package handlers

import (
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"net/http"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/gin-contrib/sessions"
	"github.com/gin-gonic/gin"
	"go_blog/models"

	"gorm.io/gorm"
)

// slugSepRe matches runs of non-word characters (anything that is not a
// letter or digit); these become single dashes.
var slugSepRe = regexp.MustCompile(`[^\p{L}\p{N}]+`)

// slugDashRe matches runs of dashes to collapse.
var slugDashRe = regexp.MustCompile(`-{2,}`)

// slugAsciiRe matches a slug made only of URL-safe ASCII letters, digits and
// dashes. Slugs containing other characters (e.g. CJK, or Unicode lowercase
// quirks like the Turkish dotless i) are not URL-stable and are discarded in
// favor of a "post-<id>" fallback.
var slugAsciiRe = regexp.MustCompile(`^[a-z0-9]+(-[a-z0-9]+)*$`)

// randomToken returns a 32-byte hex token used to own pending attachments on
// the article-create page until the article is saved.
func randomToken() string {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		// Extremely unlikely; fall back to a time-based value.
		return strconv.FormatInt(time.Now().UnixNano(), 16)
	}
	return hex.EncodeToString(b)
}

// generateSlug converts a title into a URL-friendly ASCII slug. Returns "" when
// the title yields no URL-safe ASCII characters (the caller must fall back,
// e.g. to "post-<id>"). Non-ASCII letters are intentionally dropped rather
// than kept, because raw CJK in a URL slug is not stable.
func generateSlug(title string) string {
	s := strings.ToLower(strings.TrimSpace(title))
	s = slugSepRe.ReplaceAllString(s, "-")
	s = strings.Trim(s, "-")
	s = slugDashRe.ReplaceAllString(s, "-")
	if !slugAsciiRe.MatchString(s) {
		return ""
	}
	return s
}

// fallbackSlug returns a non-empty slug when title-derived slugs are empty
// (e.g. a title of only punctuation/whitespace, or all-stripped). Uses the
// article ID when available, else a short token.
func fallbackSlug(id uint) string {
	if id > 0 {
		return fmt.Sprintf("post-%d", id)
	}
	return "post-" + randomToken()[:8]
}

// articleForm holds the parsed article form fields, shared by the create and
// edit handlers and their validation-error repopulation paths.
type articleForm struct {
	Title        string
	Slug         string
	Summary      string
	Content      string
	Cover        string
	StatusStr    string
	IsTop        bool
	Action       string // form action URL
	TitleText    string // page heading text (create vs edit)
	ArticleID    uint   // existing article ID (edit page); 0 on create
	SessionToken string // pending-attachment ownership token (create page)
}

// parseArticleForm reads and trims the article form fields from the request.
func parseArticleForm(c *gin.Context) articleForm {
	return articleForm{
		Title:     strings.TrimSpace(c.PostForm("title")),
		Slug:      strings.TrimSpace(c.PostForm("slug")),
		Summary:   strings.TrimSpace(c.PostForm("summary")),
		Content:   strings.TrimSpace(c.PostForm("content")),
		Cover:     strings.TrimSpace(c.PostForm("cover")),
		StatusStr: c.PostForm("status"),
		IsTop:     c.PostForm("is_top") == "1",
	}
}

// applyFormToData writes the form field values into the template data map so
// the form is repopulated on render (initial load or validation error).
func applyFormToData(data gin.H, f articleForm) {
	data["FormTitle"] = f.Title
	data["FormSlug"] = f.Slug
	data["FormSummary"] = f.Summary
	data["FormContent"] = f.Content
	data["FormCover"] = f.Cover
	data["FormStatus"] = f.StatusStr
	data["FormIsTop"] = f.IsTop
	data["FormAction"] = f.Action
	data["FormTitleText"] = f.TitleText
	data["FormArticleID"] = f.ArticleID
	data["SessionToken"] = f.SessionToken
}

// renderArticleForm renders the shared article form template with the given
// form values and optional error message.
func renderArticleForm(c *gin.Context, db *gorm.DB, f articleForm, errMsg string) {
	data := DefaultData(c)
	data["Title"] = f.TitleText
	if errMsg != "" {
		data["Error"] = errMsg
	}
	applyFormToData(data, f)
	c.HTML(http.StatusOK, "article_create", data)
}

// sessionAuthorID extracts the logged-in user's ID from the session, defending
// against int/uint/int64/float64 storage. Returns ok=false if absent.
func sessionAuthorID(c *gin.Context) (uint, bool) {
	session := sessions.Default(c)
	userID := session.Get("user_id")
	if userID == nil {
		return 0, false
	}
	switch v := userID.(type) {
	case uint:
		return v, true
	case int:
		return uint(v), true
	case int64:
		return uint(v), true
	case float64:
		return uint(v), true
	default:
		return 0, false
	}
}

// statusFromForm parses the status string ("0" draft, "1" published) and
// returns the model status constant, defaulting to draft.
func statusFromForm(statusStr string) int {
	if statusStr == "1" {
		return models.ArticlePublished
	}
	return models.ArticleDraft
}

// ArticleCreatePage renders the article creation form.
func ArticleCreatePage(db *gorm.DB) gin.HandlerFunc {
	return func(c *gin.Context) {
		tr := getTr(c)
		renderArticleForm(c, db, articleForm{
			Action:       "/admin/articles/new",
			TitleText:    tr["article_create_title"],
			StatusStr:    "0",
			SessionToken: randomToken(),
		}, "")
	}
}

// ArticleCreate handles the POST request to create a new article.
func ArticleCreate(db *gorm.DB) gin.HandlerFunc {
	return func(c *gin.Context) {
		tr := getTr(c)
		f := parseArticleForm(c)
		f.Action = "/admin/articles/new"
		f.TitleText = tr["article_create_title"]
		f.SessionToken = strings.TrimSpace(c.PostForm("session_token"))

		// Validate required fields.
		if f.Title == "" {
			renderArticleForm(c, db, f, tr["article_title_required"])
			return
		}
		if f.Content == "" {
			renderArticleForm(c, db, f, tr["article_content_required"])
			return
		}

		// Auto-generate slug if empty.
		if f.Slug == "" {
			f.Slug = generateSlug(f.Title)
			// Title had no usable characters (e.g. only punctuation). Use a
			// temporary token-based slug now; refine to post-<id> after insert.
			if f.Slug == "" {
				f.Slug = fallbackSlug(0)
			}
		}

		status := statusFromForm(f.StatusStr)

		authorID, ok := sessionAuthorID(c)
		if !ok {
			c.Redirect(http.StatusFound, "/login")
			return
		}

		var publishedAt *time.Time
		if status == models.ArticlePublished {
			now := time.Now()
			publishedAt = &now
		}

		article := models.Article{
			AuthorID:    authorID,
			Title:       f.Title,
			Slug:        f.Slug,
			Summary:     f.Summary,
			Content:     f.Content,
			Cover:       f.Cover,
			Status:      status,
			IsTop:       f.IsTop,
			PublishedAt: publishedAt,
		}

		if err := db.Create(&article).Error; err != nil {
			renderArticleForm(c, db, f, tr["article_error"])
			return
		}

		// Refine a token-based placeholder slug to the readable post-<id> form.
		if strings.HasPrefix(f.Slug, "post-") && len(f.Slug) > 9 {
			if newSlug := fallbackSlug(article.ID); newSlug != "" {
				db.Model(&article).Update("slug", newSlug)
			}
		}

		// Bind any attachments uploaded during creation (plan A: pending rows
		// owned by session_token, article_id=0).
		if f.SessionToken != "" {
			_ = BindPendingAttachments(db, f.SessionToken, article.ID)
		}

		// Success: redirect to dashboard.
		c.Redirect(http.StatusFound, "/admin")
	}
}

// ArticleListPage renders the admin article management list.
func ArticleListPage(db *gorm.DB) gin.HandlerFunc {
	return func(c *gin.Context) {
		tr := getTr(c)
		var articles []models.Article
		db.Order("created_at DESC").Find(&articles)
		data := DefaultData(c)
		data["Title"] = tr["article_list_title"]
		data["Articles"] = articles
		c.HTML(http.StatusOK, "article_list", data)
	}
}

// ArticleEditPage renders the shared form prefilled with an existing article.
func ArticleEditPage(db *gorm.DB) gin.HandlerFunc {
	return func(c *gin.Context) {
		tr := getTr(c)
		id := c.Param("id")

		var article models.Article
		if err := db.First(&article, "id = ?", id).Error; err != nil {
			c.Redirect(http.StatusFound, "/admin/articles")
			return
		}

		renderArticleForm(c, db, articleForm{
			Title:     article.Title,
			Slug:      article.Slug,
			Summary:   article.Summary,
			Content:   article.Content,
			Cover:     article.Cover,
			StatusStr: strconv.Itoa(article.Status),
			IsTop:     article.IsTop,
			Action:    "/admin/articles/" + id + "/edit",
			TitleText: tr["article_edit_title"],
			ArticleID: article.ID,
		}, "")
	}
}

// ArticleUpdate handles the POST request to update an existing article.
func ArticleUpdate(db *gorm.DB) gin.HandlerFunc {
	return func(c *gin.Context) {
		tr := getTr(c)
		id := c.Param("id")

		var article models.Article
		if err := db.First(&article, "id = ?", id).Error; err != nil {
			c.Redirect(http.StatusFound, "/admin/articles")
			return
		}

		f := parseArticleForm(c)
		f.Action = "/admin/articles/" + id + "/edit"
		f.TitleText = tr["article_edit_title"]

		if f.Title == "" {
			renderArticleForm(c, db, f, tr["article_title_required"])
			return
		}
		if f.Content == "" {
			renderArticleForm(c, db, f, tr["article_content_required"])
			return
		}

		if f.Slug == "" {
			f.Slug = generateSlug(f.Title)
			if f.Slug == "" {
				f.Slug = fallbackSlug(article.ID)
			}
		}

		newStatus := statusFromForm(f.StatusStr)

		// Stamp the publish time the first time an article is published.
		wasPublished := article.Status == models.ArticlePublished
		var publishedAt *time.Time = article.PublishedAt
		if newStatus == models.ArticlePublished && !wasPublished && publishedAt == nil {
			now := time.Now()
			publishedAt = &now
		}

		updates := map[string]interface{}{
			"Title":       f.Title,
			"Slug":        f.Slug,
			"Summary":     f.Summary,
			"Content":     f.Content,
			"Cover":       f.Cover,
			"Status":      newStatus,
			"IsTop":       f.IsTop,
			"PublishedAt": publishedAt,
		}

		if err := db.Model(&article).Updates(updates).Error; err != nil {
			renderArticleForm(c, db, f, tr["article_error"])
			return
		}

		c.Redirect(http.StatusFound, "/admin/articles")
	}
}

// ArticleDelete soft-deletes an article (GORM fills DeletedAt) and redirects
// back to the management list.
func ArticleDelete(db *gorm.DB) gin.HandlerFunc {
	return func(c *gin.Context) {
		id := c.Param("id")
		db.Delete(&models.Article{}, "id = ?", id)
		c.Redirect(http.StatusFound, "/admin/articles")
	}
}