TaskRepository.kt: Add option to specify a set of fields to order by

* Add generic `OrderSpec` open class

Author: EdricChan03

data/common/src/main/kotlin/com/edricchan/studybuddy/domain/common/sorting/OrderSpec.kt

@@ -0,0 +1,20 @@
+package com.edricchan.studybuddy.domain.common.sorting
+
+/**
+ * Specification for a specific field to order a list of data by.
+ * @property field Desired field to order the data by.
+ * @property direction Desired sorting direction.
+ */
+open class OrderSpec<F>(
+    open val field: F,
+    open val direction: SortDirection = SortDirection.Descending
+)
+
+/** Desired sorting direction for a given field. */
+enum class SortDirection {
+    /** Sort the resulting data in descending order, i.e. largest to smallest. */
+    Descending,
+
+    /** Sort the resulting data in ascending order, i.e. smallest to largest. */
+    Ascending
+}

features/tasks/data/src/main/kotlin/com/edricchan/studybuddy/features/tasks/data/repo/TaskRepository.kt

@@ -9,13 +9,15 @@ import androidx.paging.map
 import com.edricchan.studybuddy.data.common.QueryMapper
 import com.edricchan.studybuddy.data.paging.firestore.firestorePagingSource
 import com.edricchan.studybuddy.data.source.firestore.IDefaultFirestoreDataSource
+import com.edricchan.studybuddy.domain.common.sorting.SortDirection
 import com.edricchan.studybuddy.features.tasks.data.mapper.toDomain
 import com.edricchan.studybuddy.features.tasks.data.mapper.toDto
 import com.edricchan.studybuddy.features.tasks.data.model.TodoItem
 import com.edricchan.studybuddy.features.tasks.data.model.TodoProject
 import com.edricchan.studybuddy.features.tasks.domain.model.TaskItem
 import com.edricchan.studybuddy.features.tasks.domain.repo.ITaskRepository
 import com.google.firebase.firestore.DocumentReference
+import com.google.firebase.firestore.Query
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.combine
@@ -115,7 +117,15 @@ class TaskRepository @Inject constructor(
                 TodoItem.Field.IsDone.fieldName,
                 true
             ) else it
-        }.orderBy(config.orderByField.toDto().fieldName)
+        }.let {
+            config.orderByFields.fold(it) { query, spec ->
+                val direction = when (spec.direction) {
+                    SortDirection.Descending -> Query.Direction.DESCENDING
+                    SortDirection.Ascending -> Query.Direction.ASCENDING
+                }
+                query.orderBy(spec.field.toDto().fieldName, direction)
+            }
+        }
 
         emitAll(
             Pager(

features/tasks/domain/src/main/kotlin/com/edricchan/studybuddy/features/tasks/domain/repo/ITaskRepository.kt

@@ -2,6 +2,8 @@ package com.edricchan.studybuddy.features.tasks.domain.repo
 
 import androidx.paging.PagingData
 import androidx.paging.cachedIn
+import com.edricchan.studybuddy.domain.common.sorting.OrderSpec
+import com.edricchan.studybuddy.domain.common.sorting.SortDirection
 import com.edricchan.studybuddy.features.tasks.domain.model.TaskItem
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.flow.Flow
@@ -18,15 +20,24 @@ interface ITaskRepository {
      * @property includeArchived Whether archived tasks should be included in the list.
      * @property excludeCompleted Whether completed tasks should be excluded from the list.
      * @property pageSize Number of tasks to be shown per page.
-     * @property orderByField The [TaskItem.Field] to order the list of tasks by.
+     * @property orderByFields The set of [TaskOrderSpec] configurations to order the resulting data by,
+     * applied sequentially in-order.
      */
     data class PaginationConfig(
         val cachedCoroutineScope: CoroutineScope,
         val includeArchived: Boolean = false,
         val excludeCompleted: Boolean = false,
         val pageSize: Int = 30,
-        val orderByField: TaskItem.Field = TaskItem.Field.CreatedAt
-    )
+        val orderByFields: Set<TaskOrderSpec> = setOf(TaskOrderSpec())
+    ) {
+        data class TaskOrderSpec(
+            override val field: TaskItem.Field = TaskItem.Field.CreatedAt,
+            override val direction: SortDirection = SortDirection.Descending
+        ) : OrderSpec<TaskItem.Field>(
+            field = field,
+            direction = direction
+        )
+    }
 
     /**
      * Gets a paginated list of tasks.