package main

import (
	"bytes"
	"fmt"
	"html/template"
	"net/smtp"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"
)

type smtpConfig struct {
	Host     string
	Port     int
	User     string
	Password string
}

func getSMTPConfigFromEnv() smtpConfig {
	port := 587
	if rawPort := strings.TrimSpace(os.Getenv("STARTTLS_PORT")); rawPort != "" {
		if p, err := strconv.Atoi(rawPort); err == nil {
			port = p
		}
	}
	return smtpConfig{
		Host:     strings.TrimSpace(os.Getenv("SMTP")),
		Port:     port,
		User:     strings.TrimSpace(os.Getenv("SMTP_USER")),
		Password: strings.TrimSpace(os.Getenv("SMTP_PASSWORD")),
	}
}

func (s smtpConfig) isConfigured() bool {
	return s.Host != "" && s.User != "" && s.Password != "" && s.Port > 0
}

func getAppBaseURL() string {
	base := strings.TrimSpace(os.Getenv("SITE_URL"))
	if base == "" {
		base = strings.TrimSpace(os.Getenv("APP_BASE_URL"))
	}
	if base == "" {
		return "http://localhost:6081"
	}
	return strings.TrimRight(base, "/")
}

func sendPasswordResetEmail(config smtpConfig, recipientEmail, resetURL string) error {
	body, err := renderTransactionalTemplate("password_reset.html", map[string]string{
		"ActionURL": resetURL,
	})
	if err != nil {
		return err
	}
	return sendHTMLEmail(config, recipientEmail, "Bag Exchange - Password reset", body)
}

func sendEmailVerificationEmail(config smtpConfig, recipientEmail, verifyURL string) error {
	body, err := renderTransactionalTemplate("verify_email.html", map[string]string{
		"ActionURL": verifyURL,
	})
	if err != nil {
		return err
	}
	return sendHTMLEmail(config, recipientEmail, "Bag Exchange - Verify your email", body)
}

func sendHTMLEmail(config smtpConfig, recipientEmail, subject, htmlBody string) error {
	if isDevEmailMode() {
		return saveDevEmail(recipientEmail, subject, htmlBody)
	}

	auth := smtp.PlainAuth("", config.User, config.Password, config.Host)
	message := "From: " + config.User + "\r\n" +
		"To: " + recipientEmail + "\r\n" +
		"Subject: " + subject + "\r\n" +
		"MIME-Version: 1.0\r\n" +
		"Content-Type: text/html; charset=UTF-8\r\n\r\n" +
		htmlBody
	return smtp.SendMail(fmt.Sprintf("%s:%d", config.Host, config.Port), auth, config.User, []string{recipientEmail}, []byte(message))
}

func renderTransactionalTemplate(templateName string, data any) (string, error) {
	tmpl, err := template.ParseFiles(filepath.Join("templates", "transactionalMails", templateName))
	if err != nil {
		return "", err
	}
	var out bytes.Buffer
	if err := tmpl.Execute(&out, data); err != nil {
		return "", err
	}
	return out.String(), nil
}

func isDevEmailMode() bool {
	return strings.EqualFold(strings.TrimSpace(os.Getenv("EMAIL_MODE")), "dev")
}

func saveDevEmail(recipientEmail, subject, htmlBody string) error {
	const dir = "devEmails"
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return err
	}

	filename := fmt.Sprintf("%s_%s.html", time.Now().UTC().Format("20060102_150405"), sanitizeFilename(subject))
	path := filepath.Join(dir, filename)

	payload := "<!--\n" +
		"To: " + recipientEmail + "\n" +
		"Subject: " + subject + "\n" +
		"GeneratedAtUTC: " + time.Now().UTC().Format(time.RFC3339) + "\n" +
		"-->\n" + htmlBody

	return os.WriteFile(path, []byte(payload), 0o644)
}

func sanitizeFilename(value string) string {
	var b strings.Builder
	for _, r := range strings.ToLower(strings.TrimSpace(value)) {
		switch {
		case (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9'):
			b.WriteRune(r)
		case r == ' ' || r == '-' || r == '_':
			b.WriteRune('_')
		}
	}
	name := strings.Trim(b.String(), "_")
	if name == "" {
		return "email"
	}
	return name
}