/*
  (c) naturalprogramming.com

   2023-02-12 File created by Kari Laitinen

   2023-08-16 Material 3 in use in newer Android Studio.

   2023-09-17 Screen size, in Dp, density pixels, is displayed.
              Screen size changes if the user modifies Display size in Settings.
              androidManifest.xml was not modified.
              https://developer.android.com/guide/topics/resources/runtime-changes

   This example shows how to navigate from one screen to another
   in Jetpack Compose.

   The child screen transfers information to the main screen via
   a common ViewModel. I hope this is a good way to make the operation.

   The following page should be studied carefully.
    https://developer.android.com/jetpack/compose/navigation

   In February 2023 it was necessary to modify the build.gradle file
   of the project according to the instructions in the above page.

    This is an Android app made of this single file.

    If you want to test this app, create an Android Compose project
    using  the project name ChangingScreensC and the
    package name shown below. Then, store this file
    to the folder where MainActivity.kt is and make the following
    change to AndroidManifest.xml:
    android:name=".ChangingScreensCActivity"

    Imports may need to be modified.

    Some 'warnings':
    - tab size in this file is 3 spaces
    - underscores are used in the names invented by the programmer

*/


package changing.screensc

import android.os.Bundle
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.activity.viewModels
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material3.*
import androidx.compose.runtime.Composable
import androidx.compose.runtime.State
import androidx.compose.runtime.collectAsState
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.platform.LocalConfiguration
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import androidx.navigation.NavController
import androidx.navigation.NavType
import androidx.navigation.compose.NavHost
import androidx.navigation.compose.composable
import androidx.navigation.compose.rememberNavController
import androidx.navigation.navArgument
import changing.screensc.ui.theme.ChangingScreensCTheme
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.flow.update
import kotlinx.coroutines.launch

data class ScreensState(

   val screen_change_count : Int = 0
)

class GeneralViewModel : ViewModel()
{
   // Expose screen UI state
   private val _uiState = MutableStateFlow( ScreensState() )
//   val uiState: StateFlow<AnimationState> = _uiState.asStateFlow()

   // asStateFlow() represents this mutable state flow as a read-only state flow.
   fun consumableState() = _uiState.asStateFlow()

   fun increase_screen_change_count()
   {
      _uiState.update { currentState ->
         currentState.copy(
            screen_change_count = currentState.screen_change_count + 1
         )
      }
   }
}


@Composable
fun AnotherScreen( showOnlyPostsByUser: Boolean = false,
                   navController: NavController,
                   view_model : GeneralViewModel,
                   view_state : State<ScreensState> )
{
   Surface( modifier = Modifier.fillMaxSize(), color = Color.DarkGray )
   {
      // LocalConfiguration.current works only inside a composable
      val configuration = LocalConfiguration.current

      val screen_width = configuration.screenWidthDp
      val screen_height = configuration.screenHeightDp

      Column( horizontalAlignment = Alignment.CenterHorizontally )
      {

         Spacer( modifier = Modifier.weight( 0.5F ) )

         // Text had to be put inside a Box in order to center it
         // inside the upper half of the screen.

         Box( modifier = Modifier.weight( 0.5F ),
              contentAlignment = Alignment.Center )
         {
            Text(
               "Screen size (Dp): " + screen_width + " x " + screen_height ,
               fontSize = 24.sp, color = Color.LightGray

            )
         }

         Box( modifier = Modifier.weight( 0.5F ),
            contentAlignment = Alignment.Center )
         {
            Text("This is AnotherScreen", fontSize = 28.sp, color = Color.LightGray )
         }

         Button( onClick =
         {
            // When we started to use the navigateUp() method, the standard 'Back' button
            // stopped to work for this app.

            view_model.increase_screen_change_count()
            navController.navigateUp()
         },
            modifier = Modifier.requiredHeight( 100.dp ).
            requiredWidth( 200.dp).weight( 1F ),
            shape = RoundedCornerShape( 20.dp ),
            colors = ButtonDefaults.buttonColors( containerColor = Color.LightGray ) )
         {
            Text( text = "BACK", fontSize = 32.sp, color = Color.Blue )
         }

         Spacer( modifier = Modifier.weight( 0.5F ) )
      }
   }
}


@Composable
fun MainScreen( navController: NavController,
                view_model : GeneralViewModel,
                view_state : State<ScreensState> )
{
   Surface( modifier = Modifier.fillMaxSize(), color = Color.Black )
   {
      // LocalConfiguration.current works only inside a composable
      val configuration = LocalConfiguration.current

      val screen_width = configuration.screenWidthDp
      val screen_height = configuration.screenHeightDp

      Column( horizontalAlignment = Alignment.CenterHorizontally )
      {

         Spacer( modifier = Modifier.weight( 0.5F ) )

         Box( modifier = Modifier.weight( 0.5F ),
              contentAlignment = Alignment.Center )
         {
            Text(
               "Screen size (Dp): " + screen_width + " x " + screen_height ,
               fontSize = 24.sp, color = Color.LightGray

            )
         }

         //Spacer( modifier = Modifier.weight( 0.5F ) )

         Box( modifier = Modifier.weight( 0.5F ),
              contentAlignment = Alignment.Center )
         {
            Text(
               "" + view_state.value.screen_change_count + " SCREEN CHANGES",
               fontSize = 24.sp, color = Color.LightGray

            )
         }

         Button( onClick =
         {
            navController.navigate("AnotherScreen/true")
         },
            modifier = Modifier.requiredHeight( 100.dp ).
            requiredWidth( 200.dp).weight( 1F ),
            shape = RoundedCornerShape( 20.dp ),
            colors = ButtonDefaults.buttonColors( containerColor = Color.Cyan ) )
         {
            Text( text = "CHANGE", fontSize = 32.sp, color = Color.Blue )
         }

         Spacer( modifier = Modifier.weight( 0.5F ) )
      }

   }
}


class ChangingScreensCActivity : ComponentActivity()
{
   private val viewModel : GeneralViewModel by viewModels()

   override fun onCreate(savedInstanceState: Bundle?)
   {
      super.onCreate(savedInstanceState)
      setContent {
         ChangingScreensCTheme {
            val navController = rememberNavController()

            val viewState = viewModel.consumableState().collectAsState()

            NavHost(
               navController = navController,
               startDestination = "MainScreen"
            ) {
               
               composable("MainScreen" )
               {
                  MainScreen( navController, viewModel, viewState )
               }

               composable("AnotherScreen/{showOnlyPostsByUser}", arguments = listOf(
                  navArgument("showOnlyPostsByUser") {
                     type = NavType.BoolType
                     defaultValue = false
                  }
               )) {
                  val showOnlyPostsByUser =
                     it.arguments?.getBoolean("showOnlyPostsByUser") ?: false
                  AnotherScreen(showOnlyPostsByUser,  navController, viewModel, viewState )
               }
            }
         }
      }
   }
}

/*

One problem in this app was a light flash between screen changes.
It was solved 2023-08-16 by making the res/values/themes.xml look like:

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <style name="Theme.ChangingScreensC" parent="android:Theme.Material.NoActionBar" />
</resources>

The word "Light" was dropped form the 'equation' as was recommended on the
page https://stackoverflow.com/questions/71108210/

*/