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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) {
val key = params.key ?: 0
val limit = when (params) {
is LoadParams.Prepend -> minOf(key, params.loadSize)
else -> params.loadSize
}
val loadResult = transacter.transactionWithResult {
val count = countQuery.executeAsOne()
val offset = when (params) {
is LoadParams.Prepend -> maxOf(0, key - params.loadSize)
is LoadParams.Append -> key
is LoadParams.Refresh -> if (key >= count) maxOf(0, count - params.loadSize) else key
}
val data = queryProvider(limit, offset)
.also { currentQuery = it }
.executeAsList()
val nextPosToLoad = offset + data.size
LoadResult.Page(
data = data,
prevKey = offset.takeIf { it > 0 && data.isNotEmpty() },
nextKey = nextPosToLoad.takeIf { data.isNotEmpty() && data.size >= limit && it < count },
itemsBefore = offset,
itemsAfter = maxOf(0, count - nextPosToLoad),
)
}
if (invalid) LoadResult.Invalid() else loadResult
}
override fun getRefreshKey(state: PagingState<Int, RowType>) =
state.anchorPosition?.let { maxOf(0, it - (state.config.initialLoadSize / 2)) }
}