ConflatedValues.kt

import kotlinx.coroutines.experimental.channels.ConflatedChannel
import kotlinx.coroutines.experimental.channels.ReceiveChannel
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

abstract class ConflatedValues<CV : ConflatedValues<CV, T>, T> private constructor(
        private val updateChannel: ConflatedChannel<T>,
        private val conflateAll: CV.() -> T
) : ReceiveChannel<T> by updateChannel {
    constructor(conflateAll: CV.() -> T) : this(ConflatedChannel(), conflateAll)

    /** Can be called from a subclass method to perform an arbitrary update/refresh. */
    protected fun triggerUpdate() {
        @Suppress("UNCHECKED_CAST")
        updateChannel.offer((this as CV).conflateAll())
    }

    protected fun <E> conflatedValue(initialValue: E): ReadWriteProperty<Any?, E> = Value(initialValue)

    private inner class Value<E>(private var value: E) : ReadWriteProperty<Any?, E> {
        override fun getValue(thisRef: Any?, property: KProperty<*>) = value
        override fun setValue(thisRef: Any?, property: KProperty<*>, value: E) {
            this.value = value // TODO: Allow optional ignore if values are equal
            triggerUpdate()
        }
    }

    init {
        updateChannel.invokeOnClose { onClose() }
    }

    protected open fun onClose() = Unit
}

abstract class ConflatedUpdates<CV : ConflatedUpdates<CV>> : ConflatedValues<CV, Unit>({})