feat: add notifier Sender interface and digest formatter

internal/notifier/sender.go

@@ -0,0 +1,78 @@
+package notifier
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+
+	"naviwatcher/internal/config"
+)
+
+// Sender delivers a notification message to a destination (e.g. Telegram).
+// It is an interface so the real HTTP bot can be swapped for a stub in tests.
+type Sender interface {
+	Send(ctx context.Context, message string) error
+}
+
+// telegramSender sends messages via the Telegram Bot API sendMessage method.
+type telegramSender struct {
+	httpClient *http.Client
+	token      string
+	chatID     string
+	baseURL    string
+}
+
+// NewTelegramSender constructs a Sender that posts to the Telegram Bot API
+// using the token and chat ID from the given TelegramConfig.
+func NewTelegramSender(cfg config.TelegramConfig) *telegramSender {
+	return &telegramSender{
+		httpClient: &http.Client{Timeout: 30 * time.Second},
+		token:      cfg.Token,
+		chatID:     cfg.ChatID,
+		baseURL:    "https://api.telegram.org",
+	}
+}
+
+// sendMessageRequest is the JSON payload for the Telegram sendMessage endpoint.
+type sendMessageRequest struct {
+	ChatID                string `json:"chat_id"`
+	Text                  string `json:"text"`
+	DisableWebPagePreview bool   `json:"disable_web_page_preview"`
+}
+
+// Send posts the message to the configured Telegram chat. It returns an error
+// if the request cannot be built/sent or the API responds with a non-2xx code.
+func (s *telegramSender) Send(ctx context.Context, message string) error {
+	payload := sendMessageRequest{
+		ChatID:                s.chatID,
+		Text:                  message,
+		DisableWebPagePreview: true,
+	}
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshal telegram payload: %w", err)
+	}
+
+	url := fmt.Sprintf("%s/bot%s/sendMessage", s.baseURL, s.token)
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
+	if err != nil {
+		return fmt.Errorf("build telegram request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := s.httpClient.Do(req)
+	if err != nil {
+		return fmt.Errorf("send telegram message: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
+		return fmt.Errorf("telegram API returned status %d: %s", resp.StatusCode, string(respBody))
+	}
+	return nil
+}