//
// [The "BSD license"]
//  Copyright (c) 2012 Terence Parr
//  Copyright (c) 2012 Sam Harwell
//  Copyright (c) 2014 Eric Vergnaud
//  All rights reserved.
//
//  Redistribution and use in source and binary forms, with or without
//  modification, are permitted provided that the following conditions
//  are met:
//
//  1. Redistributions of source code must retain the above copyright
//     notice, this list of conditions and the following disclaimer.
//  2. Redistributions in binary form must reproduce the above copyright
//     notice, this list of conditions and the following disclaimer in the
//     documentation and/or other materials provided with the distribution.
//  3. The name of the author may not be used to endorse or promote products
//     derived from this software without specific prior written permission.
//
//  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
//  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
//  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
//  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
//  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
//  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
//  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
//  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
//  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
//  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//
// This enumeration defines the prediction modes available in ANTLR 4 along with
// utility methods for analyzing configuration sets for conflicts and/or
// ambiguities.

var Set = require('./../Utils').Set;
var BitSet = require('./../Utils').BitSet;
var AltDict = require('./../Utils').AltDict;
var ATN = require('./ATN').ATN;
var RuleStopState = require('./ATNState').RuleStopState;
var ATNConfigSet = require('./ATNConfigSet').ATNConfigSet;
var ATNConfig = require('./ATNConfig').ATNConfig;
var SemanticContext = require('./SemanticContext').SemanticContext;

function PredictionMode() {
	return this;
}

//
// The SLL(*) prediction mode. This prediction mode ignores the current
// parser context when making predictions. This is the fastest prediction
// mode, and provides correct results for many grammars. This prediction
// mode is more powerful than the prediction mode provided by ANTLR 3, but
// may result in syntax errors for grammar and input combinations which are
// not SLL.
//
// <p>
// When using this prediction mode, the parser will either return a correct
// parse tree (i.e. the same parse tree that would be returned with the
// {@link //LL} prediction mode), or it will report a syntax error. If a
// syntax error is encountered when using the {@link //SLL} prediction mode,
// it may be due to either an actual syntax error in the input or indicate
// that the particular combination of grammar and input requires the more
// powerful {@link //LL} prediction abilities to complete successfully.</p>
//
// <p>
// This prediction mode does not provide any guarantees for prediction
// behavior for syntactically-incorrect inputs.</p>
//
PredictionMode.SLL = 0;
//
// The LL(*) prediction mode. This prediction mode allows the current parser
// context to be used for resolving SLL conflicts that occur during
// prediction. This is the fastest prediction mode that guarantees correct
// parse results for all combinations of grammars with syntactically correct
// inputs.
//
// <p>
// When using this prediction mode, the parser will make correct decisions
// for all syntactically-correct grammar and input combinations. However, in
// cases where the grammar is truly ambiguous this prediction mode might not
// report a precise answer for <em>exactly which</em> alternatives are
// ambiguous.</p>
//
// <p>
// This prediction mode does not provide any guarantees for prediction
// behavior for syntactically-incorrect inputs.</p>
//
PredictionMode.LL = 1;
//
// The LL(*) prediction mode with exact ambiguity detection. In addition to
// the correctness guarantees provided by the {@link //LL} prediction mode,
// this prediction mode instructs the prediction algorithm to determine the
// complete and exact set of ambiguous alternatives for every ambiguous
// decision encountered while parsing.
//
// <p>
// This prediction mode may be used for diagnosing ambiguities during
// grammar development. Due to the performance overhead of calculating sets
// of ambiguous alternatives, this prediction mode should be avoided when
// the exact results are not necessary.</p>
//
// <p>
// This prediction mode does not provide any guarantees for prediction
// behavior for syntactically-incorrect inputs.</p>
//
PredictionMode.LL_EXACT_AMBIG_DETECTION = 2;


//
// Computes the SLL prediction termination condition.
//
// <p>
// This method computes the SLL prediction termination condition for both of
// the following cases.</p>
//
// <ul>
// <li>The usual SLL+LL fallback upon SLL conflict</li>
// <li>Pure SLL without LL fallback</li>
// </ul>
//
// <p><strong>COMBINED SLL+LL PARSING</strong></p>
//
// <p>When LL-fallback is enabled upon SLL conflict, correct predictions are
// ensured regardless of how the termination condition is computed by this
// method. Due to the substantially higher cost of LL prediction, the
// prediction should only fall back to LL when the additional lookahead
// cannot lead to a unique SLL prediction.</p>
//
// <p>Assuming combined SLL+LL parsing, an SLL configuration set with only
// conflicting subsets should fall back to full LL, even if the
// configuration sets don't resolve to the same alternative (e.g.
// {@code {1,2}} and {@code {3,4}}. If there is at least one non-conflicting
// configuration, SLL could continue with the hopes that more lookahead will
// resolve via one of those non-conflicting configurations.</p>
//
// <p>Here's the prediction termination rule them: SLL (for SLL+LL parsing)
// stops when it sees only conflicting configuration subsets. In contrast,
// full LL keeps going when there is uncertainty.</p>
//
// <p><strong>HEURISTIC</strong></p>
//
// <p>As a heuristic, we stop prediction when we see any conflicting subset
// unless we see a state that only has one alternative associated with it.
// The single-alt-state thing lets prediction continue upon rules like
// (otherwise, it would admit defeat too soon):</p>
//
// <p>{@code [12|1|[], 6|2|[], 12|2|[]]. s : (ID | ID ID?) ';' ;}</p>
//
// <p>When the ATN simulation reaches the state before {@code ';'}, it has a
// DFA state that looks like: {@code [12|1|[], 6|2|[], 12|2|[]]}. Naturally
// {@code 12|1|[]} and {@code 12|2|[]} conflict, but we cannot stop
// processing this node because alternative to has another way to continue,
// via {@code [6|2|[]]}.</p>
//
// <p>It also let's us continue for this rule:</p>
//
// <p>{@code [1|1|[], 1|2|[], 8|3|[]] a : A | A | A B ;}</p>
//
// <p>After matching input A, we reach the stop state for rule A, state 1.
// State 8 is the state right before B. Clearly alternatives 1 and 2
// conflict and no amount of further lookahead will separate the two.
// However, alternative 3 will be able to continue and so we do not stop
// working on this state. In the previous example, we're concerned with
// states associated with the conflicting alternatives. Here alt 3 is not
// associated with the conflicting configs, but since we can continue
// looking for input reasonably, don't declare the state done.</p>
//
// <p><strong>PURE SLL PARSING</strong></p>
//
// <p>To handle pure SLL parsing, all we have to do is make sure that we
// combine stack contexts for configurations that differ only by semantic
// predicate. From there, we can do the usual SLL termination heuristic.</p>
//
// <p><strong>PREDICATES IN SLL+LL PARSING</strong></p>
//
// <p>SLL decisions don't evaluate predicates until after they reach DFA stop
// states because they need to create the DFA cache that works in all
// semantic situations. In contrast, full LL evaluates predicates collected
// during start state computation so it can ignore predicates thereafter.
// This means that SLL termination detection can totally ignore semantic
// predicates.</p>
//
// <p>Implementation-wise, {@link ATNConfigSet} combines stack contexts but not
// semantic predicate contexts so we might see two configurations like the
// following.</p>
//
// <p>{@code (s, 1, x, {}), (s, 1, x', {p})}</p>
//
// <p>Before testing these configurations against others, we have to merge
// {@code x} and {@code x'} (without modifying the existing configurations).
// For example, we test {@code (x+x')==x''} when looking for conflicts in
// the following configurations.</p>
//
// <p>{@code (s, 1, x, {}), (s, 1, x', {p}), (s, 2, x'', {})}</p>
//
// <p>If the configuration set has predicates (as indicated by
// {@link ATNConfigSet//hasSemanticContext}), this algorithm makes a copy of
// the configurations to strip out all of the predicates so that a standard
// {@link ATNConfigSet} will merge everything ignoring predicates.</p>
//
PredictionMode.hasSLLConflictTerminatingPrediction = function( mode, configs) {
    // Configs in rule stop states indicate reaching the end of the decision
    // rule (local context) or end of start rule (full context). If all
    // configs meet this condition, then none of the configurations is able
    // to match additional input so we terminate prediction.
    //
    if (PredictionMode.allConfigsInRuleStopStates(configs)) {
        return true;
    }
    // pure SLL mode parsing
    if (mode === PredictionMode.SLL) {
        // Don't bother with combining configs from different semantic
        // contexts if we can fail over to full LL; costs more time
        // since we'll often fail over anyway.
        if (configs.hasSemanticContext) {
            // dup configs, tossing out semantic predicates
            var dup = new ATNConfigSet();
            for(var i=0;i<configs.items.length;i++) {
            	var c = configs.items[i];
                c = new ATNConfig({semanticContext:SemanticContext.NONE}, c);
                dup.add(c);
            }
            configs = dup;
        }
        // now we have combined contexts for configs with dissimilar preds
    }
    // pure SLL or combined SLL+LL mode parsing
    var altsets = PredictionMode.getConflictingAltSubsets(configs);
    return PredictionMode.hasConflictingAltSet(altsets) && !PredictionMode.hasStateAssociatedWithOneAlt(configs);
};

// Checks if any configuration in {@code configs} is in a
// {@link RuleStopState}. Configurations meeting this condition have reached
// the end of the decision rule (local context) or end of start rule (full
// context).
//
// @param configs the configuration set to test
// @return {@code true} if any configuration in {@code configs} is in a
// {@link RuleStopState}, otherwise {@code false}
PredictionMode.hasConfigInRuleStopState = function(configs) {
	for(var i=0;i<configs.items.length;i++) {
		var c = configs.items[i];
        if (c.state instanceof RuleStopState) {
            return true;
        }
	}
    return false;
};

// Checks if all configurations in {@code configs} are in a
// {@link RuleStopState}. Configurations meeting this condition have reached
// the end of the decision rule (local context) or end of start rule (full
// context).
//
// @param configs the configuration set to test
// @return {@code true} if all configurations in {@code configs} are in a
// {@link RuleStopState}, otherwise {@code false}
PredictionMode.allConfigsInRuleStopStates = function(configs) {
	for(var i=0;i<configs.items.length;i++) {
		var c = configs.items[i];
        if (!(c.state instanceof RuleStopState)) {
            return false;
        }
	}
    return true;
};

//
// Full LL prediction termination.
//
// <p>Can we stop looking ahead during ATN simulation or is there some
// uncertainty as to which alternative we will ultimately pick, after
// consuming more input? Even if there are partial conflicts, we might know
// that everything is going to resolve to the same minimum alternative. That
// means we can stop since no more lookahead will change that fact. On the
// other hand, there might be multiple conflicts that resolve to different
// minimums. That means we need more look ahead to decide which of those
// alternatives we should predict.</p>
//
// <p>The basic idea is to split the set of configurations {@code C}, into
// conflicting subsets {@code (s, _, ctx, _)} and singleton subsets with
// non-conflicting configurations. Two configurations conflict if they have
// identical {@link ATNConfig//state} and {@link ATNConfig//context} values
// but different {@link ATNConfig//alt} value, e.g. {@code (s, i, ctx, _)}
// and {@code (s, j, ctx, _)} for {@code i!=j}.</p>
//
// <p>Reduce these configuration subsets to the set of possible alternatives.
// You can compute the alternative subsets in one pass as follows:</p>
//
// <p>{@code A_s,ctx = {i | (s, i, ctx, _)}} for each configuration in
// {@code C} holding {@code s} and {@code ctx} fixed.</p>
//
// <p>Or in pseudo-code, for each configuration {@code c} in {@code C}:</p>
//
// <pre>
// map[c] U= c.{@link ATNConfig//alt alt} // map hash/equals uses s and x, not
// alt and not pred
// </pre>
//
// <p>The values in {@code map} are the set of {@code A_s,ctx} sets.</p>
//
// <p>If {@code |A_s,ctx|=1} then there is no conflict associated with
// {@code s} and {@code ctx}.</p>
//
// <p>Reduce the subsets to singletons by choosing a minimum of each subset. If
// the union of these alternative subsets is a singleton, then no amount of
// more lookahead will help us. We will always pick that alternative. If,
// however, there is more than one alternative, then we are uncertain which
// alternative to predict and must continue looking for resolution. We may
// or may not discover an ambiguity in the future, even if there are no
// conflicting subsets this round.</p>
//
// <p>The biggest sin is to terminate early because it means we've made a
// decision but were uncertain as to the eventual outcome. We haven't used
// enough lookahead. On the other hand, announcing a conflict too late is no
// big deal; you will still have the conflict. It's just inefficient. It
// might even look until the end of file.</p>
//
// <p>No special consideration for semantic predicates is required because
// predicates are evaluated on-the-fly for full LL prediction, ensuring that
// no configuration contains a semantic context during the termination
// check.</p>
//
// <p><strong>CONFLICTING CONFIGS</strong></p>
//
// <p>Two configurations {@code (s, i, x)} and {@code (s, j, x')}, conflict
// when {@code i!=j} but {@code x=x'}. Because we merge all
// {@code (s, i, _)} configurations together, that means that there are at
// most {@code n} configurations associated with state {@code s} for
// {@code n} possible alternatives in the decision. The merged stacks
// complicate the comparison of configuration contexts {@code x} and
// {@code x'}. Sam checks to see if one is a subset of the other by calling
// merge and checking to see if the merged result is either {@code x} or
// {@code x'}. If the {@code x} associated with lowest alternative {@code i}
// is the superset, then {@code i} is the only possible prediction since the
// others resolve to {@code min(i)} as well. However, if {@code x} is
// associated with {@code j>i} then at least one stack configuration for
// {@code j} is not in conflict with alternative {@code i}. The algorithm
// should keep going, looking for more lookahead due to the uncertainty.</p>
//
// <p>For simplicity, I'm doing a equality check between {@code x} and
// {@code x'} that lets the algorithm continue to consume lookahead longer
// than necessary. The reason I like the equality is of course the
// simplicity but also because that is the test you need to detect the
// alternatives that are actually in conflict.</p>
//
// <p><strong>CONTINUE/STOP RULE</strong></p>
//
// <p>Continue if union of resolved alternative sets from non-conflicting and
// conflicting alternative subsets has more than one alternative. We are
// uncertain about which alternative to predict.</p>
//
// <p>The complete set of alternatives, {@code [i for (_,i,_)]}, tells us which
// alternatives are still in the running for the amount of input we've
// consumed at this point. The conflicting sets let us to strip away
// configurations that won't lead to more states because we resolve
// conflicts to the configuration with a minimum alternate for the
// conflicting set.</p>
//
// <p><strong>CASES</strong></p>
//
// <ul>
//
// <li>no conflicts and more than 1 alternative in set =&gt; continue</li>
//
// <li> {@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s, 3, z)},
// {@code (s', 1, y)}, {@code (s', 2, y)} yields non-conflicting set
// {@code {3}} U conflicting sets {@code min({1,2})} U {@code min({1,2})} =
// {@code {1,3}} =&gt; continue
// </li>
//
// <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 1, y)},
// {@code (s', 2, y)}, {@code (s'', 1, z)} yields non-conflicting set
// {@code {1}} U conflicting sets {@code min({1,2})} U {@code min({1,2})} =
// {@code {1}} =&gt; stop and predict 1</li>
//
// <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 1, y)},
// {@code (s', 2, y)} yields conflicting, reduced sets {@code {1}} U
// {@code {1}} = {@code {1}} =&gt; stop and predict 1, can announce
// ambiguity {@code {1,2}}</li>
//
// <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 2, y)},
// {@code (s', 3, y)} yields conflicting, reduced sets {@code {1}} U
// {@code {2}} = {@code {1,2}} =&gt; continue</li>
//
// <li>{@code (s, 1, x)}, {@code (s, 2, x)}, {@code (s', 3, y)},
// {@code (s', 4, y)} yields conflicting, reduced sets {@code {1}} U
// {@code {3}} = {@code {1,3}} =&gt; continue</li>
//
// </ul>
//
// <p><strong>EXACT AMBIGUITY DETECTION</strong></p>
//
// <p>If all states report the same conflicting set of alternatives, then we
// know we have the exact ambiguity set.</p>
//
// <p><code>|A_<em>i</em>|&gt;1</code> and
// <code>A_<em>i</em> = A_<em>j</em></code> for all <em>i</em>, <em>j</em>.</p>
//
// <p>In other words, we continue examining lookahead until all {@code A_i}
// have more than one alternative and all {@code A_i} are the same. If
// {@code A={{1,2}, {1,3}}}, then regular LL prediction would terminate
// because the resolved set is {@code {1}}. To determine what the real
// ambiguity is, we have to know whether the ambiguity is between one and
// two or one and three so we keep going. We can only stop prediction when
// we need exact ambiguity detection when the sets look like
// {@code A={{1,2}}} or {@code {{1,2},{1,2}}}, etc...</p>
//
PredictionMode.resolvesToJustOneViableAlt = function(altsets) {
    return PredictionMode.getSingleViableAlt(altsets);
};

//
// Determines if every alternative subset in {@code altsets} contains more
// than one alternative.
//
// @param altsets a collection of alternative subsets
// @return {@code true} if every {@link BitSet} in {@code altsets} has
// {@link BitSet//cardinality cardinality} &gt; 1, otherwise {@code false}
//
PredictionMode.allSubsetsConflict = function(altsets) {
    return ! PredictionMode.hasNonConflictingAltSet(altsets);
};
//
// Determines if any single alternative subset in {@code altsets} contains
// exactly one alternative.
//
// @param altsets a collection of alternative subsets
// @return {@code true} if {@code altsets} contains a {@link BitSet} with
// {@link BitSet//cardinality cardinality} 1, otherwise {@code false}
//
PredictionMode.hasNonConflictingAltSet = function(altsets) {
	for(var i=0;i<altsets.length;i++) {
		var alts = altsets[i];
        if (alts.length===1) {
            return true;
        }
	}
    return false;
};

//
// Determines if any single alternative subset in {@code altsets} contains
// more than one alternative.
//
// @param altsets a collection of alternative subsets
// @return {@code true} if {@code altsets} contains a {@link BitSet} with
// {@link BitSet//cardinality cardinality} &gt; 1, otherwise {@code false}
//
PredictionMode.hasConflictingAltSet = function(altsets) {
	for(var i=0;i<altsets.length;i++) {
		var alts = altsets[i];
        if (alts.length>1) {
            return true;
        }
	}
    return false;
};

//
// Determines if every alternative subset in {@code altsets} is equivalent.
//
// @param altsets a collection of alternative subsets
// @return {@code true} if every member of {@code altsets} is equal to the
// others, otherwise {@code false}
//
PredictionMode.allSubsetsEqual = function(altsets) {
    var first = null;
	for(var i=0;i<altsets.length;i++) {
		var alts = altsets[i];
        if (first === null) {
            first = alts;
        } else if (alts!==first) {
            return false;
        }
	}
    return true;
};

//
// Returns the unique alternative predicted by all alternative subsets in
// {@code altsets}. If no such alternative exists, this method returns
// {@link ATN//INVALID_ALT_NUMBER}.
//
// @param altsets a collection of alternative subsets
//
PredictionMode.getUniqueAlt = function(altsets) {
    var all = PredictionMode.getAlts(altsets);
    if (all.length===1) {
        return all.minValue();
    } else {
        return ATN.INVALID_ALT_NUMBER;
    }
};

// Gets the complete set of represented alternatives for a collection of
// alternative subsets. This method returns the union of each {@link BitSet}
// in {@code altsets}.
//
// @param altsets a collection of alternative subsets
// @return the set of represented alternatives in {@code altsets}
//
PredictionMode.getAlts = function(altsets) {
    var all = new BitSet();
    altsets.map( function(alts) { all.or(alts); });
    return all;
};

//
// This function gets the conflicting alt subsets from a configuration set.
// For each configuration {@code c} in {@code configs}:
//
// <pre>
// map[c] U= c.{@link ATNConfig//alt alt} // map hash/equals uses s and x, not
// alt and not pred
// </pre>
//
PredictionMode.getConflictingAltSubsets = function(configs) {
    var configToAlts = {};
	for(var i=0;i<configs.items.length;i++) {
		var c = configs.items[i];
        var key = "key_" + c.state.stateNumber + "/" + c.context;
        var alts = configToAlts[key] || null;
        if (alts === null) {
            alts = new BitSet();
            configToAlts[key] = alts;
        }
        alts.add(c.alt);
	}
	var values = [];
	for(var k in configToAlts) {
		if(k.indexOf("key_")!==0) {
			continue;
		}
		values.push(configToAlts[k]);
	}
    return values;
};

//
// Get a map from state to alt subset from a configuration set. For each
// configuration {@code c} in {@code configs}:
//
// <pre>
// map[c.{@link ATNConfig//state state}] U= c.{@link ATNConfig//alt alt}
// </pre>
//
PredictionMode.getStateToAltMap = function(configs) {
    var m = new AltDict();
    configs.items.map(function(c) {
        var alts = m.get(c.state);
        if (alts === null) {
            alts = new BitSet();
            m.put(c.state, alts);
        }
        alts.add(c.alt);
    });
    return m;
};

PredictionMode.hasStateAssociatedWithOneAlt = function(configs) {
    var values = PredictionMode.getStateToAltMap(configs).values();
    for(var i=0;i<values.length;i++) {
        if (values[i].length===1) {
            return true;
        }
    }
    return false;
};

PredictionMode.getSingleViableAlt = function(altsets) {
    var result = null;
	for(var i=0;i<altsets.length;i++) {
		var alts = altsets[i];
        var minAlt = alts.minValue();
        if(result===null) {
            result = minAlt;
        } else if(result!==minAlt) { // more than 1 viable alt
            return ATN.INVALID_ALT_NUMBER;
        }
	}
    return result;
};

exports.PredictionMode = PredictionMode;
