// SPDX-FileCopyrightText: 2020 Luke Granger-Brown <depot@lukegb.com>
//
// SPDX-License-Identifier: Apache-2.0
package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"net/url"
	"os"
	"os/signal"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/dghubble/oauth1"
	"github.com/jackc/pgtype"
	"github.com/jackc/pgx/v4"
	"github.com/jackc/pgx/v4/pgxpool"
)

var (
	databaseURL  = flag.String("database_url", "", "Database URL")
	tickInterval = flag.Duration("tick_interval", 1*time.Minute, "Tick interval")
	workerCount  = flag.Int("workers", 20, "Workers to spawn for fetching info from Twitter API")
	workAtOnce   = flag.Int("work_at_once", 40, "Work to enqueue at once (i.e. we will only look for this much work to do).")

	mediaFetchDestination = flag.String("media_fetch_destination", "/tmp", "Path to write fetched media to.")
	mediaTickInterval     = flag.Duration("media_tick_interval", 0, "Tick interval for media - takes priority over --tick_interval if non-zero.")
	mediaWorkAtOnce       = flag.Int("media_work_at_once", 0, "Work to enqueue at once for media - takes priority over --work_at_once if non-zero.")

	relatedTickInterval = flag.Duration("related_tick_interval", 0, "Tick interval for related - takes priority over --tick_interval if non-zero.")
	relatedWorkAtOnce   = flag.Int("related_work_at_once", 200, "Work to enqueue at once for related - takes priority over --work_at_once if non-zero.")
	relatedMaxFetch     = flag.Int("related_max_fetch", 900/15, "Cap of tweets to try to fetch at once.")
)

type WorkerConfig struct {
	Name string

	TickInterval time.Duration
	OAuthConfig  *oauth1.Config
	WorkAtOnce   int
	DatabasePool *pgxpool.Pool

	WorkQueue chan func(context.Context)
}

func (wc WorkerConfig) Merge(other WorkerConfig) WorkerConfig {
	if other.Name != "" {
		wc.Name = other.Name
	}
	if other.TickInterval > 0 {
		wc.TickInterval = other.TickInterval
	}
	if other.OAuthConfig != nil {
		wc.OAuthConfig = other.OAuthConfig
	}
	if other.WorkAtOnce != 0 {
		wc.WorkAtOnce = other.WorkAtOnce
	}
	if other.DatabasePool != nil {
		wc.DatabasePool = other.DatabasePool
	}
	if other.WorkQueue != nil {
		wc.WorkQueue = other.WorkQueue
	}
	return wc
}

type worker func(context.Context, WorkerConfig) error

type tweetVideoVariant struct {
	Bitrate     int    `json:"bitrate"`
	ContentType string `json:"content_type"`
	URL         string `json:"url"`
}

type tweetVideoInfo struct {
	Variants []tweetVideoVariant `json:"variants"`
}

type tweetExtendedMedia struct {
	ID            int64           `json:"id"`
	Type          string          `json:"type"`
	MediaURLHTTPS string          `json:"media_url_https"`
	VideoInfo     *tweetVideoInfo `json:"video_info"`
}

type tweetExtendedEntities struct {
	Media []tweetExtendedMedia `json:"media"`
}

type tweetData struct {
	ID                int64                 `json:"id"`
	Text              string                `json:"full_text"`
	QuotedStatus      *tweetData            `json:"quoted_status"`
	RetweetedStatus   *tweetData            `json:"retweeted_status"`
	InReplyToStatusID *int64                `json:"in_reply_to_status_id"`
	ExtendedEntities  tweetExtendedEntities `json:"extended_entities"`

	Data json.RawMessage `json:"-"`
}

func mediaFetchOutputPath(u string) (string, error) {
	p, err := url.Parse(u)
	if err != nil {
		return "", err
	}
	path := strings.TrimLeft(p.Path, "/")

	return filepath.Join(*mediaFetchDestination, p.Host, path), nil
}

type databaseQuerier interface {
	Query(context.Context, string, ...interface{}) (pgx.Rows, error)
}

func fetchTweets(ctx context.Context, conn databaseQuerier, query string, args ...interface{}) ([]tweetData, error) {
	rows, err := conn.Query(ctx, query, args...)
	if err != nil {
		return nil, fmt.Errorf("querying: %w", err)
	}

	var tweets []tweetData
	for rows.Next() {
		var tweetJSON pgtype.JSONB
		if err := rows.Scan(&tweetJSON); err != nil {
			return nil, fmt.Errorf("scanning: %w", err)
		}

		var tweet tweetData
		if err := json.Unmarshal(tweetJSON.Bytes, &tweet); err != nil {
			return nil, fmt.Errorf("unmarshaling: %w", err)
		}
		tweets = append(tweets, tweet)
	}
	if rows.Err() != nil {
		return nil, fmt.Errorf("retrieving: %w", err)
	}
	return tweets, nil
}

func mediaFetchTick(ctx context.Context, cfg WorkerConfig) error {
	tweets, err := fetchTweets(ctx, cfg.DatabasePool, "SELECT object FROM tweets WHERE NOT fetched_media LIMIT $1", cfg.WorkAtOnce)
	if err != nil {
		return fmt.Errorf("fetching unfetched media tweet IDs: %w", err)
	}
	var ids []int64
	for _, t := range tweets {
		ids = append(ids, t.ID)
	}
	log.Printf("[%v] Got %d tweets (%v)", cfg.Name, len(tweets), ids)

	var wg sync.WaitGroup
	wg.Add(len(tweets))
	for _, t := range tweets {
		t := t
		cfg.WorkQueue <- func(ctx context.Context) {
			defer wg.Done()

			// Abbreviated message for tweets with no media, which is the majority of them.
			if len(t.ExtendedEntities.Media) == 0 {
				if _, err := cfg.DatabasePool.Exec(ctx, "UPDATE tweets SET fetched_media=true WHERE id=$1", t.ID); err != nil {
					log.Printf("[%v:%d] Failed to update tweets table: %v", cfg.Name, t.ID, err)
				}
				log.Printf("[%v:%d] No media", cfg.Name, t.ID)
				return
			}

			log.Printf("[%v:%d] Starting work", cfg.Name, t.ID)
			defer log.Printf("[%v:%d] Done with work", cfg.Name, t.ID)

			var mediaURLs []string
			for _, m := range t.ExtendedEntities.Media {
				if m.MediaURLHTTPS != "" {
					mediaURLs = append(mediaURLs, m.MediaURLHTTPS)
				}
				if m.VideoInfo != nil {
					bestBitrate := -1
					var bestURL string
					for _, v := range m.VideoInfo.Variants {
						if v.ContentType == "application/x-mpegURL" {
							// m3u8 isn't very interesting since we'd have to parse it to get a playlist.
							continue
						}
						if v.Bitrate > bestBitrate {
							bestBitrate = v.Bitrate
							bestURL = v.URL
						}
					}
					if bestURL != "" {
						mediaURLs = append(mediaURLs, bestURL)
					}
				}
			}

			log.Printf("[%v:%d] %d media URLs to fetch: %v", cfg.Name, t.ID, len(mediaURLs), mediaURLs)
			for _, u := range mediaURLs {
				out, err := mediaFetchOutputPath(u)
				if err != nil {
					log.Printf("[%v:%d:%v] fetching output path: %v", cfg.Name, t.ID, u, err)
					return
				}

				// Fetch u -> out
				if fi, err := os.Stat(out); err == nil {
					// File already exists, does it have non-zero size?
					if fi.Size() > 0 {
						// It does!
						log.Printf("[%v:%d:%v] %v already exists; skipping", cfg.Name, t.ID, u, out)
						continue
					}
					log.Printf("[%v:%d:%v] %v already exists but has zero size; refetching", cfg.Name, t.ID, u, out)
				} else if !os.IsNotExist(err) {
					log.Printf("[%v:%d:%v] checking output path %v: %v", cfg.Name, t.ID, u, out, err)
					return
				}

				if err := os.MkdirAll(filepath.Dir(out), 0755); err != nil {
					log.Printf("[%v:%d:%v] creating output path %v: %v", cfg.Name, t.ID, u, out, err)
					return
				}

				if err := func() error {
					resp, err := http.Get(u)
					if err != nil {
						return fmt.Errorf("http.Get: %w", err)
					}
					defer resp.Body.Close()

					switch resp.StatusCode {
					case http.StatusOK:
						break // This is what we expect.
					case http.StatusNotFound, http.StatusForbidden:
						log.Printf("[%v:%d:%v] got a %d; marking as successful since this has probably been deleted.", cfg.Name, t.ID, u, resp.StatusCode)
						return nil
					default:
						return fmt.Errorf("HTTP status %d - %v", resp.StatusCode, resp.Status)
					}

					f, err := os.Create(out)
					if err != nil {
						return err
					}
					defer f.Close()

					written, err := io.Copy(f, resp.Body)
					if err != nil {
						// Try to delete the file we created to force a refetch next time.
						_ = f.Truncate(0) // Ignore the error, though.
						return fmt.Errorf("IO error: %w", err)
					}
					log.Printf("[%v:%d:%v] downloaded %d bytes.", cfg.Name, t.ID, u, written)

					return nil
				}(); err != nil {
					log.Printf("[%v:%d:%v] %v", cfg.Name, t.ID, u, err)
					return
				}
			}
			log.Printf("[%v:%d] Done downloading media, marking as complete.", cfg.Name, t.ID)

			if _, err := cfg.DatabasePool.Exec(ctx, "UPDATE tweets SET fetched_media=true WHERE id=$1", t.ID); err != nil {
				log.Printf("[%v:%d] Failed to update tweets table: %v", cfg.Name, t.ID, err)
			}
		}
	}
	wg.Wait()
	log.Printf("[%v] Done with work.", cfg.Name)

	return nil
}

func relatedFetchTick(ctx context.Context, cfg WorkerConfig) error {
	tweets, err := fetchTweets(ctx, cfg.DatabasePool, "SELECT object FROM tweets WHERE NOT fetched_related_tweets LIMIT $1", cfg.WorkAtOnce)
	if err != nil {
		return fmt.Errorf("fetching unfetched related tweet IDs: %w", err)
	}
	var ids []int64
	for _, t := range tweets {
		ids = append(ids, t.ID)
	}
	log.Printf("[%v] Got %d tweets (%v)", cfg.Name, len(tweets), ids)

	fetchLimited := make(chan struct{}, *relatedMaxFetch)
	for i := 0; i < *relatedMaxFetch; i++ {
		fetchLimited <- struct{}{}
	}
	close(fetchLimited)

	var wg sync.WaitGroup
	for _, t := range tweets {
		var tweetIDsToFetch []int64
		if t.QuotedStatus != nil {
			tweetIDsToFetch = append(tweetIDsToFetch, t.QuotedStatus.ID)
		}
		if t.RetweetedStatus != nil {
			tweetIDsToFetch = append(tweetIDsToFetch, t.RetweetedStatus.ID)
		}
		if t.InReplyToStatusID != nil {
			tweetIDsToFetch = append(tweetIDsToFetch, *t.InReplyToStatusID)
		}

		log.Printf("[%v:%d] Got %d tweets to fetch (%v)", cfg.Name, t.ID, len(tweetIDsToFetch), tweetIDsToFetch)
		if len(tweetIDsToFetch) == 0 {
			if _, err := cfg.DatabasePool.Exec(ctx, "UPDATE tweets SET fetched_related_tweets=true WHERE id=$1", t.ID); err != nil {
				log.Printf("[%v:%d] Updating tweet to mark as completed: %v", cfg.Name, t.ID, err)
			} else {
				log.Printf("[%v:%d] Successfully marked as done (no tweets to fetch).", cfg.Name, t.ID)
			}
			continue
		}

		wg.Add(1)
		t := t
		cfg.WorkQueue <- func(ctx context.Context) {
			defer wg.Done()

			// Fetch user credentials for this.
			// TODO(lukegb): maybe this needs to be smarter (e.g. for protected accounts?), but for now we just pick someone who could see the original tweet.
			var accessToken, accessSecret string
			if err := cfg.DatabasePool.QueryRow(ctx, "SELECT ua.access_token, ua.access_secret FROM user_accounts ua INNER JOIN user_accounts_tweets uat ON uat.userid=ua.userid WHERE uat.tweetid=$1 LIMIT 1", t.ID).Scan(&accessToken, &accessSecret); err != nil {
				log.Printf("[%v:%d] Retrieving OAuth user credentials: %v", cfg.Name, t.ID, err)
				return
			}
			httpClient := cfg.OAuthConfig.Client(ctx, oauth1.NewToken(accessToken, accessSecret))

			for _, tid := range tweetIDsToFetch {
				// Check if we already have tid.
				log.Printf("[%v:%d] Fetching %d", cfg.Name, t.ID, tid)

				var cnt int
				if err := cfg.DatabasePool.QueryRow(ctx, "SELECT COUNT(1) FROM tweets WHERE id=$1", tid).Scan(&cnt); err != nil {
					log.Printf("[%v:%d:%d] Existence check failed: %v", cfg.Name, t.ID, tid, err)
					return
				}
				if cnt > 0 {
					log.Printf("[%v:%d] Already have %d", cfg.Name, t.ID, tid)
					continue
				}

				if _, ok := <-fetchLimited; !ok {
					log.Printf("[%v:%d] Out of fetch tokens", cfg.Name, t.ID)
					break
				}

				// We don't have it already; let's fetch it from ze Twitterz.
				req, err := http.NewRequest("GET", fmt.Sprintf("https://api.twitter.com/1.1/statuses/show.json?id=%d&include_entities=true&include_ext_alt_text=true", tid), nil)
				if err != nil {
					log.Printf("[%v:%d:%d] Constructing GET request: %v", cfg.Name, t.ID, tid, err)
					return
				}
				resp, err := httpClient.Do(req.WithContext(ctx))
				if err != nil {
					log.Printf("[%v:%d:%d] Executing GET request: %v", cfg.Name, t.ID, tid, err)
					return
				}
				defer resp.Body.Close()
				switch resp.StatusCode {
				case http.StatusOK:
					// Expected.
					break
				case http.StatusNotFound:
					// Tweet has probably been deleted, or is otherwise ACLed.
					log.Printf("[%v:%d:%d] Not found response; assuming that it's been deleted and treating as a success.", cfg.Name, t.ID, tid)
					continue
				default:
					log.Printf("[%v:%d:%d] GET statuses/show.json returned %d - %v", cfg.Name, t.ID, tid, resp.StatusCode, resp.Status)
					return
				}

				tweetBytes, err := ioutil.ReadAll(resp.Body)
				if err != nil {
					log.Printf("[%v:%d:%d] ReadAll: %v", cfg.Name, t.ID, tid, err)
					return
				}
				var subtweet tweetData
				if err := json.Unmarshal(tweetBytes, &subtweet); err != nil {
					log.Printf("[%v:%d:%d] Decoding tweet as JSON: %v", cfg.Name, t.ID, tid, err)
					return
				}

				// Insert it into the database.
				if _, err := cfg.DatabasePool.Exec(ctx, "INSERT INTO tweets (id, text, object) VALUES ($1, $2, $3) ON CONFLICT DO NOTHING", subtweet.ID, subtweet.Text, tweetBytes); err != nil {
					log.Printf("[%v:%d:%d] Inserting tweet into database: %v", cfg.Name, t.ID, tid, err)
					return
				}

				// Insert the ACLs.
				if _, err := cfg.DatabasePool.Exec(ctx, "INSERT INTO user_accounts_tweets SELECT userid, $1 tweetid, false on_timeline FROM user_accounts_tweets WHERE tweetid=$2 ON CONFLICT DO NOTHING", tid, t.ID); err != nil {
					log.Printf("[%v:%d:%d] Inserting ACLs into table failed: %v", cfg.Name, t.ID, tid, err)
					return
				}
			}

			// We have fetched all the subtweets, mark the tweet as complete.
			if _, err := cfg.DatabasePool.Exec(ctx, "UPDATE tweets SET fetched_related_tweets=true WHERE id=$1", t.ID); err != nil {
				log.Printf("[%v:%d] Updating tweet to mark as completed: %v", cfg.Name, t.ID, err)
			} else {
				log.Printf("[%v:%d] Successfully processed.", cfg.Name, t.ID)
			}
		}
	}
	wg.Wait()
	log.Printf("[%v] Done with work.", cfg.Name)

	return nil
}

func tickToWorker(w worker) worker {
	return func(ctx context.Context, cfg WorkerConfig) error {
		log.Printf("[%v] Performing initial tick.", cfg.Name)
		if err := w(ctx, cfg); err != nil {
			log.Printf("[%v] Initial tick failed: %v", cfg.Name, err)
		}
		t := time.NewTicker(cfg.TickInterval)
		defer t.Stop()
		for {
			select {
			case <-ctx.Done():
				return nil
			case <-t.C:
				log.Printf("[%v] Tick...", cfg.Name)
				if err := w(ctx, cfg); err != nil {
					log.Printf("[%v] Tick failed: %v", cfg.Name, err)
				}
			}
		}
	}
}

var (
	mediaFetchWorker   = tickToWorker(mediaFetchTick)
	relatedFetchWorker = tickToWorker(relatedFetchTick)
)

func main() {
	flag.Parse()

	ctx := context.Background()

	conn, err := pgxpool.Connect(ctx, *databaseURL)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Unable to connect to database: %v\n", err)
		os.Exit(1)
	}
	defer conn.Close()

	ckey, csecret := os.Getenv("TWITTER_OAUTH_CONSUMER_KEY"), os.Getenv("TWITTER_OAUTH_CONSUMER_SECRET")
	if ckey == "" || csecret == "" {
		fmt.Fprintf(os.Stderr, "No TWITTER_OAUTH_CONSUMER_KEY or TWITTER_OAUTH_CONSUMER_SECRET\n")
		os.Exit(1)
	}
	twitterOAuthConfig := oauth1.NewConfig(ckey, csecret)

	stop := func() <-chan struct{} {
		st := make(chan os.Signal)
		signal.Notify(st, os.Interrupt)
		stopCh := make(chan struct{})
		go func() {
			<-st
			log.Printf("Shutting down")
			close(stopCh)
			signal.Reset(os.Interrupt)
		}()
		return stopCh
	}()
	cctx, cancel := context.WithCancel(ctx)
	var wg sync.WaitGroup

	workQueue := make(chan func(context.Context))
	wg.Add(*workerCount)
	for n := 0; n < *workerCount; n++ {
		go func() {
			ctx := cctx
			defer wg.Done()
			for {
				select {
				case <-ctx.Done():
					return
				case f := <-workQueue:
					f(ctx)
				}
			}
		}()
	}

	workers := map[string]worker{
		"media":   mediaFetchWorker,
		"related": relatedFetchWorker,
	}
	wg.Add(len(workers))
	cfg := WorkerConfig{
		TickInterval: *tickInterval,
		OAuthConfig:  twitterOAuthConfig,
		WorkAtOnce:   *workAtOnce,

		DatabasePool: conn,
		WorkQueue:    workQueue,
	}
	configs := map[string]WorkerConfig{
		"media": cfg.Merge(WorkerConfig{
			Name:         "media",
			TickInterval: *mediaTickInterval,
			WorkAtOnce:   *mediaWorkAtOnce,
		}),
		"related": cfg.Merge(WorkerConfig{
			Name:         "related",
			TickInterval: *relatedTickInterval,
			WorkAtOnce:   *relatedWorkAtOnce,
		}),
	}
	for wn, w := range workers {
		wn, w := wn, w
		wcfg, ok := configs[wn]
		if !ok {
			wcfg = cfg
		}
		go func() {
			defer wg.Done()
			log.Printf("Starting worker %v.", wn)
			if err := w(cctx, wcfg); err != nil {
				log.Printf("[%v] %v", wn, err)
			}
		}()
	}

	<-stop
	log.Printf("Got stop signal. Shutting down...")
	cancel()
	wg.Wait()
}