package main

import (
	"context"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"net/smtp"
	"os"
	"os/signal"
	"time"
)

func main() {
	ctx, stop := signal.NotifyContext(
		context.Background(), os.Interrupt, os.Kill)
	defer stop()

	const httpTimeout = 10 * time.Second
	client := &http.Client{
		Timeout: httpTimeout,
	}

	const (
		restAPI = "https://domain.com/v1"
		url     = restAPI + "/resource/321312"
	)

	result, err := getAPIData(ctx, client, url)
	if err != nil {
		log.Println(err)
		return
	}

	const (
		smtpUser       = "user"
		smtpPassword   = "password"
		smtpServerHost = "mail.example.com:25"
		recipient      = "target@example.com"
		sender         = "sender@example.com"
	)

	err = sendMailWithSMTP(smtpUser, smtpPassword,
		smtpServerHost, recipient, sender, result)
	if err != nil {
		log.Println(err)
		return
	}

	log.Println("Email successfully sent to " + recipient + " with API result " + result)
}

func getAPIData(ctx context.Context, client *http.Client, url string) (
	result string, err error) {
	request, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return "", err
	}

	response, err := client.Do(request)
	if err != nil {
		return "", err
	}

	if response.StatusCode != http.StatusOK {
		_ = response.Body.Close()
		return "", fmt.Errorf("Bad HTTP status code: " + response.Status)
	}

	data, err := io.ReadAll(response.Body)
	if err != nil {
		return "", err
	}

	if err := response.Body.Close(); err != nil {
		return "", err
	}

	return string(data), nil
}

func sendMailWithSMTP(user, password, serverHost,
	recipient, sender, apiResult string) (err error) {
	hostname, _, err := net.SplitHostPort(serverHost)
	if err != nil {
		return err
	}

	auth := smtp.PlainAuth("", user, password, hostname)
	recipients := []string{recipient}
	message := []byte("To: " + recipient + "\r\n" +
		"Subject: REST API response\r\n" +
		"\r\n" +
		"Response is:" + apiResult + ".\r\n")
	return smtp.SendMail(serverHost, auth, sender, recipients, message)
}