Fix photo & camera permission management (#140)

* Check photo & camera perms and alert the user if not available (close #64)

- Adds perms checks with a prompt to update settings if needed
- Moves initial access of photos in the composer so that the initial prompt
  occurs at an intuitive time.

* Add react-native-permissions test mock

* Fix issue causing multiple access requests

* Use longer var names

* Update podfile.lock

* Lint fix

* Move photo perm request in composer to the gallery btn instead of when the carousel is opened

src/lib/permissions.ts

@@ -0,0 +1,61 @@
+import {Alert} from 'react-native'
+import {
+  check,
+  openSettings,
+  Permission,
+  PermissionStatus,
+  PERMISSIONS,
+  RESULTS,
+} from 'react-native-permissions'
+
+export const PHOTO_LIBRARY = PERMISSIONS.IOS.PHOTO_LIBRARY
+export const CAMERA = PERMISSIONS.IOS.CAMERA
+
+/**
+ * Returns `true` if the user has granted permission or hasn't made
+ * a decision yet. Returns `false` if unavailable or not granted.
+ */
+export async function hasAccess(perm: Permission): Promise<boolean> {
+  const status = await check(perm)
+  return isntANo(status)
+}
+
+export async function requestAccessIfNeeded(
+  perm: Permission,
+): Promise<boolean> {
+  if (await hasAccess(perm)) {
+    return true
+  }
+  let permDescription
+  if (perm === PHOTO_LIBRARY) {
+    permDescription = 'photo library'
+  } else if (perm === CAMERA) {
+    permDescription = 'camera'
+  } else {
+    return false
+  }
+  Alert.alert(
+    'Permission needed',
+    `Bluesky does not have permission to access your ${permDescription}.`,
+    [
+      {
+        text: 'Cancel',
+        style: 'cancel',
+      },
+      {text: 'Open Settings', onPress: () => openSettings()},
+    ],
+  )
+  return false
+}
+
+export async function requestPhotoAccessIfNeeded() {
+  return requestAccessIfNeeded(PHOTO_LIBRARY)
+}
+
+export async function requestCameraAccessIfNeeded() {
+  return requestAccessIfNeeded(CAMERA)
+}
+
+function isntANo(status: PermissionStatus): boolean {
+  return status !== RESULTS.UNAVAILABLE && status !== RESULTS.BLOCKED
+}