// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! Lightning message signing and verification lives here. These tools can be used to sign messages using the node's
//! secret so receivers are sure that they come from you. You can also use this to verify that a given message comes
//! from a specific node.
//! Furthermore, these tools can be used to sign / verify messages using ephemeral keys not tied to node's identities.
//!
//! Note this is not part of the specs, but follows lnd's signing and verifying protocol, which can is defined as follows:
//!
//! signature = zbase32(SigRec(sha256d(("Lightning Signed Message:" + msg)))
//! zbase32 from <https://philzimmermann.com/docs/human-oriented-base-32-encoding.txt>
//! SigRec has first byte 31 + recovery id, followed by 64 byte sig.
//!
//! This implementation is compatible with both lnd's and c-lightning's
//!
//! <https://lightning.readthedocs.io/lightning-signmessage.7.html>
//! <https://api.lightning.community/#signmessage>

use crate::prelude::*;
use crate::util::base32;
use bitcoin::hashes::{sha256d, Hash};
use bitcoin::secp256k1::ecdsa::{RecoverableSignature, RecoveryId};
use bitcoin::secp256k1::{Error, Message, PublicKey, Secp256k1, SecretKey};

static LN_MESSAGE_PREFIX: &[u8] = b"Lightning Signed Message:";

fn sigrec_encode(sig_rec: RecoverableSignature) -> Vec<u8> {
	let (rid, rsig) = sig_rec.serialize_compact();
	let prefix = rid.to_i32() as u8 + 31;

	[&[prefix], &rsig[..]].concat()
}

fn sigrec_decode(sig_rec: Vec<u8>) -> Result<RecoverableSignature, Error> {
	// Signature must be 64 + 1 bytes long (compact signature + recovery id)
	if sig_rec.len() != 65 {
		return Err(Error::InvalidSignature);
	}

	let rsig = &sig_rec[1..];
	let rid = sig_rec[0] as i32 - 31;

	match RecoveryId::from_i32(rid) {
		Ok(x) => RecoverableSignature::from_compact(rsig, x),
		Err(e) => Err(e)
	}
}

/// Creates a digital signature of a message given a SecretKey, like the node's secret.
/// A receiver knowing the PublicKey (e.g. the node's id) and the message can be sure that the signature was generated by the caller.
/// Signatures are EC recoverable, meaning that given the message and the signature the PublicKey of the signer can be extracted.
pub fn sign(msg: &[u8], sk: &SecretKey) -> Result<String, Error> {
	let secp_ctx = Secp256k1::signing_only();
	let msg_hash = sha256d::Hash::hash(&[LN_MESSAGE_PREFIX, msg].concat());

	let sig = secp_ctx.sign_ecdsa_recoverable(&Message::from_slice(msg_hash.as_byte_array())?, sk);
	Ok(base32::Alphabet::ZBase32.encode(&sigrec_encode(sig)))
}

/// Recovers the PublicKey of the signer of the message given the message and the signature.
pub fn recover_pk(msg: &[u8], sig: &str) ->  Result<PublicKey, Error> {
	let secp_ctx = Secp256k1::verification_only();
	let msg_hash = sha256d::Hash::hash(&[LN_MESSAGE_PREFIX, msg].concat());

	match base32::Alphabet::ZBase32.decode(&sig) {
		Ok(sig_rec) => {
			match sigrec_decode(sig_rec) {
				Ok(sig) => secp_ctx.recover_ecdsa(&Message::from_slice(msg_hash.as_byte_array())?, &sig),
				Err(e) => Err(e)
			}
		},
		Err(_) => Err(Error::InvalidSignature)
	}
}

/// Verifies a message was signed by a PrivateKey that derives to a given PublicKey, given a message, a signature,
/// and the PublicKey.
pub fn verify(msg: &[u8], sig: &str, pk: &PublicKey) -> bool {
	match recover_pk(msg, sig) {
		Ok(x) => x == *pk,
		Err(_) => false
	}
}

#[cfg(test)]
mod test {
	use core::str::FromStr;
	use crate::util::message_signing::{sign, recover_pk, verify};
	use bitcoin::secp256k1::constants::ONE;
	use bitcoin::secp256k1::{PublicKey, SecretKey, Secp256k1};

	#[test]
	fn test_sign() {
		let message = "test message";
		let one_key = SecretKey::from_slice(&ONE).unwrap();
		let zbase32_sig = sign(message.as_bytes(), &one_key);

		assert_eq!(zbase32_sig.unwrap(), "d9tibmnic9t5y41hg7hkakdcra94akas9ku3rmmj4ag9mritc8ok4p5qzefs78c9pqfhpuftqqzhydbdwfg7u6w6wdxcqpqn4sj4e73e")
	}

	#[test]
	fn test_recover_pk() {
		let message = "test message";
		let one_key = SecretKey::from_slice(&ONE).unwrap();
		let sig = "d9tibmnic9t5y41hg7hkakdcra94akas9ku3rmmj4ag9mritc8ok4p5qzefs78c9pqfhpuftqqzhydbdwfg7u6w6wdxcqpqn4sj4e73e";
		let pk = recover_pk(message.as_bytes(), sig);

		assert_eq!(pk.unwrap(), PublicKey::from_secret_key(&Secp256k1::signing_only(), &one_key))
	}

	#[test]
	fn test_verify() {
		let message = "another message";
		let one_key = SecretKey::from_slice(&ONE).unwrap();
		let sig = sign(message.as_bytes(), &one_key).unwrap();
		let pk = PublicKey::from_secret_key(&Secp256k1::signing_only(), &one_key);

		assert!(verify(message.as_bytes(), &sig, &pk))
	}

	#[test]
	fn test_verify_ground_truth_ish() {
		// There are no standard tests vectors for Sign/Verify, using the same tests vectors as c-lightning to see if they are compatible.
		// Taken from https://github.com/ElementsProject/lightning/blob/1275af6fbb02460c8eb2f00990bb0ef9179ce8f3/tests/test_misc.py#L1925-L1938

		let corpus = [
			["@bitconner",
			"is this compatible?",
			"rbgfioj114mh48d8egqx8o9qxqw4fmhe8jbeeabdioxnjk8z3t1ma1hu1fiswpakgucwwzwo6ofycffbsqusqdimugbh41n1g698hr9t",
			"02b80cabdf82638aac86948e4c06e82064f547768dcef977677b9ea931ea75bab5"],
			["@duck1123",
			"hi",
			"rnrphcjswusbacjnmmmrynh9pqip7sy5cx695h6mfu64iac6qmcmsd8xnsyczwmpqp9shqkth3h4jmkgyqu5z47jfn1q7gpxtaqpx4xg",
			"02de60d194e1ca5947b59fe8e2efd6aadeabfb67f2e89e13ae1a799c1e08e4a43b"],
			["@jochemin",
			"hi",
			"ry8bbsopmduhxy3dr5d9ekfeabdpimfx95kagdem7914wtca79jwamtbw4rxh69hg7n6x9ty8cqk33knbxaqftgxsfsaeprxkn1k48p3",
			"022b8ece90ee891cbcdac0c1cc6af46b73c47212d8defbce80265ac81a6b794931"],
		];

		for c in &corpus {
			assert!(verify(c[1].as_bytes(), c[2], &PublicKey::from_str(c[3]).unwrap()))
		}
	}
}