Refactor AWS client creation

src/main/java/com/conveyal/datatools/common/utils/AWSClientManager.java

@@ -0,0 +1,77 @@
+package com.conveyal.datatools.common.utils;
+
+import java.util.HashMap;
+
+import static com.conveyal.datatools.common.utils.AWSUtils.DEFAULT_EXPIRING_AWS_ASSET_VALID_DURATION_MILLIS;
+
+/**
+ * This abstract class provides a framework for managing the creation of AWS Clients. Three types of clients are stored
+ * in this class:
+ * 1. A default client to use when not requesting a client using a specific role and/or region
+ * 2. A client to use when using a specific region, but not with a role
+ * 3. A client to use with a specific role and region combination (including null regions)
+ *
+ * The {@link AWSClientManager#getClient(String, String)} handles the creation and caching of clients based on the given
+ * role and region inputs.
+ */
+public abstract class AWSClientManager<T> {
+    protected final T defaultClient;
+    private HashMap<String, T> nonRoleClientsByRegion = new HashMap<>();
+    private HashMap<String, ExpiringAsset<T>> clientsByRoleAndRegion = new HashMap<>();
+
+    public AWSClientManager (T defaultClient) {
+        this.defaultClient = defaultClient;
+    }
+
+    /**
+     * An abstract method where the implementation will create a client with the specified region, but not with a role.
+     */
+    public abstract T buildDefaultClientWithRegion(String region);
+
+    /**
+     * An abstract method where the implementation will create a client with the specified role and region.
+     */
+    protected abstract T buildCredentialedClientForRoleAndRegion(String role, String region)
+        throws CheckedAWSException;
+
+    /**
+     * Obtain a potentially cached AWS client for the provided role ARN and region. If the role and region are null, the
+     * default AWS client will be used. If just the role is null a cached client configured for the specified
+     * region will be returned. For clients that require using a role, a client will be obtained (either via a cache or
+     * by creation and then insertion into the cache) that has obtained the proper credentials.
+     */
+    public T getClient(String role, String region) throws CheckedAWSException {
+        // return default client for null region and role
+        if (role == null && region == null) {
+            return defaultClient;
+        }
+
+        // if the role is null, return a potentially cached EC2 client with the region configured
+        T client;
+        if (role == null) {
+            client = nonRoleClientsByRegion.get(region);
+            if (client == null) {
+                client = buildDefaultClientWithRegion(region);
+                nonRoleClientsByRegion.put(region, client);
+            }
+            return client;
+        }
+
+        // check for the availability of a client already associated with the given role and region
+        String roleRegionKey = makeRoleRegionKey(role, region);
+        ExpiringAsset<T> clientWithRole = clientsByRoleAndRegion.get(roleRegionKey);
+        if (clientWithRole != null && clientWithRole.isActive()) return clientWithRole.asset;
+
+        // Either a new client hasn't been created or it has expired. Create a new client and cache it.
+        T credentialedClientForRoleAndRegion = buildCredentialedClientForRoleAndRegion(role, region);
+        clientsByRoleAndRegion.put(
+            roleRegionKey, 
+            new ExpiringAsset<T>(credentialedClientForRoleAndRegion, DEFAULT_EXPIRING_AWS_ASSET_VALID_DURATION_MILLIS)
+        );
+        return credentialedClientForRoleAndRegion;
+    }
+
+    private static String makeRoleRegionKey(String role, String region) {
+        return String.format("role=%s,region=%s", role, region);
+    }
+}