# server

nonce = 1 + SecureRandom.random_number(ECDSA::Group::Secp256k1.order - 1)

# send nonce

# client

require 'bitcoin'
require 'net/http'
require 'json'
include Bitcoin::Opcodes

Bitcoin.chain_params = :signet
client = Bitcoin::RPC::BitcoinCoreClient.new({ schema: 'http', host: 'localhost', port: 38332, user: 'hoge', password: 'hoge' })


# payment transaction
payment_txid = "c2789578340200af3769b7d325986a5a72dfdf36e9ea14dfcbdc4b0b6222c8df"
payment_tx = Bitcoin::Tx.parse_from_payload(client.getrawtransaction(payment_txid).htb)

# pop transaction
pop_tx = Bitcoin::Tx.new

# nonce
nonce = # receive nonce

# input
payment_tx.in.each do |input|
  pop_tx.in << Bitcoin::TxIn.new(out_point: input.out_point, sequence: 0)
end

# output
output_script = Bitcoin::Script.new << OP_RETURN << "0x01 #{payment_txid} #{nonce}".bth
pop_tx.out << Bitcoin::TxOut.new(value: 0, script_pubkey: output_script)

# ロックタイム
pop_tx.lock_time = 499999999

# 署名
pop_tx.in.each_with_index do |input, index|
  source_tx_output = Bitcoin::Tx.parse_from_payload(client.getrawtransaction(input.out_point.txid).htb).out[input.out_point.index]
  key = Bitcoin::Key.from_wif(client.dumpprivkey(source_tx_output.script_pubkey.to_addr))
  sig_hash = pop_tx.sighash_for_input(index, source_tx_output.script_pubkey, sig_version: :witness_v0, amount: source_tx_output.value)
  signature = key.sign(sig_hash) + [Bitcoin::SIGHASH_TYPE[:all]].pack('C')
  input.script_witness.stack << signature
  input.script_witness.stack << key.pubkey.htb
end

# send tx
# pop_tx.txid
# => "adff2bacbb3772f0b3b5493ae6856b9143fe89ea48dbe7a3b776f61da01378c0"

# server

# receive pop_tx_id
pop_tx = Bitcoin::Tx.parse_from_payload(client.getrawtransaction(pop_tx_id).htb)

# 1. Check the format of the PoP.
# 送金済みであることを除いて検証が成功することを確認。

# 2. Check that lock_time is 499999999.
raise StandardError if pop_tx.lock_time != 499999999

# 3. Check that there is exactly one output. 
raise StandardError if pop_tx.out.size != 1

# This output must have value 0 
raise StandardError if pop_tx.out[0].value != 0

# and conform to the OP_RETURN output format outlined above.
pop_op_return = pop_tx.outputs[0].script_pubkey.op_return_data.split
raise StandardError if pop_op_return.size != 3 or !(['0x00', '0x01'].include?(pop_op_return[0]))

# 4. Check that the nonce is the same as the one requested.
pop_nonce = pop_op_return[2].to_i
raise StandardError if nonce != pop_nonce

# 5. Check that the inputs of the PoP are exactly the same as in transaction T, except that the sequence numbers must all be 0.
payment_tx = Bitcoin::Tx.parse_from_payload(client.getrawtransaction(pop_payment_txid).htb)
payment_tx.in.each_with_index do |t_input, index|
	raise StandardError if t_input.out_point.to_s != pop_tx.in[index].out_point.to_s
	raise StandardError if pop_tx.in[index].sequence != 0
end

# 6. Run the scripts of all the inputs. All scripts must return true.
pop_tx.in.each_with_index do |input, index|
	source_tx_output = Bitcoin::Tx.parse_from_payload(client.getrawtransaction(input.out_point.txid).htb).out[input.out_point.index]
	pop_tx.verify_input_sig(index, source_tx_output.script_pubkey, amount: source_tx_output.value)
end

# 7. Check that the txid in the PoP output is the transaction you actually want proof for.

# 8. Return "valid".
true