Engine uses parsed parameter XML and the user's response to decide which item is next. This engine using branching (eg. A->C or B->F) instead of gates and thresholds.

SequenceBranchEngineByGate.m

//
//  SequenceBranchEngineByGate.m
//  mss-cognition
//
//  Created by Mike Rose on 9/11/14.
//  Copyright (c) 2014 Northwestern University. All rights reserved.
//

#import "SequenceBranchEngineByGate.h"

#import "ListSortingRangeCriteria.h"
#import "ListSortingRestartCriteria.h"
#import "ListSortingBranchingCriteria.h"
#import "ListSortingGateCriteria.h"

#import "ListSortingConstants.h"

@interface SequenceBranchEngineByGate ()
@property (strong, nonatomic, readonly) MSSUser *user;
@property (strong, nonatomic, readonly) NSArray *items;
@property (strong, nonatomic, readonly) MSSItem *currentItem;
@property (strong, nonatomic, readonly) NSDictionary *branchingCriteria;
@property (strong, nonatomic, readonly) NSDictionary *gateCriteria;
@property (strong, nonatomic, readonly) NSArray *rangeCriteria;
@property (strong, nonatomic, readonly) NSDictionary *restartCriteria;
@end

@implementation SequenceBranchEngineByGate

-(id)initWithParameterDictionary:(NSDictionary *)parameterDictionary andConfigurationDictionary:(NSDictionary *)configurationDictionary
{
    self = [super init];
    if (self) {
        _branchingCriteria = parameterDictionary[ListSortingParameterBranchingCriteriaKey];
        _gateCriteria = parameterDictionary[ListSortingParameterGateCriteriaKey];
        _rangeCriteria = parameterDictionary[ListSortingParameterRangeCriteriaKey];
        _restartCriteria = parameterDictionary[ListSortingParameterRestartCriteriaKey];
    }
    
    return self;
}

// TODO: remove, add to init method
-(void)setUser:(MSSUser *)user
{
    _user = user;
}

// TODO: remove, add to init method
-(void)setItemList: (NSArray *) value
{
    // filter and sort the item list
    NSMutableArray *items = [NSMutableArray array];
    for (ListSortingRangeCriteria *range in _rangeCriteria) {
        // MR   Hard-coded to one range (7+), remove reference to user.age, 2/2/2015
        // if (_user.age >= range.minAge && _user.age <= range.maxAge) {
            for (ListSortingRangeCriteriaSection *section in range.sections) {
                NSPredicate *sectionPredicate = [NSPredicate predicateWithFormat:@"Section = %ld", (long)section.identifier];
                NSArray *filteredItemsBySection = [value filteredArrayUsingPredicate:sectionPredicate];
                [items addObjectsFromArray:filteredItemsBySection];
            }
            break;
        // }
    }
    _items = items;
    
    // MR   Check for administered items (restart)
    
    //      Use the restart criteria dictionary to ignore items from the administered items list
    
    //      The current implementation ignores any practice items answered so it always
    //      starts you at the beginning of practice (intro)
    
    if (self.administeredItems.count) {
        NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT (FormItemOID IN %@)", _restartCriteria.allKeys];
        _currentItem = [[self.administeredItems filteredArrayUsingPredicate:predicate] lastObject];
    }
}

- (MSSItem *)previousItem
{
    MSSItem *item = self.administeredItems.lastObject;
    if (item) {
        item.ItemResponseOID = nil;
        item.Position = nil;
        item.Response = nil;
        item.ResponseDescription = nil;
        item.ResponseTime = nil;
        item.score = nil;
        
        _currentItem = item;
    }
    
    return _currentItem;
}

- (MSSItem *)nextItem
{
    ListSortingBranchingCriteria *branch = [_branchingCriteria objectForKey:_currentItem.FormItemOID];
    if ([branch.criteriaItemResponseOID isEqualToString:_currentItem.ItemResponseOID]) {
        NSString *formItemOID;
        if (branch.criteriaOperator == 2) {
            // get the next item based on gate criteria
            NSArray *gates = [_gateCriteria objectForKey:_currentItem.FormItemOID];
            ListSortingGateCriteria *gate = [gates objectAtIndex:0];
            NSArray *formItemOIDs = [gate.items valueForKeyPath:@"formItemOID"];
            NSInteger score = [self rawScoreForFormItemOIDs:formItemOIDs];
            for (ListSortingGateCriteria *gate in gates) {
                if (gate.criteriaItemResponseValueTotal == score) {
                    formItemOID = gate.targetFormItemOID;
                    break;
                }
            }
        } else {
            // get the next item based on the branch criteria's form item oid
            formItemOID = branch.targetFormItemOID;
        }
        _currentItem = [self itemForFormItemOID:formItemOID];
    } else {
        // get the next item in the items array list
        NSUInteger index = [_items indexOfObject:_currentItem];
        index = (index == NSNotFound) ? 0 : (index + 1);
        _currentItem = (index < _items.count) ? [_items objectAtIndex:index] : nil;
    }
    
    return _currentItem;
}

- (NSArray *)processUserGeneratedResponses:(NSArray *)responses score:(NSNumber *)score responseTime:(NSTimeInterval)responseTime
{
    NSString *response = [responses firstObject];
    MSSMap *selectedMap = [MSSResponseHelper mapForResponseWithID:[responses firstObject] forItem:_currentItem];
    if (selectedMap != nil) {
        _currentItem.Response = selectedMap.Value;
        _currentItem.ResponseDescription = selectedMap.Description;
    } else {
        _currentItem.Response = response;
    }
    _currentItem.ItemResponseOID = response;
    _currentItem.ResponseTime = [NSString stringWithFormat:@"%f", responseTime];
    _currentItem.score = score;
    _currentItem.Position = [NSString stringWithFormat:@"%td", (self.administeredItems.count + 1)];
    
    return @[ _currentItem ];
}

- (NSArray *)administeredItems
{
    // only administed items have a position (set in processUserGeneratedResponses)
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"Position.length > 0"];
    NSArray *administeredItems = [_items filteredArrayUsingPredicate:predicate];

    NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"Position" ascending:YES selector:@selector(localizedStandardCompare:)];
    
    return [administeredItems sortedArrayUsingDescriptors:@[sort]];
}

- (NSInteger)rawScoreForFormItemOIDs:(NSArray *)formItemOIDs
{
    NSInteger rawScore = 0;
    for (NSString *formItemOID in formItemOIDs) {
        MSSItem *item = [self itemForFormItemOID:formItemOID];
        rawScore += item.score.integerValue;
    }
    
    return rawScore;
}

- (MSSItem *)itemForFormItemOID:(NSString *)formItemOID
{
    for (MSSItem *item in _items) {
        if ([formItemOID isEqualToString:item.FormItemOID]) {
            return item;
        }
    }
    
    return nil;
}

@end