// Copyright 2025 the libevm authors.
//
// The libevm additions to go-ethereum are free software: you can redistribute
// them and/or modify them under the terms of the GNU Lesser General Public License
// as published by the Free Software Foundation, either version 3 of the License,
// or (at your option) any later version.
//
// The libevm additions are distributed in the hope that they will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
// General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see
// <http://www.gnu.org/licenses/>.

package rlp

import (
	"bytes"
	"io"
	"testing"

	"github.com/kr/pretty"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"

	"github.com/ava-labs/libevm/common"
)

func TestFields(t *testing.T) {
	type foo struct {
		A uint64
		B uint64
		C *uint64
		D *uint64   `rlp:"optional"`
		E []uint64  `rlp:"optional"`
		F *[]uint64 `rlp:"optional"`
	}

	const (
		a uint64 = iota
		b
		cVal
		dVal
	)
	c := common.PointerTo(cVal)
	d := common.PointerTo(dVal)
	e := []uint64{40, 41}
	f := &[]uint64{50, 51}

	tests := []foo{
		{a, b, c, d, e, f},       // 000 (which of d/e/f are nil)
		{a, b, c, d, e, nil},     // 001
		{a, b, c, d, nil, f},     // 010
		{a, b, c, d, nil, nil},   // 011
		{a, b, c, nil, e, f},     // 100
		{a, b, c, nil, e, nil},   // 101
		{a, b, c, nil, nil, f},   // 110
		{a, b, c, nil, nil, nil}, // 111
		// Empty and nil slices are treated differently when optional
		{a, b, c, nil, []uint64{}, nil},
		{a, b, c, nil, nil, &[]uint64{}},
	}

	for _, obj := range tests {
		t.Run("", func(t *testing.T) {
			t.Logf("\n%s", pretty.Sprint(obj))

			wantRLP, err := EncodeToBytes(obj)
			require.NoErrorf(t, err, "EncodeToBytes([actual struct])")

			t.Run("Fields.EncodeRLP", func(t *testing.T) {
				got, err := EncodeToBytes(&Fields{
					Required: []any{obj.A, obj.B, obj.C},
					Optional: []any{obj.D, obj.E, obj.F},
				})
				require.NoError(t, err)
				assert.Equal(t, wantRLP, got, "vs EncodeToBytes([actual struct])")
			})

			t.Run("Fields.DecodeRLP", func(t *testing.T) {
				var got foo
				err := DecodeBytes(wantRLP, &Fields{
					Required: []any{&got.A, &got.B, &got.C},
					Optional: []any{&got.D, &got.E, &got.F},
				})
				require.NoError(t, err, "DecodeBytes(..., %T)", &Fields{})

				var want foo
				err = DecodeBytes(wantRLP, &want)
				require.NoError(t, err, "DecodeBytes(..., [actual struct])")

				assert.Equal(t, want, got, "vs DecodeBytes(..., [original struct])")
			})
		})
	}
}

//nolint:testableexamples // Demonstrating code equivalence, not outputs.
func ExampleFields() {
	type inner struct {
		X uint64
	}

	type outer struct {
		A uint64
		B *inner `rlp:"nil"`
		C *inner `rlp:"optional"`
	}

	val := outer{
		A: 42,
		B: &inner{X: 42},
		C: &inner{X: 99},
	}

	// Errors are dropped for brevity for the sake of the example only.

	_ = Encode(io.Discard, val)
	// is equivalent to
	_ = Encode(
		io.Discard,
		&Fields{
			Required: []any{val.A, val.B},
			Optional: []any{val.C},
		},
	)

	var (
		r       *bytes.Reader // arbitrary RLP buffer
		decoded outer
	)

	_ = Decode(r, &decoded)
	// is equivalent to
	_ = Decode(r, &Fields{
		Required: []any{
			&decoded.A,
			Nillable(&decoded.B),
		},
		Optional: []any{&decoded.C},
	})

	// Note the parallels between the arguments passed to
	// Fields.{En,De}codeRLP() and that, when decoding an optional or
	// `rlp:"nil`-tagged field, a pointer to the _field_ is required even though
	// in this example it will be a `**inner`.
}

func TestNillable(t *testing.T) {
	type inner struct {
		X uint64
	}

	type outer struct {
		A *uint64   `rlp:"nil"`
		B *inner    `rlp:"nil"`
		C *[]uint64 `rlp:"nil"`
	}

	// Unlike the `rlp:"optional"` tag, there is no interplay between nil-tagged
	// fields so we don't need the Cartesian product of all possible
	// combinations.
	var tests []outer
	for _, a := range []*uint64{
		nil,
		common.PointerTo[uint64](0),
	} {
		tests = append(tests, outer{a, nil, nil})
	}
	for _, b := range []*inner{
		nil,
		{0},
	} {
		tests = append(tests, outer{nil, b, nil})
	}
	for _, c := range []*[]uint64{
		nil,
		{},
		{0},
	} {
		tests = append(tests, outer{nil, nil, c})
	}

	// When a Nillable encounters an empty list it MUST set the field to nil,
	// not just ignore it.
	corruptInitialValue := func() outer {
		return outer{common.PointerTo[uint64](42), &inner{42}, &[]uint64{42}}
	}

	for _, obj := range tests {
		t.Run("", func(t *testing.T) {
			rlp, err := EncodeToBytes(obj)
			require.NoErrorf(t, err, "EncodeToBytes(%+v)", obj)
			t.Logf("%s => %#x", pretty.Sprint(obj), rlp)

			// Although this is an immediate inversion of the line above, it
			// provides us with the canonical RLP decoding, which our input
			// struct may not honour.
			want := corruptInitialValue()
			err = DecodeBytes(rlp, &want)
			require.NoErrorf(t, err, "DecodeBytes(%#x, %T)", rlp, &want)

			got := corruptInitialValue()
			err = DecodeBytes(rlp, &Fields{
				Required: []any{
					Nillable(&got.A),
					Nillable(&got.B),
					Nillable(&got.C),
				},
			})
			require.NoErrorf(t, err, "DecodeBytes(..., %T)", &Fields{})

			assert.Equal(t, want, got, "DecodeBytes(..., [actual struct]) vs DecodeBytes(..., [fields wrapped in Nillable()])")
		})
	}
}