ServiceLocator.kt

package aze.talmir.task.ratesconversions

import androidx.annotation.VisibleForTesting
import aze.talmir.task.ratesconversions.data.IRatesConversionsRepository
import aze.talmir.task.ratesconversions.data.remotesource.RatesConversionsRemoteDataSource
import aze.talmir.task.ratesconversions.data.repo.RatesConversionsRepository

/**
 * The service locator pattern involves making a singleton class called
 * a [ServiceLocator] whose purpose is to store and provide dependencies.
 * The service locator does this both for the regular code and for test
 * code. Whenever you need a dependency, instead of constructing it
 * yourself you create a service locator and then you get the dependencies
 * from the service locator. For the regular app code meeting everything
 * in the main source set, but for the tests you update the service
 * locator to provide testable versions of the dependencies.
 *
 * The benefit of using a service locator over set of dependency injection,
 * is that to set a certain dependency injection, you need to set the
 * correct dependency each time that can make an instance of a class. Now,
 * with the service locator you set all the correct dependencies in the
 * beginning in the service locator and then you can be sure that those
 * dependencies are going to be used everywhere.
 */
object ServiceLocator {

    private val lock = Any()

    @Volatile
    var ratesConversionsRepository: IRatesConversionsRepository? = null
        @VisibleForTesting set

    /**
     * Function to provide a [IRatesConversionsRepository] instance.
     */
    fun provideRatesConversionsRepository(): IRatesConversionsRepository =
        synchronized(this) {
            return ratesConversionsRepository ?: createRatesConversionsRepository()
        }

    private fun createRatesConversionsRepository(): RatesConversionsRepository {
        val newRepository =
            RatesConversionsRepository(
                RatesConversionsRemoteDataSource()
            )
        ratesConversionsRepository = newRepository
        return newRepository
    }

    @VisibleForTesting
    fun resetRepository() =
        synchronized(lock) {
            ratesConversionsRepository = null
        }
}