Treat projection as a private case of 'kindMemory'

lib/kinds.js

@@ -12,6 +12,25 @@ const SCOPE = ['application', 'global', 'local'];
 const STORE = ['persistent', 'memory'];
 const ALLOW = ['write', 'append', 'read'];
 
+const KIND_STORED_DEFAULT_META = {
+  scope: 'application',
+  store: 'persistent',
+  allow: 'write',
+};
+const KIND_MEMORY_DEFAULT_META = {
+  scope: 'local',
+  store: 'memory',
+  allow: 'write',
+};
+
+const withDefaults = (meta, defaults, extra) => {
+  const result = { ...meta, ...extra };
+  for (const [key, defaultValue] of Object.entries(defaults)) {
+    if (result[key] === undefined) result[key] = defaultValue;
+  }
+  return result;
+};
+
 const projection = (kind, meta, root) => {
   const { schema: schemaName, fields: fieldNames } = meta;
   if (!schemaName) throw new Error('Invalid Projection: "schema" expected');
@@ -24,29 +43,30 @@ const projection = (kind, meta, root) => {
   if (referencedFields) {
     for (const name of fieldNames) defs[name] = referencedFields[name];
   }
-  const { scope = 'local', store = 'memory', allow = 'write', ...rest } = meta;
-  const metadata = { kind, scope, store, allow, parent: schemaName, ...rest };
+  const metadata = withDefaults(meta, KIND_MEMORY_DEFAULT_META, {
+    kind,
+    parent: schemaName,
+  });
   return { defs, metadata };
 };
 
 const kindStored = (kind, meta, root) => {
-  const { scope = 'application', store = 'persistent', allow = 'write' } = meta;
-  const metadata = { ...meta, kind, scope, store, allow };
+  if (!root) throw new Error('"root" schema expected');
   const id = root.name ? `${toLowerCamel(root.name)}Id` : 'id';
   const defs = { [id]: '?string' };
+  const metadata = withDefaults(meta, KIND_STORED_DEFAULT_META, { kind });
   return { defs, metadata };
 };
 
-const kindMemory = (kind, meta) => {
-  const { scope = 'local', store = 'memory', allow = 'write' } = meta;
-  return { metadata: { ...meta, kind, scope, store, allow }, defs: {} };
+const kindMemory = (kind, meta, root) => {
+  if (kind === 'projection') return projection(kind, meta, root);
+  const metadata = withDefaults(meta, KIND_MEMORY_DEFAULT_META, { kind });
+  return { defs: {}, metadata };
 };
 
 const getKindMetadata = (kind, meta = {}, root) => {
-  if (kind === 'projection') return projection(kind, meta, root);
-  if (KIND_MEMORY.includes(kind)) return kindMemory(kind, meta);
-  if (KIND_STORED.includes(kind)) return kindStored(kind, meta, root);
-  return kindMemory(kind, meta);
+  const processKind = KIND_STORED.includes(kind) ? kindStored : kindMemory;
+  return processKind(kind, meta, root);
 };
 
 module.exports = {