra-files (should pass - no extra files)
	opts = testOpts([]string{
		testApp, cmdCheck, "-q", testFlagNoExtra, testFlagBase, testDir, testManifest,
	}, fs)
	exitCode = runCLI(opts)
	assert.Equal(t, 0, exitCode)
}

func TestNoExtraFilesFail(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test files
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testManifest, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Add an extra file after manifest generation
	writeTestFile(t, fs, "/testdir/extra.txt", "extra")

	// Check with --no-extra-files (should fail - extra file exists)
	opts = testOpts([]string{
		testApp, cmdCheck, "-q", testFlagNoExtra, testFlagBase, testDir, testManifest,
	}, fs)
	exitCode = runCLI(opts)
	assert.Equal(t, 1, exitCode, "check should fail when extra files exist")
}

func TestNoExtraFilesWithSubdirectory(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test files with subdirectory
	require.NoError(t, fs.MkdirAll("/testdir/subdir", 0o755))
	writeTestFile(t, fs, testFile1, "hello")
	writeTestFile(t, fs, "/testdir/subdir/file2.txt", "world")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testManifest, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Add extra file in subdirectory
	writeTestFile(t, fs, "/testdir/subdir/extra.txt", "extra")

	// Check with --no-extra-files (should fail)
	opts = testOpts([]string{
		testApp, cmdCheck, "-q", testFlagNoExtra, testFlagBase, testDir, testManifest,
	}, fs)
	exitCode = runCLI(opts)
	assert.Equal(t, 1, exitCode,
		"check should fail when extra files exist in subdirectory")
}

func TestCheckWithoutNoExtraFilesIgnoresExtra(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test file
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testManifest, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Add extra file
	writeTestFile(t, fs, "/testdir/extra.txt", "extra")

	// Check WITHOUT --no-extra-files (should pass - extra files ignored)
	opts = testOpts([]string{
		testApp, cmdCheck, "-q", testFlagBase, testDir, testManifest,
	}, fs)
	exitCode = runCLI(opts)
	assert.Equal(t, 0, exitCode,
		"check without --no-extra-files should ignore extra files")
}

func TestGenerateAtomicWriteNoTempFileOnSuccess(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test file
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testOutput, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Verify output file exists
	exists, err := afero.Exists(fs, testOutput)
	require.NoError(t, err)
	assert.True(t, exists, "output file should exist")

	// Verify temp file does NOT exist
	tmpExists, err := afero.Exists(fs, testOutputTmp)
	require.NoError(t, err)
	assert.False(t, tmpExists,
		"temp file should not exist after successful generation")
}

func TestGenerateAtomicWriteOverwriteWithForce(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test file
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")

	// Create existing manifest with different content
	writeTestFile(t, fs, testOutput, "old content")

	// Generate manifest with --force
	opts := testOpts([]string{
		testApp, cmdGenerate, "-q", "-f", "-o", testOutput, testDir,
	}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Verify output file exists and was overwritten
	content, err := afero.ReadFile(fs, testOutput)
	require.NoError(t, err)
	assert.NotEqual(t, "old content", string(content),
		"manifest should be overwritten")

	// Verify temp file does NOT exist
	tmpExists, err := afero.Exists(fs, testOutputTmp)
	require.NoError(t, err)
	assert.False(t, tmpExists,
		"temp file should not exist after successful generation")
}

func TestGenerateFailsWithoutForceWhenOutputExists(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()

	// Create test file
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")

	// Create existing manifest
	writeTestFile(t, fs, testOutput, "existing")

	// Generate manifest WITHOUT --force (should fail)
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testOutput, testDir}, fs)
	exitCode := runCLI(opts)
	assert.Equal(t, 1, exitCode, "should fail when output exists without --force")

	// Verify original content is preserved
	content, err := afero.ReadFile(fs, testOutput)
	require.NoError(t, err)
	assert.Equal(t, "existing", string(content), "original file should be preserved")
}

func TestGenerateAtomicWriteUsesTemp(t *testing.T) {
	t.Parallel()

	// This test verifies that generate uses a temp file by checking
	// that the output file doesn't exist until generation completes.
	// We do this by generating to a path and verifying the temp file
	// pattern is used (output.mf.tmp -> output.mf)
	fs := afero.NewMemMapFs()

	// Create test file
	require.NoError(t, fs.MkdirAll(testDir, 0o755))
	writeTestFile(t, fs, testFile1, "hello")

	// Generate manifest
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testOutput, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode)

	// Both output file should exist and temp should not
	exists, _ := afero.Exists(fs, testOutput)
	assert.True(t, exists, "output file should exist")

	tmpExists, _ := afero.Exists(fs, testOutputTmp)
	assert.False(t, tmpExists, "temp file should be cleaned up")

	// Verify manifest is valid (not empty)
	content, err := afero.ReadFile(fs, testOutput)
	require.NoError(t, err)
	assert.NotEmpty(t, content, "manifest should not be empty")
}

// failingWriterFs wraps a filesystem and makes writes fail after N bytes
type failingWriterFs struct {
	afero.Fs

	failAfter int64
	written   int64
}

type failingFile struct {
	afero.File

	fs *failingWriterFs
}

func (f *failingFile) Write(p []byte) (int, error) {
	f.fs.written += int64(len(p))
	if f.fs.written > f.fs.failAfter {
		return 0, errSimulatedWrite
	}

	return f.File.Write(p)
}

//nolint:ireturn // Create must return afero.File to satisfy afero.Fs.
func (fs *failingWriterFs) Create(name string) (afero.File, error) {
	f, err := fs.Fs.Create(name)
	if err != nil {
		return nil, err
	}

	return &failingFile{File: f, fs: fs}, nil
}

func TestGenerateAtomicWriteCleansUpOnError(t *testing.T) {
	t.Parallel()

	baseFs := afero.NewMemMapFs()

	// Create test files - need enough content to trigger the write failure
	require.NoError(t, baseFs.MkdirAll(testDir, 0o755))
	writeTestFile(t, baseFs, testFile1, "hello world this is a test file")

	// Wrap with failing writer that fails after writing some bytes
	fs := &failingWriterFs{Fs: baseFs, failAfter: 10}

	// Generate manifest - should fail during write
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testOutput, testDir}, fs)
	exitCode := runCLI(opts)
	assert.Equal(t, 1, exitCode, "should fail due to write error")

	// With atomic writes: output.mf should NOT exist (temp was cleaned up)
	// With non-atomic writes: output.mf WOULD exist (partial/empty)
	exists, _ := afero.Exists(baseFs, testOutput)
	assert.False(t, exists,
		"output file should not exist after failed generation (atomic write)")

	// Temp file should also not exist
	tmpExists, _ := afero.Exists(baseFs, testOutputTmp)
	assert.False(t, tmpExists,
		"temp file should be cleaned up after failed generation")
}

func TestGenerateValidatesInputPaths(t *testing.T) {
	t.Parallel()

	seedValidDir := func(t *testing.T, fs afero.Fs) {
		t.Helper()

		require.NoError(t, fs.MkdirAll("/validdir", 0o755))
		writeTestFile(t, fs, "/validdir/file.txt", "content")
	}

	t.Run("nonexistent path fails fast", func(t *testing.T) {
		t.Parallel()

		fs := afero.NewMemMapFs()
		seedValidDir(t, fs)

		opts := testOpts([]string{
			testApp, cmdGenerate, "-q", "-o", testOutput, "/nonexistent",
		}, fs)
		exitCode := runCLI(opts)
		assert.Equal(t, 1, exitCode)

		stderr := testStderr(t, opts)
		assert.Contains(t, stderr, "path does not exist")
		assert.Contains(t, stderr, "/nonexistent")
	})

	t.Run("mix of valid and invalid paths fails fast", func(t *testing.T) {
		t.Parallel()

		fs := afero.NewMemMapFs()
		seedValidDir(t, fs)

		opts := testOpts([]string{
			testApp, cmdGenerate, "-q", "-o", testOutput,
			"/validdir", "/alsononexistent",
		}, fs)
		exitCode := runCLI(opts)
		assert.Equal(t, 1, exitCode)

		stderr := testStderr(t, opts)
		assert.Contains(t, stderr, "path does not exist")
		assert.Contains(t, stderr, "/alsononexistent")

		// Output file should not have been created
		exists, _ := afero.Exists(fs, testOutput)
		assert.False(t, exists,
			"output file should not exist when path validation fails")
	})

	t.Run("valid paths succeed", func(t *testing.T) {
		t.Parallel()

		fs := afero.NewMemMapFs()
		seedValidDir(t, fs)

		opts := testOpts([]string{
			testApp, cmdGenerate, "-q", "-o", testOutput, "/validdir",
		}, fs)
		exitCode := runCLI(opts)
		assert.Equal(t, 0, exitCode)
	})
}

func TestCheckDetectsManifestCorruption(t *testing.T) {
	t.Parallel()

	fs := afero.NewMemMapFs()
	rng := rand.New(rand.NewSource(42)) //nolint:gosec // deterministic test data

	// Create many small files with random names to generate a ~1MB manifest
	// Each manifest entry is roughly 50-60 bytes, so we need ~20000 files
	require.NoError(t, fs.MkdirAll(testDir, 0o755))

	numFiles := 20000
	for range numFiles {
		// Generate random filename
		filename := fmt.Sprintf("/testdir/%08x%08x%08x.dat",
			rng.Uint32(), rng.Uint32(), rng.Uint32())
		// Small random content
		content := make([]byte, 16+rng.Intn(48))
		_, _ = rng.Read(content)
		require.NoError(t, afero.WriteFile(fs, filename, content, 0o644))
	}

	// Generate manifest outside of testdir
	opts := testOpts([]string{testApp, cmdGenerate, "-q", "-o", testManifest, testDir}, fs)
	exitCode := runCLI(opts)
	require.Equal(t, 0, exitCode, "generate should succeed")

	// Read the valid manifest and verify it's approximately 1MB
	validManifest, err := afero.ReadFile(fs, testManifest)
	require.NoError(t, err)
	require.GreaterOrEqual(t, len(validManifest), 1024*1024,
		"manifest should be at least 1MB, got %d bytes", len(validManifest))
	t.Logf("manifest size: %d bytes (%d files)", len(validManifest), numFiles)

	// First corruption: truncate the manifest
	require.NoError(t, afero.WriteFile(fs, testManifest,
		validManifest[:len(validManifest)/2], 0o644))

	// Check should fail with truncated manifest
	opts = testOpts([]string{
		testApp, cmdCheck, "-q", testFlagBase, testDir, testManifest,
	}, fs)
	exitCode = runCLI(opts)
	assert.Equal(t, 1, exitCode, "check should fail with truncated manifest")

	// Verify check passes with valid manifest
	require.NoError(t, afero.WriteFile(fs, testManifest, validManifest, 0o644))

	opts = testOpts([]string{
		testApp, cmdCheck, "-q", testFlagBase, testDir, testManifest,
	}, fs)
	exitCode = runCLI(opts)
	require.Equal(t, 0, exitCode, "check should pass with valid manifest")

	// Now do 500 random corruption iterations
	for i := range 500 {
		// Corrupt: write a random byte at a random offset
		corrupted := make([]byte, len(validManifest))
		copy(corrupted, validManifest)

		offset := rng.Intn(len(corrupted))
		originalByte := corrupted[offset]

		// Make sure we actually change the byte
		buf := make([]byte, 1)

		newByte := originalByte
		for newByte == originalByte {
			_, _ = rng.Read(buf)
			newByte = buf[0]
		}

		corrupted[offset] = newByte

		require.NoError(t, afero.WriteFile(fs, testManifest, corrupted, 0o644))

		// Check should fail with corrupted manifest
		opts = testOpts([]string{
			testApp, cmdCheck, "-q", testFlagBase, testDir, testManifest,
		}, fs)
		exitCode = runCLI(opts)
		assert.Equal(t, 1, exitCode,
			"iteration %d: check should fail with corrupted manifest "+
				"(offset %d, 0x%02x -> 0x%02x)",
			i, offset, originalByte, newByte)

		// Restore valid manifest for next iteration
		require.NoError(t, afero.WriteFile(fs, testManifest, validManifest, 0o644))
	}
}