FileHandler.swift

Purpose 

FileHandler.swift is a centralized utility class in the iOS native layer that manages file creation, metadata attachment, and compression for sensor data collected by the HealthyWear app.

Design Pattern 

This class uses the Singleton pattern:

static let shared = FileHandler()

Ensures only one instance exists to handle all file-related tasks across the app.

Core Responsibilities 

Save structured sensor data to local files.
Attach metadata including location, app version, and device information.
Compress files into .gz format using zlib.
Manage cleanup (deleting old/uncompressed files).

Key Methods 

`setIdNumber(_:)` and `setAppVersion(_:)`

Set optional metadata headers such as:

User/Session identifier
Application version string

`saveDataToFile(...)`

Creates and writes structured sensor data:

Builds file name using timestamp and dataType
Saves initial JSON metadata
Appends sensor data from dataBuffer
Compresses .txt into .gz using gzipCompressed()
Deletes original file

let fileName = "\(dataType)_\(timestamp).txt"

`deleteFile(at:)`

Deletes specified file safely:

try FileManager.default.removeItem(at: url)

Used after successful .gz compression.

Metadata Construction 

Dynamically builds structured headers:

metadata: [
  ("Id", idNumber),
  ("Type", type),
  ("Structure", structure),
  ("Lat", latitude),
  ("Long", longitude),
  ("AppVersion", appVersion)
]

Also uses helper functions:

getStructureForDataType(...)
getTypeForDataType(...)
updateMetadataWithDeviceInfo(...)

Compression Logic 

Implemented in a Data extension:

func gzipCompressed() -> Data?

Uses zlib for GZIP compression
Allocates 4KB buffer and processes in blocks
Returns compressed Data? object

Integration 

Used by:

Sensor streaming handlers (e.g. MetaWearHandler, SensoriaHandler)
Data upload services in background