package ape

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

	objectV2 "git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/object"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/ape/router"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/container"
	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"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/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"
	nativeschema "git.frostfs.info/TrueCloudLab/policy-engine/schema/native"
	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
)

type checkerImpl struct {
	chainRouter     policyengine.ChainRouter
	headerProvider  HeaderProvider
	frostFSIDClient frostfsidcore.SubjectProvider
	nm              netmap.Source
	st              netmap.State
	cnrSource       container.Source
	nodePK          []byte
}

func NewChecker(chainRouter policyengine.ChainRouter, headerProvider HeaderProvider, frostFSIDClient frostfsidcore.SubjectProvider, nm netmap.Source, st netmap.State, cnrSource container.Source, nodePK []byte) Checker {
	return &checkerImpl{
		chainRouter:     chainRouter,
		headerProvider:  headerProvider,
		frostFSIDClient: frostFSIDClient,
		nm:              nm,
		st:              st,
		cnrSource:       cnrSource,
		nodePK:          nodePK,
	}
}

type Prm struct {
	Namespace string

	Container cid.ID

	// Object ID is omitted for some methods.
	Object *oid.ID

	// If Header is set, then object attributes and properties will be parsed from
	// a request/response's header.
	Header *objectV2.Header

	// Method must be represented only as a constant represented in native schema.
	Method string

	// Role must be representedonly as a constant represented in native schema.
	Role string

	// An encoded sender's public key string.
	SenderKey string

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

	// If SoftAPECheck is set to true, then NoRuleFound is interpreted as allow.
	SoftAPECheck bool

	// If true, object headers will not retrieved from storage engine.
	WithoutHeaderRequest bool

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

var (
	errMissingOID               = errors.New("object ID is not set")
	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")
)

// 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, containerID cid.ID, publicKey *keys.PublicKey, st netmap.State) error {
	if token == nil {
		return nil
	}

	// 1. First check token lifetime. Simplest verification.
	if token.InvalidAt(st.CurrentEpoch()) {
		return errBearerExpired
	}

	// 2. Then check if bearer token is signed correctly.
	if !token.VerifySignature() {
		return errBearerInvalidSignature
	}

	// 3. Then check if container is either empty or equal to the container in the request.
	apeOverride := token.APEOverride()
	if apeOverride.Target.TargetType != ape.TargetTypeContainer {
		return errInvalidTargetType
	}

	var targetCnr cid.ID
	err := targetCnr.DecodeString(apeOverride.Target.Name)
	if err != nil {
		return fmt.Errorf("invalid cid format: %s", apeOverride.Target.Name)
	}
	if !containerID.Equals(targetCnr) {
		return errBearerInvalidContainerID
	}

	// 4. Then check if container owner signed this token.
	if !bearer.ResolveIssuer(*token).Equals(ownerCnr) {
		return errBearerNotSignedByOwner
	}

	// 5. 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
}

// CheckAPE checks if a request or a response is permitted creating an ape request and passing
// it to chain router.
func (c *checkerImpl) CheckAPE(ctx context.Context, prm Prm) error {
	// APE check is ignored for some inter-node requests.
	if prm.Role == nativeschema.PropertyValueContainerRoleContainer {
		return nil
	} else if prm.Role == nativeschema.PropertyValueContainerRoleIR {
		switch prm.Method {
		case nativeschema.MethodGetObject,
			nativeschema.MethodHeadObject,
			nativeschema.MethodSearchObject,
			nativeschema.MethodRangeObject,
			nativeschema.MethodHashObject:
			return nil
		default:
		}
	}

	r, err := c.newAPERequest(ctx, prm)
	if err != nil {
		return fmt.Errorf("failed to create ape request: %w", err)
	}

	pub, err := keys.NewPublicKeyFromString(prm.SenderKey)
	if err != nil {
		return err
	}

	if prm.BearerToken != nil && !prm.BearerToken.Impersonate() {
		if err := isValidBearer(prm.BearerToken, prm.ContainerOwner, prm.Container, pub, c.st); err != nil {
			return fmt.Errorf("bearer token validation error: %w", err)
		}
		btRouter, err := router.SingleUseRouterWithBearerTokenChains([]bearer.APEOverride{prm.BearerToken.APEOverride()})
		if err != nil {
			return err
		}
		status, found, err := btRouter.IsAllowed(apechain.Ingress, policyengine.NewRequestTargetWithContainer(prm.Container.EncodeToString()), r)
		if err != nil {
			return err
		}
		if found && status == apechain.Allow {
			return nil
		}
		if status != apechain.NoRuleFound {
			return fmt.Errorf("bearer token: method %s: %s", prm.Method, status)
		}
	}

	rt := policyengine.NewRequestTargetExtended(prm.Namespace, prm.Container.EncodeToString(), fmt.Sprintf("%s:%s", prm.Namespace, pub.Address()), nil)
	status, ruleFound, err := c.chainRouter.IsAllowed(apechain.Ingress, rt, r)
	if err != nil {
		return err
	}

	if !ruleFound && prm.SoftAPECheck || status == apechain.Allow {
		return nil
	}

	return fmt.Errorf("method %s: %s", prm.Method, status)
}