// Scheduler — loops over every Plexum agent, heartbeats per-agent,
// picks the highest-priority pending slot for each, dispatches via
// host.WakeAgent. Mirrors HarborForge.OpenclawPlugin's per-agent
// scheduler loop (PLG-CAL-002).
//
// In-memory state: per-agent active slot map. A daemon restart drops
// it; next heartbeat reconciles from the backend's canonical state.
//
// Wake semantics: WakeAgent is fire-and-forget; the SDK's wake queue
// (depth 1 replace-newest) handles state-aware dispatch. We mark the
// slot Ongoing optimistically the moment we call WakeAgent; agents
// drive complete/abort/pause/resume via the harborforge_calendar_*
// tools.

package calendar

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

	sdkplugin "git.hangman-lab.top/hzhang/Plexum-sdk-go/plugin"
)

// Scheduler is the long-running calendar driver.
type Scheduler struct {
	cfg         Config
	bridge      *Bridge
	host        sdkplugin.HostAPI
	agentLister func() []ReportableAgent
	pluginInfo  PluginInfoTag

	mu                sync.Mutex
	activeByAgentID   map[string]*ActiveSlot
	activeBySlotIdent map[string]*ActiveSlot
	history           []HistoryEntry
	lastHeartbeats    map[string]time.Time
	lastErrors        map[string]string
}

// Config bundles scheduler tunables.
type Config struct {
	HeartbeatInterval time.Duration
	HistoryCap        int // bound on activity history; default 32
}

// PluginInfoTag tags heartbeat reports so the backend knows which
// plugin / version is reporting.
type PluginInfoTag struct {
	Name    string
	Version string
	Backend string // "plexum"
}

// ReportableAgent is the per-agent projection the scheduler needs for
// heartbeat enumeration.
type ReportableAgent struct {
	ID    string
	Model string
	State AgentStatusValue
}

// ActiveSlot tracks an in-flight slot from dispatch to terminal state.
type ActiveSlot struct {
	Slot          Slot
	StartedAt     time.Time
	LastHeartbeat time.Time
}

// HistoryEntry records one resolved slot for the calendar_status tool.
type HistoryEntry struct {
	Ident       string
	AgentID     string
	Status      SlotStatus
	ResolvedAt  time.Time
	Reason      string
	Summary     string
}

// NewScheduler constructs a Scheduler in stopped state.
func NewScheduler(cfg Config, bridge *Bridge, host sdkplugin.HostAPI,
	pluginInfo PluginInfoTag,
	agentLister func() []ReportableAgent) *Scheduler {
	if cfg.HeartbeatInterval <= 0 {
		cfg.HeartbeatInterval = 30 * time.Second
	}
	if cfg.HistoryCap <= 0 {
		cfg.HistoryCap = 32
	}
	return &Scheduler{
		cfg:               cfg,
		bridge:            bridge,
		host:              host,
		agentLister:       agentLister,
		pluginInfo:        pluginInfo,
		activeByAgentID:   map[string]*ActiveSlot{},
		activeBySlotIdent: map[string]*ActiveSlot{},
		lastHeartbeats:    map[string]time.Time{},
		lastErrors:        map[string]string{},
	}
}

// Run blocks until ctx cancels.
func (s *Scheduler) Run(ctx context.Context) error {
	t := time.NewTicker(s.cfg.HeartbeatInterval)
	defer t.Stop()
	s.tick(ctx)
	for {
		select {
		case <-ctx.Done():
			return nil
		case <-t.C:
			s.tick(ctx)
		}
	}
}

func (s *Scheduler) tick(ctx context.Context) {
	if s.agentLister == nil {
		return
	}
	now := time.Now().UTC()
	agents := s.agentLister()
	s.host.Log("info", "calendar tick", map[string]any{"agents": len(agents)})
	for _, agent := range agents {
		s.tickForAgent(ctx, agent, now)
	}
}

func (s *Scheduler) tickForAgent(ctx context.Context, agent ReportableAgent, now time.Time) {
	resp, err := s.bridge.Heartbeat(ctx, agent.ID)
	s.mu.Lock()
	s.lastHeartbeats[agent.ID] = now
	if err != nil {
		s.lastErrors[agent.ID] = err.Error()
		s.mu.Unlock()
		s.host.Log("warn", "calendar heartbeat failed", map[string]any{
			"agent": agent.ID, "err": err.Error(),
		})
		return
	}
	delete(s.lastErrors, agent.ID)
	s.mu.Unlock()
	s.host.Log("info", "calendar heartbeat ok", map[string]any{
		"agent": agent.ID, "slots": len(resp.Slots), "agent_status": string(resp.AgentStatus),
	})

	// Pick highest-priority NotStarted slot; defer the rest.
	var chosen *Slot
	for i := range resp.Slots {
		slot := &resp.Slots[i]
		if slot.Status != SlotNotStarted && slot.Status != SlotDeferred {
			continue
		}
		if chosen == nil || slot.Priority > chosen.Priority {
			chosen = slot
		}
	}
	if chosen != nil {
		s.dispatchSlot(ctx, agent.ID, *chosen)
	}
	// Defer the other unchosen NotStarted/Deferred slots (priority +1)
	// so they bubble up next heartbeat. We don't strictly need to push
	// the update; the backend's priority bookkeeping survives without
	// our nudge for v1. (OpenClaw plugin DOES push priority bumps —
	// future v2 work if backend feedback shows starvation.)
}

// dispatchSlot fires WakeAgent + records the slot active. Marks the
// slot Ongoing on the backend so the dashboard reflects the
// transition immediately.
func (s *Scheduler) dispatchSlot(ctx context.Context, agentID string, slot Slot) {
	ident := slot.SlotIdent()
	s.mu.Lock()
	if _, dup := s.activeBySlotIdent[ident]; dup {
		s.mu.Unlock()
		return
	}
	if _, agentBusy := s.activeByAgentID[agentID]; agentBusy {
		// Don't pick up another slot until the current one resolves.
		s.mu.Unlock()
		return
	}
	now := time.Now().UTC()
	active := &ActiveSlot{Slot: slot, StartedAt: now, LastHeartbeat: now}
	s.activeBySlotIdent[ident] = active
	s.activeByAgentID[agentID] = active
	s.mu.Unlock()

	message := buildWakeMessage(slot)
	source := "calendar:" + ident
	if err := s.host.WakeAgent(ctx, sdkplugin.WakeAgentRequest{
		AgentID: agentID, Message: message, Source: source,
	}); err != nil {
		s.resolveLocally(ident, agentID, SlotAborted, "", "wake failed: "+err.Error())
		return
	}
	// Mark Ongoing on the backend.
	update := SlotAgentUpdate{
		Status: SlotOngoing, StartedAt: now.Format("15:04:05"),
	}
	s.pushUpdate(ctx, agentID, slot, update)
}

func buildWakeMessage(slot Slot) string {
	// Backend EventData → prompt. v1 is intentionally simple; refine
	// when the prompt-engineering side of the plugin matures.
	if slot.EventType != nil {
		switch *slot.EventType {
		case EventTypeSystemEvent:
			if ev, ok := slot.EventData["event"].(string); ok {
				return fmt.Sprintf("[calendar system_event] %s", ev)
			}
		case EventTypeJob:
			code, _ := slot.EventData["code"].(string)
			typ, _ := slot.EventData["type"].(string)
			if code != "" {
				return fmt.Sprintf("[calendar job %s/%s] please handle this", typ, code)
			}
		}
	}
	return fmt.Sprintf("[calendar slot %s] scheduled work — please proceed", slot.SlotIdent())
}

// CompleteForAgent → terminal; pushes Finished to backend.
func (s *Scheduler) CompleteForAgent(ctx context.Context, agentID, summary string) error {
	act, ok := s.activeSlotForAgent(agentID)
	if !ok {
		return ErrNoActiveSlot
	}
	now := time.Now().UTC()
	duration := int(now.Sub(act.StartedAt).Minutes())
	if duration < 1 {
		duration = 1
	}
	if err := s.pushUpdate(ctx, agentID, act.Slot, SlotAgentUpdate{
		Status: SlotFinished, ActualDuration: duration,
	}); err != nil {
		return err
	}
	s.resolveLocally(act.Slot.SlotIdent(), agentID, SlotFinished, summary, "")
	return nil
}

// AbortForAgent → terminal; pushes Aborted to backend.
func (s *Scheduler) AbortForAgent(ctx context.Context, agentID, reason string) error {
	act, ok := s.activeSlotForAgent(agentID)
	if !ok {
		return ErrNoActiveSlot
	}
	if err := s.pushUpdate(ctx, agentID, act.Slot, SlotAgentUpdate{Status: SlotAborted}); err != nil {
		return err
	}
	s.resolveLocally(act.Slot.SlotIdent(), agentID, SlotAborted, "", reason)
	return nil
}

// PauseForAgent → non-terminal; pushes Paused.
func (s *Scheduler) PauseForAgent(ctx context.Context, agentID, reason string) error {
	act, ok := s.activeSlotForAgent(agentID)
	if !ok {
		return ErrNoActiveSlot
	}
	return s.pushUpdate(ctx, agentID, act.Slot, SlotAgentUpdate{Status: SlotPaused})
}

// ResumeForAgent → non-terminal; pushes Ongoing.
func (s *Scheduler) ResumeForAgent(ctx context.Context, agentID string) error {
	act, ok := s.activeSlotForAgent(agentID)
	if !ok {
		return ErrNoActiveSlot
	}
	return s.pushUpdate(ctx, agentID, act.Slot, SlotAgentUpdate{Status: SlotOngoing})
}

func (s *Scheduler) pushUpdate(ctx context.Context, agentID string, slot Slot, update SlotAgentUpdate) error {
	if slot.HasRealID() {
		return s.bridge.UpdateRealSlot(ctx, agentID, *slot.ID, update)
	}
	if slot.VirtualID != nil {
		return s.bridge.UpdateVirtualSlot(ctx, agentID, *slot.VirtualID, update)
	}
	return errors.New("calendar: slot has neither real id nor virtual id")
}

func (s *Scheduler) resolveLocally(ident, agentID string, status SlotStatus, summary, reason string) {
	s.mu.Lock()
	defer s.mu.Unlock()
	delete(s.activeBySlotIdent, ident)
	delete(s.activeByAgentID, agentID)
	s.history = append(s.history, HistoryEntry{
		Ident: ident, AgentID: agentID, Status: status,
		ResolvedAt: time.Now().UTC(), Summary: summary, Reason: reason,
	})
	if len(s.history) > s.cfg.HistoryCap {
		s.history = s.history[len(s.history)-s.cfg.HistoryCap:]
	}
}

func (s *Scheduler) activeSlotForAgent(agentID string) (ActiveSlot, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	act, ok := s.activeByAgentID[agentID]
	if !ok || act == nil {
		return ActiveSlot{}, false
	}
	return *act, true
}

// Status is the introspection shape calendar_status returns.
type Status struct {
	Enabled        bool                 `json:"enabled"`
	LastHeartbeats map[string]time.Time `json:"last_heartbeats"`
	LastErrors     map[string]string    `json:"last_errors,omitempty"`
	HeartbeatEvery time.Duration        `json:"heartbeat_every"`
	Active         []ActiveSlot         `json:"active"`
	History        []HistoryEntry       `json:"history"`
}

// SingleActiveAgentID returns the agent id when exactly one active
// slot exists, empty otherwise. Used by the plugin's bestEffortAgentID
// fallback for tool calls that don't carry agent context.
func (s *Scheduler) SingleActiveAgentID() string {
	s.mu.Lock()
	defer s.mu.Unlock()
	if len(s.activeByAgentID) != 1 {
		return ""
	}
	for k := range s.activeByAgentID {
		return k
	}
	return ""
}

// Status returns the introspection shape calendar_status returns.
func (s *Scheduler) Status() Status {
	s.mu.Lock()
	defer s.mu.Unlock()
	active := make([]ActiveSlot, 0, len(s.activeByAgentID))
	for _, a := range s.activeByAgentID {
		active = append(active, *a)
	}
	hb := make(map[string]time.Time, len(s.lastHeartbeats))
	for k, v := range s.lastHeartbeats {
		hb[k] = v
	}
	errs := make(map[string]string, len(s.lastErrors))
	for k, v := range s.lastErrors {
		errs[k] = v
	}
	history := make([]HistoryEntry, len(s.history))
	copy(history, s.history)
	return Status{
		Enabled:        true,
		LastHeartbeats: hb,
		LastErrors:     errs,
		HeartbeatEvery: s.cfg.HeartbeatInterval,
		Active:         active,
		History:        history,
	}
}

// ErrNoActiveSlot is returned when an agent calls calendar_complete /
// abort / pause / resume but has no slot active.
var ErrNoActiveSlot = errors.New("calendar: no active slot for agent")