Chapter 11 - Chat App/ChatAppFinished/Pods/FirebaseDatabase/Firebase/Database/Core/FSyncPoint.m
/*
 * Copyright 2017 Google
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#import "FSyncPoint.h"
#import "FOperation.h"
#import "FWriteTreeRef.h"
#import "FNode.h"
#import "FEventRegistration.h"
#import "FIRDatabaseQuery.h"
#import "FChildrenNode.h"
#import "FTupleRemovedQueriesEvents.h"
#import "FView.h"
#import "FOperationSource.h"
#import "FQuerySpec.h"
#import "FQueryParams.h"
#import "FPath.h"
#import "FEmptyNode.h"
#import "FViewCache.h"
#import "FCacheNode.h"
#import "FPersistenceManager.h"
#import "FDataEvent.h"

/**
* SyncPoint represents a single location in a SyncTree with 1 or more event registrations, meaning we need to
* maintain 1 or more Views at this location to cache server data and raise appropriate events for server changes
* and user writes (set, transaction, update).
*
* It's responsible for:
*  - Maintaining the set of 1 or more views necessary at this location (a SyncPoint with 0 views should be removed).
*  - Proxying user / server operations to the views as appropriate (i.e. applyServerOverwrite,
*    applyUserOverwrite, etc.)
*/
@interface FSyncPoint ()
/**
* The Views being tracked at this location in the tree, stored as a map where the key is a
* queryParams and the value is the View for that query.
*
* NOTE: This list will be quite small (usually 1, but perhaps 2 or 3; any more is an odd use case).
*
* Maps NSString -> FView
*/
@property (nonatomic, strong) NSMutableDictionary *views;

@property (nonatomic, strong) FPersistenceManager *persistenceManager;
@end

@implementation FSyncPoint

- (id) initWithPersistenceManager:(FPersistenceManager *)persistence {
    self = [super init];
    if (self) {
        self.persistenceManager = persistence;
        self.views = [[NSMutableDictionary alloc] init];
    }
    return self;
}

- (BOOL) isEmpty {
    return [self.views count] == 0;
}

- (NSArray *) applyOperation:(id<FOperation>)operation
                      toView:(FView *)view
                 writesCache:(FWriteTreeRef *)writesCache
                 serverCache:(id<FNode>)optCompleteServerCache {
    FViewOperationResult *result = [view applyOperation:operation writesCache:writesCache serverCache:optCompleteServerCache];
    if (!view.query.loadsAllData) {
        NSMutableSet *removed = [NSMutableSet set];
        NSMutableSet *added = [NSMutableSet set];
        [result.changes enumerateObjectsUsingBlock:^(FChange *change, NSUInteger idx, BOOL *stop) {
            if (change.type == FIRDataEventTypeChildAdded) {
                [added addObject:change.childKey];
            } else if (change.type == FIRDataEventTypeChildRemoved) {
                [removed addObject:change.childKey];
            }
        }];
        if ([removed count] > 0 || [added count] > 0) {
            [self.persistenceManager updateTrackedQueryKeysWithAddedKeys:added removedKeys:removed forQuery:view.query];
        }
    }
    return result.events;
}

- (NSArray *) applyOperation:(id <FOperation>)operation writesCache:(FWriteTreeRef *)writesCache serverCache:(id <FNode>)optCompleteServerCache {
    FQueryParams *queryParams = operation.source.queryParams;
    if (queryParams != nil) {
        FView *view = [self.views objectForKey:queryParams];
        NSAssert(view != nil, @"SyncTree gave us an op for an invalid query.");
        return [self applyOperation:operation toView:view writesCache:writesCache serverCache:optCompleteServerCache];
    } else {
        NSMutableArray *events = [[NSMutableArray alloc] init];
        [self.views enumerateKeysAndObjectsUsingBlock:^(FQueryParams *key, FView *view, BOOL *stop) {
            NSArray *eventsForView = [self applyOperation:operation toView:view writesCache:writesCache serverCache:optCompleteServerCache];
            [events addObjectsFromArray:eventsForView];
        }];
        return events;
    }
}

/**
* Add an event callback for the specified query
* Returns Array of FEvent events to raise.
*/
- (NSArray *) addEventRegistration:(id <FEventRegistration>)eventRegistration
        forNonExistingViewForQuery:(FQuerySpec *)query
                       writesCache:(FWriteTreeRef *)writesCache
                       serverCache:(FCacheNode *)serverCache {
    NSAssert(self.views[query.params] == nil, @"Found view for query: %@", query.params);
    // TODO: make writesCache take flag for complete server node
    id<FNode> eventCache = [writesCache calculateCompleteEventCacheWithCompleteServerCache:serverCache.isFullyInitialized ? serverCache.node : nil];
    BOOL eventCacheComplete;
    if (eventCache != nil) {
        eventCacheComplete = YES;
    } else {
        eventCache = [writesCache calculateCompleteEventChildrenWithCompleteServerChildren:serverCache.node];
        eventCacheComplete = NO;
    }

    FIndexedNode *indexed = [FIndexedNode indexedNodeWithNode:eventCache index:query.index];
    FCacheNode *eventCacheNode = [[FCacheNode alloc] initWithIndexedNode:indexed
                                                      isFullyInitialized:eventCacheComplete
                                                              isFiltered:NO];
    FViewCache *viewCache = [[FViewCache alloc] initWithEventCache:eventCacheNode serverCache:serverCache];
    FView *view = [[FView alloc] initWithQuery:query initialViewCache:viewCache];
    // If this is a non-default query we need to tell persistence our current view of the data
    if (!query.loadsAllData) {
        NSMutableSet *allKeys = [NSMutableSet set];
        [view.eventCache enumerateChildrenUsingBlock:^(NSString *key, id<FNode> node, BOOL *stop) {
            [allKeys addObject:key];
        }];
        [self.persistenceManager setTrackedQueryKeys:allKeys forQuery:query];
    }
    self.views[query.params] = view;
    return [self addEventRegistration:eventRegistration forExistingViewForQuery:query];
}

- (NSArray *)addEventRegistration:(id<FEventRegistration>)eventRegistration
          forExistingViewForQuery:(FQuerySpec *)query {
    FView *view = self.views[query.params];
    NSAssert(view != nil, @"No view for query: %@", query);
    [view addEventRegistration:eventRegistration];
    return [view initialEvents:eventRegistration];
}

/**
* Remove event callback(s). Return cancelEvents if a cancelError is specified.
*
* If query is the default query, we'll check all views for the specified eventRegistration.
* If eventRegistration is nil, we'll remove all callbacks for the specified view(s).
*
* @return FTupleRemovedQueriesEvents removed queries and any cancel events
*/
- (FTupleRemovedQueriesEvents *) removeEventRegistration:(id <FEventRegistration>)eventRegistration
                                                forQuery:(FQuerySpec *)query
                                             cancelError:(NSError *)cancelError {
    NSMutableArray *removedQueries = [[NSMutableArray alloc] init];
    __block NSMutableArray *cancelEvents = [[NSMutableArray alloc] init];
    BOOL hadCompleteView = [self hasCompleteView];
    if ([query isDefault]) {
        // When you do [ref removeObserverWithHandle:], we search all views for the registration to remove.
        [self.views enumerateKeysAndObjectsUsingBlock:^(FQueryParams *viewQueryParams, FView *view, BOOL *stop) {
            [cancelEvents addObjectsFromArray:[view removeEventRegistration:eventRegistration cancelError:cancelError]];
            if ([view isEmpty]) {
                [self.views removeObjectForKey:viewQueryParams];

                // We'll deal with complete views later
                if (![view.query loadsAllData]) {
                    [removedQueries addObject:view.query];
                }
            }
        }];
    } else {
        // remove the callback from the specific view
        FView *view = [self.views objectForKey:query.params];
        if (view != nil) {
            [cancelEvents addObjectsFromArray:[view removeEventRegistration:eventRegistration cancelError:cancelError]];

            if ([view isEmpty]) {
                [self.views removeObjectForKey:query.params];

                // We'll deal with complete views later
                if (![view.query loadsAllData]) {
                    [removedQueries addObject:view.query];
                }
            }
        }
    }

    if (hadCompleteView && ![self hasCompleteView]) {
        // We removed our last complete view
        [removedQueries addObject:[FQuerySpec defaultQueryAtPath:query.path]];
    }

    return [[FTupleRemovedQueriesEvents alloc] initWithRemovedQueries:removedQueries cancelEvents:cancelEvents];
}

- (NSArray *) queryViews {
    __block NSMutableArray *filteredViews = [[NSMutableArray alloc] init];

    [self.views enumerateKeysAndObjectsUsingBlock:^(FQueryParams *key, FView *view, BOOL *stop) {
        if (![view.query loadsAllData]) {
            [filteredViews addObject:view];
        }
    }];

    return filteredViews;
}

- (id <FNode>) completeServerCacheAtPath:(FPath *)path {
    __block id<FNode> serverCache = nil;
    [self.views enumerateKeysAndObjectsUsingBlock:^(FQueryParams *key, FView *view, BOOL *stop) {
        serverCache = [view completeServerCacheFor:path];
        *stop = (serverCache != nil);
    }];
    return serverCache;
}

- (FView *) viewForQuery:(FQuerySpec *)query {
    return [self.views objectForKey:query.params];
}

- (BOOL) viewExistsForQuery:(FQuerySpec *)query {
    return [self viewForQuery:query] != nil;
}

- (BOOL) hasCompleteView {
    return [self completeView] != nil;
}

- (FView *) completeView {
    __block FView *completeView = nil;

    [self.views enumerateKeysAndObjectsUsingBlock:^(FQueryParams *key, FView *view, BOOL *stop) {
        if ([view.query loadsAllData]) {
            completeView = view;
            *stop = YES;
        }
    }];

    return completeView;
}


@end
