// Package txsizes Copyright (c) 2016 The btcsuite developers
package txsizes

import (
	"github.com/p9c/p9/pkg/blockchain"
	h "github.com/p9c/p9/pkg/util/helpers"
	"github.com/p9c/p9/pkg/wire"
)

// Worst case script and input/output size estimates.
const (
	// RedeemP2PKHSigScriptSize is the worst case (largest) serialize size of a transaction input script that redeems a
	// compressed P2PKH output. It is calculated as:
	//
	//   - OP_DATA_73
	//   - 72 bytes DER signature + 1 byte sighash
	//   - OP_DATA_33
	//   - 33 bytes serialized compressed pubkey
	RedeemP2PKHSigScriptSize = 1 + 73 + 1 + 33
	// P2PKHPkScriptSize is the size of a transaction output script that pays to a compressed pubkey hash. It is
	// calculated as:
	//
	//   - OP_DUP
	//   - OP_HASH160
	//   - OP_DATA_20
	//   - 20 bytes pubkey hash
	//   - OP_EQUALVERIFY
	//   - OP_CHECKSIG
	P2PKHPkScriptSize = 1 + 1 + 1 + 20 + 1 + 1
	// RedeemP2PKHInputSize is the worst case (largest) serialize size of a transaction input redeeming a compressed
	// P2PKH output. It is calculated as:
	//
	//   - 32 bytes previous tx
	//   - 4 bytes output index
	//   - 1 byte compact int encoding value 107
	//   - 107 bytes signature script
	//   - 4 bytes sequence
	RedeemP2PKHInputSize = 32 + 4 + 1 + RedeemP2PKHSigScriptSize + 4
	// P2PKHOutputSize is the serialize size of a transaction output with a P2PKH output script. It is calculated as:
	//
	//   - 8 bytes output value
	//   - 1 byte compact int encoding value 25
	//   - 25 bytes P2PKH output script
	P2PKHOutputSize = 8 + 1 + P2PKHPkScriptSize
	// // P2WPKHPkScriptSize is the size of a transaction output script that pays to a
	// // witness pubkey hash. It is calculated as:
	// //
	// //   - OP_0
	// //   - OP_DATA_20
	// //   - 20 bytes pubkey hash
	// P2WPKHPkScriptSize = 1 + 1 + 20
	// // P2WPKHOutputSize is the serialize size of a transaction output with a P2WPKH output script. It is calculated as:
	// //
	// //   - 8 bytes output value
	// //   - 1 byte compact int encoding value 22
	// //   - 22 bytes P2PKH output script
	// P2WPKHOutputSize = 8 + 1 + P2WPKHPkScriptSize
	// // RedeemP2WPKHScriptSize is the size of a transaction input script that spends
	// // a pay-to-witness-public-key hash (P2WPKH). The redeem script for P2WPKH
	// // spends MUST be empty.
	// RedeemP2WPKHScriptSize = 0
	// // RedeemP2WPKHInputSize is the worst case size of a transaction input redeeming a P2WPKH output. It is calculated
	// // as:
	// //
	// //   - 32 bytes previous tx
	// //   - 4 bytes output index
	// //   - 1 byte encoding empty redeem script
	// //   - 0 bytes redeem script
	// //   - 4 bytes sequence
	// RedeemP2WPKHInputSize = 32 + 4 + 1 + RedeemP2WPKHScriptSize + 4
	// // RedeemNestedP2WPKHScriptSize is the worst case size of a transaction input
	// // script that redeems a pay-to-witness-key hash nested in P2SH (P2SH-P2WPKH).
	// // It is calculated as:
	// //
	// //   - 1 byte compact int encoding value 22
	// //   - OP_0
	// //   - 1 byte compact int encoding value 20
	// //   - 20 byte key hash
	// RedeemNestedP2WPKHScriptSize = 1 + 1 + 1 + 20
	// // RedeemNestedP2WPKHInputSize is the worst case size of a transaction input redeeming a P2SH-P2WPKH output. It is
	// // calculated as:
	// //
	// //   - 32 bytes previous tx
	// //   - 4 bytes output index
	// //   - 1 byte compact int encoding value 23
	// //   - 23 bytes redeem script (scriptSig)
	// //   - 4 bytes sequence
	// RedeemNestedP2WPKHInputSize = 32 + 4 + 1 + RedeemNestedP2WPKHScriptSize + 4
	// // RedeemP2WPKHInputWitnessWeight is the worst case weight of a witness for
	// // spending P2WPKH and nested P2WPKH outputs. It is calculated as:
	// //
	// //   - 1 wu compact int encoding value 2 (number of items)
	// //   - 1 wu compact int encoding value 73
	// //   - 72 wu DER signature + 1 wu sighash
	// //   - 1 wu compact int encoding value 33
	// //   - 33 wu serialized compressed pubkey
	// RedeemP2WPKHInputWitnessWeight = 1 + 1 + 73 + 1 + 33
)

// EstimateSerializeSize returns a worst case serialize size estimate for a signed transaction that spends inputCount
// number of compressed P2PKH outputs and contains each transaction output from txOuts. The estimated size is
// incremented for an additional P2PKH change output if addChangeOutput is true.
func EstimateSerializeSize(inputCount int, txOuts []*wire.TxOut, addChangeOutput bool) int {
	changeSize := 0
	outputCount := len(txOuts)
	if addChangeOutput {
		changeSize = P2PKHOutputSize
		outputCount++
	}
	// 8 additional bytes are for version and locktime
	return 8 + wire.VarIntSerializeSize(uint64(inputCount)) +
		wire.VarIntSerializeSize(uint64(outputCount)) +
		inputCount*RedeemP2PKHInputSize +
		h.SumOutputSerializeSizes(txOuts) +
		changeSize
}

// EstimateVirtualSize returns a worst case virtual size estimate for a signed transaction that spends the given number
// of P2PKH, P2WPKH and (nested) P2SH-P2WPKH outputs, and contains each transaction output from txOuts. The estimate is
// incremented for an additional P2PKH change output if addChangeOutput is true.
func EstimateVirtualSize(numP2PKHIns, numP2WPKHIns, numNestedP2WPKHIns int,
	txOuts []*wire.TxOut, addChangeOutput bool,
) int {
	changeSize := 0
	// outputCount := len(txOuts)
	if addChangeOutput {
		// We are always using P2WPKH as change output.
		changeSize = P2PKHOutputSize
		// outputCount++
	}
	// Version 4 bytes + LockTime 4 bytes + Serialized var int size for the number of transaction inputs and outputs +
	// size of redeem scripts + the size out the serialized outputs and change.
	baseSize := 8 +
		wire.VarIntSerializeSize(
			uint64(numP2PKHIns+numP2WPKHIns+numNestedP2WPKHIns),
		) +
		wire.VarIntSerializeSize(uint64(len(txOuts))) +
		numP2PKHIns*RedeemP2PKHInputSize +
		// numP2WPKHIns*RedeemP2PKHInputSize +
		// numNestedP2WPKHIns*RedeemNestedP2WPKHInputSize +
		h.SumOutputSerializeSizes(txOuts) +
		changeSize
	// If this transaction has any witness inputs, we must count the witness data.
	witnessWeight := 0
	// if numP2WPKHIns+numNestedP2WPKHIns > 0 {
	// 	// Additional 2 weight units for segwit marker + flag.
	// 	witnessWeight = 2 +
	// 		wire.VarIntSerializeSize(
	// 			uint64(numP2WPKHIns+numNestedP2WPKHIns)) +
	// 		numP2WPKHIns*RedeemP2WPKHInputWitnessWeight +
	// 		numNestedP2WPKHIns*RedeemP2WPKHInputWitnessWeight
	// }
	// We add 3 to the witness weight to make sure the result is always rounded up.
	return baseSize + (witnessWeight+3)/blockchain.WitnessScaleFactor
}