/*
   GoToSocial
   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org

   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 media

import (
	"context"
	"errors"
	"runtime"

	"codeberg.org/gruf/go-runners"
	"codeberg.org/gruf/go-store/kv"
	"github.com/sirupsen/logrus"
	"github.com/superseriousbusiness/gotosocial/internal/db"
)

// Manager provides an interface for managing media: parsing, storing, and retrieving media objects like photos, videos, and gifs.
type Manager interface {
	// ProcessMedia begins the process of decoding and storing the given data as an attachment.
	// It will return a pointer to a Media struct upon which further actions can be performed, such as getting
	// the finished media, thumbnail, attachment, etc.
	//
	// data should be a function that the media manager can call to return raw bytes of a piece of media.
	//
	// accountID should be the account that the media belongs to.
	//
	// ai is optional and can be nil. Any additional information about the attachment provided will be put in the database.
	ProcessMedia(ctx context.Context, data DataFunc, accountID string, ai *AdditionalMediaInfo) (*ProcessingMedia, error)
	ProcessEmoji(ctx context.Context, data DataFunc, shortcode string, ai *AdditionalEmojiInfo) (*ProcessingEmoji, error)
	// NumWorkers returns the total number of workers available to this manager.
	NumWorkers() int
	// QueueSize returns the total capacity of the queue.
	QueueSize() int
	// JobsQueued returns the number of jobs currently in the task queue.
	JobsQueued() int
	// ActiveWorkers returns the number of workers currently performing jobs.
	ActiveWorkers() int
	// Stop stops the underlying worker pool of the manager. It should be called
	// when closing GoToSocial in order to cleanly finish any in-progress jobs.
	// It will block until workers are finished processing.
	Stop() error
}

type manager struct {
	db         db.DB
	storage    *kv.KVStore
	pool       runners.WorkerPool
	numWorkers int
	queueSize  int
}

// NewManager returns a media manager with the given db and underlying storage.
//
// A worker pool will also be initialized for the manager, to ensure that only
// a limited number of media will be processed in parallel.
//
// The number of workers will be the number of CPUs available to the Go runtime,
// divided by 2 (rounding down, but always at least 1).
//
// The length of the queue will be the number of workers multiplied by 10.
//
// So for an 8 core machine, the media manager will get 4 workers, and a queue of length 40.
// For a 4 core machine, this will be 2 workers, and a queue length of 20.
// For a single or 2-core machine, the media manager will get 1 worker, and a queue of length 10.
func NewManager(database db.DB, storage *kv.KVStore) (Manager, error) {
	numWorkers := runtime.NumCPU() / 2
	// make sure we always have at least 1 worker even on single-core machines
	if numWorkers == 0 {
		numWorkers = 1
	}
	queueSize := numWorkers * 10

	m := &manager{
		db:         database,
		storage:    storage,
		pool:       runners.NewWorkerPool(numWorkers, queueSize),
		numWorkers: numWorkers,
		queueSize:  queueSize,
	}

	if start := m.pool.Start(); !start {
		return nil, errors.New("could not start worker pool")
	}
	logrus.Debugf("started media manager worker pool with %d workers and queue capacity of %d", numWorkers, queueSize)

	return m, nil
}

func (m *manager) ProcessMedia(ctx context.Context, data DataFunc, accountID string, ai *AdditionalMediaInfo) (*ProcessingMedia, error) {
	processingMedia, err := m.preProcessMedia(ctx, data, accountID, ai)
	if err != nil {
		return nil, err
	}

	logrus.Tracef("ProcessMedia: about to enqueue media with attachmentID %s, queue length is %d", processingMedia.AttachmentID(), m.pool.Queue())
	m.pool.Enqueue(func(innerCtx context.Context) {
		select {
		case <-innerCtx.Done():
			// if the inner context is done that means the worker pool is closing, so we should just return
			return
		default:
			// start loading the media already for the caller's convenience
			if _, err := processingMedia.LoadAttachment(innerCtx); err != nil {
				logrus.Errorf("ProcessMedia: error processing media with attachmentID %s: %s", processingMedia.AttachmentID(), err)
			}
		}
	})
	logrus.Tracef("ProcessMedia: succesfully queued media with attachmentID %s, queue length is %d", processingMedia.AttachmentID(), m.pool.Queue())

	return processingMedia, nil
}

func (m *manager) ProcessEmoji(ctx context.Context, data DataFunc, shortcode string, ai *AdditionalEmojiInfo) (*ProcessingEmoji, error) {
	processingEmoji, err := m.preProcessEmoji(ctx, data, shortcode, ai)
	if err != nil {
		return nil, err
	}

	logrus.Tracef("ProcessEmoji: about to enqueue emoji with id %s, queue length is %d", processingEmoji.EmojiID(), m.pool.Queue())
	m.pool.Enqueue(func(innerCtx context.Context) {
		select {
		case <-innerCtx.Done():
			// if the inner context is done that means the worker pool is closing, so we should just return
			return
		default:
			// start loading the emoji already for the caller's convenience
			if _, err := processingEmoji.LoadEmoji(innerCtx); err != nil {
				logrus.Errorf("ProcessEmoji: error processing emoji with id %s: %s", processingEmoji.EmojiID(), err)
			}
		}
	})
	logrus.Tracef("ProcessEmoji: succesfully queued emoji with id %s, queue length is %d", processingEmoji.EmojiID(), m.pool.Queue())

	return processingEmoji, nil
}

func (m *manager) NumWorkers() int {
	return m.numWorkers
}

func (m *manager) QueueSize() int {
	return m.queueSize
}

func (m *manager) JobsQueued() int {
	return m.pool.Queue()
}

func (m *manager) ActiveWorkers() int {
	return m.pool.Workers()
}

func (m *manager) Stop() error {
	logrus.Info("stopping media manager worker pool")

	stopped := m.pool.Stop()
	if !stopped {
		return errors.New("could not stop media manager worker pool")
	}
	return nil
}