sharedPreferences: Add utility delegates

Signed-off-by: Carlos Rafael Giani <crg7475@mailbox.org>

shared/src/main/java/info/nightscout/shared/sharedPreferences/Delegates.kt

@@ -0,0 +1,83 @@
+package info.nightscout.shared.sharedPreferences
+
+import kotlin.properties.ReadWriteProperty
+import kotlin.reflect.KProperty
+
+/*
+
+These classes allow to combine SP values with Kotlin delegates like this:
+
+    private var myValue: String
+        by SPDelegateString(sp, "myValueKey", "default-value")
+
+Then, accessing myValue works by simply using the Kotlin setters & getters:
+
+    val value = myValue // reading from sp
+    myValue = "newvalue" // writing to sp
+
+*/
+
+class SPDelegateBoolean(
+    private val sp: SP,
+    private val key: String,
+    private val defaultValue: Boolean = false,
+    private val commit: Boolean = false
+) : ReadWriteProperty<Any, Boolean> {
+    override fun getValue(thisRef: Any, property: KProperty<*>) =
+        sp.getBoolean(key, defaultValue)
+
+    override fun setValue(thisRef: Any, property: KProperty<*>, value: Boolean) =
+        sp.edit(commit = commit) { putBoolean(key, value) }
+}
+
+class SPDelegateDouble(
+    private val sp: SP,
+    private val key: String,
+    private val defaultValue: Double = 0.0,
+    private val commit: Boolean = false
+) : ReadWriteProperty<Any, Double> {
+    override fun getValue(thisRef: Any, property: KProperty<*>) =
+        sp.getDouble(key, defaultValue)
+
+    override fun setValue(thisRef: Any, property: KProperty<*>, value: Double) =
+        sp.edit(commit = commit) { putDouble(key, value) }
+}
+
+class SPDelegateLong(
+    private val sp: SP,
+    private val key: String,
+    private val defaultValue: Long = 0,
+    private val commit: Boolean = false
+) : ReadWriteProperty<Any, Long> {
+    override fun getValue(thisRef: Any, property: KProperty<*>) =
+        sp.getLong(key, defaultValue)
+
+    override fun setValue(thisRef: Any, property: KProperty<*>, value: Long) =
+        sp.edit(commit = commit) { putLong(key, value) }
+}
+
+class SPDelegateInt(
+    private val sp: SP,
+    private val key: String,
+    private val defaultValue: Int = 0,
+    private val commit: Boolean = false
+) : ReadWriteProperty<Any, Int> {
+    override fun getValue(thisRef: Any, property: KProperty<*>) =
+        sp.getInt(key, defaultValue)
+
+    override fun setValue(thisRef: Any, property: KProperty<*>, value: Int) =
+        sp.edit(commit = commit) { putInt(key, value) }
+}
+
+class SPDelegateString(
+    private val sp: SP,
+    private val key: String,
+    private val defaultValue: String = "",
+    private val commit: Boolean = false
+) : ReadWriteProperty<Any, String> {
+    override fun getValue(thisRef: Any, property: KProperty<*>) =
+        sp.getString(key, defaultValue)
+
+    override fun setValue(thisRef: Any, property: KProperty<*>, value: String) =
+        sp.edit(commit = commit) { putString(key, value) }
+}