/*
 * Copyright 2019 New Vector Ltd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package im.vector.matrix.rx

import androidx.lifecycle.LiveData
import androidx.lifecycle.Observer
import io.reactivex.Observable
import io.reactivex.android.MainThreadDisposable

private class LiveDataObservable<T>(
        private val liveData: LiveData<T>,
        private val valueIfNull: T? = null
) : Observable<T>() {

    override fun subscribeActual(observer: io.reactivex.Observer<in T>) {
        val relay = RemoveObserverInMainThread(observer)
        observer.onSubscribe(relay)
        liveData.observeForever(relay)
    }

    private inner class RemoveObserverInMainThread(private val observer: io.reactivex.Observer<in T>)
        : MainThreadDisposable(), Observer<T> {

        override fun onChanged(t: T?) {
            if (!isDisposed) {
                if (t == null) {
                    if (valueIfNull != null) {
                        observer.onNext(valueIfNull)
                    } else {
                        observer.onError(NullPointerException(
                                "convert liveData value t to RxJava onNext(t), t cannot be null"))
                    }
                } else {
                    observer.onNext(t)
                }
            }
        }

        override fun onDispose() {
            liveData.removeObserver(this)
        }
    }
}

fun <T> LiveData<T>.asObservable(defaultValue: T? = null): Observable<T> {
    return LiveDataObservable(this, defaultValue)
}