/* 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.
 */

const RuleContext = require('./RuleContext');
const {Hash, Map} = require('./Utils');

class PredictionContext {
	constructor(cachedHashCode) {
		this.cachedHashCode = cachedHashCode;
	}

	/**
	 * Stores the computed hash code of this {@link PredictionContext}. The hash
	 * code is computed in parts to match the following reference algorithm.
	 *
	 * <pre>
	 * private int referenceHashCode() {
	 * int hash = {@link MurmurHash//initialize MurmurHash.initialize}({@link
	 * //INITIAL_HASH});
	 *
	 * for (int i = 0; i &lt; {@link //size()}; i++) {
	 * hash = {@link MurmurHash//update MurmurHash.update}(hash, {@link //getParent
	 * getParent}(i));
	 * }
	 *
	 * for (int i = 0; i &lt; {@link //size()}; i++) {
	 * hash = {@link MurmurHash//update MurmurHash.update}(hash, {@link
	 * //getReturnState getReturnState}(i));
	 * }
	 *
	 * hash = {@link MurmurHash//finish MurmurHash.finish}(hash, 2// {@link
	 * //size()});
	 * return hash;
	 * }
	 * </pre>
	 * This means only the {@link //EMPTY} context is in set.
	 */
	isEmpty() {
		return this === PredictionContext.EMPTY;
	}

	hasEmptyPath() {
		return this.getReturnState(this.length - 1) === PredictionContext.EMPTY_RETURN_STATE;
	}

	hashCode() {
		return this.cachedHashCode;
	}

	updateHashCode(hash) {
		hash.update(this.cachedHashCode);
	}
}

/**
 * Represents {@code $} in local context prediction, which means wildcard.
 * {@code//+x =//}.
 */
PredictionContext.EMPTY = null;

/**
 * Represents {@code $} in an array in full context mode, when {@code $}
 * doesn't mean wildcard: {@code $ + x = [$,x]}. Here,
 * {@code $} = {@link //EMPTY_RETURN_STATE}.
 */
PredictionContext.EMPTY_RETURN_STATE = 0x7FFFFFFF;

PredictionContext.globalNodeCount = 1;
PredictionContext.id = PredictionContext.globalNodeCount;


/*
function calculateHashString(parent, returnState) {
	return "" + parent + returnState;
}
*/

/**
 * Used to cache {@link PredictionContext} objects. Its used for the shared
 * context cash associated with contexts in DFA states. This cache
 * can be used for both lexers and parsers.
 */
class PredictionContextCache {
	constructor() {
		this.cache = new Map();
	}

	/**
	 * Add a context to the cache and return it. If the context already exists,
	 * return that one instead and do not add a new context to the cache.
	 * Protect shared cache from unsafe thread access.
	 */
	add(ctx) {
		if (ctx === PredictionContext.EMPTY) {
			return PredictionContext.EMPTY;
		}
		const existing = this.cache.get(ctx) || null;
		if (existing !== null) {
			return existing;
		}
		this.cache.put(ctx, ctx);
		return ctx;
	}

	get(ctx) {
		return this.cache.get(ctx) || null;
	}

	get length(){
		return this.cache.length;
	}
}


class SingletonPredictionContext extends PredictionContext {
	constructor(parent, returnState) {
		let hashCode = 0;
		const hash = new Hash();
		if(parent !== null) {
			hash.update(parent, returnState);
		} else {
			hash.update(1);
		}
		hashCode = hash.finish();
		super(hashCode);
		this.parentCtx = parent;
		this.returnState = returnState;
	}

	getParent(index) {
		return this.parentCtx;
	}

	getReturnState(index) {
		return this.returnState;
	}

	equals(other) {
		if (this === other) {
			return true;
		} else if (!(other instanceof SingletonPredictionContext)) {
			return false;
		} else if (this.hashCode() !== other.hashCode()) {
			return false; // can't be same if hash is different
		} else {
			if(this.returnState !== other.returnState)
				return false;
			else if(this.parentCtx==null)
				return other.parentCtx==null
			else
				return this.parentCtx.equals(other.parentCtx);
		}
	}

	toString() {
		const up = this.parentCtx === null ? "" : this.parentCtx.toString();
		if (up.length === 0) {
			if (this.returnState === PredictionContext.EMPTY_RETURN_STATE) {
				return "$";
			} else {
				return "" + this.returnState;
			}
		} else {
			return "" + this.returnState + " " + up;
		}
	}

	get length(){
		return 1;
	}

	static create(parent, returnState) {
		if (returnState === PredictionContext.EMPTY_RETURN_STATE && parent === null) {
			// someone can pass in the bits of an array ctx that mean $
			return PredictionContext.EMPTY;
		} else {
			return new SingletonPredictionContext(parent, returnState);
		}
	}
}

class EmptyPredictionContext extends SingletonPredictionContext {
	constructor() {
		super(null, PredictionContext.EMPTY_RETURN_STATE);
	}

	isEmpty() {
		return true;
	}

	getParent(index) {
		return null;
	}

	getReturnState(index) {
		return this.returnState;
	}

	equals(other) {
		return this === other;
	}

	toString() {
		return "$";
	}
}


PredictionContext.EMPTY = new EmptyPredictionContext();

class ArrayPredictionContext extends PredictionContext {
	constructor(parents, returnStates) {
		/**
		 * Parent can be null only if full ctx mode and we make an array
		 * from {@link //EMPTY} and non-empty. We merge {@link //EMPTY} by using
		 * null parent and
		 * returnState == {@link //EMPTY_RETURN_STATE}.
		 */
		const h = new Hash();
		h.update(parents, returnStates);
		const hashCode = h.finish();
		super(hashCode);
		this.parents = parents;
		this.returnStates = returnStates;
		return this;
	}

	isEmpty() {
		// since EMPTY_RETURN_STATE can only appear in the last position, we
		// don't need to verify that size==1
		return this.returnStates[0] === PredictionContext.EMPTY_RETURN_STATE;
	}

	getParent(index) {
		return this.parents[index];
	}

	getReturnState(index) {
		return this.returnStates[index];
	}

	equals(other) {
		if (this === other) {
			return true;
		} else if (!(other instanceof ArrayPredictionContext)) {
			return false;
		} else if (this.hashCode() !== other.hashCode()) {
			return false; // can't be same if hash is different
		} else {
			return this.returnStates === other.returnStates &&
					this.parents === other.parents;
		}
	}

	toString() {
		if (this.isEmpty()) {
			return "[]";
		} else {
			let s = "[";
			for (let i = 0; i < this.returnStates.length; i++) {
				if (i > 0) {
					s = s + ", ";
				}
				if (this.returnStates[i] === PredictionContext.EMPTY_RETURN_STATE) {
					s = s + "$";
					continue;
				}
				s = s + this.returnStates[i];
				if (this.parents[i] !== null) {
					s = s + " " + this.parents[i];
				} else {
					s = s + "null";
				}
			}
			return s + "]";
		}
	}

	get length(){
		return this.returnStates.length;
	}
}


/**
 * Convert a {@link RuleContext} tree to a {@link PredictionContext} graph.
 * Return {@link //EMPTY} if {@code outerContext} is empty or null.
 */
function predictionContextFromRuleContext(atn, outerContext) {
	if (outerContext === undefined || outerContext === null) {
		outerContext = RuleContext.EMPTY;
	}
	// if we are in RuleContext of start rule, s, then PredictionContext
	// is EMPTY. Nobody called us. (if we are empty, return empty)
	if (outerContext.parentCtx === null || outerContext === RuleContext.EMPTY) {
		return PredictionContext.EMPTY;
	}
	// If we have a parent, convert it to a PredictionContext graph
	const parent = predictionContextFromRuleContext(atn, outerContext.parentCtx);
	const state = atn.states[outerContext.invokingState];
	const transition = state.transitions[0];
	return SingletonPredictionContext.create(parent, transition.followState.stateNumber);
}
/*
function calculateListsHashString(parents, returnStates) {
	const s = "";
	parents.map(function(p) {
		s = s + p;
	});
	returnStates.map(function(r) {
		s = s + r;
	});
	return s;
}
*/
function merge(a, b, rootIsWildcard, mergeCache) {
	// share same graph if both same
	if (a === b) {
		return a;
	}
	if (a instanceof SingletonPredictionContext && b instanceof SingletonPredictionContext) {
		return mergeSingletons(a, b, rootIsWildcard, mergeCache);
	}
	// At least one of a or b is array
	// If one is $ and rootIsWildcard, return $ as// wildcard
	if (rootIsWildcard) {
		if (a instanceof EmptyPredictionContext) {
			return a;
		}
		if (b instanceof EmptyPredictionContext) {
			return b;
		}
	}
	// convert singleton so both are arrays to normalize
	if (a instanceof SingletonPredictionContext) {
		a = new ArrayPredictionContext([a.getParent()], [a.returnState]);
	}
	if (b instanceof SingletonPredictionContext) {
		b = new ArrayPredictionContext([b.getParent()], [b.returnState]);
	}
	return mergeArrays(a, b, rootIsWildcard, mergeCache);
}

/**
 * Merge two {@link SingletonPredictionContext} instances.
 *
 * <p>Stack tops equal, parents merge is same; return left graph.<br>
 * <embed src="images/SingletonMerge_SameRootSamePar.svg"
 * type="image/svg+xml"/></p>
 *
 * <p>Same stack top, parents differ; merge parents giving array node, then
 * remainders of those graphs. A new root node is created to point to the
 * merged parents.<br>
 * <embed src="images/SingletonMerge_SameRootDiffPar.svg"
 * type="image/svg+xml"/></p>
 *
 * <p>Different stack tops pointing to same parent. Make array node for the
 * root where both element in the root point to the same (original)
 * parent.<br>
 * <embed src="images/SingletonMerge_DiffRootSamePar.svg"
 * type="image/svg+xml"/></p>
 *
 * <p>Different stack tops pointing to different parents. Make array node for
 * the root where each element points to the corresponding original
 * parent.<br>
 * <embed src="images/SingletonMerge_DiffRootDiffPar.svg"
 * type="image/svg+xml"/></p>
 *
 * @param a the first {@link SingletonPredictionContext}
 * @param b the second {@link SingletonPredictionContext}
 * @param rootIsWildcard {@code true} if this is a local-context merge,
 * otherwise false to indicate a full-context merge
 * @param mergeCache
 */
function mergeSingletons(a, b, rootIsWildcard, mergeCache) {
	if (mergeCache !== null) {
		let previous = mergeCache.get(a, b);
		if (previous !== null) {
			return previous;
		}
		previous = mergeCache.get(b, a);
		if (previous !== null) {
			return previous;
		}
	}

	const rootMerge = mergeRoot(a, b, rootIsWildcard);
	if (rootMerge !== null) {
		if (mergeCache !== null) {
			mergeCache.set(a, b, rootMerge);
		}
		return rootMerge;
	}
	if (a.returnState === b.returnState) {
		const parent = merge(a.parentCtx, b.parentCtx, rootIsWildcard, mergeCache);
		// if parent is same as existing a or b parent or reduced to a parent,
		// return it
		if (parent === a.parentCtx) {
			return a; // ax + bx = ax, if a=b
		}
		if (parent === b.parentCtx) {
			return b; // ax + bx = bx, if a=b
		}
		// else: ax + ay = a'[x,y]
		// merge parents x and y, giving array node with x,y then remainders
		// of those graphs. dup a, a' points at merged array
		// new joined parent so create new singleton pointing to it, a'
		const spc = SingletonPredictionContext.create(parent, a.returnState);
		if (mergeCache !== null) {
			mergeCache.set(a, b, spc);
		}
		return spc;
	} else { // a != b payloads differ
		// see if we can collapse parents due to $+x parents if local ctx
		let singleParent = null;
		if (a === b || (a.parentCtx !== null && a.parentCtx === b.parentCtx)) { // ax +
																				// bx =
																				// [a,b]x
			singleParent = a.parentCtx;
		}
		if (singleParent !== null) { // parents are same
			// sort payloads and use same parent
			const payloads = [ a.returnState, b.returnState ];
			if (a.returnState > b.returnState) {
				payloads[0] = b.returnState;
				payloads[1] = a.returnState;
			}
			const parents = [ singleParent, singleParent ];
			const apc = new ArrayPredictionContext(parents, payloads);
			if (mergeCache !== null) {
				mergeCache.set(a, b, apc);
			}
			return apc;
		}
		// parents differ and can't merge them. Just pack together
		// into array; can't merge.
		// ax + by = [ax,by]
		const payloads = [ a.returnState, b.returnState ];
		let parents = [ a.parentCtx, b.parentCtx ];
		if (a.returnState > b.returnState) { // sort by payload
			payloads[0] = b.returnState;
			payloads[1] = a.returnState;
			parents = [ b.parentCtx, a.parentCtx ];
		}
		const a_ = new ArrayPredictionContext(parents, payloads);
		if (mergeCache !== null) {
			mergeCache.set(a, b, a_);
		}
		return a_;
	}
}

/**
 * Handle case where at least one of {@code a} or {@code b} is
 * {@link //EMPTY}. In the following diagrams, the symbol {@code $} is used
 * to represent {@link //EMPTY}.
 *
 * <h2>Local-Context Merges</h2>
 *
 * <p>These local-context merge operations are used when {@code rootIsWildcard}
 * is true.</p>
 *
 * <p>{@link //EMPTY} is superset of any graph; return {@link //EMPTY}.<br>
 * <embed src="images/LocalMerge_EmptyRoot.svg" type="image/svg+xml"/></p>
 *
 * <p>{@link //EMPTY} and anything is {@code //EMPTY}, so merged parent is
 * {@code //EMPTY}; return left graph.<br>
 * <embed src="images/LocalMerge_EmptyParent.svg" type="image/svg+xml"/></p>
 *
 * <p>Special case of last merge if local context.<br>
 * <embed src="images/LocalMerge_DiffRoots.svg" type="image/svg+xml"/></p>
 *
 * <h2>Full-Context Merges</h2>
 *
 * <p>These full-context merge operations are used when {@code rootIsWildcard}
 * is false.</p>
 *
 * <p><embed src="images/FullMerge_EmptyRoots.svg" type="image/svg+xml"/></p>
 *
 * <p>Must keep all contexts; {@link //EMPTY} in array is a special value (and
 * null parent).<br>
 * <embed src="images/FullMerge_EmptyRoot.svg" type="image/svg+xml"/></p>
 *
 * <p><embed src="images/FullMerge_SameRoot.svg" type="image/svg+xml"/></p>
 *
 * @param a the first {@link SingletonPredictionContext}
 * @param b the second {@link SingletonPredictionContext}
 * @param rootIsWildcard {@code true} if this is a local-context merge,
 * otherwise false to indicate a full-context merge
 */
function mergeRoot(a, b, rootIsWildcard) {
	if (rootIsWildcard) {
		if (a === PredictionContext.EMPTY) {
			return PredictionContext.EMPTY; // // + b =//
		}
		if (b === PredictionContext.EMPTY) {
			return PredictionContext.EMPTY; // a +// =//
		}
	} else {
		if (a === PredictionContext.EMPTY && b === PredictionContext.EMPTY) {
			return PredictionContext.EMPTY; // $ + $ = $
		} else if (a === PredictionContext.EMPTY) { // $ + x = [$,x]
			const payloads = [ b.returnState,
					PredictionContext.EMPTY_RETURN_STATE ];
			const parents = [ b.parentCtx, null ];
			return new ArrayPredictionContext(parents, payloads);
		} else if (b === PredictionContext.EMPTY) { // x + $ = [$,x] ($ is always first if present)
			const payloads = [ a.returnState, PredictionContext.EMPTY_RETURN_STATE ];
			const parents = [ a.parentCtx, null ];
			return new ArrayPredictionContext(parents, payloads);
		}
	}
	return null;
}

/**
 * Merge two {@link ArrayPredictionContext} instances.
 *
 * <p>Different tops, different parents.<br>
 * <embed src="images/ArrayMerge_DiffTopDiffPar.svg" type="image/svg+xml"/></p>
 *
 * <p>Shared top, same parents.<br>
 * <embed src="images/ArrayMerge_ShareTopSamePar.svg" type="image/svg+xml"/></p>
 *
 * <p>Shared top, different parents.<br>
 * <embed src="images/ArrayMerge_ShareTopDiffPar.svg" type="image/svg+xml"/></p>
 *
 * <p>Shared top, all shared parents.<br>
 * <embed src="images/ArrayMerge_ShareTopSharePar.svg"
 * type="image/svg+xml"/></p>
 *
 * <p>Equal tops, merge parents and reduce top to
 * {@link SingletonPredictionContext}.<br>
 * <embed src="images/ArrayMerge_EqualTop.svg" type="image/svg+xml"/></p>
 */
function mergeArrays(a, b, rootIsWildcard, mergeCache) {
	if (mergeCache !== null) {
		let previous = mergeCache.get(a, b);
		if (previous !== null) {
			return previous;
		}
		previous = mergeCache.get(b, a);
		if (previous !== null) {
			return previous;
		}
	}
	// merge sorted payloads a + b => M
	let i = 0; // walks a
	let j = 0; // walks b
	let k = 0; // walks target M array

	let mergedReturnStates = [];
	let mergedParents = [];
	// walk and merge to yield mergedParents, mergedReturnStates
	while (i < a.returnStates.length && j < b.returnStates.length) {
		const a_parent = a.parents[i];
		const b_parent = b.parents[j];
		if (a.returnStates[i] === b.returnStates[j]) {
			// same payload (stack tops are equal), must yield merged singleton
			const payload = a.returnStates[i];
			// $+$ = $
			const bothDollars = payload === PredictionContext.EMPTY_RETURN_STATE &&
					a_parent === null && b_parent === null;
			const ax_ax = (a_parent !== null && b_parent !== null && a_parent === b_parent); // ax+ax
																							// ->
																							// ax
			if (bothDollars || ax_ax) {
				mergedParents[k] = a_parent; // choose left
				mergedReturnStates[k] = payload;
			} else { // ax+ay -> a'[x,y]
				mergedParents[k] = merge(a_parent, b_parent, rootIsWildcard, mergeCache);
				mergedReturnStates[k] = payload;
			}
			i += 1; // hop over left one as usual
			j += 1; // but also skip one in right side since we merge
		} else if (a.returnStates[i] < b.returnStates[j]) { // copy a[i] to M
			mergedParents[k] = a_parent;
			mergedReturnStates[k] = a.returnStates[i];
			i += 1;
		} else { // b > a, copy b[j] to M
			mergedParents[k] = b_parent;
			mergedReturnStates[k] = b.returnStates[j];
			j += 1;
		}
		k += 1;
	}
	// copy over any payloads remaining in either array
	if (i < a.returnStates.length) {
		for (let p = i; p < a.returnStates.length; p++) {
			mergedParents[k] = a.parents[p];
			mergedReturnStates[k] = a.returnStates[p];
			k += 1;
		}
	} else {
		for (let p = j; p < b.returnStates.length; p++) {
			mergedParents[k] = b.parents[p];
			mergedReturnStates[k] = b.returnStates[p];
			k += 1;
		}
	}
	// trim merged if we combined a few that had same stack tops
	if (k < mergedParents.length) { // write index < last position; trim
		if (k === 1) { // for just one merged element, return singleton top
			const a_ = SingletonPredictionContext.create(mergedParents[0],
					mergedReturnStates[0]);
			if (mergeCache !== null) {
				mergeCache.set(a, b, a_);
			}
			return a_;
		}
		mergedParents = mergedParents.slice(0, k);
		mergedReturnStates = mergedReturnStates.slice(0, k);
	}

	const M = new ArrayPredictionContext(mergedParents, mergedReturnStates);

	// if we created same array as a or b, return that instead
	// TODO: track whether this is possible above during merge sort for speed
	if (M === a) {
		if (mergeCache !== null) {
			mergeCache.set(a, b, a);
		}
		return a;
	}
	if (M === b) {
		if (mergeCache !== null) {
			mergeCache.set(a, b, b);
		}
		return b;
	}
	combineCommonParents(mergedParents);

	if (mergeCache !== null) {
		mergeCache.set(a, b, M);
	}
	return M;
}

/**
 * Make pass over all <em>M</em> {@code parents}; merge any {@code equals()}
 * ones.
 */
function combineCommonParents(parents) {
	const uniqueParents = new Map();

	for (let p = 0; p < parents.length; p++) {
		const parent = parents[p];
		if (!(uniqueParents.containsKey(parent))) {
			uniqueParents.put(parent, parent);
		}
	}
	for (let q = 0; q < parents.length; q++) {
		parents[q] = uniqueParents.get(parents[q]);
	}
}

function getCachedPredictionContext(context, contextCache, visited) {
	if (context.isEmpty()) {
		return context;
	}
	let existing = visited.get(context) || null;
	if (existing !== null) {
		return existing;
	}
	existing = contextCache.get(context);
	if (existing !== null) {
		visited.put(context, existing);
		return existing;
	}
	let changed = false;
	let parents = [];
	for (let i = 0; i < parents.length; i++) {
		const parent = getCachedPredictionContext(context.getParent(i), contextCache, visited);
		if (changed || parent !== context.getParent(i)) {
			if (!changed) {
				parents = [];
				for (let j = 0; j < context.length; j++) {
					parents[j] = context.getParent(j);
				}
				changed = true;
			}
			parents[i] = parent;
		}
	}
	if (!changed) {
		contextCache.add(context);
		visited.put(context, context);
		return context;
	}
	let updated = null;
	if (parents.length === 0) {
		updated = PredictionContext.EMPTY;
	} else if (parents.length === 1) {
		updated = SingletonPredictionContext.create(parents[0], context
				.getReturnState(0));
	} else {
		updated = new ArrayPredictionContext(parents, context.returnStates);
	}
	contextCache.add(updated);
	visited.put(updated, updated);
	visited.put(context, updated);

	return updated;
}

// ter's recursive version of Sam's getAllNodes()
function getAllContextNodes(context, nodes, visited) {
	if (nodes === null) {
		nodes = [];
		return getAllContextNodes(context, nodes, visited);
	} else if (visited === null) {
		visited = new Map();
		return getAllContextNodes(context, nodes, visited);
	} else {
		if (context === null || visited.containsKey(context)) {
			return nodes;
		}
		visited.put(context, context);
		nodes.push(context);
		for (let i = 0; i < context.length; i++) {
			getAllContextNodes(context.getParent(i), nodes, visited);
		}
		return nodes;
	}
}

module.exports = {
	merge,
	PredictionContext,
	PredictionContextCache,
	SingletonPredictionContext,
	predictionContextFromRuleContext,
	getCachedPredictionContext
}
