// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program 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 Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package federatingdb

import (
	"context"
	"errors"
	"fmt"

	"github.com/miekg/dns"
	"github.com/superseriousbusiness/activity/streams/vocab"
	"github.com/superseriousbusiness/gotosocial/internal/ap"
	"github.com/superseriousbusiness/gotosocial/internal/db"
	"github.com/superseriousbusiness/gotosocial/internal/gtscontext"
	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
	"github.com/superseriousbusiness/gotosocial/internal/id"
	"github.com/superseriousbusiness/gotosocial/internal/log"
	"github.com/superseriousbusiness/gotosocial/internal/messages"
)

// Create adds a new entry to the database which must be able to be
// keyed by its id.
//
// Note that Activity values received from federated peers may also be
// created in the database this way if the Federating Protocol is
// enabled. The client may freely decide to store only the id instead of
// the entire value.
//
// The library makes this call only after acquiring a lock first.
//
// Under certain conditions and network activities, Create may be called
// multiple times for the same ActivityStreams object.
func (f *federatingDB) Create(ctx context.Context, asType vocab.Type) error {
	log.DebugKV(ctx, "create", serialize{asType})

	activityContext := getActivityContext(ctx)
	if activityContext.internal {
		return nil // Already processed.
	}

	requestingAcct := activityContext.requestingAcct
	receivingAcct := activityContext.receivingAcct

	if requestingAcct.IsMoving() {
		// A Moving account
		// can't do this.
		return nil
	}

	switch name := asType.GetTypeName(); name {
	case ap.ActivityBlock:
		// BLOCK SOMETHING
		return f.activityBlock(ctx, asType, receivingAcct, requestingAcct)
	case ap.ActivityCreate:
		// CREATE SOMETHING
		return f.activityCreate(ctx, asType, receivingAcct, requestingAcct)
	case ap.ActivityFollow:
		// FOLLOW SOMETHING
		return f.activityFollow(ctx, asType, receivingAcct, requestingAcct)
	case ap.ActivityLike:
		// LIKE SOMETHING
		return f.activityLike(ctx, asType, receivingAcct, requestingAcct)
	case ap.ActivityFlag:
		// FLAG / REPORT SOMETHING
		return f.activityFlag(ctx, asType, receivingAcct, requestingAcct)
	default:
		log.Debugf(ctx, "unhandled object type: %s", name)
	}

	return nil
}

/*
	BLOCK HANDLERS
*/

func (f *federatingDB) activityBlock(ctx context.Context, asType vocab.Type, receiving *gtsmodel.Account, requesting *gtsmodel.Account) error {
	blockable, ok := asType.(vocab.ActivityStreamsBlock)
	if !ok {
		return errors.New("activityBlock: could not convert type to block")
	}

	block, err := f.converter.ASBlockToBlock(ctx, blockable)
	if err != nil {
		return fmt.Errorf("activityBlock: could not convert Block to gts model block")
	}

	if block.AccountID != requesting.ID {
		return fmt.Errorf(
			"activityBlock: requestingAccount %s is not Block actor account %s",
			requesting.URI, block.Account.URI,
		)
	}

	if block.TargetAccountID != receiving.ID {
		return fmt.Errorf(
			"activityBlock: inbox account %s is not Block object account %s",
			receiving.URI, block.TargetAccount.URI,
		)
	}

	block.ID = id.NewULID()

	if err := f.state.DB.PutBlock(ctx, block); err != nil {
		return fmt.Errorf("activityBlock: database error inserting block: %s", err)
	}

	f.state.Workers.Federator.Queue.Push(&messages.FromFediAPI{
		APObjectType:   ap.ActivityBlock,
		APActivityType: ap.ActivityCreate,
		GTSModel:       block,
		Receiving:      receiving,
		Requesting:     requesting,
	})

	return nil
}

/*
	CREATE HANDLERS
*/

// activityCreate handles asType Create by checking
// the Object entries of the Create and calling other
// handlers as appropriate.
func (f *federatingDB) activityCreate(
	ctx context.Context,
	asType vocab.Type,
	receivingAccount *gtsmodel.Account,
	requestingAccount *gtsmodel.Account,
) error {
	create, ok := asType.(vocab.ActivityStreamsCreate)
	if !ok {
		return gtserror.Newf("could not convert asType %T to ActivityStreamsCreate", asType)
	}

	var errs gtserror.MultiError

	// Extract objects from create activity.
	objects := ap.ExtractObjects(create)

	// Extract PollOptionables (votes!) from objects slice.
	optionables, objects := ap.ExtractPollOptionables(objects)

	if len(optionables) > 0 {
		// Handle provided poll vote(s) creation, this can
		// be for single or multiple votes in the same poll.
		err := f.createPollOptionables(ctx,
			receivingAccount,
			requestingAccount,
			optionables,
		)
		if err != nil {
			errs.Appendf("error creating poll vote(s): %w", err)
		}
	}

	// Extract Statusables from objects slice (this must be
	// done AFTER extracting options due to how AS typing works).
	statusables, objects := ap.ExtractStatusables(objects)

	for _, statusable := range statusables {
		// Check if this is a forwarded object, i.e. did
		// the account making the request also create this?
		forwarded := !isSender(statusable, requestingAccount)

		// Handle create event for this statusable.
		if err := f.createStatusable(ctx,
			receivingAccount,
			requestingAccount,
			statusable,
			forwarded,
		); err != nil {
			errs.Appendf("error creating statusable: %w", err)
		}
	}

	if len(objects) > 0 {
		// Log any unhandled objects after filtering for debug purposes.
		log.Debugf(ctx, "unhandled CREATE types: %v", typeNames(objects))
	}

	return errs.Combine()
}

// createPollOptionable handles a Create activity for a PollOptionable.
// This function doesn't handle database insertion, only validation checks
// before passing off to a worker for asynchronous processing.
func (f *federatingDB) createPollOptionables(
	ctx context.Context,
	receiver *gtsmodel.Account,
	requester *gtsmodel.Account,
	options []ap.PollOptionable,
) error {
	var (
		// the origin Status w/ Poll the vote
		// options are in. This gets set on first
		// iteration, relevant checks performed
		// then re-used in each further iteration.
		inReplyTo *gtsmodel.Status

		// the resulting slices of Poll.Option
		// choice indices passed into the new
		// created PollVote object.
		choices []int
	)

	for _, option := range options {
		// Extract the "inReplyTo" property.
		inReplyToURIs := ap.GetInReplyTo(option)
		if len(inReplyToURIs) != 1 {
			return gtserror.Newf("invalid inReplyTo property length: %d", len(inReplyToURIs))
		}

		// Stringify the inReplyTo URI.
		statusURI := inReplyToURIs[0].String()

		if inReplyTo == nil {
			var err error

			// This is the first object in the activity slice,
			// check database for the poll source status by URI.
			inReplyTo, err = f.state.DB.GetStatusByURI(ctx, statusURI)
			if err != nil {
				return gtserror.Newf("error getting poll source from database %s: %w", statusURI, err)
			}

			switch {
			// The origin status isn't a poll?
			case inReplyTo.PollID == "":
				return gtserror.Newf("poll vote in status %s without poll", statusURI)

			// We don't own the poll ...
			case !*inReplyTo.Local:
				return gtserror.Newf("poll vote in remote status %s", statusURI)
			}

			// Check whether user has already vote in this poll.
			// (we only check this for the first object, as multiple
			// may be sent in response to a multiple-choice poll).
			vote, err := f.state.DB.GetPollVoteBy(
				gtscontext.SetBarebones(ctx),
				inReplyTo.PollID,
				requester.ID,
			)
			if err != nil && !errors.Is(err, db.ErrNoEntries) {
				return gtserror.Newf("error getting status %s poll votes from database: %w", statusURI, err)
			}

			if vote != nil {
				log.Warnf(ctx, "%s has already voted in poll %s", requester.URI, statusURI)
				return nil // this is a useful warning for admins to report to us from logs
			}
		}

		if statusURI != inReplyTo.URI {
			// All activity votes should be to the same poll per activity.
			return gtserror.New("votes to multiple polls in single activity")
		}

		// Extract the poll option name.
		name := ap.ExtractName(option)

		// Check that this is a valid option name.
		choice := inReplyTo.Poll.GetChoice(name)
		if choice == -1 {
			return gtserror.Newf("poll vote in status %s invalid: %s", statusURI, name)
		}

		// Append the option index to choices.
		choices = append(choices, choice)
	}

	// Enqueue message to the fedi API worker with poll vote(s).
	f.state.Workers.Federator.Queue.Push(&messages.FromFediAPI{
		APActivityType: ap.ActivityCreate,
		APObjectType:   ap.ActivityQuestion,
		GTSModel: &gtsmodel.PollVote{
			ID:        id.NewULID(),
			Choices:   choices,
			AccountID: requester.ID,
			Account:   requester,
			PollID:    inReplyTo.PollID,
			Poll:      inReplyTo.Poll,
		},
		Receiving:  receiver,
		Requesting: requester,
	})

	return nil
}

// createStatusable handles a Create activity for a Statusable.
// This function won't insert anything in the database yet,
// but will pass the Statusable (if appropriate) through to
// the processor for further asynchronous processing.
func (f *federatingDB) createStatusable(
	ctx context.Context,
	receiver *gtsmodel.Account,
	requester *gtsmodel.Account,
	statusable ap.Statusable,
	forwarded bool,
) error {
	// Check whether this status is both
	// relevant, and doesn't look like spam.
	err := f.spamFilter.StatusableOK(ctx,
		receiver,
		requester,
		statusable,
	)

	switch {
	case err == nil:
		// No problem!

	case gtserror.IsNotRelevant(err):
		// This case is quite common if a remote (Mastodon)
		// instance forwards a message to us which is a reply
		// from someone else to a status we've also replied to.
		//
		// It does this to try to ensure thread completion, but
		// we have our own thread fetching mechanism anyway.
		log.Debugf(ctx,
			"status %s is not relevant to receiver (%v); dropping it",
			ap.GetJSONLDId(statusable), err,
		)
		return nil

	case gtserror.IsSpam(err):
		// Log this at a higher level so admins can
		// gauge how much spam is being sent to them.
		//
		// TODO: add Prometheus metrics for this.
		log.Infof(ctx,
			"status %s looked like spam (%v); dropping it",
			ap.GetJSONLDId(statusable), err,
		)
		return nil

	default:
		// A real error has occurred.
		return gtserror.Newf("error checking relevancy/spam: %w", err)
	}

	// If we do have a forward, we should ignore the content
	// and instead deref based on the URI of the statusable.
	//
	// In other words, don't automatically trust whoever sent
	// this status to us, but fetch the authentic article from
	// the server it originated from.
	if forwarded {

		// Pass the statusable URI (APIri) into the processor
		// worker and do the rest of the processing asynchronously.
		f.state.Workers.Federator.Queue.Push(&messages.FromFediAPI{
			APObjectType:   ap.ObjectNote,
			APActivityType: ap.ActivityCreate,
			APIRI:          ap.GetJSONLDId(statusable),
			APObject:       nil,
			GTSModel:       nil,
			Receiving:      receiver,
			Requesting:     requester,
		})
		return nil
	}

	// Do the rest of the processing asynchronously. The processor
	// will handle inserting/updating + further dereferencing the status.
	f.state.Workers.Federator.Queue.Push(&messages.FromFediAPI{
		APObjectType:   ap.ObjectNote,
		APActivityType: ap.ActivityCreate,
		APIRI:          nil,
		GTSModel:       nil,
		APObject:       statusable,
		Receiving:      receiver,
		Requesting:     requester,
	})

	return nil
}

/*
	FOLLOW HANDLERS
*/

func (f *federatingDB) activityFollow(ctx context.Context, asType vocab.Type, receivingAccount *gtsmodel.Account, requestingAccount *gtsmodel.Account) error {
	follow, ok := asType.(vocab.ActivityStreamsFollow)
	if !ok {
		return errors.New("activityFollow: could not convert type to follow")
	}

	followRequest, err := f.converter.ASFollowToFollowRequest(ctx, follow)
	if err != nil {
		return fmt.Errorf("activityFollow: could not convert Follow to follow request: %s", err)
	}

	if followRequest.AccountID != requestingAccount.ID {
		return fmt.Errorf(
			"activityFollow: requestingAccount %s is not Follow actor account %s",
			requestingAccount.URI, followRequest.Account.URI,
		)
	}

	if followRequest.TargetAccountID != receivingAccount.ID {
		return fmt.Errorf(
			"activityFollow: inbox account %s is not Follow object account %s",
			receivingAccount.URI, followRequest.TargetAccount.URI,
		)
	}

	followRequest.ID = id.NewULID()

	if err := f.state.DB.PutFollowRequest(ctx, followRequest); err != nil {
		return fmt.Errorf("activityFollow: database error inserting follow request: %s", err)
	}

	f.state.Workers.Federator.Queue.Push(&messages.FromFediAPI{
		APObjectType:   ap.ActivityFollow,
		APActivityType: ap.ActivityCreate,
		GTSModel:       followRequest,
		Receiving:      receivingAccount,
		Requesting:     requestingAccount,
	})

	return nil
}

/*
	LIKE HANDLERS
*/

func (f *federatingDB) activityLike(
	ctx context.Context,
	asType vocab.Type,
	receivingAcct *gtsmodel.Account,
	requestingAcct *gtsmodel.Account,
) error {
	like, ok := asType.(vocab.ActivityStreamsLike)
	if !ok {
		err := gtserror.Newf("could not convert asType %T to ActivityStreamsLike", asType)
		return gtserror.SetMalformed(err)
	}

	fave, err := f.converter.ASLikeToFave(ctx, like)
	if err != nil {
		return gtserror.Newf("could not convert Like to fave: %w", err)
	}

	// Ensure requester not trying to
	// Like on someone else's behalf.
	if fave.AccountID != requestingAcct.ID {
		text := fmt.Sprintf(
			"requestingAcct %s is not Like actor account %s",
			requestingAcct.URI, fave.Account.URI,
		)
		return gtserror.NewErrorForbidden(errors.New(text), text)
	}

	if !*fave.Status.Local {
		// Only process likes of local statuses.
		// TODO: process for remote statuses as well.
		return nil
	}

	// Ensure valid Like target for requester.
	policyResult, err := f.intFilter.StatusLikeable(ctx,
		requestingAcct,
		fave.Status,
	)
	if err != nil {
		err := gtserror.Newf("error seeing if status %s is likeable: %w", fave.Status.ID, err)
		return gtserror.NewErrorInternalError(err)
	}

	if policyResult.Forbidden() {
		const errText = "requester does not have permission to Like this status"
		err := gtserror.New(errText)
		return gtserror.NewErrorForbidden(err, errText)
	}

	// Derive pendingApproval
	// and preapproved status.
	var (
		pendingApproval bool
		preApproved     bool
	)

	switch {
	case policyResult.WithApproval():
		// Requester allowed to do
		// this pending approval.
		pendingApproval = true

	case policyResult.MatchedOnCollection():
		// Requester allowed to do this,
		// but matched on collection.
		// Preapprove Like and have the
		// processor send out an Accept.
		pendingApproval = true
		preApproved = true

	case policyResult.Permitted():
		// Requester straight up
		// permitted to do this,
		// no need for Accept.
		pendingApproval = false
	}

	// Set appropriate fields
	// on fave and store it.
	fave.ID = id.NewULID()
	fave.PendingApproval = &pendingApproval
	fave.PreApproved = preApproved

	if err := f.state.DB.PutStatusFave(ctx, fave); err != nil {
		if errors.Is(err, db.ErrAlreadyExists) {
			// The fave already exists in the
			// database, which means we've already
			// handled side effects. We can just
			// return nil here and be done with it.
			return nil
		}
		return gtserror.Newf("db error inserting fave: %w", err)
	}

	f.state.Workers.Federator.Queue.Push(&messages.FromFediAPI{
		APObjectType:   ap.ActivityLike,
		APActivityType: ap.ActivityCreate,
		GTSModel:       fave,
		Receiving:      receivingAcct,
		Requesting:     requestingAcct,
	})

	return nil
}

/*
	FLAG HANDLERS
*/

func (f *federatingDB) activityFlag(ctx context.Context, asType vocab.Type, receivingAccount *gtsmodel.Account, requestingAccount *gtsmodel.Account) error {
	flag, ok := asType.(vocab.ActivityStreamsFlag)
	if !ok {
		return errors.New("activityFlag: could not convert type to flag")
	}

	report, err := f.converter.ASFlagToReport(ctx, flag)
	if err != nil {
		return fmt.Errorf("activityFlag: could not convert Flag to report: %w", err)
	}

	// Requesting account must have at
	// least two domains from the right
	// in common with reporting account.
	if dns.CompareDomainName(
		requestingAccount.Domain,
		report.Account.Domain,
	) < 2 {
		return fmt.Errorf(
			"activityFlag: requesting account %s does not share a domain with Flag Actor account %s",
			requestingAccount.URI, report.Account.URI,
		)
	}

	if report.TargetAccountID != receivingAccount.ID {
		return fmt.Errorf(
			"activityFlag: inbox account %s is not Flag object account %s",
			receivingAccount.URI, report.TargetAccount.URI,
		)
	}

	report.ID = id.NewULID()

	if err := f.state.DB.PutReport(ctx, report); err != nil {
		return fmt.Errorf("activityFlag: database error inserting report: %w", err)
	}

	f.state.Workers.Federator.Queue.Push(&messages.FromFediAPI{
		APObjectType:   ap.ActivityFlag,
		APActivityType: ap.ActivityCreate,
		GTSModel:       report,
		Receiving:      receivingAccount,
		Requesting:     requestingAccount,
	})

	return nil
}