package gemini

import (
	"errors"
	"fmt"
	"strings"
	"time"

	"gemini-grc/config"
	"gemini-grc/logging"
	"gemini-grc/util"

	"github.com/guregu/null/v5"
	"github.com/jmoiron/sqlx"
)

func SpawnWorkers(numOfWorkers int, db *sqlx.DB) {
	logging.LogInfo("Spawning %d workers", numOfWorkers)
	for i := range numOfWorkers {
		go func(i int) {
			for {
				RunWorker(i, db, nil)
			}
		}(i)
	}
}

func RunWorker(id int, db *sqlx.DB, url *string) {
	// Each worker runs within a DB transaction.
	tx, err := db.Beginx()
	if err != nil {
		logging.LogError("Failed to begin transaction: %w", err)
	}

	// Commit/rollback at the end
	defer func() {
		err = tx.Commit()
		if err != nil {
			logging.LogError("[%d] Failed to commit transaction: %w", id, err)
			err := tx.Rollback()
			if err != nil {
				panic(fmt.Sprintf("[%d] Failed to roll back transaction: %v", id, err))
			}
		}
	}()

	var snapshots []Snapshot

	// If not given a specific URL,
	// get some random ones to visit from DB.
	if url == nil {
		snapshots, err = GetRandomSnapshotsDistinctHosts(tx)
		if err != nil {
			logging.LogError("[%d] GeminiError retrieving snapshot: %w", id, err)
			panic("This should never happen")
		} else if len(snapshots) == 0 {
			logging.LogInfo("[%d] No snapshots to visit.", id)
			time.Sleep(1 * time.Minute)
			return
		}
	} else {
		snapshotURL, err := ParseURL(*url, "")
		if err != nil {
			logging.LogError("Invalid URL given: " + *url)
			return

		}
		snapshots = []Snapshot{{
			//UID:       uid.UID(),
			URL:       *snapshotURL,
			Host:      snapshotURL.Hostname,
			Timestamp: null.TimeFrom(time.Now()),
		}}
	}

	// Start visiting URLs.
	total := len(snapshots)
	for i, s := range snapshots {
		logging.LogInfo("[%d] Starting %d/%d %s", id, i+1, total, s.URL.String())
		// We differentiate between errors:
		// Unexpected errors are the ones returned from the following function.
		// If an error is unexpected (which should never happen) we panic.
		// Expected errors are stored as strings within the snapshot,
		// so that they can also be stored in DB.
		err = workOnSnapshot(id, tx, &s)
		if err != nil {
			logging.LogError("[%d] [%s] Unexpected GeminiError %w", id, s.URL.String(), err)
			util.PrintStackAndPanic(err)
		}
		if s.Error.Valid {
			logging.LogWarn("[%d] Error: %v", id, s.Error.String)
		}
		logging.LogDebug("[%d] Done %d/%d.", id, i+1, total)
	}
	logging.LogInfo("[%d] Worker done.", id)
}

// workOnSnapshot visits a URL and stores the result.
// errors should be returned only if they are unexpected.
func workOnSnapshot(id int, tx *sqlx.Tx, s *Snapshot) (err error) {
	if IsBlacklisted(s.URL) {
		logging.LogInfo("[%d] URL matches Blacklist, ignoring %s", id, s.URL.String())
		return nil
	}

	// If URL matches a robots.txt disallow line,
	// add it as an error so next time it won't be
	// crawled.
	if RobotMatch(s.URL) {
		s.Error = null.StringFrom(ErrGeminiRobotsDisallowed.Error())
		err = UpsertSnapshot(id, tx, s)
		if err != nil {
			return fmt.Errorf("[%d] %w", id, err)
		}
		return nil
	}

	// Resolve IP address via DNS
	IPs, err := getHostIPAddresses(s.Host)
	if err != nil {
		s.Error = null.StringFrom(err.Error())
		err = UpsertSnapshot(id, tx, s)
		if err != nil {
			return fmt.Errorf("[%d] %w", id, err)
		}
		return nil
	}

	// If the host's ip is in the connections pool we stop
	IpPool.Lock.RLock()
	logging.LogDebug("[%d] [%s] Checking pool for IP", id, s.URL.String())
	for _, ip := range IPs {
		_, ok := IpPool.IPs[ip]
		if ok {
			logging.LogDebug("[%d] Another worker is visiting this host: %s", id, s.URL.String())
			IpPool.Lock.RUnlock()
			time.Sleep(1 * time.Second) // Avoid flood-retrying
			return nil
		}
	}
	IpPool.Lock.RUnlock()

	AddIPsToPool(IPs)

	// After finishing, remove the host IPs from
	// the connections pool, with a small delay
	// to avoid potentially hitting the same IP quickly.
	defer func() {
		time.Sleep(5 * time.Second)
		RemoveIPsFromPool(IPs)
	}()

	url := s.URL.String()
	logging.LogDebug("[%d] Dialing %s", id, url)

	err = Visit(s)
	if err != nil {
		if !IsKnownError(err) {
			logging.LogError("[%d] Unknown error visiting %s: %w", id, url, err)
			return err
		}
		// Check if error is redirection, and handle it
		s.Error = null.StringFrom(err.Error())
		if errors.As(err, new(*GeminiError)) &&
			err.(*GeminiError).Msg == "redirect" {
			err = handleRedirection(id, tx, s)
			if err != nil {
				return err
			}
		}
	}
	logging.LogInfo("[%d] Done, response code %d.", id, s.ResponseCode.ValueOrZero())

	// If this is a gemini page, parse possible links inside
	if !s.Error.Valid && s.MimeType.Valid && s.MimeType.String == "text/gemini" {
		links := GetPageLinks(s.URL, s.GemText.String)
		logging.LogDebug("[%d] Found %d links", id, len(links))
		if len(links) > 0 {
			s.Links = null.ValueFrom(links)
		}
	} else {
		logging.LogDebug("[%d] Not looking for page links", id)
	}

	err = UpsertSnapshot(id, tx, s)
	if err != nil {
		return err
	}

	err = storeLinks(tx, s)
	if err != nil {
		return err
	}
	return nil
}

func storeLinks(tx *sqlx.Tx, s *Snapshot) error {
	if s.Links.Valid {
		var batchSnapshots []*Snapshot
		for _, link := range s.Links.ValueOrZero() {
			if shouldPersistURL(link) {
				newSnapshot := &Snapshot{
					//UID:       uid.UID(),
					URL:       link,
					Host:      link.Hostname,
					Timestamp: null.TimeFrom(time.Now()),
				}
				batchSnapshots = append(batchSnapshots, newSnapshot)
			}
		}

		if len(batchSnapshots) > 0 {
			err := SaveLinksToDBinBatches(tx, batchSnapshots)
			if err != nil {
				return err
			}
		}
	}
	return nil
}

// shouldPersistURL returns true if we
// should save the URL in the DB.
// Only gemini:// urls are saved.
func shouldPersistURL(u URL) bool {
	return strings.HasPrefix(u.String(), "gemini://")
}

func handleRedirection(id int, tx *sqlx.Tx, s *Snapshot) error {
	newURL, err := extractRedirectTarget(s.URL, s.Error.ValueOrZero())
	if err != nil {
		return err
	}
	logging.LogDebug("[%d] Page redirects to %s", id, newURL)
	// Insert fresh snapshot with new URL
	snapshot := &Snapshot{
		//UID:       uid.UID(),
		URL:       *newURL,
		Host:      newURL.Hostname,
		Timestamp: null.TimeFrom(time.Now()),
	}
	logging.LogDebug("[%d] Saving empty snapshot for %s", id, snapshot.URL.String())
	err = SaveSnapshotIfNew(tx, snapshot)
	if err != nil {
		return err
	}
	return nil
}

func GetRandomSnapshotsDistinctHosts(tx *sqlx.Tx) ([]Snapshot, error) {
	// Old, unoptimized query

	// query := `
	//     SELECT DISTINCT ON (host) *
	//     FROM snapshots
	//     WHERE response_code IS NULL
	//       AND error IS NULL
	//     ORDER BY host, RANDOM()
	//     LIMIT $1
	// `
	query := `
	    SELECT *
	    FROM snapshots
	    WHERE response_code IS NULL
	      AND error IS NULL
	    ORDER BY RANDOM()
	    LIMIT $1
	`
	//query := `
	//    WITH RankedSnapshots AS (
	//        SELECT id, url, host, timestamp, mimetype, data, gemtext,
	//               links, lang, response_code, error,
	//               ROW_NUMBER() OVER (PARTITION BY host ORDER BY RANDOM()) as rn
	//        FROM snapshots
	//        WHERE response_code IS NULL
	//          AND error IS NULL
	//    )
	//    SELECT id, url, host, timestamp, mimetype, data, gemtext,
	//           links, lang, response_code, error
	//    FROM RankedSnapshots
	//    WHERE rn = 1
	//    LIMIT $1
	//`
	var snapshots []Snapshot
	err := tx.Select(&snapshots, query, config.CONFIG.WorkerBatchSize)
	if err != nil {
		return nil, err
	}
	return snapshots, nil
}

func GetSnapshotFromURL(tx *sqlx.Tx, url string) ([]Snapshot, error) {
	query := `
	SELECT *
	FROM snapshots
	WHERE url=$1
	LIMIT 1
	`
	var snapshots []Snapshot
	err := tx.Select(&snapshots, query, url)
	if err != nil {
		return nil, err
	}
	return snapshots, nil
}