Retrofit API call and Room update helper

gistfile1.txt

/**
 * Handles calling the Retrofit endpoints
 * [apiCallFunc] is the Retrofit endpoint you want to call
 * During runtime, [V] would be equal to the type wrapped by [Response]
 * [V] is returned as the reflection would already be executed during that time
 * giving us the contents of the inferred [V]
 */
suspend fun <V> callAPI(apiCallFunc: suspend () -> Response<V>): V? {
	val actsResult: Response<V>?
	if (utils.isInternetAvailable(ctx)) {
		try {
			actsResult = apiCallFunc.invoke()

			val respBody = retrofitErrorHandler(actsResult)
			if (respBody != null) {
				return respBody
			}
		} catch (e: Exception) {
			Log.e(TAG, "callAPI Error: ${e.localizedMessage}")
			withContext(Dispatchers.Main) {
				Toast.makeText(ctx, "Retrofit Error: ${e.localizedMessage}", Toast.LENGTH_LONG)
					.show()
			}
		}
	}
	return null
}

/**
 * Handles the checking of the diff between the server and local data, and puts those diff in the Room database 
 * [vm] is the ViewModel handling the local data
 * [inAPIData] is the list of items that came from the server, which was done partially by [callAPI]
 * [inLocalDBData] is the local data
 * [T] would be inferred from the data passed
 */
suspend fun <T> updateInfoLst(
	vm: IViewModel<T>,
	inAPIData: List<T>,
	inLocalDBData: List<T>
): List<T> {
	val toInsertLst: List<T> = if (inAPIData.size > inLocalDBData.size) {
		val diffLst =
			inAPIData.slice((if (inLocalDBData.size > 1) inLocalDBData.size - 1 else 0) until inAPIData.size)

		for (item in diffLst) {
			val id = vm.insertReturnId(item)
			Log.i(TAG, "id: $id")
		}

		withContext(Dispatchers.Main) {
			Toast.makeText(ctx, "$caller: Using server data", Toast.LENGTH_LONG).show()
			Log.i(TAG, "using server data")
		}

		diffLst
	} else {
		//update the local db with the server's data
		for (item in inAPIData) {
			vm.update(item)
		}

		withContext(Dispatchers.Main) {
			Toast.makeText(ctx, "$caller: Using local data", Toast.LENGTH_LONG).show()
			Log.i(TAG, "using local data")
		}

		//to not need to wait for the DB, which would eventually be the same as inAPIData,
		//I just returned inAPIData
		inAPIData
	}

	//this data is usually used as the list for the adapter that needs the fetched server data
	return toInsertLst
}

private fun <T> retrofitErrorHandler(res: Response<T>): T {
	if (res.isSuccessful) {
		Log.d(TAG, "retrofitErrorHandler success: ${res.body()}")
		return res.body()!!
	} else {
		Log.d(TAG, "retrofitErrorHandler errMsg: ${res.errorBody().toString()}")
		throw Exception(res.errorBody().toString())
	}
}

fun getHeaderMap(ctx: Context): Map<String, String> {
	//what this function does, at least in my use case, is get the "access_token" I saved on a sharedPreferences
	//and use it for the header on my Retrofit calls that need it
	val accessToken = PreferenceHelper.customPrefs(ctx, "project_prefs")["access_token", ""]

	if (accessToken == "") {
		return mapOf()
	}

	val headerMap = mutableMapOf<String, String>()
	headerMap["access_token"] = accessToken
	return headerMap
}

Examples:
//inside a Fragment/Activity, put these lines
private lateinit var retrofitIntf: RetrofitInterface
private lateinit var retFetchHlpr: RetrofitFetchHelper

//RetrofitHelper is the class that handles the creation of a Retrofit instance
//RetrofitInterface contains all the endpoint declarations
atlAPI = RetrofitHelper(ctx).getInstance().create(RetrofitInterface::class.java)
retFetchHlpr = RetrofitFetchHelper(ctx, "I put the fragment or activity name here just for logging purposes")

//this is a sample endpoint
@Headers("Content-Type: application/json")
@POST("/order")
suspend fun postOrder(
	@HeaderMap headers: Map<String, String>,
	@Body data: Order
): Response<OrderPostResponse>

//and the response declaration
data class OrderPostResponse(
    val order_post_response: OrderResponse
)

//then below is how you'll use the helper. quite neat, right?
val inAPIDataResp = retFetchHlpr.callAPI {
	retrofitIntf.postOrder(retFetchHlpr.getHeaderMap(ctx), someOrderObj)
}
var inAPIData = listOf<OrderResponse>()

if (inAPIDataResp != null) {
	inAPIData = inAPIDataResp.order_post_response
}

if (inAPIData != null && inAPIData.isNotEmpty()) {
	withContext(Dispatchers.Main) {
		itemLst.clear()
		itemLst.addAll(inAPIData)
		adapter.notifyDataSetChanged()
	}
}