/*
   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"
	"fmt"
	"runtime"
	"time"

	"codeberg.org/gruf/go-runners"
	"codeberg.org/gruf/go-store/kv"
	"github.com/robfig/cron/v3"
	"github.com/sirupsen/logrus"
	"github.com/spf13/viper"
	"github.com/superseriousbusiness/gotosocial/internal/config"
	"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 ProcessingMedia 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 a reader containing the media data.
	//
	// postData will be called after data has been called; it can be used to clean up any remaining resources.
	// The provided function can be nil, in which case it will not be executed.
	//
	// 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, postData PostDataCallbackFunc, accountID string, ai *AdditionalMediaInfo) (*ProcessingMedia, error)
	// ProcessEmoji begins the process of decoding and storing the given data as an emoji.
	// It will return a pointer to a ProcessingEmoji 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 a reader containing the emoji data.
	//
	// postData will be called after data has been called; it can be used to clean up any remaining resources.
	// The provided function can be nil, in which case it will not be executed.
	//
	// shortcode should be the emoji shortcode without the ':'s around it.
	//
	// id is the database ID that should be used to store the emoji.
	//
	// uri is the ActivityPub URI/ID of the emoji.
	//
	// ai is optional and can be nil. Any additional information about the emoji provided will be put in the database.
	ProcessEmoji(ctx context.Context, data DataFunc, postData PostDataCallbackFunc, shortcode string, id string, uri string, ai *AdditionalEmojiInfo) (*ProcessingEmoji, error)
	// RecacheMedia refetches, reprocesses, and recaches an existing attachment that has been uncached via pruneRemote.
	RecacheMedia(ctx context.Context, data DataFunc, postData PostDataCallbackFunc, attachmentID string) (*ProcessingMedia, error)
	// PruneRemote prunes all remote media cached on this instance that's older than the given amount of days.
	// 'Pruning' in this context means removing the locally stored data of the attachment (both thumbnail and full size),
	// and setting 'cached' to false on the associated attachment.
	PruneRemote(ctx context.Context, olderThanDays int) (int, 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
	stopCronJobs func() error
	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) {
	// configure the worker pool
	// make sure we always have at least 1 worker even on single-core machines
	numWorkers := runtime.NumCPU() / 2
	if numWorkers == 0 {
		numWorkers = 1
	}
	queueSize := numWorkers * 10

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

	// start the worker pool
	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)

	// start remote cache cleanup cronjob if configured
	cacheCleanupDays := viper.GetInt(config.Keys.MediaRemoteCacheDays)
	if cacheCleanupDays != 0 {
		// we need a way of cancelling running jobs if the media manager is told to stop
		pruneCtx, pruneCancel := context.WithCancel(context.Background())

		// create a new cron instance and add a function to it
		c := cron.New(cron.WithLogger(&logrusWrapper{}))

		pruneFunc := func() {
			begin := time.Now()
			pruned, err := m.PruneRemote(pruneCtx, cacheCleanupDays)
			if err != nil {
				logrus.Errorf("media manager: error pruning remote cache: %s", err)
				return
			}
			logrus.Infof("media manager: pruned %d remote cache entries in %s", pruned, time.Since(begin))
		}

		// run every night
		entryID, err := c.AddFunc("@midnight", pruneFunc)
		if err != nil {
			pruneCancel()
			return nil, fmt.Errorf("error starting media manager remote cache cleanup job: %s", err)
		}

		// since we're running a cron job, we should define how the manager should stop them
		m.stopCronJobs = func() error {
			// try to stop any jobs gracefully by waiting til they're finished
			cronCtx := c.Stop()

			select {
			case <-cronCtx.Done():
				logrus.Infof("media manager: cron finished jobs and stopped gracefully")
			case <-time.After(1 * time.Minute):
				logrus.Infof("media manager: cron didn't stop after 60 seconds, will force close")
				break
			}

			// whether the job is finished neatly or we had to wait a minute, cancel the context on the prune job
			pruneCancel()
			return nil
		}

		// Run an initial cache prune in case max age changed
		logrus.Infof("media manager: running initial remote cache cleanup")
		go pruneFunc()

		// now start all the cron stuff we've lined up
		c.Start()
		logrus.Infof("media manager: next scheduled remote cache cleanup is %q", c.Entry(entryID).Next)
	}

	return m, nil
}

func (m *manager) ProcessMedia(ctx context.Context, data DataFunc, postData PostDataCallbackFunc, accountID string, ai *AdditionalMediaInfo) (*ProcessingMedia, error) {
	processingMedia, err := m.preProcessMedia(ctx, data, postData, 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, postData PostDataCallbackFunc, shortcode string, id string, uri string, ai *AdditionalEmojiInfo) (*ProcessingEmoji, error) {
	processingEmoji, err := m.preProcessEmoji(ctx, data, postData, shortcode, id, uri, 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) RecacheMedia(ctx context.Context, data DataFunc, postData PostDataCallbackFunc, attachmentID string) (*ProcessingMedia, error) {
	processingRecache, err := m.preProcessRecache(ctx, data, postData, attachmentID)
	if err != nil {
		return nil, err
	}

	logrus.Tracef("RecacheMedia: about to enqueue recache with attachmentID %s, queue length is %d", processingRecache.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 := processingRecache.LoadAttachment(innerCtx); err != nil {
				logrus.Errorf("RecacheMedia: error processing recache with attachmentID %s: %s", processingRecache.AttachmentID(), err)
			}
		}
	})
	logrus.Tracef("RecacheMedia: succesfully queued recache with attachmentID %s, queue length is %d", processingRecache.AttachmentID(), m.pool.Queue())

	return processingRecache, 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")
	if !m.pool.Stop() {
		return errors.New("could not stop media manager worker pool")
	}

	if m.stopCronJobs != nil { // only defined if cron jobs are actually running
		logrus.Info("stopping media manager cache cleanup jobs")
		return m.stopCronJobs()
	}

	return nil
}