package system

import (
	"context"
	"crypto/md5"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"github.com/google/uuid"
)

var ErrUploadSessionNotFound = errors.New("upload session not found")

func validMD5(value string) bool {
	if len(value) != md5.Size*2 {
		return false
	}
	_, err := hex.DecodeString(value)
	return err == nil
}

func (uc *MediaUsecase) validateUploadLayout(size, chunkSize int64, total int) error {
	if size <= 0 || chunkSize <= 0 || total <= 0 {
		return errors.New("文件大小和分片参数必须大于 0")
	}
	if size > uc.maxMediaFileSize() {
		return ErrMediaTooLarge
	}
	expectedTotal := (size-1)/chunkSize + 1
	if int64(total) != expectedTotal {
		return fmt.Errorf("分片数量不匹配: %d/%d", total, expectedTotal)
	}
	return nil
}

func expectedChunkSize(session *UploadSession, index int) (int64, error) {
	if session == nil || session.FileSize <= 0 || session.ChunkSize <= 0 || session.ChunkTotal <= 0 {
		return 0, errors.New("上传会话分片参数非法")
	}
	if index < 0 || index >= session.ChunkTotal {
		return 0, errors.New("分片序号超出范围")
	}
	if index < session.ChunkTotal-1 {
		return session.ChunkSize, nil
	}
	last := session.FileSize - session.ChunkSize*int64(session.ChunkTotal-1)
	if last <= 0 || last > session.ChunkSize {
		return 0, errors.New("上传会话分片参数非法")
	}
	return last, nil
}

func (uc *MediaUsecase) uploadSession(ctx context.Context, id uint) (*UploadSession, error) {
	session, err := uc.FindUploadSession(ctx, id)
	if errors.Is(err, ErrUploadSessionNotFound) {
		return nil, fmt.Errorf("上传会话不存在: %w", ErrUploadSessionNotFound)
	}
	if err != nil {
		return nil, err
	}
	return session, nil
}

func (uc *MediaUsecase) chunkPrefix(uploadID uint) string {
	directory := "uploads/chunks"
	if uc.settings != nil {
		if configured := strings.Trim(uc.settings.MediaSettings().ChunkDir, "/\\ "); configured != "" {
			directory = configured
		}
	}
	return path.Join(directory, fmt.Sprintf("%d", uploadID))
}

func (uc *MediaUsecase) chunkKey(uploadID uint, index int) string {
	return path.Join(uc.chunkPrefix(uploadID), fmt.Sprintf("%08d", index))
}

func (uc *MediaUsecase) InitUpload(ctx context.Context, userID uint, name, hash string, size, chunkSize int64, total int) (*UploadSession, *MediaFile, []int, error) {
	if err := validateMediaName(name); err != nil {
		return nil, nil, nil, err
	}
	if !validMD5(hash) {
		return nil, nil, nil, errors.New("文件 MD5 非法")
	}
	if err := uc.validateUploadLayout(size, chunkSize, total); err != nil {
		return nil, nil, nil, err
	}
	completed, err := uc.FindCompletedSession(ctx, userID, strings.ToLower(hash))
	if err == nil && completed.MediaID != 0 {
		if media, findErr := uc.FindMedia(ctx, completed.MediaID); findErr == nil {
			copy := &MediaFile{Name: name, URL: media.URL, Tag: media.Tag, Key: media.Key, Size: media.Size, MD5: media.MD5, Mime: media.Mime, UserID: userID}
			if createErr := uc.CreateMedia(ctx, copy); createErr == nil {
				return nil, copy, nil, nil
			}
		}
	} else if err != nil && !errors.Is(err, ErrUploadSessionNotFound) {
		return nil, nil, nil, err
	}
	hash = strings.ToLower(hash)
	session, err := uc.FindUploadingSession(ctx, userID, hash)
	if errors.Is(err, ErrUploadSessionNotFound) {
		session = &UploadSession{UserID: userID, FileName: name, FileHash: hash, FileSize: size, ChunkSize: chunkSize, ChunkTotal: total, Status: "uploading"}
		if err = uc.CreateUploadSession(ctx, session); err != nil {
			return nil, nil, nil, err
		}
	} else if err != nil {
		return nil, nil, nil, err
	} else if session.FileSize != size || session.ChunkSize != chunkSize || session.ChunkTotal != total {
		return nil, nil, nil, errors.New("上传参数与已有会话不一致")
	}
	chunks, err := uc.ListChunks(ctx, session.ID)
	if err != nil {
		return nil, nil, nil, err
	}
	indices := make([]int, 0, len(chunks))
	for _, v := range chunks {
		indices = append(indices, v.Index)
	}
	sort.Ints(indices)
	return session, nil, indices, nil
}
func (uc *MediaUsecase) SaveChunk(ctx context.Context, userID, uploadID uint, index int, expected string, reader io.Reader) error {
	session, err := uc.uploadSession(ctx, uploadID)
	if err != nil {
		return err
	}
	if session.UserID != userID {
		return errors.New("无权操作该上传")
	}
	if session.Status != "uploading" {
		return errors.New("上传会话状态不允许收片")
	}
	expected = strings.ToLower(strings.TrimSpace(expected))
	if !validMD5(expected) {
		return errors.New("分片 MD5 非法")
	}
	wantSize, err := expectedChunkSize(session, index)
	if err != nil {
		return err
	}
	hash := md5.New()
	key := uc.chunkKey(uploadID, index)
	temporary, err := os.CreateTemp("", "kra-upload-chunk-*")
	if err != nil {
		return err
	}
	temporaryName := temporary.Name()
	defer os.Remove(temporaryName)
	defer temporary.Close()
	written, err := io.Copy(io.MultiWriter(temporary, hash), io.LimitReader(reader, wantSize+1))
	if err != nil {
		return err
	}
	if written != wantSize {
		return fmt.Errorf("分片 %d 大小不匹配: %d/%d", index, written, wantSize)
	}
	actual := hex.EncodeToString(hash.Sum(nil))
	if !strings.EqualFold(actual, expected) {
		return fmt.Errorf("分片 %d 校验失败", index)
	}
	if _, err = temporary.Seek(0, io.SeekStart); err != nil {
		return err
	}
	stored, err := uc.files.Put(ctx, key, temporary)
	if err != nil {
		return err
	}
	if stored == nil || stored.Size != written {
		_ = uc.files.Delete(ctx, key)
		return errors.New("分片存储大小不一致")
	}
	if err = uc.UpsertChunk(ctx, uploadID, &UploadChunk{Index: index, Hash: actual, Size: written}); err != nil {
		_ = uc.files.Delete(ctx, key)
		return err
	}
	return nil
}
func (uc *MediaUsecase) CompleteUpload(ctx context.Context, userID, uploadID uint, mime string) (*MediaFile, error) {
	session, err := uc.uploadSession(ctx, uploadID)
	if err != nil {
		return nil, err
	}
	if session.UserID != userID {
		return nil, errors.New("无权操作该上传")
	}
	if err = validateMediaName(session.FileName); err != nil {
		return nil, err
	}
	claimed, err := uc.ClaimUploadSession(ctx, uploadID)
	if err != nil {
		return nil, err
	}
	if !claimed {
		return nil, errors.New("上传不在可合并状态(可能已在合并或已完成)")
	}
	fail := func(value error) (*MediaFile, error) {
		_ = uc.FailUploadSession(ctx, uploadID)
		return nil, value
	}
	chunks, err := uc.ListChunks(ctx, uploadID)
	if err != nil {
		return fail(err)
	}
	if len(chunks) != session.ChunkTotal {
		return fail(fmt.Errorf("分片不全: %d/%d", len(chunks), session.ChunkTotal))
	}
	sort.Slice(chunks, func(i, j int) bool { return chunks[i].Index < chunks[j].Index })
	names := make([]string, 0, len(chunks))
	var totalSize int64
	for index, chunk := range chunks {
		if chunk.Index != index {
			return fail(errors.New("分片序号不连续"))
		}
		expectedSize, sizeErr := expectedChunkSize(session, index)
		if sizeErr != nil || chunk.Size != expectedSize || chunk.Size > session.FileSize-totalSize {
			return fail(errors.New("分片大小不一致"))
		}
		totalSize += chunk.Size
		names = append(names, uc.chunkKey(uploadID, index))
	}
	if totalSize != session.FileSize {
		return fail(fmt.Errorf("文件大小不匹配: %d/%d", totalSize, session.FileSize))
	}
	ext := strings.ToLower(filepath.Ext(session.FileName))
	key := time.Now().Format("20060102") + "/" + uuid.NewString() + ext
	stored, hash, err := uc.files.Compose(ctx, names, key)
	if err != nil {
		return fail(err)
	}
	if stored == nil || stored.Size != session.FileSize {
		if stored != nil {
			_ = uc.files.Delete(ctx, key)
		}
		return fail(errors.New("合并文件大小不匹配"))
	}
	if !strings.EqualFold(hash, session.FileHash) {
		_ = uc.files.Delete(ctx, key)
		return fail(errors.New("整文件校验失败"))
	}
	media := &MediaFile{Name: session.FileName, URL: stored.URL, Tag: strings.TrimPrefix(filepath.Ext(session.FileName), "."), Key: key, Size: stored.Size, Mime: mime, MD5: hash, UserID: userID}
	if err = uc.CreateMedia(ctx, media); err != nil {
		return fail(err)
	}
	if err = uc.CompleteUploadSession(ctx, uploadID, key, media.ID); err != nil {
		_ = uc.FailUploadSession(ctx, uploadID)
		return nil, fmt.Errorf("完成上传会话失败: %w", err)
	}
	_ = uc.DeleteChunks(ctx, uploadID)
	_ = uc.files.DeletePrefix(ctx, uc.chunkPrefix(uploadID))
	return media, nil
}
func (uc *MediaUsecase) CancelUpload(ctx context.Context, userID, uploadID uint) error {
	session, err := uc.uploadSession(ctx, uploadID)
	if err != nil {
		return err
	}
	if session.UserID != userID {
		return errors.New("无权操作该上传")
	}
	_ = uc.DeleteChunks(ctx, uploadID)
	_ = uc.files.DeletePrefix(ctx, uc.chunkPrefix(uploadID))
	return uc.DeleteUploadSession(ctx, uploadID)
}
func (uc *MediaUsecase) CleanupStale(ctx context.Context, ttlHours int) error {
	if ttlHours <= 0 {
		ttlHours = 24
	}
	// The reference cleanup job is best-effort: a stale-session query or an
	// individual storage/database cleanup failure is not propagated to the
	// scheduler. Keep the endpoint-independent background behavior compatible.
	ids, _ := uc.StaleUploadSessionIDs(ctx, time.Now().Add(-time.Duration(ttlHours)*time.Hour))
	for _, id := range ids {
		_ = uc.DeleteUploadData(ctx, id)
		_ = uc.files.DeletePrefix(ctx, uc.chunkPrefix(id))
	}
	return nil
}