use std::{collections::{HashMap, HashSet, VecDeque}, iter};

mod token;
pub use token::ParsingError;
use token::parse;

const START_NFA: usize = usize::MAX;
const START_DFA: usize = 0;

fn encode_set(set: &HashSet<usize>) -> String {
	let mut v = Vec::from_iter(set.iter());
	v.sort();
	let res: Vec<String> = v.into_iter().map(|x| x.to_string()).collect();
	return res.join(",");
}

#[derive(Debug)]
pub struct Regexp {
	rules: HashMap<(usize, char), HashSet<usize>>,
	end_states: HashSet<usize>,
	alphabet: Vec<char>
}

impl Regexp {
	pub fn new(pattern: &String) -> Result<Regexp, ParsingError> {
		let r = parse(pattern, 0)?;
		let pattern_chars = Vec::from_iter(pattern.chars());
		let mut rules: HashMap<(usize, char), HashSet<usize>> = HashMap::new();
		let mut alphabet: HashSet<char> = HashSet::new();
		
		for i in r.list_first() {
			let c = pattern_chars[i];
			alphabet.insert(c);
			let key = (START_NFA, c);
			match rules.get_mut(&key) {
				Some(set) => {set.insert(i);},
				None => {rules.insert(key, HashSet::from([i]));}
			};
		}

		for (i, j) in r.list_neighbours() {
			let c = pattern_chars[j];
			alphabet.insert(c);
			let key = (i, c);
			match rules.get_mut(&key) {
				Some(set) => {set.insert(j);},
				None => {rules.insert(key, HashSet::from([j]));}
			};
		}

		let mut end_states = HashSet::from_iter(r.list_last().into_iter());
		if r.is_skippable() {
			end_states.insert(START_NFA);
		}

		let mut alphabet_vec = Vec::from_iter(alphabet.into_iter());
		alphabet_vec.sort();

		return Ok(Regexp{rules, end_states, alphabet: alphabet_vec});
	}

	pub fn eval(&self, s: String) -> bool {
		let mut multistate = HashSet::from([START_NFA]);

		for c in s.chars() {
			let mut new_multistate = HashSet::new();

			for state in multistate {
				if let Some(x) = self.rules.get(&(state, c)) {
					new_multistate = new_multistate.union(&x).map(|&y| y).collect();
				} else if let Some(x) = self.rules.get(&(state, '.')) {
					new_multistate = new_multistate.union(&x).map(|&y| y).collect();
				}
			}
			multistate = new_multistate;
		}

		return multistate.iter().any(|x| self.end_states.contains(x));
	}

	pub fn determinize(&self) -> RegexpDFA {
		const FAIL: usize = usize::MAX;
		let alphabet_index: HashMap<char, usize> = self.alphabet.iter().enumerate().map(|(i, c)| (*c, i)).collect();
		let n = alphabet_index.len();
		let mut compact_rules = vec![FAIL; n];
		let mut end_states: HashSet<usize> = HashSet::new();
		if self.end_states.contains(&START_NFA) {end_states.insert(START_DFA);}

		// string hash -> single int DFA state
		let mut index_new = HashMap::from([(START_NFA.to_string(), START_DFA)]);
		// string hash -> HashSet NFA multistate
		let mut index_multi = HashMap::from([(START_NFA.to_string(), HashSet::from([START_NFA]))]);
		let mut stack = Vec::from([START_NFA.to_string()]);

		while !stack.is_empty() {
			let state_hash = stack.pop().unwrap();
			let multistate = &index_multi[&state_hash];
			let mut new_rules: HashMap<char, HashSet<usize>> = HashMap::new();

			for key in self.rules.keys().filter(|key| multistate.contains(&key.0)) {
				let (_st, c) = key;
				if !new_rules.contains_key(c) {
					new_rules.insert(*c, HashSet::new());
				}
				for target in &self.rules[key] {
					new_rules.get_mut(c).unwrap().insert(*target);
				}
			}

			for (c, target_set) in new_rules.into_iter() {
				let target_hash = encode_set(&target_set);
				let is_end = target_set.iter().any(|st| self.end_states.contains(st));
				if !index_new.contains_key(&target_hash) {
					let target_new = index_new.len();
					index_new.insert(target_hash.clone(), target_new);
					index_multi.insert(target_hash.clone(), target_set);
					compact_rules.extend(iter::repeat(FAIL).take(n));
					stack.push(target_hash.clone());
				}
				compact_rules[index_new[&state_hash]*n + alphabet_index[&c]] = index_new[&target_hash];
				if is_end {
					end_states.insert(index_new[&target_hash]);
				}
			}
		}

		let fail = index_new.len();
		compact_rules = compact_rules.into_iter().map(|st| if st != FAIL {st} else {fail}).collect();
		compact_rules.extend(iter::repeat(fail).take(n));

		return RegexpDFA{rules: compact_rules, end_states, alphabet_index};
	}
}

pub struct RegexpDFA {
	rules: Vec<usize>,
	end_states: HashSet<usize>,
	alphabet_index: HashMap<char, usize>
}

impl RegexpDFA {
	pub fn eval(&self, s: String) -> bool {
		let n = self.alphabet_index.len();
		if n == 0 {
			return s.len() == 0;
		}
		let fail = self.rules.len() / n;
		let mut state = START_DFA;

		for c in s.chars() {
			if let Some(ci) = self.alphabet_index.get(&c) {
				state = self.rules[state*n + ci];
			} else {
				return false;
			}
			if state == fail {
				return false;
			}
		}

		return self.end_states.contains(&state);
	}

	pub fn reduce(&self) -> RegexpDFA {
		if self.alphabet_index.len() == 0 {
			return RegexpDFA{rules: self.rules.clone(), end_states: self.end_states.clone(), alphabet_index: self.alphabet_index.clone()};
		}
		let equivalents = self.find_equivalent_states();
		return self.collapse_states(equivalents);
	}

	pub fn normalize(&self) -> RegexpDFA {
		let n = self.alphabet_index.len();
		if n == 0 {
			return RegexpDFA{rules: self.rules.clone(), end_states: self.end_states.clone(), alphabet_index: self.alphabet_index.clone()}; 
		}
		let m = self.rules.len()/n;
		let fail = m;
		let mut index: Vec<usize> = vec![fail;m];
		index[0] = 0;
		let mut queue = VecDeque::from([START_DFA]);

		let mut rules = vec![];
		let mut k = 1;

		while !queue.is_empty() {
			let si = queue.pop_front().unwrap();
			let row = &self.rules[si*n..(si+1)*n];
			for &sj in row {
				if sj != fail && index[sj] == fail {
					index[sj] = k;
					k += 1;
					queue.push_back(sj);
				}
			}
			rules.extend(row.iter().map(|&st| index[st]));
		}

		let end_states = self.end_states.iter().map(|st| index[*st]).collect();
		
		return RegexpDFA{rules, end_states, alphabet_index: self.alphabet_index.clone()};
	}

	fn find_equivalent_states(&self) -> Vec<(usize, usize)> {
		let n = self.alphabet_index.len();
		let state_vec: Vec<usize> = (0..self.rules.len()/n).collect();
		let mut equivalents = HashSet::new();
		state_vec.iter().enumerate().for_each(|(i, s1)| {
			equivalents.extend(
				state_vec[i+1..].iter()
				.filter(|s2| !(self.end_states.contains(s1)^self.end_states.contains(s2)))
				.map(|s2| (*s1, *s2))
			);
		});

		let mut m = usize::MAX;
		while equivalents.len() < m {
			m = equivalents.len();
			equivalents = equivalents.iter().filter(|(s1, s2)| {
				!(0..n).any(|ci| {
					let t1 = self.rules[s1*n + ci];
					let t2 = self.rules[s2*n + ci];
					let key = (t1.min(t2), t2.max(t1));
					return t1 != t2 && !equivalents.contains(&key);
				})
			}).copied().collect();
		}

		return Vec::from_iter(equivalents.into_iter());
	}

	fn collapse_states(&self, equivalents: Vec<(usize, usize)>) -> RegexpDFA {
		let n = self.alphabet_index.len();
		let m = self.rules.len()/n;
		let mut rules = Vec::new();

		let mut eq_mapping: Vec<usize> = ((0..m)).collect();
		for (s1, s2) in equivalents.into_iter() {
			eq_mapping[s2] = eq_mapping[s2].min(s1);
		}

		let mut discard_mapping: Vec<usize> = ((0..m)).collect();
		let mut discard_count = 0;

		for si in 0..m {
			if eq_mapping[si] != si {
				discard_count += 1;
				continue;
			}
			discard_mapping[si] = si-discard_count;
			rules.extend(self.rules[si*n..(si+1)*n].iter().map(|&st| eq_mapping[st]));
		}

		rules = rules.into_iter().map(|st| discard_mapping[st]).collect();
		let end_states = self.end_states.iter().map(|st| discard_mapping[eq_mapping[*st]]).collect();

		return RegexpDFA{rules, end_states, alphabet_index: self.alphabet_index.clone()};
	}
}