nikoksr/notify

// Package reddit implements a Reddit notifier, allowing messages to be sent to multiple recipients
package reddit

import (
    "context"
    "crypto/tls"
    "fmt"
    "net/http"

    "github.com/caarlos0/go-reddit/v3/reddit"
)

type redditMessageClient interface {
    Send(context.Context, *reddit.SendMessageRequest) (*reddit.Response, error)
}

// Compile-time check to ensure that reddit.MessageService implements the redditMessageClient interface.
var _ redditMessageClient = new(reddit.MessageService)

// Reddit struct holds necessary data to communicate with the Reddit API.
type Reddit struct {
    client     redditMessageClient
    recipients []string
}

// New returns a new instance of a Reddit notification service.
// For more information on obtaining client credentials:
//
//    -> https://github.com/reddit-archive/reddit/wiki/OAuth2
func New(clientID, clientSecret, username, password string) (*Reddit, error) {
    // Disable HTTP2 in http client
    // Details:
    // https://www.reddit.com/r/redditdev/comments/t8e8hc/getting_nothing_but_429_responses_when_using_go/i18yga2/
    h := http.Client{
        Transport: &http.Transport{
            TLSNextProto: map[string]func(authority string, c *tls.Conn) http.RoundTripper{},
        },
    }
    rClient, err := reddit.NewClient(
        reddit.Credentials{
            ID:       clientID,
            Secret:   clientSecret,
            Username: username,
            Password: password,
        },
        reddit.WithHTTPClient(&h),
        reddit.WithUserAgent("github.com/nikoksr/notify"),
    )
    if err != nil {
        return nil, fmt.Errorf("create Reddit client: %w", err)
    }

    r := &Reddit{
        client:     rClient.Message,
        recipients: []string{},
    }

    return r, nil
}

// AddReceivers takes Reddit usernames and adds them to the internal recipient list. The Send method will send
// a given message to all of those users.
func (r *Reddit) AddReceivers(recipients ...string) {
    r.recipients = append(r.recipients, recipients...)
}

// Send takes a message subject and a message body and sends them to all previously set recipients.
func (r *Reddit) Send(ctx context.Context, subject, message string) error {
    for i := range r.recipients {
        select {
        case <-ctx.Done():
            return ctx.Err()
        default:
            m := reddit.SendMessageRequest{
                To:      r.recipients[i],
                Subject: subject,
                Text:    message,
            }

            if _, err := r.client.Send(ctx, &m); err != nil {
                return fmt.Errorf("send message to user %q: %w", r.recipients[i], err)
            }
        }
    }

    return nil
}