nikoksr/notify

package slack

import (
    "context"
    "fmt"

    "github.com/slack-go/slack"
)

type slackClient interface {
    PostMessageContext(ctx context.Context, channelID string, options ...slack.MsgOption) (string, string, error)
}

// Compile-time check to ensure that slack.Client implements the slackClient interface.
var _ slackClient = new(slack.Client)

// Slack struct holds necessary data to communicate with the Slack API.
type Slack struct {
    client     slackClient
    channelIDs []string
}

// New returns a new instance of a Slack notification service.
// For more information about slack api token:
//
//    -> https://pkg.go.dev/github.com/slack-go/slack#New
func New(apiToken string) *Slack {
    client := slack.New(apiToken)

    s := &Slack{
        client:     client,
        channelIDs: []string{},
    }

    return s
}

// AddReceivers takes Slack channel IDs and adds them to the internal channel ID list. The Send method will send
// a given message to all those channels.
func (s *Slack) AddReceivers(channelIDs ...string) {
    s.channelIDs = append(s.channelIDs, channelIDs...)
}

// Send takes a message subject and a message body and sends them to all previously set channels.
// you will need a slack app with the chat:write.public and chat:write permissions.
// see https://api.slack.com/
func (s Slack) Send(ctx context.Context, subject, message string) error {
    fullMessage := subject + "\n" + message // Treating subject as message title

    for _, channelID := range s.channelIDs {
        select {
        case <-ctx.Done():
            return ctx.Err()
        default:
            _, _, err := s.client.PostMessageContext(
                ctx,
                channelID,
                slack.MsgOptionText(fullMessage, false),
            )
            if err != nil {
                return fmt.Errorf("send message to channel %q: %w", channelID, err)
            }
        }
    }

    return nil
}