package biz

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"time"

	"rag/file-system/internal/data"

	"github.com/go-kratos/kratos/v2/log"
)

// ShareRepo defines the interface for share link persistence operations.
type ShareRepo interface {
	Create(ctx context.Context, share *data.ShareLinkPO) error
	GetByToken(ctx context.Context, token string) (*data.ShareLinkPO, error)
	GetByID(ctx context.Context, id string) (*data.ShareLinkPO, error)
	Delete(ctx context.Context, id, createdBy string) error
	IncrementDownloadCount(ctx context.Context, token string) error
	ListByResource(ctx context.Context, resourceType, resourceID string) ([]data.ShareLinkPO, error)
}

// FileMetaRepoForShare is a minimal interface for share usecase to look up file metadata.
type FileMetaRepoForShare interface {
	GetByID(ctx context.Context, id string) (*data.FileMetaPO, error)
}

// ShareUsecase handles share link business logic.
type ShareUsecase struct {
	shareRepo  ShareRepo
	fileRepo   FileMetaRepoForShare
	s3Repo     FileRepo
	log        *log.Helper
}

// NewShareUsecase creates a new ShareUsecase.
func NewShareUsecase(shareRepo ShareRepo, fileRepo FileMetaRepoForShare, s3Repo FileRepo, logger log.Logger) *ShareUsecase {
	return &ShareUsecase{
		shareRepo: shareRepo,
		fileRepo:  fileRepo,
		s3Repo:    s3Repo,
		log:       log.NewHelper(logger),
	}
}

// CreateShare creates a new share link with a random token.
func (uc *ShareUsecase) CreateShare(ctx context.Context, resourceType, resourceID, password string, expiresAt *time.Time, maxDownloads *int, createdBy string) (*data.ShareLinkPO, error) {
	token, err := generateToken(16)
	if err != nil {
		return nil, fmt.Errorf("failed to generate share token: %w", err)
	}

	share := &data.ShareLinkPO{
		ResourceType: resourceType,
		ResourceID:   resourceID,
		Token:        token,
		ExpiresAt:    expiresAt,
		MaxDownloads: maxDownloads,
		CreatedBy:    createdBy,
	}
	if password != "" {
		pwd := password
		share.Password = &pwd
	}

	if err := uc.shareRepo.Create(ctx, share); err != nil {
		return nil, fmt.Errorf("failed to create share link: %w", err)
	}
	return share, nil
}

// DeleteShare removes a share link by ID and creator.
func (uc *ShareUsecase) DeleteShare(ctx context.Context, id, createdBy string) error {
	return uc.shareRepo.Delete(ctx, id, createdBy)
}

// GetShareInfo retrieves share details and the associated file metadata.
func (uc *ShareUsecase) GetShareInfo(ctx context.Context, token string) (*data.ShareLinkPO, *data.FileMetaPO, error) {
	share, err := uc.shareRepo.GetByToken(ctx, token)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to get share link: %w", err)
	}
	if share == nil {
		return nil, nil, nil
	}

	fileMeta, err := uc.fileRepo.GetByID(ctx, share.ResourceID)
	if err != nil {
		return share, nil, fmt.Errorf("failed to get file metadata: %w", err)
	}
	return share, fileMeta, nil
}

// DownloadShare validates the share link, increments download count, and returns a presigned URL + filename.
func (uc *ShareUsecase) DownloadShare(ctx context.Context, token string) (string, string, error) {
	share, err := uc.shareRepo.GetByToken(ctx, token)
	if err != nil {
		return "", "", fmt.Errorf("failed to get share link: %w", err)
	}
	if share == nil {
		return "", "", fmt.Errorf("share link not found")
	}

	// Check expiry.
	if share.ExpiresAt != nil && share.ExpiresAt.Before(time.Now().UTC()) {
		return "", "", fmt.Errorf("share link has expired")
	}

	// Check max downloads.
	if share.MaxDownloads != nil && share.DownloadCount >= *share.MaxDownloads {
		return "", "", fmt.Errorf("download limit reached")
	}

	// Get file metadata for bucket/key info.
	fileMeta, err := uc.fileRepo.GetByID(ctx, share.ResourceID)
	if err != nil {
		return "", "", fmt.Errorf("failed to get file metadata: %w", err)
	}
	if fileMeta == nil {
		return "", "", fmt.Errorf("file not found")
	}

	// Generate presigned URL.
	url, err := uc.s3Repo.GeneratePresignedURL(ctx, fileMeta.S3Bucket, fileMeta.S3Key, 15*time.Minute)
	if err != nil {
		return "", "", fmt.Errorf("failed to generate download URL: %w", err)
	}

	// Increment download count.
	if err := uc.shareRepo.IncrementDownloadCount(ctx, token); err != nil {
		uc.log.Errorf("failed to increment download count for token %s: %v", token, err)
	}

	return url, fileMeta.Name, nil
}

// generateToken creates a cryptographically secure random hex token.
func generateToken(byteLen int) (string, error) {
	b := make([]byte, byteLen)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return hex.EncodeToString(b), nil
}