package workerruntime

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

	"github.com/itworx/pulse/internal/notification"
)

// MaxNotificationBatch bounds one outbox drain.
const MaxNotificationBatch = 50

// ChannelLister lists configured notification channels.
type ChannelLister interface {
	ListChannels(ctx context.Context, limit int) ([]notification.Channel, error)
}

// NotificationDrainJob delivers due outbox items.
//
// Delivery semantics come entirely from internal/notification: ClaimDue moves a
// due item to "delivering", increments its attempt counter and takes a bounded
// lock in one transaction (FOR UPDATE SKIP LOCKED), and Complete only applies
// to the exact attempt it claimed. That is what makes retry safe: a second
// worker cannot claim a locked item, a crashed attempt is retried only after
// its lock expires, and a completion for a stale attempt is ignored instead of
// delivering twice.
type NotificationDrainJob struct {
	Store    notification.Store
	Channels ChannelLister
	// Senders maps a channel type onto its transport. A configured channel
	// whose type has no registered transport is reported, never silently
	// dropped and never retried into failure.
	Senders   map[string]notification.ChannelSender
	Factories map[string]notification.ChannelSenderFactory
	BatchSize int
	Logger    *slog.Logger
	Now       func() time.Time
}

func (j NotificationDrainJob) now() time.Time {
	if j.Now != nil {
		return j.Now().UTC()
	}
	return time.Now().UTC()
}

func (j NotificationDrainJob) logger() *slog.Logger {
	if j.Logger != nil {
		return j.Logger
	}
	return slog.Default()
}

// Run drains one bounded batch of due notifications.
func (j NotificationDrainJob) Run(ctx context.Context) (Outcome, error) {
	if j.Store == nil || j.Channels == nil {
		return Outcome{Disabled: true, Reason: "notifications_not_configured"}, nil
	}
	channels, err := j.Channels.ListChannels(ctx, 100)
	if err != nil {
		return Outcome{}, fmt.Errorf("list notification channels: %w", err)
	}
	senders := make(map[string]notification.ChannelSender, len(channels))
	counts := map[string]int64{}
	unsupported := 0
	for _, channel := range channels {
		if !channel.Enabled {
			continue
		}
		counts["channels"]++
		sender, ok := j.Senders[channel.Type]
		if (!ok || sender == nil) && j.Factories[channel.Type] != nil {
			sender, err = j.Factories[channel.Type].Sender(ctx, channel)
			ok = err == nil && sender != nil
			if err != nil {
				j.logger().Error("notification channel transport configuration failed", "channel", channel.ID, "type", channel.Type, "error", notification.RedactError(err))
			}
		}
		if !ok || sender == nil {
			unsupported++
			j.logger().Error("notification channel has no delivery transport", "channel", channel.ID, "type", channel.Type)
			continue
		}
		senders[channel.ID] = sender
	}
	counts["unsupported_channels"] = int64(unsupported)
	if counts["channels"] == 0 {
		return Outcome{Disabled: true, Reason: "no_enabled_notification_channels", Counts: counts}, nil
	}
	if len(senders) == 0 {
		// Claiming items we cannot deliver would burn their bounded attempts,
		// so the drain stops and the failure stays visible instead.
		return Outcome{Counts: counts}, fmt.Errorf("no delivery transport is registered for %d enabled notification channel(s)", unsupported)
	}
	batch := j.BatchSize
	if batch < 1 || batch > MaxNotificationBatch {
		batch = MaxNotificationBatch
	}
	dispatcher := notification.Dispatcher{Store: j.Store, Channels: senders, Limiter: &notification.RateLimiter{}}
	delivered, err := dispatcher.DispatchDue(ctx, j.now(), batch)
	counts["delivered"] = int64(delivered)
	if err != nil {
		return Outcome{Counts: counts}, fmt.Errorf("drain notification outbox: %w", err)
	}
	if unsupported > 0 {
		return Outcome{Counts: counts}, fmt.Errorf("%d enabled notification channel(s) have no delivery transport", unsupported)
	}
	return Outcome{Counts: counts}, nil
}

// DrainDeadline is the longest a single drain may take. It is exported so the
// job schedule and the outbox lock window stay visibly related: the outbox lock
// is five minutes, comfortably above this bound.
const DrainDeadline = 30 * time.Second