package api

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

	"tera-clone/services/tera-api/internal/domain"
	"tera-clone/services/tera-api/internal/portservice"
	"tera-clone/services/tera-api/internal/serial"
	"tera-clone/services/tera-api/internal/sessionhealth"
)

const (
	runtimeStatusTimeout  = 2 * time.Second
	runtimeStatusCacheTTL = 300 * time.Millisecond
)

type serialRuntimeSnapshot struct {
	states     map[string]serial.State
	links      map[string]serial.LinkState
	crProbes   map[string]serial.CRProbeState
	session    sessionhealth.Status
	stateErr   error
	linkErr    error
	crProbeErr error
	sessionErr error
}

type compactPortRuntimeStatus struct {
	Channel        string                    `json:"channel"`
	Alias          string                    `json:"alias,omitempty"`
	Status         string                    `json:"status"`
	Mode           string                    `json:"mode"`
	ConnectedUsers int                       `json:"connected_users"`
	Runtime        compactPortRuntimeDetails `json:"runtime"`
}

type compactPortRuntimeDetails struct {
	SessionActive  bool   `json:"session_active"`
	RXBytes        uint64 `json:"rx_bytes"`
	TXBytes        uint64 `json:"tx_bytes"`
	RXAgeMillis    int64  `json:"rx_age_ms,omitempty"`
	CRProbeState   string `json:"cr_probe_state,omitempty"`
	CRProbeMisses  int    `json:"cr_probe_consecutive_misses,omitempty"`
	CRProbeUp      bool   `json:"cr_probe_up"`
	CRProbeEverUp  bool   `json:"cr_probe_ever_up"`
	CRProbeMessage string `json:"cr_probe_message,omitempty"`
}

func compactPortRuntimeStatuses(ports []domain.Port) []compactPortRuntimeStatus {
	result := make([]compactPortRuntimeStatus, 0, len(ports))
	for _, port := range ports {
		status := compactPortRuntimeStatus{
			Channel: port.Channel, Alias: port.Alias, Status: port.Status,
			Mode: port.Mode, ConnectedUsers: port.ConnectedUsers,
		}
		if runtime := port.Runtime; runtime != nil {
			status.Runtime = compactPortRuntimeDetails{
				SessionActive: runtime.SessionActive,
				RXBytes:       runtime.RXBytes, TXBytes: runtime.TXBytes, RXAgeMillis: runtime.RXAgeMillis,
				CRProbeState: runtime.CRProbeState, CRProbeMisses: runtime.CRProbeMisses,
				CRProbeUp: runtime.CRProbeUp, CRProbeEverUp: runtime.CRProbeEverUp,
				CRProbeMessage: runtime.CRProbeMessage,
			}
		}
		result = append(result, status)
	}
	return result
}

// serialRuntimeCache collapses concurrent port/status requests into one
// hardware snapshot. In particular, a browser reload must not start another
// tera-seriald/sessiond sweep while the previous request is still finishing.
// The snapshot is hardware-wide and contains no actor-specific data.
type serialRuntimeCache struct {
	mu       sync.Mutex
	snapshot serialRuntimeSnapshot
	cachedAt time.Time
	ready    bool
	inFlight chan struct{}
}

func (r *Router) readSerialRuntime(parent context.Context) serialRuntimeSnapshot {
	for {
		now := time.Now()
		r.serialRuntime.mu.Lock()
		if r.serialRuntime.ready && now.Sub(r.serialRuntime.cachedAt) < runtimeStatusCacheTTL {
			result := r.serialRuntime.snapshot
			r.serialRuntime.mu.Unlock()
			return result
		}
		inFlight := r.serialRuntime.inFlight
		if inFlight == nil {
			inFlight = make(chan struct{})
			r.serialRuntime.inFlight = inFlight
			go r.refreshSerialRuntime(inFlight)
		}
		r.serialRuntime.mu.Unlock()

		select {
		case <-inFlight:
			// Re-check the cache under its lock. A completed refresh always
			// publishes its immutable snapshot before closing this channel.
			continue
		case <-parent.Done():
			return serialRuntimeErrorSnapshot(parent.Err())
		}
	}
}

func (r *Router) refreshSerialRuntime(completed chan struct{}) {
	// Keep the single shared hardware read alive across browser reloads. Each
	// caller still observes its own cancellation while waiting above, and the
	// shared read remains bounded by runtimeStatusTimeout.
	ctx, cancel := context.WithTimeout(context.Background(), runtimeStatusTimeout)
	defer cancel()
	result := r.fetchSerialRuntime(ctx)

	r.serialRuntime.mu.Lock()
	r.serialRuntime.snapshot = result
	r.serialRuntime.cachedAt = time.Now()
	r.serialRuntime.ready = true
	r.serialRuntime.inFlight = nil
	close(completed)
	r.serialRuntime.mu.Unlock()
}

func (r *Router) fetchSerialRuntime(ctx context.Context) serialRuntimeSnapshot {
	result := serialRuntimeSnapshot{
		states:   make(map[string]serial.State, serial.ChannelCount),
		links:    make(map[string]serial.LinkState, serial.ChannelCount),
		crProbes: make(map[string]serial.CRProbeState, serial.ChannelCount),
	}
	var wait sync.WaitGroup
	wait.Add(2)
	go func() {
		defer wait.Done()
		states, err := r.serialPorts.States(ctx)
		result.stateErr = err
		for _, state := range states {
			result.states[state.Channel] = state
		}
		if links, ok := r.serialPorts.(serial.LinkStateController); ok {
			values, linkErr := links.LinkStates(ctx)
			result.linkErr = linkErr
			for _, state := range values {
				current, exists := result.links[state.Channel]
				everUp := state.EverUp || current.EverUp
				if !exists || (current.State != "up" && state.State == "up") || (!current.Available && state.Available) {
					state.EverUp = everUp
					result.links[state.Channel] = state
				} else {
					current.EverUp = everUp
					result.links[state.Channel] = current
				}
			}
		} else {
			result.linkErr = fmt.Errorf("serial link-state adapter is unavailable")
		}
		if probes, ok := r.serialPorts.(serial.CRProbeStateController); ok {
			values, probeErr := probes.CRProbeStates(ctx)
			result.crProbeErr = probeErr
			for _, state := range values {
				result.crProbes[state.Channel] = state
			}
		} else {
			result.crProbeErr = fmt.Errorf("serial CR response probe adapter is unavailable")
		}
	}()
	go func() {
		defer wait.Done()
		result.session, result.sessionErr = r.sessions.Status(ctx)
	}()
	wait.Wait()
	return result
}

func serialRuntimeErrorSnapshot(err error) serialRuntimeSnapshot {
	return serialRuntimeSnapshot{
		states:     make(map[string]serial.State),
		links:      make(map[string]serial.LinkState),
		crProbes:   make(map[string]serial.CRProbeState),
		stateErr:   err,
		linkErr:    err,
		crProbeErr: err,
		sessionErr: err,
	}
}

func (s serialRuntimeSnapshot) availablePorts() int {
	count := 0
	for _, state := range s.states {
		if state.Available {
			count++
		}
	}
	return count
}

func (s serialRuntimeSnapshot) appliedProfiles() int {
	count := 0
	for _, state := range s.states {
		if state.Available && state.ProfileApplied {
			count++
		}
	}
	return count
}

func (r *Router) overlayPortRuntime(ports []domain.Port, runtime serialRuntimeSnapshot) []domain.Port {
	channels := make(map[string]struct {
		broker serialChannelRuntime
		stream serial.StreamChannelSnapshot
	}, serial.ChannelCount)
	for _, channel := range runtime.session.Broker.Channels {
		value := channels[channel.Channel]
		value.broker = serialChannelRuntime{
			attachments: channel.AttachmentCount, maxAttachments: channel.MaxAttachments,
			writer: channel.WriterSessionID, queuedBytes: channel.QueuedBytes,
		}
		channels[channel.Channel] = value
	}
	for _, stream := range runtime.session.Serial.Channels {
		value := channels[stream.Channel]
		value.stream = stream
		channels[stream.Channel] = value
	}
	operationRuntime := make(map[string][]domain.PortOperationRuntime)
	if provider, ok := r.portServices.(portservice.SnapshotProvider); ok {
		for _, service := range provider.Snapshot().Services {
			value := domain.PortOperationRuntime{
				Operation: service.Operation, Mode: service.Mode, Host: service.Host, Port: service.Port,
				State: service.State, ActiveClients: service.ActiveClients,
				Sources: append([]string(nil), service.Sources...), Targets: append([]string(nil), service.Targets...),
			}
			if service.Mode == "redirect" {
				for _, source := range service.Sources {
					operationRuntime[source] = append(operationRuntime[source], value)
				}
			} else {
				operationRuntime[service.Channel] = append(operationRuntime[service.Channel], value)
			}
		}
	}
	for index := range ports {
		port := &ports[index]
		state, stateFound := runtime.states[port.Channel]
		link, linkFound := runtime.links[port.Channel]
		probe, probeFound := runtime.crProbes[port.Channel]
		channel := channels[port.Channel]
		operationClients := 0
		for _, operation := range operationRuntime[port.Channel] {
			if operation.ActiveClients > 0 {
				operationClients += operation.ActiveClients
			}
		}
		port.ConnectedUsers = channel.broker.attachments + operationClients
		if channel.broker.maxAttachments > 0 {
			port.MaxViewers = channel.broker.maxAttachments
		}
		port.Writer = channel.broker.writer
		value := &domain.PortRuntime{
			HardwareAvailable: stateFound && state.Available,
			HardwareMessage:   state.Message,
			HardwareProfile:   state.HardwareProfile,
			MappingVersion:    state.MappingVersion,
			Device:            state.Device,
			ProfileApplied:    state.ProfileApplied,
			LinkState:         "unknown",
			LinkSignal:        "unknown",
			SessionState:      "unavailable",
			SessionActive:     channel.broker.attachments > 0 || channel.stream.Active || operationClients > 0,
			RXBytes:           channel.stream.RXBytes,
			TXBytes:           channel.stream.TXBytes,
			LastRXAt:          channel.stream.LastRXAt,
			QueuedBytes:       channel.broker.queuedBytes,
			Operations:        append([]domain.PortOperationRuntime(nil), operationRuntime[port.Channel]...),
		}
		if channel.stream.LastRXAt != nil {
			age := time.Since(*channel.stream.LastRXAt).Milliseconds()
			if age < 0 {
				age = 0
			}
			value.RXAgeMillis = age
		}
		if state.LineSettings != nil {
			value.AppliedLine = &domain.PortLineSettings{
				BaudRate: state.LineSettings.BaudRate, DataBits: state.LineSettings.DataBits,
				Parity: state.LineSettings.Parity, StopBits: state.LineSettings.StopBits,
				StopBitsMode: state.LineSettings.StopBitsMode, FlowControl: state.LineSettings.FlowControl,
				RTSControl: state.LineSettings.RTSControl, DTRControl: state.LineSettings.DTRControl,
				IgnoreJammed: state.LineSettings.IgnoreJammed,
			}
			value.ProfileApplied = state.ProfileApplied && appliedLineMatchesPort(*state.LineSettings, *port)
			if state.ProfileApplied && !value.ProfileApplied && value.HardwareMessage == "" {
				value.HardwareMessage = "applied TTY line settings do not match the running configuration"
			}
		}
		if linkFound {
			value.LinkState = link.State
			value.LinkSignal = link.Signal
			value.LinkAvailable = link.Available
			value.LinkEverUp = link.EverUp
			value.LinkMessage = link.Message
		} else if runtime.linkErr != nil {
			value.LinkMessage = runtime.linkErr.Error()
		}
		if probeFound {
			value.CRProbeEnabled = probe.Enabled
			value.CRProbeState = probe.State
			value.CRProbeMethod = probe.Method
			value.CRProbeLastAt = probe.LastProbeAt
			value.CRProbeResponseAt = probe.LastResponseAt
			value.CRProbeConfirmedAt = probe.LastConfirmedAt
			value.CRProbeBytes = probe.ResponseBytes
			value.CRProbeResponses = probe.ConsecutiveResponses
			value.CRProbeMisses = probe.ConsecutiveMisses
			value.CRProbeUp = probe.Up
			value.CRProbeEverUp = probe.EverUp
			value.CRProbeMessage = probe.Message
		} else if runtime.crProbeErr != nil {
			value.CRProbeState = serial.CRProbeStateError
			value.CRProbeMessage = runtime.crProbeErr.Error()
		}
		if runtime.stateErr != nil && value.HardwareMessage == "" {
			value.HardwareMessage = runtime.stateErr.Error()
		}
		if runtime.sessionErr == nil {
			value.SessionState = runtime.session.Status
		}
		port.Status = runtimePortStatus(value)
		port.Runtime = value
	}
	return ports
}

func appliedLineMatchesPort(line serial.LineSettings, port domain.Port) bool {
	lineStopBits := line.StopBitsMode
	if lineStopBits == "" {
		lineStopBits = fmt.Sprintf("%d", line.StopBits)
	}
	portStopBits := port.StopBitsMode
	if portStopBits == "" {
		portStopBits = fmt.Sprintf("%d", port.StopBits)
	}
	return line.BaudRate == port.BaudRate && line.DataBits == port.DataBits &&
		line.Parity == port.Parity && lineStopBits == portStopBits && line.FlowControl == port.FlowControl
}

type serialChannelRuntime struct {
	attachments    int
	maxAttachments int
	writer         string
	queuedBytes    int
}

func runtimePortStatus(runtime *domain.PortRuntime) string {
	if runtime == nil {
		return "unknown"
	}
	if runtime.SessionActive && (runtime.CRProbeEverUp || runtime.LinkEverUp) {
		return "session"
	}
	if runtime.CRProbeUp {
		return "up"
	}
	if runtime.CRProbeEverUp && runtime.CRProbeState == serial.CRProbeStateNoResponse {
		return "down"
	}
	if runtime.LinkAvailable {
		if runtime.LinkState == "up" {
			return "up"
		}
		if runtime.LinkEverUp && runtime.LinkState == "down" {
			return "down"
		}
	}
	return "unknown"
}

func (r *Router) withRuntimeHealth(ctx context.Context, health []domain.ServiceHealth) []domain.ServiceHealth {
	runtime := r.readSerialRuntime(ctx)
	checkedAt := time.Now().UTC()
	hardwareContext, cancel := context.WithTimeout(ctx, runtimeStatusTimeout)
	greenLEDs, hardwareErr := r.greenLEDs.States(hardwareContext)
	cancel()
	for index := range health {
		health[index].LastCheckedAt = checkedAt
		switch health[index].Service {
		case "tera-seriald":
			available, applied := runtime.availablePorts(), runtime.appliedProfiles()
			if runtime.stateErr != nil {
				health[index].Status = "degraded"
				health[index].Detail = "serial hardware inventory unavailable: " + runtime.stateErr.Error()
			} else if available != serial.ChannelCount || applied != serial.ChannelCount {
				health[index].Status = "degraded"
				health[index].Detail = fmt.Sprintf("serial runtime incomplete; available=%d/%d; profiles_applied=%d/%d", available, serial.ChannelCount, applied, serial.ChannelCount)
			} else if runtime.sessionErr != nil || runtime.session.SerialError != "" {
				health[index].Status = "degraded"
				health[index].Detail = "serial stream status unavailable through tera-sessiond"
			} else {
				health[index].Status = "ok"
				health[index].Detail = fmt.Sprintf("serial runtime healthy; available=%d/%d; profiles_applied=%d/%d; active_leases=%d", available, serial.ChannelCount, applied, serial.ChannelCount, runtime.session.Serial.ActiveLeases)
			}
		case "tera-sessiond":
			if runtime.sessionErr != nil {
				health[index].Status = "degraded"
				health[index].Detail = "session broker unavailable: " + runtime.sessionErr.Error()
			} else {
				health[index].Status = runtime.session.Status
				health[index].Detail = fmt.Sprintf("session broker status=%s; attachments=%d; active_channels=%d; serial_leases=%d", runtime.session.Status, runtime.session.Broker.TotalAttachments, runtime.session.Broker.ActiveChannels, runtime.session.Serial.ActiveLeases)
			}
		case "tera-hwd":
			available := 0
			for _, state := range greenLEDs {
				if state.Available {
					available++
				}
			}
			if hardwareErr != nil || available != serial.ChannelCount {
				health[index].Status = "degraded"
				if hardwareErr != nil {
					health[index].Detail = "hardware control unavailable: " + hardwareErr.Error()
				} else {
					health[index].Detail = fmt.Sprintf("green LED hardware incomplete; available=%d/%d", available, serial.ChannelCount)
				}
			} else {
				health[index].Status = "ok"
				health[index].Detail = fmt.Sprintf("green LED hardware available=%d/%d", available, serial.ChannelCount)
			}
		}
	}
	return health
}