package oss

import (
	"crypto/md5"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"hash"
	"hash/crc64"
	"io"
	"io/ioutil"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
)

// DownloadFile downloads files with multipart download.
//
// objectKey    the object key.
// filePath    the local file to download from objectKey in OSS.
// partSize    the part size in bytes.
// options    object's constraints, check out GetObject for the reference.
//
// error    it's nil when the call succeeds, otherwise it's an error object.
//
func (bucket Bucket) DownloadFile(objectKey, filePath string, partSize int64, options ...Option) error {
	if partSize < 1 {
		return errors.New("oss: part size smaller than 1")
	}

	uRange, err := getRangeConfig(options)
	if err != nil {
		return err
	}

	cpConf := getCpConfig(options)
	routines := getRoutines(options)

	if cpConf != nil && cpConf.IsEnable {
		cpFilePath := getDownloadCpFilePath(cpConf, bucket.BucketName, objectKey, filePath)
		if cpFilePath != "" {
			return bucket.downloadFileWithCp(objectKey, filePath, partSize, options, cpFilePath, routines, uRange)
		}
	}

	return bucket.downloadFile(objectKey, filePath, partSize, options, routines, uRange)
}

func getDownloadCpFilePath(cpConf *cpConfig, srcBucket, srcObject, destFile string) string {
	if cpConf.FilePath == "" && cpConf.DirPath != "" {
		src := fmt.Sprintf("oss://%v/%v", srcBucket, srcObject)
		absPath, _ := filepath.Abs(destFile)
		cpFileName := getCpFileName(src, absPath)
		cpConf.FilePath = cpConf.DirPath + string(os.PathSeparator) + cpFileName
	}
	return cpConf.FilePath
}

// getRangeConfig gets the download range from the options.
func getRangeConfig(options []Option) (*unpackedRange, error) {
	rangeOpt, err := findOption(options, HTTPHeaderRange, nil)
	if err != nil || rangeOpt == nil {
		return nil, err
	}
	return parseRange(rangeOpt.(string))
}

// ----- concurrent download without checkpoint  -----

// downloadWorkerArg is download worker's parameters
type downloadWorkerArg struct {
	bucket    *Bucket
	key       string
	filePath  string
	options   []Option
	hook      downloadPartHook
	enableCRC bool
}

// downloadPartHook is hook for test
type downloadPartHook func(part downloadPart) error

var downloadPartHooker downloadPartHook = defaultDownloadPartHook

func defaultDownloadPartHook(part downloadPart) error {
	return nil
}

// defaultDownloadProgressListener defines default ProgressListener, shields the ProgressListener in options of GetObject.
type defaultDownloadProgressListener struct {
}

// ProgressChanged no-ops
func (listener *defaultDownloadProgressListener) ProgressChanged(event *ProgressEvent) {
}

// downloadWorker
func downloadWorker(id int, arg downloadWorkerArg, jobs <-chan downloadPart, results chan<- downloadPart, failed chan<- error, die <-chan bool) {
	for part := range jobs {
		if err := arg.hook(part); err != nil {
			failed <- err
			break
		}

		// Resolve options
		r := Range(part.Start, part.End)
		p := Progress(&defaultDownloadProgressListener{})
		opts := make([]Option, len(arg.options)+2)
		// Append orderly, can not be reversed!
		opts = append(opts, arg.options...)
		opts = append(opts, r, p)

		rd, err := arg.bucket.GetObject(arg.key, opts...)
		if err != nil {
			failed <- err
			break
		}
		defer rd.Close()

		var crcCalc hash.Hash64
		if arg.enableCRC {
			crcCalc = crc64.New(crcTable())
			contentLen := part.End - part.Start + 1
			rd = ioutil.NopCloser(TeeReader(rd, crcCalc, contentLen, nil, nil))
		}
		defer rd.Close()

		select {
		case <-die:
			return
		default:
		}

		fd, err := os.OpenFile(arg.filePath, os.O_WRONLY, FilePermMode)
		if err != nil {
			failed <- err
			break
		}

		_, err = fd.Seek(part.Start-part.Offset, os.SEEK_SET)
		if err != nil {
			fd.Close()
			failed <- err
			break
		}

		_, err = io.Copy(fd, rd)
		if err != nil {
			fd.Close()
			failed <- err
			break
		}

		if arg.enableCRC {
			part.CRC64 = crcCalc.Sum64()
		}

		fd.Close()
		results <- part
	}
}

// downloadScheduler
func downloadScheduler(jobs chan downloadPart, parts []downloadPart) {
	for _, part := range parts {
		jobs <- part
	}
	close(jobs)
}

// downloadPart defines download part
type downloadPart struct {
	Index  int    // Part number, starting from 0
	Start  int64  // Start index
	End    int64  // End index
	Offset int64  // Offset
	CRC64  uint64 // CRC check value of part
}

// getDownloadParts gets download parts
func getDownloadParts(objectSize, partSize int64, uRange *unpackedRange) []downloadPart {
	parts := []downloadPart{}
	part := downloadPart{}
	i := 0
	start, end := adjustRange(uRange, objectSize)
	for offset := start; offset < end; offset += partSize {
		part.Index = i
		part.Start = offset
		part.End = GetPartEnd(offset, end, partSize)
		part.Offset = start
		part.CRC64 = 0
		parts = append(parts, part)
		i++
	}
	return parts
}

// getObjectBytes gets object bytes length
func getObjectBytes(parts []downloadPart) int64 {
	var ob int64
	for _, part := range parts {
		ob += (part.End - part.Start + 1)
	}
	return ob
}

// combineCRCInParts caculates the total CRC of continuous parts
func combineCRCInParts(dps []downloadPart) uint64 {
	if dps == nil || len(dps) == 0 {
		return 0
	}

	crc := dps[0].CRC64
	for i := 1; i < len(dps); i++ {
		crc = CRC64Combine(crc, dps[i].CRC64, (uint64)(dps[i].End-dps[i].Start+1))
	}

	return crc
}

// downloadFile downloads file concurrently without checkpoint.
func (bucket Bucket) downloadFile(objectKey, filePath string, partSize int64, options []Option, routines int, uRange *unpackedRange) error {
	tempFilePath := filePath + TempFileSuffix
	listener := getProgressListener(options)

	// If the file does not exist, create one. If exists, the download will overwrite it.
	fd, err := os.OpenFile(tempFilePath, os.O_WRONLY|os.O_CREATE, FilePermMode)
	if err != nil {
		return err
	}
	fd.Close()

	// Get the object detailed meta for object whole size
	// must delete header:range to get whole object size
	skipOptions := deleteOption(options, HTTPHeaderRange)
	meta, err := bucket.GetObjectDetailedMeta(objectKey, skipOptions...)
	if err != nil {
		return err
	}

	objectSize, err := strconv.ParseInt(meta.Get(HTTPHeaderContentLength), 10, 0)
	if err != nil {
		return err
	}

	enableCRC := false
	expectedCRC := (uint64)(0)
	if bucket.getConfig().IsEnableCRC && meta.Get(HTTPHeaderOssCRC64) != "" {
		if uRange == nil || (!uRange.hasStart && !uRange.hasEnd) {
			enableCRC = true
			expectedCRC, _ = strconv.ParseUint(meta.Get(HTTPHeaderOssCRC64), 10, 0)
		}
	}

	// Get the parts of the file
	parts := getDownloadParts(objectSize, partSize, uRange)
	jobs := make(chan downloadPart, len(parts))
	results := make(chan downloadPart, len(parts))
	failed := make(chan error)
	die := make(chan bool)

	var completedBytes int64
	totalBytes := getObjectBytes(parts)
	event := newProgressEvent(TransferStartedEvent, 0, totalBytes)
	publishProgress(listener, event)

	// Start the download workers
	arg := downloadWorkerArg{&bucket, objectKey, tempFilePath, options, downloadPartHooker, enableCRC}
	for w := 1; w <= routines; w++ {
		go downloadWorker(w, arg, jobs, results, failed, die)
	}

	// Download parts concurrently
	go downloadScheduler(jobs, parts)

	// Waiting for parts download finished
	completed := 0
	for completed < len(parts) {
		select {
		case part := <-results:
			completed++
			completedBytes += (part.End - part.Start + 1)
			parts[part.Index].CRC64 = part.CRC64
			event = newProgressEvent(TransferDataEvent, completedBytes, totalBytes)
			publishProgress(listener, event)
		case err := <-failed:
			close(die)
			event = newProgressEvent(TransferFailedEvent, completedBytes, totalBytes)
			publishProgress(listener, event)
			return err
		}

		if completed >= len(parts) {
			break
		}
	}

	event = newProgressEvent(TransferCompletedEvent, completedBytes, totalBytes)
	publishProgress(listener, event)

	if enableCRC {
		actualCRC := combineCRCInParts(parts)
		err = checkDownloadCRC(actualCRC, expectedCRC)
		if err != nil {
			return err
		}
	}

	return os.Rename(tempFilePath, filePath)
}

// ----- Concurrent download with chcekpoint  -----

const downloadCpMagic = "92611BED-89E2-46B6-89E5-72F273D4B0A3"

type downloadCheckpoint struct {
	Magic     string         // Magic
	MD5       string         // Checkpoint content MD5
	FilePath  string         // Local file
	Object    string         // Key
	ObjStat   objectStat     // Object status
	Parts     []downloadPart // All download parts
	PartStat  []bool         // Parts' download status
	Start     int64          // Start point of the file
	End       int64          // End point of the file
	enableCRC bool           // Whether has CRC check
	CRC       uint64         // CRC check value
}

type objectStat struct {
	Size         int64  // Object size
	LastModified string // Last modified time
	Etag         string // Etag
}

// isValid flags of checkpoint data is valid. It returns true when the data is valid and the checkpoint is valid and the object is not updated.
func (cp downloadCheckpoint) isValid(meta http.Header, uRange *unpackedRange) (bool, error) {
	// Compare the CP's Magic and the MD5
	cpb := cp
	cpb.MD5 = ""
	js, _ := json.Marshal(cpb)
	sum := md5.Sum(js)
	b64 := base64.StdEncoding.EncodeToString(sum[:])

	if cp.Magic != downloadCpMagic || b64 != cp.MD5 {
		return false, nil
	}

	objectSize, err := strconv.ParseInt(meta.Get(HTTPHeaderContentLength), 10, 0)
	if err != nil {
		return false, err
	}

	// Compare the object size, last modified time and etag
	if cp.ObjStat.Size != objectSize ||
		cp.ObjStat.LastModified != meta.Get(HTTPHeaderLastModified) ||
		cp.ObjStat.Etag != meta.Get(HTTPHeaderEtag) {
		return false, nil
	}

	// Check the download range
	if uRange != nil {
		start, end := adjustRange(uRange, objectSize)
		if start != cp.Start || end != cp.End {
			return false, nil
		}
	}

	return true, nil
}

// load checkpoint from local file
func (cp *downloadCheckpoint) load(filePath string) error {
	contents, err := ioutil.ReadFile(filePath)
	if err != nil {
		return err
	}

	err = json.Unmarshal(contents, cp)
	return err
}

// dump funciton dumps to file
func (cp *downloadCheckpoint) dump(filePath string) error {
	bcp := *cp

	// Calculate MD5
	bcp.MD5 = ""
	js, err := json.Marshal(bcp)
	if err != nil {
		return err
	}
	sum := md5.Sum(js)
	b64 := base64.StdEncoding.EncodeToString(sum[:])
	bcp.MD5 = b64

	// Serialize
	js, err = json.Marshal(bcp)
	if err != nil {
		return err
	}

	// Dump
	return ioutil.WriteFile(filePath, js, FilePermMode)
}

// todoParts gets unfinished parts
func (cp downloadCheckpoint) todoParts() []downloadPart {
	dps := []downloadPart{}
	for i, ps := range cp.PartStat {
		if !ps {
			dps = append(dps, cp.Parts[i])
		}
	}
	return dps
}

// getCompletedBytes gets completed size
func (cp downloadCheckpoint) getCompletedBytes() int64 {
	var completedBytes int64
	for i, part := range cp.Parts {
		if cp.PartStat[i] {
			completedBytes += (part.End - part.Start + 1)
		}
	}
	return completedBytes
}

// prepare initiates download tasks
func (cp *downloadCheckpoint) prepare(meta http.Header, bucket *Bucket, objectKey, filePath string, partSize int64, uRange *unpackedRange) error {
	// CP
	cp.Magic = downloadCpMagic
	cp.FilePath = filePath
	cp.Object = objectKey

	objectSize, err := strconv.ParseInt(meta.Get(HTTPHeaderContentLength), 10, 0)
	if err != nil {
		return err
	}

	cp.ObjStat.Size = objectSize
	cp.ObjStat.LastModified = meta.Get(HTTPHeaderLastModified)
	cp.ObjStat.Etag = meta.Get(HTTPHeaderEtag)

	if bucket.getConfig().IsEnableCRC && meta.Get(HTTPHeaderOssCRC64) != "" {
		if uRange == nil || (!uRange.hasStart && !uRange.hasEnd) {
			cp.enableCRC = true
			cp.CRC, _ = strconv.ParseUint(meta.Get(HTTPHeaderOssCRC64), 10, 0)
		}
	}

	// Parts
	cp.Parts = getDownloadParts(objectSize, partSize, uRange)
	cp.PartStat = make([]bool, len(cp.Parts))
	for i := range cp.PartStat {
		cp.PartStat[i] = false
	}

	return nil
}

func (cp *downloadCheckpoint) complete(cpFilePath, downFilepath string) error {
	os.Remove(cpFilePath)
	return os.Rename(downFilepath, cp.FilePath)
}

// downloadFileWithCp downloads files with checkpoint.
func (bucket Bucket) downloadFileWithCp(objectKey, filePath string, partSize int64, options []Option, cpFilePath string, routines int, uRange *unpackedRange) error {
	tempFilePath := filePath + TempFileSuffix
	listener := getProgressListener(options)

	// Load checkpoint data.
	dcp := downloadCheckpoint{}
	err := dcp.load(cpFilePath)
	if err != nil {
		os.Remove(cpFilePath)
	}

	// Get the object detailed meta for object whole size
	// must delete header:range to get whole object size
	skipOptions := deleteOption(options, HTTPHeaderRange)
	meta, err := bucket.GetObjectDetailedMeta(objectKey, skipOptions...)
	if err != nil {
		return err
	}

	// Load error or data invalid. Re-initialize the download.
	valid, err := dcp.isValid(meta, uRange)
	if err != nil || !valid {
		if err = dcp.prepare(meta, &bucket, objectKey, filePath, partSize, uRange); err != nil {
			return err
		}
		os.Remove(cpFilePath)
	}

	// Create the file if not exists. Otherwise the parts download will overwrite it.
	fd, err := os.OpenFile(tempFilePath, os.O_WRONLY|os.O_CREATE, FilePermMode)
	if err != nil {
		return err
	}
	fd.Close()

	// Unfinished parts
	parts := dcp.todoParts()
	jobs := make(chan downloadPart, len(parts))
	results := make(chan downloadPart, len(parts))
	failed := make(chan error)
	die := make(chan bool)

	completedBytes := dcp.getCompletedBytes()
	event := newProgressEvent(TransferStartedEvent, completedBytes, dcp.ObjStat.Size)
	publishProgress(listener, event)

	// Start the download workers routine
	arg := downloadWorkerArg{&bucket, objectKey, tempFilePath, options, downloadPartHooker, dcp.enableCRC}
	for w := 1; w <= routines; w++ {
		go downloadWorker(w, arg, jobs, results, failed, die)
	}

	// Concurrently downloads parts
	go downloadScheduler(jobs, parts)

	// Wait for the parts download finished
	completed := 0
	for completed < len(parts) {
		select {
		case part := <-results:
			completed++
			dcp.PartStat[part.Index] = true
			dcp.Parts[part.Index].CRC64 = part.CRC64
			dcp.dump(cpFilePath)
			completedBytes += (part.End - part.Start + 1)
			event = newProgressEvent(TransferDataEvent, completedBytes, dcp.ObjStat.Size)
			publishProgress(listener, event)
		case err := <-failed:
			close(die)
			event = newProgressEvent(TransferFailedEvent, completedBytes, dcp.ObjStat.Size)
			publishProgress(listener, event)
			return err
		}

		if completed >= len(parts) {
			break
		}
	}

	event = newProgressEvent(TransferCompletedEvent, completedBytes, dcp.ObjStat.Size)
	publishProgress(listener, event)

	if dcp.enableCRC {
		actualCRC := combineCRCInParts(dcp.Parts)
		err = checkDownloadCRC(actualCRC, dcp.CRC)
		if err != nil {
			return err
		}
	}

	return dcp.complete(cpFilePath, tempFilePath)
}