add utility module for AWS regions. (#259)

serverless/aws/src/aws_region.ts

@@ -0,0 +1,48 @@
+interface Bucket {
+  bucket: string;
+  region: string;
+}
+
+const REGION_MATRIX: Record<string, string[]> = {
+  "us-east-2": ["us-east-1"], // ohio
+  "us-east-1": ["us-east-2"], // virginia
+  "us-west-2": ["us-west-1"], // oregon
+  "us-west-1": ["us-west-2"], // california
+  "ap-south-1": ["ap-southeast-1"], // mumbai
+  "ap-southeast-1": ["ap-southeast-2", "ap-northeast-1", "ap-northeast-2"], // singapore
+  "ap-southeast-2": ["ap-southeast-1"], // sydney
+  "ap-northeast-2": ["ap-northeast-1", "ap-southeast-1"], // seoul
+  "ap-northeast-1": ["ap-northeast-2", "ap-southeast-1"], // tokyo
+  "eu-central-1": ["eu-west-1", "eu-west-2"], // frankfurt
+  "eu-west-1": ["eu-west-2", "eu-central-1"], // dublin
+  "eu-west-2": ["eu-west-1", "eu-central-1"], // london
+  "sa-east-1": ["us-east-1", "us-east-2"], // sao paulo
+};
+
+export let get_region = (
+  exec_region: string,
+  primary: Bucket,
+  replicas: Bucket[],
+): Bucket => {
+  if (primary.region === exec_region) {
+    return primary;
+  }
+
+  for (let replica of replicas) {
+    if (replica.region === exec_region) {
+      return replica;
+    }
+  }
+
+  if (exec_region in REGION_MATRIX) {
+    for (let region of REGION_MATRIX[exec_region]) {
+      for (let replica of replicas) {
+        if (replica.region === region) {
+          return replica;
+        }
+      }
+    }
+  }
+
+  return primary;
+};