// Copyright 2020 PingCAP, Inc. Licensed under Apache-2.0.

package storage

import (
	"context"
	"io"
	"io/ioutil"
	"path"
	"strings"

	"cloud.google.com/go/storage"
	"github.com/pingcap/errors"
	"github.com/pingcap/kvproto/pkg/backup"
	"github.com/pingcap/log"
	"github.com/spf13/pflag"
	"go.uber.org/zap"
	"golang.org/x/oauth2/google"
	"google.golang.org/api/iterator"
	"google.golang.org/api/option"

	berrors "github.com/pingcap/br/pkg/errors"
)

const (
	gcsEndpointOption     = "gcs.endpoint"
	gcsStorageClassOption = "gcs.storage-class"
	gcsPredefinedACL      = "gcs.predefined-acl"
	gcsCredentialsFile    = "gcs.credentials-file"
)

// GCSBackendOptions are options for configuration the GCS storage.
type GCSBackendOptions struct {
	Endpoint        string `json:"endpoint" toml:"endpoint"`
	StorageClass    string `json:"storage-class" toml:"storage-class"`
	PredefinedACL   string `json:"predefined-acl" toml:"predefined-acl"`
	CredentialsFile string `json:"credentials-file" toml:"credentials-file"`
}

func (options *GCSBackendOptions) apply(gcs *backup.GCS) error {
	gcs.Endpoint = options.Endpoint
	gcs.StorageClass = options.StorageClass
	gcs.PredefinedAcl = options.PredefinedACL

	if options.CredentialsFile != "" {
		b, err := ioutil.ReadFile(options.CredentialsFile)
		if err != nil {
			return errors.Trace(err)
		}
		gcs.CredentialsBlob = string(b)
	}
	return nil
}

func defineGCSFlags(flags *pflag.FlagSet) {
	// TODO: remove experimental tag if it's stable
	flags.String(gcsEndpointOption, "", "(experimental) Set the GCS endpoint URL")
	flags.String(gcsStorageClassOption, "", "(experimental) Specify the GCS storage class for objects")
	flags.String(gcsPredefinedACL, "", "(experimental) Specify the GCS predefined acl for objects")
	flags.String(gcsCredentialsFile, "", "(experimental) Set the GCS credentials file path")
}

func (options *GCSBackendOptions) parseFromFlags(flags *pflag.FlagSet) error {
	var err error
	options.Endpoint, err = flags.GetString(gcsEndpointOption)
	if err != nil {
		return errors.Trace(err)
	}

	options.StorageClass, err = flags.GetString(gcsStorageClassOption)
	if err != nil {
		return errors.Trace(err)
	}

	options.PredefinedACL, err = flags.GetString(gcsPredefinedACL)
	if err != nil {
		return errors.Trace(err)
	}

	options.CredentialsFile, err = flags.GetString(gcsCredentialsFile)
	if err != nil {
		return errors.Trace(err)
	}
	return nil
}

type gcsStorage struct {
	gcs    *backup.GCS
	bucket *storage.BucketHandle
}

func (s *gcsStorage) objectName(name string) string {
	return path.Join(s.gcs.Prefix, name)
}

// Write file to storage.
func (s *gcsStorage) Write(ctx context.Context, name string, data []byte) error {
	object := s.objectName(name)
	wc := s.bucket.Object(object).NewWriter(ctx)
	wc.StorageClass = s.gcs.StorageClass
	wc.PredefinedACL = s.gcs.PredefinedAcl
	_, err := wc.Write(data)
	if err != nil {
		return errors.Trace(err)
	}
	return wc.Close()
}

// Read storage file.
func (s *gcsStorage) Read(ctx context.Context, name string) ([]byte, error) {
	object := s.objectName(name)
	rc, err := s.bucket.Object(object).NewReader(ctx)
	if err != nil {
		return nil, errors.Trace(err)
	}
	defer rc.Close()

	size := rc.Attrs.Size
	var b []byte
	if size < 0 {
		// happened when using fake-gcs-server in integration test
		b, err = ioutil.ReadAll(rc)
	} else {
		b = make([]byte, size)
		_, err = io.ReadFull(rc, b)
	}
	return b, errors.Trace(err)
}

// FileExists return true if file exists.
func (s *gcsStorage) FileExists(ctx context.Context, name string) (bool, error) {
	object := s.objectName(name)
	_, err := s.bucket.Object(object).Attrs(ctx)
	if err != nil {
		if errors.Cause(err) == storage.ErrObjectNotExist { // nolint:errorlint
			return false, nil
		}
		return false, errors.Trace(err)
	}
	return true, nil
}

// Open a Reader by file path.
func (s *gcsStorage) Open(ctx context.Context, path string) (ReadSeekCloser, error) {
	// TODO, implement this if needed
	panic("Unsupported Operation")
}

// WalkDir traverse all the files in a dir.
//
// fn is the function called for each regular file visited by WalkDir.
// The first argument is the file path that can be used in `Open`
// function; the second argument is the size in byte of the file determined
// by path.
func (s *gcsStorage) WalkDir(ctx context.Context, opt *WalkOption, fn func(string, int64) error) error {
	// TODO, implement this if needed
	panic("Unsupported Operation")
}

func (s *gcsStorage) URI() string {
	return "gcs://" + s.gcs.Bucket + "/" + s.gcs.Prefix
}

// CreateUploader implenments ExternalStorage interface.
func (s *gcsStorage) CreateUploader(ctx context.Context, name string) (Uploader, error) {
	// TODO, implement this if needed
	panic("gcs storage not support multi-upload")
}

func newGCSStorage(ctx context.Context, gcs *backup.GCS, opts *ExternalStorageOptions) (*gcsStorage, error) {
	var clientOps []option.ClientOption
	if gcs.CredentialsBlob == "" {
		creds, err := google.FindDefaultCredentials(ctx, storage.ScopeReadWrite)
		if err != nil {
			return nil, errors.Annotatef(berrors.ErrStorageInvalidConfig, "%v Or you should provide '--gcs.credentials_file'", err)
		}
		if opts.SendCredentials {
			if len(creds.JSON) > 0 {
				gcs.CredentialsBlob = string(creds.JSON)
			} else {
				return nil, errors.Annotate(berrors.ErrStorageInvalidConfig,
					"You should provide '--gcs.credentials_file' when '--send-credentials-to-tikv' is true")
			}
		}
		if creds != nil {
			clientOps = append(clientOps, option.WithCredentials(creds))
		}
	} else {
		clientOps = append(clientOps, option.WithCredentialsJSON([]byte(gcs.GetCredentialsBlob())))
	}

	if gcs.Endpoint != "" {
		clientOps = append(clientOps, option.WithEndpoint(gcs.Endpoint))
	}
	if opts.HTTPClient != nil {
		clientOps = append(clientOps, option.WithHTTPClient(opts.HTTPClient))
	}
	client, err := storage.NewClient(ctx, clientOps...)
	if err != nil {
		return nil, errors.Trace(err)
	}

	if !opts.SendCredentials {
		// Clear the credentials if exists so that they will not be sent to TiKV
		gcs.CredentialsBlob = ""
	}

	bucket := client.Bucket(gcs.Bucket)
	// check whether it's a bug before #647, to solve case #2
	// If the storage is set as gcs://bucket/prefix/,
	// the backupmeta is written correctly to gcs://bucket/prefix/backupmeta,
	// but the SSTs are written wrongly to gcs://bucket/prefix//*.sst (note the extra slash).
	// see details about case 2 at https://github.com/pingcap/br/issues/675#issuecomment-753780742
	sstInPrefix := hasSSTFiles(ctx, bucket, gcs.Prefix)
	sstInPrefixSlash := hasSSTFiles(ctx, bucket, gcs.Prefix+"//")
	if sstInPrefixSlash && !sstInPrefix {
		// This is a old bug, but we must make it compatible.
		// so we need find sst in slash directory
		gcs.Prefix += "//"
	}
	if !opts.SkipCheckPath {
		// check bucket exists
		_, err = bucket.Attrs(ctx)
		if err != nil {
			return nil, errors.Trace(err)
		}
	}
	return &gcsStorage{gcs: gcs, bucket: bucket}, nil
}

func hasSSTFiles(ctx context.Context, bucket *storage.BucketHandle, prefix string) bool {
	query := storage.Query{Prefix: prefix}
	_ = query.SetAttrSelection([]string{"Name"})
	it := bucket.Objects(ctx, &query)
	for {
		attrs, err := it.Next()
		if err == iterator.Done { // nolint:errorlint
			break
		}
		if err != nil {
			log.Warn("failed to list objects on gcs, will use default value for `prefix`", zap.Error(err))
			break
		}
		if strings.HasSuffix(attrs.Name, ".sst") {
			log.Info("sst file found in prefix slash", zap.String("file", attrs.Name))
			return true
		}
	}
	return false
}