Vendure provider (#223)

* Minimal list/detail views working with Vendure

* Implement useCart/useAddItem

* Implement useUpdateItem & useRemoveItem

* Implement useSearch

* Add operations codegen, tidy up

* Dummy checkout page

* Implement auth/customer hooks

* Use env var for Shop API url

* Add some documentation

* Improve error handling

* Optimize preview image size

* Fix accidental change

* Update Vendure provider to latest changes

* Vendure provider: split out gql operations, remove unused files

* Update Vendure provider readme

* Add local next.config to Vendure provider, update docs

* Update to use demo server

* Fix build errors

* Use proxy for vendure api

* Simplify instructions in Vendure readme

* Refactor Vendure checkout api handler

* Improve image quality

framework/vendure/lib/array-to-tree.ts

@@ -0,0 +1,67 @@
+export type HasParent = { id: string; parent?: { id: string } | null }
+export type TreeNode<T extends HasParent> = T & {
+  children: Array<TreeNode<T>>
+  expanded: boolean
+}
+export type RootNode<T extends HasParent> = {
+  id?: string
+  children: Array<TreeNode<T>>
+}
+
+export function arrayToTree<T extends HasParent>(
+  nodes: T[],
+  currentState?: RootNode<T>
+): RootNode<T> {
+  const topLevelNodes: Array<TreeNode<T>> = []
+  const mappedArr: { [id: string]: TreeNode<T> } = {}
+  const currentStateMap = treeToMap(currentState)
+
+  // First map the nodes of the array to an object -> create a hash table.
+  for (const node of nodes) {
+    mappedArr[node.id] = { ...(node as any), children: [] }
+  }
+
+  for (const id of nodes.map((n) => n.id)) {
+    if (mappedArr.hasOwnProperty(id)) {
+      const mappedElem = mappedArr[id]
+      mappedElem.expanded = currentStateMap.get(id)?.expanded ?? false
+      const parent = mappedElem.parent
+      if (!parent) {
+        continue
+      }
+      // If the element is not at the root level, add it to its parent array of children.
+      const parentIsRoot = !mappedArr[parent.id]
+      if (!parentIsRoot) {
+        if (mappedArr[parent.id]) {
+          mappedArr[parent.id].children.push(mappedElem)
+        } else {
+          mappedArr[parent.id] = { children: [mappedElem] } as any
+        }
+      } else {
+        topLevelNodes.push(mappedElem)
+      }
+    }
+  }
+  // tslint:disable-next-line:no-non-null-assertion
+  const rootId = topLevelNodes.length ? topLevelNodes[0].parent!.id : undefined
+  return { id: rootId, children: topLevelNodes }
+}
+
+/**
+ * Converts an existing tree (as generated by the arrayToTree function) into a flat
+ * Map. This is used to persist certain states (e.g. `expanded`) when re-building the
+ * tree.
+ */
+function treeToMap<T extends HasParent>(
+  tree?: RootNode<T>
+): Map<string, TreeNode<T>> {
+  const nodeMap = new Map<string, TreeNode<T>>()
+  function visit(node: TreeNode<T>) {
+    nodeMap.set(node.id, node)
+    node.children.forEach(visit)
+  }
+  if (tree) {
+    visit(tree as TreeNode<T>)
+  }
+  return nodeMap
+}