package mesh

import (
	"context"
	"fmt"
	"strings"
	"time"

	"github.com/example/remote-access-platform/agents/rap-node-agent/internal/fabricproto"
)

type FabricChannelRuntimeConfig struct {
	RouterConfig   FabricChannelRouterConfig
	StreamID       uint64
	TrafficClass   fabricproto.TrafficClass
	Timeout        time.Duration
	MaxPayload     int
	RouteHealthTTL time.Duration
}

type FabricChannelRuntime struct {
	Transport FabricTransport
	Router    FabricChannelRouter
	Pressure  *FabricRoutePressureTracker
	Health    *FabricRouteHealthTracker
	Config    FabricChannelRuntimeConfig
}

type FabricChannelRuntimeResult struct {
	Channel         FabricChannel
	BytesSent       uint64
	BytesRecv       uint64
	FramesSent      uint64
	FramesRecv      uint64
	AcksReceived    uint64
	RouteEvents     []FabricChannelRouteEvent
	RouteAttempts   []string
	MigrationEvents int
	RoutePressure   FabricRoutePressureSnapshot
	RouteHealth     FabricRouteHealthSnapshot
}

type FabricChannelRequestResponseResult struct {
	FabricChannelRuntimeResult
	ResponsePayload []byte
}

func NewFabricChannelRuntime(transport FabricTransport, cfg FabricChannelRuntimeConfig) *FabricChannelRuntime {
	if cfg.StreamID == 0 {
		cfg.StreamID = 2
	}
	if cfg.TrafficClass == 0 {
		cfg.TrafficClass = fabricproto.TrafficClassBulk
	}
	if cfg.Timeout <= 0 {
		cfg.Timeout = 30 * time.Second
	}
	if cfg.MaxPayload <= 0 {
		cfg.MaxPayload = fabricproto.DefaultMaxPayload
	}
	return &FabricChannelRuntime{
		Transport: transport,
		Router:    NewFabricChannelRouter(cfg.RouterConfig),
		Pressure:  NewFabricRoutePressureTracker(),
		Health:    NewFabricRouteHealthTracker(cfg.RouteHealthTTL),
		Config:    cfg,
	}
}

func (r *FabricChannelRuntime) SendReliable(ctx context.Context, spec FabricChannelSpec, routeSet FabricRouteSet, payloads [][]byte) (FabricChannelRuntimeResult, error) {
	if r == nil || r.Transport == nil {
		return FabricChannelRuntimeResult{}, ErrForwardRuntimeUnavailable
	}
	now := time.Now().UTC()
	routeSet = r.routeSetForScheduling(routeSet)
	channel, event, err := r.Router.OpenChannel(spec, routeSet, now)
	if err != nil {
		return FabricChannelRuntimeResult{}, err
	}
	result := FabricChannelRuntimeResult{Channel: channel, RouteEvents: []FabricChannelRouteEvent{event}}
	sequence := uint64(0)
	index := 0
	for index < len(payloads) {
		routeSet = r.routeSetForScheduling(routeSet)
		route, ok := findFabricRoute(routeSet, channel.RouteID)
		if !ok {
			return result, ErrFabricRouteNotFound
		}
		result.RouteAttempts = append(result.RouteAttempts, route.RouteID)
		target, err := FabricTransportTargetForRoute(route)
		if err != nil {
			return result, err
		}
		releaseRoute := r.acquireRoute(route.RouteID)
		session, err := r.Transport.Connect(ctx, target)
		if err != nil {
			releaseRoute()
			r.markRouteFailure(route.RouteID, err)
			updated, event, rerouteErr := r.Router.ObserveChannel(channel, routeSet, FabricChannelObservation{
				ChannelID:  spec.ChannelID,
				RouteID:    route.RouteID,
				Failed:     true,
				Reason:     "connect_failed",
				ObservedAt: time.Now().UTC(),
			}, time.Now().UTC())
			channel = updated
			result.Channel = channel
			if event.Type == FabricChannelRouteEventReroute {
				result.RouteEvents = append(result.RouteEvents, event)
				result.MigrationEvents++
				continue
			}
			if rerouteErr != nil {
				return result, rerouteErr
			}
			return result, err
		}
		migrated, sendErr := r.sendOnSession(ctx, session, &channel, routeSet, route, payloads, &index, &sequence, &result)
		_ = session.Close()
		releaseRoute()
		result.Channel = channel
		if sendErr != nil {
			return result, sendErr
		}
		if !migrated {
			break
		}
	}
	result.Channel = channel
	result.RoutePressure = r.snapshotRoutePressure()
	result.RouteHealth = r.snapshotRouteHealth()
	return result, nil
}

func (r *FabricChannelRuntime) SendRequestResponse(ctx context.Context, spec FabricChannelSpec, routeSet FabricRouteSet, payload []byte) (FabricChannelRequestResponseResult, error) {
	if r == nil || r.Transport == nil {
		return FabricChannelRequestResponseResult{}, ErrForwardRuntimeUnavailable
	}
	if len(payload) > r.Config.MaxPayload {
		return FabricChannelRequestResponseResult{}, fmt.Errorf("%w: %d > %d", fabricproto.ErrInvalidPayloadLen, len(payload), r.Config.MaxPayload)
	}
	now := time.Now().UTC()
	routeSet = r.routeSetForScheduling(routeSet)
	channel, event, err := r.Router.OpenChannel(spec, routeSet, now)
	if err != nil {
		return FabricChannelRequestResponseResult{}, err
	}
	result := FabricChannelRequestResponseResult{
		FabricChannelRuntimeResult: FabricChannelRuntimeResult{Channel: channel, RouteEvents: []FabricChannelRouteEvent{event}},
	}
	sequence := uint64(1)
	for {
		routeSet = r.routeSetForScheduling(routeSet)
		route, ok := findFabricRoute(routeSet, channel.RouteID)
		if !ok {
			return result, ErrFabricRouteNotFound
		}
		result.RouteAttempts = append(result.RouteAttempts, route.RouteID)
		target, err := FabricTransportTargetForRoute(route)
		if err != nil {
			return result, err
		}
		releaseRoute := r.acquireRoute(route.RouteID)
		session, err := r.Transport.Connect(ctx, target)
		if err != nil {
			releaseRoute()
			r.markRouteFailure(route.RouteID, err)
			updated, routeEvent, rerouteErr := r.Router.ObserveChannel(channel, routeSet, FabricChannelObservation{
				ChannelID:  spec.ChannelID,
				RouteID:    route.RouteID,
				Failed:     true,
				Reason:     "connect_failed",
				ObservedAt: time.Now().UTC(),
			}, time.Now().UTC())
			channel = updated
			result.Channel = channel
			if routeEvent.Type == FabricChannelRouteEventReroute {
				result.RouteEvents = append(result.RouteEvents, routeEvent)
				result.MigrationEvents++
				continue
			}
			if rerouteErr != nil {
				return result, rerouteErr
			}
			return result, err
		}
		response, ackMs, sendErr := r.sendRequestResponseOnSession(ctx, session, route.RouteID, spec.ChannelID, payload, sequence)
		_ = session.Close()
		releaseRoute()
		result.Channel = channel
		if sendErr == nil {
			r.markRouteSuccess(route.RouteID)
			result.BytesSent += uint64(len(payload))
			result.FramesSent++
			result.BytesRecv += uint64(len(response))
			result.FramesRecv++
			result.AcksReceived++
			updated, routeEvent, observeErr := r.Router.ObserveChannel(channel, routeSet, FabricChannelObservation{
				ChannelID:    spec.ChannelID,
				RouteID:      route.RouteID,
				AckLatencyMs: ackMs,
				BytesSent:    uint64(len(payload)),
				FramesSent:   1,
				BytesRecv:    uint64(len(response)),
				FramesRecv:   1,
				ObservedAt:   time.Now().UTC(),
			}, time.Now().UTC())
			channel = updated
			result.Channel = channel
			if observeErr != nil {
				return result, observeErr
			}
			if routeEvent.Type == FabricChannelRouteEventReroute {
				result.RouteEvents = append(result.RouteEvents, routeEvent)
				result.MigrationEvents++
			}
			result.ResponsePayload = response
			result.RoutePressure = r.snapshotRoutePressure()
			result.RouteHealth = r.snapshotRouteHealth()
			return result, nil
		}
		r.markRouteFailure(route.RouteID, sendErr)
		updated, routeEvent, rerouteErr := r.Router.ObserveChannel(channel, routeSet, FabricChannelObservation{
			ChannelID:  spec.ChannelID,
			RouteID:    route.RouteID,
			Failed:     true,
			Reason:     "response_failed",
			ObservedAt: time.Now().UTC(),
		}, time.Now().UTC())
		channel = updated
		result.Channel = channel
		if routeEvent.Type == FabricChannelRouteEventReroute {
			result.RouteEvents = append(result.RouteEvents, routeEvent)
			result.MigrationEvents++
			continue
		}
		if rerouteErr != nil {
			return result, rerouteErr
		}
		return result, sendErr
	}
}

func (r *FabricChannelRuntime) routeSetForScheduling(routeSet FabricRouteSet) FabricRouteSet {
	if r != nil && r.Health != nil {
		routeSet = r.Health.Apply(routeSet, time.Now().UTC())
	}
	return r.routeSetWithActiveChannels(routeSet)
}

func (r *FabricChannelRuntime) routeSetWithActiveChannels(routeSet FabricRouteSet) FabricRouteSet {
	if r == nil || r.Pressure == nil {
		return routeSet
	}
	return r.Pressure.Apply(routeSet)
}

func (r *FabricChannelRuntime) acquireRoute(routeID string) func() {
	if r == nil || r.Pressure == nil {
		return func() {}
	}
	return r.Pressure.Acquire(routeID)
}

func (r *FabricChannelRuntime) snapshotRoutePressure() FabricRoutePressureSnapshot {
	if r == nil || r.Pressure == nil {
		return FabricRoutePressureSnapshot{}
	}
	return r.Pressure.SnapshotPressure()
}

func (r *FabricChannelRuntime) snapshotRouteHealth() FabricRouteHealthSnapshot {
	if r == nil || r.Health == nil {
		return FabricRouteHealthSnapshot{}
	}
	return r.Health.Snapshot(time.Now().UTC())
}

func (r *FabricChannelRuntime) markRouteFailure(routeID string, err error) {
	if r == nil || r.Health == nil || err == nil {
		return
	}
	r.Health.MarkFailure(routeID, err.Error(), time.Now().UTC())
}

func (r *FabricChannelRuntime) markRouteSuccess(routeID string) {
	if r == nil || r.Health == nil {
		return
	}
	r.Health.MarkSuccess(routeID)
}

func (r *FabricChannelRuntime) sendOnSession(ctx context.Context, session FabricTransportSession, channel *FabricChannel, routeSet FabricRouteSet, route FabricRoute, payloads [][]byte, index *int, sequence *uint64, result *FabricChannelRuntimeResult) (bool, error) {
	cfg := r.Config
	if err := session.Send(ctx, fabricproto.Frame{
		Type:         fabricproto.FrameOpenStream,
		TrafficClass: cfg.TrafficClass,
		StreamID:     cfg.StreamID,
	}); err != nil {
		r.markRouteFailure(route.RouteID, err)
		return false, err
	}
	for *index < len(payloads) {
		payload := payloads[*index]
		if len(payload) > cfg.MaxPayload {
			return false, fmt.Errorf("%w: %d > %d", fabricproto.ErrInvalidPayloadLen, len(payload), cfg.MaxPayload)
		}
		(*sequence)++
		if err := session.Send(ctx, fabricproto.Frame{
			Type:         fabricproto.FrameData,
			TrafficClass: cfg.TrafficClass,
			StreamID:     cfg.StreamID,
			Sequence:     *sequence,
			Payload:      payload,
		}); err != nil {
			r.markRouteFailure(route.RouteID, err)
			return false, err
		}
		ackOK, ackMs := waitForFabricRuntimeAck(ctx, session, cfg.StreamID, *sequence, cfg.Timeout)
		if !ackOK {
			r.markRouteFailure(route.RouteID, fmt.Errorf("ack_failed"))
			updated, event, err := r.Router.ObserveChannel(*channel, routeSet, FabricChannelObservation{
				ChannelID:  channel.Spec.ChannelID,
				RouteID:    route.RouteID,
				Failed:     true,
				Reason:     "ack_failed",
				ObservedAt: time.Now().UTC(),
			}, time.Now().UTC())
			*channel = updated
			if event.Type == FabricChannelRouteEventReroute {
				result.RouteEvents = append(result.RouteEvents, event)
				result.MigrationEvents++
				return true, nil
			}
			return false, err
		}
		r.markRouteSuccess(route.RouteID)
		*index++
		result.BytesSent += uint64(len(payload))
		result.FramesSent++
		result.AcksReceived++
		updated, event, err := r.Router.ObserveChannel(*channel, routeSet, FabricChannelObservation{
			ChannelID:    channel.Spec.ChannelID,
			RouteID:      route.RouteID,
			AckLatencyMs: ackMs,
			BytesSent:    uint64(len(payload)),
			FramesSent:   1,
			ObservedAt:   time.Now().UTC(),
		}, time.Now().UTC())
		*channel = updated
		if err != nil {
			return false, err
		}
		if event.Type == FabricChannelRouteEventReroute {
			result.RouteEvents = append(result.RouteEvents, event)
			result.MigrationEvents++
			return true, nil
		}
	}
	_ = session.Send(context.Background(), fabricproto.Frame{
		Type:         fabricproto.FrameCloseStream,
		TrafficClass: cfg.TrafficClass,
		StreamID:     cfg.StreamID,
	})
	return false, nil
}

func (r *FabricChannelRuntime) sendRequestResponseOnSession(ctx context.Context, session FabricTransportSession, routeID string, channelID string, payload []byte, sequence uint64) ([]byte, int64, error) {
	cfg := r.Config
	if err := session.Send(ctx, fabricproto.Frame{
		Type:         fabricproto.FrameOpenStream,
		TrafficClass: cfg.TrafficClass,
		StreamID:     cfg.StreamID,
	}); err != nil {
		r.markRouteFailure(routeID, err)
		return nil, 0, err
	}
	started := time.Now()
	if err := session.Send(ctx, fabricproto.Frame{
		Type:         fabricproto.FrameData,
		TrafficClass: cfg.TrafficClass,
		StreamID:     cfg.StreamID,
		Sequence:     sequence,
		Payload:      payload,
	}); err != nil {
		r.markRouteFailure(routeID, err)
		return nil, 0, err
	}
	waitCtx := ctx
	if cfg.Timeout > 0 {
		var cancel context.CancelFunc
		waitCtx, cancel = context.WithTimeout(ctx, cfg.Timeout)
		defer cancel()
	}
	for {
		select {
		case <-waitCtx.Done():
			return nil, 0, waitCtx.Err()
		case err, ok := <-session.Errors():
			if !ok {
				return nil, 0, ErrForwardPeerUnavailable
			}
			if err != nil {
				return nil, 0, err
			}
		case frame, ok := <-session.Frames():
			if !ok {
				return nil, 0, ErrForwardPeerUnavailable
			}
			if frame.Type != fabricproto.FrameData || frame.StreamID != cfg.StreamID || frame.Sequence != sequence {
				continue
			}
			_ = session.Send(context.Background(), fabricproto.Frame{
				Type:         fabricproto.FrameCloseStream,
				TrafficClass: cfg.TrafficClass,
				StreamID:     cfg.StreamID,
			})
			return append([]byte(nil), frame.Payload...), time.Since(started).Milliseconds(), nil
		}
	}
}

func FabricTransportTargetForRoute(route FabricRoute) (FabricTransportTarget, error) {
	if strings.TrimSpace(route.RouteID) == "" {
		return FabricTransportTarget{}, ErrFabricRouteNotFound
	}
	if route.RelayCount > 0 {
		for _, hop := range route.Hops {
			if hop.Mode != FabricRouteRelay {
				continue
			}
			if target, ok := fabricTransportTargetForHop(hop); ok {
				return target, nil
			}
		}
	}
	for i := len(route.Hops) - 1; i >= 0; i-- {
		if target, ok := fabricTransportTargetForHop(route.Hops[i]); ok {
			return target, nil
		}
	}
	return FabricTransportTarget{}, fmt.Errorf("%w: route %s has no transport endpoint", ErrFabricRouteNotFound, route.RouteID)
}

func fabricTransportTargetForHop(hop FabricRouteHop) (FabricTransportTarget, bool) {
	endpoint := strings.TrimSpace(hop.Address)
	if endpoint == "" {
		return FabricTransportTarget{}, false
	}
	transport := string(hop.Mode)
	if transport == "" {
		transport = "quic"
	}
	return FabricTransportTarget{
		EndpointID:     hop.EndpointID,
		PeerID:         strings.TrimSpace(hop.NodeID),
		Endpoint:       endpoint,
		Transport:      transport,
		PeerCertSHA256: strings.TrimSpace(hop.PeerCertSHA256),
	}, true
}

func waitForFabricRuntimeAck(ctx context.Context, session FabricTransportSession, streamID uint64, sequence uint64, timeout time.Duration) (bool, int64) {
	started := time.Now()
	if timeout > 0 {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, timeout)
		defer cancel()
	}
	for {
		select {
		case <-ctx.Done():
			return false, 0
		case err, ok := <-session.Errors():
			if !ok || err != nil {
				return false, 0
			}
		case frame, ok := <-session.Frames():
			if !ok {
				return false, 0
			}
			if frame.Type == fabricproto.FrameAck && frame.StreamID == streamID && frame.Sequence == sequence {
				return true, time.Since(started).Milliseconds()
			}
		}
	}
}