refactor: extract paging helpers

feature/convos/src/main/kotlin/dev/meloda/fast/convos/ConvosViewModel.kt

@@ -14,6 +14,10 @@ import dev.meloda.fast.common.extensions.findWithIndex
 import dev.meloda.fast.common.extensions.listenValue
 import dev.meloda.fast.common.extensions.setValue
 import dev.meloda.fast.common.extensions.updateValue
+import dev.meloda.fast.common.paging.canPaginate as canPaginatePage
+import dev.meloda.fast.common.paging.isPaginationExhausted as isPaginationExhaustedPage
+import dev.meloda.fast.common.paging.loadingFlags
+import dev.meloda.fast.common.paging.mergePage
 import dev.meloda.fast.convos.model.ConvoDialog
 import dev.meloda.fast.convos.model.ConvoNavigation
 import dev.meloda.fast.convos.model.ConvosScreenState
@@ -264,17 +268,12 @@ class ConvosViewModel(
                     _baseError.update { newBaseError }
                 },
                 success = { response ->
-                    val convos = response
-                    val fullConvos = if (offset == 0) {
-                        convos
-                    } else {
-                        this.convos.value.plus(convos)
-                    }
-
-                    val itemsCountSufficient = response.size == LOAD_COUNT
-
-                    val paginationExhausted = !itemsCountSufficient &&
-                            this.convos.value.isNotEmpty()
+                    val itemsCountSufficient = canPaginatePage(LOAD_COUNT, response.size)
+                    val paginationExhausted = isPaginationExhaustedPage(
+                        pageSize = LOAD_COUNT,
+                        loadedCount = response.size,
+                        hasExistingItems = this.convos.value.isNotEmpty()
+                    )
 
                     _screenState.updateValue {
                         copy(isPaginationExhausted = paginationExhausted)
@@ -293,16 +292,17 @@ class ConvosViewModel(
 
                     convoUseCase.storeConvos(response)
 
-                    _convos.emit(fullConvos)
+                    _convos.emit(mergePage(this.convos.value, response, offset))
                     syncUiConvos()
                     _canPaginate.setValue { itemsCountSufficient }
                 }
             )
 
+            val flags = loadingFlags(offset, state.isLoading())
             _screenState.setValue { old ->
                 old.copy(
-                    isLoading = offset == 0 && state.isLoading(),
-                    isPaginating = offset > 0 && state.isLoading()
+                    isLoading = flags.isLoading,
+                    isPaginating = flags.isPaginating
                 )
             }
         }