package handlers

import (
	"encoding/xml"
	"fmt"
	"html"
	"net/http"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"go_blog/models"
	"gorm.io/gorm"
)

// RSS 2.0 XML structure definitions.

// RSS is the root element of an RSS 2.0 feed.
type RSS struct {
	XMLName xml.Name `xml:"rss"`
	Version string   `xml:"version,attr"`
	Channel *Channel `xml:"channel"`
}

// Channel represents the RSS channel containing feed metadata and items.
type Channel struct {
	Title         string `xml:"title"`
	Link          string `xml:"link"`
	Description   string `xml:"description"`
	Language      string `xml:"language"`
	LastBuildDate string `xml:"lastBuildDate,omitempty"`
	Items         []Item `xml:"item"`
}

// Item represents a single article in the RSS feed.
type Item struct {
	Title       string `xml:"title"`
	Link        string `xml:"link"`
	Description string `xml:"description"`
	Author      string `xml:"author,omitempty"`
	PubDate     string `xml:"pubDate"`
	GUID        string `xml:"guid"`
}

// RSSFeed generates an RSS 2.0 feed of the latest published articles.
func RSSFeed(db *gorm.DB) gin.HandlerFunc {
	return func(c *gin.Context) {
		// Determine the current language for site metadata.
		lang, exists := c.Get("lang")
		if !exists {
			lang = "en"
		}
		langStr := lang.(string)

		// Get site settings for feed metadata.
		siteSetting := &models.SiteSetting{}
		db.First(siteSetting)

		// Construct the base URL from the request.
		scheme := "http"
		if c.Request.TLS != nil || c.GetHeader("X-Forwarded-Proto") == "https" {
			scheme = "https"
		}
		baseURL := fmt.Sprintf("%s://%s", scheme, c.Request.Host)

		// Get the latest 20 published articles.
		var articles []models.Article
		db.Where("status = ?", models.ArticlePublished).
			Preload("Author").
			Order(publishedArticleOrder).
			Limit(20).
			Find(&articles)

		// Build channel metadata.
		channel := &Channel{
			Title:       siteSetting.LogoText(langStr),
			Link:        baseURL,
			Description: siteSetting.HomeSubtitle(langStr),
			Language:    getRSSLanguage(langStr),
			Items:       make([]Item, 0, len(articles)),
		}

		// Set lastBuildDate to the most recent article's publish date.
		if len(articles) > 0 && articles[0].PublishedAt != nil {
			channel.LastBuildDate = formatRSSTime(*articles[0].PublishedAt)
		}

		// Convert articles to RSS items.
		for _, article := range articles {
			item := Item{
				Title:       article.Title,
				Link:        fmt.Sprintf("%s/article/%s", baseURL, article.Slug),
				Description: getArticleDescription(&article),
				PubDate:     formatRSSTime(getArticlePubDate(&article)),
				GUID:        fmt.Sprintf("%s/article/%s", baseURL, article.Slug),
			}

			// Add author information.
			if article.Author.DisplayName != "" {
				item.Author = article.Author.DisplayName
			} else {
				item.Author = article.Author.Username
			}

			channel.Items = append(channel.Items, item)
		}

		// Build the RSS feed.
		feed := &RSS{
			Version: "2.0",
			Channel: channel,
		}

		// Set the correct content type and return XML.
		c.Header("Content-Type", "application/rss+xml; charset=utf-8")
		c.XML(http.StatusOK, feed)
	}
}

// getRSSLanguage converts the internal language code to RSS language format.
func getRSSLanguage(lang string) string {
	switch lang {
	case "zh":
		return "zh-CN"
	case "en":
		return "en-US"
	default:
		return "en-US"
	}
}

// formatRSSTime formats a time.Time to RFC1123Z format required by RSS 2.0.
func formatRSSTime(t time.Time) string {
	return t.Format(time.RFC1123Z)
}

// getArticlePubDate returns the article's publish date, falling back to created date.
func getArticlePubDate(article *models.Article) time.Time {
	if article.PublishedAt != nil {
		return *article.PublishedAt
	}
	return article.CreatedAt
}

// getArticleDescription returns the article description for RSS.
// Prefers the summary field; falls back to truncated content.
func getArticleDescription(article *models.Article) string {
	if article.Summary != "" {
		return html.EscapeString(article.Summary)
	}

	// Strip HTML tags and truncate content to 200 characters.
	content := stripHTMLTags(article.Content)
	if len(content) > 200 {
		content = content[:200] + "..."
	}
	return html.EscapeString(content)
}

// stripHTMLTags removes HTML tags from a string (basic implementation).
func stripHTMLTags(s string) string {
	// Remove HTML tags by finding < and > pairs.
	var result strings.Builder
	inTag := false
	for _, r := range s {
		if r == '<' {
			inTag = true
			continue
		}
		if r == '>' {
			inTag = false
			continue
		}
		if !inTag {
			result.WriteRune(r)
		}
	}
	// Clean up multiple spaces and trim.
	cleaned := strings.Join(strings.Fields(result.String()), " ")
	return cleaned
}