package ws

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

	"gitea.dcglab.co.uk/steve/restic-manager/internal/store"
)

// updateTimeout bounds how long the watcher waits for an agent to come
// back with its new version after a command.update dispatch. var (not
// const) so tests can shrink it.
var updateTimeout = 90 * time.Second

// AlertRaiser is the slim subset of *alert.Engine the update watcher
// touches. Defined here (not in the alert package) so the dependency
// arrow points the right way.
type AlertRaiser interface {
	RaiseUpdateFailed(ctx context.Context, hostID, jobID, reason string, when time.Time)
	ResolveUpdateFailed(ctx context.Context, hostID string, when time.Time)
}

// UpdateWatcher tracks in-flight agent-update dispatches and reconciles
// them against incoming hello envelopes. Entries land on Track and
// resolve via OnHello (success path) or the periodic sweep (timeout).
type UpdateWatcher struct {
	store  *store.Store
	alerts AlertRaiser

	mu      sync.Mutex
	entries map[string]*updateEntry // hostID → entry

	tickPeriod time.Duration
}

type updateEntry struct {
	jobID     string
	startedAt time.Time
	// terminated is set once the entry has reached a terminal state so
	// late OnHellos don't resurrect it.
	terminated bool
}

// NewUpdateWatcher builds an unstarted watcher. Call Run in a goroutine
// to start the periodic sweep.
func NewUpdateWatcher(st *store.Store, alerts AlertRaiser) *UpdateWatcher {
	return &UpdateWatcher{
		store:      st,
		alerts:     alerts,
		entries:    make(map[string]*updateEntry),
		tickPeriod: 5 * time.Second,
	}
}

// Track registers a freshly-dispatched update job. A subsequent Track
// for the same host replaces the prior entry (last-write-wins).
func (w *UpdateWatcher) Track(jobID, hostID string) {
	if w == nil {
		return
	}
	w.mu.Lock()
	w.entries[hostID] = &updateEntry{jobID: jobID, startedAt: time.Now()}
	w.mu.Unlock()
}

// OnHello is called by the WS handler after a successful hello has been
// persisted. If a tracked update for the host matches the targetVersion,
// the job is marked succeeded and any open update_failed alert is
// auto-resolved. A non-matching version is a no-op (the watcher keeps
// waiting until the timeout).
func (w *UpdateWatcher) OnHello(ctx context.Context, hostID, agentVersion, targetVersion string) {
	if w == nil {
		return
	}
	w.mu.Lock()
	e, ok := w.entries[hostID]
	if !ok || e.terminated {
		w.mu.Unlock()
		return
	}
	if agentVersion != targetVersion {
		// Not the version we asked for — keep waiting.
		w.mu.Unlock()
		return
	}
	e.terminated = true
	jobID := e.jobID
	delete(w.entries, hostID)
	w.mu.Unlock()

	now := time.Now().UTC()
	if err := w.store.MarkJobFinished(ctx, jobID, "succeeded", 0, nil, "", now); err != nil {
		slog.Warn("ws update watcher: mark succeeded", "job_id", jobID, "host_id", hostID, "err", err)
	}
	if w.alerts != nil {
		w.alerts.ResolveUpdateFailed(ctx, hostID, now)
	}
}

// Run drives the periodic sweep. Returns when ctx is done.
func (w *UpdateWatcher) Run(ctx context.Context) {
	if w == nil {
		return
	}
	t := time.NewTicker(w.tickPeriod)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case now := <-t.C:
			w.sweep(ctx, now)
		}
	}
}

func (w *UpdateWatcher) sweep(ctx context.Context, now time.Time) {
	type expired struct {
		hostID string
		jobID  string
		age    time.Duration
	}
	var toFail []expired
	w.mu.Lock()
	for hostID, e := range w.entries {
		if e.terminated {
			continue
		}
		if now.Sub(e.startedAt) >= updateTimeout {
			toFail = append(toFail, expired{hostID: hostID, jobID: e.jobID, age: now.Sub(e.startedAt)})
			e.terminated = true
			delete(w.entries, hostID)
		}
	}
	w.mu.Unlock()

	for _, x := range toFail {
		reason := fmt.Sprintf("timeout: agent did not reconnect within %s", updateTimeout)
		stamp := now.UTC()
		errMsg := reason
		if err := w.store.MarkJobFinished(ctx, x.jobID, "failed", -1, nil, errMsg, stamp); err != nil {
			slog.Warn("ws update watcher: mark failed", "job_id", x.jobID, "host_id", x.hostID, "err", err)
		}
		if w.alerts != nil {
			w.alerts.RaiseUpdateFailed(ctx, x.hostID, x.jobID, reason, stamp)
		}
	}
}