npm package: @medyx/cordova-plugin-firestore
Description: A Google Firebase Firestore plugin aiming at being a drop-in replacement for the firebase-js-sdk
Author: Richard Windley
Latest version: 3.1.0

# Cordova Firestore Plugin (Medyx)
A Google Firebase Firestore plugin to enable realtime synchronisation between app and cloud and automatically handle limited connectivity.

This plugin aims at being a drop-in replacement for the firebase-js-sdk to make supporting the web platform easier, and to ease the transition for cordova applications built with the javascript SDK.

# What is Firestore?
From the Google documentation (https://firebase.google.com/docs/firestore/):

> Cloud Firestore is a flexible, scalable database for mobile, web, and server development from Firebase and Google Cloud Platform. Like Firebase Realtime Database, it keeps your data in sync across client apps through realtime listeners and offers offline support for mobile and web so you can build responsive apps that work regardless of network latency or Internet connectivity. Cloud Firestore also offers seamless integration with other Firebase and Google Cloud Platform products, including Cloud Functions

# Supported platforms
This plugin supports the following platforms:

- Android
- iOS
- Browser # As of version 2.0 browser support is deprecated and will be dropped or refactored in the future in favor of a transparent firebase-js-sdk implementation

# Installation
## Install the plugin

```bash
cordova plugin add cordova-firestore-dropin-medyx --save
```

or

```bash
phonegap plugin add cordova-firestore-dropin-medyx
```

### Optional installation variables for Android

#### ANDROID_FIREBASE_FIRESTORE_VERSION
Version of `com.google.firebase:firebase-firestore`. This defaults to `21.3.0`.

You can find the latest versions of these [here](https://firebase.google.com/docs/android/setup#available_libraries).

## Android specific installation
Download `google-services.json` to `(your_project_dir)/google-services.json`

Hint: [Get a config file for your Android App](https://support.google.com/firebase/answer/7015592#android)

You must ensure that `google-services.json` is put in the correct location. This can be achieved using the following in your `config.xml`:

```xml
<platform name="android">
    <resource-file src="google-services.json" target="google-services.json" />
</platform>
```

### Dependencies
#### cordova-support-google-services

In order to ensure Firebase initialises correctly on Android this plugin can be used. This is not automatically added as a dependency to allow for the configuration it performs to be done manually if desired.

## iOS specific installation

Download `GoogleService-Info.plist` to `(your_project_dir)/GoogleService-Info.plist`

Hint: [Get a config file for your iOS App](https://support.google.com/firebase/answer/7015592#ios)

You must ensure that `GoogleService-Info.plist` is put in the correct location. This can be done as follows:

```xml
<platform name="ios">
    <resource-file src="GoogleService-Info.plist" />
</platform>
```

#### Keychain Sharing Capability
If using multiple Firebase plugins it may be necessary to enable this.

## Firestore configuration
It is good practice to make sure your Firestore database is only accessible for authorised users, at least for write operations. It is recommended you take time to understand [Firestore rules](https://firebase.google.com/docs/firestore/security/get-started).

An example that only allows access for authorised users is shown below:

```
service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write : if request.auth != null;
    }
  }
}
```

Authenticating users is beyond the scope of this plugin, but the `cordova-plugin-firebase-authentication` is one such plugin you can use to achieve this which will work alongside this plugin.

## Dependencies
### Promises
This plugin uses Promises. If you want to use this with Android 4.4 then you will need to include a `Promise` polyfill.


# Example
A simple example is shown below which sets up the necessary options, initialises the database and then adds a document to a `users` collection:

```js
var options = {
  "datePrefix": '__DATE:',
  "fieldValueDelete": "__DELETE",
  "fieldValueServerTimestamp" : "__SERVERTIMESTAMP",
  "persist": true,
  "config" : {}
};

if (cordova.platformId === "browser") {

  options.config = {
    apiKey: "(your api key)",
    authDomain: "localhost",
    projectId: "(your project id)"
  };
}

Firestore.initialise(options).then(function(db) {
  // Add a second document with a generated ID.
  db.collection("users").add({
      first: "Alan",
      middle: "Mathison",
      last: "Turing",
      born: 1912
  })
  .then(function(docRef) {
      console.log("Document written with ID: ", docRef.id);
  })
  .catch(function(error) {
      console.error("Error adding document: ", error);
  });
});
```

## options.config
In the above example this is being used for the browser version, but it can also be used for Android and iOS to specify different databases than the default in the `google-services.json` and `GoogleService-Info.plist` files.

# What is supported?

## Firestore
- collection()
- runTransaction(updateFunction)
- batch # NOT SUPPORTED

## DocumentSnapshot and QueryDataSnapshot
- data()
- get(fieldPath)
- exists
- id
- ref

## QuerySnapshot
- docs
- empty
- size

## DocumentReference
- collection(collectionPath)
- delete()
- get()
- onSnapshot(optionsOrObserverOrOnNext, observerOrOnNextOrOnError, onError)
- set(data, options)
- update(data)
- id
- parent

## Query
- endAt(snapshotOrVarArgs)
- endBefore(snapshotOrVarArgs)
- limit(limit)
- orderBy(field, direction)
- get()
- onSnapshot(callback, options)
- startAfter(snapshotOrVarArgs)
- startAt(snapshotOrVarArgs)
- where(fieldPath, opStr, passedValue)

## CollectionReference (inherits from Query)
- add(data)
- id
- doc(<id>)

## Transaction
- get()
- delete()
- set()
- update()

## FieldValue
- FieldValue.delete()
- FieldValue.serverTimestamp()

## GeoPoint
- Firestore.GeoPoint(latitude, longitude)

## Timestamp
- Firestore.Timestamp(seconds, nanoseconds)

## Dates
Because data is transferred to the client as JSON there is extra logic in place to handle the conversion of dates for some operations.

When initialising the plugin you can set up a prefix that is applied to a string value which is used to identify it as a date. The default prefix is `__DATE:`

Therefore, when a date field is retrieved from the database by the native code it will be transferred in the JSON looking similar to the following:

```json
{
    "dateField" : "__DATE:123456789"
}
```

The number is seconds since epoch.

The client will receive the field as a Javascript Date.

This conversion also happens when specifying a field in a where condition.

### timestampsInSnapshots
By default this option is set to `false` to mirror the current default. [This explains the setting](https://firebase.google.com/docs/reference/js/firebase.firestore.Settings).

Not setting this to `true` will result in the following message when running in the browser:

```
The behavior for Date objects stored in Firestore is going to change
AND YOUR APP MAY BREAK.
To hide this warning and ensure your app does not break, you need to add the
following code to your app before calling any other Cloud Firestore methods:

  const firestore = firebase.firestore();
  const settings = {/* your settings... */ timestampsInSnapshots: true};
  firestore.settings(settings);

With this change, timestamps stored in Cloud Firestore will be read back as
Firebase Timestamp objects instead of as system Date objects. So you will also
need to update code expecting a Date to instead expect a Timestamp. For example:

  // Old:
  const date = snapshot.get('created_at');
  // New:
  const timestamp = snapshot.get('created_at');
  const date = timestamp.toDate();

Please audit all existing usages of Date when you enable the new behavior. In a
future release, the behavior will change to the new behavior, so if you do not
follow these steps, YOUR APP MAY BREAK.
```

## FieldValue constants
Similar to the situation with dates, there are special values used for `FieldValue` values:

- FieldValue.delete() equates to `__DELETE`
- FieldValue.serverTimestamp() equates to `__SERVERTIMESTAMP`

These values can be changed when initialisation is performed.

## Learnings and notes
I have learnt a number of things whilst implementing this:
- The documentation states that the database cannot be initialised in a seperate thread when using persistence. In my experience this should say it cannot be *used* in multiple threads.
- When used on Android ensure that at least `com.google.gms:google-services:3.1.1` is used in build dependencies. Earlier versions did not work for me.
- Yes, I did spell initialise() with an 's' - Original plugin developer @ReallySmallSoftware is from the UK