package blockchain

import (
	"bytes"
	"crypto/sha256"
	"encoding/gob"
	"encoding/hex"
	"fmt"
	"log"
	"math"
)

var (
	// zeroHash is the zero value for a Hash and is defined as
	// a package level variable to avoid the need to create a new instance
	// every time a check is needed.
	zeroHash TxID
)

type Transaction struct {
	ID        [32]byte // 32 byte hash
	TxInput   []TXInput
	TxOutput  []TXOutput
	Signature [64]byte

	Proofs []CrossShardTxProof // The proofs for crossShard tx unlock-to-commit/abort
}

// TXOutput is the struct of transaction output in a transaction.
type TXOutput struct {
	Amount  int
	Address [20]byte // last 20 bytes of the hash of public key
	ShardID uint32   // The Id of the shard where this UTXO belongs
}

type TxID = [32]byte

// Output defines a data type that is used to track previous
// transaction outputs.
// TxID is the transaction id
// Index is the index of the transaction ouput in the previous transaction
type OutPoint struct {
	TxID  TxID
	Index uint32
}

// NewOutPoint returns a new transaction outpoint point with the
// provided txID and index.
func NewOutPoint(txID *TxID, index uint32) *OutPoint {
	return &OutPoint{
		TxID:  *txID,
		Index: index,
	}
}

// TXInput is the struct of transaction input (a UTXO) in a transaction.
type TXInput struct {
	PreviousOutPoint OutPoint
	Address          [20]byte // TODO: @minh do we really need this?
	ShardID          uint32   // The Id of the shard where this UTXO belongs
}

// NewTXInput returns a new transaction input with the provided
// previous outpoint point, output address and shardID
func NewTXInput(prevOut *OutPoint, address [20]byte, shardID uint32) *TXInput {
	return &TXInput{
		PreviousOutPoint: *prevOut,
		Address:          address,
		ShardID:          shardID,
	}
}

// The proof of accept or reject in the cross shard transaction locking phase.
// This is created by the shard leader, filled with proof signatures after consensus, and returned back to the client.
// One proof structure is only tied to one shard. Therefore, the utxos in the proof are all with the same shard.
type CrossShardTxProof struct {
	Accept    bool      // false means proof-of-reject, true means proof-of-accept
	TxID      [32]byte  // Id of the transaction which this proof is on
	TxInput   []TXInput // The list of Utxo that this proof is on. They should be in the same shard.
	BlockHash [32]byte  // The hash of the block where the proof is registered
	// Signatures
}

// This is a internal data structure that doesn't go across network
type CrossShardTxAndProof struct {
	Transaction *Transaction       // The cross shard tx
	Proof       *CrossShardTxProof // The proof
}

// DefaultCoinbaseValue is the default value of coinbase transaction.
const DefaultCoinbaseValue = 1000

// SetID sets ID of a transaction (32 byte hash of the whole transaction)
func (tx *Transaction) SetID() {
	var encoded bytes.Buffer
	var hash [32]byte

	enc := gob.NewEncoder(&encoded)
	err := enc.Encode(tx)
	if err != nil {
		log.Panic(err)
	}
	hash = sha256.Sum256(encoded.Bytes())
	tx.ID = hash
}

// NewCoinbaseTX creates a new coinbase transaction
func NewCoinbaseTX(toAddress [20]byte, data string, shardID uint32) *Transaction {
	if data == "" {
		data = fmt.Sprintf("Reward to '%b'", toAddress)
	}

	txin := NewTXInput(NewOutPoint(&TxID{}, math.MaxUint32), toAddress, shardID)
	txout := TXOutput{DefaultCoinbaseValue, toAddress, shardID}
	tx := Transaction{ID: [32]byte{}, TxInput: []TXInput{*txin}, TxOutput: []TXOutput{txout}, Proofs: nil}
	tx.SetID()
	return &tx
}

// Used for debuging.
func (txInput *TXInput) String() string {
	res := fmt.Sprintf("TxID: %v, ", hex.EncodeToString(txInput.PreviousOutPoint.TxID[:]))
	res += fmt.Sprintf("TxOutputIndex: %v, ", txInput.PreviousOutPoint.Index)
	res += fmt.Sprintf("Address: %v, ", txInput.Address)
	res += fmt.Sprintf("Shard Id: %v", txInput.ShardID)
	return res
}

// Used for debuging.
func (txOutput *TXOutput) String() string {
	res := fmt.Sprintf("Amount: %v, ", txOutput.Amount)
	res += fmt.Sprintf("Address: %v", txOutput.Address)
	return res
}

// Used for debuging.
func (proof *CrossShardTxProof) String() string {
	res := fmt.Sprintf("Accept: %v, ", proof.Accept)
	return res
}

// Used for debuging.
func (tx *Transaction) String() string {
	res := fmt.Sprintf("ID: %v\n", hex.EncodeToString(tx.ID[:]))
	res += fmt.Sprintf("TxInput:\n")
	for id, value := range tx.TxInput {
		res += fmt.Sprintf("%v: %v\n", id, value.String())
	}
	res += fmt.Sprintf("TxOutput:\n")
	for id, value := range tx.TxOutput {
		res += fmt.Sprintf("%v: %v\n", id, value.String())
	}
	for id, value := range tx.Proofs {
		res += fmt.Sprintf("%v: %v\n", id, value.String())
	}
	return res
}