// 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 stream

import (
	"context"
	"errors"
	"fmt"

	"codeberg.org/gruf/go-kv"
	"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/stream"
)

// Open returns a new Stream for the given account, which will contain a channel for passing messages back to the caller.
func (p *Processor) Open(ctx context.Context, account *gtsmodel.Account, streamType string) (*stream.Stream, gtserror.WithCode) {
	l := log.WithContext(ctx).WithFields(kv.Fields{
		{"account", account.ID},
		{"streamType", streamType},
	}...)
	l.Debug("received open stream request")

	var (
		streamID string
		err      error
	)

	// Each stream needs a unique ID so we know to close it.
	streamID, err = id.NewRandomULID()
	if err != nil {
		return nil, gtserror.NewErrorInternalError(fmt.Errorf("error generating stream id: %w", err))
	}

	// Each stream can be subscibed to multiple types.
	// Record them in a set, and include the initial one
	// if it was given to us.
	streamTypes := map[string]any{}
	if streamType != "" {
		streamTypes[streamType] = true
	}

	newStream := &stream.Stream{
		ID:          streamID,
		StreamTypes: streamTypes,
		Messages:    make(chan *stream.Message, 100),
		Hangup:      make(chan interface{}, 1),
		Connected:   true,
	}
	go p.waitToCloseStream(account, newStream)

	v, ok := p.streamMap.Load(account.ID)
	if ok {
		// There is an entry in the streamMap
		// for this account. Parse it out.
		streamsForAccount, ok := v.(*stream.StreamsForAccount)
		if !ok {
			return nil, gtserror.NewErrorInternalError(errors.New("stream map error"))
		}

		// Append new stream to existing entry.
		streamsForAccount.Lock()
		streamsForAccount.Streams = append(streamsForAccount.Streams, newStream)
		streamsForAccount.Unlock()
	} else {
		// There is no entry in the streamMap for
		// this account yet. Create one and store it.
		p.streamMap.Store(account.ID, &stream.StreamsForAccount{
			Streams: []*stream.Stream{
				newStream,
			},
		})
	}

	return newStream, nil
}

// waitToCloseStream waits until the hangup channel is closed for the given stream.
// It then iterates through the map of streams stored by the processor, removes the stream from it,
// and then closes the messages channel of the stream to indicate that the channel should no longer be read from.
func (p *Processor) waitToCloseStream(account *gtsmodel.Account, thisStream *stream.Stream) {
	<-thisStream.Hangup // wait for a hangup message

	// lock the stream to prevent more messages being put in it while we work
	thisStream.Lock()
	defer thisStream.Unlock()

	// indicate the stream is no longer connected
	thisStream.Connected = false

	// load and parse the entry for this account from the stream map
	v, ok := p.streamMap.Load(account.ID)
	if !ok || v == nil {
		return
	}
	streamsForAccount, ok := v.(*stream.StreamsForAccount)
	if !ok {
		return
	}

	// lock the streams for account while we remove this stream from its slice
	streamsForAccount.Lock()
	defer streamsForAccount.Unlock()

	// put everything into modified streams *except* the stream we're removing
	modifiedStreams := []*stream.Stream{}
	for _, s := range streamsForAccount.Streams {
		if s.ID != thisStream.ID {
			modifiedStreams = append(modifiedStreams, s)
		}
	}
	streamsForAccount.Streams = modifiedStreams

	// finally close the messages channel so no more messages can be read from it
	close(thisStream.Messages)
}