feat(notifications): add auto-detect webhook formatters for slack and discord

Author: pgagnidze

README.md

@@ -300,27 +300,17 @@ updo aws destroy --regions all
 
 ## Webhook Notifications
 
-Updo can send webhook notifications when targets go up or down. This enables integration with various services like Slack, Discord, PagerDuty, or custom alerting systems.
+Updo can send webhook notifications when targets go up or down. Updo **automatically detects** Slack and Discord webhooks by URL pattern and formats messages accordingly with rich formatting. Custom webhooks receive a generic JSON payload.
 
-### Webhook Payload
+### Supported Platforms
 
-When a target status changes, Updo sends a JSON payload:
-
-```json
-{
-  "event": "target_down",  // or "target_up"
-  "target": "Critical API",
-  "url": "https://api.example.com",
-  "timestamp": "2024-01-01T12:00:00Z",
-  "response_time_ms": 1500,
-  "status_code": 500,
-  "error": "Internal Server Error"  // only for down events
-}
-```
+- **Slack** - Auto-detected via `hooks.slack.com` URL, sends rich messages with attachments and color coding
+- **Discord** - Auto-detected via `discord.com/api/webhooks` URL, sends embeds with color and structured fields
+- **Custom** - Any other webhook URL receives generic JSON format
 
 ### Integration Examples
 
-**Slack Webhook:**
+**Slack Webhook (Auto-Detected):**
 
 ```toml
 [[targets]]
@@ -329,7 +319,41 @@ name = "Production API"
 webhook_url = "https://hooks.slack.com/services/YOUR/WEBHOOK/URL"
 ```
 
-**Custom Webhook with Headers:**
+Updo automatically formats Slack messages with:
+- Color-coded attachments (red for down, green for up)
+- Emoji indicators (🔴 for down, ✅ for up)
+- Structured fields for URL, error, status code, response time, and timestamp
+
+**Discord Webhook (Auto-Detected):**
+
+```toml
+[[targets]]
+url = "https://api.example.com"
+name = "Production API"
+webhook_url = "https://discord.com/api/webhooks/123456789/YOUR_WEBHOOK_TOKEN"
+```
+
+Updo automatically formats Discord messages with:
+- Color-coded embeds (red for down, green for up)
+- Emoji indicators (🔴 for down, ✅ for up)
+- Structured fields with inline formatting
+- Clickable URL links
+
+**Custom Webhook:**
+
+For custom webhooks, Updo sends a generic JSON payload:
+
+```json
+{
+  "event": "target_down",
+  "target": "Production API",
+  "url": "https://api.example.com",
+  "timestamp": "2024-01-01T12:00:00Z",
+  "response_time_ms": 1500,
+  "status_code": 500,
+  "error": "Internal Server Error"
+}
+```
 
 ```toml
 [[targets]]

notifications/formatter.go

@@ -0,0 +1,23 @@
+package notifications
+
+import (
+	"strings"
+)
+
+type WebhookFormatter interface {
+	Format(payload WebhookPayload) ([]byte, error)
+}
+
+func SelectFormatter(url string) WebhookFormatter {
+	lowerURL := strings.ToLower(url)
+
+	if strings.Contains(lowerURL, "hooks.slack.com") {
+		return &SlackFormatter{}
+	}
+
+	if strings.Contains(lowerURL, "discord.com/api/webhooks") {
+		return &DiscordFormatter{}
+	}
+
+	return &GenericFormatter{}
+}

notifications/formatter_discord.go

@@ -0,0 +1,87 @@
+package notifications
+
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+const (
+	_discordColorRed   = 15158332
+	_discordColorGreen = 3066993
+)
+
+type discordMessage struct {
+	Content string         `json:"content"`
+	Embeds  []discordEmbed `json:"embeds,omitempty"`
+}
+
+type discordEmbed struct {
+	Title     string         `json:"title"`
+	URL       string         `json:"url,omitempty"`
+	Color     int            `json:"color"`
+	Fields    []discordField `json:"fields,omitempty"`
+	Timestamp time.Time      `json:"timestamp"`
+}
+
+type discordField struct {
+	Name   string `json:"name"`
+	Value  string `json:"value"`
+	Inline bool   `json:"inline,omitempty"`
+}
+
+type DiscordFormatter struct{}
+
+func (f *DiscordFormatter) Format(payload WebhookPayload) ([]byte, error) {
+	symbol := _symbolDown
+	color := _discordColorRed
+	if payload.Event == _eventTargetUp {
+		symbol = _symbolUp
+		color = _discordColorGreen
+	}
+
+	content := fmt.Sprintf("%s %s", symbol, payload.Event)
+
+	var fields []discordField
+
+	if payload.Error != "" {
+		fields = append(fields, discordField{
+			Name:  "Error",
+			Value: payload.Error,
+		})
+	}
+
+	if payload.StatusCode > 0 {
+		fields = append(fields, discordField{
+			Name:   "Status Code",
+			Value:  fmt.Sprintf("%d", payload.StatusCode),
+			Inline: true,
+		})
+	}
+
+	fields = append(fields, discordField{
+		Name:   "Response Time",
+		Value:  fmt.Sprintf("%dms", payload.ResponseTimeMs),
+		Inline: true,
+	})
+
+	msg := discordMessage{
+		Content: content,
+		Embeds: []discordEmbed{
+			{
+				Title:     payload.Target,
+				URL:       payload.URL,
+				Color:     color,
+				Fields:    fields,
+				Timestamp: payload.Timestamp,
+			},
+		},
+	}
+
+	data, err := json.Marshal(msg)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal Discord webhook payload: %w", err)
+	}
+
+	return data, nil
+}

notifications/formatter_generic.go

@@ -0,0 +1,16 @@
+package notifications
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+type GenericFormatter struct{}
+
+func (f *GenericFormatter) Format(payload WebhookPayload) ([]byte, error) {
+	data, err := json.Marshal(payload)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal generic webhook payload: %w", err)
+	}
+	return data, nil
+}

notifications/formatter_slack.go

@@ -0,0 +1,94 @@
+package notifications
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+const (
+	_eventTargetDown = "target_down"
+	_eventTargetUp   = "target_up"
+	_colorDanger     = "danger"
+	_colorGood       = "good"
+	_symbolDown      = "✘"
+	_symbolUp        = "✔"
+)
+
+type slackMessage struct {
+	Text        string            `json:"text"`
+	Attachments []slackAttachment `json:"attachments,omitempty"`
+}
+
+type slackAttachment struct {
+	Color  string       `json:"color"`
+	Fields []slackField `json:"fields,omitempty"`
+}
+
+type slackField struct {
+	Title string `json:"title"`
+	Value string `json:"value"`
+	Short bool   `json:"short"`
+}
+
+type SlackFormatter struct{}
+
+func (f *SlackFormatter) Format(payload WebhookPayload) ([]byte, error) {
+	symbol := _symbolDown
+	color := _colorDanger
+	if payload.Event == _eventTargetUp {
+		symbol = _symbolUp
+		color = _colorGood
+	}
+
+	text := fmt.Sprintf("%s %s: %s", symbol, payload.Event, payload.Target)
+
+	var fields []slackField
+
+	fields = append(fields, slackField{
+		Title: "URL",
+		Value: payload.URL,
+	})
+
+	if payload.Error != "" {
+		fields = append(fields, slackField{
+			Title: "Error",
+			Value: payload.Error,
+		})
+	}
+
+	if payload.StatusCode > 0 {
+		fields = append(fields, slackField{
+			Title: "Status Code",
+			Value: fmt.Sprintf("%d", payload.StatusCode),
+			Short: true,
+		})
+	}
+
+	fields = append(fields, slackField{
+		Title: "Response Time",
+		Value: fmt.Sprintf("%dms", payload.ResponseTimeMs),
+		Short: true,
+	})
+
+	fields = append(fields, slackField{
+		Title: "Timestamp",
+		Value: payload.Timestamp.Format("2006-01-02 15:04:05 UTC"),
+	})
+
+	msg := slackMessage{
+		Text: text,
+		Attachments: []slackAttachment{
+			{
+				Color:  color,
+				Fields: fields,
+			},
+		},
+	}
+
+	data, err := json.Marshal(msg)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal Slack webhook payload: %w", err)
+	}
+
+	return data, nil
+}