package ab1.impl.GRUPPE;

import ab1.FinalizedStateException;
import ab1.NFA;
import ab1.NFAFactory;
import ab1.Transition;
import lombok.Getter;

import java.util.*;
import java.util.stream.Collectors;

public class NFAImpl implements NFA {
    private Set<String> states;
    private Set<Transition> transitions;

    private String initialState;
    private Set<String> acceptingStates;

    @Getter
    private Set<Character> alphabet;

    private boolean isFinalized;

    public NFAImpl(String startState) {
        this.initialState = startState;
        this.states = new HashSet<>();
        this.states.add(startState);
        this.transitions = new HashSet<>();
        this.acceptingStates = new HashSet<>();
        this.alphabet = new HashSet<>();
        this.isFinalized = false;

    }

    @Override
    public Set<String> getStates() {
        return this.states;
    }

    @Override
    public Collection<Transition> getTransitions() {
        return this.transitions;
    }

    @Override
    public Set<String> getAcceptingStates() {
        return this.acceptingStates;
    }

    @Override
    public String getInitialState() {
        return this.initialState;
    }

    @Override
    public void addTransition(Transition transition) throws FinalizedStateException {
        if (this.isFinalized) {
            throw new FinalizedStateException();
        }
        if (!states.contains(transition.fromState())) {
            this.states.add(transition.fromState());
        }
        if (!states.contains(transition.toState())) {
            this.states.add(transition.toState());
        }
        // add symbol to alphabet. If it is already in the alphabet, nothing happens
        this.alphabet.add(transition.readSymbol());
        this.transitions.add(transition);
    }

    public void addAllTransition(Set<Transition> transitions) throws FinalizedStateException {
        if(this.isFinalized){
            throw new FinalizedStateException();
        }
        for (Transition transition : transitions) {
            this.addTransition(transition);
        }
    }

    @Override
    public void addAcceptingState(String state) throws FinalizedStateException {
        if (this.isFinalized) {
            throw new FinalizedStateException();
        }
        this.states.add(state);
        this.acceptingStates.add(state);
    }

    public void addAllAcceptingStates(Set<String> states) throws FinalizedStateException {
        if(this.isFinalized){
            throw new FinalizedStateException();
        }
        for (String state : states) {
            this.addAcceptingState(state);
        }
    }

    // #TODO
    @Override
    public NFA union(NFA other) throws FinalizedStateException {
        if (!this.isFinalized || !other.isFinalized()) {
            throw new FinalizedStateException();
        }
        NFAImpl unionNFA = new NFAImpl(this.initialState);

        unionNFA.states.addAll(this.states);
        unionNFA.states.addAll(other.getStates());

        unionNFA.transitions.addAll(this.transitions);
        unionNFA.transitions.addAll(other.getTransitions());


        return unionNFA;
    }

    // #TODO
    @Override
    public NFA intersection(NFA other) throws FinalizedStateException {
        if (!this.isFinalized || !other.isFinalized()) {
            throw new FinalizedStateException();
        }
        NFAImpl intersectionNFA = new NFAImpl(this.initialState);

        intersectionNFA.states.addAll(this.states);
        intersectionNFA.states.retainAll(other.getStates());

        intersectionNFA.transitions.addAll(this.transitions);
        intersectionNFA.transitions.retainAll(other.getTransitions());

        return intersectionNFA;
    }

    // #TODO
    @Override
    public NFA concatenation(NFA other) throws FinalizedStateException {
        if (!this.isFinalized || !other.isFinalized()) {
            throw new FinalizedStateException();
        }
        NFAImpl concatenationNFA = new NFAImpl(this.initialState);

        concatenationNFA.states.addAll(this.states);
        concatenationNFA.states.addAll(other.getStates());

        concatenationNFA.transitions.addAll(this.transitions);
        concatenationNFA.transitions.addAll(other.getTransitions());

        for (String accceptingState : this.acceptingStates) {
            Transition epsilon = new Transition(accceptingState, null, other.getInitialState());
            concatenationNFA.transitions.add(epsilon);
        }

        return concatenationNFA;
    }

    @Override
    public NFA kleeneStar() throws FinalizedStateException {
        if (!this.isFinalized) {
            throw new FinalizedStateException();
        }

        NFAImpl nfa = new NFAImpl(this.initialState);

        // copy, but without accepting states
        nfa.states.addAll(this.states);
        nfa.transitions.addAll(this.transitions);

        // adding the initial state as accepting state because we have to accept the empty string
        nfa.acceptingStates.add(this.initialState);

        // for each accepting state
        for (String acceptingState : this.acceptingStates) {
            Transition loopBackTransition =
                    // creating an epsilon transition (null) for each accepting state
                    new Transition(acceptingState, null, this.initialState);
            if (!nfa.transitions.contains(loopBackTransition)) {
                nfa.transitions.add(loopBackTransition);
            }
        }

        return nfa;
    }

    @Override
    public NFA plusOperator() throws FinalizedStateException {
        if (!this.isFinalized) {
            throw new FinalizedStateException();
        }

        NFAImpl nfa = new NFAImpl(this.initialState);

        // simple copy
        nfa.states.addAll(this.states);
        nfa.transitions.addAll(this.transitions);
        nfa.acceptingStates.addAll(this.acceptingStates);

        // for each accepting state
        for (String acceptingState : this.acceptingStates) {
            Transition loopBackTransition =
                    // creating an epsilon transition (null) for each accepting state
                    new Transition(acceptingState, null, this.initialState);
            if (!nfa.transitions.contains(loopBackTransition)) {
                nfa.transitions.add(loopBackTransition);
            }
        }

        return nfa;
    }

    // #TODO
    @Override
    public NFA complement() throws FinalizedStateException {
        if (!this.isFinalized) {
            throw new FinalizedStateException();
        }

        NFAImpl complementNFA = new NFAImpl(this.initialState);
        complementNFA.states.addAll(this.states);
        complementNFA.transitions.addAll(this.transitions);

        /*
        for(String state : this.states){

        }
        */

        return null;
    }

    @Override
    public boolean isFinalized() {
        return isFinalized;
    }

    @Override
    public void finalizeAutomaton() {
        this.isFinalized = true;
    }

    // #TODO
    @Override
    public boolean isFinite() {
        //transitions={fromState==toState}
        //states={A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z}
        //obergrenze = anzahl der states (26)
        return false;
    }

    // #TODO
    @Override
    public boolean acceptsWord(String word) throws FinalizedStateException {
        //check if word is accepted
        return false;
    }

    public NFA convertNFAtoDFA(NFAImpl input) {

        /*
        What do we need to do?

        Helper Methods:
        - epsilonClosure
        - getStateAfterTransition
        - determineAcceptingStates

         */

        Set<String> dfaAcceptingStates = new HashSet<>();
        // all states of the DFA
        List<Set<String>> dfaStates = new ArrayList<>();
        // all transitions of the DFA
        Set<Transition> dfaTransitions = new HashSet<>();

        // all states of the NFA
        Set<String> startState = new HashSet<>();
        startState.add(input.getInitialState());

        // getting the epsilon closure of the start state
        startState = epsilonClosure(startState, input);
        dfaStates.add(startState);
        if (isAcceptingState(startState, input)){
            dfaAcceptingStates.add(getIndexOfSet(startState, dfaStates));
        }

        // do the above with each DFA state
        Queue<Set<String>> queue = new LinkedList<>();
        queue.add(startState);
        // iterate each Letter
        while (!queue.isEmpty()) {
            Set<String> currentState = queue.poll();
            // for each possible Letter
            for (char letter : input.getAlphabet()) {
                // get the new state after the transition
                Set<String> newState = epsilonClosure(getStateAfterTransition(currentState, letter, input), input);
                if (!dfaStates.contains(newState)) {
                    queue.add(newState);
                    dfaStates.add(newState);
                    if (isAcceptingState(newState, input)) {
                        dfaAcceptingStates.add(getIndexOfSet(newState, dfaStates));
                    }

                }
                // build new Transition
                dfaTransitions.add(new Transition(getIndexOfSet(currentState, dfaStates), letter, getIndexOfSet(newState, dfaStates)));

                // we got to change this to only a string is given
                //dfaTransitions.add(new Transition(currentState, letter, newState));
            }
        }

        NFAImpl newDFA = new NFAImpl("0");

        for(int i=1;i<dfaStates.size();i++){
            newDFA.states.add(""+i);
        }

        newDFA.addAllTransition(dfaTransitions);
        newDFA.addAllAcceptingStates(dfaAcceptingStates);

        newDFA.finalizeAutomaton();

        return newDFA;
    }

    private Set<String> epsilonClosure(Set<String> states, NFA nfa) {
        /*
        Original:

        boolean isAccepting = false;

        int index = 0;

        List<Set<String>> DFA_states = new ArrayList<>();
        Set<Transition> DFA_transitions = new HashSet<>();

        // start state alle verbindungen mit epsilon als set
        for(String state : states) {
            for (Transition transition : input.transitions) {
                if (state.equals(transition.fromState()) && transition.readSymbol() == null) {
                    if(!isAccepting) {
                        for (String acceptingState : acceptingStates)
                            if (transition.toState().equals(acceptingState)) {
                                isAccepting = true;
                                break;
                            }
                    }
                    states.add(transition.toState());
                    // funktioniert immer noch, wenn w epsilon Übergänge hintereinander?
                }
            }
        }
        DFA_states.add(new HashSet<>(states));
         */

        Set<String> closure = new HashSet<>(states);
        Stack<String> stack = new Stack<>();
        stack.addAll(states);
        while (!stack.isEmpty()) {
            String state = stack.pop();
            for (Transition transition : nfa.getTransitions()) {
                if (transition.fromState().equals(state) && transition.readSymbol() == null) {
                    if (closure.add(transition.toState())) {
                        stack.push(transition.toState());
                    }
                }
            }
        }
        return closure;
    }

    private Set<String> getStateAfterTransition(Set<String> states, char symbol, NFA nfa) {
        Set<String> result = new HashSet<>();
        for (String state : states) {
            for (Transition transition : nfa.getTransitions()) {
                if (transition.fromState().equals(state) && transition.readSymbol() != null && transition.readSymbol() == symbol) {
                    result.add(transition.toState());
                }
            }
        }
        return result;
    }

    private boolean isAcceptingState(Set<String> states, NFA input) {
        for (String accState : input.getAcceptingStates()) {
            if (states.contains(accState)) {
                return true;
            }
        }
        return false;
    }

    private String getIndexOfSet(Set<String> set, List<Set<String>> dfaStates){
        return Integer.toString(dfaStates.indexOf(set));
    }

}