// Package models provides the models for the KermaGo application
package models

import (
	"bytes"
	"crypto/ed25519"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"kerma/helpers"
	"strconv"

	"github.com/docker/go/canonical/json"
)

/*
An Outpoint is a struct that represents an outpoint as per the Kerma specification
*/
type Outpoint struct {
	Txid  string `json:"txid" binding:"required"`
	Index int64  `json:"index" binding:"required"`
}

/*
An Input is a struct that represents an input as per the Kerma specification
*/
type Input struct {
	Outpoint Outpoint `json:"outpoint" binding:"required"`
	Sig      string   `json:"sig" binding:"required"`
}

type inputVerifier struct {
	Outpoint Outpoint `json:"outpoint" binding:"required"`
	Sig      *string  `json:"sig" binding:"required"`
}

/*
An Output is a struct that represents an output as per the Kerma specification
*/
type Output struct {
	Pubkey string `json:"pubkey" binding:"required"`
	Value  uint64 `json:"value" binding:"required"`
}

/*
A Transaction is a struct that represents a transaction as per the Kerma specification
*/
type Transaction struct {
	Type      string   `json:"type" binding:"required"`
	Height    *uint64  `json:"height,omitempty"`
	Inputs    []Input  `json:"inputs,omitempty"`
	Outputs   []Output `json:"outputs,omitempty"`
	Confirmed bool     `json:"-"`
}

type transactionVerifier struct {
	Type    string          `json:"type" binding:"required"`
	Inputs  []inputVerifier `json:"inputs,omitempty"`
	Outputs []Output        `json:"outputs,omitempty"`
}

/*
Hash returns the sha256 hash of the canonical JSON of the transaction
*/
func (t *Transaction) Hash() (string, error) {
	transaction, err := t.MarshalJson()
	if err != nil {
		return "", errors.New("could not parse transaction as json")
	}
	hashSum := sha256.Sum256(transaction)

	return hex.EncodeToString(hashSum[:]), nil
}

/*
GetID returns the transaction id
*/
func (b *Transaction) GetID() string {
	id, err := b.Hash()
	if err != nil {
		return ""
	}

	return id
}

/*
GetType returns the type of the transaction
*/
func (t *Transaction) GetType() string {
	return t.Type
}

/*
GetEntity returns the transaction
*/
func (t *Transaction) GetEntity() interface{} {
	return t
}

/*
MarshalJson returns the canonical JSON of the transaction
*/
func (t *Transaction) MarshalJson() ([]byte, error) {
	return json.MarshalCanonical(t)
}

/*
UnmarshalJSON creates a transaction from the input JSON byte array
*/
func (t *Transaction) UnmarshalJSON(data []byte) error {
	if len(data) == 0 {
		return nil
	}

	type tmp Transaction
	err := json.Unmarshal(data, (*tmp)(t))
	if err != nil {
		return err
	}

	err = t.Validate()
	if err != nil {
		return err
	}

	return nil
}

/*
Validate is responsible for validating the transaction; returns an error if unsuccessful
*/
func (t *Transaction) Validate() error {
	if t.Type != "transaction" {
		return errors.New("object not a transaction")
	}

	if t.IsCoinbaseTx() {
		if len(t.Inputs) > 0 {
			return errors.New("coinbase transactions cannot have an input")
		}

		if len(t.Outputs) != 1 {
			return errors.New("coinbase transactions must have exactly one output")
		}
	}

	txOutpoints := map[string]int{}

	for _, input := range t.Inputs {
		if input.Outpoint.Index < 0 {
			return errors.New("transaction input index cannot be negative")
		}

		outpointId := input.Outpoint.Txid + "-" + strconv.FormatInt(input.Outpoint.Index, 10)
		if _, ok := txOutpoints[outpointId]; ok {
			return errors.New("multiple transaction inputs with same outpoint found")
		}

		txOutpoints[outpointId] = 1
	}

	for _, output := range t.Outputs {
		if output.Value < 0 {
			return errors.New("transaction output value cannot be negative")
		}

		pubkeyBytes, err := hex.DecodeString(output.Pubkey)
		if err != nil {
			return err
		}

		if ed25519.PublicKey(string(pubkeyBytes)) == nil {
			return errors.New("invalid public key value, transaction invalid")
		}
	}
	return nil
}

/*
String returns the canonical JSON of the transaction as a string
*/
func (t *Transaction) String() string {
	res, _ := t.MarshalJson()
	return string(res)
}

/*
VerifySign verifies whether the signature of the transaction with the provided pubkey matches the signature provided
*/
func (t *Transaction) VerifySign(sig string, pubkeyString string) bool {
	var logger helpers.Logger

	newTransaction := transactionVerifier{
		Type:    t.Type,
		Inputs:  []inputVerifier{},
		Outputs: t.Outputs,
	}

	for _, i := range t.Inputs {
		newInput := inputVerifier{
			Outpoint: i.Outpoint,
			Sig:      nil,
		}

		newTransaction.Inputs = append(newTransaction.Inputs, newInput)
	}

	txBytes := new(bytes.Buffer)
	encoder := json.NewEncoder(txBytes)
	encoder.Canonical()
	encoder.Encode(newTransaction)

	pubkeyBytes, err := hex.DecodeString(pubkeyString)
	if err != nil {
		return false
	}

	sigBytes, err := hex.DecodeString(sig)
	if err != nil {
		return false
	}

	logger.Debug("Checking transaction signature with params: SIGNATURE(" + sig + "), PUBKEY(" + pubkeyString + "), TRANSACTION(" + txBytes.String() + ")")

	pubkey := ed25519.PublicKey(string(pubkeyBytes))
	if len(pubkey) != ed25519.PublicKeySize {
		return false
	}

	return ed25519.Verify(ed25519.PublicKey(pubkey), txBytes.Bytes(), sigBytes)
}

/*
IsTxInput checks if the transaction ID supplied is an input of the current transaction
*/
func (t *Transaction) IsTxInput(txid string) bool {
	for _, input := range t.Inputs {
		if txid == input.Outpoint.Txid {
			return true
		}
	}
	return false
}

/*
IsCoinbaseTx checks if the transaction is a coinbase transaction
*/
func (t *Transaction) IsCoinbaseTx() bool {
	return t.Height != nil
}