question.go

package zhihu

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/url"
	"strconv"
	"strings"

	"github.com/PuerkitoBio/goquery"
)

// Question 表示一个知乎问题，可以用于获取其标题、详情、答案等信息
type Question struct {
	*Page

	// title 是该问题的标题
	title string
}

// NewQuestion 通过给定的 URL 创建一个 Question 对象
func NewQuestion(link string, title string) *Question {
	if !validQuestionURL(link) {
		panic("问题链接不正确: " + link)
	}

	return &Question{
		Page:  newZhihuPage(link),
		title: title,
	}
}

// GetTitle 获取问题标题
func (q *Question) GetTitle() string {
	if q.title != "" {
		return q.title
	}

	doc := q.Doc()
	q.title = strip(doc.Find("h2.zm-item-title").First().Text())
	return q.title
}

// GetDetail 获取问题描述
func (q *Question) GetDetail() string {
	if got, ok := q.getStringField("detail"); ok {
		return got
	}

	doc := q.Doc()
	detail := strip(doc.Find("div#zh-question-detail").First().Text())
	q.setField("detail", detail)
	return detail
}

// GetAnswersNum 获取问题回答数量
func (q *Question) GetAnswersNum() int {
	if got, ok := q.getIntField("answers-num"); ok {
		return got
	}

	doc := q.Doc()
	data, exists := doc.Find("h3#zh-question-answer-num").Attr("data-num")
	answerNum := 0
	if exists {
		answerNum, _ = strconv.Atoi(data)
	}
	q.setField("answers-num", answerNum)
	return answerNum
}

// GetFollowersNum 获取问题关注数量
func (q *Question) GetFollowersNum() int {
	if got, ok := q.getIntField("followers-num"); ok {
		return got
	}

	doc := q.Doc()
	text := doc.Find("div.zg-gray-normal>a>strong").Text()
	followersNum, _ := strconv.Atoi(text)
	q.setField("followers-num", followersNum)
	return followersNum
}

// GetTopics 获取问题的话题列表
func (q *Question) GetTopics() []*Topic {
	var topics []*Topic
	q.Doc().Find("a.zm-item-tag").Each(func(index int, sel *goquery.Selection) {
		name := strip(sel.Text())
		href, _ := sel.Attr("href")
		thisTopic := NewTopic(makeZhihuLink(href), name)
		topics = append(topics, thisTopic)
	})
	return topics
}

// GetFollowersN 返回 n 个关注者，如果 n < 0，返回所有关注者
func (q *Question) GetFollowersN(n int) []*User {
	var (
		link = urlJoin(q.Link, "/followers")
		xsrf = q.GetXSRF()
	)
	users, err := ajaxGetFollowers(link, xsrf, n)
	if err != nil {
		return nil
	}
	return users
}

// GetFollowers 获取关注该问题的用户
func (q *Question) GetFollowers() []*User {
	return q.GetFollowersN(q.GetFollowersNum())
}

// GetAllAnswers 获取问题的所有答案
func (q *Question) GetAllAnswers() []*Answer {
	return q.GetTopXAnswers(q.GetAnswersNum())
}

// GetTopXAnswers 获取问题 Top X 的答案
func (q *Question) GetTopXAnswers(x int) []*Answer {
	if x < 0 || x > q.GetAnswersNum() {
		x = q.GetAnswersNum()
	}

	// 1. 首页的回答
	answers := q.getAnswersOnIndex()

	if x < len(answers) {
		return answers[:x]
	}

	// 2. "更多"，调用 Ajax 接口
	moreCount := x - pageSize
	if moreCount > 0 {
		answers = append(answers, q.getMoreAnswers(moreCount)...)
	}

	return answers
}

// GetTopAnswer 获取问题排名第一的答案
func (q *Question) GetTopAnswer() *Answer {
	topAnswers := q.GetTopXAnswers(1)
	if len(topAnswers) >= 1 {
		return topAnswers[0]
	}
	return nil
}

// GetCommentsNum 返回问题的评论数量
func (q *Question) GetCommentsNum() int {
	if value, ok := q.getIntField("comment-num"); ok {
		return value
	}

	doc := q.Doc()
	text := doc.Find("div.zm-meta-panel a.toggle-comment").Text()
	rv := reMatchInt(strip(text))
	q.setField("comment-num", rv)
	return rv
}

// GetVisitTimes 获取问题的访问次数
func (q *Question) GetVisitTimes() int {
	if got, ok := q.getIntField("visit-times"); ok {
		return got
	}

	doc := q.Doc()
	content, exists := doc.Find(`meta[itemprop="visitsCount"]`).Attr("content")
	visitTimes := 0
	if exists {
		visitTimes, _ = strconv.Atoi(content)
	}
	q.setField("visit-times", visitTimes)
	return visitTimes
}

func (q *Question) String() string {
	return fmt.Sprintf("<Question: %s - %s>", q.GetTitle(), q.Link)
}

// getAnswersOnIndex 解析问题页面，返回第一页的回答
func (q *Question) getAnswersOnIndex() []*Answer {
	totalNum := q.GetAnswersNum()
	answers := make([]*Answer, 0, minInt(pageSize, totalNum))

	doc := q.Doc()

	doc.Find("div.zm-item-answer").Each(func(index int, sel *goquery.Selection) {
		answers = append(answers, q.processSingleAnswer(sel))
	})
	return answers
}

// getAnswersByAjax 处理 “更多” 回答，调用 Ajax 接口
func (q *Question) getAnswersByAjax(page int) ([]*Answer, error) {
	offset := page * pageSize
	if offset > q.GetAnswersNum() {
		return nil, errors.New("No more answers.")
	}

	// 如果 URL 是 https://www.zhihu.com/question/23759686，则 urlToken 是 23759686
	urlToken, _ := strconv.Atoi(q.Link[len(q.Link)-8 : len(q.Link)])

	form := url.Values{}
	form.Set("_xsrf", q.GetXSRF())
	form.Set("method", "next")
	form.Set("params", fmt.Sprintf(`{"url_token":%d,"pagesize":%d,"offset":%d}`, urlToken, pageSize, offset))

	link := makeZhihuLink("/node/QuestionAnswerListV2")
	body := strings.NewReader(form.Encode())
	resp, err := gSession.Ajax(link, body, q.Link)
	if err != nil {
		return nil, err
	}

	defer resp.Body.Close()
	result := nodeListResult{}
	err = json.NewDecoder(resp.Body).Decode(&result)
	if err != nil {
		return nil, err
	}

	answers := make([]*Answer, 0, len(result.Msg))
	for _, answerHtml := range result.Msg {
		doc, err := goquery.NewDocumentFromReader(strings.NewReader(answerHtml))
		if err != nil {
			return nil, err
		}
		thisAnswer := q.processSingleAnswer(doc.Selection)
		answers = append(answers, thisAnswer)
	}

	return answers, nil
}

// getMoreAnswers 执行多次“更多”
func (q *Question) getMoreAnswers(limit int) []*Answer {
	answers := make([]*Answer, 0, limit)
	index := 0
	totalPage := (limit + pageSize - 1) / pageSize
	for index < totalPage {
		page := index + 1
		moreAnswers, err := q.getAnswersByAjax(page)
		if err != nil {
			logger.Error("加载第 %d 页回答失败，问题：%s，错误：%s", page, q.Link, err.Error())
		} else {
			answers = append(answers, moreAnswers...)
		}
		index++
	}
	return answers
}

// processSingleAnswer 处理一个回答的 HTML 片段，
// 这段 HTML 可能来自问题页面，也可能来自 Ajax 接口
func (q *Question) processSingleAnswer(sel *goquery.Selection) *Answer {
	// 1. 获取链接
	answerHref, _ := sel.Find("a.answer-date-link").Attr("href")
	answerLink := makeZhihuLink(answerHref)

	// 2. 获取作者
	authorSel := sel.Find("div.zm-item-answer-author-info")
	var author *User
	if authorSel.Find("a.author-link").Size() == 0 {
		// 匿名用户
		author = ANONYMOUS
	} else {
		// 具名用户
		x := authorSel.Find("a.author-link")
		userID := strip(x.Text())
		userHref, _ := x.Attr("href")
		author = NewUser(makeZhihuLink(userHref), userID)
	}

	answer := NewAnswer(answerLink, q, author)

	// 3. 获取赞同数
	dataIsOwner, _ := sel.Attr("data-isowner")
	isOwner := dataIsOwner == "1" // 判断是否本人的回答
	var voteText string
	if isOwner {
		voteText = strip(sel.Find("a.zm-item-vote-count").Text())
	} else {
		voteText = strip(sel.Find("div.zm-votebar").Find("span.count").Text())
	}
	answer.setUpvote(upvoteTextToNum(voteText))

	// 4. 获取内容
	content, _ := answerSelectionToHtml(sel.Find("div.zm-editable-content"))
	answer.setContent(content)

	return answer
}

func (q *Question) setFollowersNum(value int) {
	q.setField("followers-num", value)
}

func (q *Question) setAnswersNum(value int) {
	q.setField("answers-num", value)
}

func (q *Question) setVisitTimes(value int) {
	q.setField("visit-times", value)
}