editor.kt

package molikto.apps.ui

import androidx.compose.*
import androidx.ui.core.Modifier
import androidx.ui.foundation.Text
import androidx.ui.foundation.TextField
import androidx.ui.layout.Column
import androidx.ui.layout.Row
import androidx.ui.layout.fillMaxHeight
import androidx.ui.material.Scaffold
import androidx.ui.material.Surface
import androidx.ui.unit.dp
import com.badoo.reaktive.observable.Observable
import com.badoo.reaktive.subject.behavior.BehaviorSubject
import kotlinx.serialization.KSerializer
import kotlinx.serialization.builtins.serializer


@Composable
fun <T> AbstractEditorScaffold(
    source: Observable<T?>,
    autoUpdate: Boolean = false,
    topAppBar: @Composable() (Pair<T, T>?) -> Unit,
    page0: @Composable() (MutableState<T>) -> Unit
) {
    val backstack = backstack
    val approved = state<T?>() { null }
    val editing = state<T?>(StructurallyEqual) { null }
    Scaffold(topAppBar = {
        /* THIS IS THE VALUE READ DURING SAME FRAME  */
        if (editing.value == null) { 
            topAppBar(null)
        } else {
            topAppBar(Pair(approved.value!!, editing.value!!))
        }
    }) {
        Column(Modifier.fillMaxHeight()) { 
            Observe(source) { so ->  /* observable might fire when subscribe, then read-then-write in same frame  */
                /* move out directly is not stright forward, because it either change some state, or compose in-place */
                if (approved.value == null) {
                    if (so == null) {
                        Banner(AppsCopy.AbstractEditor.ContentNotExist) {
                            SimpleTextButton(AppsCopy.Exit) {
                                backstack.pop()
                            }
                        }
                    } else {
                        approved.value = so
                        editing.value = so
                    }
                } else {
                    if (so == null) {
                        // deleted
                        Banner(if (autoUpdate) AppsCopy.AbstractEditor.ContentDeleted else AppsCopy.AbstractEditor.ContentDeletedSaving) {
                            SimpleTextButton(AppsCopy.Exit) {
                                backstack.pop()
                            }
                        }
                    } else {
                        if (autoUpdate) {
                            approved.value = so
                            editing.value = so
                        } else if (approved.value != so) {
                            Banner(AppsCopy.AbstractEditor.ContentUpdated) {
                                SimpleTextButton(AppsCopy.Overwrite) {
                                    approved.value = so
                                    editing.value = so
                                }
                            }
                        }
                    }
                }
            }
            approved.value.let { av ->
                if (av != null) {
                    key(av) {
                        @Suppress("UNCHECKED_CAST")
                        page0(editing as MutableState<T>)
                    }
                }
            }
        }
    }
}