Add cache policy contract

See issue: #17

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

@@ -0,0 +1,49 @@
+/*
+ * 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.contract
+
+import org.threeten.bp.Instant
+import org.threeten.bp.temporal.TemporalAmount
+
+internal interface CacheStorePolicy {
+
+    /**
+     * Checks if the given [entityId] has been requested before a certain time [instant]
+     */
+    suspend fun isRequestBefore(entityId: Long, instant: Instant): Boolean
+
+    /**
+     * Checks if the given [entityId] has expired using a [threshold]
+     *
+     * @see isRequestBefore
+     */
+    suspend fun isRequestExpired(entityId: Long, threshold: TemporalAmount): Boolean
+
+    /**
+     * Checks if the given [entityId] has been requested before, regardless of when
+     */
+    suspend fun hasBeenRequested(entityId: Long): Boolean
+
+    /**
+     * Check if a resource with a given [entityId] is permitted to refresh
+     */
+    suspend fun shouldRefresh(
+        entityId: Long,
+        expiresAfter: Instant
+    ): Boolean
+}