2 files changed, 181 insertions, 0 deletions
diff --git a/internal/notify/notify.go b/internal/notify/notify.go
new file mode 100644
index 0000000..86e641f
--- /dev/null
+++ b/internal/notify/notify.go
@@ -0,0 +1,95 @@
+package notify
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"net/http"
+	"time"
+)
+
+// Notifier sends notifications when tasks complete.
+type Notifier interface {
+	Notify(event Event) error
+}
+
+// Event represents a task completion event.
+type Event struct {
+	TaskID   string  `json:"task_id"`
+	TaskName string  `json:"task_name"`
+	Status   string  `json:"status"`
+	CostUSD  float64 `json:"cost_usd"`
+	Duration string  `json:"duration"`
+	Error    string  `json:"error,omitempty"`
+}
+
+// WebhookNotifier sends POST requests to a configured URL.
+type WebhookNotifier struct {
+	URL    string
+	client *http.Client
+	logger *slog.Logger
+}
+
+func NewWebhookNotifier(url string, logger *slog.Logger) *WebhookNotifier {
+	return &WebhookNotifier{
+		URL:    url,
+		client: &http.Client{Timeout: 10 * time.Second},
+		logger: logger,
+	}
+}
+
+func (w *WebhookNotifier) Notify(event Event) error {
+	body, err := json.Marshal(event)
+	if err != nil {
+		return fmt.Errorf("marshaling event: %w", err)
+	}
+
+	resp, err := w.client.Post(w.URL, "application/json", bytes.NewReader(body))
+	if err != nil {
+		return fmt.Errorf("sending webhook: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode >= 400 {
+		return fmt.Errorf("webhook returned %d", resp.StatusCode)
+	}
+	return nil
+}
+
+// MultiNotifier fans out to multiple notifiers.
+type MultiNotifier struct {
+	notifiers []Notifier
+	logger    *slog.Logger
+}
+
+func NewMultiNotifier(logger *slog.Logger, notifiers ...Notifier) *MultiNotifier {
+	return &MultiNotifier{notifiers: notifiers, logger: logger}
+}
+
+func (m *MultiNotifier) Notify(event Event) error {
+	var lastErr error
+	for _, n := range m.notifiers {
+		if err := n.Notify(event); err != nil {
+			m.logger.Error("notification failed", "error", err)
+			lastErr = err
+		}
+	}
+	return lastErr
+}
+
+// LogNotifier logs events (useful as a default/fallback).
+type LogNotifier struct {
+	Logger *slog.Logger
+}
+
+func (l *LogNotifier) Notify(event Event) error {
+	l.Logger.Info("task completed",
+		"task_id", event.TaskID,
+		"task_name", event.TaskName,
+		"status", event.Status,
+		"cost_usd", event.CostUSD,
+		"duration", event.Duration,
+	)
+	return nil
+}
diff --git a/internal/notify/notify_test.go b/internal/notify/notify_test.go
new file mode 100644
index 0000000..fcb5345
--- /dev/null
+++ b/internal/notify/notify_test.go
@@ -0,0 +1,86 @@
+package notify
+
+import (
+	"encoding/json"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+)
+
+func TestWebhookNotifier_Success(t *testing.T) {
+	var received Event
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		json.Unmarshal(body, &received)
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError}))
+	notifier := NewWebhookNotifier(server.URL, logger)
+
+	event := Event{
+		TaskID:   "t-1",
+		TaskName: "Test",
+		Status:   "COMPLETED",
+		CostUSD:  0.50,
+		Duration: "2m30s",
+	}
+
+	if err := notifier.Notify(event); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if received.TaskID != "t-1" {
+		t.Errorf("task_id: want 't-1', got %q", received.TaskID)
+	}
+	if received.CostUSD != 0.50 {
+		t.Errorf("cost: want 0.50, got %f", received.CostUSD)
+	}
+}
+
+func TestWebhookNotifier_ServerError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer server.Close()
+
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError}))
+	notifier := NewWebhookNotifier(server.URL, logger)
+
+	err := notifier.Notify(Event{TaskID: "t-1", Status: "COMPLETED"})
+	if err == nil {
+		t.Fatal("expected error for 500 response")
+	}
+}
+
+func TestMultiNotifier_FansOut(t *testing.T) {
+	var count int
+	counter := &countingNotifier{count: &count}
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError}))
+	multi := NewMultiNotifier(logger, counter, counter, counter)
+
+	multi.Notify(Event{TaskID: "t-1"})
+	if count != 3 {
+		t.Errorf("want 3 notifications, got %d", count)
+	}
+}
+
+func TestLogNotifier_NoError(t *testing.T) {
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{Level: slog.LevelError}))
+	notifier := &LogNotifier{Logger: logger}
+	if err := notifier.Notify(Event{TaskID: "t-1", Status: "COMPLETED"}); err != nil {
+		t.Errorf("unexpected error: %v", err)
+	}
+}
+
+type countingNotifier struct {
+	count *int
+}
+
+func (c *countingNotifier) Notify(_ Event) error {
+	*c.count++
+	return nil
+}