package orchestrator

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

	"vetting/internal/logs"
	"vetting/internal/model"
	"vetting/internal/store"
)

// HostHeartbeatStaleAfter is how long we tolerate a host's last_seen_at
// being in the past before treating the host as offline. Set to 2× the
// default reporter heartbeat interval (30s) so a single dropped heartbeat
// doesn't block dispatch. Used by the StartRun preflight and the
// dispatcher itself — both must agree or the operator's click-time
// validation wouldn't match the dispatch-time check.
const HostHeartbeatStaleAfter = 60 * time.Second

// Dispatcher picks Queued runs off the DB and drives them to
// WaitingReboot — the happy path is heartbeat-first: we transition and
// rely on the host-mode reporter's next heartbeat to fetch the
// reboot_for_vetting command. WoL is not fired in the default flow
// because every supported host already runs the reporter in-OS.
//
// Pre-stage log lines (picked, heartbeating, agent-claimed) are
// written into the per-run log via Logs so the detail page's log pane
// can show what's happening before the agent is alive.
//
// For Phase 2 the dispatcher's job ends at WaitingReboot; further
// transitions are driven by iPXE and agent callbacks. Phase 4+ will
// return here and shepherd each run through stage execution.
type Dispatcher struct {
	Max    int
	Runs   *store.Runs
	Hosts  *store.Hosts
	Runner *Runner
	Logs   *logs.Hub

	active chan struct{}
	stop   chan struct{}

	// heartbeat tracks the last time we emitted a "still waiting"
	// line for a given run, so the ticker doesn't spam the log.
	hbMu       sync.Mutex
	lastBeat   map[int64]time.Time
	beatEvery  time.Duration
}

func NewDispatcher(max int, runs *store.Runs, hosts *store.Hosts, runner *Runner, logHub *logs.Hub) *Dispatcher {
	if max < 1 {
		max = 1
	}
	return &Dispatcher{
		Max:       max,
		Runs:      runs,
		Hosts:     hosts,
		Runner:    runner,
		Logs:      logHub,
		active:    make(chan struct{}, max),
		stop:      make(chan struct{}),
		lastBeat:  map[int64]time.Time{},
		beatEvery: 30 * time.Second,
	}
}

func (d *Dispatcher) Start(ctx context.Context) {
	go d.loop(ctx)
}

func (d *Dispatcher) Stop() {
	close(d.stop)
}

func (d *Dispatcher) loop(ctx context.Context) {
	t := time.NewTicker(2 * time.Second)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-d.stop:
			return
		case <-t.C:
			d.pickNext(ctx)
			d.heartbeatWaiting(ctx)
		}
	}
}

func (d *Dispatcher) pickNext(ctx context.Context) {
	select {
	case d.active <- struct{}{}:
	default:
		return // at capacity
	}
	released := false
	defer func() {
		if !released {
			<-d.active
		}
	}()

	runs, err := d.Runs.Active(ctx)
	if err != nil {
		log.Printf("dispatcher: list active: %v", err)
		return
	}

	var queued *model.Run
	inFlight := 0
	for i := range runs {
		switch runs[i].State {
		case model.StateQueued:
			if queued == nil {
				queued = &runs[i]
			}
		case model.StateWaitingWoL, model.StateWaitingReboot, model.StateBooting,
			model.StateInventoryCheck, model.StateSpecValidate, model.StateSMART,
			model.StateCPUStress, model.StateStorage, model.StateNetwork,
			model.StateGPU, model.StatePSU, model.StateReporting:
			inFlight++
		}
	}

	if inFlight >= d.Max || queued == nil {
		return
	}

	host, err := d.Hosts.Get(ctx, queued.HostID)
	if err != nil {
		log.Printf("dispatcher: get host %d: %v", queued.HostID, err)
		return
	}

	// Heartbeat gate: the StartRun preflight catches this at click time,
	// but a run can sit in Queued long enough for the host to go offline
	// between click and dispatch. Re-check here so we never fire a
	// reboot command at a host that can't receive it.
	if host.LastSeenAt == nil || time.Since(*host.LastSeenAt) > HostHeartbeatStaleAfter {
		var ageMsg string
		if host.LastSeenAt == nil {
			ageMsg = "never heartbeated"
		} else {
			ageMsg = fmt.Sprintf("last heartbeat %s ago", time.Since(*host.LastSeenAt).Truncate(time.Second))
		}
		d.runLog(queued.ID, "error", fmt.Sprintf(
			"dispatcher: host %s is offline (%s) — refusing to dispatch; install the reporter via /register/quick.sh on the target and retry",
			host.Name, ageMsg))
		if err := d.Runs.MarkDispatchFailed(ctx, queued.ID, "dispatch", "host stopped heartbeating before dispatch"); err != nil {
			log.Printf("dispatcher: mark run %d dispatch-failed: %v", queued.ID, err)
		}
		if d.Runner != nil {
			d.Runner.PublishTileUpdate(ctx, host.ID)
		}
		return
	}

	age := time.Since(*host.LastSeenAt).Truncate(time.Second)
	d.runLog(queued.ID, "info", fmt.Sprintf(
		"dispatcher: picked run for host %s (mac=%s, heartbeating, last seen %s ago)",
		host.Name, host.MAC, age))
	if _, err := d.Runner.Transition(ctx, queued.ID, TriggerRebootCommanded); err != nil {
		log.Printf("dispatcher: transition run %d: %v", queued.ID, err)
		d.runLog(queued.ID, "error", fmt.Sprintf("dispatcher: transition to WaitingReboot failed: %v", err))
		return
	}
	log.Printf("dispatcher: run %d host %s → WaitingReboot (heartbeat-driven)", queued.ID, host.Name)
	d.runLog(queued.ID, "info", fmt.Sprintf(
		"dispatcher: host %s heartbeating — waiting for next reporter heartbeat to deliver reboot_for_vetting",
		host.Name))

	// Prime the heartbeat so the first "still waiting" fires 30s after
	// dispatch, not immediately.
	d.hbMu.Lock()
	d.lastBeat[queued.ID] = time.Now()
	d.hbMu.Unlock()

	// Slot stays reserved until the run leaves active (Phase 4+).
	// Phase 2 lets the loop observe inFlight via DB state.
	released = true
	<-d.active
}

// heartbeatWaiting emits a "still waiting" log line every beatEvery for
// each run still sitting in WaitingReboot (or legacy WaitingWoL). Helps
// the operator spot hangs without having to tail journalctl on the LXC.
func (d *Dispatcher) heartbeatWaiting(ctx context.Context) {
	if d.Logs == nil {
		return
	}
	runs, err := d.Runs.Active(ctx)
	if err != nil {
		return
	}
	now := time.Now()
	d.hbMu.Lock()
	defer d.hbMu.Unlock()
	seen := map[int64]bool{}
	for i := range runs {
		r := &runs[i]
		seen[r.ID] = true
		if r.State != model.StateWaitingReboot && r.State != model.StateWaitingWoL {
			continue
		}
		last, ok := d.lastBeat[r.ID]
		if !ok {
			// Run already waiting from a previous process lifetime — prime
			// so we don't spam immediately.
			d.lastBeat[r.ID] = now
			continue
		}
		if now.Sub(last) < d.beatEvery {
			continue
		}
		elapsed := now.Sub(r.StartedAt).Truncate(time.Second)
		d.runLog(r.ID, "info", fmt.Sprintf(
			"waiting for reporter to reboot + PXE-boot into live image (%s) — if this exceeds 2m, verify pxe.enabled in vetting.yaml and that the reporter actually invoked systemctl reboot",
			elapsed))
		d.lastBeat[r.ID] = now
	}
	// Garbage-collect entries for runs that have left the waiting states.
	for id := range d.lastBeat {
		if !seen[id] {
			delete(d.lastBeat, id)
		}
	}
}

// runLog writes a single line into the per-run log. Safe to call with a
// nil hub (tests construct Dispatcher directly) — it degrades to a
// stderr log line so nothing silently disappears.
func (d *Dispatcher) runLog(runID int64, level, text string) {
	if d.Logs == nil {
		log.Printf("run-%d %s: %s", runID, level, text)
		return
	}
	w, err := d.Logs.WriterFor(runID)
	if err != nil {
		log.Printf("dispatcher: open log for run %d: %v", runID, err)
		return
	}
	w.Append(logs.Line{Level: level, Text: text})
}