package types

import (
	"bytes"
	"errors"
	"fmt"

	"github.com/tendermint/tendermint/crypto/merkle"
	"github.com/tendermint/tendermint/crypto/tmhash"
	tmbytes "github.com/tendermint/tendermint/libs/bytes"
)

// Tx is an arbitrary byte array.
// NOTE: Tx has no types at this level, so when wire encoded it's just length-prefixed.
// Might we want types here ?
type Tx []byte

// Hash computes the TMHASH hash of the wire encoded transaction.
func (tx Tx) Hash() []byte {
	return tmhash.Sum(tx)
}

// String returns the hex-encoded transaction as a string.
func (tx Tx) String() string {
	return fmt.Sprintf("Tx{%X}", []byte(tx))
}

// Txs is a slice of Tx.
type Txs []Tx

// Hash returns the Merkle root hash of the transaction hashes.
// i.e. the leaves of the tree are the hashes of the txs.
func (txs Txs) Hash() []byte {
	// These allocations will be removed once Txs is switched to [][]byte,
	// ref #2603. This is because golang does not allow type casting slices without unsafe
	txBzs := make([][]byte, len(txs))
	for i := 0; i < len(txs); i++ {
		txBzs[i] = txs[i].Hash()
	}
	return merkle.SimpleHashFromByteSlices(txBzs)
}

// Index returns the index of this transaction in the list, or -1 if not found
func (txs Txs) Index(tx Tx) int {
	for i := range txs {
		if bytes.Equal(txs[i], tx) {
			return i
		}
	}
	return -1
}

// IndexByHash returns the index of this transaction hash in the list, or -1 if not found
func (txs Txs) IndexByHash(hash []byte) int {
	for i := range txs {
		if bytes.Equal(txs[i].Hash(), hash) {
			return i
		}
	}
	return -1
}

// Proof returns a simple merkle proof for this node.
// Panics if i < 0 or i >= len(txs)
// TODO: optimize this!
func (txs Txs) Proof(i int) TxProof {
	l := len(txs)
	bzs := make([][]byte, l)
	for i := 0; i < l; i++ {
		bzs[i] = txs[i].Hash()
	}
	root, proofs := merkle.SimpleProofsFromByteSlices(bzs)

	return TxProof{
		RootHash: root,
		Data:     txs[i],
		Proof:    *proofs[i],
	}
}

// TxProof represents a Merkle proof of the presence of a transaction in the Merkle tree.
type TxProof struct {
	RootHash tmbytes.HexBytes   `json:"root_hash"`
	Data     Tx                 `json:"data"`
	Proof    merkle.SimpleProof `json:"proof"`
}

// Leaf returns the hash(tx), which is the leaf in the merkle tree which this proof refers to.
func (tp TxProof) Leaf() []byte {
	return tp.Data.Hash()
}

// Validate verifies the proof. It returns nil if the RootHash matches the dataHash argument,
// and if the proof is internally consistent. Otherwise, it returns a sensible error.
func (tp TxProof) Validate(dataHash []byte) error {
	if !bytes.Equal(dataHash, tp.RootHash) {
		return errors.New("proof matches different data hash")
	}
	if tp.Proof.Index < 0 {
		return errors.New("proof index cannot be negative")
	}
	if tp.Proof.Total <= 0 {
		return errors.New("proof total must be positive")
	}
	valid := tp.Proof.Verify(tp.RootHash, tp.Leaf())
	if valid != nil {
		return errors.New("proof is not internally consistent")
	}
	return nil
}