feat: serializers, serializers, oh my

src/index.ts

@@ -2,3 +2,4 @@ import '@tsmetadata/polyfill';
 
 export * from './decorators';
 export * from './types';
+export * from './serializers';

src/serializers/index.ts

@@ -0,0 +1,3 @@
+export * from './utils';
+export * from './serializeResourceObject';
+export * from './serializeResourceRelationshipObject';

src/serializers/serializeResourceObject.ts

@@ -0,0 +1,27 @@
+import { attributesSymbol, idSymbol, linksSymbol, metaSymbol, relationshipsSymbol, resourceSymbol } from "../decorators";
+import { collect } from "./utils/collect";
+import { getMetadataBySymbol } from "./utils/getMetadataBySymbol";
+import { serializeResourceRelationshipObject } from "./serializeResourceRelationshipObject";
+
+import type { JSONAPILinksObject, JSONAPIMetaObject, JSONAPIRelationshipObject, JSONAPIResourceObject, JSONObject } from "../types";
+
+export const serializeResourceObject = <I extends object>(classInstance: I): JSONAPIResourceObject => {
+  const relationshipTuples = getMetadataBySymbol<[keyof I, string][]>(classInstance, relationshipsSymbol);
+
+  const relationships = relationshipTuples.reduce((acc, [key]) => {
+    const related = classInstance[key] as object;
+
+    acc[key] = Array.isArray(related) ? related.map(serializeResourceRelationshipObject) : serializeResourceRelationshipObject(related);
+
+    return acc;
+  }, {} as Record<keyof I, JSONAPIRelationshipObject | JSONAPIRelationshipObject[]>);
+
+  return {
+    type: getMetadataBySymbol<string>(classInstance, resourceSymbol),
+    id: collect<string>(classInstance, idSymbol),
+    attributes: collect<JSONObject>(classInstance, attributesSymbol),
+    relationships,
+    links: collect<JSONAPILinksObject>(classInstance, linksSymbol),
+    meta: collect<JSONAPIMetaObject>(classInstance, metaSymbol),
+  };
+};

src/serializers/serializeResourceRelationshipObject.ts

@@ -0,0 +1,14 @@
+import { idSymbol, linksSymbol, metaSymbol, resourceSymbol } from "../decorators";
+import { collect } from "./utils/collect";
+import { getMetadataBySymbol } from "./utils/getMetadataBySymbol";
+
+import type { JSONAPILinksObject, JSONAPIMetaObject, JSONAPIRelationshipObject } from "../types";
+
+export const serializeResourceRelationshipObject = <I extends object>(classInstance: I): JSONAPIRelationshipObject => ({
+  data: {
+    type: getMetadataBySymbol<string>(classInstance, resourceSymbol),
+    id: collect<string>(classInstance, idSymbol),
+  },
+  links: collect<JSONAPILinksObject>(classInstance, linksSymbol),
+  meta: collect<JSONAPIMetaObject>(classInstance, metaSymbol),
+});

src/serializers/utils/assertMetadataIsPresent.ts

@@ -0,0 +1,27 @@
+export const assertMetadataIsPresent = (candidate: unknown | unknown[]): true => {
+  if (Symbol.metadata === undefined) {
+    throw new Error(
+      'Failed to assert the presence of metadata because the metadata symbol is undefined. You may need to import the `@tsmetadata/polyfill` package.',
+    );
+  }
+
+  const objects = Array.isArray(candidate) ? candidate : [candidate];
+
+  for (const object of objects) {
+    if(typeof object !== 'object') {
+      throw new Error(
+        'Failed to assert the presence of metadata because at least one candidate is not an object, meaning no constructor is present.',
+      );
+    }
+
+    const metadata = object.constructor[Symbol.metadata];
+
+    if (metadata === undefined || metadata === null) {
+      throw new Error(
+        'No metadata was found on an object constructor.'
+      );
+    }
+  }
+
+  return true;
+};

src/serializers/utils/collect.ts

@@ -0,0 +1,32 @@
+import { assertMetadataIsPresent } from "./assertMetadataIsPresent";
+import { getMetadataBySymbol } from "./getMetadataBySymbol";
+
+export const collect = <T = unknown, O extends object = object>(object: O, symbol: symbol) => {
+  assertMetadataIsPresent(object);
+
+  const keyOrKeys = getMetadataBySymbol<keyof O | (keyof O)[]>(object, symbol);
+
+  if(Array.isArray(keyOrKeys)) {
+    const keys = keyOrKeys;
+
+    if (keys.length === 0) {
+      return {} as T;
+    }
+
+    return keys.reduce((acc, key) => {
+      const value = object[key];
+
+      if (value === undefined) {
+        return acc;
+      }
+
+      acc[key] = value;
+
+      return acc;
+    }, {} as Record<keyof O, unknown>) as T;
+  }
+
+  const key = keyOrKeys;
+
+  return object[key] as T;
+};

src/serializers/utils/getMetadataBySymbol.ts

@@ -0,0 +1,9 @@
+import { assertMetadataIsPresent } from "./assertMetadataIsPresent";
+
+export const getMetadataBySymbol = <T = unknown, O extends object = object>(object: O, symbol: symbol) => {
+  assertMetadataIsPresent(object);
+
+  const metadata = object.constructor[Symbol.metadata] as DecoratorMetadataObject;
+
+  return metadata[symbol] as T;
+};

src/serializers/utils/index.ts

@@ -0,0 +1,3 @@
+export * from './assertMetadataIsPresent';
+export * from './getMetadataBySymbol';
+export * from './collect';

src/types/relationshipsObject.ts

@@ -3,6 +3,6 @@ import type { JSONObject } from './json/object';
 import type { JSONAPIRelationshipObject } from './relationshipObject';
 
 export type JSONAPIRelationshipsObject = Satisfies<
-  { [key: string]: JSONAPIRelationshipObject },
+  { [key: string]: JSONAPIRelationshipObject | JSONAPIRelationshipObject[] },
   JSONObject
 >;