/*
 * This file is part of GNU Taler
 * (C) 2020 Taler Systems S.A.
 *
 * GNU Taler is free software; you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation; either version 3, or (at your option) any later version.
 *
 * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
 */

package net.taler.common

import androidx.lifecycle.LiveData
import androidx.lifecycle.MediatorLiveData
import androidx.lifecycle.Observer

class CombinedLiveData<T, K, S>(
    source1: LiveData<T>,
    source2: LiveData<K>,
    private val combine: (data1: T?, data2: K?) -> S
) : MediatorLiveData<S>() {

    private var data1: T? = null
    private var data2: K? = null

    init {
        super.addSource(source1) { t ->
            data1 = t
            value = combine(data1, data2)
        }
        super.addSource(source2) { k ->
            data2 = k
            value = combine(data1, data2)
        }
    }

    override fun <S : Any?> addSource(source: LiveData<S>, onChanged: Observer<in S>) {
        throw UnsupportedOperationException()
    }

    override fun <T : Any?> removeSource(toRemote: LiveData<T>) {
        throw UnsupportedOperationException()
    }

}