package azure

import (
	"bytes"
	"context"
	"crypto/md5"
	"encoding/base64"
	"fmt"
	"hash"
	"io"
	"net/http"
	"path"
	"strings"

	"github.com/restic/restic/internal/backend"
	"github.com/restic/restic/internal/backend/layout"
	"github.com/restic/restic/internal/backend/sema"
	"github.com/restic/restic/internal/debug"
	"github.com/restic/restic/internal/errors"
	"github.com/restic/restic/internal/restic"

	"github.com/Azure/azure-sdk-for-go/sdk/azcore"
	"github.com/Azure/azure-sdk-for-go/sdk/azcore/streaming"
	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob"
	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blob"
	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/bloberror"
	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blockblob"
	azContainer "github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/container"
	"github.com/cenkalti/backoff/v4"
)

// Backend stores data on an azure endpoint.
type Backend struct {
	cfg          Config
	container    *azContainer.Client
	connections  uint
	sem          sema.Semaphore
	prefix       string
	listMaxItems int
	layout.Layout
}

const saveLargeSize = 256 * 1024 * 1024
const defaultListMaxItems = 5000

// make sure that *Backend implements backend.Backend
var _ restic.Backend = &Backend{}

func open(cfg Config, rt http.RoundTripper) (*Backend, error) {
	debug.Log("open, config %#v", cfg)
	var client *azContainer.Client
	var err error

	url := fmt.Sprintf("https://%s.blob.core.windows.net/%s", cfg.AccountName, cfg.Container)
	opts := &azContainer.ClientOptions{
		ClientOptions: azcore.ClientOptions{
			Transport: http.DefaultClient,
		},
	}

	if cfg.AccountKey.String() != "" {
		// We have an account key value, find the BlobServiceClient
		// from with a BasicClient
		debug.Log(" - using account key")
		cred, err := azblob.NewSharedKeyCredential(cfg.AccountName, cfg.AccountKey.Unwrap())
		if err != nil {
			return nil, errors.Wrap(err, "NewSharedKeyCredential")
		}

		client, err = azContainer.NewClientWithSharedKeyCredential(url, cred, opts)

		if err != nil {
			return nil, errors.Wrap(err, "NewClientWithSharedKeyCredential")
		}
	} else if cfg.AccountSAS.String() != "" {
		// Get the client using the SAS Token as authentication, this
		// is longer winded than above because the SDK wants a URL for the Account
		// if your using a SAS token, and not just the account name
		// we (as per the SDK ) assume the default Azure portal.
		// https://github.com/Azure/azure-storage-blob-go/issues/130
		debug.Log(" - using sas token")
		sas := cfg.AccountSAS.Unwrap()

		// strip query sign prefix
		if sas[0] == '?' {
			sas = sas[1:]
		}

		urlWithSAS := fmt.Sprintf("%s?%s", url, sas)

		client, err = azContainer.NewClientWithNoCredential(urlWithSAS, opts)
		if err != nil {
			return nil, errors.Wrap(err, "NewAccountSASClientFromEndpointToken")
		}
	} else {
		return nil, errors.New("no azure authentication information found")
	}

	sem, err := sema.New(cfg.Connections)
	if err != nil {
		return nil, err
	}

	be := &Backend{
		container:   client,
		cfg:         cfg,
		connections: cfg.Connections,
		sem:         sem,
		Layout: &layout.DefaultLayout{
			Path: cfg.Prefix,
			Join: path.Join,
		},
		listMaxItems: defaultListMaxItems,
	}

	return be, nil
}

// Open opens the Azure backend at specified container.
func Open(ctx context.Context, cfg Config, rt http.RoundTripper) (*Backend, error) {
	return open(cfg, rt)
}

// Create opens the Azure backend at specified container and creates the container if
// it does not exist yet.
func Create(ctx context.Context, cfg Config, rt http.RoundTripper) (*Backend, error) {
	be, err := open(cfg, rt)

	if err != nil {
		return nil, errors.Wrap(err, "open")
	}

	_, err = be.container.GetProperties(ctx, &azContainer.GetPropertiesOptions{})

	if err != nil && bloberror.HasCode(err, bloberror.ContainerNotFound) {
		_, err = be.container.Create(ctx, &azContainer.CreateOptions{})

		if err != nil {
			return nil, errors.Wrap(err, "container.Create")
		}
	} else if err != nil {
		return be, err
	}

	return be, nil
}

// SetListMaxItems sets the number of list items to load per request.
func (be *Backend) SetListMaxItems(i int) {
	be.listMaxItems = i
}

// IsNotExist returns true if the error is caused by a not existing file.
func (be *Backend) IsNotExist(err error) bool {
	debug.Log("IsNotExist(%T, %#v)", err, err)
	return bloberror.HasCode(err, bloberror.BlobNotFound)
}

// Join combines path components with slashes.
func (be *Backend) Join(p ...string) string {
	return path.Join(p...)
}

func (be *Backend) Connections() uint {
	return be.connections
}

// Location returns this backend's location (the container name).
func (be *Backend) Location() string {
	return be.Join(be.cfg.AccountName, be.cfg.Prefix)
}

// Hasher may return a hash function for calculating a content hash for the backend
func (be *Backend) Hasher() hash.Hash {
	return md5.New()
}

// HasAtomicReplace returns whether Save() can atomically replace files
func (be *Backend) HasAtomicReplace() bool {
	return true
}

// Path returns the path in the bucket that is used for this backend.
func (be *Backend) Path() string {
	return be.prefix
}

// Save stores data in the backend at the handle.
func (be *Backend) Save(ctx context.Context, h restic.Handle, rd restic.RewindReader) error {
	if err := h.Valid(); err != nil {
		return backoff.Permanent(err)
	}

	objName := be.Filename(h)

	debug.Log("Save %v at %v", h, objName)

	be.sem.GetToken()

	debug.Log("InsertObject(%v, %v)", be.cfg.AccountName, objName)

	var err error
	if rd.Length() < saveLargeSize {
		// if it's smaller than 256miB, then just create the file directly from the reader
		err = be.saveSmall(ctx, objName, rd)
	} else {
		// otherwise use the more complicated method
		err = be.saveLarge(ctx, objName, rd)
	}

	be.sem.ReleaseToken()
	debug.Log("%v, err %#v", objName, err)

	return err
}

func (be *Backend) saveSmall(ctx context.Context, objName string, rd restic.RewindReader) error {
	blockBlobClient := be.container.NewBlockBlobClient(objName)

	// upload it as a new "block", use the base64 hash for the ID
	id := base64.StdEncoding.EncodeToString(rd.Hash())

	buf := make([]byte, rd.Length())
	_, err := io.ReadFull(rd, buf)
	if err != nil {
		return errors.Wrap(err, "ReadFull")
	}

	reader := bytes.NewReader(buf)
	_, err = blockBlobClient.StageBlock(ctx, id, streaming.NopCloser(reader), &blockblob.StageBlockOptions{
		TransactionalContentMD5: rd.Hash(),
	})
	if err != nil {
		return errors.Wrap(err, "StageBlock")
	}

	blocks := []string{id}
	_, err = blockBlobClient.CommitBlockList(ctx, blocks, &blockblob.CommitBlockListOptions{})
	return errors.Wrap(err, "CommitBlockList")
}

func (be *Backend) saveLarge(ctx context.Context, objName string, rd restic.RewindReader) error {
	blockBlobClient := be.container.NewBlockBlobClient(objName)

	buf := make([]byte, 100*1024*1024)
	blocks := []string{}
	uploadedBytes := 0

	for {
		n, err := io.ReadFull(rd, buf)
		if err == io.ErrUnexpectedEOF {
			err = nil
		}

		if err == io.EOF {
			// end of file reached, no bytes have been read at all
			break
		}

		if err != nil {
			return errors.Wrap(err, "ReadFull")
		}

		buf = buf[:n]
		uploadedBytes += n

		// upload it as a new "block", use the base64 hash for the ID
		h := md5.Sum(buf)
		id := base64.StdEncoding.EncodeToString(h[:])

		reader := bytes.NewReader(buf)
		debug.Log("StageBlock %v with %d bytes", id, len(buf))
		_, err = blockBlobClient.StageBlock(ctx, id, streaming.NopCloser(reader), &blockblob.StageBlockOptions{
			TransactionalContentMD5: h[:],
		})

		if err != nil {
			return errors.Wrap(err, "StageBlock")
		}

		blocks = append(blocks, id)
	}

	// sanity check
	if uploadedBytes != int(rd.Length()) {
		return errors.Errorf("wrote %d bytes instead of the expected %d bytes", uploadedBytes, rd.Length())
	}

	_, err := blockBlobClient.CommitBlockList(ctx, blocks, &blockblob.CommitBlockListOptions{})

	debug.Log("uploaded %d parts: %v", len(blocks), blocks)
	return errors.Wrap(err, "CommitBlockList")
}

// Load runs fn with a reader that yields the contents of the file at h at the
// given offset.
func (be *Backend) Load(ctx context.Context, h restic.Handle, length int, offset int64, fn func(rd io.Reader) error) error {
	return backend.DefaultLoad(ctx, h, length, offset, be.openReader, fn)
}

func (be *Backend) openReader(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error) {
	debug.Log("Load %v, length %v, offset %v from %v", h, length, offset, be.Filename(h))
	if err := h.Valid(); err != nil {
		return nil, backoff.Permanent(err)
	}

	if offset < 0 {
		return nil, errors.New("offset is negative")
	}

	if length < 0 {
		return nil, errors.Errorf("invalid length %d", length)
	}

	objName := be.Filename(h)
	blockBlobClient := be.container.NewBlobClient(objName)

	be.sem.GetToken()
	resp, err := blockBlobClient.DownloadStream(ctx, &blob.DownloadStreamOptions{
		Range: azblob.HTTPRange{
			Offset: offset,
			Count:  int64(length),
		},
	})

	if err != nil {
		be.sem.ReleaseToken()
		return nil, err
	}

	return be.sem.ReleaseTokenOnClose(resp.Body, nil), err
}

// Stat returns information about a blob.
func (be *Backend) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo, error) {
	debug.Log("%v", h)

	objName := be.Filename(h)
	blobClient := be.container.NewBlobClient(objName)

	be.sem.GetToken()
	props, err := blobClient.GetProperties(ctx, nil)
	be.sem.ReleaseToken()

	if err != nil {
		debug.Log("blob.GetProperties err %v", err)
		return restic.FileInfo{}, errors.Wrap(err, "blob.GetProperties")
	}

	fi := restic.FileInfo{
		Size: *props.ContentLength,
		Name: h.Name,
	}
	return fi, nil
}

// Remove removes the blob with the given name and type.
func (be *Backend) Remove(ctx context.Context, h restic.Handle) error {
	objName := be.Filename(h)
	blob := be.container.NewBlobClient(objName)

	be.sem.GetToken()
	_, err := blob.Delete(ctx, &azblob.DeleteBlobOptions{})
	be.sem.ReleaseToken()

	debug.Log("Remove(%v) at %v -> err %v", h, objName, err)

	if be.IsNotExist(err) {
		return nil
	}

	return errors.Wrap(err, "client.RemoveObject")
}

// List runs fn for each file in the backend which has the type t. When an
// error occurs (or fn returns an error), List stops and returns it.
func (be *Backend) List(ctx context.Context, t restic.FileType, fn func(restic.FileInfo) error) error {
	debug.Log("listing %v", t)

	prefix, _ := be.Basedir(t)

	// make sure prefix ends with a slash
	if !strings.HasSuffix(prefix, "/") {
		prefix += "/"
	}

	max := int32(be.listMaxItems)

	opts := &azContainer.ListBlobsFlatOptions{
		MaxResults: &max,
		Prefix:     &prefix,
	}
	lister := be.container.NewListBlobsFlatPager(opts)

	for lister.More() {
		be.sem.GetToken()
		resp, err := lister.NextPage(ctx)
		be.sem.ReleaseToken()

		if err != nil {
			return err
		}

		debug.Log("got %v objects", len(resp.Segment.BlobItems))

		for _, item := range resp.Segment.BlobItems {
			m := strings.TrimPrefix(*item.Name, prefix)
			if m == "" {
				continue
			}

			fi := restic.FileInfo{
				Name: path.Base(m),
				Size: *item.Properties.ContentLength,
			}

			if ctx.Err() != nil {
				return ctx.Err()
			}

			err := fn(fi)
			if err != nil {
				return err
			}

			if ctx.Err() != nil {
				return ctx.Err()
			}

		}
	}

	return ctx.Err()
}

// Remove keys for a specified backend type.
func (be *Backend) removeKeys(ctx context.Context, t restic.FileType) error {
	return be.List(ctx, t, func(fi restic.FileInfo) error {
		return be.Remove(ctx, restic.Handle{Type: t, Name: fi.Name})
	})
}

// Delete removes all restic keys in the bucket. It will not remove the bucket itself.
func (be *Backend) Delete(ctx context.Context) error {
	alltypes := []restic.FileType{
		restic.PackFile,
		restic.KeyFile,
		restic.LockFile,
		restic.SnapshotFile,
		restic.IndexFile}

	for _, t := range alltypes {
		err := be.removeKeys(ctx, t)
		if err != nil {
			return nil
		}
	}

	return be.Remove(ctx, restic.Handle{Type: restic.ConfigFile})
}

// Close does nothing
func (be *Backend) Close() error { return nil }