// Copyright 2025 Versity Software
// This file is licensed under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package meta

import (
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"syscall"

	"github.com/versity/versitygw/s3err"
)

// SideCar is a metadata storer that uses sidecar files to store metadata.
type SideCar struct {
	dir string
}

const (
	sidecarmeta = "meta"
)

// NewSideCar creates a new SideCar metadata storer.
func NewSideCar(dir string) (SideCar, error) {
	fi, err := os.Lstat(dir)
	if err != nil {
		return SideCar{}, fmt.Errorf("failed to stat directory: %v", err)
	}
	if !fi.IsDir() {
		return SideCar{}, fmt.Errorf("not a directory")
	}

	return SideCar{dir: dir}, nil
}

// RetrieveAttribute retrieves the value of a specific attribute for an object or a bucket.
func (s SideCar) RetrieveAttribute(_ *os.File, bucket, object, attribute string) ([]byte, error) {
	bucket, object = trimVolume(bucket), trimVolume(object)
	metadir := filepath.Join(s.dir, bucket, object, sidecarmeta)
	if object == "" {
		metadir = filepath.Join(s.dir, bucket, sidecarmeta)
	}
	attr := filepath.Join(metadir, attribute)

	value, err := os.ReadFile(attr)
	if errors.Is(err, os.ErrNotExist) {
		return nil, ErrNoSuchKey
	}
	if err != nil {
		return nil, fmt.Errorf("failed to read attribute: %v", err)
	}

	return value, nil
}

// StoreAttribute stores the value of a specific attribute for an object or a bucket.
func (s SideCar) StoreAttribute(_ *os.File, bucket, object, attribute string, value []byte) error {
	bucket, object = trimVolume(bucket), trimVolume(object)
	metadir := filepath.Join(s.dir, bucket, object, sidecarmeta)
	if object == "" {
		metadir = filepath.Join(s.dir, bucket, sidecarmeta)
	}
	err := os.MkdirAll(metadir, 0777)
	if err != nil {
		if errors.Is(err, syscall.ENOSPC) {
			return s3err.GetAPIError(s3err.ErrNoSpaceLeftOnDevice)
		}
		return fmt.Errorf("failed to create metadata directory: %v", err)
	}

	attr := filepath.Join(metadir, attribute)
	tempfile, err := os.CreateTemp(metadir, attribute)
	if err != nil {
		if errors.Is(err, syscall.ENOSPC) {
			return s3err.GetAPIError(s3err.ErrNoSpaceLeftOnDevice)
		}
		return fmt.Errorf("failed to create temporary file: %v", err)
	}
	defer os.Remove(tempfile.Name())

	_, err = tempfile.Write(value)
	if err != nil {
		tempfile.Close()
		if errors.Is(err, syscall.ENOSPC) {
			return s3err.GetAPIError(s3err.ErrNoSpaceLeftOnDevice)
		}
		return fmt.Errorf("failed to write attribute: %v", err)
	}

	// Close explicitly before rename to prevent error on Windows:
	// The process cannot access the file because it is being used by another process.
	if err = tempfile.Close(); err != nil {
		return fmt.Errorf("failed to close temporary file: %v", err)
	}

	err = os.Rename(tempfile.Name(), attr)
	if err != nil {
		return fmt.Errorf("failed to rename temporary file: %v", err)
	}
	return nil
}

// DeleteAttribute removes the value of a specific attribute for an object or a bucket.
func (s SideCar) DeleteAttribute(bucket, object, attribute string) error {
	bucket, object = trimVolume(bucket), trimVolume(object)
	metadir := filepath.Join(s.dir, bucket, object, sidecarmeta)
	if object == "" {
		metadir = filepath.Join(s.dir, bucket, sidecarmeta)
	}
	attr := filepath.Join(metadir, attribute)

	err := os.Remove(attr)
	if errors.Is(err, os.ErrNotExist) {
		return ErrNoSuchKey
	}
	if err != nil {
		return fmt.Errorf("failed to remove attribute: %v", err)
	}

	s.cleanupEmptyDirs(metadir, bucket, object)

	return nil
}

// ListAttributes lists all attributes for an object or a bucket.
func (s SideCar) ListAttributes(bucket, object string) ([]string, error) {
	bucket, object = trimVolume(bucket), trimVolume(object)
	metadir := filepath.Join(s.dir, bucket, object, sidecarmeta)
	if object == "" {
		metadir = filepath.Join(s.dir, bucket, sidecarmeta)
	}

	ents, err := os.ReadDir(metadir)
	if errors.Is(err, os.ErrNotExist) {
		return []string{}, nil
	}
	if err != nil {
		return nil, fmt.Errorf("failed to list attributes: %v", err)
	}

	var attrs []string
	for _, ent := range ents {
		attrs = append(attrs, ent.Name())
	}

	return attrs, nil
}

// DeleteAttributes removes all attributes for an object or a bucket.
// When object is empty the entire bucket sidecar directory is removed,
// cleaning up any orphaned object or multipart metadata within it.
func (s SideCar) DeleteAttributes(bucket, object string) error {
	bucket, object = trimVolume(bucket), trimVolume(object)
	if object == "" {
		// Remove the entire bucket sidecar directory so that orphaned
		// object/multipart metadata does not accumulate after DeleteBucket.
		bucketDir := filepath.Join(s.dir, bucket)
		err := os.RemoveAll(bucketDir)
		if err != nil && !errors.Is(err, os.ErrNotExist) {
			return fmt.Errorf("failed to remove bucket attributes: %w", err)
		}
		return nil
	}

	metadir := filepath.Join(s.dir, bucket, object, sidecarmeta)
	err := os.RemoveAll(metadir)
	if err != nil && !errors.Is(err, os.ErrNotExist) {
		return fmt.Errorf("failed to remove attributes: %w", err)
	}
	s.cleanupEmptyDirs(metadir, bucket, object)
	return nil
}

// RenameObject renames the sidecar metadata directory from oldObject to
// newObject so that path-based lookups continue to work after the data
// directory has been renamed.
func (s SideCar) RenameObject(bucket, oldObject, newObject string) error {
	bucket = trimVolume(bucket)
	oldPath := filepath.Join(s.dir, bucket, trimVolume(oldObject))
	newPath := filepath.Join(s.dir, bucket, trimVolume(newObject))

	if err := os.MkdirAll(filepath.Dir(newPath), 0777); err != nil {
		if errors.Is(err, syscall.ENOSPC) {
			return s3err.GetAPIError(s3err.ErrNoSpaceLeftOnDevice)
		}
		return fmt.Errorf("create parent for renamed metadata: %w", err)
	}

	err := os.Rename(oldPath, newPath)
	if errors.Is(err, os.ErrNotExist) {
		// No metadata stored yet — nothing to rename.
		return nil
	}
	return err
}

func (s SideCar) cleanupEmptyDirs(metadir, bucket, object string) {
	removeIfEmpty(metadir)
	if bucket == "" {
		return
	}
	bucketDir := filepath.Join(s.dir, bucket)
	if object != "" {
		removeEmptyParents(filepath.Dir(metadir), bucketDir)
	}
	removeIfEmpty(bucketDir)
}

func removeIfEmpty(dir string) {
	empty, err := isDirEmpty(dir)
	if err != nil || !empty {
		return
	}
	_ = os.Remove(dir)
}

func removeEmptyParents(dir, stopDir string) {
	for {
		if dir == stopDir || dir == "." || dir == string(filepath.Separator) {
			return
		}
		empty, err := isDirEmpty(dir)
		if err != nil || !empty {
			return
		}
		err = os.Remove(dir)
		if err != nil {
			return
		}
		dir = filepath.Dir(dir)
	}
}

func isDirEmpty(dir string) (bool, error) {
	f, err := os.Open(dir)
	if err != nil {
		return false, err
	}
	defer f.Close()

	ents, err := f.Readdirnames(1)
	if err == io.EOF {
		return true, nil
	}
	if err != nil {
		return false, err
	}
	return len(ents) == 0, nil
}