Add vetoing functionality to the selection state (#68)

- Removed: `onSelectionChange` callback
- Added: `confirmSelectionChange` callback

README.md

@@ -184,6 +184,7 @@ Selection modes are represented by `SelectionMode` enum, with following values:
 - `Single` - only single day is selectable - selection will contain one or zero days selected.
 - `Multiple` - a list of dates can be selected.
 - `Period` - selectable period - implemented by `start` and `end` dates. - selection will contain all dates between start and the end date.
+This implementation of SelectionState also allows for handling side-effects and vetoing the state change via `confirmSelectionChange` callback.
 
 ## KotlinX DateTime
 As the core of the library is built on `java.time` library, on Android it requires to use [core libary desugaring](https://developer.android.com/studio/write/java8-support) to be able to access it's API.

library/api/library.api

@@ -107,6 +107,7 @@ public final class io/github/boguszpawlowski/composecalendar/selection/DynamicSe
 
 public final class io/github/boguszpawlowski/composecalendar/selection/DynamicSelectionState : io/github/boguszpawlowski/composecalendar/selection/SelectionState {
 	public fun <init> (Lkotlin/jvm/functions/Function1;Ljava/util/List;Lio/github/boguszpawlowski/composecalendar/selection/SelectionMode;)V
+	public synthetic fun <init> (Lkotlin/jvm/functions/Function1;Ljava/util/List;Lio/github/boguszpawlowski/composecalendar/selection/SelectionMode;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun getSelection ()Ljava/util/List;
 	public final fun getSelectionMode ()Lio/github/boguszpawlowski/composecalendar/selection/SelectionMode;
 	public fun isDateSelected (Ljava/time/LocalDate;)Z

library/src/main/java/io/github/boguszpawlowski/composecalendar/Calendar.kt

@@ -218,23 +218,21 @@ public fun <T : SelectionState> Calendar(
  * @param initialMonth initially rendered month
  * @param initialSelection initial selection of the composable
  * @param initialSelectionMode initial mode of the selection
- * @param onSelectionChanged callback for side effects triggered when the selection state changes
+ * @param confirmSelectionChange callback for optional side-effects handling and vetoing the state change
  */
 @Composable
 public fun rememberSelectableCalendarState(
   initialMonth: YearMonth = YearMonth.now(),
   initialSelection: List<LocalDate> = emptyList(),
   initialSelectionMode: SelectionMode = SelectionMode.Single,
-  onSelectionChanged: (List<LocalDate>) -> Unit = {},
+  confirmSelectionChange: (newValue: List<LocalDate>) -> Boolean = { true },
   monthState: MonthState = rememberSaveable(saver = MonthState.Saver()) {
     MonthState(initialMonth = initialMonth)
   },
   selectionState: DynamicSelectionState = rememberSaveable(
-    saver = DynamicSelectionState.Saver(
-      onSelectionChanged
-    )
+    saver = DynamicSelectionState.Saver(confirmSelectionChange),
   ) {
-    DynamicSelectionState(onSelectionChanged, initialSelection, initialSelectionMode)
+    DynamicSelectionState(confirmSelectionChange, initialSelection, initialSelectionMode)
   },
 ): CalendarState<DynamicSelectionState> = remember { CalendarState(monthState, selectionState) }
 

library/src/main/java/io/github/boguszpawlowski/composecalendar/selection/SelectionState.kt

@@ -18,10 +18,11 @@ public interface SelectionState {
 /**
  * Class that enables for dynamically changing selection modes in the runtime. Depending on the mode, selection changes differently.
  * Mode can be varied by setting desired [SelectionMode] in the [selectionMode] mutable property.
+ * @param confirmSelectionChange return false from this callback to veto the selection change
  */
 @Stable
 public class DynamicSelectionState(
-  private val onSelectionChanged: (List<LocalDate>) -> Unit,
+  private val confirmSelectionChange: (newValue: List<LocalDate>) -> Boolean = { true },
   selection: List<LocalDate>,
   selectionMode: SelectionMode,
 ) : SelectionState {
@@ -32,9 +33,8 @@ public class DynamicSelectionState(
   public var selection: List<LocalDate>
     get() = _selection
     set(value) {
-      if (value != selection) {
+      if (value != selection && confirmSelectionChange(value)) {
         _selection = value
-        onSelectionChanged(value)
       }
     }
 
@@ -55,14 +55,16 @@ public class DynamicSelectionState(
 
   internal companion object {
     @Suppress("FunctionName", "UNCHECKED_CAST") // Factory function
-    fun Saver(onSelectionChanged: (List<LocalDate>) -> Unit): Saver<DynamicSelectionState, Any> =
+    fun Saver(
+      confirmSelectionChange: (newValue: List<LocalDate>) -> Boolean,
+    ): Saver<DynamicSelectionState, Any> =
       listSaver(
         save = { raw ->
           listOf(raw.selectionMode, raw.selection.map { it.toString() })
         },
         restore = { restored ->
           DynamicSelectionState(
-            onSelectionChanged = onSelectionChanged,
+            confirmSelectionChange = confirmSelectionChange,
             selectionMode = restored[0] as SelectionMode,
             selection = (restored[1] as? List<String>)?.map { LocalDate.parse(it) }.orEmpty(),
           )

library/src/test/java/io/github/boguszpawlowski/composecalendar/selection/SelectionStateTest.kt

@@ -2,6 +2,7 @@
 
 package io.github.boguszpawlowski.composecalendar.selection
 
+import io.github.boguszpawlowski.composecalendar.selection.SelectionMode.Multiple
 import io.kotest.assertions.throwables.shouldNotThrowAny
 import io.kotest.core.spec.style.ShouldSpec
 import io.kotest.matchers.collections.shouldContainExactly
@@ -17,15 +18,15 @@ internal class SelectionStateTest : ShouldSpec({
 
   context("Selection state with SelectionMode.None") {
     should("not change selection after new value arrives") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.None)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.None)
 
       state.onDateSelected(LocalDate.now())
 
       state.selection shouldBe emptyList()
     }
 
     should("be able to change if mode has been changed") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.None)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.None)
 
       state.selectionMode = SelectionMode.Single
       state.onDateSelected(today)
@@ -36,15 +37,15 @@ internal class SelectionStateTest : ShouldSpec({
 
   context("Selection state with SelectionMode.Single") {
     should("change state to single after day is selected") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Single)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Single)
 
       state.onDateSelected(today)
 
       state.selection shouldBe listOf(today)
     }
 
     should("change state to none when same day is selected") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Single)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Single)
 
       state.onDateSelected(today)
       state.onDateSelected(today)
@@ -53,7 +54,7 @@ internal class SelectionStateTest : ShouldSpec({
     }
 
     should("change to other day when selected") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Single)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Single)
 
       state.onDateSelected(today)
       state.onDateSelected(tomorrow)
@@ -62,7 +63,7 @@ internal class SelectionStateTest : ShouldSpec({
     }
 
     should("not be mutable after selection mode is changed to None") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Single)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Single)
 
       state.selectionMode = SelectionMode.None
       state.onDateSelected(today)
@@ -73,7 +74,7 @@ internal class SelectionStateTest : ShouldSpec({
 
   context("Selection state with SelectionMode.Multiple") {
     should("allow for multiple days selected") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Multiple)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Multiple)
 
       state.onDateSelected(today)
       state.onDateSelected(tomorrow)
@@ -85,7 +86,7 @@ internal class SelectionStateTest : ShouldSpec({
     }
 
     should("switch selection off once day is selected second time") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Multiple)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Multiple)
 
       state.onDateSelected(today)
       state.onDateSelected(tomorrow)
@@ -97,7 +98,7 @@ internal class SelectionStateTest : ShouldSpec({
 
   context("Selection state with SelectionMode.Period") {
     should("allow for period of days selected") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Period)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Period)
 
       state.onDateSelected(today)
       state.onDateSelected(tomorrow)
@@ -107,7 +108,7 @@ internal class SelectionStateTest : ShouldSpec({
     }
 
     should("switch selection off once start day is selected") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Period)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Period)
 
       state.onDateSelected(today)
       state.onDateSelected(tomorrow)
@@ -116,7 +117,7 @@ internal class SelectionStateTest : ShouldSpec({
       state.selection shouldBe emptyList()
     }
     should("change end date once the date selected is between start and the end") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Period)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Period)
 
       state.onDateSelected(yesterday)
       state.onDateSelected(tomorrow)
@@ -126,7 +127,7 @@ internal class SelectionStateTest : ShouldSpec({
       state.selection.last() shouldBe today
     }
     should("change start day once day before start is selected") {
-      val state = DynamicSelectionState({}, emptyList(), SelectionMode.Period)
+      val state = DynamicSelectionState({ true }, emptyList(), SelectionMode.Period)
 
       state.onDateSelected(today)
       state.onDateSelected(tomorrow)
@@ -150,4 +151,27 @@ internal class SelectionStateTest : ShouldSpec({
       }
     }
   }
+  context("Selection State with confirm state change callback") {
+    var nextVetoResult = false
+    val initialSelection = LocalDate.of(1999, 10, 12)
+    val newSelection = initialSelection.plusDays(1)
+
+    val selectionState = DynamicSelectionState(
+      confirmSelectionChange = { nextVetoResult },
+      selection = listOf(initialSelection),
+      selectionMode = Multiple,
+    )
+    should("Not change the selection when change is vetoed") {
+      selectionState.onDateSelected(newSelection)
+
+      selectionState.selection shouldBe listOf(initialSelection)
+    }
+    should("Change the selection when change is not vetoed") {
+      nextVetoResult = true
+
+      selectionState.onDateSelected(newSelection)
+
+      selectionState.selection shouldBe listOf(initialSelection, newSelection)
+    }
+  }
 })

sample/src/main/java/io/github/boguszpawlowski/composecalendar/sample/KotlinDateTimeSample.kt

@@ -76,7 +76,7 @@ fun DateTimeCalendar(
 ) {
   SelectableCalendar(
     calendarState = rememberSelectableCalendarState(
-      onSelectionChanged = { selection -> onSelectionChanged(selection.map { it.toKotlinLocalDate() }) },
+      confirmSelectionChange = { selection -> onSelectionChanged(selection.map { it.toKotlinLocalDate() }); true },
       initialSelectionMode = Multiple,
     ),
     today = today.toJavaLocalDate(),

sample/src/main/java/io/github/boguszpawlowski/composecalendar/sample/ViewModelSample.kt

@@ -53,7 +53,7 @@ fun ViewModelSample() {
   val selectedPrice by viewModel.selectedRecipesPriceFlow.collectAsState(0)
 
   val state = rememberSelectableCalendarState(
-    onSelectionChanged = viewModel::onSelectionChanged,
+    confirmSelectionChange = { viewModel.onSelectionChanged(it); true },
     initialSelectionMode = Period,
   )