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guru.go
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guru.go
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package main
import (
"strings"
"net/http"
"net/url"
"io"
"github.com/PuerkitoBio/goquery"
"fmt"
"context"
"log"
)
const (
NoResults = "Could not find what you were looking for."
GoogleSearchString = "https://google.com/search?q=site:stackoverflow.com%20"
CacheTTLSeconds = 3600
NoResultsCacheTTLSeconds = 1800
)
type CodeGuru interface {
FindAnswer(ctx context.Context, question string) (answer string, err error)
}
func NewGuru() CodeGuru {
return &WebCrawlerCodeGuru{questionCache:NewCache(1000), webLinkCache:NewCache(1000)}
}
type WebCrawlerCodeGuru struct {
questionCache QueryCache
webLinkCache QueryCache
}
func (g *WebCrawlerCodeGuru) FindAnswer(ctx context.Context, question string) (answer string, err error) {
results, errors := g.answerAsync(ctx, question)
select {
case answer := <- results:
return answer, nil
case err := <- errors:
return "", err
case <- ctx.Done():
fmt.Printf("[WARN] Context was cancelled for query = '%s'", question)
return "", ctx.Err()
}
}
func (g *WebCrawlerCodeGuru) answerAsync(ctx context.Context, question string) (<-chan string, <-chan error) {
resultChan := make(chan string, 1)
errChan := make(chan error, 1)
go func() {
defer close(resultChan)
defer close(errChan)
cached, hit := g.questionCache.Get(question)
if hit {
log.Printf("[INFO] Hit questions cache for '%s'", question)
resultChan <- cached
return
}
searchLink := fmtSearchString(question)
searchResp, err := http.Get(searchLink)
if err != nil {
errChan <- err
return
}
defer searchResp.Body.Close()
links, err := parseQuestionLinks(ctx, searchResp.Body, 1)
if err != nil {
errChan <- err
return
}
if len(links) == 0 {
resultChan <- NoResults
g.questionCache.Put(question, NoResults, NoResultsCacheTTLSeconds)
return
}
link := links[0]
cached, hit = g.webLinkCache.Get(link)
if hit {
log.Printf("[INFO] Hit link cache for '%s'", link)
resultChan <- cached
g.questionCache.Put(question, cached, CacheTTLSeconds)
return
}
questionResp, err := http.Get(link + "?answertab=votes")
if err != nil {
errChan <- err
return
}
defer questionResp.Body.Close()
answer, err := parseAnswers(questionResp.Body)
if err != nil {
errChan <- err
return
}
if answer == "" {
resultChan <- NoResults
g.questionCache.Put(question, NoResults, NoResultsCacheTTLSeconds)
g.questionCache.Put(link, NoResults, NoResultsCacheTTLSeconds)
return
}
resultChan <- answer
g.questionCache.Put(question, answer, CacheTTLSeconds)
g.webLinkCache.Put(link, answer, CacheTTLSeconds)
}()
return resultChan, errChan
}
func fmtSearchString(query string) string {
return GoogleSearchString + url.QueryEscape(query)
}
func parseQuestionLinks(ctx context.Context, htmlReader io.Reader, maxResults int) ([]string, error) {
doc, err := goquery.NewDocumentFromReader(htmlReader)
if err != nil {
return nil, err
}
var links []string
var found = 0
doc.Find(".r a").EachWithBreak(
func(_ int, next *goquery.Selection) bool {
select {
case <-ctx.Done():
err = ctx.Err()
return false
default:
href, exists := next.Attr("href")
if exists && strings.Contains(href, "/questions/") {
href = strings.Replace(href, "/url?q=", "", 1)
link := strings.Split(href, "&sa")[0]
links = append(links, link)
found = found + 1
if found >= maxResults {
return false
}
}
return true
}
})
return links, err
}
func parseAnswers(htmlReader io.Reader) (string, error) {
doc, err := goquery.NewDocumentFromReader(htmlReader)
if err != nil {
return "", err
}
firstAnswer := doc.Find(".answer").First()
if firstAnswer != nil {
preformat := firstAnswer.Find("pre").First()
if preformat != nil {
code := preformat.Find("code").First()
if code != nil {
return code.Text(), nil
}
}
code := firstAnswer.Find("code").First()
if code != nil {
return code.Text(), nil
}
postText := firstAnswer.Find(".post-text").First()
if postText != nil {
return postText.Text(), nil
}
}
return "", nil
}