From 07c3303f9c6b8d46763d270f47b730d5519eb204 Mon Sep 17 00:00:00 2001
From: vlad <vlad@driver.xyz>
Date: Tue, 19 Sep 2017 20:47:28 -0700
Subject: Utils from pds-common

---
 src/main/scala/xyz/driver/core/cache.scala | 109 +++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 src/main/scala/xyz/driver/core/cache.scala

(limited to 'src/main/scala/xyz/driver/core/cache.scala')

diff --git a/src/main/scala/xyz/driver/core/cache.scala b/src/main/scala/xyz/driver/core/cache.scala
new file mode 100644
index 0000000..79ba2d7
--- /dev/null
+++ b/src/main/scala/xyz/driver/core/cache.scala
@@ -0,0 +1,109 @@
+package xyz.driver.core
+
+import java.util.concurrent.{Callable, TimeUnit}
+
+import com.google.common.cache.{CacheBuilder, Cache => GuavaCache}
+import com.typesafe.scalalogging.Logger
+
+import scala.concurrent.duration.{Duration, _}
+import scala.concurrent.{ExecutionContext, Future}
+
+object cache {
+
+  /**
+    * FutureCache is used to represent an in-memory, in-process, asynchronous cache.
+    *
+    * Every cache operation is atomic.
+    *
+    * This implementation evicts failed results,
+    * and doesn't interrupt the underlying request that has been fired off.
+    */
+  class AsyncCache[K, V](name: String, cache: GuavaCache[K, Future[V]])(implicit executionContext: ExecutionContext) {
+
+    private[this] val log        = Logger(s"AsyncCache.$name")
+    private[this] val underlying = cache.asMap()
+
+    private[this] def evictOnFailure(key: K, f: Future[V]): Future[V] = {
+      f onFailure {
+        case ex: Throwable =>
+          log.debug(s"Evict key $key due to exception $ex")
+          evict(key, f)
+      }
+      f // we return the original future to make evict(k, f) easier to work with.
+    }
+
+    /**
+      * Equivalent to getOrElseUpdate
+      */
+    def apply(key: K)(value: => Future[V]): Future[V] = getOrElseUpdate(key)(value)
+
+    /**
+      * Gets the cached Future.
+      *
+      * @return None if a value hasn't been specified for that key yet
+      *         Some(ksync computation) if the value has been specified.  Just
+      *         because this returns Some(..) doesn't mean that it has been
+      *         satisfied, but if it hasn't been satisfied, it's probably
+      *         in-flight.
+      */
+    def get(key: K): Option[Future[V]] = Option(underlying.get(key))
+
+    /**
+      * Gets the cached Future, or if it hasn't been returned yet, computes it and
+      * returns that value.
+      */
+    def getOrElseUpdate(key: K)(compute: => Future[V]): Future[V] = {
+      log.debug(s"Try to retrieve key $key from cache")
+      evictOnFailure(key, cache.get(key, new Callable[Future[V]] {
+        def call(): Future[V] = {
+          log.debug(s"Cache miss, load the key: $key")
+          compute
+        }
+      }))
+    }
+
+    /**
+      * Unconditionally sets a value for a given key
+      */
+    def set(key: K, value: Future[V]): Unit = {
+      cache.put(key, value)
+      evictOnFailure(key, value)
+    }
+
+    /**
+      * Evicts the contents of a `key` if the old value is `value`.
+      *
+      * Since `scala.concurrent.Future` uses reference equality, you must use the
+      * same object reference to evict a value.
+      *
+      * @return true if the key was evicted
+      *         false if the key was not evicted
+      */
+    def evict(key: K, value: Future[V]): Boolean = underlying.remove(key, value)
+
+    /**
+      * @return the number of results that have been computed successfully or are in flight.
+      */
+    def size: Int = cache.size.toInt
+  }
+
+  object AsyncCache {
+    val DEFAULT_CAPACITY: Long             = 10000L
+    val DEFAULT_READ_EXPIRATION: Duration  = 10 minutes
+    val DEFAULT_WRITE_EXPIRATION: Duration = 1 hour
+
+    def apply[K <: AnyRef, V <: AnyRef](name: String,
+                                        capacity: Long = DEFAULT_CAPACITY,
+                                        readExpiration: Duration = DEFAULT_READ_EXPIRATION,
+                                        writeExpiration: Duration = DEFAULT_WRITE_EXPIRATION)(
+            implicit executionContext: ExecutionContext): AsyncCache[K, V] = {
+      val guavaCache = CacheBuilder
+        .newBuilder()
+        .maximumSize(capacity)
+        .expireAfterAccess(readExpiration.toSeconds, TimeUnit.SECONDS)
+        .expireAfterWrite(writeExpiration.toSeconds, TimeUnit.SECONDS)
+        .build[K, Future[V]]()
+      new AsyncCache(name, guavaCache)
+    }
+  }
+}
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