// Copyright 2020 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it 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 go-ethereum library is distributed in the hope that it 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 stacktrie

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"hash"
	"io"
	"sort"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/trie"
	"golang.org/x/crypto/sha3"
)

type fuzzer struct {
	input     io.Reader
	exhausted bool
	debugging bool
}

func (f *fuzzer) read(size int) []byte {
	out := make([]byte, size)
	if _, err := f.input.Read(out); err != nil {
		f.exhausted = true
	}
	return out
}

func (f *fuzzer) readSlice(min, max int) []byte {
	var a uint16
	binary.Read(f.input, binary.LittleEndian, &a)
	size := min + int(a)%(max-min)
	out := make([]byte, size)
	if _, err := f.input.Read(out); err != nil {
		f.exhausted = true
	}
	return out
}

// spongeDb is a dummy db backend which accumulates writes in a sponge
type spongeDb struct {
	sponge hash.Hash
	debug  bool
}

func (s *spongeDb) Has(key []byte) (bool, error)             { panic("implement me") }
func (s *spongeDb) Get(key []byte) ([]byte, error)           { return nil, errors.New("no such elem") }
func (s *spongeDb) Delete(key []byte) error                  { panic("implement me") }
func (s *spongeDb) NewBatch() ethdb.Batch                    { return &spongeBatch{s} }
func (s *spongeDb) Stat(property string) (string, error)     { panic("implement me") }
func (s *spongeDb) Compact(start []byte, limit []byte) error { panic("implement me") }
func (s *spongeDb) Close() error                             { return nil }

func (s *spongeDb) Put(key []byte, value []byte) error {
	if s.debug {
		fmt.Printf("db.Put %x : %x\n", key, value)
	}
	s.sponge.Write(key)
	s.sponge.Write(value)
	return nil
}
func (s *spongeDb) NewIterator(prefix []byte, start []byte) ethdb.Iterator { panic("implement me") }

// spongeBatch is a dummy batch which immediately writes to the underlying spongedb
type spongeBatch struct {
	db *spongeDb
}

func (b *spongeBatch) Put(key, value []byte) error {
	b.db.Put(key, value)
	return nil
}
func (b *spongeBatch) Delete(key []byte) error             { panic("implement me") }
func (b *spongeBatch) ValueSize() int                      { return 100 }
func (b *spongeBatch) Write() error                        { return nil }
func (b *spongeBatch) Reset()                              {}
func (b *spongeBatch) Replay(w ethdb.KeyValueWriter) error { return nil }

type kv struct {
	k, v []byte
}
type kvs []kv

func (k kvs) Len() int {
	return len(k)
}

func (k kvs) Less(i, j int) bool {
	return bytes.Compare(k[i].k, k[j].k) < 0
}

func (k kvs) Swap(i, j int) {
	k[j], k[i] = k[i], k[j]
}

// The function must return
// 1 if the fuzzer should increase priority of the
//    given input during subsequent fuzzing (for example, the input is lexically
//    correct and was parsed successfully);
// -1 if the input must not be added to corpus even if gives new coverage; and
// 0  otherwise
// other values are reserved for future use.
func Fuzz(data []byte) int {
	f := fuzzer{
		input:     bytes.NewReader(data),
		exhausted: false,
	}
	return f.fuzz()
}

func Debug(data []byte) int {
	f := fuzzer{
		input:     bytes.NewReader(data),
		exhausted: false,
		debugging: true,
	}
	return f.fuzz()
}

func (f *fuzzer) fuzz() int {

	// This spongeDb is used to check the sequence of disk-db-writes
	var (
		spongeA     = &spongeDb{sponge: sha3.NewLegacyKeccak256()}
		dbA         = trie.NewDatabase(spongeA)
		trieA, _    = trie.New(common.Hash{}, dbA)
		spongeB     = &spongeDb{sponge: sha3.NewLegacyKeccak256()}
		trieB       = trie.NewStackTrie(spongeB)
		vals        kvs
		useful      bool
		maxElements = 10000
	)
	// Fill the trie with elements
	for i := 0; !f.exhausted && i < maxElements; i++ {
		k := f.read(32)
		v := f.readSlice(1, 500)
		if f.exhausted {
			// If it was exhausted while reading, the value may be all zeroes,
			// thus 'deletion' which is not supported on stacktrie
			break
		}
		vals = append(vals, kv{k: k, v: v})
		trieA.Update(k, v)
		useful = true
	}
	if !useful {
		return 0
	}
	// Flush trie -> database
	rootA, err := trieA.Commit(nil)
	if err != nil {
		panic(err)
	}
	// Flush memdb -> disk (sponge)
	dbA.Commit(rootA, false, nil)

	// Stacktrie requires sorted insertion
	sort.Sort(vals)
	for _, kv := range vals {
		if f.debugging {
			fmt.Printf("{\"0x%x\" , \"0x%x\"} // stacktrie.Update\n", kv.k, kv.v)
		}
		trieB.Update(kv.k, kv.v)
	}
	rootB := trieB.Hash()
	if _, err := trieB.Commit(); err != nil {
		panic(err)
	}
	if rootA != rootB {
		panic(fmt.Sprintf("roots differ: (trie) %x != %x (stacktrie)", rootA, rootB))
	}
	sumA := spongeA.sponge.Sum(nil)
	sumB := spongeB.sponge.Sum(nil)
	if !bytes.Equal(sumA, sumB) {
		panic(fmt.Sprintf("sequence differ: (trie) %x != %x (stacktrie)", sumA, sumB))
	}
	return 1
}