package ape

import (
	"crypto/ecdsa"
	"errors"
	"fmt"

	aperequest "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/ape/request"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/ape/router"
	frostfsidcore "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/frostfsid"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/netmap"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/ape"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/bearer"
	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/user"
	apechain "git.frostfs.info/TrueCloudLab/policy-engine/pkg/chain"
	policyengine "git.frostfs.info/TrueCloudLab/policy-engine/pkg/engine"
	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
)

var (
	errInvalidTargetType        = errors.New("bearer token defines non-container target override")
	errBearerExpired            = errors.New("bearer token has expired")
	errBearerInvalidSignature   = errors.New("bearer token has invalid signature")
	errBearerInvalidContainerID = errors.New("bearer token was created for another container")
	errBearerNotSignedByOwner   = errors.New("bearer token is not signed by the container owner")
	errBearerInvalidOwner       = errors.New("bearer token owner differs from the request sender")
)

type CheckPrm struct {
	// Request is an APE-request that is checked by policy engine.
	Request aperequest.Request

	Namespace string

	Container cid.ID

	// An encoded container's owner user ID.
	ContainerOwner user.ID

	// PublicKey is public key of the request sender.
	PublicKey *keys.PublicKey

	// The request's bearer token. It is used in order to check APE overrides with the token.
	BearerToken *bearer.Token
}

// CheckCore provides methods to perform the common logic of APE check.
type CheckCore interface {
	// CheckAPE performs the common policy-engine check logic on a prepared request.
	CheckAPE(prm CheckPrm) error
}

type checkerCoreImpl struct {
	LocalOverrideStorage   policyengine.LocalOverrideStorage
	MorphChainStorage      policyengine.MorphRuleChainStorageReader
	FrostFSSubjectProvider frostfsidcore.SubjectProvider
	State                  netmap.State
}

func New(localOverrideStorage policyengine.LocalOverrideStorage, morphChainStorage policyengine.MorphRuleChainStorageReader,
	frostFSSubjectProvider frostfsidcore.SubjectProvider, state netmap.State,
) CheckCore {
	return &checkerCoreImpl{
		LocalOverrideStorage:   localOverrideStorage,
		MorphChainStorage:      morphChainStorage,
		FrostFSSubjectProvider: frostFSSubjectProvider,
		State:                  state,
	}
}

// CheckAPE performs the common policy-engine check logic on a prepared request.
func (c *checkerCoreImpl) CheckAPE(prm CheckPrm) error {
	var cr policyengine.ChainRouter
	if prm.BearerToken != nil && !prm.BearerToken.Impersonate() {
		var err error
		if err = isValidBearer(prm.BearerToken, prm.ContainerOwner, prm.Container, prm.PublicKey, c.State); err != nil {
			return fmt.Errorf("bearer validation error: %w", err)
		}
		cr, err = router.BearerChainFeedRouter(c.LocalOverrideStorage, c.MorphChainStorage, prm.BearerToken.APEOverride())
		if err != nil {
			return fmt.Errorf("create chain router error: %w", err)
		}
	} else {
		cr = policyengine.NewDefaultChainRouterWithLocalOverrides(c.MorphChainStorage, c.LocalOverrideStorage)
	}

	groups, err := aperequest.Groups(c.FrostFSSubjectProvider, prm.PublicKey)
	if err != nil {
		return fmt.Errorf("failed to get group ids: %w", err)
	}

	// Policy contract keeps group related chains as namespace-group pair.
	for i := range groups {
		groups[i] = fmt.Sprintf("%s:%s", prm.Namespace, groups[i])
	}

	rt := policyengine.NewRequestTargetExtended(prm.Namespace, prm.Container.EncodeToString(), fmt.Sprintf("%s:%s", prm.Namespace, prm.PublicKey.Address()), groups)
	status, found, err := cr.IsAllowed(apechain.Ingress, rt, prm.Request)
	if err != nil {
		return err
	}
	if found && status == apechain.Allow {
		return nil
	}
	return fmt.Errorf("access to operation %s is denied by access policy engine: %s", prm.Request.Operation(), status.String())
}

// isValidBearer checks whether bearer token was correctly signed by authorized
// entity. This method might be defined on whole ACL service because it will
// require fetching current epoch to check lifetime.
func isValidBearer(token *bearer.Token, ownerCnr user.ID, cntID cid.ID, publicKey *keys.PublicKey, st netmap.State) error {
	if token == nil {
		return nil
	}

	// First check token lifetime. Simplest verification.
	if token.InvalidAt(st.CurrentEpoch()) {
		return errBearerExpired
	}

	// Then check if bearer token is signed correctly.
	if !token.VerifySignature() {
		return errBearerInvalidSignature
	}

	// Check for ape overrides defined in the bearer token.
	apeOverride := token.APEOverride()
	if len(apeOverride.Chains) > 0 && apeOverride.Target.TargetType != ape.TargetTypeContainer {
		return fmt.Errorf("%w: %s", errInvalidTargetType, apeOverride.Target.TargetType.ToV2().String())
	}

	// Then check if container is either empty or equal to the container in the request.
	var targetCnr cid.ID
	err := targetCnr.DecodeString(apeOverride.Target.Name)
	if err != nil {
		return fmt.Errorf("invalid cid format: %s", apeOverride.Target.Name)
	}
	if !cntID.Equals(targetCnr) {
		return errBearerInvalidContainerID
	}

	// Then check if container owner signed this token.
	if !bearer.ResolveIssuer(*token).Equals(ownerCnr) {
		return errBearerNotSignedByOwner
	}

	// Then check if request sender has rights to use this token.
	var usrSender user.ID
	user.IDFromKey(&usrSender, (ecdsa.PublicKey)(*publicKey))

	if !token.AssertUser(usrSender) {
		return errBearerInvalidOwner
	}

	return nil
}