package blobgen_test

import (
	"bytes"
	"io"
	"testing"

	"github.com/stretchr/testify/require"
	"sneak.berlin/go/vaultik/internal/blobgen"
)

// TestLimitReaderPassesExactSize checks that a stream of exactly the limit
// reads back cleanly to EOF: the bound must not reject a legitimate blob
// whose plaintext equals its recorded size.
func TestLimitReaderPassesExactSize(t *testing.T) {
	t.Parallel()

	const n = 1000

	r := blobgen.LimitReader(bytes.NewReader(bytes.Repeat([]byte("a"), n)), n)

	got, err := io.ReadAll(r)
	require.NoError(t, err)
	require.Len(t, got, n)
}

// TestLimitReaderFailsPastLimit feeds a large, highly compressible run of
// zeros — the decompressed output a zip bomb would produce — through a
// small limit and checks it fails within the bound rather than passing
// the whole stream through.
func TestLimitReaderFailsPastLimit(t *testing.T) {
	t.Parallel()

	const limit = 1000

	r := blobgen.LimitReader(
		bytes.NewReader(bytes.Repeat([]byte{0}, limit*1000)), limit)

	n, err := io.Copy(io.Discard, r)
	require.ErrorIs(t, err, blobgen.ErrOutputTooLarge)
	require.LessOrEqual(t, n, int64(limit)+1,
		"reader must stop within one byte of the limit")
}