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reorganizing content-related packages

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Nazar Kanaev 2021-03-31 23:40:59 +01:00
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// Copyright 2017 Frédéric Guillot. All rights reserved.
// Use of this source code is governed by the Apache 2.0
// license that can be found in the LICENSE file.
package readability
import (
"bytes"
"fmt"
"io"
//"log"
"math"
"regexp"
"strings"
"github.com/nkanaev/yarr/src/content/htmlutil"
"golang.org/x/net/html"
)
const (
defaultTagsToScore = "section,h2,h3,h4,h5,h6,p,td,pre,div"
)
var (
divToPElementsRegexp = regexp.MustCompile(`(?i)<(a|blockquote|dl|div|img|ol|p|pre|table|ul)`)
sentenceRegexp = regexp.MustCompile(`\.( |$)`)
blacklistCandidatesRegexp = regexp.MustCompile(`(?i)popupbody|-ad|g-plus`)
okMaybeItsACandidateRegexp = regexp.MustCompile(`(?i)and|article|body|column|main|shadow`)
unlikelyCandidatesRegexp = regexp.MustCompile(`(?i)banner|breadcrumbs|combx|comment|community|cover-wrap|disqus|extra|foot|header|legends|menu|modal|related|remark|replies|rss|shoutbox|sidebar|skyscraper|social|sponsor|supplemental|ad-break|agegate|pagination|pager|popup|yom-remote`)
negativeRegexp = regexp.MustCompile(`(?i)hidden|^hid$|hid$|hid|^hid |banner|combx|comment|com-|contact|foot|footer|footnote|masthead|media|meta|modal|outbrain|promo|related|scroll|share|shoutbox|sidebar|skyscraper|sponsor|shopping|tags|tool|widget|byline|author|dateline|writtenby|p-author`)
positiveRegexp = regexp.MustCompile(`(?i)article|body|content|entry|hentry|h-entry|main|page|pagination|post|text|blog|story`)
)
type nodeScores map[*html.Node]float32
// ExtractContent returns relevant content.
func ExtractContent(page io.Reader) (string, error) {
root, err := html.Parse(page)
if err != nil {
return "", err
}
for _, trash := range htmlutil.Query(root, "script,style") {
if trash.Parent != nil {
trash.Parent.RemoveChild(trash)
}
}
transformMisusedDivsIntoParagraphs(root)
removeUnlikelyCandidates(root)
scores := getCandidates(root)
//log.Printf("[Readability] Candidates: %v", candidates)
best := getTopCandidate(scores)
if best == nil {
best = root
}
//log.Printf("[Readability] TopCandidate: %v", topCandidate)
output := getArticle(best, scores)
return output, nil
}
// Now that we have the top candidate, look through its siblings for content that might also be related.
// Things like preambles, content split by ads that we removed, etc.
func getArticle(best *html.Node, scores nodeScores) string {
output := bytes.NewBufferString("<div>")
siblingScoreThreshold := float32(math.Max(10, float64(scores[best]*.2)))
nodelist := make([]*html.Node, 0)
nodelist = append(nodelist, best)
// Get the candidate's siblings
for n := best.NextSibling; n != nil; n = n.NextSibling {
nodelist = append(nodelist, n)
}
for n := best.PrevSibling; n != nil; n = n.PrevSibling {
nodelist = append(nodelist, n)
}
for _, node := range nodelist {
append := false
isP := node.Data == "p"
if node == best {
append = true
} else if scores[node] >= siblingScoreThreshold {
append = true
} else {
if isP {
linkDensity := getLinkDensity(node)
content := htmlutil.Text(node)
contentLength := len(content)
if contentLength >= 80 && linkDensity < .25 {
append = true
} else if contentLength < 80 && linkDensity == 0 && sentenceRegexp.MatchString(content) {
append = true
}
}
}
if append {
tag := "div"
if isP {
tag = "p"
}
fmt.Fprintf(output, "<%s>%s</%s>", tag, htmlutil.InnerHTML(node), tag)
}
}
output.Write([]byte("</div>"))
return output.String()
}
func removeUnlikelyCandidates(root *html.Node) {
body := htmlutil.Query(root, "body")
if len(body) == 0 {
return
}
for _, node := range htmlutil.Query(body[0], "*") {
str := htmlutil.Attr(node, "class") + htmlutil.Attr(node, "id")
blacklisted := (
blacklistCandidatesRegexp.MatchString(str) ||
(unlikelyCandidatesRegexp.MatchString(str) &&
!okMaybeItsACandidateRegexp.MatchString(str)))
if blacklisted && node.Parent != nil {
node.Parent.RemoveChild(node)
}
}
}
func getTopCandidate(scores nodeScores) *html.Node {
var top *html.Node
var max float32
for node, score := range scores {
if score > max {
top = node
max = score
}
}
return top
}
// Loop through all paragraphs, and assign a score to them based on how content-y they look.
// Then add their score to their parent node.
// A score is determined by things like number of commas, class names, etc.
// Maybe eventually link density.
func getCandidates(root *html.Node) nodeScores {
scores := make(nodeScores)
for _, node := range htmlutil.Query(root, defaultTagsToScore) {
text := htmlutil.Text(node)
// If this paragraph is less than 25 characters, don't even count it.
if len(text) < 25 {
continue
}
parentNode := node.Parent
grandParentNode := parentNode.Parent
if _, found := scores[parentNode]; !found {
scores[parentNode] = scoreNode(parentNode)
}
if grandParentNode != nil {
if _, found := scores[grandParentNode]; !found {
scores[grandParentNode] = scoreNode(grandParentNode)
}
}
// Add a point for the paragraph itself as a base.
contentScore := float32(1.0)
// Add points for any commas within this paragraph.
contentScore += float32(strings.Count(text, ",") + 1)
// For every 100 characters in this paragraph, add another point. Up to 3 points.
contentScore += float32(math.Min(float64(int(len(text)/100.0)), 3))
scores[parentNode] += contentScore
if grandParentNode != nil {
scores[grandParentNode] += contentScore / 2.0
}
}
// Scale the final candidates score based on link density. Good content
// should have a relatively small link density (5% or less) and be mostly
// unaffected by this operation
for node, _ := range scores {
scores[node] *= (1 - getLinkDensity(node))
}
return scores
}
func scoreNode(node *html.Node) float32 {
var score float32
switch node.Data {
case "div":
score += 5
case "pre", "td", "blockquote", "img":
score += 3
case "address", "ol", "ul", "dl", "dd", "dt", "li", "form":
score -= 3
case "h1", "h2", "h3", "h4", "h5", "h6", "th":
score -= 5
}
return score + getClassWeight(node)
}
// Get the density of links as a percentage of the content
// This is the amount of text that is inside a link divided by the total text in the node.
func getLinkDensity(n *html.Node) float32 {
textLength := len(htmlutil.Text(n))
if textLength == 0 {
return 0
}
linkLength := 0.0
for _, a := range htmlutil.Query(n, "a") {
linkLength += float64(len(htmlutil.Text(a)))
}
return float32(linkLength) / float32(textLength)
}
// Get an elements class/id weight. Uses regular expressions to tell if this
// element looks good or bad.
func getClassWeight(node *html.Node) float32 {
weight := 0
class := htmlutil.Attr(node, "class")
id := htmlutil.Attr(node, "id")
if class != "" {
if negativeRegexp.MatchString(class) {
weight -= 25
}
if positiveRegexp.MatchString(class) {
weight += 25
}
}
if id != "" {
if negativeRegexp.MatchString(id) {
weight -= 25
}
if positiveRegexp.MatchString(id) {
weight += 25
}
}
return float32(weight)
}
func transformMisusedDivsIntoParagraphs(root *html.Node) {
for _, node := range htmlutil.Query(root, "div") {
if !divToPElementsRegexp.MatchString(htmlutil.InnerHTML(node)) {
node.Data = "p"
}
}
}