Conditionalize execution according to various constraints about a device. All values compared against are "cached"

REBConditionals.h

//
//  REBConditionals.h
//  Rebase
//
//  Created by Robert Widmann on 8/16/13.
//  Copyright (c) 2013 CodaFi. All rights reserved.
//

#ifndef Rebase_REBConditionals_h
#define Rebase_REBConditionals_h

extern void REBMigrateToVersion(const char *version, void(^migrateBlock)());

extern void REBExecuteOnPhone(void(^block)());
extern void REBExecuteOnPad(void(^block)());

extern void REBExecuteOnSystemGreaterThan(const char *version, void(^block)());
extern void REBExecuteOnSystemGreaterThanOrEqualTo(const char *version, void(^block)());
extern void REBExecuteOnSystemLessThan(const char *version, void(^block)());
extern void REBExecuteOnSystemLessThanOrEqualTo(const char *version, void(^block)());
extern void REBExecuteOnSystemEqualTo(const char *version, void(^block)());

#endif

REBConditionals.m

//
//  REBConditionals.m
//  Rebase
//
//  Created by Robert Widmann on 8/16/13.
//  Copyright (c) 2013 CodaFi. All rights reserved.
//

#include "REBConditionals.h"

static NSString *const REBLastAppVersionKey = @"REBLastAppVersionKey";

typedef NS_ENUM(int, REBVersionOrdering) {
	REBVersionOrderingDescending,
	REBVersionOrderingAscending,
	REBVersionOrderingSame
};

static REBVersionOrdering REBCompareVersions(const char *version1, const char *version2);

@interface REBConditionalsInternal : NSObject
+ (instancetype)sharedInternals;
@property (nonatomic, copy) NSString *version;
@property (nonatomic, copy) NSString *systemVersion;
@property (nonatomic, copy) NSString *lastMigrationVersion;
@property (nonatomic) UIUserInterfaceIdiom idiom;
@end

@implementation REBConditionalsInternal

+ (void)load {
	[self.class sharedInternals];
}

+ (instancetype)sharedInternals {
	static REBConditionalsInternal *internals;
	static dispatch_once_t onceToken;
	dispatch_once(&onceToken, ^{
		internals = [REBConditionalsInternal new];
	});
	return internals;
}

- (id)init {
	self = [super init];
	_version = [NSBundle.mainBundle objectForInfoDictionaryKey:@"CFBundleShortVersionString"];
	_lastMigrationVersion = [NSUserDefaults.standardUserDefaults valueForKey:REBLastAppVersionKey] ?: @"0.0.0";
	_idiom = UIDevice.currentDevice.userInterfaceIdiom;
	_systemVersion = UIDevice.currentDevice.systemVersion;
	return self;
}

- (NSString *)systemVersion {
	if ([_systemVersion componentsSeparatedByString:@"."].count == 2) {
		return [_systemVersion stringByAppendingString:@".0"];
	}
	return _systemVersion;
}

@end

void REBMigrateToVersion(const char *version, void(^migrateBlock)()) {
	NSCParameterAssert(migrateBlock != NULL);
	
	NSString *appVersion = REBConditionalsInternal.sharedInternals.version;
	NSString *lastVersion = REBConditionalsInternal.sharedInternals.lastMigrationVersion;
	int mig_ver[3], sys_ver[3], last_ver[3];
	sscanf(version, "%d.%d.%d", &mig_ver[0], &mig_ver[1], &mig_ver[2]);
	sscanf(appVersion.UTF8String, "%d.%d.%d", &sys_ver[0], &sys_ver[1], &sys_ver[2]);
	sscanf(lastVersion.UTF8String, "%d.%d.%d", &last_ver[0], &last_ver[1], &last_ver[2]);

	for (int i = 0; i < 3; i++) {
		if (mig_ver[i] <= sys_ver[i] && mig_ver[i] > last_ver[i]) {
			migrateBlock();
			[NSUserDefaults.standardUserDefaults setValue:appVersion forKey:REBLastAppVersionKey];
			[NSUserDefaults.standardUserDefaults synchronize];
			return;
		}
	}
}

void REBExecuteOnPhone(void(^block)()) {
	NSCParameterAssert(block != NULL);

	if (REBConditionalsInternal.sharedInternals.idiom == UIUserInterfaceIdiomPhone) {
		block();
	}
}

void REBExecuteOnPad(void(^block)()) {
	NSCParameterAssert(block != NULL);

	if (REBConditionalsInternal.sharedInternals.idiom == UIUserInterfaceIdiomPad) {
		block();
	}
}

void REBExecuteOnSystemGreaterThan(const char *version, void(^block)()) {
	NSCParameterAssert(block != NULL);

	NSString *appVersion = REBConditionalsInternal.sharedInternals.systemVersion;
	if (REBCompareVersions(appVersion.UTF8String, version) == REBVersionOrderingDescending) {
		block();
	}
}

void REBExecuteOnSystemGreaterThanOrEqualTo(const char *version, void(^block)()) {
	NSCParameterAssert(block != NULL);

	NSString *appVersion = REBConditionalsInternal.sharedInternals.systemVersion;
	if (REBCompareVersions(appVersion.UTF8String, version) != REBVersionOrderingAscending) {
		block();
	}
}

void REBExecuteOnSystemLessThan(const char *version, void(^block)()) {
	NSCParameterAssert(block != NULL);

	NSString *appVersion = REBConditionalsInternal.sharedInternals.systemVersion;
	if (REBCompareVersions(appVersion.UTF8String, version) == REBVersionOrderingAscending) {
		block();
	}
}

void REBExecuteOnSystemLessThanOrEqualTo(const char *version, void(^block)()) {
	NSCParameterAssert(block != NULL);

	NSString *appVersion = REBConditionalsInternal.sharedInternals.systemVersion;
	if (REBCompareVersions(appVersion.UTF8String, version) != NSOrderedDescending) {
		block();
	}
}

void REBExecuteOnSystemEqualTo(const char *version, void(^block)()) {
	NSCParameterAssert(block != NULL);
	
	NSString *appVersion = REBConditionalsInternal.sharedInternals.systemVersion;
	if (REBCompareVersions(appVersion.UTF8String, version) == REBVersionOrderingSame) {
		block();
	}
}
	
static REBVersionOrdering REBCompareVersions(const char *version1, const char *version2) {
	int mig_ver[3], sys_ver[3];
	sscanf(version1, "%d.%d.%d", &mig_ver[0], &mig_ver[1], &mig_ver[2]);
	sscanf(version2, "%d.%d.%d", &sys_ver[0], &sys_ver[1], &sys_ver[2]);
	
	for (int i = 0; i < 3; i++) {
		if (mig_ver[i] > sys_ver[i]) {
			return REBVersionOrderingDescending;
		} else if (mig_ver[i] < sys_ver[i]) {
			return REBVersionOrderingAscending;
		}
	}
	return REBVersionOrderingSame;
}