(function (tree) {
    tree.extendFinderVisitor = function() {
        this._visitor = new tree.visitor(this);
        this.contexts = [];
        this.allExtendsStack = [[]];
    };

    tree.extendFinderVisitor.prototype = {
        run: function (root) {
            root = this._visitor.visit(root);
            root.allExtends = this.allExtendsStack[0];
            return root;
        },
        visitRule: function (ruleNode, visitArgs) {
            visitArgs.visitDeeper = false;
        },
        visitMixinDefinition: function (mixinDefinitionNode, visitArgs) {
            visitArgs.visitDeeper = false;
        },
        visitRuleset: function (rulesetNode, visitArgs) {

            if (rulesetNode.root) {
                return;
            }

            var i, j, extend, allSelectorsExtendList = [], extendList;

            // get &:extend(.a); rules which apply to all selectors in this ruleset
            for(i = 0; i < rulesetNode.rules.length; i++) {
                if (rulesetNode.rules[i] instanceof tree.Extend) {
                    allSelectorsExtendList.push(rulesetNode.rules[i]);
                }
            }

            // now find every selector and apply the extends that apply to all extends
            // and the ones which apply to an individual extend
            for(i = 0; i < rulesetNode.paths.length; i++) {
                var selectorPath = rulesetNode.paths[i],
                    selector = selectorPath[selectorPath.length-1];
                extendList = selector.extendList.slice(0).concat(allSelectorsExtendList).map(function(allSelectorsExtend) {
                    return allSelectorsExtend.clone();
                });
                for(j = 0; j < extendList.length; j++) {
                    this.foundExtends = true;
                    extend = extendList[j];
                    extend.findSelfSelectors(selectorPath);
                    extend.ruleset = rulesetNode;
                    if (j === 0) { extend.firstExtendOnThisSelectorPath = true; }
                    this.allExtendsStack[this.allExtendsStack.length-1].push(extend);
                }
            }

            this.contexts.push(rulesetNode.selectors);
        },
        visitRulesetOut: function (rulesetNode) {
            if (!rulesetNode.root) {
                this.contexts.length = this.contexts.length - 1;
            }
        },
        visitMedia: function (mediaNode, visitArgs) {
            mediaNode.allExtends = [];
            this.allExtendsStack.push(mediaNode.allExtends);
        },
        visitMediaOut: function (mediaNode) {
            this.allExtendsStack.length = this.allExtendsStack.length - 1;
        },
        visitDirective: function (directiveNode, visitArgs) {
            directiveNode.allExtends = [];
            this.allExtendsStack.push(directiveNode.allExtends);
        },
        visitDirectiveOut: function (directiveNode) {
            this.allExtendsStack.length = this.allExtendsStack.length - 1;
        }
    };

    tree.processExtendsVisitor = function() {
        this._visitor = new tree.visitor(this);
    };

    tree.processExtendsVisitor.prototype = {
        run: function(root) {
            var extendFinder = new tree.extendFinderVisitor();
            extendFinder.run(root);
            if (!extendFinder.foundExtends) { return root; }
            root.allExtends = root.allExtends.concat(this.doExtendChaining(root.allExtends, root.allExtends));
            this.allExtendsStack = [root.allExtends];
            return this._visitor.visit(root);
        },
        doExtendChaining: function (extendsList, extendsListTarget, iterationCount) {
            //
            // chaining is different from normal extension.. if we extend an extend then we are not just copying, altering and pasting
            // the selector we would do normally, but we are also adding an extend with the same target selector
            // this means this new extend can then go and alter other extends
            //
            // this method deals with all the chaining work - without it, extend is flat and doesn't work on other extend selectors
            // this is also the most expensive.. and a match on one selector can cause an extension of a selector we had already processed if
            // we look at each selector at a time, as is done in visitRuleset

            var extendIndex, targetExtendIndex, matches, extendsToAdd = [], newSelector, extendVisitor = this, selectorPath, extend, targetExtend, newExtend;

            iterationCount = iterationCount || 0;

            //loop through comparing every extend with every target extend.
            // a target extend is the one on the ruleset we are looking at copy/edit/pasting in place
            // e.g.  .a:extend(.b) {}  and .b:extend(.c) {} then the first extend extends the second one
            // and the second is the target.
            // the seperation into two lists allows us to process a subset of chains with a bigger set, as is the
            // case when processing media queries
            for(extendIndex = 0; extendIndex < extendsList.length; extendIndex++){
                for(targetExtendIndex = 0; targetExtendIndex < extendsListTarget.length; targetExtendIndex++){

                    extend = extendsList[extendIndex];
                    targetExtend = extendsListTarget[targetExtendIndex];

                    // look for circular references
                    if (this.inInheritanceChain(targetExtend, extend)) { continue; }

                    // find a match in the target extends self selector (the bit before :extend)
                    selectorPath = [targetExtend.selfSelectors[0]];
                    matches = extendVisitor.findMatch(extend, selectorPath);

                    if (matches.length) {

                        // we found a match, so for each self selector..
                        extend.selfSelectors.forEach(function(selfSelector) {

                            // process the extend as usual
                            newSelector = extendVisitor.extendSelector(matches, selectorPath, selfSelector);

                            // but now we create a new extend from it
                            newExtend = new(tree.Extend)(targetExtend.selector, targetExtend.option, 0);
                            newExtend.selfSelectors = newSelector;

                            // add the extend onto the list of extends for that selector
                            newSelector[newSelector.length-1].extendList = [newExtend];

                            // record that we need to add it.
                            extendsToAdd.push(newExtend);
                            newExtend.ruleset = targetExtend.ruleset;

                            //remember its parents for circular references
                            newExtend.parents = [targetExtend, extend];

                            // only process the selector once.. if we have :extend(.a,.b) then multiple
                            // extends will look at the same selector path, so when extending
                            // we know that any others will be duplicates in terms of what is added to the css
                            if (targetExtend.firstExtendOnThisSelectorPath) {
                                newExtend.firstExtendOnThisSelectorPath = true;
                                targetExtend.ruleset.paths.push(newSelector);
                            }
                        });
                    }
                }
            }

            if (extendsToAdd.length) {
                // try to detect circular references to stop a stack overflow.
                // may no longer be needed.
                this.extendChainCount++;
                if (iterationCount > 100) {
                    var selectorOne = "{unable to calculate}";
                    var selectorTwo = "{unable to calculate}";
                    try
                    {
                        selectorOne = extendsToAdd[0].selfSelectors[0].toCSS();
                        selectorTwo = extendsToAdd[0].selector.toCSS();
                    }
                    catch(e) {}
                    throw {message: "extend circular reference detected. One of the circular extends is currently:"+selectorOne+":extend(" + selectorTwo+")"};
                }

                // now process the new extends on the existing rules so that we can handle a extending b extending c ectending d extending e...
                return extendsToAdd.concat(extendVisitor.doExtendChaining(extendsToAdd, extendsListTarget, iterationCount+1));
            } else {
                return extendsToAdd;
            }
        },
        inInheritanceChain: function (possibleParent, possibleChild) {
            if (possibleParent === possibleChild) {
                return true;
            }
            if (possibleChild.parents) {
                if (this.inInheritanceChain(possibleParent, possibleChild.parents[0])) {
                    return true;
                }
                if (this.inInheritanceChain(possibleParent, possibleChild.parents[1])) {
                    return true;
                }
            }
            return false;
        },
        visitRule: function (ruleNode, visitArgs) {
            visitArgs.visitDeeper = false;
        },
        visitMixinDefinition: function (mixinDefinitionNode, visitArgs) {
            visitArgs.visitDeeper = false;
        },
        visitSelector: function (selectorNode, visitArgs) {
            visitArgs.visitDeeper = false;
        },
        visitRuleset: function (rulesetNode, visitArgs) {
            if (rulesetNode.root) {
                return;
            }
            var matches, pathIndex, extendIndex, allExtends = this.allExtendsStack[this.allExtendsStack.length-1], selectorsToAdd = [], extendVisitor = this, selectorPath;

            // look at each selector path in the ruleset, find any extend matches and then copy, find and replace

            for(extendIndex = 0; extendIndex < allExtends.length; extendIndex++) {
                for(pathIndex = 0; pathIndex < rulesetNode.paths.length; pathIndex++) {

                    selectorPath = rulesetNode.paths[pathIndex];

                    // extending extends happens initially, before the main pass
                    if (selectorPath[selectorPath.length-1].extendList.length) { continue; }

                    matches = this.findMatch(allExtends[extendIndex], selectorPath);

                    if (matches.length) {

                        allExtends[extendIndex].selfSelectors.forEach(function(selfSelector) {
                            selectorsToAdd.push(extendVisitor.extendSelector(matches, selectorPath, selfSelector));
                        });
                    }
                }
            }
            rulesetNode.paths = rulesetNode.paths.concat(selectorsToAdd);
        },
        findMatch: function (extend, haystackSelectorPath) {
            //
            // look through the haystack selector path to try and find the needle - extend.selector
            // returns an array of selector matches that can then be replaced
            //
            var haystackSelectorIndex, hackstackSelector, hackstackElementIndex, haystackElement,
                targetCombinator, i,
                extendVisitor = this,
                needleElements = extend.selector.elements,
                potentialMatches = [], potentialMatch, matches = [];

            // loop through the haystack elements
            for(haystackSelectorIndex = 0; haystackSelectorIndex < haystackSelectorPath.length; haystackSelectorIndex++) {
                hackstackSelector = haystackSelectorPath[haystackSelectorIndex];

                for(hackstackElementIndex = 0; hackstackElementIndex < hackstackSelector.elements.length; hackstackElementIndex++) {

                    haystackElement = hackstackSelector.elements[hackstackElementIndex];

                    // if we allow elements before our match we can add a potential match every time. otherwise only at the first element.
                    if (extend.allowBefore || (haystackSelectorIndex == 0 && hackstackElementIndex == 0)) {
                        potentialMatches.push({pathIndex: haystackSelectorIndex, index: hackstackElementIndex, matched: 0, initialCombinator: haystackElement.combinator});
                    }

                    for(i = 0; i < potentialMatches.length; i++) {
                        potentialMatch = potentialMatches[i];

                        // selectors add " " onto the first element. When we use & it joins the selectors together, but if we don't
                        // then each selector in haystackSelectorPath has a space before it added in the toCSS phase. so we need to work out
                        // what the resulting combinator will be
                        targetCombinator = haystackElement.combinator.value;
                        if (targetCombinator == '' && hackstackElementIndex === 0) {
                            targetCombinator = ' ';
                        }

                        // if we don't match, null our match to indicate failure
                        if (!extendVisitor.isElementValuesEqual(needleElements[potentialMatch.matched].value, haystackElement.value) ||
                            (potentialMatch.matched > 0 && needleElements[potentialMatch.matched].combinator.value !== targetCombinator)) {
                            potentialMatch = null;
                        } else {
                            potentialMatch.matched++;
                        }

                        // if we are still valid and have finished, test whether we have elements after and whether these are allowed
                        if (potentialMatch) {
                            potentialMatch.finished = potentialMatch.matched === needleElements.length;
                            if (potentialMatch.finished &&
                                (!extend.allowAfter && (hackstackElementIndex+1 < hackstackSelector.elements.length || haystackSelectorIndex+1 < haystackSelectorPath.length))) {
                                potentialMatch = null;
                            }
                        }
                        // if null we remove, if not, we are still valid, so either push as a valid match or continue
                        if (potentialMatch) {
                            if (potentialMatch.finished) {
                                potentialMatch.length = needleElements.length;
                                potentialMatch.endPathIndex = haystackSelectorIndex;
                                potentialMatch.endPathElementIndex = hackstackElementIndex + 1; // index after end of match
                                potentialMatches.length = 0; // we don't allow matches to overlap, so start matching again
                                matches.push(potentialMatch);
                            }
                        } else {
                            potentialMatches.splice(i, 1);
                            i--;
                        }
                    }
                }
            }
            return matches;
        },
        isElementValuesEqual: function(elementValue1, elementValue2) {
            if (typeof elementValue1 === "string" || typeof elementValue2 === "string") {
                return elementValue1 === elementValue2;
            }
            if (elementValue1 instanceof tree.Attribute) {
                if (elementValue1.op !== elementValue2.op || elementValue1.key !== elementValue2.key) {
                    return false;
                }
                if (!elementValue1.value || !elementValue2.value) {
                    if (elementValue1.value || elementValue2.value) {
                        return false;
                    }
                    return true;
                }
                elementValue1 = elementValue1.value.value || elementValue1.value;
                elementValue2 = elementValue2.value.value || elementValue2.value;
                return elementValue1 === elementValue2;
            }
            return false;
        },
        extendSelector:function (matches, selectorPath, replacementSelector) {

            //for a set of matches, replace each match with the replacement selector

            var currentSelectorPathIndex = 0,
                currentSelectorPathElementIndex = 0,
                path = [],
                matchIndex,
                selector,
                firstElement,
                match;

            for (matchIndex = 0; matchIndex < matches.length; matchIndex++) {
                match = matches[matchIndex];
                selector = selectorPath[match.pathIndex];
                firstElement = new tree.Element(
                    match.initialCombinator,
                    replacementSelector.elements[0].value,
                    replacementSelector.elements[0].index
                );

                if (match.pathIndex > currentSelectorPathIndex && currentSelectorPathElementIndex > 0) {
                    path[path.length - 1].elements = path[path.length - 1].elements.concat(selectorPath[currentSelectorPathIndex].elements.slice(currentSelectorPathElementIndex));
                    currentSelectorPathElementIndex = 0;
                    currentSelectorPathIndex++;
                }

                path = path.concat(selectorPath.slice(currentSelectorPathIndex, match.pathIndex));

                path.push(new tree.Selector(
                    selector.elements
                        .slice(currentSelectorPathElementIndex, match.index)
                        .concat([firstElement])
                        .concat(replacementSelector.elements.slice(1))
                ));
                currentSelectorPathIndex = match.endPathIndex;
                currentSelectorPathElementIndex = match.endPathElementIndex;
                if (currentSelectorPathElementIndex >= selector.elements.length) {
                    currentSelectorPathElementIndex = 0;
                    currentSelectorPathIndex++;
                }
            }

            if (currentSelectorPathIndex < selectorPath.length && currentSelectorPathElementIndex > 0) {
                path[path.length - 1].elements = path[path.length - 1].elements.concat(selectorPath[currentSelectorPathIndex].elements.slice(currentSelectorPathElementIndex));
                currentSelectorPathElementIndex = 0;
                currentSelectorPathIndex++;
            }

            path = path.concat(selectorPath.slice(currentSelectorPathIndex, selectorPath.length));

            return path;
        },
        visitRulesetOut: function (rulesetNode) {
        },
        visitMedia: function (mediaNode, visitArgs) {
            var newAllExtends = mediaNode.allExtends.concat(this.allExtendsStack[this.allExtendsStack.length-1]);
            newAllExtends = newAllExtends.concat(this.doExtendChaining(newAllExtends, mediaNode.allExtends));
            this.allExtendsStack.push(newAllExtends);
        },
        visitMediaOut: function (mediaNode) {
            this.allExtendsStack.length = this.allExtendsStack.length - 1;
        },
        visitDirective: function (directiveNode, visitArgs) {
            var newAllExtends = directiveNode.allExtends.concat(this.allExtendsStack[this.allExtendsStack.length-1]);
            newAllExtends = newAllExtends.concat(this.doExtendChaining(newAllExtends, directiveNode.allExtends));
            this.allExtendsStack.push(newAllExtends);
        },
        visitDirectiveOut: function (directiveNode) {
            this.allExtendsStack.length = this.allExtendsStack.length - 1;
        }
    };

})(require('./tree'));