// Package azure provides a storagedriver.StorageDriver implementation to
// store blobs in Microsoft Azure Blob Storage Service.
package azure

import (
	"bufio"
	"bytes"
	"context"
	"fmt"
	"io"
	"strings"
	"time"

	storagedriver "github.com/distribution/distribution/v3/registry/storage/driver"
	"github.com/distribution/distribution/v3/registry/storage/driver/base"
	"github.com/distribution/distribution/v3/registry/storage/driver/factory"

	"github.com/Azure/azure-sdk-for-go/sdk/azcore/streaming"
	"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/container"
)

const driverName = "azure"

const (
	maxChunkSize = 4 * 1024 * 1024
)

type driver struct {
	azClient      *azureClient
	client        *container.Client
	rootDirectory string
}

type baseEmbed struct{ base.Base }

// Driver is a storagedriver.StorageDriver implementation backed by
// Microsoft Azure Blob Storage Service.
type Driver struct{ baseEmbed }

func init() {
	factory.Register(driverName, &azureDriverFactory{})
}

type azureDriverFactory struct{}

func (factory *azureDriverFactory) Create(parameters map[string]interface{}) (storagedriver.StorageDriver, error) {
	params, err := NewParameters(parameters)
	if err != nil {
		return nil, err
	}
	return New(params)
}

// New constructs a new Driver from parameters
func New(params *Parameters) (*Driver, error) {
	azClient, err := newAzureClient(params)
	if err != nil {
		return nil, err
	}
	client := azClient.ContainerClient()
	d := &driver{
		azClient:      azClient,
		client:        client,
		rootDirectory: params.RootDirectory}
	return &Driver{baseEmbed: baseEmbed{Base: base.Base{StorageDriver: d}}}, nil
}

// Implement the storagedriver.StorageDriver interface.
func (d *driver) Name() string {
	return driverName
}

// GetContent retrieves the content stored at "path" as a []byte.
func (d *driver) GetContent(ctx context.Context, path string) ([]byte, error) {
	downloadResponse, err := d.client.NewBlobClient(d.blobName(path)).DownloadStream(ctx, nil)
	if err != nil {
		if is404(err) {
			return nil, storagedriver.PathNotFoundError{Path: path}
		}
		return nil, err
	}
	body := downloadResponse.Body
	defer body.Close()
	return io.ReadAll(body)
}

// PutContent stores the []byte content at a location designated by "path".
func (d *driver) PutContent(ctx context.Context, path string, contents []byte) error {
	// max size for block blobs uploaded via single "Put Blob" for version after "2016-05-31"
	// https://docs.microsoft.com/en-us/rest/api/storageservices/put-blob#remarks
	const limit = 256 * 1024 * 1024
	if len(contents) > limit {
		return fmt.Errorf("uploading %d bytes with PutContent is not supported; limit: %d bytes", len(contents), limit)
	}

	// Historically, blobs uploaded via PutContent used to be of type AppendBlob
	// (https://github.com/distribution/distribution/pull/1438). We can't replace
	// these blobs atomically via a single "Put Blob" operation without
	// deleting them first. Once we detect they are BlockBlob type, we can
	// overwrite them with an atomically "Put Blob" operation.
	//
	// While we delete the blob and create a new one, there will be a small
	// window of inconsistency and if the Put Blob fails, we may end up with
	// losing the existing data while migrating it to BlockBlob type. However,
	// expectation is the clients pushing will be retrying when they get an error
	// response.
	blobName := d.blobName(path)
	blobRef := d.client.NewBlobClient(blobName)
	props, err := blobRef.GetProperties(ctx, nil)
	if err != nil && !is404(err) {
		return fmt.Errorf("failed to get blob properties: %v", err)
	}
	if err == nil && props.BlobType != nil && *props.BlobType != blob.BlobTypeBlockBlob {
		if _, err := blobRef.Delete(ctx, nil); err != nil {
			return fmt.Errorf("failed to delete legacy blob (%v): %v", *props.BlobType, err)
		}
	}

	_, err = d.client.NewBlockBlobClient(blobName).UploadBuffer(ctx, contents, nil)
	return err
}

// Reader retrieves an io.ReadCloser for the content stored at "path" with a
// given byte offset.
func (d *driver) Reader(ctx context.Context, path string, offset int64) (io.ReadCloser, error) {
	blobRef := d.client.NewBlobClient(d.blobName(path))
	options := blob.DownloadStreamOptions{
		Range: blob.HTTPRange{
			Offset: offset,
		},
	}
	props, err := blobRef.GetProperties(ctx, nil)
	if err != nil {
		if is404(err) {
			return nil, storagedriver.PathNotFoundError{Path: path}
		}
		return nil, fmt.Errorf("failed to get blob properties: %v", err)
	}
	if props.ContentLength == nil {
		return nil, fmt.Errorf("failed to get ContentLength for path: %s", path)
	}
	size := *props.ContentLength
	if offset >= size {
		return io.NopCloser(bytes.NewReader(nil)), nil
	}

	resp, err := blobRef.DownloadStream(ctx, &options)
	if err != nil {
		if is404(err) {
			return nil, storagedriver.PathNotFoundError{Path: path}
		}
		return nil, err
	}
	return resp.Body, nil
}

// Writer returns a FileWriter which will store the content written to it
// at the location designated by "path" after the call to Commit.
func (d *driver) Writer(ctx context.Context, path string, append bool) (storagedriver.FileWriter, error) {
	blobName := d.blobName(path)
	blobRef := d.client.NewBlobClient(blobName)

	props, err := blobRef.GetProperties(ctx, nil)
	blobExists := true
	if err != nil {
		if !is404(err) {
			return nil, err
		}
		blobExists = false
	}

	var size int64
	if blobExists {
		if append {
			if props.ContentLength == nil {
				return nil, fmt.Errorf("cannot append to blob because no ContentLength property was returned for: %s", blobName)
			}
			size = *props.ContentLength
		} else {
			if _, err := blobRef.Delete(ctx, nil); err != nil {
				return nil, err
			}
		}
	} else {
		if append {
			return nil, storagedriver.PathNotFoundError{Path: path}
		}
		if _, err = d.client.NewAppendBlobClient(blobName).Create(ctx, nil); err != nil {
			return nil, err
		}
	}

	return d.newWriter(ctx, blobName, size), nil
}

// Stat retrieves the FileInfo for the given path, including the current size
// in bytes and the creation time.
func (d *driver) Stat(ctx context.Context, path string) (storagedriver.FileInfo, error) {
	blobName := d.blobName(path)
	blobRef := d.client.NewBlobClient(blobName)
	// Check if the path is a blob
	props, err := blobRef.GetProperties(ctx, nil)
	if err != nil && !is404(err) {
		return nil, err
	}
	if err == nil {
		var missing []string
		if props.ContentLength == nil {
			missing = append(missing, "ContentLength")
		}
		if props.LastModified == nil {
			missing = append(missing, "LastModified")
		}

		if len(missing) > 0 {
			return nil, fmt.Errorf("required blob properties %s are missing for blob: %s", missing, blobName)
		}
		return storagedriver.FileInfoInternal{FileInfoFields: storagedriver.FileInfoFields{
			Path:    path,
			Size:    *props.ContentLength,
			ModTime: *props.LastModified,
			IsDir:   false,
		}}, nil
	}

	// Check if path is a virtual container
	virtContainerPath := blobName
	if !strings.HasSuffix(virtContainerPath, "/") {
		virtContainerPath += "/"
	}

	maxResults := int32(1)
	pager := d.client.NewListBlobsFlatPager(&container.ListBlobsFlatOptions{
		MaxResults: &maxResults,
		Prefix:     &virtContainerPath,
	})
	for pager.More() {
		resp, err := pager.NextPage(ctx)
		if err != nil {
			return nil, err
		}
		if len(resp.Segment.BlobItems) > 0 {
			// path is a virtual container
			return storagedriver.FileInfoInternal{FileInfoFields: storagedriver.FileInfoFields{
				Path:  path,
				IsDir: true,
			}}, nil
		}
	}

	// path is not a blob or virtual container
	return nil, storagedriver.PathNotFoundError{Path: path}
}

// List returns a list of the objects that are direct descendants of the given
// path.
func (d *driver) List(ctx context.Context, path string) ([]string, error) {
	if path == "/" {
		path = ""
	}

	blobs, err := d.listBlobs(ctx, path)
	if err != nil {
		return blobs, err
	}

	list := directDescendants(blobs, path)
	if path != "" && len(list) == 0 {
		return nil, storagedriver.PathNotFoundError{Path: path}
	}
	return list, nil
}

// Move moves an object stored at sourcePath to destPath, removing the original
// object.
func (d *driver) Move(ctx context.Context, sourcePath string, destPath string) error {
	sourceBlobURL, err := d.URLFor(ctx, sourcePath, nil)
	if err != nil {
		return err
	}
	destBlobRef := d.client.NewBlockBlobClient(d.blobName(destPath))
	_, err = destBlobRef.CopyFromURL(ctx, sourceBlobURL, nil)
	if err != nil {
		if is404(err) {
			return storagedriver.PathNotFoundError{Path: sourcePath}
		}
		return err
	}

	_, err = d.client.NewBlobClient(d.blobName(sourcePath)).Delete(ctx, nil)
	return err
}

// Delete recursively deletes all objects stored at "path" and its subpaths.
func (d *driver) Delete(ctx context.Context, path string) error {
	blobRef := d.client.NewBlobClient(d.blobName(path))
	_, err := blobRef.Delete(ctx, nil)
	if err == nil {
		// was a blob and deleted, return
		return nil
	} else if !is404(err) {
		return err
	}

	// Not a blob, see if path is a virtual container with blobs
	blobs, err := d.listBlobs(ctx, path)
	if err != nil {
		return err
	}

	for _, b := range blobs {
		blobRef := d.client.NewBlobClient(d.blobName(b))
		if _, err := blobRef.Delete(ctx, nil); err != nil {
			return err
		}
	}

	if len(blobs) == 0 {
		return storagedriver.PathNotFoundError{Path: path}
	}
	return nil
}

// URLFor returns a publicly accessible URL for the blob stored at given path
// for specified duration by making use of Azure Storage Shared Access Signatures (SAS).
// See https://msdn.microsoft.com/en-us/library/azure/ee395415.aspx for more info.
func (d *driver) URLFor(ctx context.Context, path string, options map[string]interface{}) (string, error) {
	expiresTime := time.Now().UTC().Add(20 * time.Minute) // default expiration
	expires, ok := options["expiry"]
	if ok {
		t, ok := expires.(time.Time)
		if ok {
			expiresTime = t
		}
	}
	blobName := d.blobName(path)
	blobRef := d.client.NewBlobClient(blobName)
	return d.azClient.SignBlobURL(ctx, blobRef.URL(), expiresTime)
}

// Walk traverses a filesystem defined within driver, starting
// from the given path, calling f on each file and directory
func (d *driver) Walk(ctx context.Context, path string, f storagedriver.WalkFn) error {
	return storagedriver.WalkFallback(ctx, d, path, f)
}

// directDescendants will find direct descendants (blobs or virtual containers)
// of from list of blob paths and will return their full paths. Elements in blobs
// list must be prefixed with a "/" and
//
// Example: direct descendants of "/" in {"/foo", "/bar/1", "/bar/2"} is
// {"/foo", "/bar"} and direct descendants of "bar" is {"/bar/1", "/bar/2"}
func directDescendants(blobs []string, prefix string) []string {
	if !strings.HasPrefix(prefix, "/") { // add trailing '/'
		prefix = "/" + prefix
	}
	if !strings.HasSuffix(prefix, "/") { // containerify the path
		prefix += "/"
	}

	out := make(map[string]bool)
	for _, b := range blobs {
		if strings.HasPrefix(b, prefix) {
			rel := b[len(prefix):]
			c := strings.Count(rel, "/")
			if c == 0 {
				out[b] = true
			} else {
				out[prefix+rel[:strings.Index(rel, "/")]] = true
			}
		}
	}

	var keys []string
	for k := range out {
		keys = append(keys, k)
	}
	return keys
}

func (d *driver) listBlobs(ctx context.Context, virtPath string) ([]string, error) {
	if virtPath != "" && !strings.HasSuffix(virtPath, "/") { // containerify the path
		virtPath += "/"
	}

	// we will replace the root directory prefix before returning blob names
	blobPrefix := d.blobName("")

	// This is to cover for the cases when the rootDirectory of the driver is either "" or "/".
	// In those cases, there is no root prefix to replace and we must actually add a "/" to all
	// results in order to keep them as valid paths as recognized by storagedriver.PathRegexp
	prefix := ""
	if blobPrefix == "" {
		prefix = "/"
	}

	out := []string{}

	listPrefix := d.blobName(virtPath)
	pager := d.client.NewListBlobsFlatPager(&container.ListBlobsFlatOptions{
		Prefix: &listPrefix,
	})
	for pager.More() {
		resp, err := pager.NextPage(ctx)
		if err != nil {
			return nil, err
		}
		for _, blob := range resp.Segment.BlobItems {
			if blob.Name == nil {
				return nil, fmt.Errorf("required blob property Name is missing while listing blobs under: %s", listPrefix)
			}
			name := *blob.Name
			out = append(out, strings.Replace(name, blobPrefix, prefix, 1))
		}
	}

	return out, nil
}

func (d *driver) blobName(path string) string {
	return strings.TrimLeft(strings.TrimRight(d.rootDirectory, "/")+path, "/")
}

func is404(err error) bool {
	return bloberror.HasCode(err, bloberror.BlobNotFound, bloberror.ContainerNotFound, bloberror.ResourceNotFound)
}

type writer struct {
	driver    *driver
	path      string
	size      int64
	bw        *bufio.Writer
	closed    bool
	committed bool
	cancelled bool
}

func (d *driver) newWriter(ctx context.Context, path string, size int64) storagedriver.FileWriter {
	return &writer{
		driver: d,
		path:   path,
		size:   size,
		bw: bufio.NewWriterSize(&blockWriter{
			ctx:    ctx,
			client: d.client,
			path:   path,
		}, maxChunkSize),
	}
}

func (w *writer) Write(p []byte) (int, error) {
	if w.closed {
		return 0, fmt.Errorf("already closed")
	} else if w.committed {
		return 0, fmt.Errorf("already committed")
	} else if w.cancelled {
		return 0, fmt.Errorf("already cancelled")
	}

	n, err := w.bw.Write(p)
	w.size += int64(n)
	return n, err
}

func (w *writer) Size() int64 {
	return w.size
}

func (w *writer) Close() error {
	if w.closed {
		return fmt.Errorf("already closed")
	}
	w.closed = true
	return w.bw.Flush()
}

func (w *writer) Cancel(ctx context.Context) error {
	if w.closed {
		return fmt.Errorf("already closed")
	} else if w.committed {
		return fmt.Errorf("already committed")
	}
	w.cancelled = true
	blobRef := w.driver.client.NewBlobClient(w.path)
	_, err := blobRef.Delete(ctx, nil)
	return err
}

func (w *writer) Commit() error {
	if w.closed {
		return fmt.Errorf("already closed")
	} else if w.committed {
		return fmt.Errorf("already committed")
	} else if w.cancelled {
		return fmt.Errorf("already cancelled")
	}
	w.committed = true
	return w.bw.Flush()
}

type blockWriter struct {
	// We construct transient blockWriter objects to encapsulate a write
	// and need to keep the context passed in to the original FileWriter.Write
	ctx    context.Context
	client *container.Client
	path   string
}

func (bw *blockWriter) Write(p []byte) (int, error) {
	blobRef := bw.client.NewAppendBlobClient(bw.path)
	_, err := blobRef.AppendBlock(bw.ctx, streaming.NopCloser(bytes.NewReader(p)), nil)
	if err != nil {
		return 0, err
	}
	return len(p), nil
}