// Copyright 2018-2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.

use super::{PublicOf, PublicT, Crypto};
use sp_core::Pair;
use rand::{rngs::OsRng, RngCore};

fn good_waypoint(done: u64) -> u64 {
	match done {
		0..=1_000_000 => 100_000,
		0..=10_000_000 => 1_000_000,
		0..=100_000_000 => 10_000_000,
		_ => 100_000_000,
	}
}

fn next_seed(seed: &mut [u8]) {
	for i in 0..seed.len() {
		match seed[i] {
			255 => {
				seed[i] = 0;
			}
			_ => {
				seed[i] += 1;
				break;
			}
		}
	}
}

/// A structure used to carry both Pair and seed.
/// This should usually NOT been used. If unsure, use Pair.
pub(super) struct KeyPair<C: Crypto> {
	pub pair: C::Pair,
	pub seed: <C::Pair as Pair>::Seed,
	pub score: usize,
}

/// Calculate the score of a key based on the desired
/// input.
fn calculate_score(_desired: &str, key: &str) -> usize {
	for truncate in 0.._desired.len() {
		let snip_size = _desired.len() - truncate;
		let truncated = &_desired[0..snip_size];
		if let Some(pos) = key.find(truncated) {
			return (47 - pos) + (snip_size * 48);
		}
	}
	0
}

pub(super) fn generate_key<C: Crypto>(desired: &str) -> Result<KeyPair<C>, &str> where
		PublicOf<C>: PublicT,
{
	if desired.is_empty() {
		return Err("Pattern must not be empty");
	}

	println!("Generating key containing pattern '{}'", desired);

	let top = 45 + (desired.len() * 48);
	let mut best = 0;
	let mut seed = <C::Pair as Pair>::Seed::default();
	let mut done = 0;

	loop {
		if done % 100000 == 0 {
			OsRng.fill_bytes(seed.as_mut());
		} else {
			next_seed(seed.as_mut());
		}

		let p = C::Pair::from_seed(&seed);
		let ss58 = C::ss58_from_pair(&p);
		let score = calculate_score(&desired, &ss58);
		if score > best || desired.len() < 2 {
			best = score;
			let keypair = KeyPair {
				pair: p,
				seed: seed.clone(),
				score: score,
			};
			if best >= top {
				println!("best: {} == top: {}", best, top);
				return Ok(keypair);
			}
		}
		done += 1;

		if done % good_waypoint(done) == 0 {
			println!("{} keys searched; best is {}/{} complete", done, best, top);
		}
	}
}

#[cfg(test)]
mod tests {
	use super::super::Ed25519;
	use super::*;
	use sp_core::{crypto::Ss58Codec, Pair};
	#[cfg(feature = "bench")]
	use test::Bencher;

	#[test]
	fn test_generation_with_single_char() {
		assert!(generate_key::<Ed25519>("j")
			.unwrap()
			.pair
			.public()
			.to_ss58check()
			.contains("j"));
	}

	#[test]
	fn test_score_1_char_100() {
		let score = calculate_score("j", "5jolkadotwHY5k9GpdTgpqs9xjuNvtv8EcwCFpEeyEf3KHim");
		assert_eq!(score, 94);
	}

	#[test]
	fn test_score_100() {
		let score = calculate_score(
			"Polkadot",
			"5PolkadotwHY5k9GpdTgpqs9xjuNvtv8EcwCFpEeyEf3KHim",
		);
		assert_eq!(score, 430);
	}

	#[test]
	fn test_score_50_2() {
		// 50% for the position + 50% for the size
		assert_eq!(
			calculate_score(
				"Polkadot",
				"5PolkXXXXwHY5k9GpdTgpqs9xjuNvtv8EcwCFpEeyEf3KHim"
			),
			238
		);
	}

	#[test]
	fn test_score_0() {
		assert_eq!(
			calculate_score(
				"Polkadot",
				"5GUWv4bLCchGUHJrzULXnh4JgXsMpTKRnjuXTY7Qo1Kh9uYK"
			),
			0
		);
	}

	#[cfg(feature = "bench")]
	#[bench]
	fn bench_paranoiac(b: &mut Bencher) {
		b.iter(|| generate_key("polk"));
	}

	#[cfg(feature = "bench")]
	#[bench]
	fn bench_not_paranoiac(b: &mut Bencher) {
		b.iter(|| generate_key("polk"));
	}
}