package services

import (
	"bytes"
	"crypto/tls"
	"fmt"
	"html/template"
	"log"
	"net/smtp"
	"strings"
	"time"
)

// EmailConfig holds SMTP configuration
type EmailConfig struct {
	SMTPHost     string
	SMTPPort     string
	SMTPUser     string
	SMTPPassword string
	FromEmail    string
	ToEmail      string
}

// EmailService handles email sending operations
type EmailService struct {
	config *EmailConfig
}

// NewEmailService creates a new email service
func NewEmailService(config *EmailConfig) *EmailService {
	return &EmailService{
		config: config,
	}
}

// ContactFormData represents contact form submission data
type ContactFormData struct {
	Email   string
	Name    string
	Company string
	Subject string
	Message string
	IP      string
	Time    time.Time
}

// Validate performs validation on contact form data
func (c *ContactFormData) Validate() error {
	// Sanitize inputs
	c.Email = strings.TrimSpace(c.Email)
	c.Name = strings.TrimSpace(c.Name)
	c.Company = strings.TrimSpace(c.Company)
	c.Subject = strings.TrimSpace(c.Subject)
	c.Message = strings.TrimSpace(c.Message)

	// Required fields
	if c.Email == "" {
		return fmt.Errorf("email is required")
	}
	if c.Message == "" {
		return fmt.Errorf("message is required")
	}

	// Email format validation (basic)
	if !strings.Contains(c.Email, "@") || !strings.Contains(c.Email, ".") {
		return fmt.Errorf("invalid email format")
	}

	// Prevent email header injection
	if containsNewlines(c.Email) {
		return fmt.Errorf("invalid email: contains prohibited characters")
	}
	if containsNewlines(c.Subject) {
		return fmt.Errorf("invalid subject: contains prohibited characters")
	}

	// Length validation
	if len(c.Email) > 254 {
		return fmt.Errorf("email too long (max 254 characters)")
	}
	if len(c.Name) > 100 {
		return fmt.Errorf("name too long (max 100 characters)")
	}
	if len(c.Company) > 100 {
		return fmt.Errorf("company too long (max 100 characters)")
	}
	if len(c.Subject) > 200 {
		return fmt.Errorf("subject too long (max 200 characters)")
	}
	if len(c.Message) > 5000 {
		return fmt.Errorf("message too long (max 5000 characters)")
	}
	if len(c.Message) < 10 {
		return fmt.Errorf("message too short (min 10 characters)")
	}

	return nil
}

// containsNewlines checks for newline characters that could enable header injection
func containsNewlines(s string) bool {
	return strings.ContainsAny(s, "\r\n")
}

// SendContactForm sends a contact form email
func (e *EmailService) SendContactForm(data *ContactFormData) error {
	// Validate data
	if err := data.Validate(); err != nil {
		return fmt.Errorf("validation failed: %w", err)
	}

	// Prepare email content
	subject := "[CV Contact] "
	if data.Subject != "" {
		subject += data.Subject
	} else {
		subject += "New Message"
	}

	// Build email body
	body, err := e.buildEmailBody(data)
	if err != nil {
		return fmt.Errorf("failed to build email body: %w", err)
	}

	// Send email
	if err := e.sendEmail(subject, body); err != nil {
		return fmt.Errorf("failed to send email: %w", err)
	}

	// Log successful send (without sensitive data)
	log.Printf("Contact form email sent successfully to %s from %s", e.config.ToEmail, data.Email)

	return nil
}

// buildEmailBody creates the email body from template
func (e *EmailService) buildEmailBody(data *ContactFormData) (string, error) {
	emailTemplate := `New contact form submission:

From: {{.Email}}
Name: {{if .Name}}{{.Name}}{{else}}Not provided{{end}}
Company: {{if .Company}}{{.Company}}{{else}}Not provided{{end}}
Subject: {{if .Subject}}{{.Subject}}{{else}}Not provided{{end}}

Message:
{{.Message}}

---
IP: {{.IP}}
Time: {{.Time.Format "2006-01-02 15:04:05 MST"}}
`

	tmpl, err := template.New("contact").Parse(emailTemplate)
	if err != nil {
		return "", err
	}

	var body bytes.Buffer
	if err := tmpl.Execute(&body, data); err != nil {
		return "", err
	}

	return body.String(), nil
}

// sendEmail sends an email using SMTP
func (e *EmailService) sendEmail(subject, body string) error {
	// Validate config
	if e.config.SMTPHost == "" || e.config.SMTPPort == "" {
		return fmt.Errorf("SMTP configuration incomplete")
	}
	if e.config.SMTPUser == "" || e.config.SMTPPassword == "" {
		return fmt.Errorf("SMTP credentials missing")
	}
	if e.config.ToEmail == "" {
		return fmt.Errorf("recipient email not configured")
	}

	// Build email message
	from := e.config.FromEmail
	if from == "" {
		from = e.config.SMTPUser
	}

	to := e.config.ToEmail
	message := e.formatMessage(from, to, subject, body)

	// SMTP server address
	addr := fmt.Sprintf("%s:%s", e.config.SMTPHost, e.config.SMTPPort)

	// Setup authentication
	auth := smtp.PlainAuth("", e.config.SMTPUser, e.config.SMTPPassword, e.config.SMTPHost)

	// Connect to SMTP server with TLS
	client, err := e.connectSMTP(addr)
	if err != nil {
		return fmt.Errorf("failed to connect to SMTP server: %w", err)
	}
	defer client.Close()

	// Authenticate
	if err = client.Auth(auth); err != nil {
		return fmt.Errorf("SMTP authentication failed: %w", err)
	}

	// Set sender and recipient
	if err = client.Mail(from); err != nil {
		return fmt.Errorf("failed to set sender: %w", err)
	}
	if err = client.Rcpt(to); err != nil {
		return fmt.Errorf("failed to set recipient: %w", err)
	}

	// Send message
	w, err := client.Data()
	if err != nil {
		return fmt.Errorf("failed to get data writer: %w", err)
	}

	_, err = w.Write([]byte(message))
	if err != nil {
		return fmt.Errorf("failed to write message: %w", err)
	}

	err = w.Close()
	if err != nil {
		return fmt.Errorf("failed to close writer: %w", err)
	}

	return client.Quit()
}

// connectSMTP establishes an SMTP connection with TLS
func (e *EmailService) connectSMTP(addr string) (*smtp.Client, error) {
	// Connect to server
	client, err := smtp.Dial(addr)
	if err != nil {
		return nil, err
	}

	// Start TLS
	tlsConfig := &tls.Config{
		ServerName: e.config.SMTPHost,
		MinVersion: tls.VersionTLS12,
	}

	if err = client.StartTLS(tlsConfig); err != nil {
		client.Close()
		return nil, err
	}

	return client, nil
}

// formatMessage formats an email message with proper headers
func (e *EmailService) formatMessage(from, to, subject, body string) string {
	headers := make(map[string]string)
	headers["From"] = from
	headers["To"] = to
	headers["Subject"] = subject
	headers["MIME-Version"] = "1.0"
	headers["Content-Type"] = "text/plain; charset=\"utf-8\""
	headers["Date"] = time.Now().Format(time.RFC1123Z)

	var message strings.Builder
	for k, v := range headers {
		message.WriteString(fmt.Sprintf("%s: %s\r\n", k, v))
	}
	message.WriteString("\r\n")
	message.WriteString(body)

	return message.String()
}