SCBinding.h

//
//  SCBinding.h
//  StateCode
//
//  Created by Erich Ocean on 9/7/08.
//  Copyright 2008 Erich Atlas Ocean. All rights reserved.
//

@interface SCBinding : NSObject
{
    id from;
    id to;

    // set to true if you don't want changes to -> from to relay.
    BOOL oneWay;

    // set this to some value if you want a placeholder when the source
    // value is an empty array or null (if you don't also set a nullPlaceholder)
    id emptyPlaceholder;

    // set this to some value if you want a placeholder value when the source
    // value is null.  If you don't set this but you do set an emptyPlaceholder
    // then the emptyPlaceholder will be used instead.
    id nullPlaceholder;

    // set this to some value if you want a placeholder when the value is 
    // an array with multiple values.  If you set this, arrays with single
    // values will be converted to indivdual objects.  If this is set ot null,
    // multiple values will be allowed to pass untouched.
    id multiplePlaceholder;

    // set this to a function if you want a transform performed on an input
    // value.  This transform is performed both ways and before placeholder
    // values are applied.
    SEL transform; // should take three parameters: (BOOL) toIsRelayingValue, (NSString *) key, (id) value
    SEL ext;
  
    // private
    BOOL _connected;
    id _lastFromValue;
    id _lastToValue;
}

+ binding: (NSDictionary *) config;

- (void) connect;
- (void) disconnect;
- (void) relay;

@end

@interface SCBindingFrom : SCBinding {} @end
@interface SCBindingNoChange : SCBindingFrom {} @end

@interface SCBindingNoError : SCBinding {} @end
@interface SCBindingNoErrorExt : SCBindingNoError {} @end

@interface SCBindingSingle : SCBinding {} @end
@interface SCBindingSingleNil : SCBinding {} @end
@interface SCBindingSingleNoError : SCBindingNoErrorExt {} @end
@interface SCBindingSingleNilNoError : SCBindingNoErrorExt {} @end
@interface SCBindingSingleNoChange : SCBindingNoChange {} @end // adds default SC placeholders (useful in views)

@interface SCBindingMultiple : SCBinding {} @end
@interface SCBindingMultipleNoError : SCBindingNoErrorExt {} @end

@interface SCBindingBool : SCBinding {} @end
@interface SCBindingBoolNoError : SCBindingNoErrorExt {} @end
@interface SCBindingNotNull : SCBinding {} @end
@interface SCBindingNotNullNoError : SCBindingNoErrorExt {} @end
@interface SCBindingNot : SCBinding {} @end
@interface SCBindingNotNoError : SCBindingNoErrorExt {} @end
@interface SCBindingIsNull : SCBinding {} @end
@interface SCBindingIsNullNoError : SCBindingNoErrorExt {} @end

SCBinding.m

//
//  SCBinding.m
//  StateCode
//
//  Created by Erich Ocean on 9/7/08.
//  Copyright 2008 Erich Atlas Ocean. All rights reserved.
//

#import "SCBinding.h"

char *incoming = "incoming";
char *outgoing = "outgoing";

NSMutableArray *_bindings; // prevent GC of bindings

@interface SCBinding (Private)
- (void) _fromObserverForTarget: (id) target key: (NSString *) key value: (id) value;
- (void) _toObserverForTarget: (id) target key: (NSString *) key value: (id) value;
- (BOOL) _didChangeFrom: (id) lastValue to: (id) newValue;
- (NSArray *) _walkTuple: (NSArray *) tuple;
@end

@interface NSObject (SCTruthiness) 

- (BOOL) isTruthy;

@end

@implementation NSObject (SCTruthiness)

- (BOOL) isTruthy { return YES; }

@end

@implementation NSArray (SCTruthiness)

- (BOOL) isTruthy { return ( [self count] == 0 ) ? NO : YES; }

@end

@implementation NSDictionary (SCTruthiness)

- (BOOL) isTruthy { return ( [self count] == 0 ) ? NO : YES; }

@end

@implementation NSSet (SCTruthiness)

- (BOOL) isTruthy { return ( [self count] == 0 ) ? NO : YES; }

@end

@implementation NSString (SCTruthiness)

- (BOOL) isTruthy { return ( [self length] == 0 ) ? NO : YES; }

@end

@implementation NSNull (SCTruthiness)

- (BOOL) isTruthy { return NO; }

@end

@implementation NSNumber (SCTruthiness)

- (BOOL) isTruthy { return ( [self isEqualToNumber: [NSNumber numberWithInt: 0]] ) ? NO : YES; }

@end


@implementation SCBinding

+ (void) initialize
{
    static BOOL initialized = NO;
    
    if ( !initialized ) {
        _bindings = [NSMutableArray array];
        initialized = YES;
    }
}

+ binding: (NSDictionary *) config
{
    SCBinding *binding = [[self alloc] init];
    
    for ( NSString *key in [config allKeys] ) {
        if ( [key isEqualToString: @"transform"] ) {
            binding->transform = NSSelectorFromString( [config objectForKey: key] );
        }
        else [binding setValue: [config objectForKey: key] forKey: key];
    }
    
    [_bindings addObject: binding];
    
    [binding connect];
    return binding;
}

- init
{
    if ( self = [super init] ) {
        from = nil;
        to = nil;
        oneWay = NO;
        emptyPlaceholder = nil;
        nullPlaceholder = nil;
        multiplePlaceholder = nil;
        transform = NULL;
        ext = NULL;
        
        _connected = NO;
        _lastFromValue = nil;
        _lastToValue = nil;
    }
    return self;
}

- (NSString *) description
{
    return [NSString stringWithFormat: @"%@ from: %@ to: %@", [super description], from, to];
}

- (void) connect
{
    if ( !_connected ) {
        @try {
            NSArray *tuple = [SC tupleForPropertyPath: from];
            if ( tuple && (tuple = [self _walkTuple: tuple])) {
                [[tuple objectAtIndex: 0]
                        addObserver: self
                        forKeyPath:  [tuple objectAtIndex: 1]
                        options:     NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew
                        context:     (void *)incoming ];
            }
            
            if ( !oneWay ) {
                tuple = [SC tupleForPropertyPath: to];
                if ( tuple && (tuple = [self _walkTuple: tuple])) {
                    [[tuple objectAtIndex: 0]
                            addObserver: self
                            forKeyPath:  [tuple objectAtIndex: 1]
                            options:     NSKeyValueObservingOptionNew // don't care what value "to" starts with initially
                            context:     (void *)outgoing ];
                }
            }
            _connected = YES ;
        }
        @catch (id e) { NSLog( @"an exception occurred while connecting %@", self ); } // ignore
    }
}

- (void) disconnect
{
    if ( _connected ) {
        _connected = NO;

        NSArray *tuple = [SC tupleForPropertyPath: from];
        if ( tuple && (tuple = [self _walkTuple: tuple])) {
            [[tuple objectAtIndex: 0] removeObserver: self forKeyPath: [tuple objectAtIndex: 1]];
        }
        
        if ( !oneWay ) {
            NSArray *tuple = [SC tupleForPropertyPath: to];
            if ( tuple && (tuple = [self _walkTuple: tuple])) {
                [[tuple objectAtIndex: 0] removeObserver: self forKeyPath: [tuple objectAtIndex: 1]];
            }
        }
    }
}

// simulate a from -> to relay.
- (void) relay
{
    NSArray *tuple = [SC tupleForPropertyPath: from];
    if ( tuple && (tuple = [self _walkTuple: tuple])) {
        [self _fromObserverForTarget: [tuple objectAtIndex: 0]
                key: [tuple objectAtIndex: 1]
                value: [[tuple objectAtIndex: 0] valueForKey: [tuple objectAtIndex: 1]] ];
    }
}

// private
- (void) observeValueForKeyPath: (NSString *) keyPath ofObject: (id) object change: (NSDictionary *) change context: (void *) context
{
    if ( context == incoming ) {
        [self _fromObserverForTarget: object key: keyPath value: [change objectForKey: NSKeyValueChangeNewKey]];
    }
    else if ( context = outgoing ) {
        [self _toObserverForTarget: object key: keyPath value: [change objectForKey: NSKeyValueChangeNewKey]];
    }
    else NSLog( @"observeValueForKeyPath not handled (should not happen)" );
}

- (void) _fromObserverForTarget: (id) target key: (NSString *) key value: (id) value
{
    if ( value == [NSNull null] ) value = nil;
    
    // no need to forward values if they haven't actually changed.
    if ( ![self _didChangeFrom: _lastFromValue to: value ] ) return;
    _lastFromValue = value ;

    // try to get the to object.
    NSArray *tuple = [SC tupleForPropertyPath: to];
    if ( tuple && (tuple = [self _walkTuple: tuple]) ) {

        // transform the value
        if ( transform ) {
            id (*transformImp)(id, SEL, BOOL, NSString *, id);
            transformImp = (id (*)(id, SEL, BOOL, NSString *, id))[self methodForSelector: transform];
            value = transformImp( self, transform, NO, key, value );
        }
        _lastToValue = value ;

        // apply placeholder settings
        if ( value ) {
            if ( [value isKindOfClass: [NSArray class]] ) {
                switch ( [value count] ) {
                    case 0:
                        value = ( emptyPlaceholder ) ? emptyPlaceholder : value;
                        break;
                    case 1:
                        value = [value objectAtIndex: 0];
                        break;
                    default:
                        value = ( multiplePlaceholder ) ? multiplePlaceholder : value;
                        break;
                }
            }
        }

        // now handle null placeholder
        if ( !value ) value = ( nullPlaceholder ) ? nullPlaceholder : value;
        if ( !value ) value = ( emptyPlaceholder ) ? emptyPlaceholder : value;
        
        // send the value along to 'to'
        [[tuple objectAtIndex: 0] setValue: value forKey: [tuple objectAtIndex: 1]];      
    }
}

- (void) _toObserverForTarget: (id) target key: (NSString *) key value: (id) value
{
    if ( oneWay ) return; // don't propogate changes...
    
    if ( value == [NSNull null] ) value = nil;
    
    // no need to forward values if they haven't actually changed.
    if ( ![self _didChangeFrom: _lastToValue to: value ] ) return;
    _lastToValue = value ;

    // try to get the to object.
    NSArray *tuple = [SC tupleForPropertyPath: from];
    if ( tuple && (tuple = [self _walkTuple: tuple]) ) {
        // transform the value
        if ( transform ) {
            id (*transformImp)(id, SEL, BOOL, NSString *, id);
            transformImp = (id (*)(id, SEL, BOOL, NSString *, id))[self methodForSelector: transform];
            value = transformImp( self, transform, YES, key, value );
        }
        _lastFromValue = value ;

        // send along to the 'from' source.
        [[tuple objectAtIndex: 0] setValue: value forKey: [tuple objectAtIndex: 1]];      

        id result = [[tuple objectAtIndex: 0] valueForKey: [tuple objectAtIndex: 1]];

        // Now that it has been set, the FROM object might not allow some 
        // changes.  If that is the case, then we need to set this back on the sender.
        if ( ![result isEqual: value] ) [target setValue: result forKey: key];
    } 
}

- (BOOL) _didChangeFrom: (id) lastValue to: (id) newValue
{
    if ( newValue && lastValue ) return ![newValue isEqual: lastValue];
    else if ( !newValue && !lastValue ) return NO ;
    else return YES;
}

- (NSArray *) _walkTuple: (NSArray *) tuple
{
    NSArray *parts = [[tuple objectAtIndex: 1] componentsSeparatedByString: @"."];
    
    if ( parts.length > 1 )
    {
        id obj = [tuple objectAtIndex: 0];
        
        NSString *key = [parts lastObject];
        parts = [parts subarrayWithRange: NSMakeRange( 0, parts.length -1 )];
        
        NSUInteger len = parts.length;
        NSUInteger loc;
        for ( NSUInteger loc = 0; obj && (loc < len); loc++ ) {
            obj = [obj valueForKey: [parts objectAtIndex: loc]];
        }
        
        return ( loc < len || !obj )
            ? nil // hit a nil while walking the key path
            : [NSArray arrayWithObjects: obj, key, nil];
    }
    else if ( parts.length == 1 ) return tuple; // already "walked"
    else return nil; // can't be walked -- no key for object
}

- (id) _noErrorUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    return ( [value isKindOfClass: [NSError class]] ) ? nil : value ;
}

- (id) _noErrorExtUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    if ( ext ) {
        id (*transformImp)(id, SEL, BOOL, NSString *, id);
        transformImp = (id (*)(id, SEL, BOOL, NSString *, id))[self methodForSelector: ext];
        value = transformImp( self, ext, yn, key, value );
    }
    return [self _noErrorUp: yn key: key value: value];
}

- (id) _singleUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    if ( [value isKindOfClass: [NSArray class]] ) {
        switch ( [value count] ) {
            case 0:
                value = nil;
                break;
            case 1:
                value = [value objectAtIndex: 0];
                break;
            default:
                value = SC_MULTIPLE_PLACEHOLDER;
        }
    }
    return value;
}

- (id) _singleNilUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    if ( [value isKindOfClass: [NSArray class]] ) {
        switch ( [value count] ) {
            case 0:
                value = nil;
                break;
            case 1:
                value = [value objectAtIndex: 0];
                break;
            default:
                value = nil;
        }
    }
    return value;
}

// nil => [], x => [x], error => error, [x] => [x]
- (id) _multipleUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    if ( !value ) value = [NSArray array];
    else if ( ![value isKindOfClass: [NSArray class]] && ![value isKindOfClass: [NSError class]] ) value = [NSArray arrayWithObject: value];
    return value;
}

- (id) _boolUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    if ( !value ) return [NSNumber numberWithBool: NO];
    else return [NSNumber numberWithBool: [value isTruthy]];
}

- (id) _notNullUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    return [NSNumber numberWithBool: (value) ? YES : NO];
}

- (id) _notUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    if ( !value ) return [NSNumber numberWithBool: YES];
    else return [NSNumber numberWithBool: ![value isTruthy]];
}

- (id) _isNullUp: (BOOL) yn key: (NSString *) key value: (id) value
{
    return [NSNumber numberWithBool: (value) ? NO : YES];
}

@end

@implementation SCBindingFrom

- init
{
    if ( self = [super init] ) {
        oneWay = YES;
    }
    return self;
}

@end
@implementation SCBindingNoChange @end // identical to SCBindingFrom

@implementation SCBindingNoError

- init
{
    if ( self = [super init] ) {
        transform = @selector(_noErrorUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingNoErrorExt

- init
{
    if ( self = [super init] ) {
        transform = @selector(_noErrorExtUp:key:value:);
    }
    return self;
}

@end


@implementation SCBindingSingle

- init
{
    if ( self = [super init] ) {
        transform = @selector(_singleUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingSingleNil

- init
{
    if ( self = [super init] ) {
        transform = @selector(_singleNilUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingSingleNoError

- init
{
    if ( self = [super init] ) {
        ext = @selector(_singleUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingSingleNilNoError

- init
{
    if ( self = [super init] ) {
        ext = @selector(_singleNilUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingSingleNoChange

- init
{
    if ( self = [super init] ) {
        multiplePlaceholder: SC_MULTIPLE_PLACEHOLDER;
        emptyPlaceholder: SC_EMPTY_PLACEHOLDER;
        nullPlaceholder: SC_NULL_PLACEHOLDER;
    }
    return self;
}

@end

@implementation SCBindingMultiple

- init
{
    if ( self = [super init] ) {
        transform = @selector(_multipleUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingMultipleNoError

- init
{
    if ( self = [super init] ) {
        ext = @selector(_multipleUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingBool

- init
{
    if ( self = [super init] ) {
        transform = @selector(_boolUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingBoolNoError

- init
{
    if ( self = [super init] ) {
        ext = @selector(_boolUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingNotNull

- init
{
    if ( self = [super init] ) {
        transform = @selector(_notNullUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingNotNullNoError

- init
{
    if ( self = [super init] ) {
        ext = @selector(_notNullUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingNot

- init
{
    if ( self = [super init] ) {
        transform = @selector(_notUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingNotNoError

- init
{
    if ( self = [super init] ) {
        ext = @selector(_notUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingIsNull

- init
{
    if ( self = [super init] ) {
        transform = @selector(_isNullUp:key:value:);
    }
    return self;
}

@end

@implementation SCBindingIsNullNoError

- init
{
    if ( self = [super init] ) {
        ext = @selector(_isNullUp:key:value:);
    }
    return self;
}

@end