SharedPreferencesDelegate.kt

package com.straucorp.datastorepreferences.delegates

/**
 * @author Andre Straube - Created on 29/08/2021
 */
import android.content.Context
import android.content.SharedPreferences
import androidx.annotation.GuardedBy
import kotlinx.coroutines.*
import kotlin.properties.ReadOnlyProperty
import kotlin.reflect.KProperty

/**
 * Kotlin Delegate patra trabalhar com SharedPreferences
 *
 * Exemplo de uso:
 *
 * ```
 * val Context.sharedPrefs by sharedPreferences(name = "app_settings")
 *
 * var appLaunchCount by IntPreference(
 *      preferences = context.sharedPrefs,
 *      key = "app_launch_count",
 *      defaultValue = 0
 * )
 * ```
 */
@Suppress("MissingJvmstatic")
fun sharedPreferences(
    name: String,
    scope: CoroutineScope = CoroutineScope(Dispatchers.IO + SupervisorJob())
): ReadOnlyProperty<Context, SharedPreferences> {
    return SharedPreferencesDelegate(name, scope)
}

/**
 * Classe utilizada para facilitar o trabalho com SharedPreferences.
 */
internal class SharedPreferencesDelegate internal constructor(
    private val name: String,
    private val scope: CoroutineScope
) : ReadOnlyProperty<Context, SharedPreferences> {

    private val lock = Any()

    @GuardedBy("lock")
    @Volatile
    private var INSTANCE: SharedPreferences? = null

    /**
     * Obtem a instância do SharedPreferences.
     * Uma vez executado, não cria nova instancia da classe [SharedPreferences].
     * [INSTANCE] Funciona como uma variavel Singleton.
     * [Context.getSharedPreferences] É executa em uma nova coroutine evitando
     * bloqueio de UI e erros de [StrictMode].
     *
     * @param thisRef deve ser uma instancia de [Context]
     * @param property não utilizado
     */
    override fun getValue(thisRef: Context, property: KProperty<*>): SharedPreferences {
        return INSTANCE ?: synchronized(lock) {
            if (INSTANCE == null) {

                // Executa em uma nova coroutine
                INSTANCE = runBlocking(scope.coroutineContext) {
                    withContext(scope.coroutineContext) {
                        thisRef.applicationContext.getSharedPreferences(name, Context.MODE_PRIVATE)
                    }
                }
            }
            INSTANCE!!
        }
    }
}