/*
 * MinIO Object Storage (c) 2021 MinIO, Inc.
 *
 * 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 s3

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"net/http"
	"time"

	jsoniter "github.com/json-iterator/go"
	minio "github.com/minio/minio/cmd"
	"github.com/minio/minio/cmd/logger"
	"github.com/minio/minio/pkg/hash"
)

var (
	errGWMetaNotFound      = errors.New("dare.meta file not found")
	errGWMetaInvalidFormat = errors.New("dare.meta format is invalid")
)

// A gwMetaV1 represents `gw.json` metadata header.
type gwMetaV1 struct {
	Version string         `json:"version"` // Version of the current `gw.json`.
	Format  string         `json:"format"`  // Format of the current `gw.json`.
	Stat    minio.StatInfo `json:"stat"`    // Stat of the current object `gw.json`.
	ETag    string         `json:"etag"`    // ETag of the current object

	// Metadata map for current object `gw.json`.
	Meta map[string]string `json:"meta,omitempty"`
	// Captures all the individual object `gw.json`.
	Parts []minio.ObjectPartInfo `json:"parts,omitempty"`
}

// Gateway metadata constants.
const (
	// Gateway meta version.
	gwMetaVersion = "1.0.0"

	// Gateway meta version.
	gwMetaVersion100 = "1.0.0"

	// Gateway meta format string.
	gwMetaFormat = "gw"

	// Add new constants here.
)

// newGWMetaV1 - initializes new gwMetaV1, adds version.
func newGWMetaV1() (gwMeta gwMetaV1) {
	gwMeta = gwMetaV1{}
	gwMeta.Version = gwMetaVersion
	gwMeta.Format = gwMetaFormat
	return gwMeta
}

// IsValid - tells if the format is sane by validating the version
// string, format fields.
func (m gwMetaV1) IsValid() bool {
	return ((m.Version == gwMetaVersion || m.Version == gwMetaVersion100) &&
		m.Format == gwMetaFormat)
}

// Converts metadata to object info.
func (m gwMetaV1) ToObjectInfo(bucket, object string) minio.ObjectInfo {
	filterKeys := append([]string{
		"ETag",
		"Content-Length",
		"Last-Modified",
		"Content-Type",
		"Expires",
	}, defaultFilterKeys...)
	objInfo := minio.ObjectInfo{
		IsDir:           false,
		Bucket:          bucket,
		Name:            object,
		Size:            m.Stat.Size,
		ModTime:         m.Stat.ModTime,
		ContentType:     m.Meta["content-type"],
		ContentEncoding: m.Meta["content-encoding"],
		ETag:            minio.CanonicalizeETag(m.ETag),
		UserDefined:     minio.CleanMinioInternalMetadataKeys(minio.CleanMetadataKeys(m.Meta, filterKeys...)),
		Parts:           m.Parts,
	}

	if sc, ok := m.Meta["x-amz-storage-class"]; ok {
		objInfo.StorageClass = sc
	}
	var (
		t time.Time
		e error
	)
	if exp, ok := m.Meta["expires"]; ok {
		if t, e = time.Parse(http.TimeFormat, exp); e == nil {
			objInfo.Expires = t.UTC()
		}
	}
	// Success.
	return objInfo
}

// ObjectToPartOffset - translate offset of an object to offset of its individual part.
func (m gwMetaV1) ObjectToPartOffset(ctx context.Context, offset int64) (partIndex int, partOffset int64, err error) {
	if offset == 0 {
		// Special case - if offset is 0, then partIndex and partOffset are always 0.
		return 0, 0, nil
	}
	partOffset = offset
	// Seek until object offset maps to a particular part offset.
	for i, part := range m.Parts {
		partIndex = i
		// Offset is smaller than size we have reached the proper part offset.
		if partOffset < part.Size {
			return partIndex, partOffset, nil
		}
		// Continue to towards the next part.
		partOffset -= part.Size
	}
	logger.LogIf(ctx, minio.InvalidRange{})
	// Offset beyond the size of the object return InvalidRange.
	return 0, 0, minio.InvalidRange{}
}

// Constructs GWMetaV1 using `jsoniter` lib to retrieve each field.
func gwMetaUnmarshalJSON(ctx context.Context, gwMetaBuf []byte) (gwMeta gwMetaV1, err error) {
	var json = jsoniter.ConfigCompatibleWithStandardLibrary
	err = json.Unmarshal(gwMetaBuf, &gwMeta)
	return gwMeta, err
}

// readGWMeta reads `dare.meta` and returns back GW metadata structure.
func readGWMetadata(ctx context.Context, buf bytes.Buffer) (gwMeta gwMetaV1, err error) {
	if buf.Len() == 0 {
		return gwMetaV1{}, errGWMetaNotFound
	}
	gwMeta, err = gwMetaUnmarshalJSON(ctx, buf.Bytes())
	if err != nil {
		return gwMetaV1{}, err
	}
	if !gwMeta.IsValid() {
		return gwMetaV1{}, errGWMetaInvalidFormat
	}
	// Return structured `dare.meta`.
	return gwMeta, nil
}

// getGWMetadata - unmarshals dare.meta into a *minio.PutObjReader
func getGWMetadata(ctx context.Context, bucket, prefix string, gwMeta gwMetaV1) (*minio.PutObjReader, error) {
	// Marshal json.
	metadataBytes, err := json.Marshal(&gwMeta)
	if err != nil {
		logger.LogIf(ctx, err)
		return nil, err
	}
	hashReader, err := hash.NewReader(bytes.NewReader(metadataBytes), int64(len(metadataBytes)), "", "", int64(len(metadataBytes)))
	if err != nil {
		return nil, err
	}
	return minio.NewPutObjReader(hashReader), nil
}