package storage

import (
	"bytes"
	"context"
	"errors"
	"io"
	"strconv"
	"sync"

	api "github.com/qiniu/go-sdk/v7"
)

// 分片上传过程中可能遇到的错误
var ErrUnmatchedChecksum = errors.New("unmatched checksum")

const (
	// 获取下一个分片Reader失败
	ErrNextReader = "ErrNextReader"
	// 超过了最大的重试上传次数
	ErrMaxUpRetry = "ErrMaxUpRetry"
)

const (
	blockBits = 22
	blockMask = (1 << blockBits) - 1
	blockSize = 1 << blockBits

	uploadRecordVersion = "1.0.0"
)

// Settings 为分片上传设置
type Settings struct {
	TaskQsize int   // 可选。任务队列大小。为 0 表示取 Workers * 4。
	Workers   int   // 并行 Goroutine 数目。
	ChunkSize int   // 默认的Chunk大小，不设定则为4M（仅在分片上传 v1 中使用）
	PartSize  int64 // 默认的Part大小，不设定则为4M（仅在分片上传 v2 中使用）
	TryTimes  int   // 默认的尝试次数，不设定则为3
}

// 分片上传默认参数设置
const (
	defaultWorkers   = 4               // 默认的并发上传的块数量
	defaultChunkSize = 4 * 1024 * 1024 // 默认的分片大小，4MB（仅在分片上传 v1 中使用）
	defaultPartSize  = 4 * 1024 * 1024 // 默认的分片大小，4MB（仅在分片上传 v2 中使用）
	defaultTryTimes  = 3               // mkblk / bput / uploadParts 失败重试次数
)

// 分片上传的默认设置
var settings = Settings{
	TaskQsize: defaultWorkers * 4,
	Workers:   defaultWorkers,
	ChunkSize: defaultChunkSize,
	PartSize:  defaultPartSize,
	TryTimes:  defaultTryTimes,
}

// SetSettings 可以用来设置分片上传参数
func SetSettings(v *Settings) {
	settings = *v
	if settings.Workers == 0 {
		settings.Workers = defaultWorkers
	}
	if settings.TaskQsize == 0 {
		settings.TaskQsize = settings.Workers * 4
	}
	if settings.ChunkSize == 0 {
		settings.ChunkSize = defaultChunkSize
	}
	if settings.PartSize == 0 {
		settings.PartSize = defaultPartSize
	}
	if settings.TryTimes == 0 {
		settings.TryTimes = defaultTryTimes
	}
}

var (
	tasks chan func()
	once  sync.Once
)

func worker(tasks chan func()) {
	for task := range tasks {
		task()
	}
}

func _initWorkers() {
	tasks = make(chan func(), settings.TaskQsize)
	for i := 0; i < settings.Workers; i++ {
		go worker(tasks)
	}
}

func initWorkers() {
	once.Do(_initWorkers)
}

// 代表一块分片的基本信息
type (
	chunk struct {
		id     int64
		offset int64
		size   int64
		reader io.ReaderAt
	}

	// 代表一块分片的上传错误信息
	chunkError struct {
		chunk
		err error
	}

	// 通用分片上传接口，同时适用于分片上传 v1 和 v2 接口
	resumeUploaderBase interface {
		// 开始上传前调用一次用于初始化，在 v1 中该接口不做任何事情，而在 v2 中该接口对应 initParts
		initUploader(context.Context) ([]int64, error)
		// 上传实际的分片数据，允许并发上传。在 v1 中该接口对应 mkblk 和 bput 组合，而在 v2 中该接口对应 uploadParts
		uploadChunk(context.Context, chunk) error
		// 上传所有分片后调用一次用于结束上传，在 v1 中该接口对应 mkfile，而在 v2 中该接口对应 completeParts
		final(context.Context) error
	}

	// 将已知数据流大小的情况和未知数据流大小的情况抽象成一个接口
	chunkReader interface {
		readChunks([]int64, func(chunkID, off, size int64, reader io.ReaderAt) error) error
	}

	// 已知数据流大小的情况下读取数据流
	unsizedChunkReader struct {
		body      io.Reader
		blockSize int64
	}

	// 未知数据流大小的情况下读取数据流
	sizedChunkReader struct {
		body      io.ReaderAt
		totalSize int64
		blockSize int64
	}
)

// 使用并发 Goroutine 上传数据
func uploadByWorkers(uploader resumeUploaderBase, ctx context.Context, body chunkReader) error {

	initWorkers()

	recovered, iErr := uploader.initUploader(ctx)
	if iErr != nil {
		return iErr
	}

	// 读取 Chunk 并创建任务
	var uErr error
	var locker = sync.Mutex{}
	var waiter = sync.WaitGroup{}
	rErr := body.readChunks(recovered, func(chunkID, off, size int64, reader io.ReaderAt) error {
		locker.Lock()
		if uErr != nil {
			locker.Unlock()
			return uErr
		}
		locker.Unlock()

		waiter.Add(1)
		tasks <- func() {
			pErr := uploader.uploadChunk(ctx, chunk{
				id:     chunkID,
				offset: off,
				size:   size,
				reader: reader,
			})

			locker.Lock()
			if uErr == nil {
				uErr = pErr
			}
			locker.Unlock()
			waiter.Done()
		}
		return nil
	})
	waiter.Wait()

	if rErr != nil {
		return rErr
	}

	if uErr != nil {
		return uErr
	}

	return uploader.final(ctx)
}

func newUnsizedChunkReader(body io.Reader, blockSize int64) *unsizedChunkReader {
	return &unsizedChunkReader{body: body, blockSize: blockSize}
}

func (r *unsizedChunkReader) readChunks(recovered []int64, f func(chunkID, off, size int64, reader io.ReaderAt) error) error {
	var (
		lastChunk          = false
		chunkID      int64 = 0
		off          int64 = 0
		chunkSize    int
		err          error
		recoveredMap = make(map[int64]struct{}, len(recovered))
	)

	for _, roff := range recovered {
		recoveredMap[roff] = struct{}{}
	}

	for !lastChunk {
		buf := make([]byte, r.blockSize)
		if chunkSize, err = io.ReadFull(r.body, buf); err != nil {
			switch err {
			case io.EOF:
				lastChunk = true
				return nil
			case io.ErrUnexpectedEOF:
				buf = buf[:chunkSize]
				lastChunk = true
			default:
				return api.NewError(ErrNextReader, err.Error())
			}
		}

		if _, ok := recoveredMap[off]; !ok {
			if err = f(chunkID, off, int64(len(buf)), bytes.NewReader(buf)); err != nil {
				return err
			}
		}
		chunkID += 1
		off += int64(chunkSize)
	}
	return nil
}

func newSizedChunkReader(body io.ReaderAt, totalSize, blockSize int64) *sizedChunkReader {
	return &sizedChunkReader{body: body, totalSize: totalSize, blockSize: blockSize}
}

func (r *sizedChunkReader) readChunks(recovered []int64, f func(chunkID, off, size int64, reader io.ReaderAt) error) error {
	var (
		chunkID      int64 = 0
		off          int64 = 0
		err          error
		recoveredMap = make(map[int64]struct{}, len(recovered))
	)

	for _, roff := range recovered {
		recoveredMap[roff] = struct{}{}
	}

	for off < r.totalSize {
		shouldRead := r.totalSize - off
		if shouldRead > r.blockSize {
			shouldRead = r.blockSize
		}
		if _, ok := recoveredMap[off]; !ok {
			if err = f(chunkID, off, shouldRead, io.NewSectionReader(r.body, off, shouldRead)); err != nil {
				return err
			}
		}
		off += shouldRead
		chunkID += 1
	}
	return nil
}

func getRecorderKey(recorder Recorder, upToken string, key string,
	resumeVersion string, partSize int64, fileDetails *fileDetailsInfo) string {
	if recorder == nil || fileDetails == nil || len(upToken) == 0 {
		return ""
	}

	accessKey, bucket, err := getAkBucketFromUploadToken(upToken)
	if err != nil {
		return ""
	}

	return recorder.GenerateRecorderKey(
		[]string{accessKey, bucket, key, resumeVersion, fileDetails.fileFullPath, strconv.FormatInt(partSize, 10)},
		fileDetails.fileInfo)
}