Add cache store to manage request state

See issue: #17

app-data/src/main/kotlin/co/anitrend/data/cache/repository/CacheStore.kt

@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2020  AniTrend
+ *
+ *     This program is free software: you can redistribute it and/or modify
+ *     it under the terms of the GNU General Public License as published by
+ *     the Free Software Foundation, either version 3 of the License, or
+ *     (at your option) any later version.
+ *
+ *     This program is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *     GNU General Public License for more details.
+ *
+ *     You should have received a copy of the GNU General Public License
+ *     along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package co.anitrend.data.cache.repository
+
+import co.anitrend.data.cache.datasource.local.CacheDao
+import co.anitrend.data.cache.entity.CacheEntity
+import co.anitrend.data.cache.helper.inPast
+import co.anitrend.data.cache.model.CacheRequest
+import co.anitrend.data.cache.repository.contract.CacheStorePolicy
+import org.threeten.bp.Instant
+import org.threeten.bp.temporal.TemporalAmount
+
+internal abstract class CacheStore(
+    private val request: CacheRequest,
+    private val dao: CacheDao
+) : CacheStorePolicy {
+
+    private suspend fun getRequestInstant(
+        entityId: Long
+    ) = dao.getCacheLog(request, entityId)?.timestamp
+
+    /**
+     * Checks if the given [entityId] has been requested before a certain time [instant]
+     */
+    override suspend fun isRequestBefore(
+        entityId: Long,
+        instant: Instant
+    ) = getRequestInstant(entityId)?.isBefore(instant) ?: true
+
+    /**
+     * Checks if the given [entityId] has expired using a [threshold]
+     *
+     * @see isRequestBefore
+     */
+    override suspend fun isRequestExpired(
+        entityId: Long,
+        threshold: TemporalAmount
+    ) = isRequestBefore(entityId, threshold.inPast())
+
+    /**
+     * Checks if the given [entityId] has been requested before, regardless of when
+     */
+    override suspend fun hasBeenRequested(
+        entityId: Long
+    ) = dao.countMatching(request, entityId) > 0
+
+    suspend fun updateLastRequest(entityId: Long, timestamp: Instant = Instant.now()) {
+        dao.upsert(
+            CacheEntity(
+                request = request,
+                cacheItemId = entityId,
+                timestamp = timestamp
+            )
+        )
+    }
+
+    suspend fun invalidateLastRequest(entityId: Long) =
+        updateLastRequest(entityId, Instant.EPOCH)
+}