package imap

import (
	"context"
	"fmt"
	"io"
	"log/slog"
	"strings"
	"time"

	imapv2 "github.com/emersion/go-imap/v2"
	"github.com/emersion/go-imap/v2/imapclient"
	"github.com/archivmail/internal/index"
	"github.com/archivmail/internal/storage"
	"github.com/archivmail/pkg/mailparser"
)

const batchSize = 50

// Importer runs background IMAP import jobs.
type Importer struct {
	store     *Store
	mailStore *storage.Store
	idx       index.Indexer
	logger    *slog.Logger
}

// NewImporter creates a new Importer wired to the storage and index backends.
func NewImporter(store *Store, mailStore *storage.Store, idx index.Indexer, logger *slog.Logger) *Importer {
	return &Importer{
		store:     store,
		mailStore: mailStore,
		idx:       idx,
		logger:    logger,
	}
}

// Run performs a full IMAP import for the given account. It is designed to be
// called as a goroutine: go imp.Run(context.Background(), accountID)
func (imp *Importer) Run(ctx context.Context, accountID int64) {
	log := imp.logger.With("component", "imap-importer", "account_id", accountID)

	acc, err := imp.store.Get(ctx, accountID)
	if err != nil {
		log.Error("failed to get account", "err", err)
		return
	}

	password, err := imp.store.GetPassword(ctx, accountID)
	if err != nil {
		log.Error("failed to decrypt password", "err", err)
		_ = imp.store.UpdateStatus(ctx, accountID, "error", "failed to decrypt password", 0, 0)
		return
	}

	// Mark as running
	if err := imp.store.UpdateStatus(ctx, accountID, "running", "", 0, 0); err != nil {
		log.Error("failed to update status", "err", err)
		return
	}

	imported, err := imp.doImport(ctx, acc, password, log)
	if err != nil {
		log.Error("import failed", "err", err)
		_ = imp.store.UpdateStatus(ctx, accountID, "error", err.Error(), 0, 0)
		return
	}

	if err := imp.store.UpdateDone(ctx, accountID, imported); err != nil {
		log.Error("failed to update done", "err", err)
	}

	log.Info("import completed", "imported", imported)
}

// doImport handles the actual IMAP connection, folder iteration, and message fetching.
func (imp *Importer) doImport(ctx context.Context, acc *Account, password string, log *slog.Logger) (int, error) {
	c, err := Connect(acc.Host, acc.Port, acc.TLS)
	if err != nil {
		return 0, fmt.Errorf("connect: %w", err)
	}
	defer c.Close()

	// Login
	if err := c.Login(acc.Username, password).Wait(); err != nil {
		return 0, fmt.Errorf("login: %w", err)
	}

	// List all folders
	folders, err := ListFolders(c)
	if err != nil {
		return 0, fmt.Errorf("list folders: %w", err)
	}

	// Build excluded set from account config
	excluded := make(map[string]bool)
	for _, f := range acc.ExcludedFolders {
		excluded[f] = true
	}

	// Collect included folders
	var includedFolders []string
	for _, f := range folders {
		if !excluded[f.Name] {
			includedFolders = append(includedFolders, f.Name)
		}
	}

	// Count total messages across all folders first
	totalMsgs := 0
	folderUIDs := make(map[string][]imapv2.UID)

	for _, folder := range includedFolders {
		selectData, err := c.Select(folder, nil).Wait()
		if err != nil {
			log.Warn("failed to select folder, skipping", "folder", folder, "err", err)
			continue
		}
		_ = selectData

		searchCmd := c.UIDSearch(&imapv2.SearchCriteria{}, nil)
		searchData, err := searchCmd.Wait()
		if err != nil {
			log.Warn("failed to search folder, skipping", "folder", folder, "err", err)
			continue
		}

		uids := searchData.AllUIDs()
		folderUIDs[folder] = uids
		totalMsgs += len(uids)
	}

	log.Info("starting import", "folders", len(includedFolders), "total_messages", totalMsgs)
	_ = imp.store.UpdateStatus(ctx, acc.ID, "running", "", 0, totalMsgs)

	imported := 0
	processed := 0

	for _, folder := range includedFolders {
		uids, ok := folderUIDs[folder]
		if !ok || len(uids) == 0 {
			continue
		}

		// Need to re-select the folder before fetching
		if _, err := c.Select(folder, nil).Wait(); err != nil {
			log.Warn("failed to re-select folder", "folder", folder, "err", err)
			continue
		}

		log.Info("importing folder", "folder", folder, "messages", len(uids))

		// Process in batches
		for i := 0; i < len(uids); i += batchSize {
			end := i + batchSize
			if end > len(uids) {
				end = len(uids)
			}
			batch := uids[i:end]

			count, err := imp.fetchBatch(ctx, c, batch, log)
			if err != nil {
				log.Error("batch fetch error", "folder", folder, "offset", i, "err", err)
				// Continue with the next batch rather than aborting entirely
				continue
			}

			imported += count
			processed += len(batch)

			_ = imp.store.UpdateStatus(ctx, acc.ID, "running", "", processed, totalMsgs)
		}
	}

	return imported, nil
}

// fetchBatch fetches and stores a batch of messages by UID.
func (imp *Importer) fetchBatch(ctx context.Context, c *imapclient.Client, uids []imapv2.UID, log *slog.Logger) (int, error) {
	if len(uids) == 0 {
		return 0, nil
	}

	fetchOptions := &imapv2.FetchOptions{
		UID:         true,
		BodySection: []*imapv2.FetchItemBodySection{{}},
	}

	seqSet := imapv2.UIDSetNum(uids...)
	fetchCmd := c.Fetch(seqSet, fetchOptions)

	imported := 0
	for {
		msg := fetchCmd.Next()
		if msg == nil {
			break
		}

		// Collect body sections from this message
		for {
			item := msg.Next()
			if item == nil {
				break
			}

			switch body := item.(type) {
			case imapclient.FetchItemDataBodySection:
				raw, err := io.ReadAll(body.Literal)
				if err != nil {
					log.Warn("failed to read message body", "err", err)
					continue
				}

				if err := imp.storeAndIndex(raw, log); err != nil {
					log.Warn("failed to store/index message", "err", err)
					continue
				}
				imported++
			}
		}
	}

	if err := fetchCmd.Close(); err != nil {
		return imported, fmt.Errorf("fetch close: %w", err)
	}

	return imported, nil
}

// storeAndIndex saves a raw email to storage and indexes it.
func (imp *Importer) storeAndIndex(raw []byte, log *slog.Logger) error {
	// Save to file storage (deduplicates by SHA256 automatically)
	id, err := imp.mailStore.Save(raw, time.Now())
	if err != nil {
		return fmt.Errorf("save: %w", err)
	}

	// Parse for indexing
	pm, err := mailparser.Parse(raw)
	if err != nil {
		log.Warn("failed to parse mail for indexing", "id", id, "err", err)
		// Store succeeded, just skip indexing for unparseable mails
		return nil
	}

	// Build attachment names string
	var attachNames []string
	for _, a := range pm.Attachments {
		if a.Filename != "" {
			attachNames = append(attachNames, a.Filename)
		}
	}

	doc := index.MailDocument{
		ID:            id,
		From:          pm.From,
		To:            strings.Join(pm.To, ", "),
		Subject:       pm.Subject,
		Body:          pm.TextBody,
		AttachNames:   strings.Join(attachNames, " "),
		HasAttachment: len(pm.Attachments) > 0,
		Date:          pm.Date,
		Size:          int64(len(raw)),
	}

	if err := imp.idx.IndexSync(doc); err != nil {
		log.Warn("failed to index mail", "id", id, "err", err)
		// Non-fatal: mail is stored, just not searchable yet
	}

	return nil
}