package handlers

import (
	"context"
	"errors"
	"fmt"
	"math"
	"strconv"
	"strings"
	"time"

	objectv2 "github.com/TrueCloudLab/frostfs-api-go/v2/object"
	sessionv2 "github.com/TrueCloudLab/frostfs-api-go/v2/session"
	"github.com/TrueCloudLab/frostfs-rest-gw/gen/models"
	"github.com/TrueCloudLab/frostfs-sdk-go/container/acl"
	"github.com/TrueCloudLab/frostfs-sdk-go/object"
	"github.com/TrueCloudLab/frostfs-sdk-go/pool"
)

// PrmAttributes groups parameters to form attributes from request headers.
type PrmAttributes struct {
	DefaultTimestamp bool
	DefaultFileName  string
}

type epochDurations struct {
	currentEpoch  uint64
	msPerBlock    int64
	blockPerEpoch uint64
}

const (
	SystemAttributePrefix = "__NEOFS__"

	ExpirationDurationAttr  = SystemAttributePrefix + "EXPIRATION_DURATION"
	ExpirationTimestampAttr = SystemAttributePrefix + "EXPIRATION_TIMESTAMP"
	ExpirationRFC3339Attr   = SystemAttributePrefix + "EXPIRATION_RFC3339"
)

// GetObjectAttributes forms object attributes from request headers.
func GetObjectAttributes(ctx context.Context, pool *pool.Pool, attrs []*models.Attribute, prm PrmAttributes) ([]object.Attribute, error) {
	headers := make(map[string]string, len(attrs))

	for _, attr := range attrs {
		headers[*attr.Key] = *attr.Value
	}
	delete(headers, object.AttributeFileName)

	if needParseExpiration(headers) {
		epochDuration, err := getEpochDurations(ctx, pool)
		if err != nil {
			return nil, fmt.Errorf("could not get epoch durations from network info: %w", err)
		}
		if err = prepareExpirationHeader(headers, epochDuration); err != nil {
			return nil, fmt.Errorf("could not prepare expiration header: %w", err)
		}
	}

	attributes := make([]object.Attribute, 0, len(headers))
	for key, val := range headers {
		attribute := object.NewAttribute()
		attribute.SetKey(key)
		attribute.SetValue(val)
		attributes = append(attributes, *attribute)
	}

	filename := object.NewAttribute()
	filename.SetKey(object.AttributeFileName)
	filename.SetValue(prm.DefaultFileName)
	attributes = append(attributes, *filename)

	if _, ok := headers[object.AttributeTimestamp]; !ok && prm.DefaultTimestamp {
		timestamp := object.NewAttribute()
		timestamp.SetKey(object.AttributeTimestamp)
		timestamp.SetValue(strconv.FormatInt(time.Now().Unix(), 10))
		attributes = append(attributes, *timestamp)
	}

	return attributes, nil
}

func getEpochDurations(ctx context.Context, p *pool.Pool) (*epochDurations, error) {
	networkInfo, err := p.NetworkInfo(ctx)
	if err != nil {
		return nil, err
	}

	res := &epochDurations{
		currentEpoch:  networkInfo.CurrentEpoch(),
		msPerBlock:    networkInfo.MsPerBlock(),
		blockPerEpoch: networkInfo.EpochDuration(),
	}

	if res.blockPerEpoch == 0 {
		return nil, fmt.Errorf("EpochDuration is zero")
	}
	return res, nil
}

func needParseExpiration(headers map[string]string) bool {
	_, ok1 := headers[ExpirationDurationAttr]
	_, ok2 := headers[ExpirationRFC3339Attr]
	_, ok3 := headers[ExpirationTimestampAttr]
	return ok1 || ok2 || ok3
}

func prepareExpirationHeader(headers map[string]string, epochDurations *epochDurations) error {
	expirationInEpoch := headers[objectv2.SysAttributeExpEpoch]

	if timeRFC3339, ok := headers[ExpirationRFC3339Attr]; ok {
		expTime, err := time.Parse(time.RFC3339, timeRFC3339)
		if err != nil {
			return fmt.Errorf("couldn't parse value %s of header %s", timeRFC3339, ExpirationRFC3339Attr)
		}

		now := time.Now().UTC()
		if expTime.Before(now) {
			return fmt.Errorf("value %s of header %s must be in the future", timeRFC3339, ExpirationRFC3339Attr)
		}
		updateExpirationHeader(headers, epochDurations, expTime.Sub(now))
		delete(headers, ExpirationRFC3339Attr)
	}

	if timestamp, ok := headers[ExpirationTimestampAttr]; ok {
		value, err := strconv.ParseInt(timestamp, 10, 64)
		if err != nil {
			return fmt.Errorf("couldn't parse value %s of header %s", timestamp, ExpirationTimestampAttr)
		}
		expTime := time.Unix(value, 0)

		now := time.Now()
		if expTime.Before(now) {
			return fmt.Errorf("value %s of header %s must be in the future", timestamp, ExpirationTimestampAttr)
		}
		updateExpirationHeader(headers, epochDurations, expTime.Sub(now))
		delete(headers, ExpirationTimestampAttr)
	}

	if duration, ok := headers[ExpirationDurationAttr]; ok {
		expDuration, err := time.ParseDuration(duration)
		if err != nil {
			return fmt.Errorf("couldn't parse value %s of header %s", duration, ExpirationDurationAttr)
		}
		if expDuration <= 0 {
			return fmt.Errorf("value %s of header %s must be positive", expDuration, ExpirationDurationAttr)
		}
		updateExpirationHeader(headers, epochDurations, expDuration)
		delete(headers, ExpirationDurationAttr)
	}

	if expirationInEpoch != "" {
		headers[objectv2.SysAttributeExpEpoch] = expirationInEpoch
	}

	return nil
}

func updateExpirationHeader(headers map[string]string, durations *epochDurations, expDuration time.Duration) {
	epochDuration := uint64(durations.msPerBlock) * durations.blockPerEpoch
	currentEpoch := durations.currentEpoch
	numEpoch := uint64(expDuration.Milliseconds()) / epochDuration

	if uint64(expDuration.Milliseconds())%epochDuration != 0 {
		numEpoch++
	}

	expirationEpoch := uint64(math.MaxUint64)
	if numEpoch < math.MaxUint64-currentEpoch {
		expirationEpoch = currentEpoch + numEpoch
	}

	headers[objectv2.SysAttributeExpEpoch] = strconv.FormatUint(expirationEpoch, 10)
}

// IsObjectToken check that provided token is for object.
func IsObjectToken(token *models.Bearer) (bool, error) {
	isObject := len(token.Object) != 0
	isContainer := token.Container != nil

	if !isObject && !isContainer {
		return false, fmt.Errorf("token '%s': rules must not be empty", token.Name)
	}

	if isObject && isContainer {
		return false, fmt.Errorf("token '%s': only one type rules can be provided: object or container, not both", token.Name)
	}

	return isObject, nil
}

func formSessionTokenFromHeaders(principal *models.Principal, signature, key *string, verb sessionv2.ContainerSessionVerb) (*SessionToken, error) {
	if signature == nil || key == nil {
		return nil, errors.New("missed signature or key header")
	}

	return &SessionToken{
		BearerToken: BearerToken{
			Token:     string(*principal),
			Signature: *signature,
			Key:       *key,
		},
		Verb: verb,
	}, nil
}

// decodeBasicACL is the same as DecodeString on acl.Basic but
// it also checks length for hex formatted acl.
func decodeBasicACL(input string) (acl.Basic, error) {
	switch input {
	case acl.NamePrivate:
		return acl.Private, nil
	case acl.NamePrivateExtended:
		return acl.PrivateExtended, nil
	case acl.NamePublicRO:
		return acl.PublicRO, nil
	case acl.NamePublicROExtended:
		return acl.PublicROExtended, nil
	case acl.NamePublicRW:
		return acl.PublicRW, nil
	case acl.NamePublicRWExtended:
		return acl.PublicRWExtended, nil
	case acl.NamePublicAppend:
		return acl.PublicAppend, nil
	case acl.NamePublicAppendExtended:
		return acl.PublicAppendExtended, nil
	default:
		trimmedInput := strings.TrimPrefix(strings.ToLower(input), "0x")
		if len(trimmedInput) != 8 {
			return 0, fmt.Errorf("invalid basic ACL size: %s", input)
		}

		v, err := strconv.ParseUint(trimmedInput, 16, 32)
		if err != nil {
			return 0, fmt.Errorf("parse hex: %w", err)
		}

		var res acl.Basic
		res.FromBits(uint32(v))
		return res, nil
	}
}