package store

import (
	"context"
	"fmt"
	"time"

	"github.com/gorilla/sessions"
)

var defaultInterval = time.Minute * 5

// Cleanup runs a background goroutine every interval that deletes expired
// sessions from the database.
func (db *PGStore) Cleanup(interval time.Duration) (chan<- struct{}, <-chan struct{}) {
	if interval <= 0 {
		interval = defaultInterval
	}

	quit, done := make(chan struct{}), make(chan struct{})
	go db.cleanup(interval, quit, done)
	return quit, done
}

// StopCleanup stops the background cleanup from running.
func (db *PGStore) StopCleanup(quit chan<- struct{}, done <-chan struct{}) {
	quit <- struct{}{}
	<-done
}

// cleanup deletes expired sessions at set intervals.
func (db *PGStore) cleanup(interval time.Duration, quit <-chan struct{}, done chan<- struct{}) {
	ticker := time.NewTicker(interval)

	defer func() {
		ticker.Stop()
	}()

	for {
		select {
		case <-quit:
			// Handle the quit signal.
			done <- struct{}{}
			return
		case <-ticker.C:
			// Delete expired sessions on each tick.
			var count int
			rows, err := db.DbPool.QueryContext(context.Background(), "SELECT key FROM http_sessions WHERE expires_on < now()")
			if err != nil {
				db.log.Error(err, "pgstore: unable to get expired sessions")
				done <- struct{}{}
				return
			}
			for rows.Next() {
				var id string
				if err := rows.Scan(&id); err != nil {
					db.log.Error(err, "an error occurred scanning expired session")
					continue
				}
				sess := sessions.NewSession(db, SessionIdentifier)
				sess.ID = id
				if err := db.load(sess); err != nil {
					db.log.Error(err, "failed to load session", "operation_name", CleanupExpiredSessionOp)
					continue
				}
				db.log.Info("deleting expired session", enrichLogWithSession(CleanupExpiredSessionOp, sess)...)
				count++
			}
			err = db.deleteExpired()
			if err != nil {
				db.log.Error(err, "pgstore: unable to delete expired sessions")
			} else {
				db.log.Info(fmt.Sprintf("deleted %v expired sessions", count), "operation_name", CleanupExpiredSessionOp)
			}
		}
	}
}

// deleteExpired deletes expired sessions from the database.
func (db *PGStore) deleteExpired() error {
	_, err := db.DbPool.Exec("DELETE FROM http_sessions WHERE expires_on < now()")
	return err
}