// Copyright (c) 2022 Proton AG
//
// This file is part of Proton Mail Bridge.
//
// Proton Mail Bridge is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Proton Mail Bridge is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.

package user

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/ProtonMail/gluon/imap"
	"github.com/ProtonMail/gluon/queue"
	"github.com/ProtonMail/gopenpgp/v2/crypto"
	"github.com/ProtonMail/proton-bridge/v2/internal/events"
	"github.com/ProtonMail/proton-bridge/v2/internal/safe"
	"github.com/ProtonMail/proton-bridge/v2/internal/vault"
	"github.com/bradenaw/juniper/stream"
	"github.com/bradenaw/juniper/xslices"
	"github.com/google/uuid"
	"gitlab.protontech.ch/go/liteapi"
	"golang.org/x/exp/maps"
)

const (
	maxUpdateSize = 1 << 27 // 128 MiB
	maxBatchSize  = 1 << 7  // 128
)

// doSync begins syncing the users data.
// It first ensures the latest event ID is known; if not, it fetches it.
// It sends a SyncStarted event and then either SyncFinished or SyncFailed
// depending on whether the sync was successful.
func (user *User) doSync(ctx context.Context) error {
	if user.vault.EventID() == "" {
		eventID, err := user.client.GetLatestEventID(ctx)
		if err != nil {
			return fmt.Errorf("failed to get latest event ID: %w", err)
		}

		if err := user.vault.SetEventID(eventID); err != nil {
			return fmt.Errorf("failed to set latest event ID: %w", err)
		}
	}

	start := time.Now()

	user.log.WithField("start", start).Info("Beginning user sync")

	user.eventCh.Enqueue(events.SyncStarted{
		UserID: user.ID(),
	})

	if err := user.sync(ctx); err != nil {
		user.log.WithError(err).Warn("Failed to sync user")

		user.eventCh.Enqueue(events.SyncFailed{
			UserID: user.ID(),
			Error:  err,
		})

		return fmt.Errorf("failed to sync: %w", err)
	}

	user.log.WithField("duration", time.Since(start)).Info("Finished user sync")

	user.eventCh.Enqueue(events.SyncFinished{
		UserID: user.ID(),
	})

	return nil
}

func (user *User) sync(ctx context.Context) error {
	return safe.RLockRet(func() error {
		return withAddrKRs(user.apiUser, user.apiAddrs, user.vault.KeyPass(), func(_ *crypto.KeyRing, addrKRs map[string]*crypto.KeyRing) error {
			if !user.vault.SyncStatus().HasLabels {
				user.log.Info("Syncing labels")

				if err := syncLabels(ctx, user.apiLabels, xslices.Unique(maps.Values(user.updateCh))...); err != nil {
					return fmt.Errorf("failed to sync labels: %w", err)
				}

				if err := user.vault.SetHasLabels(true); err != nil {
					return fmt.Errorf("failed to set has labels: %w", err)
				}

				user.log.Info("Synced labels")
			} else {
				user.log.Info("Labels are already synced, skipping")
			}

			if !user.vault.SyncStatus().HasMessages {
				user.log.Info("Syncing messages")

				if err := syncMessages(
					ctx,
					user.ID(),
					user.client,
					user.vault,
					addrKRs,
					user.updateCh,
					user.eventCh,
					user.syncWorkers,
					user.syncBuffer,
				); err != nil {
					return fmt.Errorf("failed to sync messages: %w", err)
				}

				if err := user.vault.SetHasMessages(true); err != nil {
					return fmt.Errorf("failed to set has messages: %w", err)
				}

				user.log.Info("Synced messages")
			} else {
				user.log.Info("Messages are already synced, skipping")
			}

			return nil
		})
	}, user.apiUserLock, user.apiAddrsLock, user.apiLabelsLock, user.updateChLock)
}

// nolint:exhaustive
func syncLabels(ctx context.Context, apiLabels map[string]liteapi.Label, updateCh ...*queue.QueuedChannel[imap.Update]) error {
	// Create placeholder Folders/Labels mailboxes with a random ID and with the \Noselect attribute.
	for _, prefix := range []string{folderPrefix, labelPrefix} {
		for _, updateCh := range updateCh {
			updateCh.Enqueue(newPlaceHolderMailboxCreatedUpdate(prefix))
		}
	}

	// Sync the user's labels.
	for labelID, label := range apiLabels {
		switch label.Type {
		case liteapi.LabelTypeSystem:
			if wantLabelID(labelID) {
				for _, updateCh := range updateCh {
					updateCh.Enqueue(newSystemMailboxCreatedUpdate(imap.MailboxID(label.ID), label.Name))
				}
			}

		case liteapi.LabelTypeFolder, liteapi.LabelTypeLabel:
			for _, updateCh := range updateCh {
				updateCh.Enqueue(newMailboxCreatedUpdate(imap.MailboxID(labelID), getMailboxName(label)))
			}

		default:
			return fmt.Errorf("unknown label type: %d", label.Type)
		}
	}

	// Wait for all label updates to be applied.
	for _, updateCh := range updateCh {
		update := imap.NewNoop()
		defer update.WaitContext(ctx)

		updateCh.Enqueue(update)
	}

	return nil
}

func syncMessages( //nolint:funlen
	ctx context.Context,
	userID string,
	client *liteapi.Client,
	vault *vault.User,
	addrKRs map[string]*crypto.KeyRing,
	updateCh map[string]*queue.QueuedChannel[imap.Update],
	eventCh *queue.QueuedChannel[events.Event],
	syncWorkers, syncBuffer int,
) error {
	// Determine which messages to sync.
	messageIDs, err := client.GetMessageIDs(ctx, vault.SyncStatus().LastMessageID)
	if err != nil {
		return fmt.Errorf("failed to get message IDs to sync: %w", err)
	}

	// Fetch and build each message.
	buildCh := stream.Map(
		client.GetFullMessages(ctx, syncWorkers, syncBuffer, messageIDs...),
		func(_ context.Context, full liteapi.FullMessage) (*buildRes, error) {
			return buildRFC822(full, addrKRs[full.AddressID])
		},
	)

	// Create the flushers, one per update channel.
	flushers := make(map[string]*flusher)

	for addrID, updateCh := range updateCh {
		flusher := newFlusher(updateCh, maxUpdateSize)
		defer flusher.flush(ctx, true)

		flushers[addrID] = flusher
	}

	// Create a reporter to report sync progress updates.
	reporter := newReporter(userID, eventCh, len(messageIDs), time.Second)
	defer reporter.done()

	// Send each update to the appropriate flusher.
	return forEach(ctx, stream.Chunk(buildCh, maxBatchSize), func(batch []*buildRes) error {
		for _, res := range batch {
			flushers[res.addressID].push(ctx, res.update)
		}

		for _, flusher := range flushers {
			flusher.flush(ctx, true)
		}

		if err := vault.SetLastMessageID(batch[len(batch)-1].messageID); err != nil {
			return fmt.Errorf("failed to set last synced message ID: %w", err)
		}

		reporter.add(len(batch))

		return nil
	})
}

func newSystemMailboxCreatedUpdate(labelID imap.MailboxID, labelName string) *imap.MailboxCreated {
	if strings.EqualFold(labelName, imap.Inbox) {
		labelName = imap.Inbox
	}

	attrs := imap.NewFlagSet(imap.AttrNoInferiors)

	switch labelID {
	case liteapi.TrashLabel:
		attrs = attrs.Add(imap.AttrTrash)

	case liteapi.SpamLabel:
		attrs = attrs.Add(imap.AttrJunk)

	case liteapi.AllMailLabel:
		attrs = attrs.Add(imap.AttrAll)

	case liteapi.ArchiveLabel:
		attrs = attrs.Add(imap.AttrArchive)

	case liteapi.SentLabel:
		attrs = attrs.Add(imap.AttrSent)

	case liteapi.DraftsLabel:
		attrs = attrs.Add(imap.AttrDrafts)

	case liteapi.StarredLabel:
		attrs = attrs.Add(imap.AttrFlagged)
	}

	return imap.NewMailboxCreated(imap.Mailbox{
		ID:             labelID,
		Name:           []string{labelName},
		Flags:          defaultFlags,
		PermanentFlags: defaultPermanentFlags,
		Attributes:     attrs,
	})
}

func newPlaceHolderMailboxCreatedUpdate(labelName string) *imap.MailboxCreated {
	return imap.NewMailboxCreated(imap.Mailbox{
		ID:             imap.MailboxID(uuid.NewString()),
		Name:           []string{labelName},
		Flags:          defaultFlags,
		PermanentFlags: defaultPermanentFlags,
		Attributes:     imap.NewFlagSet(imap.AttrNoSelect),
	})
}

func newMailboxCreatedUpdate(labelID imap.MailboxID, labelName []string) *imap.MailboxCreated {
	return imap.NewMailboxCreated(imap.Mailbox{
		ID:             labelID,
		Name:           labelName,
		Flags:          defaultFlags,
		PermanentFlags: defaultPermanentFlags,
		Attributes:     imap.NewFlagSet(),
	})
}

func wantLabelID(labelID string) bool {
	switch labelID {
	case liteapi.AllDraftsLabel, liteapi.AllSentLabel, liteapi.OutboxLabel:
		return false

	default:
		return true
	}
}

func forEach[T any](ctx context.Context, streamer stream.Stream[T], fn func(T) error) error {
	defer streamer.Close()

	for {
		res, err := streamer.Next(ctx)
		if errors.Is(err, stream.End) {
			return nil
		} else if err != nil {
			return fmt.Errorf("failed to get next stream item: %w", err)
		}

		if err := fn(res); err != nil {
			return fmt.Errorf("failed to process stream item: %w", err)
		}
	}
}