fixes in pagination

CHANGELOG.md

@@ -7,6 +7,7 @@
         * Extension `Pagination#reverse` has been added
         * Factory `PaginationByIndexes`
         * Shortcut `calculatePagesNumber` with reversed parameters
+        * Value `emptyPagination` for empty `SimplePagination` cases
 
 ## 0.2.0
 

pagination/common/src/commonMain/kotlin/dev/inmo/micro_utils/pagination/SimplePagination.kt

@@ -14,6 +14,8 @@ inline fun FirstPagePagination(size: Int = defaultMediumPageSize) =
         size = size
     )
 
+val emptyPagination = Pagination(0, 0)
+
 @Suppress("NOTHING_TO_INLINE")
 inline fun Pagination.nextPage() =
     SimplePagination(

pagination/common/src/commonMain/kotlin/dev/inmo/micro_utils/pagination/utils/PaginationReversing.kt

@@ -13,15 +13,15 @@ import dev.inmo.micro_utils.pagination.*
 fun Pagination.reverse(objectsCount: Long): SimplePagination {
     val firstIndex = (objectsCount - (this.lastIndex + 1)).let {
         when {
-            it < 0 -> it
+            it < 0 -> 0
-            it > objectsCount -> objectsCount
+            it >= objectsCount -> return emptyPagination
             else -> it
         }
     }.toInt()
     val lastIndex = (objectsCount - (this.firstIndex + 1)).let {
         when {
-            it < 0 -> it
+            it < 0 -> return emptyPagination
-            it > objectsCount -> objectsCount
+            it >= objectsCount -> objectsCount - 1
             else -> it
         }
     }.toInt()

pagination/common/src/commonTest/kotlin/dev/inmo/micro_utils/pagination/utils/PaginationReversing.kt

@@ -7,18 +7,19 @@ import kotlin.test.assertEquals
 class PaginationReversingTests {
     @Test
     fun testThatCommonCaseWorksOk() {
-        val pageSize = 2
+        val pageSize = 3
-        val collectionSize = 8
+        val collectionSize = 9
         val pages = calculatePage(collectionSize, pageSize)
 
-        doWithPagination(FirstPagePagination(pageSize)) {
+        assertEquals(Pagination(-1, pageSize).reverse(collectionSize), Pagination(0, 0))
-            val reversed = it.reverse(collectionSize.toLong())
+
-            assertEquals(Pagination(calculatePage(collectionSize - it.firstIndex - it.size, it.size), it.size), reversed)
+        val middleFirstIndex = collectionSize / 2 - pageSize / 2
-            if (it.page < pages) {
+        val middleLastIndex = middleFirstIndex + pageSize - 1
-                it.nextPage()
+        assertEquals(
-            } else {
+            PaginationByIndexes(middleFirstIndex, middleLastIndex).reverse(collectionSize),
-                null
+            PaginationByIndexes(middleFirstIndex, middleLastIndex)
-            }
+        )
-        }
+
+        assertEquals(Pagination(calculatePagesNumber(collectionSize, pageSize), pageSize).reverse(collectionSize), Pagination(0, 0))
     }
 }