Prepare exercise#4

Author: LukasLechnerDev

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/coroutines/usecase12/CalculationInSeveralCoroutinesViewModel.kt

@@ -1,11 +1,8 @@
 package com.lukaslechner.coroutineusecasesonandroid.usecases.coroutines.usecase12
 
-import androidx.lifecycle.viewModelScope
 import com.lukaslechner.coroutineusecasesonandroid.base.BaseViewModel
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.launch
-import kotlinx.coroutines.withContext
 import java.math.BigInteger
 import kotlin.system.measureTimeMillis
 
@@ -19,31 +16,25 @@ class CalculationInSeveralCoroutinesViewModel(
         numberOfCoroutines: Int
     ) {
         uiState.value = UiState.Loading
-        viewModelScope.launch {
 
-            var factorialResult = BigInteger.ZERO
-            val computationDuration = measureTimeMillis {
-                factorialResult =
-                    factorialCalculator.calculateFactorial(
-                        factorialOf,
-                        numberOfCoroutines
-                    )
-            }
-
-            var resultString = ""
-            val stringConversionDuration = measureTimeMillis {
-                resultString = convertToString(factorialResult)
-            }
+        var factorialResult = BigInteger.ZERO
+        val computationDuration = measureTimeMillis {
+            factorialResult =
+                factorialCalculator.calculateFactorial(
+                    factorialOf,
+                    numberOfCoroutines
+                )
+        }
 
-            uiState.value =
-                UiState.Success(resultString, computationDuration, stringConversionDuration)
+        var resultString = ""
+        val stringConversionDuration = measureTimeMillis {
+            resultString = convertToString(factorialResult)
         }
+
+        uiState.value =
+            UiState.Success(resultString, computationDuration, stringConversionDuration)
     }
 
-    private suspend fun convertToString(
-        number: BigInteger
-    ): String =
-        withContext(defaultDispatcher) {
-            number.toString()
-        }
+    // TODO: execute on background thread
+    private fun convertToString(number: BigInteger): String = number.toString()
 }

app/src/main/java/com/lukaslechner/coroutineusecasesonandroid/usecases/coroutines/usecase12/FactorialCalculator.kt

@@ -1,44 +1,41 @@
 package com.lukaslechner.coroutineusecasesonandroid.usecases.coroutines.usecase12
 
-import com.lukaslechner.coroutineusecasesonandroid.utils.addCoroutineDebugInfo
-import kotlinx.coroutines.*
-import timber.log.Timber
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.Dispatchers
 import java.math.BigInteger
 
 class FactorialCalculator(
     private val defaultDispatcher: CoroutineDispatcher = Dispatchers.Default
 ) {
 
-    suspend fun calculateFactorial(
+    fun calculateFactorial(
         factorialOf: Int,
         numberOfCoroutines: Int
     ): BigInteger {
-        return withContext(defaultDispatcher) {
-            val subRanges = createSubRangeList(factorialOf, numberOfCoroutines)
-            subRanges.map { subRange ->
-                async {
-                    calculateFactorialOfSubRange(subRange)
-                }
-            }.awaitAll()
-                .fold(BigInteger.ONE, { acc, element ->
-                    ensureActive()
-                    acc.multiply(element)
-                })
-        }
+
+        // TODO: create sub range list *on background thread*
+        val subRanges = createSubRangeList(factorialOf, numberOfCoroutines)
+
+
+        // TODO: calculate factorial of each subrange in separate coroutine
+        // use calculateFactorialOfSubRange(subRange) therefore
+
+
+        // TODO: create factorial result by multiplying all sub-results and return this
+        // result
+
+        return BigInteger.ZERO
     }
 
-    suspend fun calculateFactorialOfSubRange(
+    // TODO: execute on background thread
+    fun calculateFactorialOfSubRange(
         subRange: SubRange
     ): BigInteger {
-        return withContext(defaultDispatcher) {
-            Timber.d(addCoroutineDebugInfo("Calculate factorial of $subRange"))
-            var factorial = BigInteger.ONE
-            for (i in subRange.start..subRange.end) {
-                ensureActive()
-                factorial = factorial.multiply(BigInteger.valueOf(i.toLong()))
-            }
-            factorial
+        var factorial = BigInteger.ONE
+        for (i in subRange.start..subRange.end) {
+            factorial = factorial.multiply(BigInteger.valueOf(i.toLong()))
         }
+        return factorial
     }
 
     fun createSubRangeList(
@@ -63,4 +60,5 @@ class FactorialCalculator(
     }
 }
 
+
 data class SubRange(val start: Int, val end: Int)