/*
 * Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

package org.antlr.v4.runtime.atn;

import org.antlr.v4.runtime.Parser;
import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.TokenStream;
import org.antlr.v4.runtime.dfa.DFA;
import org.antlr.v4.runtime.dfa.DFAState;

import java.util.BitSet;

Since:
4.3/**
 * @since 4.3
 */
public class ProfilingATNSimulator extends ParserATNSimulator {
	protected final DecisionInfo[] decisions;
	protected int numDecisions;

	protected int _sllStopIndex;
	protected int _llStopIndex;

	protected int currentDecision;
	protected DFAState currentState;

 	
At the point of LL failover, we record how SLL would resolve the conflict so that
 we can determine whether or not a decision / input pair is context-sensitive.
 If LL gives a different result than SLL's predicted alternative, we have a
 context sensitivity for sure. The converse is not necessarily true, however.
 It's possible that after conflict resolution chooses minimum alternatives,
 SLL could get the same answer as LL. Regardless of whether or not the result indicates
 an ambiguity, it is not treated as a context sensitivity because LL prediction
 was not required in order to produce a correct prediction for this decision and input sequence.
 It may in fact still be a context sensitivity but we don't know by looking at the
 minimum alternatives for the current input.
/** At the point of LL failover, we record how SLL would resolve the conflict so that
	 *  we can determine whether or not a decision / input pair is context-sensitive.
	 *  If LL gives a different result than SLL's predicted alternative, we have a
	 *  context sensitivity for sure. The converse is not necessarily true, however.
	 *  It's possible that after conflict resolution chooses minimum alternatives,
	 *  SLL could get the same answer as LL. Regardless of whether or not the result indicates
	 *  an ambiguity, it is not treated as a context sensitivity because LL prediction
	 *  was not required in order to produce a correct prediction for this decision and input sequence.
	 *  It may in fact still be a context sensitivity but we don't know by looking at the
	 *  minimum alternatives for the current input.
 	 */
	protected int conflictingAltResolvedBySLL;

	public ProfilingATNSimulator(Parser parser) {
		super(parser,
				parser.getInterpreter().atn,
				parser.getInterpreter().decisionToDFA,
				parser.getInterpreter().sharedContextCache);
		numDecisions = atn.decisionToState.size();
		decisions = new DecisionInfo[numDecisions];
		for (int i=0; i<numDecisions; i++) {
			decisions[i] = new DecisionInfo(i);
		}
	}

	@Override
	public int adaptivePredict(TokenStream input, int decision, ParserRuleContext outerContext) {
		try {
			this._sllStopIndex = -1;
			this._llStopIndex = -1;
			this.currentDecision = decision;
			long start = System.nanoTime(); // expensive but useful info
			int alt = super.adaptivePredict(input, decision, outerContext);
			long stop = System.nanoTime();
			decisions[decision].timeInPrediction += (stop-start);
			decisions[decision].invocations++;

			int SLL_k = _sllStopIndex - _startIndex + 1;
			decisions[decision].SLL_TotalLook += SLL_k;
			decisions[decision].SLL_MinLook = decisions[decision].SLL_MinLook==0 ? SLL_k : Math.min(decisions[decision].SLL_MinLook, SLL_k);
			if ( SLL_k > decisions[decision].SLL_MaxLook ) {
				decisions[decision].SLL_MaxLook = SLL_k;
				decisions[decision].SLL_MaxLookEvent =
						new LookaheadEventInfo(decision, null, alt, input, _startIndex, _sllStopIndex, false);
			}

			if (_llStopIndex >= 0) {
				int LL_k = _llStopIndex - _startIndex + 1;
				decisions[decision].LL_TotalLook += LL_k;
				decisions[decision].LL_MinLook = decisions[decision].LL_MinLook==0 ? LL_k : Math.min(decisions[decision].LL_MinLook, LL_k);
				if ( LL_k > decisions[decision].LL_MaxLook ) {
					decisions[decision].LL_MaxLook = LL_k;
					decisions[decision].LL_MaxLookEvent =
							new LookaheadEventInfo(decision, null, alt, input, _startIndex, _llStopIndex, true);
				}
			}

			return alt;
		}
		finally {
			this.currentDecision = -1;
		}
	}

	@Override
	protected DFAState getExistingTargetState(DFAState previousD, int t) {
		// this method is called after each time the input position advances
		// during SLL prediction
		_sllStopIndex = _input.index();

		DFAState existingTargetState = super.getExistingTargetState(previousD, t);
		if ( existingTargetState!=null ) {
			decisions[currentDecision].SLL_DFATransitions++; // count only if we transition over a DFA state
			if ( existingTargetState==ERROR ) {
				decisions[currentDecision].errors.add(
						new ErrorInfo(currentDecision, previousD.configs, _input, _startIndex, _sllStopIndex, false)
				);
			}
		}

		currentState = existingTargetState;
		return existingTargetState;
	}

	@Override
	protected DFAState computeTargetState(DFA dfa, DFAState previousD, int t) {
		DFAState state = super.computeTargetState(dfa, previousD, t);
		currentState = state;
		return state;
	}

	@Override
	protected ATNConfigSet computeReachSet(ATNConfigSet closure, int t, boolean fullCtx) {
		if (fullCtx) {
			// this method is called after each time the input position advances
			// during full context prediction
			_llStopIndex = _input.index();
		}

		ATNConfigSet reachConfigs = super.computeReachSet(closure, t, fullCtx);
		if (fullCtx) {
			decisions[currentDecision].LL_ATNTransitions++; // count computation even if error
			if ( reachConfigs!=null ) {
			}
			else { // no reach on current lookahead symbol. ERROR.
				// TODO: does not handle delayed errors per getSynValidOrSemInvalidAltThatFinishedDecisionEntryRule()
				decisions[currentDecision].errors.add(
					new ErrorInfo(currentDecision, closure, _input, _startIndex, _llStopIndex, true)
				);
			}
		}
		else {
			decisions[currentDecision].SLL_ATNTransitions++;
			if ( reachConfigs!=null ) {
			}
			else { // no reach on current lookahead symbol. ERROR.
				decisions[currentDecision].errors.add(
					new ErrorInfo(currentDecision, closure, _input, _startIndex, _sllStopIndex, false)
				);
			}
		}
		return reachConfigs;
	}

	@Override
	protected boolean evalSemanticContext(SemanticContext pred, ParserRuleContext parserCallStack, int alt, boolean fullCtx) {
		boolean result = super.evalSemanticContext(pred, parserCallStack, alt, fullCtx);
		if (!(pred instanceof SemanticContext.PrecedencePredicate)) {
			boolean fullContext = _llStopIndex >= 0;
			int stopIndex = fullContext ? _llStopIndex : _sllStopIndex;
			decisions[currentDecision].predicateEvals.add(
				new PredicateEvalInfo(currentDecision, _input, _startIndex, stopIndex, pred, result, alt, fullCtx)
			);
		}

		return result;
	}

	@Override
	protected void reportAttemptingFullContext(DFA dfa, BitSet conflictingAlts, ATNConfigSet configs, int startIndex, int stopIndex) {
		if ( conflictingAlts!=null ) {
			conflictingAltResolvedBySLL = conflictingAlts.nextSetBit(0);
		}
		else {
			conflictingAltResolvedBySLL = configs.getAlts().nextSetBit(0);
		}
		decisions[currentDecision].LL_Fallback++;
		super.reportAttemptingFullContext(dfa, conflictingAlts, configs, startIndex, stopIndex);
	}

	@Override
	protected void reportContextSensitivity(DFA dfa, int prediction, ATNConfigSet configs, int startIndex, int stopIndex) {
		if ( prediction != conflictingAltResolvedBySLL ) {
			decisions[currentDecision].contextSensitivities.add(
					new ContextSensitivityInfo(currentDecision, configs, _input, startIndex, stopIndex)
			);
		}
		super.reportContextSensitivity(dfa, prediction, configs, startIndex, stopIndex);
	}

	@Override
	protected void reportAmbiguity(DFA dfa, DFAState D, int startIndex, int stopIndex, boolean exact,
								   BitSet ambigAlts, ATNConfigSet configs)
	{
		int prediction;
		if ( ambigAlts!=null ) {
			prediction = ambigAlts.nextSetBit(0);
		}
		else {
			prediction = configs.getAlts().nextSetBit(0);
		}
		if ( configs.fullCtx && prediction != conflictingAltResolvedBySLL ) {
			// Even though this is an ambiguity we are reporting, we can
			// still detect some context sensitivities.  Both SLL and LL
			// are showing a conflict, hence an ambiguity, but if they resolve
			// to different minimum alternatives we have also identified a
			// context sensitivity.
			decisions[currentDecision].contextSensitivities.add(
					new ContextSensitivityInfo(currentDecision, configs, _input, startIndex, stopIndex)
			);
		}
		decisions[currentDecision].ambiguities.add(
			new AmbiguityInfo(currentDecision, configs, ambigAlts,
							  _input, startIndex, stopIndex, configs.fullCtx)
		);
		super.reportAmbiguity(dfa, D, startIndex, stopIndex, exact, ambigAlts, configs);
	}

	// ---------------------------------------------------------------------

	public DecisionInfo[] getDecisionInfo() {
		return decisions;
	}

	public DFAState getCurrentState() {
		return currentState;
	}
}