package imap

import (
	"bytes"
	"fmt"
	"io"
	"mime"
	"mime/multipart"
	"net/mail"
	"paraclub-ai-mailer/config"
	"strings"
	"time"

	"github.com/emersion/go-imap"
	"github.com/emersion/go-imap/client"
)

type IMAPClient struct {
	client    *client.Client
	config    config.IMAPConfig
	processed map[string]bool
}

// MessageLiteral implements imap.Literal for draft messages
type MessageLiteral struct {
	content []byte
	pos     int
}

func (m *MessageLiteral) Read(p []byte) (n int, err error) {
	if m.pos >= len(m.content) {
		return 0, io.EOF
	}
	n = copy(p, m.content[m.pos:])
	m.pos += n
	if m.pos >= len(m.content) {
		err = io.EOF
	}
	return
}

func (m *MessageLiteral) Len() int {
	return len(m.content)
}

func New(cfg config.IMAPConfig) (*IMAPClient, error) {
	addr := fmt.Sprintf("%s:%d", cfg.Server, cfg.Port)
	var c *client.Client
	var err error

	if cfg.UseTLS {
		c, err = client.DialTLS(addr, nil)
	} else {
		c, err = client.Dial(addr)
	}

	if err != nil {
		return nil, fmt.Errorf("failed to connect to IMAP server: %v", err)
	}

	if err := c.Login(cfg.Username, cfg.Password); err != nil {
		return nil, fmt.Errorf("failed to login: %v", err)
	}

	return &IMAPClient{
		client:    c,
		config:    cfg,
		processed: make(map[string]bool),
	}, nil
}

type Email struct {
	ID      string
	Subject string
	From    string
	Body    string
}

func (ic *IMAPClient) ensureConnection() error {
	if ic.client == nil {
		return ic.reconnect()
	}

	// Try to check connection by NOOPing
	if err := ic.client.Noop(); err != nil {
		return ic.reconnect()
	}
	return nil
}

func (ic *IMAPClient) reconnect() error {
	addr := fmt.Sprintf("%s:%d", ic.config.Server, ic.config.Port)
	var c *client.Client
	var err error

	if ic.config.UseTLS {
		c, err = client.DialTLS(addr, nil)
	} else {
		c, err = client.Dial(addr)
	}
	if err != nil {
		return fmt.Errorf("failed to connect to IMAP server: %v", err)
	}

	if err := c.Login(ic.config.Username, ic.config.Password); err != nil {
		c.Close()
		return fmt.Errorf("failed to login: %v", err)
	}

	if ic.client != nil {
		ic.client.Close()
	}
	ic.client = c
	return nil
}

func (ic *IMAPClient) FetchUnprocessedEmails() ([]Email, error) {
	if err := ic.ensureConnection(); err != nil {
		return nil, fmt.Errorf("failed to ensure IMAP connection: %v", err)
	}

	// Make sure we have a valid mailbox name
	if ic.config.MailboxIn == "" {
		return nil, fmt.Errorf("mailbox_in not configured")
	}

	// Select mailbox and get status
	mbox, err := ic.client.Select(ic.config.MailboxIn, false)
	if err != nil {
		return nil, fmt.Errorf("failed to select mailbox %s: %v", ic.config.MailboxIn, err)
	}

	// If mailbox is empty, return early
	if mbox.Messages == 0 {
		return nil, nil
	}

	criteria := imap.NewSearchCriteria()
	criteria.WithoutFlags = []string{"\\Seen", "Processed"}

	uids, err := ic.client.Search(criteria)
	if err != nil {
		return nil, fmt.Errorf("search failed: %v", err)
	}

	if len(uids) == 0 {
		return nil, nil
	}

	seqSet := new(imap.SeqSet)
	seqSet.AddNum(uids...)

	// Fetch both envelope and body
	section := &imap.BodySectionName{Peek: true}
	items := []imap.FetchItem{imap.FetchEnvelope, section.FetchItem()}

	messages := make(chan *imap.Message, 10)
	done := make(chan error, 1)

	go func() {
		done <- ic.client.Fetch(seqSet, items, messages)
	}()

	var emails []Email
	for msg := range messages {
		// Skip if message doesn't have an envelope
		if msg.Envelope == nil {
			continue
		}

		// Skip if already processed
		if ic.processed[msg.Envelope.MessageId] {
			continue
		}

		// Skip if no message ID
		if msg.Envelope.MessageId == "" {
			continue
		}

		r := msg.GetBody(section)
		if r == nil {
			continue
		}

		var bodyBuilder strings.Builder
		if _, err := io.Copy(&bodyBuilder, r); err != nil {
			continue
		}

		// Make sure we have a valid from address
		var from string
		if len(msg.Envelope.From) > 0 {
			from = msg.Envelope.From[0].Address()
		}

		emails = append(emails, Email{
			ID:      msg.Envelope.MessageId,
			Subject: msg.Envelope.Subject,
			From:    from,
			Body:    bodyBuilder.String(),
		})

		ic.processed[msg.Envelope.MessageId] = true
	}

	if err := <-done; err != nil {
		return nil, fmt.Errorf("fetch failed: %v", err)
	}

	return emails, nil
}

func (ic *IMAPClient) SaveDraft(email Email, response string) error {
	if err := ic.ensureConnection(); err != nil {
		return fmt.Errorf("failed to ensure IMAP connection: %v", err)
	}

	_, err := ic.client.Select(ic.config.DraftBox, false)
	if err != nil {
		return fmt.Errorf("failed to select draft box: %v", err)
	}

	// Format the draft message with HTML response and original email headers + content
	draft := fmt.Sprintf("From: %s\r\n"+
		"To: %s\r\n"+
		"Subject: Re: %s\r\n"+
		"MIME-Version: 1.0\r\n"+
		"Content-Type: text/html; charset=UTF-8\r\n"+
		"\r\n"+
		"%s\r\n"+
		"<br><br>\r\n"+
		"<div style=\"border-top: 1px solid #B5C4DF; padding-top: 10px; margin-top: 10px;\">\r\n"+
		"<div style=\"font-family: Arial, sans-serif; color: #666666; margin-bottom: 10px;\">\r\n"+
		"<b>From:</b> %s<br>\r\n"+
		"<b>Subject:</b> %s<br>\r\n"+
		"<b>Date:</b> %s<br>\r\n"+
		"</div>\r\n"+
		"<div style=\"margin-left: 10px; padding-left: 10px; border-left: 2px solid #B5C4DF;\">\r\n"+
		"%s\r\n"+
		"</div></div>",
		ic.config.Username,
		email.From,
		email.Subject,
		response,
		email.From,
		email.Subject,
		time.Now().Format("Mon, 02 Jan 2006 15:04:05 -0700"),
		extractMessageContent(email.Body))

	literal := &MessageLiteral{
		content: []byte(draft),
		pos:     0,
	}

	// Save the draft
	flags := []string{"\\Draft"}
	if err := ic.client.Append(ic.config.DraftBox, flags, time.Now(), literal); err != nil {
		return fmt.Errorf("failed to append draft: %v", err)
	}

	return nil
}

// extractMessageContent attempts to extract just the message content
// by removing email headers and MIME boundaries
func extractMessageContent(body string) string {
	msg, err := mail.ReadMessage(strings.NewReader(body))
	if err != nil {
		// Fallback to previous method if parsing fails
		return fallbackExtractContent(body)
	}

	mediaType, params, err := mime.ParseMediaType(msg.Header.Get("Content-Type"))
	if err != nil {
		return fallbackExtractContent(body)
	}

	if strings.HasPrefix(mediaType, "multipart/") {
		boundary := params["boundary"]
		if boundary == "" {
			return fallbackExtractContent(body)
		}

		reader := multipart.NewReader(msg.Body, boundary)
		var textContent string

		for {
			part, err := reader.NextPart()
			if err == io.EOF {
				break
			}
			if err != nil {
				return fallbackExtractContent(body)
			}

			// Check Content-Type of the part
			contentType := part.Header.Get("Content-Type")
			if strings.HasPrefix(contentType, "text/plain") {
				buf := new(bytes.Buffer)
				_, err := buf.ReadFrom(part)
				if err != nil {
					continue
				}
				textContent = buf.String()
				break
			}
		}

		if textContent != "" {
			return strings.TrimSpace(textContent)
		}
	}

	// For non-multipart messages, just read the body
	buf := new(bytes.Buffer)
	_, err = buf.ReadFrom(msg.Body)
	if err != nil {
		return fallbackExtractContent(body)
	}

	return strings.TrimSpace(buf.String())
}

// fallbackExtractContent is the previous implementation used as fallback
func fallbackExtractContent(body string) string {
	parts := strings.Split(body, "\r\n\r\n")
	if len(parts) > 1 {
		return strings.TrimSpace(strings.Join(parts[1:], "\r\n\r\n"))
	}
	return strings.TrimSpace(body)
}

func (ic *IMAPClient) MarkAsProcessed(email Email) error {
	if err := ic.ensureConnection(); err != nil {
		return fmt.Errorf("failed to ensure IMAP connection: %v", err)
	}

	_, err := ic.client.Select(ic.config.MailboxIn, false)
	if err != nil {
		return err
	}

	criteria := imap.NewSearchCriteria()
	criteria.Header.Set("Message-Id", email.ID)

	uids, err := ic.client.Search(criteria)
	if err != nil {
		return err
	}

	if len(uids) == 0 {
		return fmt.Errorf("email not found")
	}

	seqSet := new(imap.SeqSet)
	seqSet.AddNum(uids...)

	return ic.client.Store(seqSet, imap.FormatFlagsOp(imap.AddFlags, true), []interface{}{"Processed"}, nil)
}

func (ic *IMAPClient) Close() error {
	if ic.client != nil {
		ic.client.Logout()
	}
	return nil
}