/*

     File: TransactionsController_Sorting.m

 Abstract: This category implements automatic re-sorting for entries in the transactions table.  We use Key value observing to observe when a transaction is added, or when a sorted value in a transaction changes. In either case, we schedule a call to rearrangeObjects to re-sort the table.

  Version: 1.2

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#import "TransactionsController.h"

static NSString *TransactionsContext = @"TransactionsController.transactions";

static NSString *SortContext = @"TransactionsController.sort";

@implementation TransactionsController(Sorting)

// -bind:toObject:withKeyPath:options: is invoked because we have bound the contentArray of this arrayController to transactions in the document.  Use this as a hook to set up an observation of the transactions array, which we will use for sorting.

- (void)bind:(NSString *)binding toObject:(id)observable withKeyPath:(NSString *)keyPath options:(NSDictionary *)options {

    [super bind:binding toObject:observable withKeyPath:keyPath options:options];

    // set this controller as an observer of the object and keyPath to which its contentArray is bound (should be MyDocument.transactions)

    if ([binding isEqualToString:@"contentArray"]) {

        [observable addObserver:self forKeyPath:keyPath options:NSKeyValueObservingOptionOld|NSKeyValueObservingOptionNew context:TransactionsContext];

        _observedKeyPath = keyPath;

    }

}

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

    // Note that we use pointer comparison for the context argument.  If this observation was set up by super, we can't be sure context will be an object, so we shouldn't use isEqual:. 

    if (context == TransactionsContext) {

        // observeValueForKeyPath:ofObject:change:context: is invoked with the context we specified above whenever an entry is added or removed from the transactions array

        NSKeyValueChange changeKind = [[change objectForKey:NSKeyValueChangeKindKey] integerValue];

        if (changeKind != NSKeyValueChangeRemoval) {

            // schedule a call to rearrangeObjects at the end of this iteration through the runloop

            [self scheduleRearrangeObjects];

        }

        // in order to update sort order when a value is changed within a transaction, we also need to observe these key paths

        [self updateObservationForOldTransactions:[change objectForKey:NSKeyValueChangeOldKey] newTransactions:[change objectForKey:NSKeyValueChangeNewKey]];

    } 

    else if (context == SortContext) {

        // a key path for a sort descriptor has been changed in a transaction

        [self scheduleRearrangeObjects];

    } 

    else {

        // be sure to call super.  Since we didn't recognize this context, this observation was probably set up by super.

        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];

    }

}

- (void)scheduleRearrangeObjects {

    // if there is already a call to rearrangeObjects scheduled, we don't need to schedule another one

    if (!_pendingArrangement) {

        _pendingArrangement = YES;

        [self performSelector:@selector(rearrangeObjects) withObject:nil afterDelay:0.0];

    }

}

- (void)rearrangeObjects {

    [super rearrangeObjects];

    _pendingArrangement = NO;

}

- (void)setSortDescriptors:(NSArray *)sortDescriptors {

    // if the sort descriptors change, we need to update our observation of the key paths in the transactions

    [self removeSortObserversForTransactions:[self arrangedObjects] sortDescriptors:[self sortDescriptors]];

    [super setSortDescriptors:sortDescriptors];

    [self addSortObserversForTransactions:[self arrangedObjects] sortDescriptors:[self sortDescriptors]];

}

- (void)updateObservationForOldTransactions:(NSArray *)oldTransactions newTransactions:(NSArray *)newTransactions {

    if ([oldTransactions count] > 0) {

        // stop observing key paths for sort descriptors in transactions that have been removed

        [self removeSortObserversForTransactions:oldTransactions sortDescriptors:[self sortDescriptors]];

    }

    if ([newTransactions count] > 0) {

        // stop observing key paths for sort descriptors in transactions that have been removed

        [self addSortObserversForTransactions:newTransactions sortDescriptors:[self sortDescriptors]];

    }

}

- (void)addSortObserversForTransactions:(NSArray *)transactions sortDescriptors:(NSArray *)sortDescriptors {

    NSSortDescriptor *sortDescriptor;

    NSIndexSet *allIndexes = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, [transactions count])]; 

    for (sortDescriptor in sortDescriptors) {

        [transactions addObserver:self toObjectsAtIndexes:allIndexes forKeyPath:[sortDescriptor key] options:0 context:SortContext];

    }

}

- (void)removeSortObserversForTransactions:(NSArray *)transactions sortDescriptors:(NSArray *)sortDescriptors {

    NSSortDescriptor *sortDescriptor;

    NSIndexSet *allIndexes = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, [transactions count])]; 

    for (sortDescriptor in sortDescriptors) {

        [transactions removeObserver:self fromObjectsAtIndexes:allIndexes forKeyPath:[sortDescriptor key]];

    }

}

- (void)unbind:(NSString *)binding {

    if ([binding isEqualToString:@"contentArray"] && _observedKeyPath != nil) {

        [_document removeObserver:self forKeyPath:_observedKeyPath];

        _observedKeyPath = nil;

    }

    [super unbind:binding];

}

- (void)dealloc {

    if (_observedKeyPath != nil) {

        [_document removeObserver:self forKeyPath:_observedKeyPath];

    }

    [self removeSortObserversForTransactions:[self arrangedObjects] sortDescriptors:[self sortDescriptors]];

    _document = nil;

    _observedKeyPath = nil;

    [super dealloc];

}

@end