// Copyright 2017 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

// Package gcs provides wrappers around Google Cloud Storage (GCS) APIs.
// Package uses Application Default Credentials assuming that the program runs on GCE.
//
// See the following links for details and API reference:
// https://cloud.google.com/go/getting-started/using-cloud-storage
// https://godoc.org/cloud.google.com/go/storage
package gcs

import (
	"context"
	"fmt"
	"io"
	"os"
	"strings"
	"time"

	"cloud.google.com/go/storage"
)

type Client struct {
	client *storage.Client
	ctx    context.Context
}

type File struct {
	Updated time.Time

	ctx    context.Context
	handle *storage.ObjectHandle
}

func (file *File) Reader() (io.ReadCloser, error) {
	return file.handle.NewReader(file.ctx)
}

func NewClient() (*Client, error) {
	ctx := context.Background()
	storageClient, err := storage.NewClient(ctx)
	if err != nil {
		return nil, err
	}
	client := &Client{
		client: storageClient,
		ctx:    ctx,
	}
	return client, nil
}

func (client *Client) Close() {
	client.client.Close()
}

func (client *Client) Read(gcsFile string) (*File, error) {
	bucket, filename, err := split(gcsFile)
	if err != nil {
		return nil, err
	}
	bkt := client.client.Bucket(bucket)
	f := bkt.Object(filename)
	attrs, err := f.Attrs(client.ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to read %v attributes: %v", gcsFile, err)
	}
	if !attrs.Deleted.IsZero() {
		return nil, fmt.Errorf("file %v is deleted", gcsFile)
	}
	handle := f.If(storage.Conditions{
		GenerationMatch:     attrs.Generation,
		MetagenerationMatch: attrs.Metageneration,
	})
	file := &File{
		Updated: attrs.Updated,
		ctx:     client.ctx,
		handle:  handle,
	}
	return file, nil
}

func (client *Client) UploadFile(localFile, gcsFile string) error {
	local, err := os.Open(localFile)
	if err != nil {
		return err
	}
	defer local.Close()

	w, err := client.FileWriter(gcsFile)
	if err != nil {
		return err
	}
	defer w.Close()

	_, err = io.Copy(w, local)
	return err
}

func (client *Client) FileWriter(gcsFile string) (io.WriteCloser, error) {
	bucket, filename, err := split(gcsFile)
	if err != nil {
		return nil, err
	}
	bkt := client.client.Bucket(bucket)
	f := bkt.Object(filename)
	w := f.NewWriter(client.ctx)
	return w, nil
}

func split(file string) (bucket, filename string, err error) {
	pos := strings.IndexByte(file, '/')
	if pos == -1 {
		return "", "", fmt.Errorf("invalid GCS file name: %v", file)
	}
	return file[:pos], file[pos+1:], nil
}