ZKSwizzle.m

//
//  ZKSwizzle.m
//  ZKSwizzle
//
//  Created by Alexander S Zielenski on 7/24/14.
//  Copyright (c) 2014 Alexander S Zielenski. All rights reserved.
//

#import "ZKSwizzle.h"
static NSMutableDictionary *classTable;

@interface NSObject (ZKSwizzle)
+ (void)_ZK_unconditionallySwizzle;
@end

void *ZKIvarPointer(id self, const char *name) {
    Ivar ivar = class_getInstanceVariable(object_getClass(self), name);
    return ivar == NULL ? NULL : (__bridge void *)self + ivar_getOffset(ivar);
}

static SEL destinationSelectorForSelector(SEL cmd, Class dst) {
    return NSSelectorFromString([@"_ZK_old_" stringByAppendingFormat:@"%s_%@", class_getName(dst), NSStringFromSelector(cmd)]);
}

static Class classFromInfo(const char *info) {
    NSUInteger bracket_index = -1;
    for (NSUInteger i = 0; i < strlen(info); i++) {
        if (info[i] == '[') {
            bracket_index = i;
        }
    }
    bracket_index++;
    
    if (bracket_index == -1) {
        [NSException raise:@"Failed to parse info" format:@"Couldn't find swizzle class for info: %s", info];
        return NULL;
    }
    
    char after_bracket[255];
    memcpy(after_bracket, &info[bracket_index], strlen(info) - bracket_index - 1);
    
    for (NSUInteger i = 0; i < strlen(info); i++) {
        if (after_bracket[i] == ' ') {
            after_bracket[i] = '\0';
        }
    }

    return objc_getClass(after_bracket);
}

// takes __PRETTY_FUNCTION__ for info which gives the name of the swizzle source class
/*
 
 We add the original implementation onto the swizzle class
 On ZKOrig, we use __PRETTY_FUNCTION__ to get the name of the swizzle class
 Then we get the implementation of that selector on the swizzle class
 Then we call it directly, passing in the correct selector and self
 
 */
ZKIMP ZKOriginalImplementation(id self, SEL sel, const char *info) {
    if (sel == NULL || self == NULL || info == NULL) {
        [NSException raise:@"Invalid Arguments" format:@"One of self: %@, self: %@, or info: %s is NULL", self, NSStringFromSelector(sel), info];
        return NULL;
    }
    
    Class cls = classFromInfo(info);
    Class dest = object_getClass(self);
    
    if (cls == NULL || dest == NULL) {
        [NSException raise:@"Failed obtain class pair" format:@"src: %@ | dst: %@ | sel: %@", NSStringFromClass(cls), NSStringFromClass(dest), NSStringFromSelector(sel)];
        return NULL;
    }
    
    SEL destSel = destinationSelectorForSelector(sel, cls);
    
    Method method =  class_getInstanceMethod(dest, destSel);
    
    if (method == NULL) {
        [NSException raise:@"Failed to retrieve method" format:@"Got null for the source class %@ with selector %@ (%@)", NSStringFromClass(cls), NSStringFromSelector(sel), NSStringFromSelector(destSel)];
        return NULL;
    }
    
    ZKIMP implementation = (ZKIMP)method_getImplementation(method);
    if (implementation == NULL) {
        [NSException raise:@"Failed to get implementation" format:@"The objective-c runtime could not get the implementation for %@ on the class %@. There is no fix for this", NSStringFromClass(cls), NSStringFromSelector(sel)];
    }
    
    return implementation;
}

ZKIMP ZKSuperImplementation(id object, SEL sel, const char *info) {
    if (sel == NULL || object == NULL) {
        [NSException raise:@"Invalid Arguments" format:@"One of self: %@, self: %@ is NULL", object, NSStringFromSelector(sel)];
        return NULL;
    }
    
    Class cls = object_getClass(object);
    if (cls == NULL) {
        [NSException raise:@"Invalid Argument" format:@"Could not obtain class for the passed object"];
        return NULL;
    }
    
    // Two scenarios:
    // 1.) The superclass was not swizzled, no problem
    // 2.) The superclass was swizzled, problem
    
    // We want to return the swizzled class's superclass implementation
    // If this is a subclass of such a class, we want two behaviors:
    // a.) If this imp was also swizzled, no problem, return the superclass's swizzled imp
    // b.) This imp was not swizzled, return the class that was originally swizzled's superclass's imp
    Class sourceClass = classFromInfo(info);
    if (sourceClass != NULL) {
        BOOL isClassMethod = class_isMetaClass(cls);
        // This was called from a swizzled method, get the class it was swizzled with
        NSString *className = classTable[NSStringFromClass(sourceClass)];
        if (className != NULL) {
            cls = NSClassFromString(className);
            // make sure we get a class method if we asked for one
            if (isClassMethod) {
                cls = object_getClass(cls);
            }
        }
    }
    
    cls = class_getSuperclass(cls);

    // This is a root class, it has no super class
    if (cls == NULL) {
        [NSException raise:@"Invalid Argument" format:@"Could not obtain superclass for the passed object"];
        return NULL;
    }
    
    Method method = class_getInstanceMethod(cls, sel);
    if (method == NULL) {
        [NSException raise:@"Failed to retrieve method" format:@"We could not find the super implementation for the class %@ and selector %@, are you sure it exists?", NSStringFromClass(cls), NSStringFromSelector(sel)];
        return NULL;
    }
    
    ZKIMP implementation = (ZKIMP)method_getImplementation(method);
    if (implementation == NULL) {
        [NSException raise:@"Failed to get implementation" format:@"The objective-c runtime could not get the implementation for %@ on the class %@. There is no fix for this", NSStringFromClass(cls), NSStringFromSelector(sel)];
    }
    
    return implementation;
}

static BOOL enumerateMethods(Class, Class);
BOOL _ZKSwizzle(Class src, Class dest) {
    if (dest == NULL)
        return NO;
    
    NSString *destName = NSStringFromClass(dest);
    if (!destName) {
        return NO;
    }
    
    if (!classTable) {
        classTable = [[NSMutableDictionary alloc] init];
    }
    
    if ([classTable objectForKey:NSStringFromClass(src)]) {
        [NSException raise:@"Invalid Argument"
                    format:@"This source class (%@) was already swizzled with another, (%@)", NSStringFromClass(src), classTable[NSStringFromClass(src)]];
        return NO;
    }
    
    BOOL success = enumerateMethods(dest, src);
    // The above method only gets instance methods. Do the same method for the metaclass of the class
    success     &= enumerateMethods(object_getClass(dest), object_getClass(src));
    
    [classTable setObject:destName forKey:NSStringFromClass(src)];
    return success;
}

BOOL _ZKSwizzleClass(Class cls) {
    return _ZKSwizzle(cls, [cls superclass]);
}

static BOOL enumerateMethods(Class destination, Class source) {
#if OBJC_API_VERSION < 2
    [NSException raise:@"Unsupported feature" format:@"ZKSwizzle is only available in objc 2.0"];
    return NO;
    
#else
    
    unsigned int methodCount;
    Method *methodList = class_copyMethodList(source, &methodCount);
    BOOL success = YES;
    for (int i = 0; i < methodCount; i++) {
        Method method = methodList[i];
        SEL selector  = method_getName(method);
        NSString *methodName = NSStringFromSelector(selector);
        
        // Don't do anything with the unconditional swizzle
        if (sel_isEqual(selector, @selector(_ZK_unconditionallySwizzle))) {
            continue;
        }
        
        // We only swizzle methods that are implemented
        if (class_respondsToSelector(destination, selector)) {
            Method originalMethod = class_getInstanceMethod(destination, selector);
            
            const char *originalType = method_getTypeEncoding(originalMethod);
            const char *newType = method_getTypeEncoding(method);
            if (strcmp(originalType, newType) != 0) {
                NSLog(@"ZKSwizzle: incompatible type encoding for %@. (expected %s, got %s)", methodName, originalType, newType);
                // Incompatible type encoding
                success = NO;
                continue;
            }
            
            // We are re-adding the destination selector because it could be on a superclass and not on the class itself. This method could fail
            class_addMethod(destination, selector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
            
            SEL destSel = destinationSelectorForSelector(selector, source);
            if (!class_addMethod(destination, destSel, method_getImplementation(method), method_getTypeEncoding(originalMethod))) {
                NSLog(@"ZKSwizzle: failed to add method %@ onto class %@ with selector %@", NSStringFromSelector(selector), NSStringFromClass(source), NSStringFromSelector(destSel));
                success = NO;
                continue;
            }
            
            method_exchangeImplementations(class_getInstanceMethod(destination, selector), class_getInstanceMethod(destination, destSel));
        } else {
            // Add any extra methods to the class but don't swizzle them
            success &= class_addMethod(destination, selector, method_getImplementation(method), method_getTypeEncoding(method));
        }
    }
    
    unsigned int propertyCount;
    objc_property_t *propertyList = class_copyPropertyList(source, &propertyCount);
    for (int i = 0; i < propertyCount; i++) {
        objc_property_t property = propertyList[i];
        const char *name = property_getName(property);
        unsigned int attributeCount;
        objc_property_attribute_t *attributes = property_copyAttributeList(property, &attributeCount);
        
        if (class_getProperty(destination, name) == NULL) {
            class_addProperty(destination, name, attributes, attributeCount);
        } else {
            class_replaceProperty(destination, name, attributes, attributeCount);
        }
        
        free(attributes);
    }
    
    free(propertyList);
    free(methodList);
    return success;
#endif
}

// Options were to use a group class and traverse its subclasses
// or to create a groups dictionary
// This works because +load on NSObject is called before attribute((constructor))
static NSMutableDictionary *groups = nil;
void _$ZKRegisterInterface(Class cls, const char *groupName) {
    if (!groups)
        groups = [NSMutableDictionary dictionary];
    
    NSString *groupString = @(groupName);
    NSMutableArray *groupList = groups[groupString];
    if (!groupList) {
        groupList = [NSMutableArray array];
        groups[groupString] = groupList;
    }
    
    [groupList addObject:NSStringFromClass(cls)];
}

BOOL _ZKSwizzleGroup(const char *groupName) {
    NSArray *groupList = groups[@(groupName)];
    if (!groupList) {
        [NSException raise:@"Invalid Argument" format:@"ZKSwizzle: There is no group by the name of %s", groupName];
        return NO;
    }
    
    BOOL success = YES;
    for (NSString *className in groupList) {
        Class cls = NSClassFromString(className);
        if (cls == NULL)
            continue;
        
        if (class_respondsToSelector(object_getClass(cls), @selector(_ZK_unconditionallySwizzle))) {
            [cls _ZK_unconditionallySwizzle];
        } else {
            success = NO;
        }
    }
    
    return success;
}