Shopify Provider (#186)

* Start of Shopify provider

* add missing comment to documentation

* add missing env vars to documentation

* update reference to types file

framework/shopify/api/index.ts

@@ -0,0 +1,60 @@
+import type { CommerceAPIConfig } from '@commerce/api'
+import fetchGraphqlApi from './utils/fetch-graphql-api'
+
+export interface ShopifyConfig extends CommerceAPIConfig {}
+
+// No I don't like this - will fix it later
+const API_URL =
+  process.env.SHOPIFY_STORE_DOMAIN ||
+  process.env.NEXT_PUBLIC_SHOPIFY_STORE_DOMAIN
+const API_TOKEN =
+  process.env.SHOPIFY_STOREFRONT_ACCESS_TOKEN ||
+  process.env.NEXT_PUBLIC_SHOPIFY_STOREFRONT_ACCESS_TOKEN
+
+if (!API_URL) {
+  throw new Error(
+    `The environment variable SHOPIFY_STORE_DOMAIN is missing and it's required to access your store`
+  )
+}
+
+if (!API_TOKEN) {
+  throw new Error(
+    `The environment variable SHOPIFY_STOREFRONT_ACCESS_TOKEN is missing and it's required to access your store`
+  )
+}
+
+export class Config {
+  private config: ShopifyConfig
+
+  constructor(config: ShopifyConfig) {
+    this.config = config
+  }
+
+  getConfig(userConfig: Partial<ShopifyConfig> = {}) {
+    return Object.entries(userConfig).reduce<ShopifyConfig>(
+      (cfg, [key, value]) => Object.assign(cfg, { [key]: value }),
+      { ...this.config }
+    )
+  }
+
+  setConfig(newConfig: Partial<ShopifyConfig>) {
+    Object.assign(this.config, newConfig)
+  }
+}
+
+const config = new Config({
+  commerceUrl: API_URL,
+  apiToken: API_TOKEN,
+  // TODO
+  // @ts-ignore
+  fetch: fetchGraphqlApi,
+  customerCookie: 'SHOP_TOKEN',
+})
+
+export function getConfig(userConfig?: Partial<ShopifyConfig>) {
+  return config.getConfig(userConfig)
+}
+
+export function setConfig(newConfig: Partial<ShopifyConfig>) {
+  return config.setConfig(newConfig)
+}