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OffsetQueryPagingSource.kt
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OffsetQueryPagingSource.kt
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/*
* Copyright (C) 2016 Square, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package app.cash.sqldelight.paging3
import androidx.paging.PagingState
import app.cash.sqldelight.Query
import app.cash.sqldelight.Transacter
import kotlinx.coroutines.withContext
import kotlin.coroutines.CoroutineContext
internal class OffsetQueryPagingSource<RowType : Any>(
private val queryProvider: (limit: Int, offset: Int) -> Query<RowType>,
private val countQuery: Query<Int>,
private val transacter: Transacter,
private val context: CoroutineContext,
) : QueryPagingSource<Int, RowType>() {
override val jumpingSupported get() = true
override suspend fun load(
params: LoadParams<Int>,
): LoadResult<Int, RowType> = withContext(context) {
try {
val key = params.key ?: 0
transacter.transactionWithResult {
val count = countQuery.executeAsOne()
if (count != 0 && key >= count) throw IndexOutOfBoundsException()
val loadSize = if (key < 0) params.loadSize + key else params.loadSize
val data = queryProvider(loadSize, maxOf(0, key))
.also { currentQuery = it }
.executeAsList()
LoadResult.Page(
data = data,
// allow one, and only one negative prevKey in a paging set. This is done for
// misaligned prepend queries to avoid duplicates.
prevKey = if (key <= 0L) null else key - params.loadSize,
nextKey = if (key + params.loadSize >= count) null else key + params.loadSize,
itemsBefore = maxOf(0, key),
itemsAfter = maxOf(0, (count - (key + params.loadSize))),
)
}
} catch (e: Exception) {
if (e is IndexOutOfBoundsException) throw e
LoadResult.Error(e)
}
}
override fun getRefreshKey(state: PagingState<Int, RowType>) = state.anchorPosition
}