/*
 * SPDX-FileCopyrightText: 2020 The Calyx Institute
 * SPDX-License-Identifier: Apache-2.0
 */

package com.stevesoltys.seedvault.ui

import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.LiveData
import androidx.lifecycle.Observer
import com.stevesoltys.seedvault.ui.LiveEvent.ConsumableEvent

open class LiveEvent<T> : LiveData<ConsumableEvent<T>>() {

    fun observeEvent(owner: LifecycleOwner, handler: LiveEventHandler<in T>) {
        val observer = LiveEventObserver(handler)
        super.observe(owner, observer)
    }

    class ConsumableEvent<T>(private val content: T) {
        private var consumed = false

        val contentIfNotConsumed: T?
            get() {
                if (consumed) return null
                consumed = true
                return content
            }
    }

    internal class LiveEventObserver<T>(private val handler: LiveEventHandler<in T>) :
        Observer<ConsumableEvent<T>> {
        override fun onChanged(value: ConsumableEvent<T>) {
            val content = value.contentIfNotConsumed
            if (content != null) handler.onEvent(content)
        }
    }
}