package main

import (
	"bytes"
	"crypto/md5"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"mime/multipart"
	"mime/quotedprintable"
	"net/smtp"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

var (
	smtpHost     = os.Getenv("SMTP_HOST")
	smtpPort     = os.Getenv("SMTP_PORT")
	smtpUser     = os.Getenv("SMTP_USER")
	smtpPassword = os.Getenv("SMTP_PASSWORD")
	senderEmail  = os.Getenv("SENDER_EMAIL")
	recipient    = os.Getenv("RECIPIENT_EMAIL")
	watchDir     = os.Getenv("WATCH_DIR")
	sentDir      string
	sentFileLock sync.Mutex
)

type SentFileEntry struct {
	Path   string    `json:"path"`
	SentAt time.Time `json:"sent_at"`
	Hash   string    `json:"hash"`
}

func isEbookFile(name string) bool {
	lower := strings.ToLower(name)
	return strings.HasSuffix(lower, ".mobi") || strings.HasSuffix(lower, ".epub") ||
		strings.HasSuffix(lower, ".pdf") || strings.HasSuffix(lower, ".azw3")
}

func sendEmailWithAttachment(filePath string) error {
	data, err := os.ReadFile(filePath)
	if err != nil {
		return fmt.Errorf("failed to read file: %w", err)
	}

	var buf bytes.Buffer
	writer := multipart.NewWriter(&buf)

	header := map[string]string{
		"From":         senderEmail,
		"To":           recipient,
		"Subject":      "Ebook Delivery",
		"MIME-Version": "1.0",
		"Content-Type": "multipart/mixed; boundary=\"" + writer.Boundary() + "\"",
	}

	for k, v := range header {
		fmt.Fprintf(&buf, "%s: %s\r\n", k, v)
	}
	fmt.Fprint(&buf, "\r\n")

	textPart, _ := writer.CreatePart(map[string][]string{
		"Content-Type":              {"text/plain; charset=utf-8"},
		"Content-Transfer-Encoding": {"quoted-printable"},
	})
	qp := quotedprintable.NewWriter(textPart)
	qp.Write([]byte("Attached is your ebook."))
	qp.Close()

	attachmentHeader := map[string][]string{
		"Content-Type":              {"application/octet-stream"},
		"Content-Transfer-Encoding": {"base64"},
		"Content-Disposition":       {fmt.Sprintf("attachment; filename=\"%s\"", filepath.Base(filePath))},
	}
	attachmentPart, _ := writer.CreatePart(attachmentHeader)
	encoded := make([]byte, base64.StdEncoding.EncodedLen(len(data)))
	base64.StdEncoding.Encode(encoded, data)
	attachmentPart.Write(encoded)

	writer.Close()

	auth := smtp.PlainAuth("", smtpUser, smtpPassword, smtpHost)
	return smtp.SendMail(smtpHost+":"+smtpPort, auth, senderEmail, []string{recipient}, buf.Bytes())
}

func fileHash(path string) (string, error) {
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()

	h := md5.New()
	if _, err := io.Copy(h, f); err != nil {
		return "", err
	}
	return hex.EncodeToString(h.Sum(nil)), nil
}

func sentFilePath(hash string) string {
	return filepath.Join(sentDir, hash+".json")
}

func hasBeenSent(hash string) bool {
	sentFileLock.Lock()
	defer sentFileLock.Unlock()
	_, err := os.Stat(sentFilePath(hash))
	return err == nil
}

func markAsSent(filePath, hash string) {
	sentFileLock.Lock()
	defer sentFileLock.Unlock()

	entry := SentFileEntry{
		Path:   filePath,
		SentAt: time.Now().UTC(),
		Hash: hash,
	}
	f, err := os.Create(sentFilePath(hash))
	if err != nil {
		log.Printf("Failed to record sent file %s: %v", filePath, err)
		return
	}
	defer f.Close()
	json.NewEncoder(f).Encode(entry)
}

func setupFileTracking() error {
	sentDir = filepath.Join(watchDir, ".sent")
	return os.MkdirAll(sentDir, 0755)
}

func scanAndSendEbooks() {
	err := filepath.Walk(watchDir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if info.IsDir() || !isEbookFile(info.Name()) {
			return nil
		}
		hash, err := fileHash(path)
		if err != nil {
			log.Printf("Error hashing file %s: %v", path, err)
			return nil
		}
		if hasBeenSent(hash) {
			log.Printf("Already sent (hash match): %s\n", path)
			return nil
		}
		log.Printf("Detected ebook file: %s\n", path)
		time.Sleep(1 * time.Second)
		if err := sendEmailWithAttachment(path); err != nil {
			log.Printf("Error sending email: %v\n", err)
		} else {
			markAsSent(path, hash)
			log.Printf("Sent %s to %s\n", path, recipient)
		}
		return nil
	})
	if err != nil {
		log.Printf("Error walking directory: %v\n", err)
	}
}

func main() {
	if watchDir == "" {
		log.Fatal("WATCH_DIR environment variable is required")
	}

	if err := setupFileTracking(); err != nil {
		log.Fatalf("Failed to setup tracking directory: %v", err)
	}

	log.Printf("Scanning folder: %s\n", watchDir)
	for {
		scanAndSendEbooks()
		time.Sleep(10 * time.Second)
	}
}