images.go

package goose

import (
	"github.com/PuerkitoBio/goquery"
	"net/url"
	"regexp"
	"strconv"
	"strings"
)

type candidate struct {
	url     string
	surface int
	score   int
}

func (c *candidate) GetUrl() string {
	return c.url
}

var largebig = regexp.MustCompile("(large|big|full)")

var classRules = map[*regexp.Regexp]int{
	regexp.MustCompile("(promo|ads|banner)"): -1}

var rules = map[*regexp.Regexp]int{
	largebig:                                   1,
	regexp.MustCompile("upload"):               1,
	regexp.MustCompile("media"):                1,
	regexp.MustCompile("gravatar.com"):         -1,
	regexp.MustCompile("feeds.feedburner.com"): -1,
	regexp.MustCompile("(?i)icon"):             -1,
	regexp.MustCompile("(?i)logo"):             -1,
	regexp.MustCompile("(?i)spinner"):          -1,
	regexp.MustCompile("(?i)loading"):          -1,
	regexp.MustCompile("(?i)ads"):              -1,
	regexp.MustCompile("badge"):                -1,
	regexp.MustCompile("1x1"):                  -1,
	regexp.MustCompile("pixel"):                -1,
	regexp.MustCompile("thumbnail[s]*"):        -1,
	regexp.MustCompile(".html|" +
		".gif|" +
		".ico|" +
		"button|" +
		"twitter.jpg|" +
		"facebook.jpg|" +
		"ap_buy_photo|" +
		"digg.jpg|" +
		"digg.png|" +
		"delicious.png|" +
		"facebook.png|" +
		"reddit.jpg|" +
		"doubleclick|" +
		"diggthis|" +
		"diggThis|" +
		"adserver|" +
		"/(ads|promos|banners)/|" +
		"ec.atdmt.com|" +
		"mediaplex.com|" +
		"adsatt|" +
		"view.atdmt"): -1}

func getImageSrc(tag *goquery.Selection) string {
	src, _ := tag.Attr("src")
	// skip inline images
	if strings.Contains(src, "data:image/") {
		src = ""
	}
	if src == "" {
		src, _ = tag.Attr("data-src")
	}
	if src == "" {
		src, _ = tag.Attr("data-lazy-src")
	}
	return src
}

func score(tag *goquery.Selection) int {
	src := getImageSrc(tag)
	if src == "" {
		return -1
	}
	tagScore := 0
	for rule, score := range rules {
		if rule.MatchString(src) {
			tagScore += score
		}
	}

	alt, exists := tag.Attr("alt")
	if exists {
		if strings.Contains(alt, "thumbnail") {
			tagScore--
		}
	}

	id, exists := tag.Attr("id")
	if exists {
		if id == "fbPhotoImage" {
			tagScore++
		}
	}

	class, exists := tag.Attr("class")
	if exists {
		for rule, score := range classRules {
			if rule.MatchString(class) {
				tagScore += score
			}
		}
	}

	return tagScore
}

// WebPageResolver fetches all candidate images from the HTML page
func WebPageImageResolver(doc *goquery.Document) ([]candidate, int) {
	imgs := doc.Find("img")

	var candidates []candidate
	significantSurface := 320 * 200
	significantSurfaceCount := 0
	src := ""
	imgs.Each(func(i int, tag *goquery.Selection) {
		var surface int
		src = getImageSrc(tag)
		if src == "" {
			return
		}

		width, _ := tag.Attr("width")
		height, _ := tag.Attr("height")
		if width != "" {
			w, _ := strconv.Atoi(width)
			if height != "" {
				h, _ := strconv.Atoi(height)
				surface = w * h
			} else {
				surface = w
			}
		} else {
			if height != "" {
				surface, _ = strconv.Atoi(height)
			} else {
				surface = 0
			}
		}

		if surface > significantSurface {
			significantSurfaceCount++
		}

		tagscore := score(tag)
		if tagscore >= 0 {
			c := candidate{
				url:     src,
				surface: surface,
				score:   score(tag),
			}
			candidates = append(candidates, c)
		}
	})

	if len(candidates) == 0 {
		return nil, 0
	}

	return candidates, significantSurfaceCount

}

// WebPageResolver fetches the main image from the HTML page
func WebPageResolver(article *Article) string {
	candidates, significantSurfaceCount := WebPageImageResolver(article.Doc)
	if candidates == nil {
		return ""
	}
	var bestCandidate candidate
	var topImage string
	if significantSurfaceCount > 0 {
		bestCandidate = findBestCandidateFromSurface(candidates)
	} else {
		bestCandidate = findBestCandidateFromScore(candidates)
	}

	topImage = bestCandidate.url
	a, err := url.Parse(topImage)
	if err != nil {
		return topImage
	}
	finalURL, err := url.Parse(article.FinalURL)
	if err != nil {
		return topImage
	}
	b := finalURL.ResolveReference(a)
	topImage = b.String()

	return topImage
}

func findBestCandidateFromSurface(candidates []candidate) candidate {
	max := 0
	var bestCandidate candidate
	for _, candidate := range candidates {
		surface := candidate.surface
		if surface >= max {
			max = surface
			bestCandidate = candidate
		}
	}

	return bestCandidate
}

func findBestCandidateFromScore(candidates []candidate) candidate {
	max := 0
	var bestCandidate candidate
	for _, candidate := range candidates {
		score := candidate.score
		if score >= max {
			max = score
			bestCandidate = candidate
		}
	}

	return bestCandidate
}

type ogTag struct {
	tpe       string
	attribute string
	name      string
	value     string
}

var ogTags = [4]ogTag{
	{
		tpe:       "facebook",
		attribute: "property",
		name:      "og:image",
		value:     "content",
	},
	{
		tpe:       "facebook",
		attribute: "rel",
		name:      "image_src",
		value:     "href",
	},
	{
		tpe:       "twitter",
		attribute: "name",
		name:      "twitter:image",
		value:     "value",
	},
	{
		tpe:       "twitter",
		attribute: "name",
		name:      "twitter:image",
		value:     "content",
	},
}

type ogImage struct {
	url   string
	tpe   string
	score int
}

// OpenGraphResolver return OpenGraph properties
func OpenGraphResolver(doc *goquery.Document) string {
	meta := doc.Find("meta")
	links := doc.Find("link")
	var topImage string
	meta = meta.Union(links)
	var ogImages []ogImage
	meta.Each(func(i int, tag *goquery.Selection) {
		for _, ogTag := range ogTags {
			attr, exist := tag.Attr(ogTag.attribute)
			value, vexist := tag.Attr(ogTag.value)
			if exist && attr == ogTag.name && vexist {
				ogImage := ogImage{
					url:   value,
					tpe:   ogTag.tpe,
					score: 0,
				}

				ogImages = append(ogImages, ogImage)
			}
		}
	})
	if len(ogImages) == 0 {
		return ""
	}
	if len(ogImages) == 1 {
		topImage = ogImages[0].url
		goto IMAGE_FINALIZE
	}
	for _, ogImage := range ogImages {
		if largebig.MatchString(ogImage.url) {
			ogImage.score++
		}
		if ogImage.tpe == "twitter" {
			ogImage.score++
		}
	}
	topImage = findBestImageFromScore(ogImages).url
IMAGE_FINALIZE:
	if !strings.HasPrefix(topImage, "http") {
		topImage = "http://" + topImage
	}

	return topImage
}

// assume that len(ogImages)>=2
func findBestImageFromScore(ogImages []ogImage) ogImage {
	max := 0
	bestOGImage := ogImages[0]
	for _, ogImage := range ogImages[1:] {
		score := ogImage.score
		if score > max {
			max = score
			bestOGImage = ogImage
		}
	}

	return bestOGImage
}