Swiftgram/Classes/BITChannel.m

#import "BITChannel.h"

#if HOCKEYSDK_FEATURE_TELEMETRY

#import "HockeySDK.h"
#import "BITTelemetryContext.h"
#import "BITTelemetryData.h"
#import "HockeySDKPrivate.h"

static char *const BITDataItemsOperationsQueue = "com.microsoft.ApplicationInsights.senderQueue";
char *BITSafeJsonEventsString;

NSInteger const defaultBatchInterval  = 20;
NSInteger const defaultMaxBatchCount  = 50;

@implementation BITChannel

static BITChannel *_sharedChannel = nil;

#pragma mark - Initialisation

- (instancetype)init {
  if(self = [super init]) {
    bit_resetSafeJsonStream(&BITSafeJsonEventsString);
    _dataItemCount = 0;
    dispatch_queue_t serialQueue = dispatch_queue_create(BITDataItemsOperationsQueue, DISPATCH_QUEUE_SERIAL);
    _dataItemsOperations = serialQueue;
  }
  return self;
}

- (instancetype)initWithTelemetryContext:(BITTelemetryContext *)telemetryContext persistence:(BITPersistence *) persistence {
  if(self = [self init]) {
    _telemetryContext = telemetryContext;
    _persistence = persistence;
  }
  return self;
}

#pragma mark - Queue management

- (BOOL)isQueueBusy{
  
  // TODO: Check file count
  return true;
}

- (void)persistDataItemQueue {
  [self invalidateTimer];
  if(!BITSafeJsonEventsString || strlen(BITSafeJsonEventsString) == 0) {
    return;
  }
  
  NSData *bundle = [NSData dataWithBytes:BITSafeJsonEventsString length:strlen(BITSafeJsonEventsString)];
  // TODO: Persist bundle
  
  // Reset both, the async-signal-safe and item counter.
  [self resetQueue];
}

- (void)resetQueue {
  bit_resetSafeJsonStream(&BITSafeJsonEventsString);
  _dataItemCount = 0;
}

#pragma mark - Adding to queue

- (void)enqueueTelemetryItem:(BITTelemetryData *)item {
  if(item) {
    BITOrderedDictionary *dict = [self dictionaryForTelemetryData:item];
    __weak typeof(self) weakSelf = self;
    
    dispatch_async(self.dataItemsOperations, ^{
      typeof(self) strongSelf = weakSelf;
      
      // Enqueue item
      [strongSelf appendDictionaryToJsonStream:dict];
      
      if(strongSelf->_dataItemCount >= defaultMaxBatchCount) {
        // Max batch count has been reached, so write queue to disk and delete all items.
        [strongSelf persistDataItemQueue];
        
      } else if(strongSelf->_dataItemCount == 1) {
        // It is the first item, let's start the timer
        [strongSelf startTimer];
      }
    });
  }
}

#pragma mark - Envelope telemerty items

- (BITOrderedDictionary *)dictionaryForTelemetryData:(BITTelemetryData *) telemetryData {
  BITOrderedDictionary *dict = nil;
  
  // TODO: Put telemetry data into envelope and convert to ordered dict
  return dict;
}

#pragma mark - Serialization Helper

- (NSString *)serializeDictionaryToJSONString:(BITOrderedDictionary *)dictionary {
  NSError *error;
  NSData *data = [NSJSONSerialization dataWithJSONObject:dictionary options:(NSJSONWritingOptions)0 error:&error];
  if (!data) {
    BITHockeyLog(@"ERROR: JSONSerialization error: %@", error.localizedDescription);
    return @"{}";
  } else {
    return [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
  }
}

#pragma mark JSON Stream

- (void)appendDictionaryToJsonStream:(BITOrderedDictionary *)dictionary {
  if(dictionary) {
    NSString *string = [self serializeDictionaryToJSONString:dictionary];
    
    // Since we can't persist every event right away, we write it to a simple C string.
    // This can then be written to disk by a signal handler in case of a crash.
    bit_appendStringToSafeJsonStream(string, &(BITSafeJsonEventsString));
    _dataItemCount += 1;
  }
}

void bit_appendStringToSafeJsonStream(NSString *string, char **jsonString) {
  if (jsonString == NULL) { return; }
  
  if (!string) { return; }
  
  if (*jsonString == NULL || strlen(*jsonString) == 0) {
    bit_resetSafeJsonStream(jsonString);
  }
  
  if (string.length == 0) { return; }
  
  char *new_string = NULL;
  // Concatenate old string with new JSON string and add a comma.
  asprintf(&new_string, "%s%.*s\n", *jsonString, (int)MIN(string.length, (NSUInteger)INT_MAX), string.UTF8String);
  free(*jsonString);
  *jsonString = new_string;
}

void bit_resetSafeJsonStream(char **string) {
  if (!string) { return; }
  free(*string);
  *string = strdup("");
}

#pragma mark - Batching

- (void)invalidateTimer {
  if(self.timerSource) {
    dispatch_source_cancel(self.timerSource);
    self.timerSource = nil;
  }
}

- (void)startTimer {
  
  // Reset timer, if it is already running
  if(self.timerSource) {
    [self invalidateTimer];
  }
  
  self.timerSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, self.dataItemsOperations);
  dispatch_source_set_timer(self.timerSource, dispatch_walltime(NULL, NSEC_PER_SEC * defaultMaxBatchCount), 1ull * NSEC_PER_SEC, 1ull * NSEC_PER_SEC);
  dispatch_source_set_event_handler(self.timerSource, ^{
    
    // On completion: Reset timer and persist items
    [self persistDataItemQueue];
  });
  dispatch_resume(self.timerSource);
}

@end

#endif /* HOCKEYSDK_FEATURE_TELEMETRY */