package internal

import (
	"errors"
	"fmt"
	"regexp"
	"time"

	"git.mills.io/prologic/spyda"
	"github.com/gocolly/colly/v2"
	log "github.com/sirupsen/logrus"
)

var (
	ErrInvalidURL = errors.New("error: invalid or empty URL")
)

func GetLinks(url string) (links chan string, err error) {
	if url == "" {
		return nil, ErrInvalidURL
	}

	match, err := regexp.MatchString(`^https?://.*`, url)
	if err != nil {
		log.WithError(err).Error("error parsing url")
		return nil, fmt.Errorf("error parsing url %s: %w", url, err)
	}

	if !match {
		return nil, ErrInvalidURL
	}

	return FindLinks(url), nil
}

func FindLinks(url string) chan string {
	c := colly.NewCollector(
		colly.Async(),
		colly.UserAgent(fmt.Sprintf("%s (+https://spyda.search)", spyda.FullVersion())),
	)

	// Limit the number of threads started by colly to two
	c.Limit(&colly.LimitRule{
		Parallelism: 2,
		RandomDelay: 5 * time.Second,
	})

	links := make(chan string)

	c.OnHTML("a[href]", func(e *colly.HTMLElement) {
		link := e.Request.AbsoluteURL(e.Attr("href"))
		if link != "" {
			links <- link
		}
	})

	go func() {
		links <- url
		c.Visit(url)
		c.Wait()
		close(links)
	}()

	return links
}