PreferenceDelegates.kt

import kotlin.properties.ReadWriteProperty
import android.content.SharedPreferences
import android.app.Activity
import android.content.Context
import android.app.Fragment
import android.support.v4.app.Fragment as SupportFragment
import kotlin.properties.Delegates

public fun Activity.intPreference(prefs: String, key: String, default: Int): ReadWriteProperty<Any, Int> = intPref(prefs, key, default)
public fun Activity.stringPreference(prefs: String, key: String, default: String): ReadWriteProperty<Any, String> = stringPref(prefs, key, default)
public fun Activity.booleanPreference(prefs: String, key: String, default: Boolean): ReadWriteProperty<Any, Boolean> = booleanPref(prefs, key, default)
public fun Activity.floatPreference(prefs: String, key: String, default: Float): ReadWriteProperty<Any, Float> = floatPref(prefs, key, default)

public fun Fragment.intPreference(prefs: String, key: String, default: Int): ReadWriteProperty<Any, Int> = intPref(prefs, key, default)
public fun Fragment.stringPreference(prefs: String, key: String, default: String): ReadWriteProperty<Any, String> = stringPref(prefs, key, default)
public fun Fragment.booleanPreference(prefs: String, key: String, default: Boolean): ReadWriteProperty<Any, Boolean> = booleanPref(prefs, key, default)
public fun Fragment.floatPreference(prefs: String, key: String, default: Float): ReadWriteProperty<Any, Float> = floatPref(prefs, key, default)

public fun SupportFragment.intPreference(prefs: String, key: String, default: Int): ReadWriteProperty<Any, Int> = intPref(prefs, key, default)
public fun SupportFragment.stringPreference(prefs: String, key: String, default: String): ReadWriteProperty<Any, String> = stringPref(prefs, key, default)
public fun SupportFragment.booleanPreference(prefs: String, key: String, default: Boolean): ReadWriteProperty<Any, Boolean> = booleanPref(prefs, key, default)
public fun SupportFragment.floatPreference(prefs: String, key: String, default: Float): ReadWriteProperty<Any, Float> = floatPref(prefs, key, default)

public fun ContextProvider.intPreference(prefs: String, key: String, default: Int): ReadWriteProperty<Any, Int> = intPref(prefs, key, default)
public fun ContextProvider.stringPreference(prefs: String, key: String, default: String): ReadWriteProperty<Any, String> = stringPref(prefs, key, default)
public fun ContextProvider.booleanPreference(prefs: String, key: String, default: Boolean): ReadWriteProperty<Any, Boolean> = booleanPref(prefs, key, default)
public fun ContextProvider.floatPreference(prefs: String, key: String, default: Float): ReadWriteProperty<Any, Float> = floatPref(prefs, key, default)

private fun intPref(prefs: String, key: String, default: Int): ReadWriteProperty<Any, Int> = PreferenceVal(prefs, key, default, { this.getInt(key, default) }, { i -> this.putInt(key, i) })
private fun stringPref(prefs: String, key: String, default: String): ReadWriteProperty<Any, String> = PreferenceVal(prefs, key, default, { this.getString(key, default) }, { s -> this.putString(key, s) })
private fun booleanPref(prefs: String, key: String, default: Boolean): ReadWriteProperty<Any, Boolean> = PreferenceVal(prefs, key, default, { this.getBoolean(key, default) }, { b -> this.putBoolean(key, b) })
private fun floatPref(prefs: String, key: String, default: Float): ReadWriteProperty<Any, Float> = PreferenceVal(prefs, key, default, { this.getFloat(key, default) }, { f -> this.putFloat(key, f) })

public trait ContextProvider {
  val context: Context
}

private class PreferenceVal<T>(val prefs: String,
                               val key: String,
                               val default: T,
                               val read: SharedPreferences.() -> T,
                               val write: SharedPreferences.Editor.(T) -> Unit) : ReadWriteProperty<Any, T> {

  private var sp: SharedPreferences? = null

  override fun set(thisRef: Any, desc: PropertyMetadata, value: T) {
    if (sp == null) {
      sp = get(thisRef)
    }

    val edit = sp!!.edit()
    edit.write(value)
    edit.apply()
  }

  override fun get(thisRef: Any, desc: PropertyMetadata): T {
    if (sp == null) {
      sp = get(thisRef)
    }

    return sp!!.read()
  }

  private fun get(ref: Any): SharedPreferences =
      when (ref) {
        is Activity -> ref.getSharedPreferences(prefs, Context.MODE_PRIVATE)
        is Fragment -> ref.getActivity().getSharedPreferences(prefs, Context.MODE_PRIVATE)
        is SupportFragment -> ref.getActivity().getSharedPreferences(prefs, Context.MODE_PRIVATE)
        is ContextProvider -> ref.context.getSharedPreferences(prefs, Context.MODE_PRIVATE)
        else -> throw IllegalStateException("Unsupported type")
      }
}