package actor

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

	"github.com/nspcc-dev/neo-go/pkg/core/block"
	"github.com/nspcc-dev/neo-go/pkg/core/state"
	"github.com/nspcc-dev/neo-go/pkg/neorpc"
	"github.com/nspcc-dev/neo-go/pkg/neorpc/result"
	"github.com/nspcc-dev/neo-go/pkg/smartcontract/trigger"
	"github.com/nspcc-dev/neo-go/pkg/util"
)

// PollingWaiterRetryCount is a threshold for a number of subsequent failed
// attempts to get block count from the RPC server for PollingWaiter. If it fails
// to retrieve block count PollingWaiterRetryCount times in a raw then transaction
// awaiting attempt considered to be failed and an error is returned.
const PollingWaiterRetryCount = 3

var (
	// ErrTxNotAccepted is returned when transaction wasn't accepted to the chain
	// even after ValidUntilBlock block persist.
	ErrTxNotAccepted = errors.New("transaction was not accepted to chain")
	// ErrContextDone is returned when Waiter context has been done in the middle
	// of transaction awaiting process and no result was received yet.
	ErrContextDone = errors.New("waiter context done")
	// ErrAwaitingNotSupported is returned from Wait method if Waiter instance
	// doesn't support transaction awaiting.
	ErrAwaitingNotSupported = errors.New("awaiting not supported")
	// ErrMissedEvent is returned when RPCEventWaiter closes receiver channel
	// which happens if missed event was received from the RPC server.
	ErrMissedEvent = errors.New("some event was missed")
)

type (
	// Waiter is an interface providing transaction awaiting functionality to Actor.
	Waiter interface {
		// Wait allows to wait until transaction will be accepted to the chain. It can be
		// used as a wrapper for Send or SignAndSend and accepts transaction hash,
		// ValidUntilBlock value and an error. It returns transaction execution result
		// or an error if transaction wasn't accepted to the chain.
		Wait(h util.Uint256, vub uint32, err error) (*state.AppExecResult, error)
		// WaitAny waits until at least one of the specified transactions will be accepted
		// to the chain until vub (including). It returns execution result of this
		// transaction or an error if none of the transactions was accepted to the chain.
		// It uses underlying RPCPollingWaiter or RPCEventWaiter context to interrupt
		// awaiting process, but additional ctx can be passed as an argument for the same
		// purpose.
		WaitAny(ctx context.Context, vub uint32, hashes ...util.Uint256) (*state.AppExecResult, error)
	}
	// RPCPollingWaiter is an interface that enables transaction awaiting functionality
	// for Actor instance based on periodical BlockCount and ApplicationLog polls.
	RPCPollingWaiter interface {
		// Context should return the RPC client context to be able to gracefully
		// shut down all running processes (if so).
		Context() context.Context
		GetVersion() (*result.Version, error)
		GetBlockCount() (uint32, error)
		GetApplicationLog(hash util.Uint256, trig *trigger.Type) (*result.ApplicationLog, error)
	}
	// RPCEventWaiter is an interface that enables improved transaction awaiting functionality
	// for Actor instance based on web-socket Block and ApplicationLog notifications. RPCEventWaiter
	// contains RPCPollingWaiter under the hood and falls back to polling when subscription-based
	// awaiting fails.
	RPCEventWaiter interface {
		RPCPollingWaiter

		ReceiveBlocks(flt *neorpc.BlockFilter, rcvr chan<- *block.Block) (string, error)
		ReceiveExecutions(flt *neorpc.ExecutionFilter, rcvr chan<- *state.AppExecResult) (string, error)
		Unsubscribe(id string) error
	}
)

// NullWaiter is a Waiter stub that doesn't support transaction awaiting functionality.
type NullWaiter struct{}

// PollingWaiter is a polling-based Waiter.
type PollingWaiter struct {
	polling RPCPollingWaiter
	version *result.Version
}

// EventWaiter is a websocket-based Waiter.
type EventWaiter struct {
	ws      RPCEventWaiter
	polling Waiter
}

// newWaiter creates Waiter instance. It can be either websocket-based or
// polling-base, otherwise Waiter stub is returned.
func newWaiter(ra RPCActor, v *result.Version) Waiter {
	if eventW, ok := ra.(RPCEventWaiter); ok {
		return &EventWaiter{
			ws: eventW,
			polling: &PollingWaiter{
				polling: eventW,
				version: v,
			},
		}
	}
	if pollW, ok := ra.(RPCPollingWaiter); ok {
		return &PollingWaiter{
			polling: pollW,
			version: v,
		}
	}
	return NewNullWaiter()
}

// NewNullWaiter creates an instance of Waiter stub.
func NewNullWaiter() NullWaiter {
	return NullWaiter{}
}

// Wait implements Waiter interface.
func (NullWaiter) Wait(h util.Uint256, vub uint32, err error) (*state.AppExecResult, error) {
	return nil, ErrAwaitingNotSupported
}

// WaitAny implements Waiter interface.
func (NullWaiter) WaitAny(ctx context.Context, vub uint32, hashes ...util.Uint256) (*state.AppExecResult, error) {
	return nil, ErrAwaitingNotSupported
}

// NewPollingWaiter creates an instance of Waiter supporting poll-based transaction awaiting.
func NewPollingWaiter(waiter RPCPollingWaiter) (*PollingWaiter, error) {
	v, err := waiter.GetVersion()
	if err != nil {
		return nil, err
	}
	return &PollingWaiter{
		polling: waiter,
		version: v,
	}, nil
}

// Wait implements Waiter interface.
func (w *PollingWaiter) Wait(h util.Uint256, vub uint32, err error) (*state.AppExecResult, error) {
	if err != nil {
		return nil, err
	}
	return w.WaitAny(context.TODO(), vub, h)
}

// WaitAny implements Waiter interface.
func (w *PollingWaiter) WaitAny(ctx context.Context, vub uint32, hashes ...util.Uint256) (*state.AppExecResult, error) {
	var (
		currentHeight uint32
		failedAttempt int
		pollTime      = time.Millisecond * time.Duration(w.version.Protocol.MillisecondsPerBlock) / 2
	)
	if pollTime == 0 {
		pollTime = time.Second
	}
	timer := time.NewTicker(pollTime)
	defer timer.Stop()
	for {
		select {
		case <-timer.C:
			blockCount, err := w.polling.GetBlockCount()
			if err != nil {
				failedAttempt++
				if failedAttempt > PollingWaiterRetryCount {
					return nil, fmt.Errorf("failed to retrieve block count: %w", err)
				}
				continue
			}
			failedAttempt = 0
			if blockCount-1 > currentHeight {
				currentHeight = blockCount - 1
			}
			t := trigger.Application
			for _, h := range hashes {
				res, err := w.polling.GetApplicationLog(h, &t)
				if err == nil {
					return &state.AppExecResult{
						Container: res.Container,
						Execution: res.Executions[0],
					}, nil
				}
			}
			if currentHeight >= vub {
				return nil, ErrTxNotAccepted
			}
		case <-w.polling.Context().Done():
			return nil, fmt.Errorf("%w: %v", ErrContextDone, w.polling.Context().Err())
		case <-ctx.Done():
			return nil, fmt.Errorf("%w: %v", ErrContextDone, ctx.Err())
		}
	}
}

// NewEventWaiter creates an instance of Waiter supporting websocket event-based transaction awaiting.
// EventWaiter contains PollingWaiter under the hood and falls back to polling when subscription-based
// awaiting fails.
func NewEventWaiter(waiter RPCEventWaiter) (*EventWaiter, error) {
	polling, err := NewPollingWaiter(waiter)
	if err != nil {
		return nil, err
	}
	return &EventWaiter{
		ws:      waiter,
		polling: polling,
	}, nil
}

// Wait implements Waiter interface.
func (w *EventWaiter) Wait(h util.Uint256, vub uint32, err error) (res *state.AppExecResult, waitErr error) {
	if err != nil {
		return nil, err
	}
	return w.WaitAny(context.TODO(), vub, h)
}

// WaitAny implements Waiter interface.
func (w *EventWaiter) WaitAny(ctx context.Context, vub uint32, hashes ...util.Uint256) (res *state.AppExecResult, waitErr error) {
	var (
		wsWaitErr     error
		waitersActive int
		bRcvr         = make(chan *block.Block, 2)
		aerRcvr       = make(chan *state.AppExecResult, len(hashes))
		unsubErrs     = make(chan error)
		exit          = make(chan struct{})
	)

	// Execution event preceded the block event, thus wait until the VUB-th block to be sure.
	since := vub
	blocksID, err := w.ws.ReceiveBlocks(&neorpc.BlockFilter{Since: &since}, bRcvr)
	if err != nil {
		wsWaitErr = fmt.Errorf("failed to subscribe for new blocks: %w", err)
	} else {
		waitersActive++
		go func() {
			<-exit
			err = w.ws.Unsubscribe(blocksID)
			if err != nil {
				unsubErrs <- fmt.Errorf("failed to unsubscribe from blocks (id: %s): %w", blocksID, err)
				return
			}
			unsubErrs <- nil
		}()
	}
	if wsWaitErr == nil {
		trig := trigger.Application
		for _, h := range hashes {
			txsID, err := w.ws.ReceiveExecutions(&neorpc.ExecutionFilter{Container: &h}, aerRcvr)
			if err != nil {
				wsWaitErr = fmt.Errorf("failed to subscribe for execution results: %w", err)
				break
			}
			waitersActive++
			go func() {
				<-exit
				err = w.ws.Unsubscribe(txsID)
				if err != nil {
					unsubErrs <- fmt.Errorf("failed to unsubscribe from transactions (id: %s): %w", txsID, err)
					return
				}
				unsubErrs <- nil
			}()
			// There is a potential race between subscription and acceptance, so
			// do a polling check once _after_ the subscription.
			appLog, err := w.ws.GetApplicationLog(h, &trig)
			if err == nil {
				res = &state.AppExecResult{
					Container: appLog.Container,
					Execution: appLog.Executions[0],
				}
				break // We have the result, no need for other subscriptions.
			}
		}
	}

	if wsWaitErr == nil && res == nil {
		select {
		case _, ok := <-bRcvr:
			if !ok {
				// We're toast, retry with non-ws client.
				wsWaitErr = ErrMissedEvent
				break
			}
			waitErr = ErrTxNotAccepted
		case aer, ok := <-aerRcvr:
			if !ok {
				// We're toast, retry with non-ws client.
				wsWaitErr = ErrMissedEvent
				break
			}
			res = aer
		case <-w.ws.Context().Done():
			waitErr = fmt.Errorf("%w: %v", ErrContextDone, w.ws.Context().Err())
		case <-ctx.Done():
			waitErr = fmt.Errorf("%w: %v", ErrContextDone, ctx.Err())
		}
	}
	close(exit)

	if waitersActive > 0 {
		// Drain receivers to avoid other notification receivers blocking.
	drainLoop:
		for {
			select {
			case <-bRcvr:
			case <-aerRcvr:
			case unsubErr := <-unsubErrs:
				if unsubErr != nil {
					errFmt := "unsubscription error: %v"
					errArgs := []interface{}{unsubErr}
					if waitErr != nil {
						errFmt = "%w; " + errFmt
						errArgs = append([]interface{}{waitErr}, errArgs...)
					}
					waitErr = fmt.Errorf(errFmt, errArgs...)
				}
				waitersActive--
				// Wait until all receiver channels finish their work.
				if waitersActive == 0 {
					break drainLoop
				}
			}
		}
	}
	if wsWaitErr == nil || !errors.Is(wsWaitErr, ErrMissedEvent) {
		close(bRcvr)
		close(aerRcvr)
	}
	close(unsubErrs)

	// Rollback to a poll-based waiter if needed.
	if wsWaitErr != nil && waitErr == nil {
		res, waitErr = w.polling.WaitAny(ctx, vub, hashes...)
		if waitErr != nil {
			// Wrap the poll-based error, it's more important.
			waitErr = fmt.Errorf("event-based error: %v; poll-based waiter error: %w", wsWaitErr, waitErr)
		}
	}
	return
}