feat(service): add fcm

[svaloumas]

Description

Adds Firebase Cloud Messaging (FCM) service.

Motivation and Context

Adds a new service to the list of the currently supported ones.

How Has This Been Tested?

Unit tests implemented under service/fcm/fcm_test.go.

Integration tests have been performed using FCM toolbox.

Sample code to run an integration test.

package main

import (
	"context"
	"log"

	"github.com/nikoksr/notify"
	"github.com/nikoksr/notify/service/fcm"
)

func main() {
	fcmSvc, err := fcm.New("server_api_key")
	if err != nil {
		log.Fatalf("fcm.New() failed: %s", err.Error())
	}

	fcmSvc.AddReceivers("deviceToken1")

	notifier := notify.New()
	notifier.UseServices(fcmSvc)

	// Use context.Background() if you want to send a simple notification message.
	ctx := context.Background()

	// Optionally, you can include additional data in the message payload by adding the corresponding value to the context.
	ctxWithData := context.WithValue(ctx, fcm.DataKey, map[string]interface{}{
		"some-key":  "some-value",
		"other-key": "other-value",
	})

	// Optionally, you can specify a total of retry attempts per each message by adding the corresponding value to the context.
	ctxWithDataAndRetries := context.WithValue(ctxWithData, fcm.RetriesKey, 3)

	err = notifier.Send(ctxWithDataAndRetries, "subject", "message")
	if err != nil {
		log.Fatalf("notifier.Send() failed: %s", err.Error())
	}

	log.Println("notification sent")
}

Please find below sample images from the results of the integration tests.

Screenshots / Output (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (no code change)
• Refactor (refactoring production code)
• Other

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

Merging #272 (a38dbb0) into main (4564e02) will increase coverage by 3.23%.
The diff coverage is 75.34%.

@@            Coverage Diff             @@
##             main     #272      +/-   ##
==========================================
+ Coverage   51.39%   54.62%   +3.23%     
==========================================
  Files          12       14       +2     
  Lines         467      540      +73     
==========================================
+ Hits          240      295      +55     
- Misses        208      222      +14     
- Partials       19       23       +4     

Impacted Files	Coverage Δ
service/fcm/mock_fcmClient.go	73.91% <73.91%> (ø)
service/fcm/fcm.go	76.00% <76.00%> (ø)

---

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[nikoksr]

Hey @svaloumas, this one of the cleanest and most complete PRs, yet. I'm really impressed by and appreciative for your contribution! I would be very excited to see more contributions from you.

[svaloumas]

Thanks for your kind comment @nikoksr ! I'm glad you liked it, I enjoyed it myself as well ✌️