package api

import (
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"testing"
	"testing/fstest"

	"github.com/umputun/remark42/backend/app/webassets"

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

func TestWebFiles_Open(t *testing.T) {
	frontend := fstest.MapFS{
		"both.html":          {Data: []byte("from the frontend build")},
		"only-frontend.html": {Data: []byte("frontend only")},
	}
	embedded := fstest.MapFS{
		"both.html":          {Data: []byte("from the embedded assets")},
		"only-embedded.html": {Data: []byte("embedded only")},
	}
	w := webFiles{frontend: frontend, embedded: embedded}

	tbl := []struct {
		name    string
		lookup  string
		want    string
		wantErr error
	}{
		{name: "present in both is served from the frontend build", lookup: "both.html", want: "from the frontend build"},
		{name: "frontend only", lookup: "only-frontend.html", want: "frontend only"},
		{name: "embedded only", lookup: "only-embedded.html", want: "embedded only"},
		{name: "missing in both", lookup: "neither.html", wantErr: fs.ErrNotExist},
	}

	for _, tt := range tbl {
		t.Run(tt.name, func(t *testing.T) {
			f, err := w.Open(tt.lookup)
			if tt.wantErr != nil {
				require.Error(t, err)
				assert.ErrorIs(t, err, tt.wantErr)
				return
			}
			require.NoError(t, err)
			defer f.Close()
			b, err := io.ReadAll(f)
			require.NoError(t, err)
			assert.Equal(t, tt.want, string(b))
		})
	}
}

// TestEmptyFS_ServesNothing pins the stand-in used when the frontend source cannot be opened:
// every name must report as missing rather than panicking, since it backs a nil-free fallback.
func TestEmptyFS_ServesNothing(t *testing.T) {
	for _, name := range []string{".", "index.html", "web/index.html"} {
		t.Run(name, func(t *testing.T) {
			f, err := emptyFS{}.Open(name)
			require.Error(t, err)
			assert.ErrorIs(t, err, fs.ErrNotExist)
			assert.Nil(t, f)
		})
	}
}

// TestWebFiles_EmptyFrontendFallsThrough covers the shape routes() builds when fs.Sub refuses:
// the embedded assets must still answer even though the frontend source serves nothing.
func TestWebFiles_EmptyFrontendFallsThrough(t *testing.T) {
	w := webFiles{frontend: emptyFS{}, embedded: webassets.FS}

	want, err := fs.ReadFile(webassets.FS, "privacy.html")
	require.NoError(t, err)

	f, err := w.Open("privacy.html")
	require.NoError(t, err)
	defer f.Close()
	got, err := io.ReadAll(f)
	require.NoError(t, err)
	assert.Equal(t, string(want), string(got))
}

// TestWebFiles_OpenRootIsNotListed keeps the embedded assets from being browsable: they answer
// for their own names only, so a web root that has gone missing reports as missing.
func TestWebFiles_OpenRootIsNotListed(t *testing.T) {
	w := webFiles{frontend: os.DirFS(filepath.Join(t.TempDir(), "absent")), embedded: webassets.FS}

	f, err := w.Open(".")
	require.Error(t, err, "the embedded assets must not answer for the directory itself")
	assert.ErrorIs(t, err, fs.ErrNotExist)
	if err == nil {
		_ = f.Close()
	}

	// the assets themselves still serve
	f, err = w.Open("privacy.html")
	require.NoError(t, err)
	require.NoError(t, f.Close())
}

// TestWebFiles_OpenInvalidName pins that a name fs rejects reports as missing rather than invalid.
// os.DirFS returns fs.ErrInvalid for these, which http.FileServer renders as 500, so the check has
// to happen before the lookup. A memory filesystem cannot show this: it reports missing either way.
func TestWebFiles_OpenInvalidName(t *testing.T) {
	dir := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(dir, "privacy.html"), []byte("frontend"), 0o600))
	w := webFiles{frontend: os.DirFS(dir), embedded: webassets.FS}

	for _, name := range []string{"../escape.html", "/etc/passwd", "a\x00b.html", "./privacy.html"} {
		t.Run(name, func(t *testing.T) {
			f, err := w.Open(name)
			require.Error(t, err)
			assert.ErrorIs(t, err, fs.ErrNotExist)
			assert.NotErrorIs(t, err, fs.ErrInvalid, "an invalid name must not surface as 500")
			if err == nil {
				_ = f.Close()
			}
		})
	}
}

// TestWebFiles_OpenUnreadableFrontendFile pins the rule that only a missing file falls through:
// a frontend file that cannot be read must report that, not be masked by the embedded copy.
func TestWebFiles_OpenUnreadableFrontendFile(t *testing.T) {
	if os.Geteuid() == 0 {
		t.Skip("root ignores file permissions")
	}

	dir := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(dir, "privacy.html"), []byte("operator's own"), 0o000))

	w := webFiles{
		frontend: os.DirFS(dir),
		embedded: fstest.MapFS{"privacy.html": {Data: []byte("built in")}},
	}

	f, err := w.Open("privacy.html")
	require.Error(t, err, "an unreadable frontend file must not be replaced by the embedded copy")
	assert.NotErrorIs(t, err, fs.ErrNotExist, "the error must stay a permission error so it does not render as 404")
	assert.ErrorIs(t, err, fs.ErrPermission)
	if err == nil {
		_ = f.Close()
	}
}