package policer

import (
	"context"
	"errors"
	"fmt"

	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
	containercore "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/container"
	objectcore "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/object"
	policycore "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/policy"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/services/replicator"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client"
	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap"
	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"go.uber.org/zap"
)

func (p *Policer) processObject(ctx context.Context, addrWithType objectcore.AddressWithType) error {
	addr := addrWithType.Address
	idCnr := addr.Container()
	idObj := addr.Object()

	cnr, err := p.cnrSrc.Get(idCnr)
	if err != nil {
		if client.IsErrContainerNotFound(err) {
			existed, errWasRemoved := containercore.WasRemoved(p.cnrSrc, idCnr)
			if errWasRemoved != nil {
				return fmt.Errorf("%s: %w", logs.PolicerCouldNotConfirmContainerRemoval, errWasRemoved)
			} else if existed {
				err := p.buryFn(ctx, addrWithType.Address)
				if err != nil {
					return fmt.Errorf("%s: %w", logs.PolicerCouldNotInhumeObjectWithMissingContainer, err)
				}
			}
		}

		return fmt.Errorf("%s: %w", logs.PolicerCouldNotGetContainer, err)
	}

	policy := cnr.Value.PlacementPolicy()
	if policycore.IsECPlacement(policy) {
		// EC not supported yet by policer
		return nil
	}

	nn, err := p.placementBuilder.BuildPlacement(idCnr, &idObj, policy)
	if err != nil {
		return fmt.Errorf("%s: %w", logs.PolicerCouldNotBuildPlacementVectorForObject, err)
	}

	c := &placementRequirements{}

	var numOfContainerNodes int
	for i := range nn {
		numOfContainerNodes += len(nn[i])
	}

	// cached info about already checked nodes
	checkedNodes := newNodeCache()

	for i := range nn {
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		p.processNodes(ctx, c, addrWithType, nn[i], policy.ReplicaDescriptor(i).NumberOfObjects(), checkedNodes)
	}

	if !c.needLocalCopy && c.removeLocalCopy {
		p.log.Info(logs.PolicerRedundantLocalObjectCopyDetected,
			zap.Stringer("object", addr),
		)

		p.cbRedundantCopy(ctx, addr)
	}
	return nil
}

type placementRequirements struct {
	// needLocalCopy is true if the current node must store an object according to the storage policy.
	needLocalCopy bool
	// removeLocalCopy is true if all copies are stored according to the storage policy
	// and the current node doesn't need to store an object.
	removeLocalCopy bool
}

func (p *Policer) processNodes(ctx context.Context, requirements *placementRequirements, addrWithType objectcore.AddressWithType,
	nodes []netmap.NodeInfo, shortage uint32, checkedNodes nodeCache,
) {
	addr := addrWithType.Address
	typ := addrWithType.Type

	// Number of copies that are stored on maintenance nodes.
	var uncheckedCopies int

	if typ == objectSDK.TypeLock || typ == objectSDK.TypeTombstone || addrWithType.IsLinkingObject {
		// all nodes of a container must store the `LOCK`, `TOMBSTONE` and linking objects
		// for correct object removal protection:
		//   - `LOCK`, `TOMBSTONE` and linking objects are broadcast on their PUT requests;
		//   - `LOCK` object removal is a prohibited action in the GC.
		shortage = uint32(len(nodes))
	}

	for i := 0; shortage > 0 && i < len(nodes); i++ {
		select {
		case <-ctx.Done():
			return
		default:
		}

		if p.netmapKeys.IsLocalKey(nodes[i].PublicKey()) {
			requirements.needLocalCopy = true

			shortage--
		} else if nodes[i].IsMaintenance() {
			shortage, uncheckedCopies = p.handleMaintenance(nodes[i], checkedNodes, shortage, uncheckedCopies)
		} else {
			if status := checkedNodes.processStatus(nodes[i]); status.Processed() {
				if status == nodeHoldsObject {
					// node already contains replica, no need to replicate
					nodes = append(nodes[:i], nodes[i+1:]...)
					i--
					shortage--
				}

				continue
			}

			callCtx, cancel := context.WithTimeout(ctx, p.headTimeout)

			_, err := p.remoteHeader(callCtx, nodes[i], addr)

			cancel()

			if err == nil {
				shortage--
				checkedNodes.submitReplicaHolder(nodes[i])
			} else {
				if client.IsErrObjectNotFound(err) {
					checkedNodes.submitReplicaCandidate(nodes[i])
					continue
				} else if isClientErrMaintenance(err) {
					shortage, uncheckedCopies = p.handleMaintenance(nodes[i], checkedNodes, shortage, uncheckedCopies)
				} else {
					p.log.Error(logs.PolicerReceiveObjectHeaderToCheckPolicyCompliance,
						zap.Stringer("object", addr),
						zap.String("error", err.Error()),
					)
				}
			}
		}

		nodes = append(nodes[:i], nodes[i+1:]...)
		i--
	}

	p.handleProcessNodesResult(ctx, addr, requirements, nodes, checkedNodes, shortage, uncheckedCopies)
}

// handleMaintenance handles node in maintenance mode and returns new shortage and uncheckedCopies values
//
// consider remote nodes under maintenance as problem OK. Such
// nodes MAY not respond with object, however, this is how we
// prevent spam with new replicas.
// However, additional copies should not be removed in this case,
// because we can remove the only copy this way.
func (p *Policer) handleMaintenance(node netmap.NodeInfo, checkedNodes nodeCache, shortage uint32, uncheckedCopies int) (uint32, int) {
	checkedNodes.submitReplicaHolder(node)
	shortage--
	uncheckedCopies++

	p.log.Debug(logs.PolicerConsiderNodeUnderMaintenanceAsOK,
		zap.String("node", netmap.StringifyPublicKey(node)),
	)
	return shortage, uncheckedCopies
}

func (p *Policer) handleProcessNodesResult(ctx context.Context, addr oid.Address, requirements *placementRequirements,
	nodes []netmap.NodeInfo, checkedNodes nodeCache, shortage uint32, uncheckedCopies int,
) {
	switch {
	case shortage > 0:
		p.log.Debug(logs.PolicerShortageOfObjectCopiesDetected,
			zap.Stringer("object", addr),
			zap.Uint32("shortage", shortage),
		)

		task := replicator.Task{
			NumCopies: shortage,
			Addr:      addr,
			Nodes:     nodes,
		}

		p.replicator.HandleTask(ctx, task, checkedNodes)

	case uncheckedCopies > 0:
		// If we have more copies than needed, but some of them are from the maintenance nodes,
		// save the local copy.
		p.log.Debug(logs.PolicerSomeOfTheCopiesAreStoredOnNodesUnderMaintenance,
			zap.Int("count", uncheckedCopies))

	case uncheckedCopies == 0:
		// Safe to remove: checked all copies, shortage == 0.
		requirements.removeLocalCopy = true
	}
}

// isClientErrMaintenance checks if err corresponds to FrostFS status return
// which tells that node is currently under maintenance. Supports wrapped
// errors.
//
// Similar to client.IsErr___ errors, consider replacing to FrostFS SDK.
func isClientErrMaintenance(err error) bool {
	switch unwrapErr(err).(type) {
	default:
		return false
	case *apistatus.NodeUnderMaintenance:
		return true
	}
}

// unwrapErr unwraps error using errors.Unwrap.
func unwrapErr(err error) error {
	for e := errors.Unwrap(err); e != nil; e = errors.Unwrap(err) {
		err = e
	}

	return err
}