package main

import (
	"bytes"
	"context"
	"crypto/tls"
	"encoding/base64"
	"fmt"
	"log"
	"mime"
	"net/smtp"
	"strings"
	"sync"
	"time"

	"github.com/emersion/go-imap/v2"
	"github.com/emersion/go-imap/v2/imapclient"
)

// EmailConnector implements Connector for IMAP email accounts
type EmailConnector struct {
	name       string
	config     AccountConfig
	smtpConfig SMTPConfig
	ctx        context.Context
	cancel     context.CancelFunc
	callback   func()
	mu         sync.Mutex
}

// SMTPConfig holds SMTP settings for sending replies
type SMTPConfig struct {
	Host     string
	Port     int
	Username string
	Password string
	From     string
}

// NewEmailConnector creates a new email connector
func NewEmailConnector(name string, config AccountConfig, smtpConfig SMTPConfig) *EmailConnector {
	return &EmailConnector{
		name:       name,
		config:     config,
		smtpConfig: smtpConfig,
	}
}

func (e *EmailConnector) Name() string {
	return e.name
}

func (e *EmailConnector) connect() (*imapclient.Client, error) {
	addr := fmt.Sprintf("%s:%d", e.config.Host, e.config.Port)

	var client *imapclient.Client
	var err error

	tlsConfig := &tls.Config{InsecureSkipVerify: true}
	switch e.config.TLS {
	case "ssl":
		client, err = imapclient.DialTLS(addr, &imapclient.Options{TLSConfig: tlsConfig})
	case "starttls":
		client, err = imapclient.DialStartTLS(addr, &imapclient.Options{TLSConfig: tlsConfig})
	default:
		client, err = imapclient.DialInsecure(addr, nil)
	}
	if err != nil {
		return nil, fmt.Errorf("dial: %w", err)
	}

	if err := client.Login(e.config.Username, e.config.Password).Wait(); err != nil {
		client.Close()
		return nil, fmt.Errorf("login: %w", err)
	}

	return client, nil
}

func (e *EmailConnector) FetchNew() ([]UnifiedMessage, error) {
	client, err := e.connect()
	if err != nil {
		return nil, err
	}
	defer client.Close()

	// Get messages from watched folders (default INBOX)
	folders := e.config.Watch
	if len(folders) == 0 {
		folders = []string{"INBOX"}
	}

	var messages []UnifiedMessage
	for _, folder := range folders {
		msgs, err := e.fetchFromFolder(client, folder, true, time.Time{})
		if err != nil {
			log.Printf("[%s] Error fetching from %s: %v", e.name, folder, err)
			continue
		}
		messages = append(messages, msgs...)
	}

	return messages, nil
}

func (e *EmailConnector) FetchSince(since time.Time) ([]UnifiedMessage, error) {
	client, err := e.connect()
	if err != nil {
		return nil, err
	}
	defer client.Close()

	// Search all folders including Archive so we can find recently-processed messages
	folders := e.config.Watch
	if len(folders) == 0 {
		folders = []string{"INBOX"}
	}
	folders = appendIfMissing(folders, "Archive", "Trash", "Folders/Shopping")

	var messages []UnifiedMessage
	for _, folder := range folders {
		msgs, err := e.fetchFromFolder(client, folder, false, since)
		if err != nil {
			log.Printf("[%s] Error fetching from %s: %v", e.name, folder, err)
			continue
		}
		messages = append(messages, msgs...)
	}

	return messages, nil
}

func (e *EmailConnector) fetchFromFolder(client *imapclient.Client, folder string, unseenOnly bool, since time.Time) ([]UnifiedMessage, error) {
	_, err := client.Select(folder, nil).Wait()
	if err != nil {
		return nil, fmt.Errorf("select %s: %w", folder, err)
	}

	// Build search criteria
	criteria := &imap.SearchCriteria{}
	if unseenOnly {
		criteria.NotFlag = []imap.Flag{imap.FlagSeen}
	}
	if !since.IsZero() {
		criteria.Since = since
	}

	searchData, err := client.Search(criteria, nil).Wait()
	if err != nil {
		return nil, fmt.Errorf("search: %w", err)
	}

	seqNums := searchData.AllSeqNums()
	if len(seqNums) == 0 {
		return nil, nil
	}

	var seqSet imap.SeqSet
	for _, num := range seqNums {
		seqSet.AddNum(num)
	}

	return e.fetchMessages(client, seqSet, folder)
}

func (e *EmailConnector) fetchMessages(client *imapclient.Client, seqSet imap.SeqSet, folder string) ([]UnifiedMessage, error) {
	options := &imap.FetchOptions{
		Envelope:      true,
		Flags:         true,
		UID:           true,
		BodyStructure: &imap.FetchItemBodyStructure{},
		BodySection:   []*imap.FetchItemBodySection{{}},
	}

	fetchCmd := client.Fetch(seqSet, options)

	var messages []UnifiedMessage
	for {
		msgData := fetchCmd.Next()
		if msgData == nil {
			break
		}

		buf, err := msgData.Collect()
		if err != nil {
			continue
		}

		msg := e.convertMessage(*buf, folder)
		messages = append(messages, msg)
	}

	if err := fetchCmd.Close(); err != nil {
		return nil, err
	}

	return messages, nil
}

func (e *EmailConnector) convertMessage(buf imapclient.FetchMessageBuffer, folder string) UnifiedMessage {
	msg := UnifiedMessage{
		Source:      e.name,
		SourceUID:   fmt.Sprintf("%d", buf.UID),
		SourceExtra: folder,
		Seen:        false,
		Attachments: []AttachmentMeta{},
	}

	// Generate unified ID
	msg.ID = fmt.Sprintf("%s:%d", e.name, buf.UID)

	// Parse envelope
	if env := buf.Envelope; env != nil {
		msg.Subject = env.Subject
		msg.Timestamp = env.Date
		if msg.Timestamp.IsZero() {
			msg.Timestamp = buf.InternalDate
		}

		if len(env.From) > 0 {
			from := env.From[0]
			msg.From = fmt.Sprintf("%s@%s", from.Mailbox, from.Host)
			if from.Name != "" {
				msg.FromName = from.Name
			}
		}

		if len(env.To) > 0 {
			to := env.To[0]
			msg.To = fmt.Sprintf("%s@%s", to.Mailbox, to.Host)
		}
	}

	// Check seen flag
	for _, f := range buf.Flags {
		if f == imap.FlagSeen {
			msg.Seen = true
			break
		}
	}

	// Parse body
	if len(buf.BodySection) > 0 {
		raw := buf.BodySection[0].Bytes
		parsed := ParseMIMEBody(raw)
		msg.Body = parsed.Text
		if msg.Body == "" {
			msg.Body = stripHTML(parsed.HTML)
		}

		// Extract attachment metadata
		attachments := ExtractAttachments(raw)
		for _, att := range attachments {
			msg.Attachments = append(msg.Attachments, AttachmentMeta{
				Name: att.Filename,
				Mime: att.ContentType,
				Size: att.Size,
			})
		}
	}

	return msg
}

func (e *EmailConnector) FetchOne(sourceID string) (*UnifiedMessage, error) {
	client, err := e.connect()
	if err != nil {
		return nil, err
	}
	defer client.Close()

	// Parse UID from sourceID
	var uid uint32
	if _, err := fmt.Sscanf(sourceID, "%d", &uid); err != nil {
		return nil, fmt.Errorf("invalid source ID: %s", sourceID)
	}

	// Try watched folders first, then Archive/Trash/All Mail
	folders := e.config.Watch
	if len(folders) == 0 {
		folders = []string{"INBOX"}
	}
	// Append fallback folders for finding archived/deleted messages
	folders = appendIfMissing(folders, "Archive", "Trash", "All Mail", "Folders/Shopping")

	for _, folder := range folders {
		_, err := client.Select(folder, nil).Wait()
		if err != nil {
			continue
		}

		uidSet := imap.UIDSetNum(imap.UID(uid))
		options := &imap.FetchOptions{
			Envelope:      true,
			Flags:         true,
			UID:           true,
			BodyStructure: &imap.FetchItemBodyStructure{},
			BodySection:   []*imap.FetchItemBodySection{{}},
		}

		fetchCmd := client.Fetch(uidSet, options)
		msgData := fetchCmd.Next()
		if msgData != nil {
			buf, err := msgData.Collect()
			fetchCmd.Close()
			if err == nil {
				msg := e.convertMessage(*buf, folder)
				return &msg, nil
			}
		}
		fetchCmd.Close()
	}

	return nil, fmt.Errorf("message not found: %s", sourceID)
}

func (e *EmailConnector) Archive(sourceID string) error {
	return e.moveMessage(sourceID, "Archive")
}

func (e *EmailConnector) Delete(sourceID string) error {
	client, err := e.connect()
	if err != nil {
		return err
	}
	defer client.Close()

	var uid uint32
	if _, err := fmt.Sscanf(sourceID, "%d", &uid); err != nil {
		return fmt.Errorf("invalid source ID: %s", sourceID)
	}

	folders := e.config.Watch
	if len(folders) == 0 {
		folders = []string{"INBOX"}
	}

	for _, folder := range folders {
		_, err := client.Select(folder, nil).Wait()
		if err != nil {
			continue
		}

		uidSet := imap.UIDSetNum(imap.UID(uid))

		// Mark deleted
		storeCmd := client.Store(uidSet, &imap.StoreFlags{
			Op:     imap.StoreFlagsAdd,
			Silent: true,
			Flags:  []imap.Flag{imap.FlagDeleted},
		}, nil)
		storeCmd.Close()

		// Expunge
		expungeCmd := client.Expunge()
		expungeCmd.Close()
		return nil
	}

	return fmt.Errorf("message not found: %s", sourceID)
}

func (e *EmailConnector) moveMessage(sourceID, destFolder string) error {
	client, err := e.connect()
	if err != nil {
		return err
	}
	defer client.Close()

	var uid uint32
	if _, err := fmt.Sscanf(sourceID, "%d", &uid); err != nil {
		return fmt.Errorf("invalid source ID: %s", sourceID)
	}

	folders := e.config.Watch
	if len(folders) == 0 {
		folders = []string{"INBOX"}
	}

	for _, folder := range folders {
		_, err := client.Select(folder, nil).Wait()
		if err != nil {
			continue
		}

		uidSet := imap.UIDSetNum(imap.UID(uid))
		moveCmd := client.Move(uidSet, destFolder)
		if _, err := moveCmd.Wait(); err != nil {
			// Try creating folder
			if strings.Contains(err.Error(), "TRYCREATE") || strings.Contains(err.Error(), "no such mailbox") {
				client.Create(destFolder, nil).Wait()
				moveCmd2 := client.Move(uidSet, destFolder)
				if _, err2 := moveCmd2.Wait(); err2 != nil {
					return err2
				}
			} else {
				continue
			}
		}
		return nil
	}

	return fmt.Errorf("message not found: %s", sourceID)
}

func (e *EmailConnector) Reply(sourceID string, body string, attachments []string) error {
	// Get original message to extract reply-to address
	msg, err := e.FetchOne(sourceID)
	if err != nil {
		return err
	}

	// Build email
	to := msg.From
	subject := msg.Subject
	if !strings.HasPrefix(strings.ToLower(subject), "re:") {
		subject = "Re: " + subject
	}

	// Simple SMTP send
	smtpAddr := fmt.Sprintf("%s:%d", e.smtpConfig.Host, e.smtpConfig.Port)

	var msgBuf bytes.Buffer
	msgBuf.WriteString(fmt.Sprintf("To: %s\r\n", to))
	msgBuf.WriteString(fmt.Sprintf("From: %s\r\n", e.smtpConfig.From))
	msgBuf.WriteString(fmt.Sprintf("Subject: %s\r\n", mime.QEncoding.Encode("utf-8", subject)))
	msgBuf.WriteString("MIME-Version: 1.0\r\n")
	msgBuf.WriteString("Content-Type: text/plain; charset=utf-8\r\n")
	msgBuf.WriteString("\r\n")
	msgBuf.WriteString(body)

	auth := smtp.PlainAuth("", e.smtpConfig.Username, e.smtpConfig.Password, e.smtpConfig.Host)
	return smtp.SendMail(smtpAddr, auth, e.smtpConfig.From, []string{to}, msgBuf.Bytes())
}

func (e *EmailConnector) MarkSeen(sourceID string) error {
	client, err := e.connect()
	if err != nil {
		return err
	}
	defer client.Close()

	var uid uint32
	if _, err := fmt.Sscanf(sourceID, "%d", &uid); err != nil {
		return fmt.Errorf("invalid source ID: %s", sourceID)
	}

	folders := e.config.Watch
	if len(folders) == 0 {
		folders = []string{"INBOX"}
	}

	for _, folder := range folders {
		_, err := client.Select(folder, nil).Wait()
		if err != nil {
			continue
		}

		uidSet := imap.UIDSetNum(imap.UID(uid))
		storeCmd := client.Store(uidSet, &imap.StoreFlags{
			Op:     imap.StoreFlagsAdd,
			Silent: true,
			Flags:  []imap.Flag{imap.FlagSeen},
		}, nil)
		storeCmd.Close()
		return nil
	}

	return fmt.Errorf("message not found: %s", sourceID)
}

func (e *EmailConnector) GetAttachment(sourceID string, filename string) ([]byte, error) {
	client, err := e.connect()
	if err != nil {
		return nil, err
	}
	defer client.Close()

	var uid uint32
	if _, err := fmt.Sscanf(sourceID, "%d", &uid); err != nil {
		return nil, fmt.Errorf("invalid source ID: %s", sourceID)
	}

	folders := e.config.Watch
	if len(folders) == 0 {
		folders = []string{"INBOX"}
	}

	for _, folder := range folders {
		_, err := client.Select(folder, nil).Wait()
		if err != nil {
			continue
		}

		uidSet := imap.UIDSetNum(imap.UID(uid))
		options := &imap.FetchOptions{
			UID:         true,
			BodySection: []*imap.FetchItemBodySection{{}},
		}

		fetchCmd := client.Fetch(uidSet, options)
		msgData := fetchCmd.Next()
		if msgData == nil {
			fetchCmd.Close()
			continue
		}

		buf, err := msgData.Collect()
		fetchCmd.Close()
		if err != nil {
			continue
		}

		if len(buf.BodySection) == 0 {
			continue
		}

		raw := buf.BodySection[0].Bytes
		attachments := ExtractAttachments(raw)
		for _, att := range attachments {
			if att.Filename == filename {
				decoded, err := base64.StdEncoding.DecodeString(att.Content)
				if err != nil {
					return nil, err
				}
				return decoded, nil
			}
		}
	}

	return nil, fmt.Errorf("attachment not found: %s", filename)
}

func (e *EmailConnector) Start(callback func()) error {
	e.mu.Lock()
	defer e.mu.Unlock()

	e.ctx, e.cancel = context.WithCancel(context.Background())
	e.callback = callback

	for _, folder := range e.config.Watch {
		go e.watchFolder(folder)
	}

	return nil
}

func (e *EmailConnector) watchFolder(folder string) {
	log.Printf("[%s] Starting IDLE watcher for %s", e.name, folder)

	for {
		select {
		case <-e.ctx.Done():
			return
		default:
		}

		err := e.runIDLE(folder)
		if err != nil {
			log.Printf("[%s] IDLE error on %s: %v, reconnecting in 10s", e.name, folder, err)
			select {
			case <-e.ctx.Done():
				return
			case <-time.After(10 * time.Second):
			}
		}
	}
}

func (e *EmailConnector) runIDLE(folder string) error {
	client, err := e.connect()
	if err != nil {
		return fmt.Errorf("connect: %w", err)
	}
	defer client.Close()

	mbox, err := client.Select(folder, nil).Wait()
	if err != nil {
		return fmt.Errorf("select %s: %w", folder, err)
	}

	prevCount := mbox.NumMessages
	log.Printf("[%s] IDLE connected to %s (%d messages)", e.name, folder, prevCount)

	for {
		idleCmd, err := client.Idle()
		if err != nil {
			return fmt.Errorf("idle start: %w", err)
		}

		idleDone := make(chan error, 1)
		go func() {
			idleDone <- idleCmd.Wait()
		}()

		select {
		case <-e.ctx.Done():
			idleCmd.Close()
			return nil
		case <-time.After(4 * time.Minute):
			idleCmd.Close()
		case err := <-idleDone:
			if err != nil {
				log.Printf("[%s] IDLE ended with error: %v", e.name, err)
			}
		}

		mbox, err = client.Select(folder, nil).Wait()
		if err != nil {
			return fmt.Errorf("re-select %s: %w", folder, err)
		}

		if mbox.NumMessages > prevCount {
			log.Printf("[%s] New mail in %s: %d -> %d", e.name, folder, prevCount, mbox.NumMessages)
			if e.callback != nil {
				go e.callback()
			}
			prevCount = mbox.NumMessages
		} else {
			prevCount = mbox.NumMessages
		}
	}
}

func (e *EmailConnector) Stop() {
	e.mu.Lock()
	defer e.mu.Unlock()

	if e.cancel != nil {
		e.cancel()
	}
}

// appendIfMissing adds folders to the slice if not already present
func appendIfMissing(slice []string, items ...string) []string {
	result := make([]string, len(slice))
	copy(result, slice)
	for _, item := range items {
		found := false
		for _, s := range result {
			if s == item {
				found = true
				break
			}
		}
		if !found {
			result = append(result, item)
		}
	}
	return result
}