package service

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"mime"
	"os"
	"path/filepath"
	"strings"
	"unicode/utf8"

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

const (
	FileMaxBytes       = 20 << 20 // 20 MiB
	MaxPostAttachments = 10
)

var (
	ErrAttachmentNotFound = errors.New("附件不存在")
	ErrAttachmentForbidden = errors.New("无权操作此附件")
	ErrTooManyAttachments = errors.New("附件数量超过上限")
)

// PostFileService 帖子文件附件（私有目录 + API 下载）
type PostFileService struct {
	db  *gorm.DB
	dir string // data/private/files
}

func NewPostFileService(db *gorm.DB, privateDir string) *PostFileService {
	return &PostFileService{db: db, dir: filepath.Join(privateDir, "files")}
}

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

func absPath(dir, stored string) string {
	return filepath.Join(dir, stored)
}

// SaveDraftFile 上传附件（先挂 post_id=0，发帖时绑定）
func (s *PostFileService) SaveDraftFile(userID uint, originalName string, data []byte, pricePoints int) (*model.PostAttachment, error) {
	if len(data) == 0 {
		return nil, errors.New("文件为空")
	}
	if len(data) > FileMaxBytes {
		return nil, errors.New("附件不能超过 20MB")
	}
	if pricePoints < 0 {
		pricePoints = 0
	}
	if pricePoints > 100000 {
		return nil, errors.New("积分定价过高")
	}
	name := sanitizeFilename(originalName)
	if name == "" {
		name = "file"
	}

	var orphan int64
	if err := s.db.Model(&model.PostAttachment{}).
		Where("user_id = ? AND post_id = 0", userID).Count(&orphan).Error; err != nil {
		return nil, err
	}
	if orphan >= MaxPostAttachments {
		return nil, ErrTooManyAttachments
	}

	ext := filepath.Ext(name)
	if utf8.RuneCountInString(ext) > 16 {
		ext = ""
	}
	raw := make([]byte, 16)
	if _, err := rand.Read(raw); err != nil {
		return nil, err
	}
	stored := hex.EncodeToString(raw) + ext
	full := absPath(s.dir, stored)
	if err := os.WriteFile(full, data, 0o600); err != nil {
		return nil, err
	}

	mimeType := mime.TypeByExtension(ext)
	if mimeType == "" {
		mimeType = "application/octet-stream"
	}

	att := &model.PostAttachment{
		PostID:      0,
		UserID:      userID,
		Name:        name,
		StoredName:  stored,
		MIME:        mimeType,
		Size:        len(data),
		PricePoints: pricePoints,
	}
	if err := s.db.Create(att).Error; err != nil {
		_ = os.Remove(full)
		return nil, err
	}
	return att, nil
}

func sanitizeFilename(name string) string {
	name = filepath.Base(strings.ReplaceAll(name, "\\", "/"))
	name = strings.TrimSpace(name)
	name = strings.Map(func(r rune) rune {
		switch r {
		case '/', '\\', '\x00', ':', '*', '?', '"', '<', '>', '|':
			return '_'
		default:
			return r
		}
	}, name)
	if utf8.RuneCountInString(name) > 200 {
		runes := []rune(name)
		name = string(runes[:200])
	}
	return name
}

// BindToPost 将草稿附件绑定到帖子（仅本人、未绑定）
func (s *PostFileService) BindToPost(userID, postID uint, ids []uint) error {
	if len(ids) == 0 {
		return nil
	}
	if len(ids) > MaxPostAttachments {
		return ErrTooManyAttachments
	}
	return s.db.Transaction(func(tx *gorm.DB) error {
		var atts []model.PostAttachment
		if err := tx.Where("id IN ? AND user_id = ? AND post_id = 0", ids, userID).Find(&atts).Error; err != nil {
			return err
		}
		if len(atts) != len(ids) {
			return errors.New("部分附件无效或无权使用")
		}
		return tx.Model(&model.PostAttachment{}).
			Where("id IN ? AND user_id = ? AND post_id = 0", ids, userID).
			Update("post_id", postID).Error
	})
}

// ReplacePostAttachments 编辑时重绑附件列表（ids 为最终列表；可含已绑定本帖的）
func (s *PostFileService) ReplacePostAttachments(userID, postID uint, ids []uint) error {
	if len(ids) > MaxPostAttachments {
		return ErrTooManyAttachments
	}
	return s.db.Transaction(func(tx *gorm.DB) error {
		var keep []model.PostAttachment
		if len(ids) > 0 {
			if err := tx.Where(
				"id IN ? AND user_id = ? AND (post_id = 0 OR post_id = ?)",
				ids, userID, postID,
			).Find(&keep).Error; err != nil {
				return err
			}
			if len(keep) != len(ids) {
				return errors.New("部分附件无效或无权使用")
			}
		}
		// 解绑本帖旧附件（软删物理文件可选：P1 仅解绑）
		if err := tx.Model(&model.PostAttachment{}).
			Where("post_id = ? AND user_id = ?", postID, userID).
			Update("post_id", 0).Error; err != nil {
			return err
		}
		if len(ids) == 0 {
			return nil
		}
		return tx.Model(&model.PostAttachment{}).
			Where("id IN ? AND user_id = ?", ids, userID).
			Update("post_id", postID).Error
	})
}

// ListByPost 帖子附件列表
func (s *PostFileService) ListByPost(postID uint) ([]model.PostAttachment, error) {
	var list []model.PostAttachment
	err := s.db.Where("post_id = ?", postID).Order("id ASC").Find(&list).Error
	return list, err
}

// UpdatePrice 更新附件积分定价（作者）
func (s *PostFileService) UpdatePrice(userID, attID uint, price int) error {
	if price < 0 {
		price = 0
	}
	res := s.db.Model(&model.PostAttachment{}).
		Where("id = ? AND user_id = ?", attID, userID).
		Update("price_points", price)
	if res.Error != nil {
		return res.Error
	}
	if res.RowsAffected == 0 {
		return ErrAttachmentNotFound
	}
	return nil
}

// DeleteOwn 删除本人未绑定或本帖附件
func (s *PostFileService) DeleteOwn(userID, attID uint) error {
	var att model.PostAttachment
	if err := s.db.First(&att, attID).Error; err != nil {
		return ErrAttachmentNotFound
	}
	if att.UserID != userID {
		return ErrAttachmentForbidden
	}
	path := absPath(s.dir, att.StoredName)
	if err := s.db.Delete(&att).Error; err != nil {
		return err
	}
	_ = os.Remove(path)
	return nil
}

// OpenForDownload 鉴权后打开文件；需先确认帖子可见与积分
func (s *PostFileService) Get(attID uint) (*model.PostAttachment, error) {
	var att model.PostAttachment
	if err := s.db.First(&att, attID).Error; err != nil {
		return nil, ErrAttachmentNotFound
	}
	return &att, nil
}

func (s *PostFileService) FilePath(att *model.PostAttachment) string {
	return absPath(s.dir, att.StoredName)
}

func (s *PostFileService) IncDownload(attID uint) {
	s.db.Model(&model.PostAttachment{}).Where("id = ?", attID).
		UpdateColumn("download_count", gorm.Expr("download_count + 1"))
}

// EnsureAttachmentUnlocked 免费或已购/作者；积分附件扣费一次
func (s *PostFileService) EnsureAttachmentUnlocked(userID uint, att *model.PostAttachment) error {
	if att.PricePoints <= 0 {
		return nil
	}
	if att.UserID == userID {
		return nil
	}
	var n int64
	if err := s.db.Model(&model.PostAttachmentUnlock{}).
		Where("attachment_id = ? AND user_id = ?", att.ID, userID).
		Count(&n).Error; err != nil {
		return err
	}
	if n > 0 {
		return nil
	}
	return s.db.Transaction(func(tx *gorm.DB) error {
		var again int64
		if err := tx.Model(&model.PostAttachmentUnlock{}).
			Where("attachment_id = ? AND user_id = ?", att.ID, userID).
			Count(&again).Error; err != nil {
			return err
		}
		if again > 0 {
			return nil
		}
		if _, err := DebitTx(tx, userID, att.PricePoints, model.PointReasonDownloadFile, "attachment", att.ID, "下载附件："+att.Name); err != nil {
			return err
		}
		// 积分转给作者
		if att.UserID > 0 && att.UserID != userID {
			if _, err := CreditTx(tx, att.UserID, att.PricePoints, model.PointReasonDownloadFile, "attachment_earn", att.ID, "附件收益："+att.Name); err != nil {
				return err
			}
		}
		return tx.Create(&model.PostAttachmentUnlock{
			AttachmentID: att.ID,
			UserID:       userID,
			Points:       att.PricePoints,
		}).Error
	})
}