package email

import (
	"bytes"
	"context"
	"crypto/tls"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/mail"
	"net/smtp"
	"regexp"
	"strings"
	"sync"

	"gitea.com/texpixel/document_ai/config"
	"gitea.com/texpixel/document_ai/pkg/log"
)

var (
	once   sync.Once
	client *Client
)

// chineseDomainRe matches email domains that should be routed via Aliyun SMTP.
var chineseDomainRe = regexp.MustCompile(`(?i)(\.edu\.cn|qq\.com|163\.com|126\.com|sina\.com|sohu\.com)$`)

type Client struct {
	cfg config.EmailConfig
}

func InitEmailClient() *Client {
	once.Do(func() {
		client = &Client{cfg: config.GlobalConfig.Email}
	})
	return client
}

// Send routes the email to the appropriate provider based on the recipient domain.
func Send(ctx context.Context, to, subject, body string) error {
	if client == nil {
		return fmt.Errorf("email client not initialized, call InitEmailClient first")
	}
	return client.Send(ctx, to, subject, body)
}

func (c *Client) Send(ctx context.Context, to, subject, body string) error {
	if _, err := mail.ParseAddress(to); err != nil {
		return fmt.Errorf("invalid email address %q: %w", to, err)
	}

	domain := to[strings.LastIndex(to, "@")+1:]
	if chineseDomainRe.MatchString(domain) {
		return c.sendViaAliyunSMTP(ctx, to, subject, body)
	}
	return c.sendViaResend(ctx, to, subject, body)
}

func (c *Client) sendViaAliyunSMTP(ctx context.Context, to, subject, body string) error {
	cfg := c.cfg.AliyunSMTP
	addr := fmt.Sprintf("%s:%d", cfg.Host, cfg.Port)

	tlsConfig := &tls.Config{ServerName: cfg.Host}
	conn, err := tls.Dial("tcp", addr, tlsConfig)
	if err != nil {
		log.Error(ctx, "func", "sendViaAliyunSMTP", "msg", "tls dial failed", "error", err)
		return err
	}

	smtpClient, err := smtp.NewClient(conn, cfg.Host)
	if err != nil {
		conn.Close()
		log.Error(ctx, "func", "sendViaAliyunSMTP", "msg", "smtp new client failed", "error", err)
		return err
	}
	defer smtpClient.Close()

	auth := smtp.PlainAuth("", cfg.Username, cfg.Password, cfg.Host)
	if err = smtpClient.Auth(auth); err != nil {
		log.Error(ctx, "func", "sendViaAliyunSMTP", "msg", "smtp auth failed", "error", err)
		return err
	}

	from := c.cfg.FromAddr
	if err = smtpClient.Mail(from); err != nil {
		return err
	}
	if err = smtpClient.Rcpt(to); err != nil {
		return err
	}

	wc, err := smtpClient.Data()
	if err != nil {
		return err
	}
	defer wc.Close()

	if _, err = wc.Write([]byte(buildMessage(c.cfg.FromName, from, to, subject, body))); err != nil {
		return err
	}

	log.Info(ctx, "func", "sendViaAliyunSMTP", "msg", "email sent via aliyun smtp", "to", to)
	return nil
}

type resendRequest struct {
	From    string   `json:"from"`
	To      []string `json:"to"`
	Subject string   `json:"subject"`
	Html    string   `json:"html"`
}

func (c *Client) sendViaResend(ctx context.Context, to, subject, body string) error {
	payload := resendRequest{
		From:    fmt.Sprintf("%s <%s>", c.cfg.FromName, c.cfg.FromAddr),
		To:      []string{to},
		Subject: subject,
		Html:    body,
	}
	jsonData, err := json.Marshal(payload)
	if err != nil {
		return err
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, "https://api.resend.com/emails", bytes.NewReader(jsonData))
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+c.cfg.Resend.APIKey)

	resp, err := (&http.Client{}).Do(req)
	if err != nil {
		log.Error(ctx, "func", "sendViaResend", "msg", "http request failed", "error", err)
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusCreated {
		respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 1024))
		log.Error(ctx, "func", "sendViaResend", "msg", "resend api returned non-2xx", "status", resp.StatusCode, "to", to, "body", string(respBody))
		return fmt.Errorf("resend api returned status %d: %s", resp.StatusCode, string(respBody))
	}

	log.Info(ctx, "func", "sendViaResend", "msg", "email sent via resend", "to", to)
	return nil
}

func buildMessage(fromName, fromAddr, to, subject, body string) string {
	var buf bytes.Buffer
	buf.WriteString(fmt.Sprintf("From: %s <%s>\r\n", fromName, fromAddr))
	buf.WriteString(fmt.Sprintf("To: %s\r\n", to))
	buf.WriteString(fmt.Sprintf("Subject: %s\r\n", subject))
	buf.WriteString("MIME-Version: 1.0\r\n")
	buf.WriteString("Content-Type: text/html; charset=UTF-8\r\n")
	buf.WriteString("\r\n")
	buf.WriteString(body)
	return buf.String()
}