home-services/alert-bridge/internal/adapters/secondary/discordwebhook/client.go

package discordwebhook

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"gitea.nik4nao.com/nik/home-services/alert-bridge/internal/core/domain"
)

// Discord embed colors (decimal RGB), matching Alert severity.
const (
	colorInfo  = 3447003  // blue
	colorWarn  = 15844367 // yellow
	colorError = 15158332 // red
)

// Client posts Alerts to a single Discord Incoming Webhook.
type Client struct {
	webhookURL    string
	mentionUserID string
	httpClient    *http.Client
}

// New constructs a Discord webhook Notifier. mentionUserID may be empty, in
// which case level=error alerts are posted without a mention.
func New(webhookURL, mentionUserID string) *Client {
	return &Client{
		webhookURL:    webhookURL,
		mentionUserID: mentionUserID,
		httpClient:    &http.Client{Timeout: 10 * time.Second},
	}
}

type embed struct {
	Title       string `json:"title"`
	Description string `json:"description"`
	Color       int    `json:"color"`
}

// allowedMentions is spelled out explicitly (rather than relying on Discord's
// default) so a mention only ever pings the specific configured user, never
// @everyone/@here/roles even if alert.Message text happens to contain them.
type allowedMentions struct {
	Parse []string `json:"parse"`
	Users []string `json:"users"`
}

type webhookPayload struct {
	Content         string          `json:"content,omitempty"`
	Embeds          []embed         `json:"embeds"`
	AllowedMentions allowedMentions `json:"allowed_mentions"`
}

// Notify posts alert to the configured Discord webhook. level=error alerts
// mention mentionUserID (if configured) in the message content — Discord
// embeds alone never trigger a ping, only plain message content can.
func (c *Client) Notify(ctx context.Context, alert domain.Alert) error {
	payload := webhookPayload{
		Embeds: []embed{{
			Title:       fmt.Sprintf("[%s]", alert.Source),
			Description: alert.Message,
			Color:       colorFor(alert.Level),
		}},
		AllowedMentions: allowedMentions{Parse: []string{}, Users: []string{}},
	}

	if alert.Level == domain.LevelError && c.mentionUserID != "" {
		payload.Content = fmt.Sprintf("<@%s>", c.mentionUserID)
		payload.AllowedMentions.Users = []string{c.mentionUserID}
	}

	body, err := json.Marshal(payload)
	if err != nil {
		return fmt.Errorf("marshal webhook payload: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.webhookURL, bytes.NewReader(body))
	if err != nil {
		return fmt.Errorf("build webhook request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("send webhook request: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 300 {
		return fmt.Errorf("discord webhook returned status %d", resp.StatusCode)
	}
	return nil
}

func colorFor(level domain.Level) int {
	switch level {
	case domain.LevelWarn:
		return colorWarn
	case domain.LevelError:
		return colorError
	default:
		return colorInfo
	}
}