// Package stateless implements a PinTracker component for IPFS Cluster, which
// aims to reduce the memory footprint when handling really large cluster
// states.
package stateless

import (
	"context"
	"errors"
	"fmt"
	"sync"
	"time"

	"github.com/ipfs/ipfs-cluster/api"
	"github.com/ipfs/ipfs-cluster/pintracker/optracker"
	"github.com/ipfs/ipfs-cluster/state"

	logging "github.com/ipfs/go-log/v2"
	peer "github.com/libp2p/go-libp2p-core/peer"
	rpc "github.com/libp2p/go-libp2p-gorpc"

	"go.opencensus.io/trace"
)

var logger = logging.Logger("pintracker")

const pinsChannelSize = 1024

var (
	// ErrFullQueue is the error used when pin or unpin operation channel is full.
	ErrFullQueue = errors.New("pin/unpin operation queue is full. Try increasing max_pin_queue_size")

	// items with this error should be recovered
	errUnexpectedlyUnpinned = errors.New("the item should be pinned but it is not")
)

// Tracker uses the optracker.OperationTracker to manage
// transitioning shared ipfs-cluster state (Pins) to the local IPFS node.
type Tracker struct {
	config *Config

	optracker *optracker.OperationTracker

	peerID   peer.ID
	peerName string

	ctx    context.Context
	cancel func()

	getState func(ctx context.Context) (state.ReadOnly, error)

	rpcClient *rpc.Client
	rpcReady  chan struct{}

	priorityPinCh chan *optracker.Operation
	pinCh         chan *optracker.Operation
	unpinCh       chan *optracker.Operation

	shutdownMu sync.Mutex
	shutdown   bool
	wg         sync.WaitGroup
}

// New creates a new StatelessPinTracker.
func New(cfg *Config, pid peer.ID, peerName string, getState func(ctx context.Context) (state.ReadOnly, error)) *Tracker {
	ctx, cancel := context.WithCancel(context.Background())

	spt := &Tracker{
		config:        cfg,
		peerID:        pid,
		peerName:      peerName,
		ctx:           ctx,
		cancel:        cancel,
		getState:      getState,
		optracker:     optracker.NewOperationTracker(ctx, pid, peerName),
		rpcReady:      make(chan struct{}, 1),
		priorityPinCh: make(chan *optracker.Operation, cfg.MaxPinQueueSize),
		pinCh:         make(chan *optracker.Operation, cfg.MaxPinQueueSize),
		unpinCh:       make(chan *optracker.Operation, cfg.MaxPinQueueSize),
	}

	for i := 0; i < spt.config.ConcurrentPins; i++ {
		go spt.opWorker(spt.pin, spt.priorityPinCh, spt.pinCh)
	}
	go spt.opWorker(spt.unpin, spt.unpinCh, nil)

	return spt
}

// we can get our IPFS id from our own monitor ping metrics which
// are refreshed regularly.
func (spt *Tracker) getIPFSID(ctx context.Context) api.IPFSID {
	// Wait until RPC is ready
	<-spt.rpcReady

	var ipfsid api.IPFSID
	err := spt.rpcClient.CallContext(
		ctx,
		"",
		"Cluster",
		"IPFSID",
		peer.ID(""), // local peer
		&ipfsid,
	)
	if err != nil {
		logger.Error(err)
	}
	return ipfsid
}

// receives a pin Function (pin or unpin) and channels.  Used for both pinning
// and unpinning.
func (spt *Tracker) opWorker(pinF func(*optracker.Operation) error, prioCh, normalCh chan *optracker.Operation) {

	var op *optracker.Operation

	for {
		// Process the priority channel first.
		select {
		case op = <-prioCh:
			goto APPLY_OP
		case <-spt.ctx.Done():
			return
		default:
		}

		// Then process things on the other channels.
		// Block if there are no things to process.
		select {
		case op = <-prioCh:
			goto APPLY_OP
		case op = <-normalCh:
			goto APPLY_OP
		case <-spt.ctx.Done():
			return
		}

		// apply operations that came from some channel
	APPLY_OP:
		if clean := applyPinF(pinF, op); clean {
			spt.optracker.Clean(op.Context(), op)
		}
	}
}

// applyPinF returns true if the operation can be considered "DONE".
func applyPinF(pinF func(*optracker.Operation) error, op *optracker.Operation) bool {
	if op.Cancelled() {
		// operation was cancelled. Move on.
		// This saves some time, but not 100% needed.
		return false
	}
	op.SetPhase(optracker.PhaseInProgress)
	op.IncAttempt()
	err := pinF(op) // call pin/unpin
	if err != nil {
		if op.Cancelled() {
			// there was an error because
			// we were cancelled. Move on.
			return false
		}
		op.SetError(err)
		op.Cancel()
		return false
	}
	op.SetPhase(optracker.PhaseDone)
	op.Cancel()
	return true // this tells the opWorker to clean the operation from the tracker.
}

func (spt *Tracker) pin(op *optracker.Operation) error {
	ctx, span := trace.StartSpan(op.Context(), "tracker/stateless/pin")
	defer span.End()

	logger.Debugf("issuing pin call for %s", op.Cid())
	err := spt.rpcClient.CallContext(
		ctx,
		"",
		"IPFSConnector",
		"Pin",
		op.Pin(),
		&struct{}{},
	)
	if err != nil {
		return err
	}
	return nil
}

func (spt *Tracker) unpin(op *optracker.Operation) error {
	ctx, span := trace.StartSpan(op.Context(), "tracker/stateless/unpin")
	defer span.End()

	logger.Debugf("issuing unpin call for %s", op.Cid())
	err := spt.rpcClient.CallContext(
		ctx,
		"",
		"IPFSConnector",
		"Unpin",
		op.Pin(),
		&struct{}{},
	)
	if err != nil {
		return err
	}
	return nil
}

// Enqueue puts a new operation on the queue, unless ongoing exists.
func (spt *Tracker) enqueue(ctx context.Context, c api.Pin, typ optracker.OperationType) error {
	ctx, span := trace.StartSpan(ctx, "tracker/stateless/enqueue")
	defer span.End()

	logger.Debugf("entering enqueue: pin: %+v", c)
	op := spt.optracker.TrackNewOperation(ctx, c, typ, optracker.PhaseQueued)
	if op == nil {
		return nil // the operation exists and must be queued already.
	}

	var ch chan *optracker.Operation

	switch typ {
	case optracker.OperationPin:
		isPriorityPin := time.Now().Before(c.Timestamp.Add(spt.config.PriorityPinMaxAge)) &&
			op.AttemptCount() <= spt.config.PriorityPinMaxRetries
		op.SetPriorityPin(isPriorityPin)

		if isPriorityPin {
			ch = spt.priorityPinCh
		} else {
			ch = spt.pinCh
		}
	case optracker.OperationUnpin:
		ch = spt.unpinCh
	}

	select {
	case ch <- op:
	default:
		err := ErrFullQueue
		op.SetError(err)
		op.Cancel()
		logger.Error(err.Error())
		return err
	}
	return nil
}

// SetClient makes the StatelessPinTracker ready to perform RPC requests to
// other components.
func (spt *Tracker) SetClient(c *rpc.Client) {
	spt.rpcClient = c
	close(spt.rpcReady)
}

// Shutdown finishes the services provided by the StatelessPinTracker
// and cancels any active context.
func (spt *Tracker) Shutdown(ctx context.Context) error {
	ctx, span := trace.StartSpan(ctx, "tracker/stateless/Shutdown")
	_ = ctx
	defer span.End()

	spt.shutdownMu.Lock()
	defer spt.shutdownMu.Unlock()

	if spt.shutdown {
		logger.Debug("already shutdown")
		return nil
	}

	logger.Info("stopping StatelessPinTracker")
	spt.cancel()
	spt.wg.Wait()
	spt.shutdown = true
	return nil
}

// Track tells the StatelessPinTracker to start managing a Cid,
// possibly triggering Pin operations on the IPFS daemon.
func (spt *Tracker) Track(ctx context.Context, c api.Pin) error {
	ctx, span := trace.StartSpan(ctx, "tracker/stateless/Track")
	defer span.End()

	logger.Debugf("tracking %s", c.Cid)

	// Sharded pins are never pinned. A sharded pin cannot turn into
	// something else or viceversa like it happens with Remote pins so
	// we just ignore them.
	if c.Type == api.MetaType {
		return nil
	}

	// Trigger unpin whenever something remote is tracked
	// Note, IPFSConn checks with pin/ls before triggering
	// pin/rm.
	if c.IsRemotePin(spt.peerID) {
		op := spt.optracker.TrackNewOperation(ctx, c, optracker.OperationRemote, optracker.PhaseInProgress)
		if op == nil {
			return nil // ongoing unpin
		}
		err := spt.unpin(op)
		op.Cancel()
		if err != nil {
			op.SetError(err)
			return nil
		}

		op.SetPhase(optracker.PhaseDone)
		spt.optracker.Clean(ctx, op)
		return nil
	}

	return spt.enqueue(ctx, c, optracker.OperationPin)
}

// Untrack tells the StatelessPinTracker to stop managing a Cid.
// If the Cid is pinned locally, it will be unpinned.
func (spt *Tracker) Untrack(ctx context.Context, c api.Cid) error {
	ctx, span := trace.StartSpan(ctx, "tracker/stateless/Untrack")
	defer span.End()

	logger.Debugf("untracking %s", c)
	return spt.enqueue(ctx, api.PinCid(c), optracker.OperationUnpin)
}

// StatusAll returns information for all Cids pinned to the local IPFS node.
func (spt *Tracker) StatusAll(ctx context.Context, filter api.TrackerStatus, out chan<- api.PinInfo) error {
	ctx, span := trace.StartSpan(ctx, "tracker/stateless/StatusAll")
	defer span.End()

	ipfsid := spt.getIPFSID(ctx)

	// Any other states are just operation-tracker states, so we just give
	// those and return.
	if !filter.Match(
		api.TrackerStatusPinned | api.TrackerStatusUnexpectedlyUnpinned |
			api.TrackerStatusSharded | api.TrackerStatusRemote) {
		return spt.optracker.GetAllChannel(ctx, filter, ipfsid, out)
	}

	defer close(out)

	// get global state - cluster pinset
	st, err := spt.getState(ctx)
	if err != nil {
		logger.Error(err)
		return err
	}

	var ipfsRecursivePins map[api.Cid]api.IPFSPinStatus
	// Only query IPFS if we want to status for pinned items
	if filter.Match(api.TrackerStatusPinned | api.TrackerStatusUnexpectedlyUnpinned) {
		ipfsRecursivePins = make(map[api.Cid]api.IPFSPinStatus)
		// At some point we need a full map of what we have and what
		// we don't. The IPFS pinset is the smallest thing we can keep
		// on memory.
		ipfsPinsCh, err := spt.ipfsPins(ctx)
		if err != nil {
			logger.Error(err)
			return err
		}
		for ipfsPinInfo := range ipfsPinsCh {
			ipfsRecursivePins[ipfsPinInfo.Cid] = ipfsPinInfo.Type
		}
	}

	// Prepare pinset streaming
	statePins := make(chan api.Pin, pinsChannelSize)
	go func() {
		err = st.List(ctx, statePins)
		if err != nil {
			logger.Error(err)
		}
	}()

	// a shorthand for this select.
	trySend := func(info api.PinInfo) bool {
		select {
		case <-ctx.Done():
			return false
		case out <- info:
			return true
		}
	}

	// For every item in the state.
	for p := range statePins {
		select {
		case <-ctx.Done():
		default:
		}

		// if there is an operation, issue that and move on
		info, ok := spt.optracker.GetExists(ctx, p.Cid, ipfsid)
		if ok && filter.Match(info.Status) {
			if !trySend(info) {
				return fmt.Errorf("error issuing PinInfo: %w", ctx.Err())
			}
			continue // next pin
		}

		// Preliminary PinInfo for this Pin.
		info = api.PinInfo{
			Cid:         p.Cid,
			Name:        p.Name,
			Peer:        spt.peerID,
			Allocations: p.Allocations,
			Origins:     p.Origins,
			Created:     p.Timestamp,
			Metadata:    p.Metadata,

			PinInfoShort: api.PinInfoShort{
				PeerName:      spt.peerName,
				IPFS:          ipfsid.ID,
				IPFSAddresses: ipfsid.Addresses,
				Status:        api.TrackerStatusUndefined, // TBD
				TS:            p.Timestamp,
				Error:         "",
				AttemptCount:  0,
				PriorityPin:   false,
			},
		}

		ipfsStatus, pinnedInIpfs := ipfsRecursivePins[api.Cid(p.Cid)]

		switch {
		case p.Type == api.MetaType:
			info.Status = api.TrackerStatusSharded
		case p.IsRemotePin(spt.peerID):
			info.Status = api.TrackerStatusRemote
		case pinnedInIpfs:
			// No need to filter. pinnedInIpfs is false
			// unless the filter is Pinned |
			// UnexpectedlyUnpinned. We filter at the end.
			info.Status = ipfsStatus.ToTrackerStatus()
		default:
			// Not on an operation
			// Not a meta pin
			// Not a remote pin
			// Not a pin on ipfs

			// We understand that this is something that
			// should be pinned on IPFS and it is not.
			info.Status = api.TrackerStatusUnexpectedlyUnpinned
			info.Error = errUnexpectedlyUnpinned.Error()
		}
		if !filter.Match(info.Status) {
			continue
		}

		if !trySend(info) {
			return fmt.Errorf("error issuing PinInfo: %w", ctx.Err())
		}
	}
	return nil
}

// Status returns information for a Cid pinned to the local IPFS node.
func (spt *Tracker) Status(ctx context.Context, c api.Cid) api.PinInfo {
	ctx, span := trace.StartSpan(ctx, "tracker/stateless/Status")
	defer span.End()

	ipfsid := spt.getIPFSID(ctx)

	// check if c has an inflight operation or errorred operation in optracker
	if oppi, ok := spt.optracker.GetExists(ctx, c, ipfsid); ok {
		return oppi
	}

	pinInfo := api.PinInfo{
		Cid:  c,
		Peer: spt.peerID,
		Name: "", // etc to be filled later
		PinInfoShort: api.PinInfoShort{
			PeerName:      spt.peerName,
			IPFS:          ipfsid.ID,
			IPFSAddresses: ipfsid.Addresses,
			TS:            time.Now(),
			AttemptCount:  0,
			PriorityPin:   false,
		},
	}

	// check global state to see if cluster should even be caring about
	// the provided cid
	var gpin api.Pin
	st, err := spt.getState(ctx)
	if err != nil {
		logger.Error(err)
		addError(&pinInfo, err)
		return pinInfo
	}

	gpin, err = st.Get(ctx, c)
	if err == state.ErrNotFound {
		pinInfo.Status = api.TrackerStatusUnpinned
		return pinInfo
	}
	if err != nil {
		logger.Error(err)
		addError(&pinInfo, err)
		return pinInfo
	}
	// The pin IS in the state.
	pinInfo.Name = gpin.Name
	pinInfo.TS = gpin.Timestamp
	pinInfo.Allocations = gpin.Allocations
	pinInfo.Origins = gpin.Origins
	pinInfo.Created = gpin.Timestamp
	pinInfo.Metadata = gpin.Metadata

	// check if pin is a meta pin
	if gpin.Type == api.MetaType {
		pinInfo.Status = api.TrackerStatusSharded
		return pinInfo
	}

	// check if pin is a remote pin
	if gpin.IsRemotePin(spt.peerID) {
		pinInfo.Status = api.TrackerStatusRemote
		return pinInfo
	}

	// else attempt to get status from ipfs node
	var ips api.IPFSPinStatus
	err = spt.rpcClient.CallContext(
		ctx,
		"",
		"IPFSConnector",
		"PinLsCid",
		gpin,
		&ips,
	)
	if err != nil {
		logger.Error(err)
		addError(&pinInfo, err)
		return pinInfo
	}

	ipfsStatus := ips.ToTrackerStatus()
	switch ipfsStatus {
	case api.TrackerStatusUnpinned:
		// The item is in the state but not in IPFS:
		// PinError. Should be pinned.
		pinInfo.Status = api.TrackerStatusUnexpectedlyUnpinned
		pinInfo.Error = errUnexpectedlyUnpinned.Error()
	default:
		pinInfo.Status = ipfsStatus
	}
	return pinInfo
}

// RecoverAll attempts to recover all items tracked by this peer. It returns
// any errors or when it is done re-tracking.
func (spt *Tracker) RecoverAll(ctx context.Context, out chan<- api.PinInfo) error {
	defer close(out)

	ctx, span := trace.StartSpan(ctx, "tracker/stateless/RecoverAll")
	defer span.End()

	statusesCh := make(chan api.PinInfo, 1024)
	go func() {
		err := spt.StatusAll(ctx, api.TrackerStatusUndefined, statusesCh)
		if err != nil {
			logger.Error(err)
		}
	}()

	for st := range statusesCh {
		// Break out if we shutdown. We might be going through
		// a very long list of statuses.
		select {
		case <-spt.ctx.Done():
			err := fmt.Errorf("RecoverAll aborted: %w", ctx.Err())
			logger.Error(err)
			return err
		default:
			p, err := spt.recoverWithPinInfo(ctx, st)
			if err != nil {
				err = fmt.Errorf("RecoverAll error: %w", err)
				logger.Error(err)
				return err
			}
			if p.Defined() {
				select {
				case <-ctx.Done():
					err = fmt.Errorf("RecoverAll aborted: %w", ctx.Err())
					logger.Error(err)
					return err
				case out <- p:
				}
			}
		}
	}
	return nil
}

// Recover will trigger pinning or unpinning for items in
// PinError or UnpinError states.
func (spt *Tracker) Recover(ctx context.Context, c api.Cid) (api.PinInfo, error) {
	ctx, span := trace.StartSpan(ctx, "tracker/stateless/Recover")
	defer span.End()

	pi := spt.Status(ctx, c)

	recPi, err := spt.recoverWithPinInfo(ctx, pi)
	// if it was not enqueued, no updated pin-info is returned.
	// Use the one we had.
	if !recPi.Defined() {
		recPi = pi
	}
	return recPi, err
}

func (spt *Tracker) recoverWithPinInfo(ctx context.Context, pi api.PinInfo) (api.PinInfo, error) {
	var err error
	switch pi.Status {
	case api.TrackerStatusPinError, api.TrackerStatusUnexpectedlyUnpinned:
		logger.Infof("Restarting pin operation for %s", pi.Cid)
		err = spt.enqueue(ctx, api.PinCid(pi.Cid), optracker.OperationPin)
	case api.TrackerStatusUnpinError:
		logger.Infof("Restarting unpin operation for %s", pi.Cid)
		err = spt.enqueue(ctx, api.PinCid(pi.Cid), optracker.OperationUnpin)
	default:
		// We do not return any information when recover was a no-op
		return api.PinInfo{}, nil
	}
	if err != nil {
		return spt.Status(ctx, pi.Cid), err
	}

	// This status call should be cheap as it would normally come from the
	// optracker and does not need to hit ipfs.
	return spt.Status(ctx, pi.Cid), nil
}

func (spt *Tracker) ipfsPins(ctx context.Context) (<-chan api.IPFSPinInfo, error) {
	ctx, span := trace.StartSpan(ctx, "tracker/stateless/ipfsStatusAll")
	defer span.End()

	in := make(chan []string, 1) // type filter.
	in <- []string{"recursive", "direct"}
	close(in)
	out := make(chan api.IPFSPinInfo, pinsChannelSize)

	go func() {
		err := spt.rpcClient.Stream(
			ctx,
			"",
			"IPFSConnector",
			"PinLs",
			in,
			out,
		)
		if err != nil {
			logger.Error(err)
		}
	}()
	return out, nil
}

// func (spt *Tracker) getErrorsAll(ctx context.Context) []api.PinInfo {
// 	return spt.optracker.Filter(ctx, optracker.PhaseError)
// }

// OpContext exports the internal optracker's OpContext method.
// For testing purposes only.
func (spt *Tracker) OpContext(ctx context.Context, c api.Cid) context.Context {
	return spt.optracker.OpContext(ctx, c)
}

func addError(pinInfo *api.PinInfo, err error) {
	pinInfo.Error = err.Error()
	pinInfo.Status = api.TrackerStatusClusterError
}