Cache

Cache.m

#import <CommonCrypto/CommonDigest.h>

#import "Cache.h"

@implementation Cache

+ (void)cacheObject:(id)object forKey:(NSString *)key {
  NSString *path = [self pathForKey:key];
  [NSKeyedArchiver archiveRootObject:object toFile:path];
}

+ (id)objectForCacheKey:(NSString *)key {
  NSString *path = [self pathForKey:key];
  if ([[NSFileManager defaultManager] fileExistsAtPath:path]) {
    return [NSKeyedUnarchiver unarchiveObjectWithFile:path];
  } else {
    return nil;
  }
}

+ (NSString *)MD5:(NSString *)str {
  const char *ptr = [str UTF8String];
  unsigned char md5Buffer[CC_MD5_DIGEST_LENGTH];
  CC_MD5(ptr, strlen(ptr), md5Buffer);
  NSMutableString *output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
  for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) {
    [output appendFormat:@"%02x", md5Buffer[i]];
  }
  return output;
}

+ (NSString *)pathForKey:(NSString *)key {
  NSString *hash = [self MD5:key];
  
  NSString *documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];
  NSString *topicDirectory = [documentsPath stringByAppendingPathComponent:@"cache"];
  
  if (![[NSFileManager defaultManager] fileExistsAtPath:topicDirectory]) {
    [[NSFileManager defaultManager] createDirectoryAtPath:topicDirectory
                              withIntermediateDirectories:NO
                                               attributes:nil
                                                    error:nil];
  }
  
  NSString *path = [topicDirectory stringByAppendingPathComponent:hash];
  return path;
}

@end