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

package xdr

import (
	"testing"
)

// FuzzDecoder feeds arbitrary bytes through every read of the decoder:
// no input may panic, hang or index out of range, and every failure
// arrives as an error.
func FuzzDecoder(f *testing.F) {
	f.Add([]byte{0, 0, 0, 1})
	f.Add([]byte{0xff, 0xff, 0xff, 0xff})
	f.Add([]byte{0, 0, 0, 2, 'a', 'b', 0})
	f.Add([]byte{0, 0, 0, 5, 'h', 'e', 'l', 'l', 'o'})
	f.Add([]byte{0x7f})
	f.Add(make([]byte, 64))
	f.Fuzz(func(t *testing.T, data []byte) {
		d := NewDecoder(data)
		_, _ = d.Uint32()
		_, _ = d.Int64()
		_, _ = d.Uint64()
		_, _ = d.Bool()
		_, _ = d.String()
		_, _ = d.VarOpaque()
		_, _ = d.FixedOpaque(4)
		_, _ = d.Raw(3)
		_ = d.Remaining()

		// The writers must accept the decoded values back and the
		// re-decode must agree or fail cleanly.
		d2 := NewDecoder(data)
		if s, err := d2.String(); err == nil {
			again, aerr := NewDecoder(AppendString(nil, s)).String()
			if aerr != nil || again != s {
				t.Fatalf("string round trip: %q %v %q", s, aerr, again)
			}
		}
		if o, err := d2.VarOpaque(); err == nil {
			again, aerr := NewDecoder(AppendVarOpaque(nil, o)).VarOpaque()
			if aerr != nil || string(again) != string(o) {
				t.Fatal("opaque round trip")
			}
		}
	})
}

// FuzzPadding checks the pad arithmetic against the property that an
// encoded value always decodes back to itself, whatever the length.
func FuzzPadding(f *testing.F) {
	f.Add([]byte{})
	f.Add([]byte("a"))
	f.Add([]byte("abc"))
	f.Add([]byte("abcd"))
	f.Fuzz(func(t *testing.T, data []byte) {
		enc := AppendVarOpaque(nil, data)
		got, err := NewDecoder(enc).VarOpaque()
		if err != nil {
			t.Fatalf("decode of a value this package encoded: %v", err)
		}
		if string(got) != string(data) {
			t.Fatalf("round trip: %q became %q", data, got)
		}
	})
}