/*

 Copyright (C) 2015 Apple Inc. All Rights Reserved.

  See LICENSE.txt for this sample’s licensing information

  Abstract:

  Data model for a photo search query. 

 */

#import "SearchQuery.h"

NSString *SearchQueryChildrenDidChangeNotification = @"SearchQueryChildrenDidChangeNotification";

@interface SearchQuery ()

@property (strong) NSMetadataQuery *query;

@property (strong) NSArray *children;

@end

#pragma mark -

@implementation SearchQuery

- (instancetype)init {

    return [self initWithSearchPredicate:nil title:@"" scopeURL:nil];

}

- (instancetype)initWithSearchPredicate:(NSPredicate *)searchPredicate title:(NSString *)title scopeURL:(NSURL *)url {

    self = [super init];

    if (self != nil) {

        _title = title;

        _query = [[NSMetadataQuery alloc] init];

        _searchURL = url;

        // We want the items in the query to automatically be sorted by the file system name;

        // this way, we don't have to do any special sorting

        self.query.sortDescriptors = @[[[NSSortDescriptor alloc] initWithKey:(id)kMDItemFSName ascending:YES]];

        self.query.predicate = searchPredicate;

        // Use KVO to watch the results of the query

        [self.query addObserver:self forKeyPath:@"results" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

        self.query.delegate = self;

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(queryNote:) name:nil object:self.query];

        // define the scope/where the search will take placce

        self.query.searchScopes = (url != nil) ? @[url] : nil;

        [self.query startQuery];

    }

    return self;    

}

- (void)dealloc {

    [[NSNotificationCenter defaultCenter] removeObserver:self];    

    [self.query removeObserver:self forKeyPath:@"results"];

}

- (void)sendChildrenDidChangeNote {

    [[NSNotificationCenter defaultCenter] postNotificationName:SearchQueryChildrenDidChangeNotification object:self];

}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {

    // Delegate the KVO notification by sending a children changed note.

    // We could check the keyPath, but there is no need, since we only observe one value.

    //

    _children = self.query.results;

    [self sendChildrenDidChangeNote];

}

#pragma NSMetadataQuery Delegate

- (id)metadataQuery:(NSMetadataQuery *)query replacementObjectForResultObject:(NSMetadataItem *)result {

    // We keep our own search item for the result in order to maintian state (image, thumbnail, title, etc)

    return [[SearchItem alloc] initWithItem:result];

}

- (void)queryNote:(NSNotification *)note {

    // The NSMetadataQuery will send back a note when updates are happening.

    // By looking at the [note name], we can tell what is happening

    //

    if ([note.name isEqualToString:NSMetadataQueryDidFinishGatheringNotification]) {

        // At this point, the query will be done. You may recieve an update later on.

        if (self.children.count == 0) {

            SearchItem *emptyItem = [[SearchItem alloc] initWithItem:nil];

            [emptyItem setTitle:NSLocalizedString(@"No results", @"Text to display when there are no results")];

            _children = @[emptyItem];

            [self sendChildrenDidChangeNote];

        }        

    }

}

@end