// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum 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.

// OpenEthereum 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 OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

use std::collections::HashSet;

use edit_distance::edit_distance;
use parity_wordlist;

use super::{Address, Brain, Generator};

/// Tries to find a phrase for address, given the number
/// of expected words and a partial phrase.
///
/// Returns `None` if phrase couldn't be found.
pub fn brain_recover(
    address: &Address,
    known_phrase: &str,
    expected_words: usize,
) -> Option<String> {
    let it = PhrasesIterator::from_known_phrase(known_phrase, expected_words);
    for phrase in it {
        let keypair = Brain::new(phrase.clone())
            .generate()
            .expect("Brain wallets are infallible; qed");
        trace!("Testing: {}, got: {:?}", phrase, keypair.address());
        if &keypair.address() == address {
            return Some(phrase);
        }
    }

    None
}

fn generate_substitutions(word: &str) -> Vec<&'static str> {
    let mut words = parity_wordlist::WORDS
        .iter()
        .cloned()
        .map(|w| (edit_distance(w, word), w))
        .collect::<Vec<_>>();
    words.sort_by(|a, b| a.0.cmp(&b.0));

    words.into_iter().map(|pair| pair.1).collect()
}

/// Iterator over possible
pub struct PhrasesIterator {
    words: Vec<Vec<&'static str>>,
    combinations: u64,
    indexes: Vec<usize>,
    has_next: bool,
}

impl PhrasesIterator {
    pub fn from_known_phrase(known_phrase: &str, expected_words: usize) -> Self {
        let known_words = parity_wordlist::WORDS
            .iter()
            .cloned()
            .collect::<HashSet<_>>();
        let mut words = known_phrase
            .split(' ')
            .map(|word| match known_words.get(word) {
                None => {
                    info!(
                        "Invalid word '{}', looking for potential substitutions.",
                        word
                    );
                    let substitutions = generate_substitutions(word);
                    info!("Closest words: {:?}", &substitutions[..10]);
                    substitutions
                }
                Some(word) => vec![*word],
            })
            .collect::<Vec<_>>();

        // add missing words
        if words.len() < expected_words {
            let to_add = expected_words - words.len();
            info!("Number of words is insuficcient adding {} more.", to_add);
            for _ in 0..to_add {
                words.push(parity_wordlist::WORDS.iter().cloned().collect());
            }
        }

        // start searching
        PhrasesIterator::new(words)
    }

    pub fn new(words: Vec<Vec<&'static str>>) -> Self {
        let combinations = words.iter().fold(1u64, |acc, x| acc * x.len() as u64);
        let indexes = words.iter().map(|_| 0).collect();
        info!("Starting to test {} possible combinations.", combinations);

        PhrasesIterator {
            words,
            combinations,
            indexes,
            has_next: combinations > 0,
        }
    }

    pub fn combinations(&self) -> u64 {
        self.combinations
    }

    fn current(&self) -> String {
        let mut s = self.words[0][self.indexes[0]].to_owned();
        for i in 1..self.indexes.len() {
            s.push(' ');
            s.push_str(self.words[i][self.indexes[i]]);
        }
        s
    }

    fn next_index(&mut self) -> bool {
        let mut pos = self.indexes.len();
        while pos > 0 {
            pos -= 1;
            self.indexes[pos] += 1;
            if self.indexes[pos] >= self.words[pos].len() {
                self.indexes[pos] = 0;
            } else {
                return true;
            }
        }

        false
    }
}

impl Iterator for PhrasesIterator {
    type Item = String;

    fn next(&mut self) -> Option<String> {
        if !self.has_next {
            return None;
        }

        let phrase = self.current();
        self.has_next = self.next_index();
        Some(phrase)
    }
}

#[cfg(test)]
mod tests {
    use super::PhrasesIterator;

    #[test]
    fn should_generate_possible_combinations() {
        let mut it =
            PhrasesIterator::new(vec![vec!["1", "2", "3"], vec!["test"], vec!["a", "b", "c"]]);

        assert_eq!(it.combinations(), 9);
        assert_eq!(it.next(), Some("1 test a".to_owned()));
        assert_eq!(it.next(), Some("1 test b".to_owned()));
        assert_eq!(it.next(), Some("1 test c".to_owned()));
        assert_eq!(it.next(), Some("2 test a".to_owned()));
        assert_eq!(it.next(), Some("2 test b".to_owned()));
        assert_eq!(it.next(), Some("2 test c".to_owned()));
        assert_eq!(it.next(), Some("3 test a".to_owned()));
        assert_eq!(it.next(), Some("3 test b".to_owned()));
        assert_eq!(it.next(), Some("3 test c".to_owned()));
        assert_eq!(it.next(), None);
    }
}