package transfer

import (
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"strconv"

	"github.com/github/git-lfs/api"
	"github.com/github/git-lfs/errutil"
	"github.com/github/git-lfs/httputil"
	"github.com/github/git-lfs/progress"
	"github.com/rubyist/tracerx"
)

const (
	TusAdapterName = "tus"
	TusVersion     = "1.0.0"
)

// Adapter for tus.io protocol resumaable uploads
type tusUploadAdapter struct {
	*adapterBase
}

func (a *tusUploadAdapter) ClearTempStorage() error {
	// nothing to do, all temp state is on the server end
	return nil
}

func (a *tusUploadAdapter) DoTransfer(t *Transfer, cb TransferProgressCallback, authOkFunc func()) error {
	rel, ok := t.Object.Rel("upload")
	if !ok {
		return fmt.Errorf("No upload action for this object.")
	}

	// Note not supporting the Creation extension since the batch API generates URLs
	// Also not supporting Concatenation to support parallel uploads of chunks; forward only

	// 1. Send HEAD request to determine upload start point
	//    Request must include Tus-Resumable header (version)
	tracerx.Printf("xfer: sending tus.io HEAD request for %q", t.Object.Oid)
	req, err := httputil.NewHttpRequest("HEAD", rel.Href, rel.Header)
	if err != nil {
		return err
	}
	req.Header.Set("Tus-Resumable", TusVersion)
	res, err := httputil.DoHttpRequest(req, false)
	if err != nil {
		return errutil.NewRetriableError(err)
	}

	//    Response will contain Upload-Offset if supported
	offHdr := res.Header.Get("Upload-Offset")
	if len(offHdr) == 0 {
		return fmt.Errorf("Missing Upload-Offset header from tus.io HEAD response at %q, contact server admin", rel.Href)
	}
	offset, err := strconv.ParseInt(offHdr, 10, 64)
	if err != nil || offset < 0 {
		return fmt.Errorf("Invalid Upload-Offset value %q in response from tus.io HEAD at %q, contact server admin", offHdr, rel.Href)
	}
	// Upload-Offset=size means already completed (skip)
	// Batch API will probably already detect this, but handle just in case
	if offset >= t.Object.Size {
		tracerx.Printf("xfer: tus.io HEAD offset %d indicates %q is already fully uploaded, skipping", offset, t.Object.Oid)
		advanceCallbackProgress(cb, t, t.Object.Size)
		return nil
	}

	// Open file for uploading
	f, err := os.OpenFile(t.Path, os.O_RDONLY, 0644)
	if err != nil {
		return errutil.Error(err)
	}
	defer f.Close()

	// Upload-Offset=0 means start from scratch, but still send PATCH
	if offset == 0 {
		tracerx.Printf("xfer: tus.io uploading %q from start", t.Object.Oid)
	} else {
		tracerx.Printf("xfer: tus.io resuming upload %q from %d", t.Object.Oid, offset)
		advanceCallbackProgress(cb, t, offset)
		_, err := f.Seek(offset, os.SEEK_CUR)
		if err != nil {
			return errutil.Error(err)
		}
	}

	// 2. Send PATCH request with byte start point (even if 0) in Upload-Offset
	//    Response status must be 204
	//    Response Upload-Offset must be request Upload-Offset plus sent bytes
	//    Response may include Upload-Expires header in which case check not passed

	tracerx.Printf("xfer: sending tus.io PATCH request for %q", t.Object.Oid)
	req, err = httputil.NewHttpRequest("PATCH", rel.Href, rel.Header)
	if err != nil {
		return err
	}
	req.Header.Set("Tus-Resumable", TusVersion)
	req.Header.Set("Upload-Offset", strconv.FormatInt(offset, 10))
	req.Header.Set("Content-Type", "application/offset+octet-stream")
	req.Header.Set("Content-Length", strconv.FormatInt(t.Object.Size-offset, 10))
	req.ContentLength = t.Object.Size - offset

	// Ensure progress callbacks made while uploading
	// Wrap callback to give name context
	ccb := func(totalSize int64, readSoFar int64, readSinceLast int) error {
		if cb != nil {
			return cb(t.Name, totalSize, readSoFar, readSinceLast)
		}
		return nil
	}
	var reader io.Reader
	reader = &progress.CallbackReader{
		C:         ccb,
		TotalSize: t.Object.Size,
		Reader:    f,
	}

	// Signal auth was ok on first read; this frees up other workers to start
	if authOkFunc != nil {
		reader = newStartCallbackReader(reader, func(*startCallbackReader) {
			authOkFunc()
		})
	}

	req.Body = ioutil.NopCloser(reader)

	res, err = httputil.DoHttpRequest(req, false)
	if err != nil {
		return errutil.NewRetriableError(err)
	}
	httputil.LogTransfer("lfs.data.upload", res)

	// A status code of 403 likely means that an authentication token for the
	// upload has expired. This can be safely retried.
	if res.StatusCode == 403 {
		return errutil.NewRetriableError(err)
	}

	if res.StatusCode > 299 {
		return errutil.Errorf(nil, "Invalid status for %s: %d", httputil.TraceHttpReq(req), res.StatusCode)
	}

	io.Copy(ioutil.Discard, res.Body)
	res.Body.Close()

	return api.VerifyUpload(t.Object)
}

func init() {
	newfunc := func(name string, dir Direction) TransferAdapter {
		switch dir {
		case Upload:
			bu := &tusUploadAdapter{newAdapterBase(name, dir, nil)}
			// self implements impl
			bu.transferImpl = bu
			return bu
		case Download:
			panic("Should never ask tus.io to download")
		}
		return nil
	}
	RegisterNewTransferAdapterFunc(TusAdapterName, Upload, newfunc)
}