/*
 * Copyright (C) 2024 The Android Open Source Project
 *
 * 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 com.android.customization.picker.mode.ui.viewmodel

import com.android.customization.module.logging.ThemesUserEventLogger
import com.android.customization.picker.mode.domain.interactor.DarkModeInteractor
import com.android.wallpaper.picker.customization.ui.viewmodel.ColorUpdateViewModel
import dagger.hilt.android.scopes.ViewModelScoped
import javax.inject.Inject
import kotlinx.coroutines.coroutineScope
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.flow.combine
import kotlinx.coroutines.flow.drop
import kotlinx.coroutines.flow.take
import kotlinx.coroutines.launch

@ViewModelScoped
class DarkModeViewModel
@Inject
constructor(
    private val colorUpdateViewModel: ColorUpdateViewModel,
    private val interactor: DarkModeInteractor,
    private val logger: ThemesUserEventLogger,
) {
    private val isDarkMode = interactor.isDarkMode
    val isEnabled = interactor.isEnabled

    private val _overridingIsDarkMode = MutableStateFlow<Boolean?>(null)
    val overridingIsDarkMode = _overridingIsDarkMode.asStateFlow()
    val previewingIsDarkMode =
        combine(overridingIsDarkMode, isDarkMode, isEnabled) { override, current, isEnabled ->
            if (isEnabled) {
                override ?: current
            } else current
        }

    val toggleDarkMode =
        combine(overridingIsDarkMode, isDarkMode) { override, current ->
            // Only set override if its value is different from current, else set to null
            {
                _overridingIsDarkMode.value =
                    if (override == null || override == current) !current else null
            }
        }

    val onApply: Flow<(suspend () -> Unit)?> =
        combine(overridingIsDarkMode, isDarkMode, isEnabled) { override, current, isEnabled ->
            if (override != null && override != current && isEnabled) {
                {
                    coroutineScope {
                        launch { interactor.setIsDarkMode(override) }
                        // Dark mode change also invokes a color update. Suspend until both dark
                        // mode and color are updated.
                        combine(
                                // Omit the first value which is emitted on subscribe.
                                isDarkMode.drop(1).take(1),
                                colorUpdateViewModel.systemColorsUpdatedNoReplay.take(1),
                                ::Pair,
                            )
                            .collect { (_, _) ->
                                return@collect
                            }
                        logger.logDarkThemeApplied(override)
                    }
                }
            } else null
        }

    fun resetPreview() {
        _overridingIsDarkMode.value = null
    }
}