package service

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"io"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"
	"unicode/utf8"

	"github.com/freefire/jiang13-bbs/model"
	"gorm.io/gorm"
)

// 书库文件扩展名白名单（小写、不含点）；附件仅提供下载分发，
// 书籍正文走章节阅读，不做在线预览
var libraryAllowedExts = map[string]struct{}{
	"html": {}, "htm": {}, "pdf": {}, "epub": {}, "mobi": {}, "azw3": {},
	"zip": {}, "7z": {}, "rar": {}, "txt": {}, "md": {},
	"doc": {}, "docx": {}, "ppt": {}, "pptx": {},
}

const (
	MaxLibraryFilesPerDoc = 20
	libraryDescriptionMax = 20000
)

var (
	ErrLibraryNotFound   = errors.New("书库条目不存在")
	ErrLibraryExtDenied  = errors.New("不支持该文档格式")
	ErrLibraryTooMany    = errors.New("文件数量超过上限")
	ErrLibraryNotDeleted = errors.New("仅已删除的条目可彻底删除")
)

// LibraryExtAllowed 上传扩展名是否在书库白名单内
func LibraryExtAllowed(ext string) bool {
	_, ok := libraryAllowedExts[strings.ToLower(strings.TrimPrefix(ext, "."))]
	return ok
}

// 写入时显式列出字段（独立 Select 参数，同 sitePageWriteFields）
var libraryDocWriteFields = []string{
	"Slug", "Title", "Description", "CoverURL", "Published", "SortOrder", "EntriesAuto",
}

// LibraryDocDetail 条目 + 文件列表 + 章节树（管理端与公开详情共用）
type LibraryDocDetail struct {
	model.LibraryDoc
	Deleted  bool                   `json:"deleted"` // 软删标记（DeletedAt json:"-" 不出模型）
	Files    []model.LibraryFile    `json:"files"`
	Sections []model.LibrarySection `json:"sections"`
}

// LibraryDocListItem 公开目录条目（不含 description 全文，含文件概要）
type LibraryDocListItem struct {
	ID        uint                `json:"id"`
	Slug      string              `json:"slug"`
	Title     string              `json:"title"`
	CoverURL  string              `json:"cover_url"`
	SortOrder int                 `json:"sort_order"`
	FileCount int                 `json:"file_count"`
	Files     []model.LibraryFile `json:"files"`
	CreatedAt time.Time           `json:"created_at"`
	UpdatedAt time.Time           `json:"updated_at"`
}

// LibraryInput 创建/更新书库条目入参
type LibraryInput struct {
	Slug        string `json:"slug"`
	Title       string `json:"title"`
	Description string `json:"description"`
	CoverURL    string `json:"cover_url"`
	Published   *bool  `json:"published"`
	SortOrder   *int   `json:"sort_order"`
	EntriesAuto *bool  `json:"entries_auto"` // 全章节条目卡模式（nil=不修改）
}

func (in *LibraryInput) normalize() error {
	in.Slug = strings.ToLower(strings.TrimSpace(in.Slug))
	if in.Slug == "" {
		return errors.New("slug 不能为空")
	}
	if len(in.Slug) > 64 {
		return errors.New("slug 不能超过 64 字符")
	}
	if !sitePageSlugRe.MatchString(in.Slug) {
		return errors.New("slug 仅允许小写字母、数字与连字符")
	}

	in.Title = strings.TrimSpace(in.Title)
	if in.Title == "" {
		return errors.New("标题不能为空")
	}
	if utf8.RuneCountInString(in.Title) > 200 {
		return errors.New("标题不能超过 200 字")
	}

	in.Description = strings.TrimSpace(in.Description)
	if utf8.RuneCountInString(in.Description) > libraryDescriptionMax {
		return errors.New("介绍不能超过 20000 字")
	}

	in.CoverURL = strings.TrimSpace(in.CoverURL)
	if utf8.RuneCountInString(in.CoverURL) > 512 {
		return errors.New("封面地址过长")
	}

	return nil
}

func (in *LibraryInput) applyTo(d *model.LibraryDoc) {
	d.Slug = in.Slug
	d.Title = in.Title
	d.Description = in.Description
	d.CoverURL = in.CoverURL
	if in.Published != nil {
		d.Published = *in.Published
	}
	if in.SortOrder != nil {
		d.SortOrder = *in.SortOrder
	}
	if in.EntriesAuto != nil {
		d.EntriesAuto = *in.EntriesAuto
	}
}

// LibraryService 书库服务（条目 CRUD + 文件落盘/下载/预览）
type LibraryService struct {
	db      *gorm.DB
	dir     string // data/library（绝不放 data/uploads：静态目录会按扩展名原样 serve html）
	setting *SettingService
}

func NewLibraryService(db *gorm.DB, dataDir string) *LibraryService {
	return &LibraryService{db: db, dir: filepath.Join(dataDir, "library")}
}

// WithSetting 注入站点设置（文件大小上限复用附件设置）
func (s *LibraryService) WithSetting(setting *SettingService) *LibraryService {
	s.setting = setting
	return s
}

func (s *LibraryService) EnsureDir() error {
	return os.MkdirAll(s.dir, 0o755)
}

func (s *LibraryService) FilePath(f *model.LibraryFile) string {
	return filepath.Join(s.dir, f.StoredName)
}

// slugTaken 查询 slug 占用情况（Unscoped 含软删行：软删行仍占用数据库唯一索引）
// active=在用条目占用；deleted=已删除条目占用
func (s *LibraryService) slugTaken(slug string, excludeID uint) (active, deleted bool, err error) {
	q := s.db.Unscoped().Model(&model.LibraryDoc{}).Where("slug = ?", slug).Select("deleted_at")
	if excludeID > 0 {
		q = q.Where("id <> ?", excludeID)
	}
	var rows []struct {
		DeletedAt gorm.DeletedAt
	}
	if err := q.Find(&rows).Error; err != nil {
		return false, false, err
	}
	for _, r := range rows {
		if r.DeletedAt.Valid {
			deleted = true
		} else {
			active = true
		}
	}
	return active, deleted, nil
}

// ---------- 条目：管理端 ----------

// ListAll 管理后台全部条目（含未发布与已软删，带文件；已删条目仅供查看与彻底删除）
func (s *LibraryService) ListAll() ([]LibraryDocDetail, error) {
	var docs []model.LibraryDoc
	if err := s.db.Unscoped().Order("sort_order ASC, id ASC").Limit(200).Find(&docs).Error; err != nil {
		return nil, err
	}
	return s.attachFiles(docs), nil
}

// Get 管理后台按 ID 取条目
func (s *LibraryService) Get(id uint) (*LibraryDocDetail, error) {
	var d model.LibraryDoc
	if err := s.db.First(&d, id).Error; err != nil {
		return nil, ErrLibraryNotFound
	}
	out := s.attachFiles([]model.LibraryDoc{d})
	return &out[0], nil
}

func (s *LibraryService) attachFiles(docs []model.LibraryDoc) []LibraryDocDetail {
	out := make([]LibraryDocDetail, 0, len(docs))
	if len(docs) == 0 {
		return out
	}
	ids := make([]uint, 0, len(docs))
	for _, d := range docs {
		ids = append(ids, d.ID)
	}
	var files []model.LibraryFile
	if err := s.db.Where("doc_id IN ?", ids).
		Order("sort_order ASC, id ASC").Find(&files).Error; err != nil {
		files = nil
	}
	byDoc := make(map[uint][]model.LibraryFile, len(docs))
	for _, f := range files {
		byDoc[f.DocID] = append(byDoc[f.DocID], f)
	}
	var sections []model.LibrarySection
	if err := s.db.Where("doc_id IN ?", ids).
		Order("sort_order ASC, id ASC").Find(&sections).Error; err != nil {
		sections = nil
	}
	secByDoc := make(map[uint][]model.LibrarySection, len(docs))
	for _, sec := range sections {
		secByDoc[sec.DocID] = append(secByDoc[sec.DocID], sec)
	}
	for _, d := range docs {
		fs := byDoc[d.ID]
		if fs == nil {
			fs = []model.LibraryFile{}
		}
		ss := secByDoc[d.ID]
		if ss == nil {
			ss = []model.LibrarySection{}
		}
		out = append(out, LibraryDocDetail{LibraryDoc: d, Deleted: d.DeletedAt.Valid, Files: fs, Sections: ss})
	}
	return out
}

func (s *LibraryService) Create(in *LibraryInput) (*model.LibraryDoc, error) {
	if err := in.normalize(); err != nil {
		return nil, err
	}
	active, deleted, err := s.slugTaken(in.Slug, 0)
	if err != nil {
		return nil, err
	}
	if active {
		return nil, errors.New("slug 已被占用")
	}
	if deleted {
		return nil, errors.New("该地址已被已删除条目占用，可在书库管理列表中彻底删除后重新使用")
	}
	d := &model.LibraryDoc{Published: false, SortOrder: 0}
	in.applyTo(d)
	if err := s.db.Select(libraryDocWriteFields).Create(d).Error; err != nil {
		return nil, err
	}
	return d, nil
}

func (s *LibraryService) Update(id uint, in *LibraryInput) (*model.LibraryDoc, error) {
	var d model.LibraryDoc
	if err := s.db.First(&d, id).Error; err != nil {
		return nil, ErrLibraryNotFound
	}
	if err := in.normalize(); err != nil {
		return nil, err
	}
	active, deleted, err := s.slugTaken(in.Slug, id)
	if err != nil {
		return nil, err
	}
	if active {
		return nil, errors.New("slug 已被占用")
	}
	if deleted {
		return nil, errors.New("该地址已被已删除条目占用，可在书库管理列表中彻底删除后重新使用")
	}
	in.applyTo(&d)
	// map 更新确保 false/空串写入（同 SitePage.Update）
	if err := s.db.Model(&model.LibraryDoc{}).Where("id = ?", d.ID).Updates(map[string]interface{}{
		"slug":         d.Slug,
		"title":        d.Title,
		"description":  d.Description,
		"cover_url":    d.CoverURL,
		"published":    d.Published,
		"sort_order":   d.SortOrder,
		"entries_auto": d.EntriesAuto,
	}).Error; err != nil {
		return nil, err
	}
	return &d, nil
}

func (s *LibraryService) Delete(id uint) error {
	result := s.db.Delete(&model.LibraryDoc{}, id)
	if result.Error != nil {
		return result.Error
	}
	if result.RowsAffected == 0 {
		return ErrLibraryNotFound
	}
	return nil
}

// Purge 彻底删除已软删的条目（章节/文件行与磁盘文件一并清除，slug 释放可复用）
func (s *LibraryService) Purge(id uint) error {
	var d model.LibraryDoc
	if err := s.db.Unscoped().First(&d, id).Error; err != nil {
		return ErrLibraryNotFound
	}
	if !d.DeletedAt.Valid {
		return ErrLibraryNotDeleted
	}
	// 先取出文件清单（含此前单独软删的文件行），事务成功后统一删磁盘
	var files []model.LibraryFile
	if err := s.db.Unscoped().Where("doc_id = ?", id).Find(&files).Error; err != nil {
		return err
	}
	err := s.db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Unscoped().Where("doc_id = ?", id).Delete(&model.LibrarySection{}).Error; err != nil {
			return err
		}
		if err := tx.Unscoped().Where("doc_id = ?", id).Delete(&model.LibraryFile{}).Error; err != nil {
			return err
		}
		return tx.Unscoped().Delete(&model.LibraryDoc{}, id).Error
	})
	if err != nil {
		return err
	}
	// 事务外尽力删除磁盘文件（同 DeleteFile 惯例，失败不影响返回）
	for i := range files {
		_ = os.Remove(s.FilePath(&files[i]))
	}
	return nil
}

// ---------- 条目：公开端 ----------

// ListPublished 已发布条目目录（含文件概要，不含 description 全文）
func (s *LibraryService) ListPublished() ([]LibraryDocListItem, error) {
	details, err := s.publishedDetails()
	if err != nil {
		return nil, err
	}
	out := make([]LibraryDocListItem, 0, len(details))
	for _, d := range details {
		out = append(out, LibraryDocListItem{
			ID: d.ID, Slug: d.Slug, Title: d.Title, CoverURL: d.CoverURL,
			SortOrder: d.SortOrder, FileCount: len(d.Files), Files: d.Files,
			CreatedAt: d.CreatedAt, UpdatedAt: d.UpdatedAt,
		})
	}
	return out, nil
}

// GetPublishedBySlug 公开详情（仅已发布）
func (s *LibraryService) GetPublishedBySlug(slug string) (*LibraryDocDetail, error) {
	slug = strings.ToLower(strings.TrimSpace(slug))
	var d model.LibraryDoc
	if err := s.db.Where("slug = ? AND published = ?", slug, true).First(&d).Error; err != nil {
		return nil, ErrLibraryNotFound
	}
	out := s.attachFiles([]model.LibraryDoc{d})
	return &out[0], nil
}

func (s *LibraryService) publishedDetails() ([]LibraryDocDetail, error) {
	var docs []model.LibraryDoc
	if err := s.db.Where("published = ?", true).
		Order("sort_order ASC, id ASC").Limit(100).Find(&docs).Error; err != nil {
		return nil, err
	}
	return s.attachFiles(docs), nil
}

// ---------- 文件 ----------

func (s *LibraryService) maxBytes() int64 {
	if s.setting == nil {
		return FileMaxBytes
	}
	n, err := s.setting.AttachmentMaxBytes()
	if err != nil || n < 1 {
		return FileMaxBytes
	}
	return n
}

// AddFile 上传文件到条目（落盘 data/library + 建行）
func (s *LibraryService) AddFile(docID, userID uint, originalName string, src io.Reader) (*model.LibraryFile, error) {
	if src == nil {
		return nil, errors.New("文件为空")
	}
	var doc model.LibraryDoc
	if err := s.db.First(&doc, docID).Error; err != nil {
		return nil, ErrLibraryNotFound
	}

	name := sanitizeFilename(originalName)
	if name == "" {
		name = "file"
	}
	ext := strings.TrimPrefix(ExtOfFilename(name), ".")
	if !LibraryExtAllowed(ext) {
		return nil, ErrLibraryExtDenied
	}

	var count int64
	if err := s.db.Model(&model.LibraryFile{}).Where("doc_id = ?", docID).Count(&count).Error; err != nil {
		return nil, err
	}
	if count >= MaxLibraryFilesPerDoc {
		return nil, ErrLibraryTooMany
	}

	raw := make([]byte, 16)
	if _, err := rand.Read(raw); err != nil {
		return nil, err
	}
	stored := hex.EncodeToString(raw) + "." + ext
	full := filepath.Join(s.dir, stored)

	f, err := os.OpenFile(full, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o600)
	if err != nil {
		return nil, err
	}
	maxB := s.maxBytes()
	written, copyErr := io.Copy(f, io.LimitReader(src, maxB+1))
	_ = f.Close()
	if copyErr != nil {
		_ = os.Remove(full)
		return nil, copyErr
	}
	if written == 0 {
		_ = os.Remove(full)
		return nil, errors.New("文件为空")
	}
	if written > maxB {
		_ = os.Remove(full)
		mb := int(maxB >> 20)
		if mb < 1 {
			mb = 1
		}
		return nil, errors.New("文件过大：不能超过 " + strconv.Itoa(mb) + "MB")
	}

	file := &model.LibraryFile{
		DocID:      docID,
		UserID:     userID,
		Name:       name,
		StoredName: stored,
		Ext:        ext,
		MIME:       MimeForAttachmentExt("." + ext),
		Size:       int(written),
	}
	if err := s.db.Create(file).Error; err != nil {
		_ = os.Remove(full)
		return nil, err
	}
	return file, nil
}

// DeleteFile 删除文件（软删行 + 磁盘尽力删除）
func (s *LibraryService) DeleteFile(id uint) error {
	var f model.LibraryFile
	if err := s.db.First(&f, id).Error; err != nil {
		return ErrLibraryNotFound
	}
	if err := s.db.Delete(&f).Error; err != nil {
		return err
	}
	_ = os.Remove(s.FilePath(&f))
	return nil
}

// GetPublicFile 公开取文件（要求所属条目存在且已发布；软删条目的文件不可达）
func (s *LibraryService) GetPublicFile(id uint) (*model.LibraryFile, error) {
	var f model.LibraryFile
	if err := s.db.First(&f, id).Error; err != nil {
		return nil, ErrLibraryNotFound
	}
	if f.DocID == 0 {
		return nil, ErrLibraryNotFound
	}
	var n int64
	if err := s.db.Model(&model.LibraryDoc{}).
		Where("id = ? AND published = ?", f.DocID, true).Count(&n).Error; err != nil {
		return nil, err
	}
	if n == 0 {
		return nil, ErrLibraryNotFound
	}
	return &f, nil
}

// IncrDownload 下载计数原子递增
func (s *LibraryService) IncrDownload(id uint) {
	s.db.Model(&model.LibraryFile{}).Where("id = ?", id).
		UpdateColumn("download_count", gorm.Expr("download_count + 1"))
}