package s3

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	neturl "net/url"
	"os"
	"strings"
	"time"

	"github.com/minio/minio-go/v7"
	"github.com/minio/minio-go/v7/pkg/credentials"
	"github.com/spf13/afero"
)

const (
	readWriteOnlyFlag = os.O_RDONLY | os.O_WRONLY // 0b1
	supportedFlags    = os.O_CREATE | os.O_TRUNC | readWriteOnlyFlag
)

var (
	ErrUnsupported     = errors.New("unsupported operation")
	ErrInvalidProtocol = errors.New("invalid protocol")
	ErrInvalidOpenFlag = errors.New("invalid open flag, expects either O_WRONLY or O_RDONLY")
	ErrNotDirectory    = errors.New("not a directory")
)

type Fs struct {
	client *minio.Client
	bucket string

	// Configurables
	Timeout time.Duration
}

func NewFs(endpoint, bucket, accessKeyID, secretAccessKey string, useSSL bool) (*Fs, error) {
	// Initialize minio client object.
	client, err := minio.New(endpoint, &minio.Options{
		Creds:  credentials.NewStaticV4(accessKeyID, secretAccessKey, ""),
		Secure: useSSL,
	})
	if err != nil {
		return nil, err
	}

	return &Fs{
		client: client,
		bucket: bucket,

		Timeout: 10 * time.Second,
	}, nil
}

func NewFsFromURL(url string) (*Fs, error) {
	endpoint, bucket, accessKeyID, secretAccessKey, useSSL, err := parseUrl(url)
	if err != nil {
		return nil, fmt.Errorf("failed to parse url: %w", err)
	}
	return NewFs(endpoint, bucket, accessKeyID, secretAccessKey, useSSL)
}

// The name of this FileSystem
func (fs *Fs) Name() string {
	return "s3"
}

// Create creates a file in the filesystem, returning the file and an
// error, if any happens.
func (fs *Fs) Create(name string) (afero.File, error) {
	return fs.OpenFile(name, os.O_WRONLY, 0)
}

// Mkdir creates a directory in the filesystem, return an error if any
// happens.
func (fs *Fs) Mkdir(name string, perm os.FileMode) error {
	return ErrUnsupported
}

// MkdirAll creates a directory path and all parents that does not exist
// yet.
func (fs *Fs) MkdirAll(path string, perm os.FileMode) error {
	return ErrUnsupported
}

// Open opens a file, returning it or an error, if any happens.
func (fs *Fs) Open(name string) (afero.File, error) {
	return fs.OpenFile(name, os.O_RDONLY, 0)
}

// OpenFile opens a file using the given flags and the given mode.
func (fs *Fs) OpenFile(name string, flag int, perm os.FileMode) (afero.File, error) {
	if flag&(^supportedFlags) != 0 {
		return nil, ErrInvalidOpenFlag
	}

	f := &File{fs: fs, key: name}
	if isDirPath(name) {
		if flag&os.O_WRONLY != 0 {
			return nil, ErrInvalidOpenFlag
		}
		return f, nil
	}

	var err error
	if flag&os.O_WRONLY != 0 {
		f.w, f.cancel, f.werrc = fs.newObjectWriter(name)
		if err != nil {
			return nil, err
		}
	} else { // os.O_RDONLY
		f.r, f.cancel, err = fs.newObjectReader(name)
		if err != nil {
			return nil, err
		}
	}
	return f, nil
}

// Remove removes a file identified by name, returning an error, if any
// happens.
func (fs *Fs) Remove(name string) error {
	ctx, cancel := fs.contextWithTimeout()
	defer cancel()
	err := fs.client.RemoveObject(ctx, fs.bucket, name, minio.RemoveObjectOptions{})
	if err != nil {
		return fromErrorResponse(err)
	}
	return nil
}

// RemoveAll removes a directory path and any children it contains. It
// does not fail if the path does not exist (return nil).
func (fs *Fs) RemoveAll(path string) error {
	ctx, cancel := fs.contextWithTimeout()
	defer cancel()

	if !isDirPath(path) {
		return ErrNotDirectory
	}
	objectsCh := fs.client.ListObjects(ctx, fs.bucket, minio.ListObjectsOptions{Prefix: path, Recursive: true})
	errc := fs.client.RemoveObjects(ctx, fs.bucket, objectsCh, minio.RemoveObjectsOptions{})
	for err := range errc {
		if err.Err != nil {
			return fromErrorResponse(err.Err)
		}
	}
	return nil
}

// Rename renames a file.
func (fs *Fs) Rename(oldname, newname string) error {
	ctx, cancel := fs.contextWithTimeout()
	defer cancel()

	_, err := fs.client.CopyObject(ctx,
		minio.CopyDestOptions{Bucket: fs.bucket, Object: newname},
		minio.CopySrcOptions{Bucket: fs.bucket, Object: oldname})
	if err != nil {
		return fromErrorResponse(err)
	}
	err = fs.client.RemoveObject(ctx, fs.bucket, oldname, minio.RemoveObjectOptions{})
	if err != nil {
		return fromErrorResponse(err)
	}

	return nil
}

// Stat returns a FileInfo describing the named file, or an error, if any
// happens.
func (fs *Fs) Stat(name string) (os.FileInfo, error) {
	ctx, cancel := fs.contextWithTimeout()
	defer cancel()
	info, err := fs.client.StatObject(ctx, fs.bucket, name, minio.GetObjectOptions{})
	if err != nil {
		return nil, fromErrorResponse(err)
	}
	return fromObjectInfo(info), nil
}

// Chmod changes the mode of the named file to mode.
func (fs *Fs) Chmod(name string, mode os.FileMode) error {
	return ErrUnsupported
}

// Chown changes the uid and gid of the named file.
func (fs *Fs) Chown(name string, uid, gid int) error {
	return ErrUnsupported
}

// Chtimes changes the access and modification times of the named file
func (fs *Fs) Chtimes(name string, atime time.Time, mtime time.Time) error {
	return ErrUnsupported
}

func (fs *Fs) contextWithTimeout() (context.Context, context.CancelFunc) {
	return context.WithTimeout(context.Background(), fs.Timeout)
}

func (fs *Fs) newObjectReader(key string) (io.ReadSeekCloser, context.CancelFunc, error) {
	ctx, cancel := context.WithCancel(context.Background())
	obj, err := fs.client.GetObject(ctx, fs.bucket, key, minio.GetObjectOptions{})
	if err != nil {
		cancel()
		return nil, nil, fromErrorResponse(err)
	}
	return obj, cancel, nil
}

func (fs *Fs) newObjectWriter(key string) (io.WriteCloser, context.CancelFunc, <-chan error) {
	ctx, cancel := context.WithCancel(context.Background())
	r, w := io.Pipe()

	errc := make(chan error, 1)
	go func() {
		maxAtomicSize := int64(16 * (1 << 20))
		lr := io.LimitReader(r, maxAtomicSize)
		b, err := io.ReadAll(lr)
		if err != nil {
			errc <- err
			return
		}
		if ctx.Err() != nil {
			errc <- ctx.Err()
			return
		}
		var rd io.Reader
		var size int64
		if int64(len(b)) == maxAtomicSize {
			rd = io.MultiReader(bytes.NewReader(b), r)
			size = -1
		} else {
			rd = bytes.NewReader(b)
			size = int64(len(b))
		}

		_, err = fs.client.PutObject(ctx, fs.bucket, key, rd, size, minio.PutObjectOptions{})
		errc <- fromErrorResponse(err)
	}()

	return w, cancel, errc
}

func (fs *Fs) readdir(directory string, count int, onlyDir bool) ([]os.FileInfo, error) {
	if !isDirPath(directory) {
		return nil, ErrNotDirectory
	}
	if count == 0 {
		return []os.FileInfo{}, nil
	}
	ctx, cancel := fs.contextWithTimeout()
	defer cancel()
	objectsCh := fs.client.ListObjects(ctx, fs.bucket, minio.ListObjectsOptions{Prefix: directory})
	n := uint(0)
	maxcount := uint(count)
	results := make([]os.FileInfo, 0)
	for objectInfo := range objectsCh {
		if onlyDir && !isDirPath(objectInfo.Key) {
			continue
		}
		results = append(results, fromObjectInfo(objectInfo))
		n += 1
		if n > maxcount {
			break
		}
	}

	return results, nil
}

func isDirPath(p string) bool {
	return p == "" || strings.HasSuffix(p, "/")
}

func parseUrl(url string) (endpoint, bucket, accessKeyID, secretAccessKey string, useSSL bool, err error) {
	var r *neturl.URL
	if r, err = neturl.ParseRequestURI(url); err != nil {
		return
	}
	switch r.Scheme {
	case "http":
	case "https":
		useSSL = true
	default:
		err = ErrInvalidProtocol
		return
	}
	endpoint = r.Host
	bucket = r.Path[1:]
	accessKeyID = r.User.Username()
	secretAccessKey, _ = r.User.Password()
	return
}