Chapter 11 - Chat App/ChatAppFinished/Pods/FirebaseDatabase/Firebase/Database/Core/View/FView.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 "FView.h"
#import "FNode.h"
#import "FWriteTreeRef.h"
#import "FOperation.h"
#import "FIRDatabaseQuery.h"
#import "FIRDatabaseQuery_Private.h"
#import "FEventRegistration.h"
#import "FQueryParams.h"
#import "FQuerySpec.h"
#import "FViewCache.h"
#import "FPath.h"
#import "FEventGenerator.h"
#import "FOperationSource.h"
#import "FCancelEvent.h"
#import "FIndexedFilter.h"
#import "FCacheNode.h"
#import "FEmptyNode.h"
#import "FViewProcessor.h"
#import "FViewProcessorResult.h"
#import "FIndexedNode.h"

@interface FViewOperationResult ()

@property (nonatomic, strong, readwrite) NSArray *changes;
@property (nonatomic, strong, readwrite) NSArray *events;

@end

@implementation FViewOperationResult

- (id)initWithChanges:(NSArray *)changes events:(NSArray *)events {
    self = [super init];
    if (self != nil) {
        self->_changes = changes;
        self->_events = events;
    }
    return self;
}

@end

/**
* A view represents a specific location and query that has 1 or more event registrations.
*
* It does several things:
* - Maintains the list of event registration for this location/query.
* - Maintains a cache of the data visible for this location/query.
* - Applies new operations (via applyOperation), updates the cache, and based on the event
*   registrations returns the set of events to be raised.
*/
@interface FView ()

@property (nonatomic, strong, readwrite) FQuerySpec *query;
@property (nonatomic, strong) FViewProcessor *processor;
@property (nonatomic, strong) FViewCache *viewCache;
@property (nonatomic, strong) NSMutableArray *eventRegistrations;
@property (nonatomic, strong) FEventGenerator *eventGenerator;

@end

@implementation FView
- (id) initWithQuery:(FQuerySpec *)query initialViewCache:(FViewCache *)initialViewCache {
    self = [super init];
    if (self) {
        self.query = query;

        FIndexedFilter *indexFilter = [[FIndexedFilter alloc] initWithIndex:query.index];
        id<FNodeFilter> filter = query.params.nodeFilter;
        self.processor = [[FViewProcessor alloc] initWithFilter:filter];
        FCacheNode *initialServerCache = initialViewCache.cachedServerSnap;
        FCacheNode *initialEventCache = initialViewCache.cachedEventSnap;

        // Don't filter server node with other filter than index, wait for tagged listen
        FIndexedNode *emptyIndexedNode = [FIndexedNode indexedNodeWithNode:[FEmptyNode emptyNode] index:query.index];
        FIndexedNode *serverSnap = [indexFilter updateFullNode:emptyIndexedNode
                                                   withNewNode:initialServerCache.indexedNode
                                                   accumulator:nil];
        FIndexedNode *eventSnap = [filter updateFullNode:emptyIndexedNode
                                             withNewNode:initialEventCache.indexedNode
                                             accumulator:nil];
        FCacheNode *newServerCache = [[FCacheNode alloc] initWithIndexedNode:serverSnap
                                                          isFullyInitialized:initialServerCache.isFullyInitialized
                                                                  isFiltered:indexFilter.filtersNodes];
        FCacheNode *newEventCache = [[FCacheNode alloc] initWithIndexedNode:eventSnap
                                                         isFullyInitialized:initialEventCache.isFullyInitialized
                                                                 isFiltered:filter.filtersNodes];

        self.viewCache = [[FViewCache alloc] initWithEventCache:newEventCache serverCache:newServerCache];

        self.eventRegistrations = [[NSMutableArray alloc] init];

        self.eventGenerator = [[FEventGenerator alloc] initWithQuery:query];
    }

    return self;
}

- (id <FNode>) serverCache {
    return self.viewCache.cachedServerSnap.node;
}

- (id <FNode>) eventCache {
    return self.viewCache.cachedEventSnap.node;
}

- (id <FNode>) completeServerCacheFor:(FPath*)path {
    id<FNode> cache = self.viewCache.completeServerSnap;
    if (cache) {
            // If this isn't a "loadsAllData" view, then cache isn't actually a complete cache and
            // we need to see if it contains the child we're interested in.
            if ([self.query loadsAllData] ||
                (!path.isEmpty && ![cache getImmediateChild:path.getFront].isEmpty)) {
            return [cache getChild:path];
        }
    }
    return nil;
}

- (BOOL) isEmpty {
    return self.eventRegistrations.count == 0;
}

- (void) addEventRegistration:(id <FEventRegistration>)eventRegistration {
    [self.eventRegistrations addObject:eventRegistration];
}

/**
* @param eventRegistration If null, remove all callbacks.
* @param cancelError If a cancelError is provided, appropriate cancel events will be returned.
* @return Cancel events, if cancelError was provided.
*/
- (NSArray *) removeEventRegistration:(id <FEventRegistration>)eventRegistration cancelError:(NSError *)cancelError {
    NSMutableArray *cancelEvents = [[NSMutableArray alloc] init];
    if (cancelError != nil) {
        NSAssert(eventRegistration == nil, @"A cancel should cancel all event registrations.");
        FPath *path = self.query.path;
        for (id <FEventRegistration> registration in self.eventRegistrations) {
            FCancelEvent *maybeEvent = [registration createCancelEventFromError:cancelError path:path];
            if (maybeEvent) {
                [cancelEvents addObject:maybeEvent];
            }
        }
    }

    if (eventRegistration) {
        NSUInteger i = 0;
        while (i < self.eventRegistrations.count) {
            id<FEventRegistration> existing = self.eventRegistrations[i];
            if ([existing matches:eventRegistration]) {
                [self.eventRegistrations removeObjectAtIndex:i];
            } else {
                i++;
            }
        }
    } else {
        [self.eventRegistrations removeAllObjects];
    }
    return cancelEvents;
}

/**
 * Applies the given Operation, updates our cache, and returns the appropriate events and changes
 */
- (FViewOperationResult *) applyOperation:(id <FOperation>)operation writesCache:(FWriteTreeRef *)writesCache serverCache:(id <FNode>)optCompleteServerCache {
    if (operation.type == FOperationTypeMerge && operation.source.queryParams != nil) {
        NSAssert(self.viewCache.completeServerSnap != nil, @"We should always have a full cache before handling merges");
        NSAssert(self.viewCache.completeEventSnap != nil, @"Missing event cache, even though we have a server cache");
    }
    FViewCache *oldViewCache = self.viewCache;
    FViewProcessorResult *result = [self.processor applyOperationOn:oldViewCache operation:operation writesCache:writesCache completeCache:optCompleteServerCache];

    NSAssert(result.viewCache.cachedServerSnap.isFullyInitialized || !oldViewCache.cachedServerSnap.isFullyInitialized, @"Once a server snap is complete, it should never go back.");

    self.viewCache = result.viewCache;
    NSArray *events = [self generateEventsForChanges:result.changes eventCache:result.viewCache.cachedEventSnap.indexedNode registration:nil];
    return [[FViewOperationResult alloc] initWithChanges:result.changes events:events];
}

- (NSArray *) initialEvents:(id<FEventRegistration>)registration {
    FCacheNode *eventSnap = self.viewCache.cachedEventSnap;
    NSMutableArray *initialChanges = [[NSMutableArray alloc] init];
    [eventSnap.indexedNode.node enumerateChildrenUsingBlock:^(NSString *key, id<FNode> node, BOOL *stop) {
        FIndexedNode *indexed = [FIndexedNode indexedNodeWithNode:node];
        FChange *change = [[FChange alloc] initWithType:FIRDataEventTypeChildAdded indexedNode:indexed childKey:key];
        [initialChanges addObject:change];
    }];
    if (eventSnap.isFullyInitialized) {
        FChange *change = [[FChange alloc] initWithType:FIRDataEventTypeValue indexedNode:eventSnap.indexedNode];
        [initialChanges addObject:change];
    }
    return [self generateEventsForChanges:initialChanges eventCache:eventSnap.indexedNode registration:registration];
}

- (NSArray *) generateEventsForChanges:(NSArray *)changes eventCache:(FIndexedNode *)eventCache registration:(id<FEventRegistration>)registration {
    NSArray *registrations;
    if (registration == nil) {
        registrations = [[NSArray alloc] initWithArray:self.eventRegistrations];
    } else {
        registrations = [[NSArray alloc] initWithObjects:registration, nil];
    }
    return [self.eventGenerator generateEventsForChanges:changes eventCache:eventCache eventRegistrations:registrations];
}

- (NSString *) description {
    return [NSString stringWithFormat:@"FView (%@)", self.query];
}
@end
