// checkInputsStandard performs a series of checks on a transaction's inputs
// to ensure they are "standard".  A standard transaction input within the
// context of this function is one whose referenced public key script is of a
// standard form and, for pay-to-script-hash, does not have more than
// maxStandardP2SHSigOps signature operations.  However, it should also be noted
// that standard inputs also are those which have a clean stack after execution
// and only contain pushed data in their signature scripts.  This function does
// not perform those checks because the script engine already does this more
// accurately and concisely via the txscript.ScriptVerifyCleanStack and
// txscript.ScriptVerifySigPushOnly flags.
func checkInputsStandard(tx *btcutil.Tx, utxoView *blockchain.UtxoViewpoint) error {
	// NOTE: The reference implementation also does a coinbase check here,
	// but coinbases have already been rejected prior to calling this
	// function so no need to recheck.

	for i, txIn := range tx.MsgTx().TxIn {
		// It is safe to elide existence and index checks here since
		// they have already been checked prior to calling this
		// function.
		prevOut := txIn.PreviousOutPoint
		entry := utxoView.LookupEntry(&prevOut.Hash)
		originPkScript := entry.PkScriptByIndex(prevOut.Index)
		switch txscript.GetScriptClass(originPkScript) {
		case txscript.ScriptHashTy:
			numSigOps := txscript.GetPreciseSigOpCount(
				txIn.SignatureScript, originPkScript, true)
			if numSigOps > maxStandardP2SHSigOps {
				str := fmt.Sprintf("transaction input #%d has "+
					"%d signature operations which is more "+
					"than the allowed max amount of %d",
					i, numSigOps, maxStandardP2SHSigOps)
				return txRuleError(wire.RejectNonstandard, str)
			}

		case txscript.NonStandardTy:
			str := fmt.Sprintf("transaction input #%d has a "+
				"non-standard script form", i)
			return txRuleError(wire.RejectNonstandard, str)
		}
	}

	return nil
}

// calcInputValueAge is a helper function used to calculate the input age of
// a transaction.  The input age for a txin is the number of confirmations
// since the referenced txout multiplied by its output value.  The total input
// age is the sum of this value for each txin.  Any inputs to the transaction
// which are currently in the mempool and hence not mined into a block yet,
// contribute no additional input age to the transaction.
func calcInputValueAge(tx *wire.MsgTx, utxoView *blockchain.UtxoViewpoint, nextBlockHeight int32) float64 {
	var totalInputAge float64
	for _, txIn := range tx.TxIn {
		// Don't attempt to accumulate the total input age if the
		// referenced transaction output doesn't exist.
		originHash := &txIn.PreviousOutPoint.Hash
		originIndex := txIn.PreviousOutPoint.Index
		txEntry := utxoView.LookupEntry(originHash)
		if txEntry != nil && !txEntry.IsOutputSpent(originIndex) {
			// Inputs with dependencies currently in the mempool
			// have their block height set to a special constant.
			// Their input age should computed as zero since their
			// parent hasn't made it into a block yet.
			var inputAge int32
			originHeight := txEntry.BlockHeight()
			if originHeight == UnminedHeight {
				inputAge = 0
			} else {
				inputAge = nextBlockHeight - originHeight
			}

			// Sum the input value times age.
			inputValue := txEntry.AmountByIndex(originIndex)
			totalInputAge += float64(inputValue * int64(inputAge))
		}
	}

	return totalInputAge
}

// indexBlock extract all of the standard addresses from all of the transactions
// in the passed block and maps each of them to the assocaited transaction using
// the passed map.
func (idx *AddrIndex) indexBlock(data writeIndexData, block *btcutil.Block, view *blockchain.UtxoViewpoint) {
	for txIdx, tx := range block.Transactions() {
		// Coinbases do not reference any inputs.  Since the block is
		// required to have already gone through full validation, it has
		// already been proven on the first transaction in the block is
		// a coinbase.
		if txIdx != 0 {
			for _, txIn := range tx.MsgTx().TxIn {
				// The view should always have the input since
				// the index contract requires it, however, be
				// safe and simply ignore any missing entries.
				origin := &txIn.PreviousOutPoint
				entry := view.LookupEntry(&origin.Hash)
				if entry == nil {
					continue
				}

				pkScript := entry.PkScriptByIndex(origin.Index)
				idx.indexPkScript(data, pkScript, txIdx)
			}
		}

		for _, txOut := range tx.MsgTx().TxOut {
			idx.indexPkScript(data, txOut.PkScript, txIdx)
		}
	}
}

// mergeUtxoView adds all of the entries in view to viewA.  The result is that
// viewA will contain all of its original entries plus all of the entries
// in viewB.  It will replace any entries in viewB which also exist in viewA
// if the entry in viewA is fully spent.
func mergeUtxoView(viewA *blockchain.UtxoViewpoint, viewB *blockchain.UtxoViewpoint) {
	viewAEntries := viewA.Entries()
	for hash, entryB := range viewB.Entries() {
		if entryA, exists := viewAEntries[hash]; !exists ||
			entryA == nil || entryA.IsFullySpent() {

			viewAEntries[hash] = entryB
		}
	}
}

// spendTransaction updates the passed view by marking the inputs to the passed
// transaction as spent.  It also adds all outputs in the passed transaction
// which are not provably unspendable as available unspent transaction outputs.
func spendTransaction(utxoView *blockchain.UtxoViewpoint, tx *btcutil.Tx, height int32) error {
	for _, txIn := range tx.MsgTx().TxIn {
		originHash := &txIn.PreviousOutPoint.Hash
		originIndex := txIn.PreviousOutPoint.Index
		entry := utxoView.LookupEntry(originHash)
		if entry != nil {
			entry.SpendOutput(originIndex)
		}
	}

	utxoView.AddTxOuts(tx, height)
	return nil
}

// checkInputsStandard performs a series of checks on a transaction's inputs
// to ensure they are "standard".  A standard transaction input is one that
// that consumes the expected number of elements from the stack and that number
// is the same as the output script pushes.  This help prevent resource
// exhaustion attacks by "creative" use of scripts that are super expensive to
// process like OP_DUP OP_CHECKSIG OP_DROP repeated a large number of times
// followed by a final OP_TRUE.
func checkInputsStandard(tx *btcutil.Tx, utxoView *blockchain.UtxoViewpoint) error {
	// NOTE: The reference implementation also does a coinbase check here,
	// but coinbases have already been rejected prior to calling this
	// function so no need to recheck.

	for i, txIn := range tx.MsgTx().TxIn {
		// It is safe to elide existence and index checks here since
		// they have already been checked prior to calling this
		// function.
		prevOut := txIn.PreviousOutPoint
		entry := utxoView.LookupEntry(&prevOut.Hash)
		originPkScript := entry.PkScriptByIndex(prevOut.Index)

		// Calculate stats for the script pair.
		scriptInfo, err := txscript.CalcScriptInfo(txIn.SignatureScript,
			originPkScript, true)
		if err != nil {
			str := fmt.Sprintf("transaction input #%d script parse "+
				"failure: %v", i, err)
			return txRuleError(wire.RejectNonstandard, str)
		}

		// A negative value for expected inputs indicates the script is
		// non-standard in some way.
		if scriptInfo.ExpectedInputs < 0 {
			str := fmt.Sprintf("transaction input #%d expects %d "+
				"inputs", i, scriptInfo.ExpectedInputs)
			return txRuleError(wire.RejectNonstandard, str)
		}

		// The script pair is non-standard if the number of available
		// inputs does not match the number of expected inputs.
		if scriptInfo.NumInputs != scriptInfo.ExpectedInputs {
			str := fmt.Sprintf("transaction input #%d expects %d "+
				"inputs, but referenced output script provides "+
				"%d", i, scriptInfo.ExpectedInputs,
				scriptInfo.NumInputs)
			return txRuleError(wire.RejectNonstandard, str)
		}
	}

	return nil
}

// AddUnconfirmedTx adds all addresses related to the transaction to the
// unconfirmed (memory-only) address index.
//
// NOTE: This transaction MUST have already been validated by the memory pool
// before calling this function with it and have all of the inputs available in
// the provided utxo view.  Failure to do so could result in some or all
// addresses not being indexed.
//
// This function is safe for concurrent access.
func (idx *AddrIndex) AddUnconfirmedTx(tx *btcutil.Tx, utxoView *blockchain.UtxoViewpoint) {
	// Index addresses of all referenced previous transaction outputs.
	//
	// The existence checks are elided since this is only called after the
	// transaction has already been validated and thus all inputs are
	// already known to exist.
	for _, txIn := range tx.MsgTx().TxIn {
		entry := utxoView.LookupEntry(&txIn.PreviousOutPoint.Hash)
		if entry == nil {
			// Ignore missing entries.  This should never happen
			// in practice since the function comments specifically
			// call out all inputs must be available.
			continue
		}
		pkScript := entry.PkScriptByIndex(txIn.PreviousOutPoint.Index)
		idx.indexUnconfirmedAddresses(pkScript, tx)
	}

	// Index addresses of all created outputs.
	for _, txOut := range tx.MsgTx().TxOut {
		idx.indexUnconfirmedAddresses(txOut.PkScript, tx)
	}
}