package blockchain

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

// Transaction represents a Bitcoin transaction
type Transaction struct {
	ID       []byte
	TxInput  []TXInput
	TxOutput []TXOutput
}

// TXOutput is the struct of transaction output in a transaction.
type TXOutput struct {
	Value   int
	Address string
}

// TXInput is the struct of transaction input in a transaction.
type TXInput struct {
	TxID          []byte
	TxOutputIndex int
	Address       string
}

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

// SetID sets ID of a 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(to, data string) *Transaction {
	if data == "" {
		data = fmt.Sprintf("Reward to '%s'", to)
	}

	txin := TXInput{[]byte{}, -1, data}
	txout := TXOutput{DefaultCoinbaseValue, to}
	tx := Transaction{nil, []TXInput{txin}, []TXOutput{txout}}
	tx.SetID()

	return &tx
}

// NewUTXOTransaction creates a new transaction
func NewUTXOTransaction(from, to string, amount int, bc *Blockchain) *Transaction {
	var inputs []TXInput
	var outputs []TXOutput

	acc, validOutputs := bc.FindSpendableOutputs(from, amount)

	if acc < amount {
		return nil
	}

	// Build a list of inputs
	for txid, outs := range validOutputs {
		txID, err := hex.DecodeString(txid)
		if err != nil {
			return nil
		}

		for _, out := range outs {
			input := TXInput{txID, out, from}
			inputs = append(inputs, input)
		}
	}

	// Build a list of outputs
	outputs = append(outputs, TXOutput{amount, to})
	if acc > amount {
		outputs = append(outputs, TXOutput{acc - amount, from}) // a change
	}

	tx := Transaction{nil, inputs, outputs}
	tx.SetID()

	return &tx
}