EnvironmentManager.kt

class EnvironmentManager(
    // We use shared prefs to save currently selected env between app launches
    private val store: SharedPreferences
) {
    // This is a key for saving env in prefs
    private val currentEnvironmentKey = "current_environment"
    
    /*
    * Here we need to describe all our strings
    * for all of the supported environments.
    * I use mapping `Env -> EnvVars`, but you can use anything
    * (database, files, etc)
    */
    private val parameters: Map<Environment, EnvironmentVariables> = mapOf(
        Environment.DEVELOPMENT to EnvironmentVariables(
            baseUrl = "https://api-dev.myproject.com",
            algoliaSearchKey = "dev_search_key"
        ),
        Environment.PRODUCTION to EnvironmentVariables(
            baseUrl = "https://api.myproject.com",
            algoliaSearchKey = "prod_search_key"
        )
    )

    /*
    * Here is an interesting part.
    * We use `currentEnvironment` variable to store and retrieve current env from
    * SharedPreferences and decide which variables to pull depending on Environment.
    * 
    * We will explore `BuildConfig.DEFAULT_ENV` later on.
    */
    var currentEnvironment: Environment
        get() {
            val default = Environment.create(BuildConfig.DEFAULT_ENV)
            val current = store.getString(currentEnvironmentKey, null)?.let {
                Environment.create(it)
            }
            return current ?: default
        }
        set(value) {
            store.edit().putString(currentEnvironmentKey, value.id).apply()
        }

    // This one allows to pull desired variable just by property reference
    fun get(property: KProperty1<EnvironmentVariables, String>): String {
        val params = parameters[currentEnvironment] ?: throw Exception("Unsupported ENV $currentEnvironment")
        return property.get(params)
    }
}