// Meetup Invite 2000
// @author: Abner Coimbre <abner@handmadecities.com>
// Copyright (c) 2024 Handmade Cities

// Based off News Blaster 2000 from the Handmade Network: https://git.handmade.network/hmn/newsblaster2000

// ============================    Contributors    =========================
// Bug & warning fixes
//  Jacob Bell (@MysteriousJ)
//  Asaf Gartner (@AsafGartner)
//  Joshua Barnett (@jshbrntt)
//  Jack Punter (@TarriestPython)
//
// Emotional Support
//  Cucui Ganon Rosario
// =========================================================================

// WARNING: This program requires a companion config.toml file provided by Abner. Without it we will crash!

package main

import (
	"bytes"
	"crypto/sha1"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"io/ioutil"
	"net/http"
	"os"
	"strconv"
	"strings"
	"time"

	"github.com/pelletier/go-toml/v2"
	"github.com/russross/blackfriday/v2"
	"github.com/spf13/cobra"
)

type Config struct {
	BatchSize int    `toml:"batch_size"`
	TestEmail string `toml:"test_email"`
	HMC       struct {
		ApiUrl       string `toml:"api_url"`
		SharedSecret string `toml:"shared_secret"`
		City         string `toml:"city"`
	} `toml:"hmc"`
	Postmark struct {
		ServerToken   string `toml:"server_token"`
		ApiUrl        string `toml:"api_url"`
		TemplateId    int    `toml:"template_id"`
		SenderName    string `toml:"sender_name"`
		SenderEmail   string `toml:"sender_email"`
		MessageStream string `toml:"message_stream"`
	} `toml:"postmark"`
}

func retrieveSubscribers(cfg *Config) ([]string, error) {
	/* Prepare request payload */
	/* *** */
	payload := map[string]string{
		"city": cfg.HMC.City,
	}

	payloadBytes, err := json.Marshal(payload)
	if err != nil {
		return nil, fmt.Errorf("error encoding payload: %v", err)
	}

	/* Prepare request */
	/* *** */
	req, err := http.NewRequest("POST", cfg.HMC.ApiUrl, bytes.NewReader(payloadBytes))
	if err != nil {
		return nil, fmt.Errorf("error creating request: %v", err)
	}

	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", cfg.HMC.SharedSecret)

	/* Execute request */
	/* *** */
	client := http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("error making request: %v", err)
	}
	defer resp.Body.Close()

	/* Fail if status code is not in the 2xx range */
	/* *** */
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, fmt.Errorf("error: HTTP status code %d", resp.StatusCode)
	}

	/* Read response's body */
	/* *** */
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("error reading response body: %v", err)
	}

	/* Parse JSON response */
	/* *** */
	var data map[string]interface{}
	if err := json.Unmarshal(body, &data); err != nil {
		return nil, fmt.Errorf("error unmarshalling JSON: %v", err)
	}

	/* Extract the emails from the response */
	/* *** */
	emails, ok := data["emails"].([]interface{})
	if !ok {
		return nil, errors.New("response format error: 'emails' field not found")
	}

    /* De-duplicate emails using a map */
	/* *** */
	emailMap := make(map[string]bool)
	for _, email := range emails {
		if emailStr, ok := email.(string); ok {
			emailMap[emailStr] = true
		}
	}

	/* Convert the map keys back to a slice */
	var subscribers []string
	for email := range emailMap {
		subscribers = append(subscribers, email)
	}

	return subscribers, nil
}

func parseMailFile(contents string) (subject string, body string, valid bool) {
	/* Remove leading and trailing newlines */
	/* *** */
	contents = strings.TrimSpace(contents)
	lines := strings.Split(contents, "\n")

	/* Check if there is at least one line */
	/* *** */
	if len(lines) == 0 {
		return "", "", false
	}

	/* Check if the first line is a title with the '#' Markdown symbol */
	/* *** */
	if strings.HasPrefix(lines[0], "#") { // Extract subject without the '#' symbol and leading/trailing spaces
		subject = strings.TrimSpace(strings.TrimPrefix(lines[0], "#"))
	} else {
		// If the first line is not a title, return an error
		return "", "", false
	}

	/* Concatenate the remaining lines to form the body */
	/* *** */
	body = strings.Join(lines[1:], "\n")

	/* Check if the body is not empty */
	/* *** */
	if body == "" {
		return "", "", false
	}

	/* If all checks pass, set valid to true */
	/* *** */
	return subject, body, true
}

func sendTest(cfg *Config, markdownFile string) {
	/* Open and parse Markdown file */
	/* *** */
	members := []string{cfg.TestEmail}
	contents, err := os.ReadFile(markdownFile)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			fmt.Printf("Can't find file %s\n", markdownFile)
		} else {
			fmt.Printf("Error reading file %s: %v\n", markdownFile, err)
		}
		return
	}
	contents = bytes.ReplaceAll(contents, []byte("\r"), []byte(""))

	subject, body, valid := parseMailFile(string(contents))
	if !valid {
		fmt.Printf("Error parsing file %s: invalid format\n", markdownFile)
		return
	}

	/* Convert Markdown to HTML */
	/* *** */
	html := blackfriday.Run([]byte(body))

	/* Send the email */
	/* *** */
	trackingFile := markdownFile + ".test.track"
	logFile := markdownFile + "." + time.Now().Format("20060102T150405") + ".test.log"
	os.Truncate(trackingFile, 0)

	blastMail(cfg, logFile, trackingFile, members, subject, string(html))

	sha1File := markdownFile + ".sha1"
	sum := sha1.Sum(contents)
	sumString := fmt.Sprintf("%x", sum)
	os.WriteFile(sha1File, []byte(sumString), 0666)
}

func sendNews(cfg *Config, markdownFile string) {
	/* Open and parse Markdown file */
	/* *** */
	contents, err := os.ReadFile(markdownFile)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			fmt.Printf("Can't find file %s\n", markdownFile)
		} else {
			fmt.Printf("Error reading file %s: %v\n", markdownFile, err)
		}
		return
	}
	contents = bytes.ReplaceAll(contents, []byte("\r"), []byte(""))

	subject, body, valid := parseMailFile(string(contents))
	if !valid {
		fmt.Printf("Error parsing file %s: invalid format\n", markdownFile)
		return
	}

	/* Convert Markdown to HTML */
	/* *** */
	html := blackfriday.Run([]byte(body))

	/* Checksum test */
	/* *** */
	sha1File := markdownFile + ".sha1"
	sum := sha1.Sum(contents)
	sumString := fmt.Sprintf("%x", sum)

	sha1, err := os.ReadFile(sha1File)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			fmt.Printf("Can't find hash file for this newsletter. Make sure you run the test command first!\n")
		} else {
			fmt.Printf("Error reading file %s: %v\n", sha1File, err)
		}
		return
	}
	if string(sha1) != sumString {
		fmt.Printf("Hash doesn't match. Did you change the newsletter's contents? Rerun the test command please!\n")
		return
	}

	/* Retrieve the mailing list from the city listed in the config file */
	/* *** */
	subscribers, err := retrieveSubscribers(cfg)

	/* Blast the member update! */
	/* *** */
	trackingFile := markdownFile + ".track"
	logFile := markdownFile + "." + time.Now().Format("20060102T150405") + ".log"

	blastMail(cfg, logFile, trackingFile, subscribers, subject, string(html))
}

func blastMail(cfg *Config, logFile string, trackingFile string, audience []string, subject, body string) {
	log, err := os.OpenFile(logFile, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
	if err != nil {
		fmt.Printf("Can't open log file %s: %v\n", logFile, err)
		return
	}
	defer log.Close()
	contents, err := os.ReadFile(trackingFile)
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		fmt.Printf("Failed to read tracking file %s: %v\n", trackingFile, err)
		return
	}
	var sentToAddresses []string
	existingRecipients := strings.Split(string(contents), "\n")
	for _, e := range existingRecipients {
		if e != "" {
			sentToAddresses = append(sentToAddresses, e)
		}
	}

    existingReaderCount := len(sentToAddresses)
    newReaderCount := 0

    if existingReaderCount > 0 {
        fmt.Println("Same email file specified: Sending only to new subscribers...")
    }

	var group []string
	for _, a := range audience {
		if a == "" {
			continue
		}
		found := false
		for _, s := range sentToAddresses {
			if a == s {
				found = true
				break
			}
		}
		if !found {
			group = append(group, a)
			if len(group) == cfg.BatchSize {
				results, err := sendMail(cfg, group, subject, body)
				if err != nil {
					fmt.Printf("Error while sending mail: %v\n", err)
					return
				}
				sentToAddresses = append(sentToAddresses, group...)
				os.WriteFile(trackingFile, []byte(strings.Join(sentToAddresses, "\n")), 0666)
				for i, res := range results {
					log.WriteString(fmt.Sprintf("%s: %s\n", group[i], res.Message))
				}
                newReaderCount += len(group)
				group = group[0:0]
			}
		}
	}
	if len(group) > 0 {
		results, err := sendMail(cfg, group, subject, body)
		if err != nil {
			fmt.Printf("Error while sending mail: %v\n", err)
			return
		}
		sentToAddresses = append(sentToAddresses, group...)
		os.WriteFile(trackingFile, []byte(strings.Join(sentToAddresses, "\n")), 0666)
		for i, res := range results {
			log.WriteString(fmt.Sprintf("%s: %s\n", group[i], res.Message))
		}
        newReaderCount += len(group)
	}

    if newReaderCount > 0 {
        newSubscribers := existingReaderCount > 0
        if newSubscribers {
            fmt.Printf("Sent to %d new subscribers!\n", newReaderCount)
        }
    } else {
        fmt.Printf("Not sent (no new subscribers)\n")
    }
}

var postmarkClient = http.Client{}

type PostmarkTemplateModel struct {
	Name    string `json:"name"`
	Email   string `json:"email"`
	Subject string `json:"subject"`
	Body    string `json:"body"`
}

type PostmarkTemplateMessage struct {
	From          string                `json:"From"`
	To            string                `json:"To"`
	TemplateId    int                   `json:"TemplateId"`
	TemplateModel PostmarkTemplateModel `json:"TemplateModel"`
	MessageStream string                `json:"MessageStream"`
}

type PostmarkBatchWithTemplateBody struct {
	Messages []PostmarkTemplateMessage `json:"Messages"`
}

type PostmarkBatchResult struct {
	ErrorCode int    `json:"ErrorCode"`
	Message   string `json:"Message"`
}

func sendMail(cfg *Config, recipients []string, subject, html string) ([]PostmarkBatchResult, error) {
	fmt.Printf("Sending batch [%d recipients]...", len(recipients))

	from := cfg.Postmark.SenderEmail
	if cfg.Postmark.SenderName != "" {
		from = fmt.Sprintf("%s <%s>", cfg.Postmark.SenderName, cfg.Postmark.SenderEmail)
	}

	body := PostmarkBatchWithTemplateBody{}
	for _, r := range recipients {
		body.Messages = append(body.Messages, PostmarkTemplateMessage{
			From:       from,
			To:         r,
			TemplateId: cfg.Postmark.TemplateId,
			TemplateModel: PostmarkTemplateModel{
				Name:    cfg.Postmark.SenderName,
				Email:   cfg.Postmark.SenderEmail,
				Subject: subject,
				Body:    html,
			},
			MessageStream: cfg.Postmark.MessageStream,
		})
	}

	reqBody, err := json.Marshal(&body)
	if err != nil {
		return nil, err
	}

	req, err := http.NewRequest(http.MethodPost, "https://api.postmarkapp.com/email/batchWithTemplates", bytes.NewReader(reqBody))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Accept", "application/json")
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("X-Postmark-Server-Token", cfg.Postmark.ServerToken)
	res, err := postmarkClient.Do(req)
	if err != nil {
		return nil, err
	}

	var results []PostmarkBatchResult
	resBody, err := io.ReadAll(res.Body)
	res.Body.Close()
	if err != nil {
		return nil, err
	}
	if res.StatusCode != 200 {
		return nil, fmt.Errorf("Bad response from postmark: %d", res.StatusCode)
	}
	err = json.Unmarshal(resBody, &results)
	if err != nil {
		fmt.Printf("Batch sent successfully, but failed to parse response from postmark.\n")
		return nil, nil
	}
	fmt.Printf("Done.\n")
	return results, nil
}

func ComplainEmpty(val string, complaint string) bool {
	if val == "" {
		fmt.Println(complaint)
		return false
	}
	return true
}

func main() {
	/* Read in credentials into Config struct */
	/* *** */
	configFile := "config.toml"

	data, err := ioutil.ReadFile(configFile)
	if err != nil {
		fmt.Println("Error reading TOML file:", err)
		os.Exit(1)
	}

	config := &Config{}

	if err := toml.Unmarshal(data, config); err != nil {
		fmt.Println("Error unmarshaling TOML:", err)
		os.Exit(1)
	}

	if config.BatchSize == 0 {
		config.BatchSize = 500
	}

	validConfig := true

	validConfig = ComplainEmpty(config.TestEmail, "* Test email address is missing in config") && validConfig
	validConfig = ComplainEmpty(config.HMC.ApiUrl, "* HMC API url is missing in config") && validConfig
	validConfig = ComplainEmpty(config.HMC.SharedSecret, "* HMC Shared secret is missing in config") && validConfig
	validConfig = ComplainEmpty(config.HMC.City, "* HMC City is missing in config") && validConfig
	validConfig = ComplainEmpty(config.Postmark.ServerToken, "* Postmark server token is missing in config") && validConfig
	validConfig = ComplainEmpty(config.Postmark.ApiUrl, "* Postmark API url is missing in config") && validConfig
	if config.Postmark.TemplateId == 0 {
		fmt.Println("* Postmark template ID is missing in config")
		validConfig = false
	}
	validConfig = ComplainEmpty(config.Postmark.SenderName, "* Sender name is missing in config") && validConfig
	validConfig = ComplainEmpty(config.Postmark.SenderEmail, "* Sender email is missing in config") && validConfig
	validConfig = ComplainEmpty(config.Postmark.MessageStream, "* Postmark message stream is missing in config") && validConfig

	if !validConfig {
		fmt.Println("Please fix your config and try again")
		os.Exit(1)
	}

	/* Setup Cobra */
	/* *** */
	cmd := &cobra.Command{
		Use:   "meetupinvite2000",
		Short: "MeetupInvite2000",
		Run: func(cmd *cobra.Command, args []string) {
			fmt.Printf(`Instructions:
	1. Create an email file
		* Name it whatever you want. Markdown is expected
		* Any newlines at the start or end of the file will be removed
		* The first line of the file will be used as {{ subject }} in the postmark template. It must start with the # symbol
		* The rest of the file will be used as {{{ content_body }}}

	2. See who's subscribed
		* ./meetupinvite2000 dump
		* Dumps the mailing list of your meetup group so far
		* List grows automatically as more people sign up for your city (at handmadecities.com/meetups)

	3. Do a test run
		* ./meetupinvite2000 test [email file]
		* You must send a test email before blasting it to everyone (update config.toml to change test recipient)
		* If you modify the email file after testing, you must test again. Otherwise MeetupInvite2000 will complain

	4. Start blasting!
		* ./meetupinvite2000 blast [email file]
		* Will batch send your invite using our Email API (Postmark)
		* Will produce a .track file that will list all email addresses that we attempted to send to
		* In case of error, you can blast again. All emails listed in the .track file will be skipped
		* Will produce a .log file with information received back from Postmark
`)
		},
	}

	dumpCmd := &cobra.Command{
		Use:   "dump",
		Short: "Dump the list of subscribers",
		Run: func(cmd *cobra.Command, args []string) {
			subscribers, err := retrieveSubscribers(config)
			if err != nil {
				fmt.Printf("Error retrieving subscribers: %v\n", err)
				return
			}

			fmt.Printf("Handmade Meetups - \033[1m%s\033[0m\n\n", config.HMC.City)
			maxIndexWidth := len(strconv.Itoa(len(subscribers)))
			for index, email := range subscribers {
				indexStr := strconv.Itoa(index + 1)
				indexStr = strings.Repeat(" ", maxIndexWidth-len(indexStr)) + indexStr // Right-align the index
				fmt.Printf("%s. \033[1m%s\033[0m\n", indexStr, email)
			}
			fmt.Printf("\nMailing list grows automatically as more subscribe at \033[1mhandmadecities.com/meetups\033[0m\n")
		},
	}

	testCmd := &cobra.Command{
		Use:   "test [email file]",
		Short: "Send a test update to the test address specified in the config",
		Run: func(cmd *cobra.Command, args []string) {
			if len(args) < 1 {
				cmd.Usage()
				os.Exit(1)
			}
			updateFile := args[0]
			sendTest(config, updateFile)
		},
	}

	blastCmd := &cobra.Command{
		Use:   "blast [email file]",
		Short: "Blast your update to your members",
		Run: func(cmd *cobra.Command, args []string) {
			if len(args) < 1 {
				cmd.Usage()
				os.Exit(1)
			}
			updateFile := args[0]
			sendNews(config, updateFile)
		},
	}

	/* Install commands and serve them to the user */
	/* *** */
	cmd.AddCommand(dumpCmd)
	cmd.AddCommand(testCmd)
	cmd.AddCommand(blastCmd)

	cmd.Execute()
}