package email

import (
	"context"
	"crypto/tls"
	"fmt"
	"strings"
	"time"

	gomail "gopkg.in/gomail.v2"
)

// Message 发信参数
type Message struct {
	To          []string
	Cc          []string
	Bcc         []string
	ReplyTo     []string
	Subject     string
	TextBody    string
	HTMLBody    string
	Attachments []string
}

type Client interface {
	IsEnabled() bool
	Config() Config
	Send(ctx context.Context, msg Message) error
}

type clientImpl struct {
	cfg Config
}

func NewClient(cfg Config) Client {
	return &clientImpl{cfg: cfg}
}

func (c *clientImpl) IsEnabled() bool {
	return c.cfg.Enabled &&
		strings.TrimSpace(c.cfg.Host) != "" &&
		c.cfg.Port > 0 &&
		strings.TrimSpace(c.cfg.FromAddress) != ""
}

func (c *clientImpl) Config() Config {
	return c.cfg
}

func (c *clientImpl) Send(ctx context.Context, msg Message) error {
	if !c.IsEnabled() {
		return fmt.Errorf("email client is disabled or misconfigured")
	}
	if len(msg.To) == 0 {
		return fmt.Errorf("email recipient is empty")
	}
	if strings.TrimSpace(msg.Subject) == "" {
		return fmt.Errorf("email subject is empty")
	}
	if strings.TrimSpace(msg.TextBody) == "" && strings.TrimSpace(msg.HTMLBody) == "" {
		return fmt.Errorf("email body is empty")
	}

	m := gomail.NewMessage()
	m.SetAddressHeader("From", c.cfg.FromAddress, c.cfg.FromName)
	m.SetHeader("To", msg.To...)
	if len(msg.Cc) > 0 {
		m.SetHeader("Cc", msg.Cc...)
	}
	if len(msg.Bcc) > 0 {
		m.SetHeader("Bcc", msg.Bcc...)
	}
	if len(msg.ReplyTo) > 0 {
		m.SetHeader("Reply-To", msg.ReplyTo...)
	}
	m.SetHeader("Subject", msg.Subject)

	if strings.TrimSpace(msg.TextBody) != "" && strings.TrimSpace(msg.HTMLBody) != "" {
		m.SetBody("text/plain", msg.TextBody)
		m.AddAlternative("text/html", msg.HTMLBody)
	} else if strings.TrimSpace(msg.HTMLBody) != "" {
		m.SetBody("text/html", msg.HTMLBody)
	} else {
		m.SetBody("text/plain", msg.TextBody)
	}

	for _, attachment := range msg.Attachments {
		if strings.TrimSpace(attachment) == "" {
			continue
		}
		m.Attach(attachment)
	}

	timeout := c.cfg.TimeoutSeconds
	if timeout <= 0 {
		timeout = 15
	}
	dialer := gomail.NewDialer(c.cfg.Host, c.cfg.Port, c.cfg.Username, c.cfg.Password)
	if c.cfg.UseTLS {
		dialer.TLSConfig = &tls.Config{
			ServerName:         c.cfg.Host,
			InsecureSkipVerify: c.cfg.InsecureSkipVerify,
		}
		// 465 端口通常要求直接 TLS（Implicit TLS）。
		if c.cfg.Port == 465 {
			dialer.SSL = true
		}
	}

	sendCtx := ctx
	cancel := func() {}
	if timeout > 0 {
		sendCtx, cancel = context.WithTimeout(ctx, time.Duration(timeout)*time.Second)
	}
	defer cancel()

	done := make(chan error, 1)
	go func() {
		done <- dialer.DialAndSend(m)
	}()

	select {
	case <-sendCtx.Done():
		return fmt.Errorf("send email canceled: %w", sendCtx.Err())
	case err := <-done:
		if err != nil {
			return fmt.Errorf("send email failed: %w", err)
		}
		return nil
	}
}