From 56e0643a30b5c56bb348af755ba6051ac4a2ee4e Mon Sep 17 00:00:00 2001
From: Josep M Sobrepere <josepot@gmail.com>
Date: Thu, 21 Jan 2021 14:23:02 +0100
Subject: [PATCH] feat(utils): add contextBinder

---
 packages/utils/src/contextBinder.test.tsx | 60 +++++++++++++++++++++++
 packages/utils/src/contextBinder.ts       | 38 ++++++++++++++
 2 files changed, 98 insertions(+)
 create mode 100644 packages/utils/src/contextBinder.test.tsx
 create mode 100644 packages/utils/src/contextBinder.ts

diff --git a/packages/utils/src/contextBinder.test.tsx b/packages/utils/src/contextBinder.test.tsx
new file mode 100644
index 0000000..b61aaba
--- /dev/null
+++ b/packages/utils/src/contextBinder.test.tsx
@@ -0,0 +1,60 @@
+import { render, screen } from "@testing-library/react"
+import React, { createContext, useContext } from "react"
+import { of } from "rxjs"
+import { contextBinder } from "./index"
+
+describe("contextBinder", () => {
+  it("bounds the provided context into the first args of the hook", () => {
+    const idContext = createContext<string>("id1")
+    const countContext = createContext<number>(3)
+    const useId = () => useContext(idContext)
+    const useCount = () => useContext(countContext)
+    const idCountBind = contextBinder(useId, useCount)
+
+    const [useSomething] = idCountBind(
+      (id: string, count: number, append: string) =>
+        of(Array(count).fill(id).concat(append).join("-")),
+      "",
+    )
+
+    const Result: React.FC = () => <span>Result {useSomething("bar")}</span>
+
+    const Component: React.FC<{ id: string; count: number }> = ({
+      id,
+      count,
+    }) => {
+      return (
+        <idContext.Provider value={id}>
+          <countContext.Provider value={count}>
+            <Result />
+          </countContext.Provider>
+        </idContext.Provider>
+      )
+    }
+
+    render(<Component id="foo" count={4} />)
+
+    expect(screen.queryByText("Result foo-foo-foo-foo-bar")).not.toBeNull()
+  })
+
+  it("the returned function matches the signature of the original one", () => {
+    const idContext = createContext<string>("id1")
+    const countContext = createContext<number>(3)
+    const useId = () => useContext(idContext)
+    const useCount = () => useContext(countContext)
+    const idCountBind = contextBinder(useId, useCount)
+
+    const [, getSomething$] = idCountBind(
+      (id: string, count: number, append: string) =>
+        of(Array(count).fill(id).concat(append).join("-")),
+      "",
+    )
+
+    let value = ""
+    getSomething$("foo", 4, "bar").subscribe((v) => {
+      value = v
+    })
+
+    expect(value).toBe("foo-foo-foo-foo-bar")
+  })
+})
diff --git a/packages/utils/src/contextBinder.ts b/packages/utils/src/contextBinder.ts
new file mode 100644
index 0000000..2c0e187
--- /dev/null
+++ b/packages/utils/src/contextBinder.ts
@@ -0,0 +1,38 @@
+import { Observable } from "rxjs"
+import { bind } from "@react-rxjs/core"
+
+type SubstractTuples<A1, A2> = A2 extends [unknown, ...infer Rest2]
+  ? A1 extends [unknown, ...infer Rest1]
+    ? SubstractTuples<Rest1, Rest2>
+    : []
+  : A1
+
+const execSelf = <T>(fn: () => T) => fn()
+
+/**
+ * Returns a version of bind where its hook will have the first parameters bound
+ * the results of the provided functions
+ *
+ * @param {...React.Context} context - The React.Context that should be bound to the hook.
+ */
+export function contextBinder<
+  A extends (() => any)[],
+  OT extends {
+    [K in keyof A]: A[K] extends () => infer V ? V : unknown
+  }
+>(
+  ...args: A
+): <AA extends any[], T, ARGS extends [...OT, ...AA]>(
+  getObservable: (...args: ARGS) => Observable<T>,
+  defaultValue?: T | undefined,
+) => [
+  (...args: SubstractTuples<ARGS, OT>) => T,
+  (...args: ARGS) => Observable<T>,
+]
+export function contextBinder(...args: any[]) {
+  const useArgs = () => args.map(execSelf)
+  return function () {
+    const [hook, getter] = bind.apply(null, arguments as any) as any
+    return [(...args: any[]) => (hook as any)(...useArgs(), ...args), getter]
+  } as any
+}