// Package alert evaluates the hardcoded rule set and persists raises
// / acknowledges / resolves. Three event sources feed it:
//   - JobFinishedEvent — pushed when a job lands a terminal state
//     (the existing MarkJobFinished site)
//   - HostOfflineEvent / HostOnlineEvent — pushed by the offline
//     sweeper and by the ws hello handler
//   - 60s ticker (internal) — drives stale-schedule + auto-resolve
//
// All output goes through store.RaiseOrTouch / Acknowledge / Resolve
// and the notification.Hub. The engine is one goroutine started at
// boot; non-blocking sends from hot paths.
package alert

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

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

// JobFinishedEvent carries everything the engine needs to evaluate
// the failed-X rules. Pushed via Engine.NotifyJobFinished from the
// MarkJobFinished site.
type JobFinishedEvent struct {
	HostID string
	JobID  string
	Kind   string // backup | forget | prune | check | unlock | restore | diff
	Status string // succeeded | failed | cancelled
	When   time.Time
}

// Engine evaluates hardcoded alert rules and dispatches via notification.Hub.
type Engine struct {
	store *store.Store
	hub   *notification.Hub

	jobs     chan JobFinishedEvent
	hostDown chan string // host_id
	hostUp   chan string

	// agentOfflineFloor is the duration a host must be offline before
	// we raise. Configurable for tests; default 15m.
	agentOfflineFloor time.Duration
	tickPeriod        time.Duration

	closeOnce sync.Once
	done      chan struct{}
}

// NewEngine builds the engine. agentOfflineFloor + tickPeriod default
// to 15min and 60s respectively when zero.
func NewEngine(st *store.Store, hub *notification.Hub) *Engine {
	return &Engine{
		store:             st,
		hub:               hub,
		jobs:              make(chan JobFinishedEvent, 32),
		hostDown:          make(chan string, 32),
		hostUp:            make(chan string, 32),
		agentOfflineFloor: 15 * time.Minute,
		tickPeriod:        60 * time.Second,
		done:              make(chan struct{}),
	}
}

// Run drives the event loop. Returns when ctx is done. Blocks; call in
// its own goroutine.
func (e *Engine) Run(ctx context.Context) {
	t := time.NewTicker(e.tickPeriod)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			e.closeOnce.Do(func() { close(e.done) })
			return
		case ev := <-e.jobs:
			e.handleJobFinished(ctx, ev)
		case hostID := <-e.hostDown:
			e.handleHostOffline(ctx, hostID)
		case hostID := <-e.hostUp:
			e.handleHostOnline(ctx, hostID)
		case now := <-t.C:
			e.tick(ctx, now)
		}
	}
}

// NotifyJobFinished is the hot-path hook called from MarkJobFinished's
// caller (ws.handler.dispatchAgentMessage). Non-blocking: drops on a
// full channel with a slog warning.
func (e *Engine) NotifyJobFinished(ev JobFinishedEvent) {
	select {
	case e.jobs <- ev:
	default:
		slog.Warn("alert: jobs channel full; dropping event", "kind", ev.Kind, "host_id", ev.HostID)
	}
}

// NotifyHostOffline notifies the engine that a host is offline.
func (e *Engine) NotifyHostOffline(hostID string) {
	select {
	case e.hostDown <- hostID:
	default:
		slog.Warn("alert: hostDown channel full; dropping", "host_id", hostID)
	}
}

// NotifyHostOnline notifies the engine that a host is online.
func (e *Engine) NotifyHostOnline(hostID string) {
	select {
	case e.hostUp <- hostID:
	default:
		slog.Warn("alert: hostUp channel full; dropping", "host_id", hostID)
	}
}

// Placeholder method stubs for C2 implementation
func (e *Engine) handleJobFinished(ctx context.Context, ev JobFinishedEvent) {
	// Implemented in C2
}

func (e *Engine) handleHostOffline(ctx context.Context, hostID string) {
	// Implemented in C2
}

func (e *Engine) handleHostOnline(ctx context.Context, hostID string) {
	// Implemented in C2
}

func (e *Engine) tick(ctx context.Context, now time.Time) {
	// Implemented in C2
}